enterobacteriaceae.pdf

Enterobacteriaceae By Marwa Mohamed Khalifa General character of Enterobacteriaceae 1-They are gram negative bacilli, primarily found as normal commensals in colon. 2-The family includes many genera; some are pathogenic (Salmonella, Shigella) others are commensals (ex. E coli and Kleb...

Enterobacteriaceae By Marwa Mohamed Khalifa General character of Enterobacteriaceae 1-They are gram negative bacilli, primarily found as normal commensals in colon. 2-The family includes many genera; some are pathogenic (Salmonella, Shigella) others are commensals (ex. E coli and Klebsiella). 3-Facultative anaerobes. 4-All ferment glucose but fermentation of other sugars varies. General character of Enterobacteriaceae 5-Oxidase negative 6-Reduce nitrates to nitrites during metabolism. 7-Contain LPS (i.e.endotoxin) in their cell walls released after bacterial cell death leading to septic shock. 8-Cause either intestinal or extraintestinal diseases or both depending on genera. 9-Antigenic composition: All species have somatic (O) antigen (located on the surface of LPS) ± flagellar (H) antigen. ± capsular (K) antigen Classification of Enterobacteriaceae: According to their effect on lactose they are divided into A)lactose fermenters ❑rose pink colonies on MacConkey. ❑E.coli, Klebsiella, Citrobacter and Enterobacter. ❑They are called coliforms. b) Non-lactose fermenters ❑ pale yellow on MacConkey. ❑Salmonella, Shigella, proteus. 1) E.coli They are normal inhabitants of the intestine, but some can cause diseases. Morphology: gram negative bacilli, motile, some strains are capsulated. Virulence factors: 1-Pili: adherence to mucosal surfaces. 2-K or capsular polysaccharide Ag which is antiphagocytic 3-LPS: Endotoxin causing fever, hypotension, shock. 4-Two exotoxins (they are enterotoxins) one is heat labile (LT) and the second is heat stable ST).Produced by Enterotoxigenic strains of E.coli. They are genetically determined by a plasmid. 5-Verotoxin or shiga like toxin: Produced by Enterohaemorrhagic E.coli  Diseases of E.coli A) Extraintestinal Diseases(Non diarhogenic E.coli) 1- Urinary Tract Infection: ▪ E.coli is the most common cause of UTI. ▪ E coli colonize the vagina and periurethral region & ascend to the bladder or kidney causing cystitits and pyelonephritis. ▪ Virulence factors: a- Pili is the major virulence factor. b-Motility ▪ Transmission: from own fecal flora → urethra 2-Nosocomial infections: including UTI which is usually associated with urinary catheterization. 3-Neonatal septicemia and neonatal meningitis: 4- Pneumonia, bacteremia, septicemia and endotoxic shock. Diseases of E.coli II-Intestinat disease: diarrhea (Gastroenteritis) : watery (ETEC, EPEC) , bloody (EIEC, EHEC). Mode of transmission: faeco-oral, undercooked hamburger in EHEC  II-Intestinat disease: Group disaese Virulence factor Pathogenesis Enterotoxigenic Traveller's 2 enterotoxins one -The LT causes watery diarrhoea by stimulating adenyl cyclase E. coli (ETEC) diarrhea is heat labile in the cells of the small intestine (LT) and the → cAMP →stimulates the excretion of chloride ions inhibits second is heat the reabsorption of Na ions stable ST) -stimulates the loss of fluids and electrolytes into the lumen of the gut. →watery diarrhoea 2-ST stimulates guanylate cyclase → cGMP →stimulates the secretion of fluids to the gut lumen →watery diarrhoea Enteropathogenic E infantile pili→localized adhere tightly to intestinal mucosa →loss of microvilli and coli (EPEC) diarrhea adherence cupping of cells→ preventing the normal functions of absorption and secretion →watery diarrhea Enteroinvasive E dysentery-like invade mucosa They invade the intestinal mucosa, no blood invasion. coli (EIEC) diarrhoea of colon → bloody diarrhea (bloody diarrhea) Entreroaggregative E.coli persistent Adherence They adhere to mucosa in patches (EAggEC): diarrhoea in children and HIV patients Enterohaemorrhagic E,coli Haemorrhagic Enterotoxin bloody diarrhoea, that follows (EHEC O157H7) colitis named ingestion of undercooked Verotoxin hamburger. or ( shiga Some patients may end up with a life like Toxin) threatening complication called Haemolytic Uraemic Syndrome (haemolytic anaemia, thrombocytopenia and acute renal failure) -Mechanism: Verotoxin ( shiga like toxin) Which inhibit protein synthesis. -Antibiotics should not be used as they increase the risk of development of haemolytic uraemic syndrome. Diagnosis of E.coli infections 1-sample: According to the site of infection: ex. pus, urine, stool, CSF. 2-Film: gram negative bacilli, motile, 3-Culture: -MacConkey’s agar: rose pink color due to lactose fermentation -EMB: small dry colonies with green metallic sheen. 