Document Sample

Common-source diseases (as is water).

          United States

                  25,000 reported foodborne disease outbreaks/ 13 million foodborne illnesses

spinach- central facilities, shipping efficiency transfer contaminated food EVERYWHERE

Table 29.6 summarizes the most prevalent foodborne diseases in the US

Food poisoning or food intoxication

Food poisoning

          ingestion of foods containing preformed microbial toxin.

          microorganisms that produced the toxins do not have to grow in the host

          illness is due to ingestion and subsequent action of the preformed bioactive toxin

                  exotoxin of Clostridium botulinum (Section 21.10)

                  superantigen toxins of Staphylococcus aureus (Section 22.16).

Food infection

          infection resulting from ingestion of pathogen-contaminated food

29.5   Staphylococcal Food Poisoning

Figure 29.4

          staphylococci are found on the skin and in the respiratory tract

          can grow in many common foods

                  some strains produce several heat-stable protein superantigen enterotoxins

                           gastroenteritis characterized by nausea, vomiting, and diarrhea, occurs

                           within 1–6 hours.


          Severe generally self-limiting enteritis, 24-48 h

185,000 cases/yr

custard- and cream-filled baked goods, poultry, meat and meat products, gravies, egg and meat

salads, puddings, and creamy salad dressings.

        infected food handler with S. aureus = rapid bacterial growth and enterotoxin production


Live S. aureus need not be present in foods causing illness

         due to the preformed toxin.

refrigeration retards growth = safety

seven different but related enterotoxins.

        Superantigens     stimulate large numbers of T cells

                 release cytokines, activate a general inflammatory response in the intestine

                 gastroenteritis - massive loss of fluids (Section 22.16).

Diagnosis, Treatment, and Prevention

ELISA for enterotoxin or exonuclease ( detects S. aureus)

bacterial plate counts to isolate S. aureus

         high-salt medium (7.5% sodium chloride or lithium chloride) -selective media

-antibiotics not useful

-sanitation and hygiene in food production and food preparation

-storiage of foods at low temperatures to inhibit bacterial growth

-Foods susceptible to colonization by S. aureus and kept for several hours above 4°C

(refrigerator temperature) should be discarded rather than eaten.

   Identify the symptoms of staphylococcal food poisoning and explain the activity of

    staphylococcal enterotoxins.

   Will antibiotics affect the outcome or the severity of staphylococcal food poisoning? Explain.
29.6    Clostridial Food Poisoning

Clostridium perfringens and Clostridium botulinum

anaerobic endospore formers (Section 12.20).

          Canning and cooking do not kill endospores

          Under anaerobic conditions, the endospores germinate -> toxin

Clostridium perfringens Food Poisoning

Clostridium perfringens i(Figure 29.5)

-lives soil and in small numbers in the intestinal tract animals and humans - found in sewage

-most prevalent reported cause of food poisoning in the United States, 248,000 /yr

    large dose of Clostridium perfringens (108 cells) in contaminated cooked and uncooked

foods, especially meat, poultry, and fish

    C. perfringens can grow in meat dishes cooked in bulk (heat penetration is poor) and then left

at 20–40°C for short time periods.

    Endospores of C. perfringens germinate under anoxic conditions, such as in a sealed

container, and grow quickly in the meat. However, the toxin is not yet present.

    After consumption of contaminated food C. perfringens sporulates in the intestine, triggering

production of the perfringens enterotoxin

    -Enterotoxin cauases diarrhea and intestinal cramps, usually with no fever or vomiting.

    -onset about 7–15 hours after consumption of the contaminated food

    -resolves within 24 hours, and fatalities are rare.

Diagnosis, Treatment, and Prevention



ELISA to detect C. perfringens enterotoxin in feces Because

Treatment is usually not necessary, although antitoxins are available


prevent contamination of raw and cooked foods and control of cooking and canning procedures
to ensure proper heat treatment of all foods

proper refrigeration ofcooked foods to rapidly lower temperatures, inhibit C. perfringens growth


Botulism is a severe food poisoning -often fatal

-occurs following the consumption of food containing the exotoxin produced by the anaerobic,

gram-positive rod Clostridium botulinum.

-soil or water, endospores may contaminate raw foods before harvest or slaughter

-viable endospores -> growth and neurotxin production

Even a small amount of the resultant neurotoxin can be poisonous

1 mg can kill 1,000,000 guinea pigs

Botulinum toxin is a neurotoxin that causes flaccid paralysis

    -affecting the autonomic nerves that control body functions such as respiration and heartbeat.

