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Transcript
Enterobacteriaceae II: Intestinal Pathogens Salmonella, Shigella, Yersinia Salmonella • Animals main reservoir of human disease: – – – – Gastroenteritis Typhoid (Enteric) fever Septicemia Asymptomatic carriage • Transmission: – Ingest contaminated food (poultry, eggs, dairy products) – Direct fecal-oral spread in children Salmonella Genera • Describe >2500 serotypes • DNA homology studies: – One Genus-species - Salmonella enterica – Seven subspecies (1, 2 ,3a ,3b ,4 ,5, and 6) – Subgroup 1 causes most human infections • Clinically Salmonella isolates often still reported as serotypes by Kauffman-White classification: – Based on O (cell) and H (flagella) antigens – H antigens occur in two phases (antigenic variation) – Polyvalent antisera used, followed by group specific antisera (A, B, C1, C2, D, and E) – Salmonella Typhi (capitalize, not italics to designate Genus-Serotype) - also has capsular Vi antigen Salmonella: Biochemical Test ID • TSI = K/A + gas, H2S – Salmonella Typhi small amount of H2S, no gas – Salmonella Paratyphi no H2S • LIA = K/K (+)lysine DC, +H2S • • • • – Salmonella Paratyphi = K/A Urea(–) PA(-) Citrate(±) Indole(-) Salmonella: Infection • MO found in all animals – poultry, reptiles, livestock, rodents, domestic animals, birds, and humans • Highly adapted strict human pathogen: – Salmonella Typhi – Salmonella Paratyphi • Peak incidence of infections in warm months via ingesting contaminated food at outdoor social gatherings • ~50,000 cases reported annually in U.S Salmonella: Infection of GI Tract • • • • Ingest contaminated food Infect GI cells Blood (systemic infection, target organs) RES (Reticuloendothelial System) – macrophages, liver, spleen, bone marrow Infection of GI Tract • MO adheres to intestinal mucosa epithelium • Invasion of enterocytes, M cells (microfold cells of Peyer patches) • Induced endocytosis by bacteria effector proteins • Salmonella multiplies within phagosome, released; may be phagocytosed by macrophages Salmonella: Gastroenteritis • Salmonellosis most common form of gastroenteritis • Due to Salmonella Enteritidis in U.S. • Symptoms 6-48 hours after consumption contaminated food: – Nausea, vomiting, non-bloody diarrhea – Also common with elevated temperature, abdominal cramps, myalgia, headache • Persist 2-7 days, spontaneous resolution • Supportive care, no antibiotics required • Incidence greatest children <5 yrs. and adults >60 yrs. Gastroenteritis • MOs multiply, induce strong inflammatory response • Causes disease symptoms (fever, diarrhea, abdominal cramps) • Inflammatory response prevents spread beyond GI tract, eventually kills MOs Salmonella: Typhoid ( Enteric) Fever • Typhoid fever - Salmonella Typhi • Paratyphoid fever (milder) - Salmonella Paratyphi • 10-14 day incubation period following ingestion of contaminated food • Fever, headache, myalgia, malaise, anorexia • Persist 1 week, followed by GI symptoms (GI→blood→GI) • Mortality ~20% if untreated Typhoid Fever • MO disseminate before high enough levels to stimulate inflammatory response • Initial symptoms low fever, constipation • MO move via lymphatics & bloodstream to liver & spleen; phagocytosis & multiplication occurs • MO re-enter bloodstream, disseminate to all organs; fever, headaches, myalgia, GI problems • Rose spots (erythema, maculopapular lesions) on abdomen • Osteomyelitis, cystitis, gall bladder infections may occur Salmonella: Septicemia • Most frequently: – Salmonella Typhimurium – Salmonella Choleraesuis – Salmonella Paratyphi • At risk: children, elderly, AIDS patients • Infection presents like Gram(-) bacteremia • 10% develop osteomyelitis, endocarditis, arthritis Salmonella: Asymptomatic Infection • Salmonella Typhi • Salmonella Paratyphi • MO’s from enteric fever maintained by human carriage • ~1-5% infected patients chronic carrier >1 year • Reservoir in gall bladder Lab Diagnosis: Typhoid Fever • Blood cultures positive during first week, after second week • Stool culture, sometimes urine culture positive after second week • Widal Test (serology): – Antibodies against Salmonella Typhi – Look for 4-fold rise in titer between acute and convalescent stage (~one month) Salmonella: Prevention • Gastroenteritis: – Public Health education – Improved hygiene, especially food handlers – Safe preparation of poultry & eggs, refrigerate food – Antibiotics not recommended, may prolong disease • Enteric fevers: – Treat with fluoroquinolone (ciprofloxacin), chloramphenicol ( decrease mortality to <2%) – Live oral vaccine (attenuated Salmonella Typhi) for travelers to endeminc countries – Clean water supply – ID, treat chronic carriers Shigella: Gastroenteritis • Shigellosis (Bacillary dysentery) • ~150 million cases annually worldwide; 450,000 in U.S. • Humans only reservoir, transmitted person-to-person by fecal-oral route • Outbreaks in communities where sanitary standards, level of hygiene low • Common in daycare centers, nurseries, custodial institutions Shigella Genera • Four species by O antigen serotype: – S. dysenteriae (Group A) – most severe; Shiga toxin – S. flexneri (Group B) – developing countries – S. boydii (Group C) – not commonly isolated – S. sonnei (Group D) – developed countries; U.S. • By DNA analysis, now shown to be biogroup within E. coli Shigella: Biochemical Test ID • • • • • TSI = K/A with NO gas LIA = K/A (-)lysine DC Urea (–) Motility(–) S. sonnei may show delayed lactose fermentation Shigella: Virulence Factors - Enterotoxin • Shiga toxin - S. dysenteriae • Smaller amounts by S. flexneri, S. sonnei • Inhibit protein synthesis by inactivating 60S ribosomal subunit • Role in ulceration intestinal mucosa Shigella: Virulence Factors Cell Wall Proteins • Expressed at body temperature • Upon contact with intestinal mucosa M cells (microfold cells, Peyer’s patches), induce phagocytosis of bacteria into vacuoles • Shigella destroys vacuoles, escape into cytoplasm • Spread laterally (actin filaments propel MO through cytoplasm) to epithelial cells; multiply • Do not usually disseminate beyond epithelium Shigella: M Cell Attachment Shigella: M Cell Penetration Shigella: Epithelial Cell (CCEC) Invasion Shigellosis • Fecal-oral route, primarily contaminated hands • Infective dose very low (100-200 MO) • Incubation 1-7 days • Fever, cramping, abdominal pain, watery diarrhea for 1-3 days (due to exotoxin) • Followed by frequent, scant stools with blood, mucous, pus (invasion of intestinal mucosa) • Rare for MO to disseminate, generally selflimited but may lead to death • Severity of disease depends upon species: – S. dysenteriae most pathogenic – Followed by S. flexneri, S. sonnei, S. boydii Shigella: Treatment and Prevention • Trimethoprim-sulfamethoxazole (SXT) or fluoroquinolone (ciprofloxacin) - shortens course of disease & fecal shedding; recommended to reduce spread to contacts • Resistant strains becoming increasingly common, so antibiotic sensitivity testing required • Infection control by proper hand washing and disposal of soiled diapers/linens • Public Health monitoring for clean water supply Comparison of Invasion: Salmonella versus Shigella Yersinia Genera • Infections are zoonotic, humans accidental host • Three species important pathogens in humans: – Yersinia pestis – plague (bubonic or pneumonic) – Yersinia enterocolitica – gastroenteritis, transfusion-related sepsis – Yersinia pseudotuberculosis – mainly disease of animals, uncommon human gastroenteritis Yersinia: Infection • Y. pestis: – Mammalian reservoir: rats, squirrels, rabbits, domestic animals – Humans infected by: • Fleas • Direct contact with infected animal tissue • Aerosols from patient with pulmonary disease • Y. enterocolitica: – Ingest contaminated food products – Infusion of contaminated blood products (growth in blood stored at 4°C) Yersinia pestis: Lab ID • Non-motile - 37°C & 25°C • Bipolar staining • Slow growth, small colonies at 37°C (grows better 25°C) • TSI = K/A • Urea(-) • ODC(-) • Guinea pig LD50<10 • Direct fluorescent antibody test • New DNA probe test Y. pestis: Bubonic Plague • By flea bite infected animal (rat, squirrel, rabbit) to human • Endemic in local So Cal mountains • MO travel to nearest lymph node, engulfed by macrophage • High fever, buboe (enlarged lymph node), MO proliferate, stimulate inflammatory response • MO multiply in lymph node, leak into bloodstream • Lysis of bacteria releases LPS causing septic shock, DIC • Subcutaneous hemorrhage, disease named Black Death in Middle Ages • High mortality rate (30-40%) if untreated Pneumonic Plague • Eventually bacteria reach lungs, engulfed by lung macrophages, cause pneumonic plague • Transmit directly to others via aerosol • Direct inhalation produces disease that progress more rapidly • Mortality rate close to 100% Y. pestis: Treatment and Prevention • Streptomycin, tetracycline, SXT • Control by reducing rodent population • Vaccine (formalin killed bacteria) for individuals at risk; no longer available Yersinia enterocolitica: Lab ID • • • • Non-motile at 37°C Motile at 25°C Bipolar staining Slow growth, small colonies at 37°C (grows better at 25°C) • TSI = A/A (sucrose fermentation) • Urea(+) • ODC(+) CIN Agar • Isolation of Y. enterocolitica from stool specimen (also Aeromonas, Plesiomonas) • Selective - antimicrobials (Cefsulodin-Irgasan-Novobiocin), bile, crystal violet inhibit NF • Differential - mannitol, neutral red • Incubate room temperature • After 48 hours at RT, Y. enterocolitica produce typical pink colonies (mannitol fermentation) with bulls-eye appearance Y. enterocolitica: Gastroenteritis • Ingestion of contaminated food or water • Common cause of human disease (mostly in children) involving fever, abdominal pain, watery diarrhea • Intestinal epithelium invasion of M cells, transcytosed through M cells, released at basal surface • Bacteria penetrate into underlying lymphoid tissue, multiply both inside and outside host cells Gastroenteritis • Inflammatory response to MO responsible for extreme pain (~acute appendicitis) • Fever due to LPS endotoxin • Sometimes drain into adjacent mesenteric lymph nodes, causing lymphadenitis • Reactive arthritis may occur in some people; thought cross reacting T cells or antibodies that attack joint • Usually self-limited • If treatment indicated, susceptible to broad-spectrum cephalosporins Summary: Yersinia Infections Lab: Enterobacteriaceae II Group Unknowns • • • • Salmonella Proteus Citrobacter Yersinia TSI K/A, H2S K/A, H2S K/A, H2S K/A LIA K/K, H2S R/A, H2S K/A, H2S K/A • • • • Lecture Exam I Thursday, Feb. 2, 2012 Introduction thru Enterobacteriaceae Lecture Reading (Chap. 14, 15, 17, 19) Key Terms, Learning assessment Questions • Case Study 1,2,3 • Exam Format: – Multiple Choice – Terms – True/False Statements – Short Essay • Review, Review, Review!