4-B.R: 1-They ferment glucose, lactose, maltose, mannite, sucrose and salicin with production of acid and gas so---on TSI medium they produce yellow (acid) butt and yellow slant. 2-IMVC tests: + + - - 3-oxidase, urease and H2S negative, reduce nitrate to nitrite. Treatment: 1-Rehydration by Fluids and electrolytes is essential to prevent dehydration for traveler's diarrhea, trimethoprim-sulfamethoxazole may shorten duration of symptoms 2-Antibiotics are given in diarrhea associated with fever, blood , pus so or septicemia. 3-No antibiotic currently recommended for O157:H7 (generally bloody diarrhea without fever). 4-Fluroquionlones for bloody diarrhea with pus and fever  2) K. pneumoniae Diseases: lobar pneumonia & UTI(nosocomial)&septicemia in immunocopromised. Morphology: gram –ve bacilli, non -motile and have large polysaccharide capsule (K Ag). Virulence factors: Capsule (77 serotypes) and endotoxin Culture: 1-MacConkey’s agar: rose pink color due to lactose fermentation 2-EMB: large, mucoid pink colonies due to production of extracellular slime. BR: 1-TSI: yellow butt and yellow slant 2-IMVC test: --++. 3-Urease +Ve Serology: Slide agglutination test, capsular swelling test. B-Non-lactose fermenters 1) SALMONELLA Morphology: Gram negative bacilli, motile with peritrichous flagella, non- capsulated. -They are facultative anaerobes, form acid and sometimes gas from glucose. -They produce H2S from sulphur containing compounds. Clinically relevant species ❑Salmonella enterica is the primary species and has the following serotypes: Typhoidal (serotypes that cause typhoid or enteric fever): S. enterica serotype typhi (formerly S. typhi), S. paratyphi Nontyphoidal (all other serotypes associated with foodborne gastroenteritis, most common in the United States): S. enteritidis, S. typhimurium  Typhoid fever or enteric fever: Description: Severe systemic illness in which bacteria enter the bloodstream and disseminate in organs and lymphoid tissue More common in: Children, young adults, Travelers (to endemic areas) Reservoir: Human only, no animal reservoir. Mode of Transmission: Fecal-oral route from human carriers (gall bladder) or urine from urinary carriers in contaminated food or drinks e.g. raw vegetables, fruits, raw shellfish and milk products. Typhoid fever or enteric fever: Pathogenesis: The organism enters orally from the stools or urine of cases or carriers the organism multiply in small intestine epithelial cells and pass to submucosa where they phagocytosed by macrophage, they survive in them and transported by the reticuloendothelial system --- pass to blood stream causing bacteremia for one week (fever) ----- then from the second week and onward, it passes to liver, gall bladder (excreted in stool), kidney (excreted in urine ),spleen and bone marrow. Typhoid fever or enteric fever: Signs: It is a severe life-threatening systemic disease characterized by and frequently abdominal symptoms. Non-specific symptoms may include chills, sweetening, headache, myalgia and constipation more common than diarrhea, faint maculo-papular rash on the truck (rose spot). The incubation period varies from 5-21 days. Complications can include intestinal hemorrhage and rarely focal infections and endocarditis. Typhoid fever or enteric fever: Carriers: mainly Gall bladder carrier or Urinary carrier. 1-After recovery, some individuals continue to carry salmonella in chronic carriers and the organism is intermittently excreted in the stools. 2-Salmonella may be carried in the urinary tract. *Such individuals should not work as food handlers. Diagnosis of Enteric Fever (Typhoid) I-During the first week (the organism is isolated from the blood) 1-sample: blood culture then Subcultures on: ❑ MacConkey's agar and DCA(deoxycholate citrate agar) -- pale yellow non-lactose fermenting colonies. ❑ Bismuth sulphite agar (selective): brown to black colonies due to reduction of sulphite to sulphide. ❑ salmonella –shigella agar 2-Film: Gram negative bacilli, motile Diagnosis of Enteric Fever (Typhoid) 3-B.R: A-sugar fermentation: Organism Glucose Maltose Mannite Lactose H2S S.Typhi +A +A +A - + S.Paratyphi A +AG +AG +AG - - S.Paratyphi B +AG +AG +AG - + Produce black butt on TSI Diagnosis of Enteric Fever (Typhoid) II. In the second week and onward (sample: Stool+urine) A stool sample is inoculated into tubes of selenite F broth and tetrathionate broth (enrichment media)?To inhibit the normal intestinal flora (E.coli) and incubated at 37C overnight. - MacConkey---pale yellow - Bismuth sulphite---black color. Diagnosis of Enteric Fever (Typhoid) Serological