Heat labile (80°C for 10 minutes) -seven distinct botulinum toxins

Source: foods that are not cooked after processing (Figure 29.6a)

        nonacid, home-canned vegetables (corn and beans)

        Smoked and fresh fish, vacuum packed in plastic

                C. botulinum endospores germinate produce toxin

                 ingestion will result in severe food poisoning.

155 cases or less each year, but up to 25% of all cases are fatal

         respiratory paralysis or cardiac arrest

Diagnosis, Treatment, and Prevention

-demonstrate botulinum toxin in patient serum or -

-finding toxin or live Clostridium botulinum in food products

Laboratory findings are coupled with clinical observations including neurological signs of localized

paralysis (impaired vision and speech) beginning 18–24 hours after ingestion of contaminated


Treatment involves
administration of antitoxin if the diagnosis is early

mechanical ventilation for symptoms of flaccid respiratory paralysis


controls over canning and preservation methods.

Heating susceptible foods to destroy endospores, or boiling for 20 minutes destroys the toxin.

Home-prepared foods - most common source of individual foodborne botulism outbreaks.

   Describe the events that lead to C. perfringens food poisoning. What is the likely outcome of

    the poisoning?

   Describe the events that lead to botulism. What is the likely outcome of botulism?


Food infection

-active infection resulting from ingestion of pathogen-contaminated food

-sufficient numbers of viable pathogens to cause infection and disease in the host

-food infection agents also cause waterborne diseases

Very common- T 28.6

29.7    Salmonellosis

salmonellosis is a gastrointestinal disease due to foodborne Salmonella infection

pathogen colonizes the intestinal epithelium

Salmonella are gram-negative facultatively aerobic rods related to Escherichia coli, Shigella, and

other enteric Bacteria

Salmonella normally inhabit the gut of animals and are thus found in sewage

Salmonella are pathogenic for humans

        S. typhi, causes typhoid fever -rare in the United States, with most of the 500 foodborne

cases imported from other countries.

Salmonella species cause foodborne gastroenteritis. In all, over

2000 serovars, are pathogenic for humans
S. typhimurium is the most common agent of salmonellosis.


40,000–45,000 cases /yr (Figure 29.7).

4% reported - cases of salmonellosis is over 1.3 million every year (Table 29.6).


fecal contamination from food handlers, chickens and cattle

finished fresh foods such as eggs, meat, and dairy products

Prepared foods

custards, cream cakes, meringues, pies, and eggnog made with uncooked eggs

meats and meat products such as meat pies, cured but uncooked sausages and meats, poultry,

milk, and milk products.

Salmonellosis - Salmonellainduced enterocolitis.

colonization of the small and large intestine.

8–48 hours after ingestion

headache, chills, vomiting, and diarrhea, fever that lasts a few days

resolves without intervention in 2 to 3 days.

after recovery, patients shed Salmonella in feces for several weeks

Some patients recover and remain asymptomatic, but shed organisms for months or even years,

resulting in a chronic carrier condition

septicemia (a blood infection) and

enteric or typhoid fever, a disease characterized by systemic infection and high fever lasting

several weeks - Mortality 15%

animal food products, such as raw meat, poultry, eggs, and powdered milk


treatment is usually unnecessary- antibiotic treatment does not shorten the disease or eliminate

the carrier state.

Antibiotic treatment, however, significantly reduces the length and severity of septicemia and
typhoid fever mortality reduced to less than 1%.


Cooked foods heated to 70°C for at least 10 minutes, held at 50°C or stored at 10°C or lower.

Salmonella infections are more common in summer than in winter

infected individuals are often banned from work as food handlers until their feces are negative for

Salmonella in three successive cultures.

   Describe salmonellosis food infection. How does it differ from food poisoning?

   How might Salmonella contamination of food production animals be contained?

29.8    Pathogenic Escherichia coli

Most Escherichia coli are not pathogenic and are common commensals

A few strains, however, are potential foodborne pathogens

        act on the intestine

200 produce potent enterotoxins

        life-threatening diarrheal disease and urinary tract infections

Enterohemorrhagic Escherichia coli (EHEC)

Enterohemorrhagic Escherichia coli (EHEC)- E. coli O157:H7 produce verotoxin, an

        enterotoxin like Shiga toxin of Shigella dysenteriae t

E. coli O157:H7 grows in the small intestine and produces the verotoxin.

Verotoxin causes both hemorrhagic (bloody) diarrhea and kidney failure.

