Chapter 16 Enterobacteriaceae

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					Chapter 16 -
Enterobacteriaceae

MLAB 2434 – Clinical Microbiology
Cecile Sanders & Keri Brophy-Martinez
Chapter 16 - Enterics

 Family Enterobacteriaceae often
  referred to as “enterics”
 Four major features:
     All ferment glucose (dextrose)
     All reduce nitrates to nitrites
     All are oxidase negative
     All except Klebsiella, Shigella and
      Yersinia are motile
    Microscopic and Colony
         Morphology
 Gram negative bacilli or coccobacilli
 Non-spore forming

 Colony morphology on BAP or CA of
  little value, as they look the same,
  except for Klebsiella
 Selective and differential media are
  used for initial colony evaluation
  (ex. MacConkey, HE, XLD agars)
    Classification of Enterics

 Due to the very large number of
  organisms in the Family
  Enterobacteriaceae (see Table 16-
  11), species are grouped into Tribes,
  which have similar characteristics
  (Table 16-1, page 466)
 Within each Tribe, species are
  further subgrouped under genera
Virulence and Antigenic
Factors of Enterics
   Ability to colonize, adhere, produce
    various toxins and invade tissues
   Some possess plasmids that may mediate
    resistance to antibiotics
   Many enterics possess antigens that can
    be used to identify groups
       O antigen – somatic, heat-stable antigen
        located in the cell wall
       H antigen – flagellar, heat labile antigen
       K antigen – capsular, heat-labile antigen
Clinical Significance of
Enterics
 Enterics are ubiquitous in nature
 Except for few, most are present in
  the intestinal tract of animals and
  humans as commensal flora;
  therefore, they are sometimes call
  “fecal coliforms”
 Some live in water, soil and sewage
Clinical Significance of
Enterics (cont’d)
   Based on clinical infections
    produced, enterics are divided into
    two categories:
     Opportunistic pathogens – normally
      part of the usual intestinal flora
      that may produce infection outside
      the intestine
     Primary intestinal pathogens –
      Salmonella, Shigella, and Yersinia sp.
Escherichia coli

 Most significant species in the
  genus
 Important potential pathogen in
  humans
 Common isolate from colon flora
Escherichia coli (cont’d)

   Characteristics
       Dry, pink (lactose positive) colony
        with surrounding pink area on
        MacConkey
Escherichia coli (cont’d)

  Ferments glucose, lactose,
   trehalose, & xylose
  Positive indole and methyl red tests
  Does NOT produce H2S or
   phenylalanine deaminase
  Simmons citrate negative
  Usually motile
  Voges-Proskauer test negative
Escherichia coli (cont’d)

   Infections
     Wide range including meningitis,
      gastrointestinal, urinary tract,
      wound, and bacteremia
     Gastrointestinal Infections
        • Enteropathogenic (EPEC) – primarily in
          infants and children; outbreaks in
          hospital nurseries and day care
          centers; stool has mucous but not
          blood; identified by serotyping
Escherichia coli (cont’d)
   • Enterotoxigenic (ETEC) – “traveler’s
     diarrhea”; watery diarrhea without
     blood; self-limiting; usually not
     identified, other than patient history
     and lactose-positive organisms cultured
     on differential media
   • Enteroinvasive (EIEC) – produce
     dysentery with bowel penetration,
     invasion and destruction of intestinal
     mucosa; watery diarrhea with blood; do
     NOT ferment lactose; identified via
     DNA probes
Escherichia coli (cont’d)
   • Enterohemorrhagic (EHEC serotype
     0157:H7) – associated with
     hemorrhagic diarrhea and hemolytic-
     uremic syndrome (HUS), which includes
     low platelet count, hemolytic anemia,
     and kidney failure; potentially fatal,
     especially in young children;
     undercooked hamburger, unpasteurized
     milk and apple cider have spread the
     infection; does NOT ferment sucrose;
     identified by serotyping
Escherichia coli (cont’d)
     • Enteroaggregative (EaggEC) – cause
       diarrhea by adhering to the mucosal
       surface of the intestine; watery
       diarrhea; symptoms may persist for
       over two weeks
    Urinary Tract Infections
     • E. coli is most common cause of UTI
       and kidney infection in humans
     • Usually originate in the large instestine
     • Able to adhere to epithelial cells in the
       urinary tract
Escherichia coli (cont’d)
       Septicemia & Meningitis
         • E. coli is one of the most common causes of
           septicemia and meningitis among neonates;
           acquired in the birth canal before or during
           delivery
         • E. coli also causes bacteremia in adults,
           primarily from a genitourinary tract infection
           or a gastrointestinal source
   Escherichia hermannii – yellow pigmented;
    isolated from CSF, wounds and blood
   Escherichia vulneris - wounds
Klebsiella, Enterobacter,
Serratia & Hafnia sp.
   Usually found in intestinal tract
   Wide variety of infections, primarily
    pneumonia, wound, and UTI
   General characteristics:
       Some species are non-motile
       Simmons citrate positive
       H2S negative
       Phenylalanine deaminase negative
       Some weakly urease positive
       MR negative; VP positive
Klebsiella species
   Usually found in GI tract
   Four major species
   K. pneumoniae is mostly commonly isolated
    species
       Possesses a polysaccharide capsule, which
        protects against phagocytosis and
        antibiotics AND makes the colonies moist
        and mucoid
       Has a distinctive “yeasty” odor
       Frequent cause of nosocomial pneumonia
Klebsiella species (cont’d)

