Enterobacteriaceae
Dr Ekta Chourasia
Lecturer, Microbiology
General Features of Enterobacteria
Present in large intestine
Gram negative bacteria
Aerobic or facultative anaerobic
Motile by peritrichate flagella or non motile
Grow on ordinary media (non fastidious)
Ferments glucose with acid & gas or only acid
Reduce nitrates to nitrites
Catalase + ve & oxidase -ve
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Classification of Enterobacteriaceae

Based on lactose fermentation – oldest method :
1.
Lactose fermenters e.g. Escherichia, Klebsiella.
2.
Late lactose fermenters e.g. Shigella sonnei
3.
Non lactose fermenters e.g Salmonella, Shigella
-
Commensal intestinal bacteria: LF
-
Intestinal pathogens: NLF
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Classification of Enterobacteriaceae
Modern taxonomy – group together bacteria that
possess:

1.
Common morphological and biochemical properties
2.
Similar DNA base compositions

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Family – Tribe / Group - Genera
Enterobacteriaceae (Tribes & Genera)
CDC 1989
Tribe 1 Eshcherichieae
Tribe 5 Klebsielleae
Klebsiella
Escherichia
Serratia
Enterobacter
Shigella
Hafnia
Pantoea
Tribe 2 Edwardsielleae
Edwardsiella
Tribe 3 Salmonelleae
Salmonella
Tribe 4 Citrobactereae
Citrobacter
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Tribe 6 Proteeae
Providentia
Tribe 7 Yersinieae
Yersinia
Tribe 8 Erwinieae
Erwinia
Proteus
Morganella
Escherichia coli

Named after Escherich, first to describe colon bacillus

Normal flora of the human & animal intestine.

Remains viable in the feces for few days.

Detection of E.coli in the drinking water – indicates
recent pollution with human or animal feces.
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Antigenic Structure of Gram –ve Bacteria

Three antigens – serotyping
of E.coli
1.
H – flagellar antigen
2.
O – somatic antigen
3.
K – capsular antigen
Majority do not possess K Ag.
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Virulence Factors
- Two types of virulence factors: Surface Ags & Toxins
1. Surface Antigens
-
LPS surface O Ag – endotoxic activity, protects from
phagocytosis and bactericidal effects of complement
-
Envelope or K Ag – protects against phagocytosis and
antibacterial factors inserum
-
Fimbriae – colonisation factors, found in strains causing
diarrhoea and urinary tract infections
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Virulence Factors
2. Toxins (Exotoxins) – two types
-
Enterotoxins – pathogenesis of diarrhoea
- 3 types : LT (heat labile toxin),
ST (heat stable toxin) &
VT (verocytotoxin or shiga- like toxin)
-
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Hemolysins – may be nephrotoxic
Heat Labile Toxin (LT)
 Resembles cholera toxin in its
structure, function and mode of
action
 Complex of polypeptide
subunits.
 LT: one subunit of A
(action- enzymic),
five subunits of B (binding)
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Heat Labile Toxin (LT)
Escherichia coli /
Vibrio cholerae
Gut lumen
Intestinal
epithelial cell
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E.coli toxins
Heat Labile Toxin (LT)
Heat Stable Toxin (ST)
Activates Adenyl cyclase
Activates guanyl cyclase
increased production of cAMP
Increased production of cGMP
Increased secretion of Na, Cl and water
from the cell
Inhibition of ionic uptake in intestinal cells
Osmotic loss of water from cells
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Pathogenicities/ Clinical Infections
1.
Urinary tract infection
2.
Diarrhoea
3.
Pyogenic infections
-
Wound infection, especially after surgery of lower intestinal tract.
-
Peritonitis.
-
Biliary tract infection.
-
Neonatal meningitis.
Septicemia – can lead to fatal conditions like
4.
-
Septic shock
-
Systemic Inflammatory Response Syndrome
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Lab Diagnosis of UTI
Specimens
Microscopy
Wet mount
Urine
Mid stream urine (MSU)
Catheter specimen urine (CSU)
Supra pubic aspiration (SPA)
Pus cells / hpf
Bacteria / crystals/ casts
Gram stain
Gram negative bacteria
(1bacteria / oil field is significant)
Urine Culture
Kass semi-qauntative method
Standard loop technique
To know significant bacteriuria
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Lab Diagnosis of E. coli UTI
Significant
bacteriuria
> 105 organism / ml of MSU
Culture
BA / MAC : LF (flat)
Identification tests
I M Vi C test: + + - TSI agar
AST
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Acid, no gas
Diarrheagenic E.coli
 Enteropathogenic E.coli (EPEC)
 Enterotoxigenic E.coli (ETEC)
 Enteroinvasive E.coli (EIEC)
 Enterohemorrhagic E.coli (EHEC) or Verotoxigenic E.coli (VTEC)
 Enteroaggregative E.coli (EAEC) : “stacked brick” appearance.
 Diffusely adherent E.coli (DAEC)
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Enteropathogenic E.coli (EPEC)
 Infantile diarrhea
 Institutional outbreaks
 Noninvasive, nontoxigenic
 Pathogenesis – adhesion via fimbria, disruption of brush border
microvilli
 Clinical features – fever, diarrhea, vomiting, nausea, non bloody stools
 Lab Diagnosis – testing colonies grown on BA/ MA with EPEC
O antisera
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Enterotoxigenic E.coli (ETEC)
 Traveller’s diarrhea
 Resembles cholera
 Noninvasive, toxigenic
 Pathogenesis – production of plasmid coded toxins (LT/ ST)
 Clinical features - Diarrhea, vomiting and abdominal pain
 Lab Diagnosis – demonstration of enterotoxin by in vitro or in vivo
methods, detection of LT/ St by gene probes
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Enteroinvasive E.coli (EIEC)

