Bacterial Infections Of The GIT PDF

Bacterial Infections of the Gastrointestinal tract(GIT) Dr S. Haffejee Dept. of Medical Microbiology  Overview Normal flora of the GIT Pathogenic bacteria causing disease of the GIT - Diarrhoeagenic E. Coli -...

Bacterial Infections of the Gastrointestinal tract(GIT) Dr S. Haffejee Dept. of Medical Microbiology  Overview Normal flora of the GIT Pathogenic bacteria causing disease of the GIT - Diarrhoeagenic E. Coli - Shigella species - Campylobacter species - Vibrio cholerae - Yersinia enterocolitica - Helicobacter pylori - Mycobacterium tuberculosis  Normal flora of the GIT AGE BACTERIAL FLORA Foetus Sterile Birth Begins as sterile, then colonisation begins as baby is fed and handled. Breastfed infants Bifidobacteria(90%), Enterobacteriaceae, Enterococcus species, Streptococci(viridans group) Bottle-fed infants Bifidobacteria not predominant, Enterobacteriaceae, Enterococcus species, Streptococci(viridans group), anaerobes Children and Adults(according to anatomical Oral cavity, Oesaphagus: Streptococcus site) viridans, anaerobes Stomach: lactobacilli Proximal small intestine: lactobacilli, Enterococcus faecalis(105-107 bacteria/ml of fluid) Distal small intestine: 108/ml as for proximal plus Enterobactericeae, and Bacteroides Colon/large intestine: 1011 bacteria/ml , Enterobacteriaceae more prominent, enterococcus, lactobacilli, Clostridium species, Pathogenic bacteria causing GIT infections  Clinical features The most prominent features are: Fever, Vomiting, Abdominal pain Diarrhoea : central feature ✔ Nature of diarrhoea forms the basis for the classification of GIT infections into 3 major syndromes ✔ 1)Watery diarrhoea; 2)Dysentery; 3)Enteric fever ✔ Enteric fever will be discussed in a separate lecture.  Clinical features Watery diarrhoea Stools have a fluid character Intestinal fluid loss is the main feature Other symptoms: nausea, vomiting, abdominal pain, fever. Lasts 1-3 days Pathogenesis: the pathogen attacks the proximal small intestine. This part of the bowel is responsible for >90% of physiologic net fluid absorption. Pathogens: Vibrio cholerae; Enterotoxigenic E. Coli(ETEC)  Clinical features Dysentery Loose stools with blood and pus Fever, abdominal pain, cramps, tenesmus. Symptoms last 2-7 days Focus of pathology is the colon Pathogenesis: bacteria produce inflammatory and/or destructive changes in the colonic mucosa either by direct invasion/cytotoxin production Pathogens: Shigella species  Epidemiology Infections are acquired by ingestion/faecal-oral route Infections occur worldwide, but more prevalent in low socio-economic groups, with poor nutrition, sanitation and unsafe water supply. Many of these infections will be self limiting. In children, infants: diarrhoeal disease remains one of the most important causes of morbidity and mortality.  Epidemiology Travellers diarrhoea(“Delhi belly”) ± 20-50% of travellers from developed countries going to less developed countries may develop diarrhoea Common causes: Enterotoxigenic E. Coli, Shigella spp. Ingestion of uncooked or incompletely cooked foods most likely source of infection. Eg. Raw vegetables/salads  Epidemiology Hospital-associated diarrhoea Causative agents: E. Coli in infants(rare), Clostridium difficile (patients on antibiotics) C. difficile: Gram positive bacillus, anaerobe, toxin-producing, spore forming C. difficile may cause mild diarrhoea to fulminant pseudomembranous colitis during or after treatment with antibiotics The toxins(A and B) produced by the organism are responsible for disease. May be resident in patient’s own intestinal flora or acquired by spread from other patients in the hospital. Antibiotics implicated include: broad spectrum penicillins, cephalosporins, clindamycin Lab diagnosis: Toxin detection by ELISA/PCR on stool sample Treatment: stop antibiotics, replace fluid and electrolytes. Oral metronidazole, oral vancomycin  Micro-organisms E. Coli: Enteroinvasive; Enterotoxigenic; Enterohaemorrhagic; Enteropathogenic Shigella species Campylobacter species Vibrio cholerae Yersinia enterocolitica Helicobacter pylori Mycobacterium tuberculosis  Escherichia coli Diarrhoea-causing E. coli are conveniently classified according to their virulence properties as: Enterotoxigenic (ETEC) Enteropathogenic (EPEC) Enteroinvasive (EIEC) Enterohaemorrhagic (EHEC), or Enteroaggregative (EAEC).  