    Significant biochemical reactions
      • Lactose positive
      • Most are urease positive
      • Non-motile
Enterobacter species

 Comprised of 12 species; E. cloacae
  and E. aerogenes are most common
 Isolated from wounds, urine, blood
  and CSF
 Major characteristics
    Colonies resemble Klebsiella
     Motile
     MR negative; VP positive
Enterobacter species
   (cont’d)
Serratia species

 Seven species, but S. marcescens is
  the only one clinically important
 Frequently found in nosocomial
  infections of urinary or respiratory
  tracts
 Implicated in bacteremic outbreaks
  in nurseries, cardiac surgery, and
  burn units
 Fairly resistant to antibiotics
Serratia species (cont’d)

   Major characteristics
     Ferments lactose slowly
     Produce characteristic pink pigment,
      especially when cultures are left at
      room temperature

    S. marscens on
    nutrient agar →
Hafnia species

   Hafnia alvei is only species
 Has been isolated from many
  anatomical sites in humans and the
  environment
 Occasionally isolated from stools

 Delayed citrate reaction is major
  characteristic
Proteus, Morganella &
Providencia species
 All are normal intestinal flora
 Opportunistic pathogens

 Deaminate phenylalanine

 All are lactose negative
Proteus species

   P. mirabilis and P. vulgaris are widely
    recognized human pathogens
   Isolated from urine, wounds, and ear and
    bacteremic infections
   Both produce swarming colonies on non-
    selective media and have a distinctive
    “burned chocolate” odor
   Both are strongly urease positive
   Both are phenylalanine deaminase positive
Proteus species (cont’d)

 A exhibits characteristic “swarming”
 B shows urease positive on right
Morganella species

   Morganella morganii is only species
 Documented cause of UTI
 Isolated from other anatomical
  sites
 Urease positive

 Phenylalanine deaminase positive
Providencia species

   Providencia rettgeri is pathogen of
  urinary tract and has caused
  nosocomial outbreaks
 Providenicia stuartii can cause
  nosocomial outbreaks in burn units
  and has been isolated from urine
 Both are phenylalanine deaminase
  positive
Citrobacter species

   Citrobacter freundii associated
  with nosocomial infections (UTI,
  pneumonias, and intraabdominal
  abscesses)
 Ferments lactose and hydrolyzes
  urea slowly
 Resembles Salmonella sp.
Salmonella

 Produce significant infections in
  humans and certain animals
 On differential selective agar,
  produces clear, colorless, non-
  lactose fermenting colonies with
  black centers (if media contains
  indicator for hydrogen sulfide)
Salmonella (cont’d)

   Salmonella on MacConkey
Salmonella (cont’d)

 Lactose negative
 Negative for indole, VP,
  phenylalanine deaminase, and urease
 Most produce H2S
 Do not grow in potassium cyanide
 Large and complex group of
  organisms; grouped by O, H, and Vi
  (for virulence) antigens
Salmonella (cont’d)

   Clinical Infections
       Acute gastroenteritis or food poisoning
         • Source = handling pets, insufficiently cooked
           eggs and chicken, and contaminated cooking
           utensils
         • Occurs 8 to 36 hours after ingestion
         • Requires a high microbial load for infection
         • Self-limiting in health individuals (antibiotics
           and antidiarrheal agents may prolong
           symptoms)
Salmonella (cont’d)

