Unformatted text preview: Review: gram pos. vs. neg. Review: gram pos. vs. neg.
Characteristic Outer membrane Cell wall LPS Teichoic acid Sporulation Capsule GramPositive Thicker Often present Some strains Sometimes present Sensitive More susceptible Some strains GramNegative + Thinner + Sometimes present Resistant More resistant Some strains Lysozyme Antibacterial activity of penicillin Exotoxin production Enterobacteriaceae Part I General Introduction Lecture 12 Classification Classification Family Enterobacteriaceae Genera Several including: Escherichia Salmonella Klebsiella Enterbacter E. coli K. pneumoniae P. Vulgaris … Yersinia Shigella Proteus Species ENTERIC BACILLI ENTERIC BACILLI ENTERIC= relating to INTESTINES The Enteric Bacilli The Enteric Bacilli Morphology Gram negative rods (16µ m) Nonspore forming Fimbriae and sex pili E. coli • may be motile via peritrichous flagella
• may have capsule The Enteric Bacilli The Enteric Bacilli
Physiology Ferment glucose Reduce nitrate Oxidase negative (diff. from other gram.neg rods) Catalase positive Facultatively anaerobic these tests used to place in family The Enteric Bacilli The Enteric Bacilli
Colony morphology (cont’d) Moist, gray, smooth colonies on nonselective media (Blood Agar) Special media used for separation of genera and species (e.g. McConkey Agar) The Enteric Bacilli The Enteric Bacilli
McConkey Agar: contains Crystal Violet (inhibits gram pos.) differentiates between lactosefermenting Enteros (E.coli, Klebsiella pneumoniae) and nonfermenting (Shigella flexneri ,Salmonella typhimurium, Yersinia pestis) via color of the colonies (pink versus colorless) Play an important role for some species in epidemiology and classification 3 groups of antigens: K or Vi antigens (Capsule) Flagellar (H) antigens Somatic (O) antigens (LPS) Antigenic Structure/Serological Antigenic Structure/Serological Classification The Enteric Bacilli
(cont’d) 325 Antigenic Structure/Serological Classification Antigenic Phase Variation!! expression of capsular K or Vi antigens and flagellar H antigens is under tight genetic control bacteria can react to selective pressure of Ab mediated host immune response capsule is not expressed by bacteria in vitro (need special conditioning medium to induce capsule formation) Flagella Flagella Multiple flagellin subunits, helical arrangement; anchored in bacterial cell wall in complex structure Up to 20µ m long Important for motility Binds epithelial cells Fimbriae/Pili Fimbriae/Pili Helicallyarranged identical protein subunits ; 1430kDa some carry adhesins at tip or side Length 0.510µ m Not involved in motility Binds to epithelial cells in intestine, respiratory tract Type III secretion system Type III secretion system All of the pathogens in the family of Enterobacteriaceae rely on TTSS for virulence TTSS: multiprotein complex, expressed only after infection of host structure resembles syringe used to inject virulence factors into host cells Core polysaccharide Ospecific oligosaccharide polymer Lipid A (endotoxin, part that causes toxic shock) Somatic (O) antigens (mostly LPS ) (cont’d) Antigenic Structure LPS/ Endotoxin LPS/ Endotoxin Toxic Shock (need high bacterial burden!) systemic manifestations of gramnegative bacterial infections initiated by LPS/endotoxin: activation of complement, release of cytokines, fever and decreased peripheral circulation, shock, and death. LPS is a very powerful LPS is a very powerful immunostimulant (Modulin)
1) Fever 2) Hypotension 3) DIC (Disseminating Intravascular Coagulation) LPS activates
