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Bacterial Pathogenesis Todar Online Textbook of Bacteriology

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					                            Bacterial Pathogenesis
      Todar's Online Textbook of Bacteriology: Bacterial Pathogens of Humans

• Transmission of human pathogens (a few examples)
• Food and water (contaminated & untreated)
    – E. coli O157:H7
        – Undercooked ground beef & unpasteurized fruit drinks (e.g., cider)
    – Clostridium botulinum spores
        – Improperly prepared canned foods (e.g., beans)
    – Poultry (undercooked)
       – Salmonella
       – Salmonella enteriditis (undercooked eggs)
    – Untreated water sources
       – Vibrio cholerae (cholera)
       – Shigella dysenteriae (bacterial dysentery)


• Aerosols (coughing and sneezing)
    – Mycobacterium tuberculosis (tuberculosis)
• Transmission of human pathogens (a few examples)

• Insects (microorganisms are most often protozoan pathogens)
    – Plasmodium vivax (malaria)


• Animal bites
    – Rabies (virus)
    – Yersinis pestis (bubonic plague) - rodents


• STDs
    – HIV (virus)
    – Neisseria gonorrhoeae (gonorrhea)
    – Treponema pallidum (syphilis)
                    Normal Flora – no need to “transmit”
•   Cause diseases when "relocated" and/or body conditions change

•   Streptococcus pneumoniae (moves from upper to lower respiratory tract)

•   Staphylococcus aureus (moves from nasal passage to skin and other sites)

•   Clostridium difficile (colon - use of antibiotics)

•   Streptotoccus mutans (if oral hygiene is substandard)

•   Streptococcus pygoenes (strep throat and rheumatic fever)

•   Propionibacterium acne (high lipid/oils on skin)
            Other ways to oxidize NADH -> NAD (for reuse)
•   Wide variety of other end products are produced depending on what is happening
•   Still starts with pyruvic acid
                    Normal Flora – no need to “transmit”
•   Cause diseases when "relocated" and/or body conditions change

•   Streptococcus pneumoniae (moves from upper to lower respiratory tract)

•   Staphylococcus aureus (moves from nasal passage to skin and other sites)

•   Clostridium difficile (colon - use of antibiotics)

•   Streptotoccus mutans (if oral hygiene is substandard)

•   Streptococcus pygoenes (strep throat and rheumatic fever)

•   Propionibacterium acne (high lipid/oils on skin)

•   Helicobacter pylori (90-95% of peptic ulcers)
                       More examples of bacterial pathogens
    Pathogenic Microbiology - The Study of Disease-Causing Bacteria: List of Bacterial Pathogens

• List of Bacterial Pathogens
     http://www.life.umd.edu/classroom/bsci424/PathogenDescriptions/PathogenList.htm
• Infectious Diseases Sorted by Etiological Agent
•    http://classes.midlandstech.edu/carterp/Courses/bio225/InfectiousDiseases_all_print.htm


• Typhus – Rickettsia typhi
      • Obligate intracellular parasite (bacterium)
• Typhoid – Salmonella typhi
• Meningitis
      • Viral
      • Bacterial
          • Neisseria meningitidis (meningococcal vaccine)
          • Streptococcus pneumoniae (Prevnar vaccine)
          • Haemophilus influenzae type b (Hib vaccine)
                 More examples of bacterial pathogens
• Whooping cough – Bordetella pertussis
• Staphylococcal aureus infections
    – antibiotic resistance - penicillin, methicillin, vancomycin, and …….
• Toxic shock syndrome (TSS)
    – Staphylococcus and Streptococcus species
• “Pneumonia”
    –   Streptococcus pneumoniae
    –   Klebsiella pneumoniae
    –   Chlamydia pneumoniae
    –   Mycoplasma pneumoniae
    –   Haemophilus influenzae
    –   Mycobacterium tuberculosis
       Emerging and re-emerging infectious diseases – why?

• Tuberculosis (Mycobacterium tuberculosis) – antibiotic resistance

• Staphylococcus aureus – vancomycin resistance

• Polio (virus disease) – decrease in, or no, use of polio vaccines

• Cholera (Vibrio cholerae) – declining sanitary conditions

• Campylobacter jejuni food contamination – reason unknown

• Whooping cough (Bordetella pertussis) – vaccine effectiveness may have
  “worn off” (“aP” portion of DaPT vaccine)

• Measles (virus) – initial vaccine (“M” part of MMR) may not have been
  effective for persons now of college age
                          Bacterial virulence factors
Todar's Online Textbook of Bacteriology: Mechanisms of Bacterial Pathogenicity MICROBIOLOGY
           101/102 INTERNET TEXT:: CHAPTER XIII: HOW MICROBES CAUSE DISEASE

• Anything that contributes to pathogenicity
• Can be a single virulence factor
• Some bacteria have a very wide variety of virulence factors
            Bacterial virulence factors – some examples
• Exotoxins (secreted enzymes and waste products)
• Cytolytic exotoxins
    – Destroy red blood cells or nucleated cells
    – Hemolysins (Streptococcus pyogenes)
    – Leukocydins (Streptococcus pyogenes – streptolysin)
• Invasive enzymes
    – Staphylococcus aureus – hyaluronidase
    – Clostridium perfringens – collagenase
• Break down clots (to release bacteria)
    – streptokinase, staphylokinase
• A-B exotoxins
    – Corynebacterium diphtheriae (diphtheria)
                         A-B exotoxins (continued)
• Neurotoxins
   – Botulism (Clostridium botulinum)
   – Tetanus (Clostridium tetanus)
                    Prevention and treatment of tetanus

•   Prevention
•   Tetanus toxoid vaccine (toxin is an A-B exotoxin)
•   Vaccine is effective for 8-10 years
•   Requires “booster” to maintain protection

• Treatment - Physician’s response to various scenarios regarding possible
  exposure to tetanus toxin
     – Patient knows her immunization history and has received a tetanus “shot” (toxoid) in the
       past 8 years
     – Patient does not know her immunization history or is not sure about any tetanus “shot”
     – Patient knows her immunization history and has not received a tetanus vaccine (or
       booster) in the past 8-10 years
           Pathology is caused by a Vibrio cholerae enterotoxin
• Exotoxins that affect the intestinal tract
• Bacterium adheres to endothelial cells
    – (via fimbriae)
• Secretes A-B enterotoxin
    – Two distinct functional parts
    – B attaches to membrane GM1 ganglioside
    – A enters - dramatically increases cAMP production
• High concentration of ions pumped into in lumen
    – Water flows out of tissues in attempt to
      create equilibrium solute concentration
• Quantity of water loss from body can be huge
• Endotoxins
• Lipid A portion of gram-negative lipopolysccharides
• Stimulates overreaction of body’s phagocytic cells
    – normal body tissue is destroyed
    – excessive inflammation
• Difficult to make effective vaccine
                             Adherence mechanisms
                (where attachment is crucial to initiating pathology)
•   Fimbriae (already discussed)
•   Capsules (in addition to providing protection from phagocytosis)
     – Polysaccharide (Streptococcus pneumoniae, Klebsiella pneumoniae)
     – Protein (Streptococcus pyogenes)
•   Biofilms
     –   extracellular DNA, proteins, polysaccharides
     –   dextrans in the oral cavity (Streptococcus mutans)
     –   Neisseria gonorrhoeae
     –   Cystic Fibrosis - Pseudomonas aeruginosa
     –   medical catheters
     –   Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus
         viridans, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Pseudomonas
         aeruginosa

				
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