Enterobacteriaceae
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Escherichia
Shigella
Edwardsiella
Salmonella
Citrobacter
Klebsiella
Enterobacter
Hafnia
Serratia
Proteus
Morganella
Providencia
Yersinia
Erwinia
1. Escherichia
E. coli
 common isolate from the colon flora
 black/green metallic sheen on EMB
 possesses O, H and K Ag.
Diarrheal Infections
1. EPEC – enteropathogenic E. coli
- infantile diarrhea
- watery stool w/ mucus but w/o blood
2. ETEC – enterotoxigenic E. coli
- traveller’s diarrhea
- infective dose of 106
- produce LT and ST toxin
- non-bloody, watery diarrhea with abdominal cramps and low grade fever
3. EIEC – entero invasive E. coli
a. cause dysentery (direct penetration, invasion and destruction of the intestinal
mucosa) – similar to dysentery
b. scanty stool with pus, mucus and blood
4. EAEC – enteroadherent E. coli
a. cause diarrhea by adhering to the mucosal surface of intestine.
b. watery diarrhea, vomiting and dehydration
5. EHEC – enterohemorrhagic E. coli or VTEC (E. coli 0157:H7)
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a. Hemorrhagic diarrhea, colitis and hemolytic uremic syndrome (HUS)
b. Bloody diarrhea and crampy abdominal pain
Other Infections
1. Septicemia and Meningitis
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accounts for 40% of neonatal meningitis
2. Urinary Tract Infections
 90% of cases of UTI
2. Shigella
Clinical Infections
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Shigellosis or Bacillary Dysentery
o watery diarrhea
o bloody stool with WBC’s & mucus
o fecal-oral route (human – only known reservoir)
o self-limiting but highly communicable, low infective dose (200 bacilli)
o Gay bowel syndrome (S. flexneri)
3. Edwardsiella
 tarda (human pathogen – bacteremia and wound infection)
 hoshinae (snakes, birds and water)
 ictaluri (enteric septicemia in fish)
4. Salmonella
 Virulence factors O, H and Vi antigens
 Do not ferment lactose
 Produce H2S
 Major cause of food poisoning in the U.S.
 Cause intestinal infections (enterocolitis); enteric fevers (typhoid fever); and
systemic infections (septicemia)
 Chickens are a major reservoir for this bacteria
 Identification on basis of antigens (O, H, Vi)
Salmonella – pathogenesis
Enterocolitis: invasion of epithelial cells of intestines
infectious dose (ID50) ~ 100,000 organisms
infection of gut - inflammation and diarrhea, self-correcting
Typhoid:
starts in small intestine: enters and multiplies in mononuclear cells; spreads to
liver, gallbladder, spleen. Leads to bacteremia with onset of fever.
carrier state - organisms excreted in feces
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Septicemia:
minority of infections, usually in patients with underlying disorder
5. Citrobacter
a. freundii (UTI, pneumonia, intraabdominal abscess)
b. diversus (neonatal meningitis)
c. amalonaticus (extraintestinal infections)
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Klebsiella
K. pneumonia (encapsulated and mucoid)
K. oxytoca – similar w/ K. pneumoniae except for its indole production
K. ozanae – from nasal secretions
K. rhinoschleromatis – causes rhinoscleromatis (infection of nasal cavity with intense
swelling and malformation of the entire face and neck)
7. Enterobacter
a. freundii (UTI, pneumonia, intraabdominal abscess)
b. diversus (neonatal meningitis)
c. amalonaticus (extra-intestinal infections)
8. Serratia
 DNAse, lipase, gelatinase
S. marcescens
S. liquefaciens
S. rubidaea
S. oderifera
9. Hafnia
Hafnia alvei
10. Proteus
rapid urease producers
swarming
burned chocolate odor
11. Morganella
M. morganii
UTI’s and wound infections
12. Providencia
13. Yersinia
 Y. pestis (plague) – bipolar staining (wayson)
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o Bubonic – bite of infected flea
o Pneumonic
o Prefered growth at 25 deg C
Y. enterocolitica (acute enteritis – appendictis like)
o Pig, cats and dogs
o Cold enrichment
o Motile at RT
Y. pseudotuberculosis
o Pathogen in animals (turkey, geese, doves, farm and domestic animals)
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Agent of bubonic plague, pneumonic and septicemic plagues
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Bubonic plague contracted via flea bites
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Y. pestis sheds capsule while growing in invertebrate host.
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In humans most of the microbe is taken up and killed by PMN cells
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Some organisms taken up by Macrophages which can’t kill pestis.
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Organism multiples in Mac and resynthesizes capsule
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Organism kills Mac and is released into extracellular environment.
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The encapsulated microbe resists phagocytosis and spreads to lymph nodes which become
swollen, and hemorrhagic giving the black buboes characteristic of the disease.
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Microbe rapidly spreads through blood, liver, spleen, lung giving rise to highly contagious
pneumonia (highly fatal).
14. Erwinia
Plant pathogens
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