1) Macrophages 2) Complement 3) Hageman factor (Coagulation) Pathogenicity determinants Pathogenicity determinants Endotoxin/ LPS Exotoxins (not in opportunistic E.coli) Stx1 and 2 (shiga toxin) LT1 (like cholera toxin) Specific virulence factors for other pathogenic members of the family Clinical infection Clinical infection Urinary tract Wound infections Pneumonia Meningitis Septicemia Gastrointestinal disorders Opportunistic vs. Pathogenic Opportunistic vs. Pathogenic Enteros Opportunistic pathogens (part of normal microflora): Escherichia, Klebsiella, Proteus Strict Pathogens (not part of the microflora): Shigella, Salmonella, Yersinia, some E.coli strains Enterobacteriaceae Part I Escherichia Coli Lecture 12 Escherichia Coli Escherichia Coli E. coliK12 (nonpathogenic lab strain) E.coli O157:H7 most famous serotype (gastroenteritis) Most disease caused by bacteria found in the common microflora (opportunistic pathogens) Exception: Gastroenteritis cause by ingestion of exogenous, virulent strains of E. coli not commonly associated with microflora Most common gram neg rod in isolates of sepsis (45%), all serotypes may cause disease Sepsis is often caused via initial UT or GIT infections (e.g.,perforation of intestine) Mortality high only in immunocompromised patients Escherichia Coli/Septicemia Escherichia Coli/UTI Causes 80% of all community acquired UTI!! (swimming pool, river, ocean) Often caused by endogenous E.coli in colon All serotypes but more common when expressing specific ADHESINS Some Bacteria can migrate up the UT into bladder, kidney, prostate Bacteria expressing hemolysin A are more virulent (HlyA lyses erythrocytes, leading to inflammation) Treatment guided by antibiotic resistance testing Escherichia Coli Neonatal Meningitis E.coli and Group B streps cause majority of CNS infections in infants <1month! 75% of E.coli are K1 serotype ECK1 is commonly presented in GI tract of pregnant woman ! Preventive treatment of pregnant woman if tests positive Immediate treatment of infant with IV antibiotic (Penicillin+Aminoglycoside); see group B Strep. Escherichia Coli/Gastroenteritis Defined by serotypes of E.coli that are NOT part of the common microflora!! Strains that cause gastroenteritis divided into five groups 1) Enteropathogenic EC (EPEC) 2) Enterotoxigenic EC (ETEC) 3) Shiga toxinproducing EC (STEC=EHEC) 4) Enteroinvasive EC (EIEC) 5) Enteroaggregative EC (EAEC) Enteropathogenic Escherichia coli (EPEC) Uncommon in US Cause watery diarrhea in infants in developing countries Cause Attachment and Effacement lesions (A/ E lesions) similar to STEC Enteropathogenic Escherichia coli Enteropathogenic Virulence Factors: BFP: bundle forming pili TTSS Intimin (Adhesin) Tir (equivalent unknown for STEC) A/E Lesions A/E Lesions disruption of microvilli Escherichia Coli/Gastroenteritis Defined by serotypes of E.coli that are NOT part of the common microflora!! Strains that cause gastroenteritis divided into five groups 1) Enteropathogenic EC (EPEC) 2) Enterotoxigenic EC (ETEC) 3) Shiga toxinproducing EC (STEC=EHEC) 4) Enteroinvasive EC (EIEC) 5) Enteroaggregative EC (EAEC) Enterotoxigenic Escherichia coli (ETEC) Very common in developing countries (650 million cases/year); affects mostly infants and travelers Infection via ingestion of contaminated food/water Symptoms: watery diarrhea, cramps, vomiting develop after 12days incubation and persist for about 34 days Virulence factors Virulence factors heat stable (STa) and heat labile (LTI) exotoxins, stimulate hypersecretion of fluids and electrolytes (diarrhea) Both toxins are AB subunit toxins LTI very similar to Cholera Toxin Either toxin sufficient to cause symptoms Fimbriae important for adherence LTI/Cholera toxin LTI/Cholera toxin Prevention/Treatment ETEC Prevention/Treatment ETEC “Boil it, cook it, peel it or forget it” (“travelers diarrhea” ETEC) Treatment of symptoms only (water, electrolytes) Escherichia Coli/Gastroenteritis Defined by serotypes of E.coli that are NOT part of the common microflora!! Strains that cause gastroenteritis divided into five groups 1) Enteropathogenic EC (EPEC) 2) Enterotoxigenic EC (ETEC) 