E. coli O157:H7 causes at least 60,000 infections and 50 deaths from foodborne disease in the

United States each year (Table 29.6).

        kidney failure in children


contaminated uncooked or undercooked meat, particularly mass-processed ground beef,

        1. regional distribution centers ship contaminated meat, caused disease in several states.

        2. processed, cured, but uncooked beef in ready-to-eat sausages

source is beef- E. coli O157:H7 probably originated from slaughtered beef carcasses
2001 - 16 documented food infection outbreaks in the United States due to E. coli O157:H7

        5 were definitely from beef

2003 - the Food Safety and Inspection Service of the U.S.D.A. - 20 positive results of 6584

samples         (0.03%) of ground beef analyzed for E. coli O157:H7.

E. coli O.157:H7 also in dairy products, fresh fruit, and raw vegetables (spinach of September-

        October 2006)

also a source of waterborne disease

        fecally contaminated public swimming areas

day care settings, where the presumed route of exposure is by oral-fecal contamination.

Other Pathogenic Escherichia coli

“traveler’s diarrhea,” - enterotoxigenic Escherichia coli (ETEC). The ETEC strains usually

produce one of two heat-labile diarrhea-producing enterotoxins. In studies done with U.S. citizens

traveling in Mexico, the infection rate with ETEC is often greater than 50%. The prime vehicles

are foods such as fresh vegetables (for example, lettuce in salads) and water. The very high

infection rate in travelers is due to contamination of local public water supplies. The local

population is usually resistant to the infecting strains, undoubtedly because they have lived with

the agent for a long period of time. Secretory antibodies (Section 22.9) present in the bowel may

prevent successful colonization of the pathogen in local residents, but the organism readily

colonizes the intestine of a nonimmune person, causing disease.

    Enteropathogenic E. coli (EPEC) cause diarrheal diseases in infants and small children, but

do not cause invasive disease or produce toxins. Enteroinvasive E. coli (EIEC) strains cause

invasive disease in the colon, producing watery to bloody diarrhea. The cells are taken up by

phagocytes, where they escape lysis in the phagolysosomes (Section 22.2), grow in the

cytoplasm, and move into other cells. This invasive disease causes diarrhea and is common in

developing countries.

Diagnosis, Treatment, and Prevention

Escherichia coli O157:H7 is reportable in US

culture from the feces

identification of the O and H antigens and toxins by serology

Subtyping by restriction fragment-length polymorphism (RFLP) and pulse-field gel electrophoresis



supportive therapy -in severe cases, antimicrobial drugs to shorten and eliminate infection


cook thoroughly- gray or brown and juices should be clear.

irradiation of ground meat eliminates reducies food infection bacteria

         contamination from one animal can contaminate the meat of several animals when the

         meat is mixed in the grinding process. grinding may distribute the pathogens throughout

         meat, not simply on the surface.

In general, proper food handling, water purification, and appropriate hygiene habits will prevent

the spread of pathogenic E. coli. Traveler’s diarrhea can be prevented by avoiding local water

sources and uncooked foods.

   Describe the pathology of Escherichia coli food infections due to EHEC, ETEC, strains.

   How might Escherichia coli contamination of food production animals be prevented?

   Why is Escherichia coli O157:H7 considered a dangerous and reportable pathogen?

29.9     Campylobacter

Campylobacter spp.

         the most prevalent bacterial foodborne infections in the United States. gram-negative,

motile, curved rod-to-spirillar-shaped microaerophiles

Campylobacter jejuni (Figure 29.8), C. coli, and C. fetus

C. jejuni and C. coli - 2 million annual cases of bacterial diarrhea (Table 29.6)

Campylobacter fetus is economically important because it is a major cause of sterility and

spontaneous abortion in cattle and sheep.


contaminated food

poultry, pork, raw clams, and other shellfish, or in surface waters not subjected to chlorinatio.

normal resident in the intestinal tract of poultry

           90% of turkey carcasses,

           88% of chicken carcasses

           32% of hog carcasses


Ingest cells of Campylobacter- multiplies in the small intestine, invades the epithelium, and

causes inflammation, resulting in disease.