E. coli -Microbiology Belongs to family Enterobacteriaceae Gram negative bacillus, lactose-fermenter, produces indole Grows readily on simple media under aerobic and anaerobic conditions eg. MacConkey agar Components of the cell wall and surface, which are antigenic include: The outer membrane lipopolysaccharide (LPS) is called the O antigen. Cell surface polysaccharides may form a well-defined capsule or an amorphous slime layer and are termed the K antigen(capsule). Motile strains have protein peritrichous flagella, which extend well beyond the cell wall and are called the H antigen. O,H,K antigens are used to divide organism into serotypes eg. E. Coli O157:H7 Possess virulence factors such as adherence pili, exotoxins, LPS GRAM STAIN SHOWING GRAM NEGATIVE BACILLI E. coli -LACTOSE FERMENTERS on MacConkey agar  Enterotoxigenic E. coli(ETEC) Epidemiology ETEC are the most important cause of traveller’s diarrhoea in visitors to developing countries. ETEC also produce diarrhoea in infants native to these countries, where they are a leading cause of morbidity and mortality during the first 2 years of life. Repeated bouts of diarrhoea caused by ETEC and other infectious agents are an important cause of growth retardation, malnutrition, and developmental delay in the third world countries where ETEC are endemic. ETEC disease is rare in industrialized nations. Transmission is by consumption of food and water contaminated by human waste The infecting dose is high. Causes watery diarrhoea. Disease lasts few days  Enterotoxigenic E. coli(ETEC) Pathogenesis ETEC strains produces 2 enterotoxins viz. labile toxin(LT) and/or stable toxin(ST), in the small intestine. Adherence to surface microvilli is mediated by the Colonising factor antigen(CFA) class of pili and is essential for the efficient delivery of toxin to the target enterocytes. The genes encoding the ST, LT, and the CFA pili are borne in plasmids. The bacteria remain on the surface, where the adenylate cyclase–stimulating action of the toxin(s) creates the flow of water and electrolytes from the enterocyte into the intestinal lumen. There is no invasion or inflammation.  Enterotoxigenic E. coli(ETEC) Labile toxin=LT: Similar to cholera toxin. Acts on the small intestine Its subunit B attaches to the GMI ganglioside at the brush border of the small intestinal mucosal epithelial cells and facilitates entry of subunit A into the cell. Subunit A activates adenyl cyclase and markedly increases cyclic AMP which results in intense and prolonged hypersecretion of water, Na, HCO3 and chlorides into the lumen and inhibits the absorption of water and electrolytes by enterocytes. Results in fluid and electrolyte loss leading to dehydration, electrolyte loss and metabolic acidosis Stable toxin=ST: Acts differently viz. Guanylate cyclase and stimulates fluid secretion ETEC PATHOGENESIS  ENTEROPATHOGENIC E. coli (EPEC) Pathogenesis The infecting dose for infants is low. Causes watery diarrhoea of few days duration EPEC initially attach to enterocytes using pili of the bundle forming pili(BFP) type to form clustered microcolonies on the enterocyte cell surface of the small intestine. The lesion then progresses with effacement/loss of the microvilli and changes in the cell morphology including the production of dramatic “pedestals” with the EPEC bacterium at their apex. The combination of these actions is called the attachment and effacing (A/E) lesion  ENTEROHEMORRHAGIC E. coli (EHEC)/(VTEC) Epidemiology This disease occurs more in developed rather than in developing countries. EHEC was first recognized in the early 1980s when outbreaks of HUS (haemolytic anemia, renal failure, and thrombocytopenia) were linked to a single E. coli serotype, O157:H7. Since then EHEC disease has emerged as an important cause of bloody diarrhoea. Initially produces watery diarrhoea followed by dysenteric illness  ENTEROHEMORRHAGIC E. coli (EHEC) Pathogenesis EHEC produce both Shiga toxins(cytotoxin) and the A/E lesions described above for EPEC. EHEC primarily attacks the colon The multiple extra-intestinal features such as HUS appear to be the result of circulating Shiga toxin. Shiga toxin production causes capillary thrombosis and inflammation of the colonic mucosa, leading to a hemorrhagic colitis. Circulating Shiga toxin binds to renal tissue where its glycoprotein receptor is particularly abundant, causing glomerular swelling and the deposition of fibrin and platelets in the microvasculature. How Shiga toxin causes haemolysis is less clear; perhaps the erythrocytes are simply damaged as they attempt to traverse the occluded capillaries. EHEC PATHOGENESIS  ENTEROINVASIVE E. coli (EIEC) EIEC infections are essentially restricted to children under 5 years of age, living in developing nations. The infecting dose for EIEC is higher than it is for Shigella. Humans are the only known reservoir. Patients develop watery diarrhoea initially followed by dysentery  ENTEROINVASIVE E. coli (EIEC) Pathogenesis Resistant to gastric acid and bile Pass rapidly