Enterobacteriaceae: Overview and Key Pathogens PDF

ENTEROBACTERIACEAE Enterobacteriaceae •The most important bacterial family in human medicine •They can cause typhoid fever, dysentery, plague and •Opportunistic infections: urinary tract infections, pneumonias, wound infections, sepsis Enterobacteriaceae • Gastrointestinal diseases – Escherichi...

ENTEROBACTERIACEAE Enterobacteriaceae •The most important bacterial family in human medicine •They can cause typhoid fever, dysentery, plague and •Opportunistic infections: urinary tract infections, pneumonias, wound infections, sepsis Enterobacteriaceae • Gastrointestinal diseases – Escherichia coli – Salmonella – Shigella – Yersinia enterocolitica Opportunistic diseases -Enterobacteriaceae – – – – Septicemia, Pneumonia, Meningitis Urinary tract infections •Citrobacter •Enterobacter •Escherichia •Hafnia •Morganella •Proteus •Providencia •Serratia Enterobacteriaceae • Gram negative facultative anaerobic bacilli – Oxidase negative (no Cytochrome oxidase) - Catalase Positive - Glucose fermenting - Grow on MacConkey agar - Reduce Nitrate to nitrite - All motile except Shigella & Klebsiella. Gram negative Enterobacteriaceae are divided in different serovars based on H, K and O antigens The most important antigens of the Enterobacteriaceae are: O antigens. Specific polysaccharide chains in the lipopolysaccharide complex of the outer membrane H antigens. Flagellar antigens consisting of proteins. K antigens. Linear polymers of the outer membrane built up of a repeated series of carbohydrate units (sometimes proteins as well). They can cover the cell densely and render them O inagglutinable F antigens. Antigens of protein attachment Escherichia coli Escherichia coli •The natural habitat of E. coli is the intestinal tract of humans and animals. •It is therefore considered an indicator organism for fecal contamination of water and foods. •Guideline regulations: •100 ml of drinking water must not contain any E. coli Morphology, culture, and antigen structure • Rods are peritrichously flagellated • Lactose is broken down rapidly • Antigen structure of these bacteria is based on O, K, and H antigens Pathogenesis and clinical picture of extraintestinal infections •Urinary tract infection: • lower urinary tract (urethritis, cystitis, urethrocystitis) or • affects the renal pelvis and kidneys (cystopyelitis, pyelonephritis). • UPEC (uropathogenic E. coli)---UPEC strains can attach specifically to receptors of the renal pelvis mucosa with pyelonephritis-associated pili or nonfimbrial adhesins Pathogenesis and clinical picture of extraintestinal infections •Sepsis. • E. coli causes about 15% of all cases of nosocomial sepsis Pathogenesis and clinical pictures of intestinal infections •E. coli that cause intestinal infections are now classified in five pathovars with differing pathogenicity and clinical pictures: 1. Enteropathogenic E. coli-EPEC Destruction of surface microvilli • fever • diarrhea • vomiting • nausea • non-bloody stools • Shiga-like toxin E.coli O157:H7 1. Enteropathogenic E. coli-EPEC  Still a main contributor to infant mortality in developing countries  EPEC attach themselves to the epithelial cells of the small intestine by means of proteins and receptors 1. Enteropathogenic E. coli-EPEC  Then inject toxic molecules into the enterocytes by means of a type III secretion system 1. Enteropathogenic E. coli-EPEC • http://www.hhmi.org/biointeractive/e-coli-infection-strategy 2. Enterotoxigenic E. coli- ETEC • Watery Diarrhea like cholera • Milder • Traveler's diarrhea • It is not invasive but produces a toxin •Toxin producing strains (heat labile and heat stable toxins). Enterotoxigenic E. coli • Heat labile toxin • Like cholera toxin • Adenyl cyclase activated • Cyclic AMP • Secretion water/ions (chloride and bicarbonate from the mucosal cells) 3. Enteroinvasive E. coli (EIEC ) • These bacteria can penetrate into the colonic mucosa, where they cause ulcerous, and inflammatory lesions 3. Enteroinvasive E. coli (EIEC ) • Dysentery - resembles shigellosis 4. Enterohemorrhagic E. coli-EHEC • Usually serotype O157:H7 Transmission electron micrograph 