diagnosis: Widal test: It is a tube dilution agglutination test which is used for detection of Abs in the serum during the second week of disease and reach maximum titre during the 4th week. The highest dilution of the serum which gives agglutination is the titre. Interpretations of the Widal test: a- High titre of O and H (>1/160) or rising titre indicates recent active infection. Note that O antibodies disappear faster than H antibodies. B-High titres of H only (> 1/160) suggest past infection or past vaccination C- Titres below 1/80 are of no significance because typhoid fever is endemic in Egypt and this may indicate previous subclinical infection. Falsities of the Widal test 1) If the test is done during the first week; it gives false negative results as the antibodies start to appear during the second week and onward. 2) Early antibiotic treatment lowers the antibody titre due to reduction of the antigenic mass. 3) Non-enteric infections by e.g. other salmonella or autoimmune diseases may cause a non-specific rise of antibody titer, due to the presence of cross-reacting antibodies. Vaccines: a-TAB vaccine: A heat killed vaccines containing, S. Typhi, S. Paratyphi A and B. b-Oral living attenuated typhoid vaccine (Vivotif) C-Inactivated single-dose vaccine containing Vi capsular polysaccharide of S. Typhi (ViCPS) Treatment: Antibiotic sensitivity of isolates is required. Ceftriaxone and ciprofloxacin is used for resistant organisms. Ampicillin and ciprofloxacin are recommended for chronic carriers of salmonella.  2- SHIGELLA ❑ Members of genus Shigella include more than 45 (O antigen based) serogroups. ❑ Disease: Bacillary dysentery =shigellosis:*Stools contain blood, mucous and pus. ❑ It is an exclusively intestinal disease without invasion of blood. ❑ Caused by Sh. dysenteriae (the most severe), Sh. flexneri, Sh. boydii and Sh. sonnei (mild and the commonest). ❑ There is no animal reservoir (It is only a human disease). Virulence factors: 1-Invasiveness: The organism invades the mucosa of the distal ileum and colon. Infection is limited to the gastrointestinal tract without blood invasion. 2-Shiga toxin produced by Sh. dysenteriae type 1; a heat labile exotoxin that has 3 activities: ❑Enterotoxic(diarrhea) ❑Cytotoxic ( inhibit protein synthesis leading to cell death). ❑Neurotoxic effects: causing meningitis and coma in severe infections. 3-Endotoxin: triggers inflammation. Pathogenesis: Mode of transmission: By the faecal-oral route. The four F’s - fingers, flies, food, and faeces- are the main factors in transmission. 1) Invades the mucosa and wall of the large intestine and terminal ileum----Membrane ulceration and bloody diarrhea 2) In case of infection by Sh. dysenteriae type 1 shiga toxin produce early non-bloody, diarrhea and the invasion of the large intestine result in late dysentery with blood and pus in stools. 3) So it causes the severest local and systemic manifestations because it acts by dual action; release of shiga toxin and by invasion while other shigella act only by invasion (no shiga toxin). Diagnosis of bacillary dysentery or shigellosis 1-Sample: fresh stool, mucus flecks and rectal swab. 2-Macroscopic examination: mucous and blood. 3-film: gram –ve bacilli, non-motile, with pus and RBCs. 4-culture: Stools samples are inoculated on Enrichment Media as selenite, tetrathionate broth, to remove the normal flora which will interfere with diagnosis then Subcultures on : MacConkey's agar: pale yellow colonies. Diagnosis of bacillary dysentery or shigellosis 5-BR: ferment sugars with acid production only. Organism Glucose maltose lactose Sh. dysenteriae +A - - Sh. flexneri &Sh. boydii +A +A - Sh. Sonnei +A +A late fermenter Treatment: 1.Fluids and electrolytes to prevent dehydration 2.Ciprofloxacin is the drug of choice in severe cases.  3-PROTEUS Proteus species are normal inhabitants of the intestine of man. They cause infections only when they leave the intestine. Virulence factors: 1) Urease: raises urine PH to cause kidney stones. 2) Motility may aid entry into bladder. 3) Endotoxin : fever and shock. Diseases: urinary tract infections associated with kidney stones, wound infections, otitis media, pneumonia and bacteremia, respiratory tract infection….etc... 3-PROTEUS Morphology: highly motile Gram-negative bacilli. Culture: 1-MacConkey's agar (pale yellow non-lactose fermenting colonies). 2-Nutrient agar: swarming in successive waves due to their high motility. Biochemical reactions: 1-urease positive; which differentiates them from salmonella and shigella. 2-On triple sugar iron (TSI) agar they produce H2S (black butt,red slant). Thank you