Enterobacteria Bpt

8/14/2019 Enterobacteria Bpt

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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

Grow on ordinary media (non fastidious)

Ferments glucose with acid & gas or only acid

Catalase + ve & oxidase -ve


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Classification ofEnterobacteriaceae

Based on lactose fermentation oldest method :

Lactose fermenters e.g. Escherichia, Klebsiella

Late lactose fermenters e.g. Shigella sonnei

Non lactose fermenters e.g Salmonella, Shigella

- Commensal intestinal bacteria: LF

- Intestinal pathogens: NLF


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Escherichia coli

Named afterEscherich, first to describe colon bacillus

Normal flora of the human & animal intestine.

Remains viable in the feces for few days.

Detection ofE. coli in the drinking water indicates recent pollutionwith human or animal feces.


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Antigenic Structure of Gram ve Bacteria

Three antigens serotyping

ofE.coli

H flagellar antigen O somatic antigen

K capsular antigen

Majority do not possess K Ag.


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Virulence Factors

- Two types of virulence factors: Surface Ags & Toxins

2. Surface Antigens

LPS surface O Ag endotoxic activity

Envelope or K Ag protects against phagocytosis

Fimbriae colonisation, found in strains causing diarrhoea andurinary tract infections

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


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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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Pathogenicity / 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.

4. Septicemia can lead to fatal conditions like Septic shock


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Lab Diagnosis of UTI

Specimens Urine Mid stream urine (MSU)Catheter specimen urine (CSU)

Microscopy

Wet mountBacteria

Gram negative bacteria

Pus cells / hpf

Gram stain

Supra pubic aspiration (SPA)

Urine Culture 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)

CLED medium

Identification tests

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) infantile diarrhea, nontoxigenic

Enterotoxigenic E. coli (ETEC) travellers diarrhea, resembles cholera

Enteroinvasive E. coli (EIEC) bloody diarrhea (blood, mucus &

leucocytes with stool)

Enterohemorrhagic E. coli (EHEC) orVerocytotoxigenic E. coli

(VTEC):- O157:H7 serotype (food poisoning)

Enteroaggregative E. coli (EAEC) : stacked brick appearance-

persistent diarrhea in children

Diffusely adherent E. coli (DAEC)


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Epidemiology & Treatment

Epidemiology

EPEC & ETEC - most important causes of diarrhea globally

EHEC in developed countries.

Treatment

Based on symptoms:

2. Primary treatment fluid replacement

3. Secondary treatment antibiotics in severe cases with systemic

involvement


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Klebsiella

Normal gut flora in the intestine

Gram negative bacilli (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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Pathogenicity ofKlebsiella pneumoniae

Pulmonary infections - Lobar Pneumonia :

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 ofnosocomial infections.


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Specimens Urine, sputum, nasal

secretions / swab, blood

Culture BA / MAC : LF (mucoid)

Biochemical

testsUrease Positive

Lab Diagnosis - Klebsiella

TSI agar Acid with gas

Citrate Positive


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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 +, H2

S +

Wound infections


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Shigella

Bacillary Dysentery frequent passage of blood

stained, mucopurulent stools.

Classification 4 species : biochemical & serologicalcharacteristics.

- Sh.dysenteriae

- Sh.flexneri Non Lactose Fermenter

- Sh.boydii

- Sh.sonnei - Late Lactose Fermenter


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Mannitol

Non Fermentation Fermentation

S. dysenteriae - 12 S. flexneri- 6

S. boydii - 18

S. sonnei(Late lactose fermenter)

Shigella species- Mannitol fermentation


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Characteristics

Gramve, nonmotile bacilli.

Enrichment broth Selenite F, Gram-ve broth.

Selective media Deoxycholate agar(DCA)

- Salmonella-Shigella agar

- XLD (Xylose Lysine deoxycholate)


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Epidemiology & Clinical Syndromes

Incubation period: 1-7 days, usually 48 hrs

Low Infectious dose: 10-100 bacilli

Feco-oral transmission

Common in pediatric age group (1-10 years) leading cause ofinfantile diarrhea.

Sh.dysenteriae type I : most serious form of dysentery.

Shigellosis : whole spectrum of disease caused by Shigella.