Bloody diarrhea (dysentery), resembles Shigella
dysentery

Passage of blood, mucus & leucocytes in stool

Pathogenesis - Invades epithelial cells by endocytosis
and can spread laterally to adjacent cells, causes tissue
destruction, necrosis and ulceration.

Lab Diagnosis:
1.
Sereny test- instillation of suspension of freshly isolated EIEC or
Shigella in the eyes of guinea pig – mucopurulent conjunctivitis
and severe keratitis
2.
Penetration of HeLa or Hep2 cells in tissue culture
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Enterohemorrhagic E.coli (EHEC)

Produces verocytotoxin (VT), a shiga-like toxin (SLT); hence also
known as Verocytotoxigenic E.coli (VTEC)

Pathogenesis – EHEC attaches to the colonic mucosa and
releases VT. VT targets vascular endothelial cells, inhibits protein
synthesis - cytotoxicity

Clinical features - Mild diarrhea (bloody) to fatal complications
(esp. in young children and elderly):
1.
Hemorrhagic colitis – destruction of mucosa followed by hemorrhage.
2.
Hemolytic Uremic syndrome – triad of acute renal failure, hemolytic
anemia and thrombocytopenia.

Serotype O157: H7 is most commonly involved.

Outbreaks of food poisonings (fast foods, contaminated
hamburgers)
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Enterohemorrhagic E.coli (EHEC)

Lab Diagnosis:
1.
Demonstration of bacilli or VT in feces or in culture
2.
Sorbitol MacConkey agar for O157:H7 – does not ferment sorbitol
unlike other E.coli
3.
Cytotoxic effects on Vero or HeLa cells
4.
DNA probes to detect toxins
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Enteroaggregative E.coli (EAEC)
 Persistent diarrhea in children in developing countries.
 Aggregate to give a “Stacked brick appearance” on Hep2 cells
or glass (due to fimbria)
 Pathogenesis – shortening of villi, mucus biofilm, heat stable
cytotoxin (hemorrhagic necrosis and edema)
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Epidemiology & Treatment
Epidemiology
 EPEC & ETEC - most important causes of diarrhea globally
 EHEC – in developed countries.
Treatment
 Based on symptoms:
1. Primary treatment – fluid replacement
2. Secondary treatment – antibiotics in severe cases with systemic
involvement
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Klebsiella
Normal gut flora in the intestine
Gram negative coccobacilli (short & plump)
Capsulated, non-motile, Mucoid LF colonies on MAC
Species
K. pneumoniae
K. oxytoca
Pneumonia, Urinary tract infections
K. ozaenae
Atrophic rhinits
K. rhinoscleromatis
Rhinoscleroma
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Pathogenicities of Klebsiella pneumoniae



Pulmonary infections - Pneumonia (lobar):
1.
High fatality
2.
In middle aged or older persons with medical problems like DM,
alcoholism, chronic bronchopulmonary disease
3.
Extensive necrosis & hemorrhage resulting in thick, mucoid, brick
red sputum “currant jelly like”
Extrapulmonary infections –
1.
Meningitis & enteritis in infants
2.
UTI
3.
Septicemia
An important cause of nosocomial infections.
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Lab Diagnosis - Klebsiella
Specimens
Urine, sputum, nasal secretions / swab,
blood
Culture
BA / MAC : LF (mucoid)
Identification tests
I M Vi C test: - - + +
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TSI agar
Acid with gas
Urease
Positive
Proteus
Normal gut flora in the intestine
Gram negative bacilli, pleomorphic
Motile, Non lactose fermenter NLF on MAC
Swarms on BA, Urease +, H2S +
Species
P mirabilis
P vulgaris
UTI
Pneumonia
Wound infections
Urease converts urea to NH4 & CO2 causing alkalinization of
urine leading to renal calculi (stones)
Proteus antigens are used in the Weil - Felix test to
diagnose Rickettsial diseases
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Lab Diagnosis - Proteus
Specimens
Urine, sputum, wound swab
Culture
BA: swarming
MAC : NLF, fishy/ seminal smell
Identification tests
Indole: PM - / PV +
TSI agar
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Urease +
K / A (H2S)
Enterobacter, Serratia, Citrobacter
 Moist environments in hospitals – common reservoirs.
 Pathogenicities –
- UTI,
- Wound & respiratory infections in hospitalized patients,
- Outbreaks in ICUs, burn units & other special units
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