GIT ModuleNormal Flora of GIT &

Bacterial infections of GITBY

Dr Khine Swe Swe-HanFC Path ( micro) SAM.Med (micro), SA

DTMH ( Wits unive) SAPDIC (Stellenbosch univ) SAMB,BS ( Yangon, Myanmar)

Pathologist , Consultant/ lecturer, Medical Microbiology Dept

IALCH Academic complex,NHLS/UKZN

• Lecture : Bacterial infections of GIT 11/8/11 08h00 – 10h00 - L2

Introduction

Lectures based on • Normal flora of the gastro-intestinal tract • Micro-organisms- bacteria causing diseases

– Escherichia coli ( EPEC, ETEC, EAEC, EHEC or VTEC,EIEC) – Vibrio– Shigella– Helicobacter pylori/ Campylobacter/Yersinnia

• Epidemiology • Virulence factors• Pathogenesis • Laboratory diagnosis • Treatment & Prevention

Normal flora of GIT

AT Birth Sterile

Breast –fed children Large numbers of lactic acid streptococci/lactobacilli

Bottle-fed children Mixed flora of gram-negative bacilli/less lactobacilli

Adults Oesophagus

Small numbersMicroorganisms arriving with saliva and food

Stomach Small numbers microorganisms arriving with saliva and food

Duodenum to rectum 103- 1011 org/g96-99% consists of anaerobes( e.gbacteroides, fusobacterium, lactobacilli, clostridia, peptostreptococci1-4% - consists of facultative anaerobes ( coliforms, enterococci, proteus, candida)

Escherichia coli

Normal flora of the intestine • Some strains have virulent factors can become

pathogenic in the intestine – Infections of the small intestine

• can cause various types of diarrhoea;– Enteropathogenic E.coli ( EPEC)– Enterotoxigenic E.coli ( ETEC)– Enterohaemorrhagic E.coli( EHEC)– Enteroadhesive E.coli( EAEC)– Enteroinvasive E.coli ( EIEC)

Enteropathogenic E.coli ( EPEC)

• Cause of infantile diarrhoea

• Certain serotypes that do not produce LT,ST/VT– Not entero-invasive

– Adhere to the enteric mucosa

– Loss of microvilli( effacement)– Formation of cup-like structures and occasionally cell

invasion

– Commonly cause watery diarrhoea in young children

Enteroinvasive ( EIEC)

• Cause of dysentery• Resistant to gastric acid and bile• Pass rapidly into the large intestine • Multiply, passing through the overlying mucous layer (

bacteria attach to the intestinal mucosal cells)• Invade the cells by induced endocytosis• Lyse the vacuole, multiply in the cytoplasm, rupture the

cell• Then invade neighbouring cells• Spread and lead to tissue destruction and inflammation

Enterotoxigenic E.coli ( ETEC)

• Cause of traveler's diarrhoea• Produce enterotoxins ( labile toxin LT and stable toxin ST)• LT is under the control of plasmid

• Its subunit B attaches to the GMI ganglioside at the brush border of SI mucosal epi cells and facilitate the entry of subunit A into the cell.

• Subunit A activates adenyl cyclase and markedly increases the cyclic AMP which results in intense and prolonged hypersecretion of water and chlorides and inhibit the absorption of sodium.

• The gut lumen distended with fluid hypermotility and diarrhoea ensues.

• ST – Also acts in the similar way and stimulates fluid secretion.

Enterohaemorrhagic E.coli( EHEC/VTEC)

• Verotoxin producing E.coli ( 0157H7)– Associated with haemorrhagic colitis and the haemolytic

ureamic syndrome

– haemorrhagic colitis• Grossly bloody diarrhoea

• Usually in the absence of pyrexia

• And preceded by abdominal pain and diarrhoea.

– haemolytic ureamic syndrome- characterized by• Acute renal failure

• Micro-angiopathic haemolytic anaemia

• Thrombocytopenia

Enteroadhesive E.coli( EAEC)

• Mild diarrhoea

• Adheres to the intestinal mucosa and causes acute and chronic mild diarrhoea

Vibrio cholerae

• Virulent and characteristic of organism– Comma-shaped, curved, facultative anaerobic

gram-negative bacillus

– Found in marine and surface waters

– Actively motile ( darting motility ) by means of its polar flagellum.