    Typhoid and Other Enteric Fevers
     • Prolonged fever
     • Bacteremia
     • Involvement of the RE system,
       particularly liver, spleen, intestines, and
       mesentery
     • Dissemination to multiple organs
     • Occurs more often in tropical and
       subtropical countries
Salmonella (cont’d)

    Salmonella Bacteremia
    Carrier State
     • Organisms shed in feces
     • Gallbladder is the site of organisms
       (removal of gallbladder may be the only
       solution to carrier state)
Shigella species

 Closely related to the Escherichia
 All species cause bacillary
  dysentery
 S. dysenteriae (Group A)

 S. flexneri (Group B)

 S. boydii (Group C)

 S. sonnei (Group D)
Shigella (cont’d)

   Characteristics
       Non-motile
       Do not produce gas from glucose
       Do not hydrolyze urea
       Do not produce H2S on TSI
       Lysine decarboxylase negative
       ONPG positive (delayed lactose +)
       Fragile organisms
       Possess O and some have K antigens
Shigella (cont’d)

   Clinical Infections
       Cause dysentery (bloody stools, mucous,
        and numerous WBC)
       S. sonnei is most common, followed by S.
        flexneri (“gay bowel syndrome”)
       Humans are only known reservoir
       Oral-fecal transmission
       Fewer than 200 bacilli are needed for
        infection in health individuals
Shigella (cont’d)
Yersinia species

   Consists of 11 named species
   Yersinia pestis
       Causes plague, which is a disease primarily
        of rodents; transmitted by fleas
       Two forms of plague, bubonic and
        pneumonic
       Gram-negative, short, plump bacillus,
        exhibiting “safety-pin” or “bipolar”
        staining
Yersinia species
   Yersinia enterocolitica
       Most common form of Yersinia
       Found worldwide
       Found in pigs, cats and dogs
       Human also infected by ingestion of contaminated
        food or water
       Some infections result from eating contaminated
        market meat and vacuum-packed beef
       Is able to survive refrigerator temperatures (can
        use “cold enrichment” to isolate)
       Mainly causes acute gastroenteritis with fever
Yersinia species

   Yersinia pseudotuberculosis
     Pathogen of rodents, particularly
      guinea pigs
     Septicemia with mesenteric
      lymphadenitis, similar to
      appendicitis
     Motile at 18 to 22 degrees C
Laboratory Diagnosis of
Enterics
   Collection and Handling
       If not processed quickly, should be
        collected and transported in Cary-
        Blair, Amies, or Stuart media
   Isolation and Identification
     Site of origin must be considered
     Enterics from sterile body sites are
      highly significant
     Routinely cultured from stool
Laboratory Diagnosis of
Enterics (cont’d)
   Media for Isolation and
    Identification of Enterics
     Most labs use BAP, CA and a
      selective/differential medium such
      as MacConkey
     On MacConkey, lactose positive are
      pink; lactose negative are clear and
      colorless
Laboratory Diagnosis of
Enterics (cont’d)
       For stools, highly selective media,
        such as Hektoen Enteric (HE), XLD,
        or SS is used along with MacConkey
        agar
   Identification
       Most labs use a miniaturized or
        automated commercial identification
        system, rather than multiple tubes
        inoculated manually
Laboratory Diagnosis of
Enterics (cont’d)
   Identification (cont’d)
       All enterics are
         • Oxidase negative
         • Ferment glucose
         • Reduce nitrates to nitrites
Laboratory Diagnosis of
Enterics (cont’d)
   Common Biochemical Tests
     Lactose fermentation and utilization
      of carbohydrates
     Triple Sugar Iron (TSI)
     ONPG
     Glucose metabolism
        • Methyl red
        • Voges-Proskauer
Laboratory Diagnosis of
Enterics (cont’d)
   Common Biochemical Tests (cont’d)
       Miscellaneous Reactions
        •   Indole
        •   Citrate utilization
        •   Urease production
        •   Motility
        •   Phenylalanine deaminase
        •   Decarboxylase tests
Screening Stools for
Pathogens
 Because stools have numerous
  microbial flora, efficient screening
  methods must be used to recover
  any pathogens
 Enteric pathogens include
    Salmonella, Shigella, Aeromonas,
    Campylobacter, Yersinia, Vibrio, and
    E. coli 0157:H7
Screening Stools for
Pathogens (cont’d)
 Most labs screen for Salmonella,
  Shigella, and Campylobacter; many
  screen for E. coli 0157:H7
 Fecal pathogens are generally
  lactose-negative (although Proteus,
    Providencia, Serratia, Citrobacter
    and Pseudomonas are also lactose-
    negative)