into the large intestine(colon) Multiply, passing through the overlying mucous layer and 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, ulceration and inflammation Results in blood, pus and mucous in stools  Vibrio cholerae Causative agent of Cholera Other Vibrio species are less important pathogens Bacteriology - Vibrios are curved, Gram-negative rods commonly found in saltwater. - They are highly motile with a single polar flagellum, - Non–spore forming, oxidase positive, and can grow under aerobic or anaerobic conditions at 37˚C. - V. cholerae has a low tolerance for acid, but grows under alkaline (pH 8.0 to 9.5) conditions that inhibit many other Gram-negative bacteria - There are over 150 O antigen serotypes, only two of which (O1 and O139) cause Cholera  Vibrio cholerae 3 serotypes of V. cholerae: Inaba, Ogawa, Hikojima - 2 biotypes: classical and El Tor Other Vibrio species that can cause diarrhoea include: Vibrio cholerae non-O1, Vibrio parahaemolyticus Curved Gram negative bacilli  Vibrio cholerae Epidemiology Pandemic and epidemic potential Epidemic cholera is spread by faecal-oral route primarily by contaminated water under conditions of poor sanitation Man is the only natural host Cholera is endemic in the Indian subcontinent and Africa.  Vibrio cholerae Pathogenesis To produce disease in healthy people, ingestion of large numbers of bacteria(108-109) is required to overcome the acid barrier of the stomach. Organisms multiply in the small intestine. Penetrates mucus(mucinase) Colonization of the entire intestinal tract from the jejunum to the colon by V. cholerae requires organism adherence to the epithelial surface, most probably by surface pili. The outstanding feature of V. cholerae is the ability of virulent strains to secrete the cholera toxin(CT), which is responsible for the disease cholera. No mucosal damage occurs The water and electrolyte shift from the cell to the intestinal lumen is the fundamental cause of the watery diarrhoea of cholera.  Vibrio cholerae Cholera Toxin=potent enterotoxin Main virulence factor Encoded by chromosomal genes Structure: polypeptide chains organized into two toxic subunits (A1, A2) and five binding (B) units. The B units bind to a GM1-ganglioside receptor found on the surface of many types of cells. Once bound, the A1 subunit is released from the toxin molecule by reduction of the disulfide bond that binds it to the A2 subunit, and it enters the cell by translocation. In the cell, it exerts its effect on the membrane-associated adenylate cyclase system at the basolateral membrane surface. This causes persistent activation of intracellular adenylate cyclase, which in turn stimulates the conversion of adenosine triphosphate to cyclic adenosine 3, 5-monophosphate (cAMP). The net effect is excessive accumulation of cAMP at the cell membrane, which causes hypersecretion of chloride, potassium, bicarbonate, and associated water molecules out of the cell and prevents absorption of Na and water. V. CHOLERAE PATHOGENESIS  Vibrio cholerae Clinical features Incubation period= 1-4 days Cholera produces the most dramatic watery diarrhoea known. Stool is watery with mucus flecks = rice water stool May also develop nausea and vomiting Intestinal fluids pour out in voluminous bowel movements; this eventually leads to dehydration and electrolyte imbalance. Severe dehydration, circulatory collapse, anuria and death may occur There is no fever, inflammation, or direct injury to the bowel mucosa.  RICE WATER STOOL SEVERE DEHYDRATION  Vibrio cholerae Laboratory diagnosis A bacteriologic diagnosis is accomplished by culture of V. Cholerae from the stool/rectal swab. If delay in transport to the lab, use transport medium eg. Cary Blair transport medium and refrigerate sample Enrichment broth : alkaline peptone water The organism grows on common clinical laboratory media such as blood agar and MacConkey agar Its isolation is enhanced by the use of a selective medium thiosulfate-citrate-bile salt-sucrose agar(TCBS). Once isolated, the organism is readily identified by biochemical reactions. Confirm with serological tests. Microscopically: wet preparation shows no blood/leukocytes  Vibrio cholerae Treatment Most important is fluid and electrolyte replacement Antimicrobial therapy may shorten the duration of illness and diminish fluid loss. Ciprofloxacin or azithromycin may be used Prevention boiling or chlorination of water Education of the community re. water handling and storage Vaccines  Shigella Clinical features Is the classic cause of dysentery. The illness begins as a watery diarrhoea but progresses to an intense colitis with frequent small-volume stools that contain blood and pus. Characteristically, presents as a dysentery syndrome—a clinical triad consisting of cramps, painful straining to pass stools (tenesmus), and a frequent, small-volume, bloody, mucoid discharge. The vast majority of shigellosis cases resolve spontaneously after 2 to 5 days.  