– Tolerant to alkali and intolerant to acid

– Mucinase enzymes

– Cholera toxin

Epidemiology

• V.cholerae that can cause cholera include –– V.cholerae serogroup O1– V.cholerae O139 Bengal

• Other vibrios that can cause diarrhoea include-– V.cholerae non-O1– V. parahaemolyticus– V.cholerae

• 3 serotypes – Inaba, Ogawa, and Hikojima• 2 biotypes - classical and E1 Tor

Epidemiology • Distribution

– Worldwide and occurs as epidemics & pandemics– 6 pandemics originating in the Bengal basin in 19th

and early 20th centuries.– in 1961

• 7th pandemic– E1 Tor biotype of V cholerae O1 spread from

Indonesia to the Far East and then swept back through much of southern Asia.

– Early in the 1970s – Pandemic invaded Africa

– 1991– It reached South America

Epidemiology:

• Fecal-oral route route of transmission and principally water-borne

• Endemic in areas of poor sanitation (India, Sub-Saharan Africa, Southern Asia)

• May persist in shellfish or plankton • 7 pandemics since 1817: First 6 from Classical biotype

and 7th from the El Tor biotype • In 1993 Cholera epidemic in Bengal was caused by

O139 which may be the cause of the 8th pandemic • The recent Cholera epidemic in Haiti occured due to El

Tor O1 strains that are predominant in South Asia.

Pathogenesis of cholera• Cholera is caused by

– V.cholerae serogroup O1– V.cholerae O139 Bengal

• In faecal contaminated water or food • Ingestion • Infective dose – large numbers ( 108- 109 orgs)

• Reach the small intestine • Invade the mucosal barrier of SI ( active motility and

mucinase e/z• Attach to the microvilli of the brush border of epi cells-

multiply – liberate cholera toxin

Pathogenesis of cholera

• Cholera toxin acts ( same as LT of ETEC)– CAUSING profuse watery diarrhoea

• Mechanism– LT is under the control of plasmid

• Its subunit B attaches to the GMI ganglioside at the brush border of SI mucosal epi cells and facilitate the entry of subunit A into the cell.

• Subunit A activates adenyl cyclase and markedly increases the cyclic AMP( Adenosine monophosphate) which results in intense and prolonged hypersecretion of water and chlorides and inhibit the absorption of sodium.

• The gut lumen distended with fluid hypermotility and diarrhoea ensues.

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Pathogenesis of cholera( clinical findings)

• Incubation period – 1-4 days

– Sudden onset of nausea, vomitting, profuse watery diarrhoea with mucus flakes ( rice water stool)

– Severe dehydration , circulatory collapse and even anuria and death.

– NB: NOT invasive infection and organism do not reach the blood stream.

clinical findings

• Consequences of severe dehydration:

• Intravascular volume depletion

• Severe metabolic acidosis

• Hypokalemia

• Cardiac and renal failure

Lab dx• Specimens

– Fresh stool, Watery stool and mucus flakes from stool

– rectal swab

– Vomitus

– Strip of blotting paper soaked in watery stoolPreservation and Transport media:When there may be delay in transmission of specimen to laboratory, it must be refrigerated at 8c to 10c for 24 hours, else following transport media may be used:

• E.g. Cary-Blair medium

– Enrichment media:

– Alkaline peptone water (pH 8.6)

• MCCS

– Smear – microscopic examination

– Culture

• Serology test

– Slide agglutination

Procedure for recovery of V.cholera O1 from fecal

specimen

Direct enrichment

APW ( alkaline peptone water)

(6-8 HRS, 35°-37° C)

TCBS

Non selective medium Optional screening tests

string

V.cholera O1 polyvalent antisera oxidase

KIA or TSI

Ogawa & inaba antisera Arginine or lysine

Treatment

• Rehydration

• Antibiotics – Tetracycline

– Ciprofloxacin • Shorten diarrhoeal illness.

• Resistant emerged !