4. Enterohemorrhagic E. coli-EHEC • Usually serotype O157:H7 • These bacteria are the causative pathogens in the hemorrhagic colitis and hemolytic-uremic syndrome (HUS) that occur in about 5% of EHEC infections, accompanied by acute renal failure, thrombocytopenia, and anemia. Enterohemorrhagic E. coli • Vero toxin – “shiga-like” toxin • Hemolysins E coli O104:H4 Outbreak 2011 5.Enteroaggregative E. coli (EAEC) •Involves binding of E.coli by pili. •Also, Shiga toxin like & Hemolysin like toxin. •Actual pathogenic mechanism not known. •Produces watery diarrhea in infants, may be prolonged in some cases. Treatment -gastrointestinal disease • Fluid & electrolyte replacement • Antibiotics • not used usually unless systemic infection. •e.g. Hemolytic-uremic syndrome Shigellae • Shigella is the causative pathogen in bacterial dysentery The genus comprises the species S. dysenteriae, S. flexneri, S. boydii, and S. sonnei Shigellae are nonmotile S. dysenteriae, S. flexneri, S. boydii can be classified in serovars (or serotypes) based on the structure of their O antigens Shigellae • Shigellae are nonmotile and therefore have no flagellar (H) antigens. Shigellae •Shigellae are characterized by invasive properties •They can penetrate the colonic mucosa to cause local necrotic infections •Humans are the sole source of infection since shigellae are pathologically active in humans only. PATHOGENESIS • Shigellae are only pathogenic in humans, orally • Only a few hundred bacteria suffice for an infective dose • Shigellae enter the terminal ileum and colon, where they are taken up by the M cells in the intestinal mucosa • Following phagocytosis by the macrophages, the shigellae lyse the phagosome and actively induce macrophage apoptosis. • The shigellae released from the dead macrophages are then taken up by enterocytes via the basolateral side of the mucosa (i.e., retrograde transport) • Adjacent enterocytes are invaded by means of lateral transfer from infected cells. • Shigellae reproduces in the enterocytes with their destruction. Shigellosis Shiga toxin •Enterotoxic •Cytotoxic •Inhibits protein synthesis • inhibits protein synthesis by eukaryotic cells by splitting the 28S rRNA Clinical picture • Following an incubation period of two to five days, the disease manifests with profuse watery diarrhea • Later, stools may contain mucus, pus, and blood • Intestinal cramps, painful stool elimination (tenesmus) • Severe effects are caused mainly by S. dysenteriae, whereas S. sonnei infections usually involve only diarrhea Shigellosis • Man only "reservoir" • Mostly young children •Fecal to oral contact •Children to adults • Transmitted by adult food handlers •Unwashed hands •Low infective dose Treating shigellosis •Manage dehydration, replace fluid and electrolytes loss •Patients respond to antibiotics ??? (last news…..says the other way around) Salmonella Salmonella • Nearly all human pathogen salmonellae are grouped under S. enterica. • Salmonellae are further subclassified in over 2000 serovars based on their O and H antigens Pathogenesis and clinical pictures •Salmonellae are classified as either typhoid or enteric regarding the relevant clinical pictures •It is not known why typhoid salmonellae only cause systemic disease in humans, whereas enteric salmonella infections occur in animals as well and are usually restricted to the intestinal tract. Typhoid salmonelloses • Are caused by the serovars typhi and paratyphi A, B, and C. • The salmonellae are taken up orally and the invasion pathway is through the intestinal tract, from where they enter lymphatic tissue. • An active vaccine is available to protect against typhoid fever Typhoid salmonelloses • Attachment of typhoid salmonellae to cells of the jejunum (M cells). Invasion by means of endocytosis, transfer, and exocytosis. • Phagocytosis in the subserosa by macrophages and translocation into the mesenteric lymph nodes. Proliferation occurs. • Lymphogenous and hematogenous dissemination. Secondary foci in the spleen, liver, bone marrow, bile ducts, skin (roseola), Peyer’s patches. Typhoid salmonelloses • Manifest illness begins with fever, rising in