C. jejuni is sensitive to gastric acid

10 4 may be required to initiate infection

ingestion of the pathogen directly in food, or ingestion by individuals taking medication to reduce

stomach acid production, may reduce this number to less than 500 bacteria.


include a high fever (usually greater than 104°F or 40°C), headache, malaise, nausea,

abdominal cramps, and profuse diarrhea with watery, frequently bloody, stools

7–10 days. - Spontaneous recovery

relapses occur in up to 25% of cases.

Diagnosis, Treatment, and Prevention

Diagnosis isolation of the organism from stool samples

identification by growth-dependent tests or immunological assays

Treatment with erythromycin

does not shorten the acute diarrhea,

shorten the time during which patients shed Campylobacter in their feces.


Personal hygiene,

proper washing of uncooked poultry (and any kitchenware coming in contact with uncooked

thorough cooking of meat

   Describe the pathology of Campylobacter food infection. What is the likely outcome?

   How might Campylobacter contamination of food production animals be controlled?

29.10 Listeriosis

Listeria monocytogenes causes listeriosis

gastrointestinal food infection that may lead to bacteremia and meningitis

short, gram-positive, nonspore-forming rod that is acid-tolerant, psychrotolerant (cold-tolerant),

facultatively aerobic, and salt-tolerant (Figure 29.9)


Listeria monocytogenes

soil and water - no fresh food source is safe from L. monocytogenes

contaminated during food growth or processing

refrigerationis ineffective - psychrotolerant

meat, dairy products, and fresh produce

ready-to-eat processed foods such as meat products

unpasteurized dairy products that are stored for long periods, even at 4°C

intracellular pathogen

enters phagocytes in the gastrointestinal tract

growth and proliferation of the bacterium, lysis of the phagocyte, and spread to surrounding cells.

Immunity to L. monocytogenes is mainly cell-mediated via TH 1 cells

Immunocompromised (weakened cellular immunity)

elderly, neonates, immunosuppressed patients ( drug treatment, AIDS)

exposure iscommo

listeriosis is quite rare

disease is characterized by septicemia/ meningitis
mortality rate - 20%

2500 / y, 500 deaths /y

diagnosed cases require hospitalization.

Diagnosis, Treatment, and Prevention


culturing Listeria monocytogenes from the blood or spinal fluid

in food by direct culture or by a variety of molecular methods - polymerase chain reaction (PCR)

Antibiotic treatment

penicillin, ampicillin, or a trimethoprim/sulfamethoxazole


recalling contaminated food

limit L. monocytogenes contamination at the food-processing site

          heat and radiation

without sterilizing the finished food product, the risk of food contamination cannot be completely

eliminated because of the widespread distribution of the pathogen.

Immunocompromised, pregnant women

          avoid foods that may transmit L. monocytogenes. (spontaneous abortion is also a

frequent outcome of listeriosis)

   What is the likely outcome of Listeria exposure in normal individuals?

   What populations are most susceptible to Listeria infection? Why?

   Describe the pathology of listeriosis.

29.11 Other Foodborne Infectious Diseases


gastroenteritis characterized by diarrhea, nausea and vomiting

Recovery is spontaneous and rapid, usually within 24–48 hours (“24-hour bug”).

Norwalk-like viruses T 29.6

          over 9 million of the estimated 13 million cases of food infection per year
Rotavirus, astrovirus, and hepatitis A collectively - 100,000 cases of foodborne disease each


transmitted to food or water with fecal matter.


proper food handling, handwashing, clean water

Prions, BSE, and nvCJD Disease

Prions - proteins, that adopt novel conformations, inhibiting normal protein function and causing

disruption in neural tissue

diseases are characterized by neurological symptoms

        depression, loss of motor coordination, and dementia.

foodborne prion disease in humans - “new variant Creutzfeldt-Jakob Disease” (nvCJD)

        consumption of meat products from cattle afflicted with bovine spongiform

        encephalopathy (BSE), “mad cow disease”

nvCJD slow-acting degenerative nervous system disorder

         latent period that extends for years after exposure to the BSE prion

200 nvCJD in United Kingdom and Europe. , none in the US

BSE prions ttle trigger structurally and functionally related human proteins to assume an altered

conformation, resulting in protein dysfunction and disease (Figure 9.29).

BSE and nvCJD are characterized by large vacuoles in brain tissue, giving the brain a “spongy”

appearance, from which BSE derives its name (Figure 29.10).

United Kingdom and Europe - 180,000 cattle have been diagnosed with BSE

Several cattle with BSE have been found in Canada and US

All have been destroyed

infecting prions were transferred to food production animals through meat and bone meal feed

from cattle or other animals not approved for human consumption.