Prevention & control

• Epidemiology – important • Carrier state – seldom exceed 3-4 weeks

chronic carrier – rare • Vibrio survive in water – up to 3 weeks • Source – contaminated water, food, flies( from person to

person)• Isolation , disinfection of excreta, contact follow up• Vaccine

– Endemic area– Only valid for 6 months

Shigellosis ( bacillary dysentery)

• Natural habitat – Limited to the intestinal tracts of humans & other

primate• Coliform and a true pathogen

– Produce bacillary dysentery• Non-motile and encapsulated• Endotoxin ( LPS)( somatic o antigen)• Heat –labile exotoxin- enterotoxin & neurotoxin

Pathogenesis

• Aetiology agents – Shigella dysenteriae ( severe) – Shigella flexneri– Shigella boydii– Shigella sonnei

• Contaminated with food and water• Incubation period – 1-2 days • Infective dose -103 organisms ( highly communicable) • Always limited to the GIT• Bloodstream invasion – quite rare

Pathogenesis

• Invade the colonic mucosa by induced phagocytosis

• Spread within the epithe cell cytoplasm and passage to adjacent cells.

• Microabscesses– In the wall of the LI & terminal ileum – leads to

necrosis of the mucous mem, superficial ulceration, bleeding, and formation of a pseudomembrane on the ulcerated area

• Dysentery

Pathogenesis ( action of toxins )

• Endotoxin ( LPS) – Autolysis

• Contribute to the irritation of the bowel wall.

• Shigella dysenteriae type 1 – Produce a heat –labile exotoxin

• Acts as both enterotoxin and neurotoxin ( gut & CNS)• Enterotoxin –

– produces early non-bloody , voluminous diarrhoea ( early)– Invasion to large intestine, dysentery with blood and pus in the

stool ( later) – Inhibit the sugar and amino acid absorption in the small

intestine.• Neurotoxin – fatal CNS reactions. ( meningism and coma)

Clinical manifestation

• Sudden onset of – abdominal pain, fever, watery diarrhoea

• Later – As involves the ileum ,colon ( stool increase, less liquid , often

contain blood & mucous– Each bowel movement is accompanied by

• Straining, tenesmus( rectal spasms), lower abdominal pain.• ½ of the adult cases – subside spontaneously in 2-5 days .• In children & elderly – loss of water & elect- dehydration , acidosis

and even death • On recovery

– Shed shigella bacilli for only short time – Remain chronic carrier- recurrent infection

Lab diagnosis

• Specimens– Fresh stool

• MCCS– M/C

– Culture

– Serology

Treatment

• Ampicillin, tetracycline ,cotrimoxazole , chloramphenicol and ciprofloxacine , nalidixicacid

• Drug resistant emerged – Transmitted by plamids.

• Opioids – should be avoided.

Epidemiology and prevention & control of Shigella

• Transmitted by – Food, fingers, feces, and flies From person to person

– Spread widely

• Humans – main host – Directed at eliminating the organisms from this reservoir

by• Sanitary control

• Fly control

• Isolation of patients and disinfection of excreta

• Detection of subclinical cases and carriers ( food handlers)

Campylobacters

• Known mainly as pathogens for various animals– Sepsis, abortion, enteritis

• Campylobacter jejuni– Common cause of diarrhoea in humans – Mainly enteritis – Occasionally systemic invasion – Gram negatic rod with comma,S ,

gull-wing shapes– Motile – Endotoxin ( LPS)– Cytopathic extracellular toxins, enterotoxin

Pathogenesis

• Acquired by – Oral route ( contaminated food, drinks, contact with

infected animals, or anal-genital-oral sexual activity.• Susceptible to gastric acid• Infective dose - 104

• Multiply in the small intestine – invade the epithelium cell & produce inflammation– Localised – enteritis – The jejunum and the ileum are the first site to become

colonised– Infection extends distally to affect the terminal ileum and usually

the colon & rectum. – Red and wbc in the stools– If invade to blood stram – clinical pictures of enteric fever

Clinical manifestation

• Acute onset of crampy abdominal pain

• Profuse diarrhoea ( may be grossly bloody)

• Head ache, malaise, fever

• Usually self-limited ( 5-8 days)

Lab diagnosis

• Specimens

• MCCS – Smear m/c

– Culture

Treatment, control

• Erythromycin ( to reduce the fecal shedding )– Severe (accompanying fevers, blood in stools) or

prolonged cases may require ciprofloxacin, erythromycin, azithromycin or norfloxacin.