Shigella Bacteriology The most common species are S. sonnei and S. flexneri, S. boydii, S. dysenteriae Gram negative bacilli Require selective media(Xylose lysine deoxycholate=XLD) to culture the organism and inhibit normal flora. Shigella species are non-lactose fermenters. All Shigella species are nonmotile. Shigella is an invasive bacterial pathogen. All species are able to invade and multiply inside a wide variety of epithelial cells, including their natural target, the enterocyte. S. dysenteriae type A1 (Shiga bacillus), the species that was first discovered, is the most potent producer of Shiga toxin  Stool wet preparation : demonstrates Gram negative bacilli leukocytes, erythrocytes XLD=XYLOSE LYSINE DEOXYCHOLATE  Shigella Epidemiology Shigellosis is strictly a human disease with no animal reservoirs. Worldwide, it is one of the most common causes of infectious diarrhoea in both developed and developing countries. The organisms can be readily transmitted by the faecal–oral route through person-to-person contact or by contamination of food or water. The infecting dose is small, less than 200 organisms.  Shigella PATHOGENESIS Shigella is acid-resistant and survives passage through the stomach to reach the distal small bowel where the organism multiplies. In 1-4 days, invasion and necrosis of the human colonic epithelium occurs. This triggers an intense acute inflammatory response with mucosal ulceration and abscess formation. Shigella initially crosses the mucosal membrane by entering the follicle-associated M cells of the intestine, which lack the highly organized brush borders of absorptive enterocytes. The Shigella adhere selectively to M cells and can transcytose through them into the underlying collection of phagocytic cells. Some Shigella produce Shiga toxin, which is not essential for disease, but does contribute to the severity of the illness. The original and most potent producer of Shiga toxin, S. dysenteriae type 1, is the only Shigella with a significant mortality rate among previously healthy individuals. This is probably due to systemic effects of the toxin, which can be the same as described for the EHEC, including HUS. SHIGELLA PATHOGENESIS  Shigella TREATMENT Fluid replacement Because the disease is usually self-limiting, the beneficial effect of antibiotic treatment is in shortening the illness and the period of excretion of organisms. Antibiotics such as quinolones and third-generation cephalosporins have been used. Antispasmodic agents may aggravate the condition and are contraindicated in shigellosis.  Shigella Prevention and control Provision of safe water Adequate sanitation, sewage disposal Fly control Personal and food hygiene. Screen and identify food handlers, subclinical carriers Isolate patients and safe disposal of excreta No vaccine available  Yersinia enterocolitica Bacteriology Yersinia are Gram negative coccobacilli and tend to retain staining at the ends of the cells (bipolar staining). Pinpoint colonies on agar surface eg. MacConkey agar Gram negative bacilli  Yersinia Clinical features Diarrhoea and vomiting Abdominal pain and fever Mesenteric adenitis(can mimic acute appendicitis) Enteric fever syndrome 1-2 weeks after onset – Arthralgia, arthritis, erythema nodosum, - suggesting immunologic reaction to infection  Yersinia Epidemiology Animal source Humans acquire infection by consumption of contaminated food or water. Uncommon in South Africa  Yersinia Pathogenesis Yersinia invade the M cells of the Peyer’s patches. Endotoxin and some exotoxin production Multiply in the ileum, cause ulceration and inflammation Spread to mesenteric lymph nodes, rarely bacteraemia  Yersinia Treatment Self limiting-treat symptomatically Antibiotics : especially if the patient is septicaemic and has complicated disease 3rd generation cephalosporins plus aminoglycoside, tetracyclines  Campylobacter species Bacteriology Campylobacters are motile, curved, oxidase-positive, Gram-negative bacilli The cells have polar flagella and are often are attached at their ends giving pairs “S” shapes or a “seagull” appearance. Campylobacter species associated with human disease include C. jejuni, and C. coli C. jejuni grows well only on enriched media eg. Skirrow’s agar under microaerophilic conditions. That is, it requires oxygen at reduced tension (5 – 10%). Growth usually requires 2 to 4 days, sometimes as much as a week. CURVED GRAM NEGATIVE BACILLI  Campylobacter species Clinical features C. jejuni infection begins with lower abdominal pain, then diarrhoea over a matter of hours. The diarrhoea may be watery or dysenteric, with blood and pus in the stool. Most patients are febrile. Few patients develop bacteraemia The illness resolves spontaneously after a few days to 1 week. There is an association between C. jejuni infection and the Guillain-Barré syndrome, an acute demyelinating neuropathy that is frequently preceded by an infection. Immunological basis for this association.  