Bans on feeding cattle with meat and bone meal

    Diagnosis of BSE is done by testing using a prion-susceptible mouse strain or by
immunohistochemical or micrographic analysis of biopsied neural tissue (Figure 29.10).

      Identify the viruses most likely to be involved in foodborne illnesses.

          How might prion contamination of food production animals be prevented in the future?


WASTEWATER                                         TREATMENT,                              WATER



I          WASTEWATER MICROBIOLOGY AND WATER PURIFICATION                                              0

28.1       Public Health and Water Quality                                                          907

28.2       Wastewater and Sewage Treatment                                                          909

28.3       Drinking Water Purification                                                              913

I        WATERBORNE MICROBIAL DISEASES                                                                 1

28.4       Sources of Waterborne Infection                                                          915

28.5       Cholera                                                                                  916

28.6       Cryptosporidiosis                                                                        917

28.7       Legionellosis (Legionnaires’ Disease)                                                    919


Water -most important potential common source of infectious diseases

-water purification is the most important single measure available for ensuring public health

-methods commonly used to assess water quality depend on standardized microbiology techniques

-water treatment and purification uses microorganisms to identify, remove, or degrade pollutants.

28.1       Public Health and Water Quality

-identify potentially harmful microorganisms in water.

- indicator organisms

-coliforms -facultatively aerobic, gram-negative, nonspore-forming, rod-shaped Bacteria that ferment

lactose with gas formation within 48 hours at 35° C

-operational definition

-Most are members of the enteric bacterial group

- Escherichia coli, a common intestinal organism

-Klebsiella pneumoniae, a less common pathogenic intestinal inhabitant

- Enterobacter aerogenes, not enteric or intestinal, is a coliform because of fermentative properties

the presence of coliform organisms in a water sample indicates fecal contamination / unsafe for human


The Coliform Test

membrane filter (MF) procedure

- 100 ml of the water sample is passed through a sterile membrane filter

         -placed on a plate of eosin-methylene blue (EMB) culture medium, which is highly selective for

coliform organisms

-coliform colonies are counted, and from this value the number of coliform Bacteria in the original water

sample can be calculated

-coliform tests should be negative

positive tests indicate a breakdown has occurred in the purification or distribution systems.

US Safe Drinking Water Act

coliform bacteria in drinking water samples cannot exceed any of the following levels:

(1) 1 per 100 ml as the arithmetic mean of all samples examined per month;

(2) 4 per 100 ml in more than one sample when fewer than 20 are examined per month; or

(3) 4 per 100 ml in more than 5% of the samples when 20 or more samples are examined per month

United States Environmental Protection Agency is the enforcement agency

-Utilities must correct the problem

-smaller communities and even large cities sometimes fail to meet these standards ("boil water alert")
Public Health and Drinking Water Purification

    Figure 28.2 - drop in incidence of typhoid fever (infection with Salmonella typhi) in a major

American city after filtration and chlorination in the early 1900s

    filtration and chlorination methods relied I on coliform tests for assessment

     public works engineering, microbiology, and public health moved forward together.

   Why do the bacterial colonies recovered from drinking water and grown on EMB media indicate fecal

    contamination of the water supply?

   What general procedures are used to reduce microbial numbers in water supplies?

28.2     Wastewater and Sewage Treatment

Wastewater - liquid derived from domestic sewage or industrial sources that cannot be discarded in

untreated form into lakes or streams due to public health, economic, environmental, and aesthetic


Wastewater treatment involves a large-scale use of microorganisms for bioconversion on an industrial

scale. the effluent water—treated wastewater discharged from the wastewater treatment facility—is

suitable for release into surface waters such as lakes and streams or to drinking water purification facilities

Wastewater and Sewage

Wastewater from domestic sewage or industrial sources cannot be discarded in untreated form into lakes or

streams. Sewage is liquid effluent contaminated with human or animal fecal materials.

-wastewater treatment involves physical, chemical, and biological (microbiological) treatments to remove

or neutralize contaminants

-100–200 gallons of water per day per person for washing, cooking, drinking, and sanitary needs.

-16,000 publicly owned treatment works (POTW)

-32 billion gallons of wastewater daily.

Domestic wastewater is made up of sewage, ―gray water‖ (the water resulting from washing, bathing, and

cooking), and wastewater from food processing.

