Download - E.coli_ Kleb & Proteus
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Enterobacteriaceae
Dr Ekta Chourasia
Lecturer, Microbiology
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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 ofEnterobacteriaceae
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 ofEnterobacteriaceae
Modern taxonomy group together bacteria that
possess:
1. Common morphological and biochemical properties
2. Similar DNA base compositions
Family Tribe / Group - Genera
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Enterobacteriaceae(Tribes & Genera)
Tribe 1 Eshcherichieae
Escherichia
Shigella
Tribe 2 Edwardsielleae
Edwardsiella
Tribe 3 Salmonelleae
Salmonella
Tribe 4 Citrobactereae
Citrobacter
Tribe 5 Klebsielleae Klebsiella
EnterobacterSerratia
Hafnia Pantoea
Tribe 6 Proteeae Proteus
Providentia Morganella
Tribe 7 Yersinieae
Yersinia
Tribe 8 Erwinieae
Erwinia
CDC 1989
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Escherich ia co l i
Named afterEscherich, 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 antigen2. 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)
- Hemolysins may be nephrotoxic
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Heat Labile Toxin (LT)
Resembles cholera toxin in its
structure, function and mode of
action
Complex of polypeptidesubunits.
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
Intestinalepithelial cell
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E.coli toxins
Heat Labile Toxin (LT)
Activates Adenyl cyclase
increased production of cAMP
Increased secretion of Na, Cl and water
from the cell
Heat Stable Toxin (ST)
Activates guanyl cyclase
Increased production of cGMP
Inhibition of ionic uptake in intestinal cells
Osmotic loss of water from cells
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Pathogenicities/ Clinical Infections
1. Urinary tract infection2. Diarrhoea
3. Pyogenic infections
- Wound infection, especially after surgery of lower intestinal tract.
- Peritonitis.- Biliary tract infection.
- Neonatal meningitis.
4. Septicemia can lead to fatal conditions like
- Septic shock- Systemic Inflammatory Response Syndrome
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Lab Diagnosis of UTI
Specimens Urine Mid stream urine (MSU)Catheter specimen urine (CSU)
Microscopy
Wet mountBacteria / crystals/ casts
Gram negative bacteria
Pus cells / hpf
Gram stain
Supra pubic aspiration (SPA)
Urine Culture
Standard loop technique
Kass semi-qauntative method
To know significant bacteriuria
(1bacteria / oil field is significant)
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Significant
bacteriuria
> 105 organism / ml of MSU
Culture BA / MAC : LF (flat)
Identification tests
AST
Lab Diagnosis of E. coli UTI
I M Vi C test: + + - -
TSI agar Acid, no gas
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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)
Travellers 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 Shigelladysentery
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 orShigella 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 alsoknown 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 offood 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
K. ozaenae
K. rhinoscleromatis
Pneumonia, Urinary tract infections
Atrophic rhinits
Rhinoscleroma
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Pathogenicities ofKlebsiel la pneumon iae
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, brickred sputum currant jelly like
Extrapulmonary infections
1. Meningitis & enteritis in infants
2. UTI
3. Septicemia
An important cause ofnosocomial infections.
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Specimens Urine, sputum, nasal secretions / swab,blood
Culture BA / MAC : LF (mucoid)
Identification tests
Urease Positive
Lab Diagnosis - Klebsiella
I M Vi C test: - - + +
TSI agar Acid with gas
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Proteus
Normal gut flora in the intestine
Gram negative bacilli, pleomorphic
Motile, Non lactose fermenter NLF on MAC
Species P mirabilis P vulgaris
Proteus antigens are used in the Weil - Felix test to
diagnose Rickettsial diseases
UTI Pneumonia
Urease converts urea to NH4 & CO2 causing alkalinization ofurine leading to renal calculi (stones)
Swarms on BA, Urease +, H2S +
Wound infections
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Specimens Urine, sputum, wound swab
Culture BA: swarming
Identification tests
Lab Diagnosis - Proteus
Indole: PM - / PV +
TSI agar K / A (H2S)
MAC : NLF, fishy/ seminal smell
Urease +
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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