Complication: Hemolytic Uremic Syndrome


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Pathogenesis Two-stage disease

Early stage

Second stage

Feverattributed toneurotoxic activity of toxin

Dysentery due toadherence and tissue invasion of large intestine

(cytotoxic activity of Shiga toxin)

Watery diarrhea attributed to the enterotoxin activity of Shiga toxin in

the small intestine

Enterotoxic, neurotoxic and cytotoxicShiga toxin

Similar to Shiga-like toxin ofEnterohemorrhagic E. coli(EHEC)


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Laboratory Diagnosis

Specimen: fresh feces mucus flakes (buffered glycerol saline transport medium)

NLF colonies .

Slide agglutination with polyvalent & monovalent sera.

Treatment

Oral rehydration

Antibiotics for severe & toxic cases Nalidixic acid or Norfloxacin.


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Salmonella

Gut of domestic animals & poultry.

Divided into 2 groups :

Enteric fever group typhoid & paratyphoid bacilli.

Food poisoning group usually animal parasites, producing

gastroenteritis, septicemia or localized infections.


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Morphological & Cultural characteristics

Motile, gram negative bacilli

Colorless (NLF) on MacConkey &DCA.

Enrichment broth- Selenite F,Tetrathionate broth

Selective media Wilson & Blair (jetblack colonies due to H2S), XLD, SS

agar.


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Pathogenesis

Source Carriers Cases

Transmission Ingestion of contaminated water or food

IP 7-14 days

Poultry, dairy

High infectious dose (108 CFU)


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Salmonella are ingested in

contaminated food or water

Organisms reach the

terminal ileumEnteritis

Organisms invade the gut wall

& cause ulcertion, perforation& hemorrhage

Organisms spread to intestinal

lymphatics & are phagocytosed by

macrophages

Organisms disseminate to

bones, kidneys, lungs,liver,

brain & blood

Enteric fever or

typhoid fever

Infecti on pattern of Sal monel la


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Pathogenicity

Enteric fever Typhoid & paratyphoid fever.

- Clinical features: nausea, vomiting, fever, bradycardia, toxemia,

splenomegaly, hepatomegaly, diarhoea alternating with constipation.

Septicemia with or without local suppurative lesions.

Gastroenteritis


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Lab diagnosis of Enteric fever

1st week Blood cultureBHI broth

2nd week Antibody detection

(serum)

Widal test

3rd week Urine culture

4th week Stool culture Use selective & enrichment

medium

Specimens Blood, Bone marrow, urine, stool, pus, CSF


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Serology - Widal Test

Tube agglutination test To detect antibodies in patient serum

Test is performed after 2 wks

Antigens used TO

To diagnose Enteric / typhoid fever

O antigen of S typhi

TH H antigen of S typhi

AH H antigen of paratyphi A

BH H antigen of paratyphi B

CHH antigen of paratyphi C

O is group specific Enteric fever

H is species specific Typhoid or paratyphoid


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CarriersFood handlers & Cooks

Repeated stool cultures

Vi agglutinins indicates carrier status

VaccinesTAB

Typhoral

Typhim

TreatmentCiprofloxacin


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Vibrio

V.cholerae, the causative agent for cholera.

Water contaminated with feces of patients & carriers.

MorphologyGram-ve slender bacilli, comma shaped.

Actively motile by a long polar flagellum

- Darting motility.


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Cultural characteristics

Aerobe, alkaline pH (> 8).

Transport media Cary Blair media,

VR (Venkataraman-

Ramakrishnan)media

Enrichment media Alkaline Peptone

Water, Monsurs taurocholate tellurite

PW.

Selective media Alk. bile salt agar,

TCBS agar.


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Biochemicals

Oxidase +ve

Ferments sucrose,

late lactose fermenter.

String test +ve

( with 0.5% sodium deoxycholate ).

Cholera red reaction conc. Sulphuric acid to peptonewater culture.


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Classification


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Pathogenicity

Cholera acute diarrhoeal disease, passage of large

volumes of rice watery stools, dehydration, hypovolemic

shock & metabolic acidosis.

ID 1011 org/ ml

Cholera toxin (CT) endotoxin

Toxin coregulated pilus (TCP)


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Laboratory Diagnosis

Stool examination before giving antibiotics.

Motility

Culture Non selective (BSA, Mac), Selective (TCBS).BA Hemodigestion.

Slide agglutination

Phage typing NICED, Calcutta (INDIA).


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Prophylaxis & Treatment

Oral vaccines immunity lasts for 6- 12 months.

ORF

Antibiotic therapy of secondary importance.

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Enterobacteria Bpt