Industrial wastewater includes liquid discharged from the petrochemical, pesticide, food and dairy,

plastics, pharmaceutical, and metallurgical industries

Wastewater Treatment and Biochemical Oxygen Demand
biochemical oxygen demand (BOD), the relative amount of dissolved oxygen consumed by

microorganisms to completely oxidize all organic and inorganic matter in a water sample -more oxidizable

organic and inorganic materials in the wastewater result in a higher BOD.

domestic wastewater and sewage ~ 200 BOD units

dairy plants- 1500 BOD units

GOAL: effluent < 5 BOD

Figure 28.3

Primary, secondary, and sometimes tertiary treatments

Primary wastewater treatment uses only physical separation methods to separate solid and particulate

organic and inorganic materials from wastewater -Figure 28.4

most treatment plants employ secondary and even tertiary

Anoxic secondary wastewater treatment -digestive and fermentative reactions carried out by bacterial

and archaeal species under anoxic conditions

- treatment of wastewater containing large quantities of insoluble organic matter high BOD) -fiber and

cellulose waste from food- and dairy-processing plants

sludge digesters or bioreactors and reactions (Figure 28.5)

-major products of anoxic treatment are CH4 (methane) and CO2

Aerobic Secondary Wastewater Treatment

- digestive reactions carried out by microorganisms under aerobic conditions to treat nonindustrial

wastewater containing low levels of organic materials

-trickling filter (Figure 28.6)

-wastewater is sprayed on a bed of crushed rocks, about 2 m thick

-liquid passes through the bed, the organic matter adsorbs to the rocks

-organic material is converted to carbon dioxide, ammonia, nitrate, sulfate, and phosphate by microbial


-activated sludge process

wastewater mixed and aerated in a large tank (Figure 28.6b)

-slime-forming bacteria, including Zoogloea ramigera, among others, grow and form flocs (larger,
aggregated masses) (Figure 28.7).

-aerated effluent containing the flocs is pumped into a holding tank or clarifier where the flocs settle

Some of the floc material (called activated sludge) is then returned to the aerator to serve as inoculum, and

the rest is pumped to the anoxic sludge digestor or is removed, dried, and burned or used for fertilizer

Wastewater normally stays in an activated sludge tank for 5 to 10 hours

-during this time much of the soluble organic matter is adsorbed to the floc and incorporated by the

microbial cells. The BOD of the liquid effluent is considerably reduced (up to 95%) by this process

-most of the BOD now contained in the settled flocs

Tertiary wastewater treatment is any physicochemical or biological process employing bioreactors,

precipitation, filtration, or chlorination procedures similar to those employed for drinking water purification

wastewater disinfection


- ultraviolet (UV) radiation to disinfect effluent water

-Ozone -O3

   What is biochemical oxygen demand (BOD)? Why is BOD reduction necessary in wastewater


   Identify the processes in primary, secondary (anoxic and oxic), and tertiary sewage treatment.

   Identify the final products of wastewater treatment. How might these end products be used?

28.3     Drinking Water Purification

Goal: produce potable,water - water that is safe for human consumption

-treatment to remove potentially pathogenic microorganisms, eliminate taste and odor, reduce nuisance

chemicals such as iron and manganese, and decrease turbidity - a measure of suspended solids

Physical and Chemical Purification

Figure 28.8 - flow of raw water (untreated water) through a typical treatment scheme

Raw water to

- sedimentation basin where anionic polymers, alum (aluminum sulfate), and chlorine are added.

Sediment, soil, sand, mineral particles, and other large particles, settle out
-clarifier or coagulation basin, a large holding tank where coagulation takes place. The alum and anionic

polymers form large particles from the much smaller suspended solids.

flocculation After mixing, the particles continue to interact, forming large, aggregated masses

         -aggregated floc, settle by gravity, trapping microorganisms, absorbing suspended organic matter

and sediment.