stages throughout the first week to 39/40/41 8C. • Further symptoms: • stupor, • leukopenia, • bradycardia, • splenic swelling, • abdominal roseola, • beginning in the third week diarrhea, sometimes with intestinal bleeding due to ulceration of the Peyer’s patches. Typhoid salmonelloses •Human reservoir •Carrier state common •‘Typhoid Mary’ • Contaminated food •Water supply •Poor sanitary conditions Typhoid -Therapy • Eliminating the infection in chronic stool carriers of typhoid salmonellae, 2–5% of cases, presents a problem • Chronic carriers are defined as convalescents who are still eliminating pathogens three months after the end of the manifest illness • The organisms usually persist in the scarified wall of the gallbladder • Antibiotics or cholecystectomy. Enteric Salmonelloses (Salmonella food poisoning or salmonella Gastroenteritis) •S. enterica enteritidis •the common salmonella infection •poultry, eggs • no human reservoir • Gastroenteritis • • • • • nausea vomiting Diarrhea non-bloody stool self-limiting (2 - 5 days) Enteric Salmonelloses • Attachment to enterocytes of the ileum and colon. • Invasion of mucosa induced by invasion proteins on the surface of the salmonella cells. Persistence in epithelial cells, possibly in macrophages* as well. • Production of Salmonella enterotoxin. Local inflammation • Salmonella are capable of persisting in the relatively mild phagosome and live inside the macrophage by subverting the formation of phagolysosome thus inhibiting digestion by lysosomal action, which provides an environment for the pathogen to hide from the immune system and replicate. from: Aderem A, Underhill DM. Mechanisms of phagocytosis in macrophages. Annu Rev Immunol. 1999;17:593–623 Yersinia •The genus Yersinia includes 11 species: • Y. pestis, • Y. pseudotuberculosis, • Y. enterocolitica, • Y. frederiksenii, • Y. intermedia, • Y. kristensenii, • Y. bercovieri, • Y. mollaretii, • Y. rohdei, • Y. aldovae and Y. ruckeri Yersiniosis •Yersinia enterocolitica • Transmission •fecal contamination, domestic animals • Water • Milk • Meat Yersinia The bacteria enter the lower intestinal tract, penetrate the mucosa and are transported with the macrophages into the mesenteric lymph nodes Diarrhea fever abdominal pain (from lymphadenopathy*) antibiotic therapy recommended occasional bacteremia * Pseudoappendicitis Yersinia -isolation •Faeces in peptone water at 4 C x 7 days, s/c McConkey agar. •Culture on Yersinia selective agar. •Yersinia bacteria grow better at 20–30 °C. o Vibrio cholerae Vibrios • Family Vibrionaceae • Gram negative rods • Comma shaped, • Monotrichously flagellated • ‘Darting motility’ • Aerobes & facultative anaerobes • Oxidase positive • Catalase positive • Reduce Nitrate to Nitrite • Simple nutritional requirements Occurrence -cholera • Developing countries,7th Pandemic continuing……… • In UAE , rare cases, imported from the Indian subcontinent, Africa, Egypt etc. •uncommon *traveler *ingestion of sea-food Cholera cases reported to the World Health Organization from 1984 to 2007. A substantial increase in the number of cases has been observed since 1990. This is the result of large epidemics of cholera caused by V. cholerae O1 in America and Africa, and the appearance of a new serogroup, O139, in Asia. At present, cholera is restricted to Africa. (Adapted from World Health Organization. Cholera. Wkly Epidemiol Rec. 2008;83:269-284.) Transmission - V. cholerae feces water – fresh – salt food Cholera - attachment Cholera toxin- Choleragen •B binds to gangliosides on the surface of the target cell •provides channel for A • subunit A activates the G protein which activates adenylate cyclase. •https://www.youtube.com/watch ?v=u8MNKvevnns 1). TCBS ( green colour) Thiosulfate citrate bile salts sucrose agar : made by boiling agar ( not autoclavable) : selective indicator medium. V.Cholerae ferments the sucrose (Yellow colonies) 2). Monsur’s agar(GTTA)- Taurocholate tellurite gelatin agar : Black colonies with clear zone in the surrounding area 3) Alkaline peptone water: Enrichment broth at pH 8.2 (show alkali tolerance (pH 9)) Vibrio cholerae Classification • 84 serovars • O1= Classical V.cholerae, • O2-84 = Non-cholera vibrios or non-O1 V.cholerae. • O1 further divided into: Biovars • 1.Classical • 2.El-Tor. • O1 further divided into: • Ogawa, Inaba, Hikojima serotypes.