e.coli_ kleb & proteus

7/29/2019 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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Escherichia coli /

Vibrio cholerae

Gut lumen

Intestinalepithelial cell


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E.coli toxins


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)


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


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

e.coli_ kleb & proteus

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