Filtration- The water is passed through a series of filters designed to remove remaining organic or

inorganic solutes, as well as suspended particles and microorganisms

sand, activated charcoal, and ion exchange filters

the filtered water is free of particulate matter, most organic and inorganic chemicals, and nearly all



finished water -clarified, filtered water that is disinfected

-now suitable for release to the supply system as pure, potable water

Chlorination - kills microorganisms within 30 min, oxidizes and neutralizes organic compounds,

improving water taste and smell (chlorine is consumed)

added to water as sodium hypochlorite, calcium hypochlorite or as a gas from pressurized tanks

chlorine residual - chlorine must remain remains to react with the microorganisms after all reactions with

organic materials have occurred -0.2-0.6 mg/ml recommended

-potable water is pumped to storage tanks from which it flows by gravity or pumps distribution system -

storage tanks and supply lines

Chlorine gas is volatile and can dissipate within hours from treated most municipal water treatment plants

also introduce ammonia gas with the chlorine to form the stable, nonvolatile chlorine-containing compound

chloramine, HOCl + NH3  NH2Cl + H2O

28.3 Concept Check

   Trace the treatment of water through a drinking water treatment plant, from the inlet to the final

    distribution point (faucet).

   What specific purposes do sedimentation, coagulation, filtration, and disinfection accomplish in the

    drinking water treatment process?

Common-source infectious diseases are caused by microbial contamination of materials shared by a large

number of individuals. Water is the most important common source of infectious disease

Inadequate drinking water treatment may result in exposure of thousands or even millions of individuals to

an infectious agent - significant cause of morbidity and mortality, especially in developing countries.

28.4        Sources of Waterborne Infection

Potable Water

In the United States, a number of different bacterial and protozoan pathogens are occasionally transmitted

in drinking water (Table 28.1).

Recreational Water

Recreational water includes freshwater recreational areas such as ponds, streams, and lakes, as well as

public swimming and wading pools- regulated by state and local health

-unregulated swimming pools, spas, and hot tubs are also occasional sources of outbreaks of waterborne


Table 28.2 categorizes these outbreaks according to the diseases produced.

Waterborne Infections in Developing Countries are much more common.

   Identify the microorganism most commonly responsible for disease outbreaks due to drinking water


   Identify the microorganism most commonly responsible for disease incidence (numbers of infections)

    due to drinking water contamination.

   Identify the organisms most likely to cause an outbreak of disease due to contaminated recreational


28.5        Cholera

Cholera - severe diarrheal disease
-largely restricted to the developing parts of the world

- controlled by application of appropriate water treatment measures.

Biology and Epidemiology

Vibrio cholerae, a gram-negative, curved rod

-transmitted through ingestion of contaminated water

-Since 1817, cholera has swept the world in seven major pandemics.

the seventh pandemic strated in Indonesia in 1961, and its spread continues to the present- not currently in

the Americas.

In 1992, a genetic variant, the V. cholerae O139 Bengal serotype, arose in Bangladesh and caused an

extensive epidemic - the beginning of the eighth pandemic?

In 2001, there were 184,311 reported cases and 2728 deaths worldwide, with over 94% of disease occurring

in Africa. The 1961 pandemic has caused over 5 million cases of cholera and more than 250,000 deaths.

Cholera is endemic in Africa, Southeast Asia, the Indian subcontinent, frequently in areas where sewage

treatment is either inadequate or absent

V. cholerae appears to be endemic and free-living in coastal waters, adhering to normal flora (Figure



ingestion of a substantial inoculum, the Vibrio cholerae cells

-grow in the small intestine

At least 108 in water, 104 in food.In the small intestine V. cholerae attaches to epithelial cells, where it

grows and releases enterotoxin -

A-B enterotoxin causes severe diarrhea

-dehydration and death unless the patient is given fluid and electrolyte therapy

fluid losses of up to 20 liters (20 kg or 44 lb) per day

mortality from untreated cholera is generally 25 to 50% - greater under conditions of severe crowding and


Diagnosis, Prevention, and Treatment

-presence of the gram-negative comma-shaped Vibrio cholerae bacilli in the ―rice water‖ stools of patients

with severe diarrhea (Figure 28.10)


Immunization is not effective

Public health measures such as adequate sewage treatment and a reliable source of safe drinking water are

the most important measures for preventing cholera.

- in cholera-endemic areas, untreated water, raw foods, fish, and shellfish should be avoided.


Intravenous or oral liquid and electrolyte replacement therapy (20 g glucose, 4.2 g NaCl, 4.0 g NaHCO 3,

1.8 g KCl, dissolved in one liter of water) Effective treatment reduces the mortality rate to about 1%.

Streptomycin or tetracycline may shorten the course of cholera, but antibiotics are of little benefit without

simultaneous fluid and electrolyte replacement.

   Identify measures for preventing cholera in endemic areas.

   Define the most likely methods for acquiring cholera.

   Identify specific measures for treating cholera.