3) Shiga toxinproducing EC (STEC=EHEC) 4) Enteroinvasive EC (EIEC) 5) Enteroaggregative EC (EAEC) Enterohemorrhagic Escherichia coli (EHEC) Enterohemorrhagic =Shiga toxin producing E.coli (STEC) Most common strains causing disease in developed countries >50 serotypes but most common in US is STEC O157:H7 Causes bloody diarrhea STEC STEC Epidemiology/Transmission ~70,000 infections and 60 death per year in US Ingestion of fewer than 100 bacteria can cause disease Most common during warm month and in children <5years old Contaminated food (undercooked meat[Hamburger]; raw vegetables [Spinach/Salad]) STEC Epidemiology/Transmission 2006 outbreak associated with spinach consumption STEC STEC Epidemiology/Transmission STEC STEC Epidemiology/Transmission STEC: Spinach outbreak 2006 STEC: Spinach outbreak 2006 Killed three people and got ~200 sick Cost company millions of $ Implemented improved testing system every bin is tested before shipment (~12h delay) September 2007: Topps Hamburger E. coli Outbreak 2nd largest beef recall in US history (67 years)
•Topps Meat Company has expanded the recall of Topps hamburgers to approximately 21.7 million pounds of hamburgers due to possible contamination with E. coli O157:H7. •At least 30 people have reported illnesses associate with this recall. •The recalled hamburgers were sold nationwide, the bulk to states in the Northeast. October 2007: Topps Meat Co. shuts down business “E. coli outbreak kills meat company” Loss in sales Transport of recall, pay for recalled product Litigation/lawyer costs Improvement of production facilities Millions of $ to fix the problem not counting the loss of consumer confidence in brand name History: E.coliHamburger History: 1993 “Jack in the box” fast food chain, undercooked hamburgers 4 children died; hundreds got sick 1997 largest recall of Hamburger meat, “Hudson Food Co.” went out of business Meat industry: E.coli prevention Meat industry: ~$350 million for prevention and testing annually in meat industry alone Investment pays off Epidemiology: EHEC=STEC Epidemiology: EHEC=STEC Disease: STEC Disease: STEC ? Severity varies uncomplicated diarrhea to hemorrhagic colitis : initial watery diarrhea (after 34 days) followed by bloody diarrhea (= hemorrhagic colitis)(3065% of cases) with abdominal cramps (no fever) complete resolution in untreated patients after 410days in young children in 510% of cases severe complication: Hemolytic Uremic Syndrome (HUS) HUS associated with Shigatoxin 2 producing strains HUS: acute renal failure can lead to death STEC/EHEC induce A/E lesions as do EPEC Express Shigalike toxin1 and 2 (AB (AB5)subunit toxin) ; Sltx1 identical to toxin produced by Shigella dysenteriae Toxin acquired by bacteriophage Toxin binds to receptor found on endothelial cells of intestine (and kidney for Sltx2) Induces death of cells (inhibits prot. Synthesis) Isoform of toxin (Sltx2) binds preferentially to renal endothelial cells and is associated with HUS Virulence Factors Virulence Factors Diagnosis Diagnosis
Many O157 strains do NOT ferment Sorbitol SorbitolMcConkey agar can be used to screen stool samples (Sorbitolnegative=colorless colony) drawback: some O157 can ferment sorbitol and also method does not assess toxin production Preferred Method: Stool sample on nonselective McConkey agar and analyze colonies for toxin production (PCR) Treatment/Prevention Treatment/Prevention
Treat symptoms!! supply water and electrolytes (IV in severe cases) Antibiotic treatment not recommended, may prolong diseases (probiotics?); Unless disseminating disease Do not undercook meat!! Wash your salad/spinach “Boil it, cook it, peel it or forget it” (“travelers diarrhea” ETEC) ...
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- Fall '08
- Escherichia coli, Enterobacteriaceae, Enteric Bacilli, STEC STEC Epidemiology/Transmission