Campylobacter species Epidemiology The primary reservoir is in animals and the bacteria are transmitted to humans by ingestion of contaminated food or by direct contact with pets. Campylobacters are commonly found in the normal gastrointestinal and genitourinary flora of sheep, cattle, chickens, wild birds, and many others. Domestic animals such as dogs may also carry the organisms and probably play a significant role in transmission to humans. The most common source of human infection is undercooked poultry, but outbreaks have been caused by contaminated rural water supplies and unpasteurized milk.  Campylobacter species Pathogenesis Infection is acquired by oral ingestion, followed by colonization of the intestinal mucosa. Affects the small intestine and colon=enterocolitis Incubation period=3-5days The bacteria have been shown to adhere to endothelial cells and then enter cells in endocytotic vacuoles. The virulence determinants of this microorganism remain uncertain.  Campylobacter species Treatment Fluid and electrolytes Antibiotics: only for severe or prolonged infections Erythromycin ( to reduce the fecal shedding ) – The drug of choice is usually erythromycin. Patients may also respond to azithromycin and ciprofloxacin  Helicobacter pylori Bacteriology Spiral –shaped gram negative rod Actively motile Strong producer of urease  Helicobacter pylori Clinical features Associated with peptic ulcer disease/gastritis Helicobacter infections are limited to the mucosa of the stomach, and most are asymptomatic even after many years. Burning pain in the upper abdomen/epigastrium, accompanied by nausea and sometimes vomiting. Ulcers may cause additional symptoms, depending on their anatomic location.  Helicobacter pylori Epidemiology The organism is found in the stomachs of 30 to 50% of adults in developed countries and it is almost universal in developing countries. The exact mode of transmission is not known, but is presumed to be person to person by the faecal–oral route or by contact with gastric secretions. Colonization increases progressively with age. Once established, the same strain persists at least for decades, probably for life. H. pylori is the most common cause of gastritis, gastric ulcers, and duodenal ulcers  Helicobacter pylori Diagnosis Diagnosis is usually made by endoscopic examination, with biopsy and culture of the gastric mucosa. The H. pylori urease activity can be demonstrated in biopsies in less than an hour. Noninvasive methods include serology and a urea breath test. For the breath test, the patient ingests 13C- or 14C-labeled urea, from which the urease in the stomach produces products that appear as labeled CO2 in the breath. Serology: detection of antibody directed against H. pylori H. pylori stool antigen test  Helicobacter pylori Treatment Proton pump inhibitors Bismuth salts (eg, Pepto-Bismol) Antibiotics treatment. Metronidazole, clarithromycin, and amoxicillin have been effective. These combination regimens must be continued for 7-14 days.  Mycobacterium tuberculosis Refer to previous lectures(Microbiology, pathogenesis of Tuberculosis) May cause abdominal tuberculosis which is a form of extrapulmonary TB(EPTB)  Pathophysiology Acquire by ingestion: infected food/milk Swallow infected sputum Haematogenous spread Lymphatic channels Contiguous spread from adjacent focus  Clinical symptoms/signs Non-specific(fever, loss of weight) Abdominal pain, vomiting Abdominal lymphadenopathy Ascites ‘Doughy’ abdomen Abdominal masses, hepatosplenomegaly  Diagnosis High index of suspicion History and clinical examination Lab diagnosis: Microbiology, chemistry, histopathology Imaging: Ultrasound, CT scan Surgery and biopsy  Laboratory diagnosis Microbiology: peritoneal fluid, tissue biopsy, lymph node biospy Microscopy: Auramine/Ziehl-Neelsen stains Acid fast bacilli Ziehl-Neelsen Auramine  Laboratory diagnosis Culture: solid/liquid culture medium Lowenstein-Jensen MGIT  Laboratory diagnosis Polymerase chain reaction(PCR)- TB GeneXpert, Line probe assays TB GeneXpert  Laboratory diagnosis Chemistry: Adenosine deaminase(ADA), protein level in ascitic fluid Histopathology: granulomas, acid fast bacilli on biopsy samples