28.6     Cryptosporidiosis

Cryptosporidium parvum was responsible for the largest single common-source outbreak of a waterborne

disease ever recorded in the United States

-Milwaukee, Wisconsin, spring 1993, over 403,000 people in the population of 1.6 million developed a

diarrheal illness that was traced to the municipal water supply. Spring rains and runoff from surrounding

farmland had drained into Lake Michigan and overburdened the water purification system, leading to

contamination by C. parvum. The protozoan is a significant intestinal parasite in dairy cattle, the likely

source of the outbreak.

protozoan Cryptosporidium parvum

-problematic even in well-regulated water supplies - found in nearly all surface waters and highly resistant

to chlorine.

Cryptosporidium parvum parasite in a variety of warm-blooded animals

2.-5 m round coccidia

-grow intracellularly in mucosal epithelial cells of the stomach and intestine

-thick-walled, chlorine-resistant, infective oocysts, which are shed into water in high numbers in the feces

of infected warm-blooded animals (Figure 28.12).

- passed on when other animals consume the fecally contaminated water

-Cryptosporidium cysts are highly resistant to chlorine and UV

- sedimentation and filtration removes Cryptosporidium

Cryptosporidiosis - self-limiting mild diarrhea that subsides in 2 weeks or less in normal individuals

-individuals with impaired immunity such as acquired immunodeficiency syndrome (AIDS) patients or the

very young or old can develop serious complications. In the Milwaukee outbreak, about 4400 people

required hospital care, and several died of complications from the disease, including severe dehydration.

-the epidemic cost the inhabitants of Milwaukee over $96 million in medical costs and lost productivity.


- demonstration of Cryptosporidium oocysts in the stool (Figure 28.12)


-unnecessary for those with normal immunity. For individuals undergoing immunosuppressive therapy

(e.g., prednisone), discontinuation of immunosuppressive drugs is recommended. Immunocompromised

individuals should be given supportive therapy (for example, intravenous fluids and electrolytes)


Adequately treated water

28.6 Concept Check

   Explain the importance of cysts in the survival and infectivity of Cryptosporidium parvum.

   Why are protozoans often associated with waterborne diseases, even in developed countries? Outline

    steps to reduce their impact.

28.7     Legionellosis (Legionnaires’ Disease)

Legionella pneumophilais an important waterborne pathogen normally transmitted in aerosols rather than
through drinking water or recreational water.

Biology and Epidemiology

Legionella pneumophila caused an outbreak of pneumonia during an American Legion convention in

Philadelphia (USA) in the summer of 1976.

-thin, gram-negative obligately aerobic rod (Figure 28.13) with complex nutritional requirements,

including an unusually high iron requirement

-detected by immunofluorescence techniques and can be isolated from terrestrial and aquatic habitats as

well as from patients suffering from legionellosis.

L. pneumophila is present in small numbers in lakes, streams, and soil

- resistant to heating and chlorination, spread through water distribution systems

-found in large numbers in cooling towers and evaporative condensers of large air conditioning systems.

-grows in the water and is disseminated in humidified aerosols

-infection is via airborne droplets- not spread person to person

-outbreaks of legionellosis tend to peak in mid-to late summer months when air conditioners are

extensively used.

-hot water tanks and spas where it grows to high numbers in warm (35–45°C), stagnant water

- 4–6 cases per million in the United States, but up to 90% of actual cases are probably not diagnosed or

properly reported


improving the maintenance and design of water-dependent cooling and heating systems and water delivery

systems. The pathogen can be eliminated from water supplies by hyperchlorination or by heating to >63 oC


L. pneumophila

intracellular parasite that invades and grows in alveolar macrophages and monocytes

- often asymptomatic or produce a mild cough, sore throat, mild headache, and fever

mild, self-limiting cases, called Pontiac fever, need no treatment, and resolve in 2–5 days

-serious infections - pneumonia often occur in elderly individuals whose resistance has been previously

Pneumonia characrterized by dry cough and chest and abdominal pains

preceded by intestinal disorders, followed by high fever, chills, and muscle aches.

Death occurs in up to 10% of cases and is usually due to respiratory failure.

Diagnosis and Treatment

Clinical detection of L. pneumophila is usually done by culture from bronchial washings, pleural fluid, or

other body fluids. Serological (antibody) tests are used as retrospective evidence for Legionella infection L.


-antigens detected in patient urine

-treatment with IV eythromycin

        Indicate the source of Legionella pneumophila.

        Identify specific measures for control of Legionella pneumophila.

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