(By slide agglutination). Pathogenesis and Clinical Picture • Infection results from oral ingestion of the pathogen • The infective dose must be large (≥108) (why?) • Based on their pronounced stability in alkaline environments, vibrios are able to colonize the mucosa of the proximal small intestine • The pathogen does not invade the mucosa Pathogenesis and Clinical Picture • The clinical picture is characterized by voluminous, watery diarrhea and vomiting • 20 L per day! • hypotension, tachycardia, anuria, and hypothermia. • Lethality can be as high as 50% in untreated cases Cholera -therapy • Therapy – fluid replacement – antibiotic therapy •Vaccination – partially effective – not generally used – international travelers Vibrio parahemolyticus • Raw sea-food • Grows best in high salt • commonly seen in coastal areas • Diarrhea •Needs 5 % salt for growth •Oxidase positive, GN bacilli •Green colonies on TCBS --- so does not ferment ? CAMPYLOBACTER & HELICOBACTER • Gram negative rods • curved or spiral • genetically related Campylobacter CAMPYLOBACTER • C. jejuni • C. coli • C. jejuni is now recognized as one of the main causes of bacterial foodborne disease in many developed countries C. jejuni • Infects the intestinal tract of animals – Cattle and sheep (zoonosis) Transmission •milk •meat products undercooked Disease: • Diarrhea (WBC+RBC present in stools) • Abdominal cramps & rarely septicemia. • The sites of tissue injury include the jejunum, the ileum, and the colon. • In some cases, a Campylobacter infection can be the underlying cause of Guillain–Barré syndrome. Campylobacter Isolation - Campylobacter • Microaerophilic • Grows best 42oC • Lysed blood agar with antibiotics. Campy agar. • Species: C.jejuni, C.coli, • Differentiation by: • Temperature • Hippurate test (hydrolize --- glycine---blue) • Cephalothin & Nalidixic acid sensitivity. Campylobacter - symptoms • diarrhea • malaise • fever • abdominal pain • usually self-limiting • antibiotics occasionally • bacteremia –small minority Helicobacter pylori •Stomach mucosa •Ulcers •Non-ulcer dyspepsia •Stomach cancers Urease • Urease positive • Important in neutralizing stomach acid • (NH2)2CO + H2O → CO2 + 2NH3 ammonia is a basic molecule Diagnosis -Helicobacter • Culture - urease detection • Mucosal endoscopy • Radioactive CO2 breath after feeding radioactive urea •Patient drinks C13 labelled urea UREA Ammonia + 13CO2 Urease by H.Pylori Patient breathes into machine, detects labelled CO2 Serological diagnosis • Serum antibody to H. pylori • Faecal antigen test Therapy -Helicobacter • Antibiotics •cures ulcers •Combination of High dose Amoxicillin, Azithromycin, Metronidazole, Tetracycline etc for 1-3 weeks. Aeromonas & Plesiomonas (curved Gram negative rods, catalase & oxidase +, actively motile) • Species: A.hydrophilia, P.shigelloides • Infections: -wound infections ( near water) - Diarrhea • Identification: - Oxidase positive - Gram neg bacillus - Lactose fermenters - very beta hemolytic colonies - Selective medium used: Ampicillin - Biochemical id.(API etc) Summary statement • Sanitary measures • protect the water supply • Food/water borne epidemics • rare US • common in developing countries • Zoonotic infections • Contaminated animal products • less well controlled • Common Therapy • Severe diarrhea – Fluid replacement essential • Antibiotic therapy sometimes used in local infection but always in systemic disease Key Words Opportunistic diseases Diarrhea/Dysentery Urinary tract infections Opportunistic infections Lactose positive/negative Enteropathogenic E. coli Enterotoxigenic E. coli Heat stable toxin Heat labile toxin Enteroinvasive E. coli Enterohemorrhagic E. coli Vero toxin (Shiga-like) Hemolysin pili Shigella Bacillary dysentery Shiga toxin Salmonella enteritidis salmonellosis Salmonella cholerae-suis Salmonella typhi Typhoid Vi Vibrio cholerae Choleragen Yersinia enterocolitica Helicobacter pylori Campylobacter jejuni