– The drug of choice is usually erythromycin. – About 90% of cases respond to ciprofloxacin

treatment.– Fluid and electrolyte replacement may be

required for serious cases. – Public health control measures

Helicobacter pylori

• Spiral –shaped gram negative rod• Actively motile • Strong producer of urease • Not grow in gastric lumen ( PH 1.0-2.0)• Epithelium surface side ( grows at PH 6.0-7.0) • Associated with

– Antral gastritis– Duodenal (peptic) ulcer– Gastric ulcer and – Gastric adenocarcinoma– Gastric lymphoma

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Pathogenesis • Produce : ( virulent factors)

– protease• Modifies the gastric mucus and reduce the ability of acid to

diffuse through the mucus.– Urease

• Production of ammonia and further buffering of acid– Ammonia may directly damage the cell also.

• Motile ( quite motile ,even in the mucus )– To find its way to the epithelial surface.

• Adhesins- highly affinity for epithelial cell receptors • Mucosal inflammation & damage are not well defined. • Invade the epithelial cell surface to a limited degree.• Toxins & LPS

– Cytotoxin– Damage the mucosal cells

Clinical manifestation

• Asymptomatic • Sign and symptoms of gastritis , DU.• DU

– 90% of pts ( associated with DU have H.pylori infection )– 10% -related to drugs

• GU – Uncertain

• Chronic and active gastritis • Destruction of epithelium cells • Glandular atrophy• Associated with carcinoma.

– H.pylori –type 1carcinogen • Gastric lymphoma

Lab dx• Specimens

– Gastric biopsy ( endoscopy )• Histology

– Mince in saline for culture – Blood

• Serum antibodies • Culture • Antibodies ( IgG,IgA)• Special tests

– RAPID test – to detect the urease activity• In vitro test • In vivo test

– C13 or C14 Labeled urea breath test

Treatment• Triple therapy

– Metronidazole + either bismuth subsalicylate or bismuth subcitrate+ either amoxicillin or tetracycline x 14 days – 80% + eradicate

– Metroniazole + omeprazole+ clarithromycin x 1 week – 90%+ eradicate

Epidemiology & control• H pylori

– < 20% of persons <30 years old– Increase 40-60% of persons age 60( asymptomatic )– Developing countries

• 80% in adults • Person to person transmission • Once acquired the infection, persists for years or for life.

– Infection associated with • Socioeconomic status • Hygiene• Water supply/sanitation • Crowding in households• Gastroenterologist/endoscopy nurse

– Transmission • Faecal –oral • Oral-oral• Via endoscope

– Prevention • Difficult and improve living condition

Yersinia enterocolitica

• Gram negative rod

• Found in the intestinal tract of animals

• Cause disease in animals and may transmit to humans

• Person to person –rare

• Produce heat stable enterotoxin– Role – not well defined

Pathogenesis • Ingestion of material ;contaminated food, water, fomites• Infective dose -108-109

• Incubation period – 5-10 days • Multiply in the gut mucosa( ileum)• Inflammation & ulceration – leucocytes in stool• Extend to mesenteric lymph nodes and rarely to bacteremia.C/F• Early symptoms

– Fever, abdo pain, diarrhoea ( watery to bloody)– Abdo pain severe at Rt lower quadrant – suggesting appendicitis

• One -2 weeks after onset– Arthralgia, arthritis, erythema nodosum, - suggesting immunologic

reaction to infection• Rarely

– Pneumonia, meningitis, sepsis • In most cases – self limited.

Lab dx

• Specimens– Stool, blood, material obtained at surgical

exploration

• MCCS – m/c

– Culture

• Serology – Cross reaction to others

Treatment

• Diarrhoea – Self limited

– Antibiotic • Benefits –unknown

• Tetracycline, aminoglycosides, chloramphenicol, ciprofloxacin, cotromoxazole

Prevention & control

• Source

• Sanitation- precaution

• Farm & domestic animals

References

• Geo.F.Brooks, Janet S.Butel ,L.Nicholas Ornston;Jawetz, Melnick & Adelberg’s ; Medical Microbiology

• http://www.springerimages.com/Images/MedicineAndPublicHealth/2-AID07E3-04-038

• http://en.bestpicturesof.com/pictures%20of%20e%20coli%20gram%20stain

• http://totallyfreeimages.com/118304/Yersinia-pestis,-Gram-negative-bacillus,-1000x-Magnification.

END

• 11/08/2011

BY Dr KSS/Han