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Unformatted text preview: Enterobacteriaceae Part II Salmonella Lecture 12 Classification Classification Family Enterobacteriaceae Genera Several including: Escherichia Salmonella Klebsiella Enterbacter E. coli K. pneumoniae P. Vulgaris … Yersinia Shigella Proteus Species Classification Classification Family Genus Species Enterobacteriaceae Salmonella -subdivided into >2500 serotypes, referred to as serovars, important species S. enterica S. paratyphi S. typhi S. enteritidis, S.choleraesuis S.typhimurium (mouse model of typhoid fever) Typhoid and Enteric Fever Enterocolitis General Characteristics gram negative rods motile, peritrichous flagella produce abundant hydrogen sulfide (opposed to Shigella) S.typhi is exception produces low amount of H2S Resistant to bile Non lactose fermenter (MacConkey agar/colorless colony) several surface antigens: O, Vi (subunit vaccine), H Peritrichous Flagella Peritrichous Flagella The Enteric Bacilli
(cont’d) 325 Epidemiology Epidemiology
Strict human pathogens (do not cause disease in other hosts): S. typhi and S. paratyphi 10e5 infectious dose persontoperson spread possible but mostly via contaminated food cause typhoid fever (s.typhi) or enteric/paratyphoid fever caused by septicemia=bacteremia Epidemiology Epidemiology
Zoonotic pathogens (adapted to animal host but may cause disease in humans) S.choleraesuis , S. typhimurium, S. enteritidis (eggs) very high infectious dose (106108) cause gastroenteritis/Enterocolitis and rarely septicemia Epidemiology/Infection Transmission “Foodborne pathogen” Seasonal variance (most during hot months) Commonly during outdoor social events (food stands at warm temperature) Poultry, eggs, dairy products (ice cream) and food prepared on contaminated work surface S.typhi infections mediated by food contaminated by asymptomatic carrier (“Typhoid Mary”) Zoonotic infections (Gastroenteritis/Enterocolitis) 50% of Salmonellosis caused by S.enteritidis or S. typhimurium S.enteritidis : often caused by contamination in eggs,due to transmission in infected chicken Salmonella spp. commonly found in feces of wild and/or domestic animals CONSTITUTES AND IMPORTANT RESERVOIR FOR INFECTION Epidemiology/Infection Transmission Epidemiology/USA Epidemiology/USA Epidemiology/USA 75% of typhoid fever in returning travelers Only small fraction of gastroenteritis(Salmonellosis) cases reported; in 2004 estimated 1.4 million cases , ~14,000 hospitalizations and ~400 deaths ~2% have immune sequelae (chronic arthritis) Epidemiology/World Typhoid Fever: >16million cases and ~500,000 deaths per year appeared in 1909 in The New York American Asymptomatic Carrier Mary Mallon (September 23, 1869 – November 11, 1938) was an Irish immigrant who was the first identified healthy carrier of typhoid in the United States Asymptomatic Carrier Mary was a cook in a house in Mamaroneck, New York, for less than two weeks in the year 1900 when the residents came down with typhoid. She moved to Manhattan in 1901, and members of that family developed fevers and diarrhea, and the laundress died. She then went to work for a lawyer, until seven of the eight household members developed typhoid. Mary spent months helping to care for the people she made sick, but her care further spread the disease through the household. In 1904, she took a position on Long Island. Within two weeks, four of ten family members were hospitalized with typhoid. She changed employment again, and three more households Asymptomatic Carrier Asymptomatic Carrier Mary refused to cooperate with public health officials Was quarantined for three years, released under condition not to cook 1915 Mary infected 25 people (2 died) Put on Quarantine for life (hospital on North Brother Island) Died of pneumonia, bacteria found in gallbladder!!! Asymptomatic Carrier Today, a Typhoid Mary is a generic term for a carrier of a disease who is a danger to the public because they refuse to take appropriate precautions S. typhi is specific to humans and is transmitted mostly via contaminated food (handled unsanitarily by asymptomatic carrier) Clinical Manifestation Clinical Manifestation Gastroenteritis/Enterocolitis most common 6 48 hours symptoms start nausea, vomiting, Mostly nonbloody diarrhea, abdominal pain Selflimiting within a couple of days The Microbiota Mediates Pathogen Clearance from the Gut Lumen after NonTyphoidal Salmonella Diarrhea Clinical Manifestations
Picture 2 Gastroenteritis
Infection remains localized in GI tract Transmission Salmonellosis Transmission Salmonellosis example: S. enteritidis Hens ingest S. enteritidis via contaminated food Hens are often asymptomatic Hens can lay infected or uninfected eggs People get infected by eating raw, undercooked or poorly refrigerated eggs/ egg products Since regulations implemented in 1970s, salmonellosis caused by external fecal contamination of egg shells extremely rare Transmission Salmonellosis Transmission Salmonellosis example: S. enteritidis Clinical Manifestations Enteric fevers Typhoid fever (only by S. typhi) (cont’d) Paratyphoid/enteric fever (S. paratyphi) (milder form) 10 14 day incubation period Feel weak, stomach pains, headache, sometime rash of flat colorless spots No diarrhea Increasing fever Can be fatal in untreated patients Survivors can become asymptomatic carriers (3%) Typhoid fever/Enteric Fever
Picture 2 Bacteria spread to secondary organs liver, gall bladder Via macrophages Followed by bacteremia Transmission S. typhi is specific to humans and is transmitted mostly via contaminated food (handled unsanitarily by asymptomatic carrier) All salmonella serovars can survive on dry surfaces for months Clinical Manifestations Septicemia All species can cause bacteremia but most common for S. typhi and S. paratyphi Humans vary in susceptibility Gut associated lymphatic tissue Gut associated lymphatic tissue (GALT) “Peyer’s Patch” ~allows rapid recognition of invading pathogens and immediate priming of acquired IR Cell types in intestinal epithelium Cell types in intestinal epithelium
M cell: antigen sampling Goblet cell: secretion of mucin Paneth cell: secretion of antibacterial proteins/peptides Enterocyte: absorption of nutrition IEL: Inter Epithelial Leucocyte DC: Dendritic cell Basal Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Infection & colonization of GI tract Adherence/Invasion Adherence/Invasion Salmonella Invasome: specific surface appendage of Salmonella; shorter and thicker than pili; expressed only early during attachment Overview: Bacteria induced host cell Overview: Bacteria induced host cell actin rearrangement “Trigger” Mechanism Salmonella Interaction of Salmonella with intestinal epithelial cells. (a) Electron micrograph of S. typhimurium infected kidney cell. (b) Immunofluorescence image showing actin cytoskeletal rearrangements (arrow) stimulated by S. typhimurium infection. F-actin was stained with rhodamine phalloidin (red), S. typhimurium with a FITC-conjugated antibody (green) and DNA with DAPI (blue). “Zipper” versus “Trigger” Mechanism Zipper: bacterium induces only local changes in actin organization; bacteria appears to sink into the cell (no ruffles) Trigger: bacterium induces largescale cytoskeletal response; actin filaments push huge sheets of plasma membrane out of the cell; engulf bacterium and surrounding medium (=Macropinocytosis) Both: need signal transduction from bacteria involve preexisting signal transduction cascade mediated by special bacterial virulence factors use energy derived from the host cell 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 Pathogenesis/Virulence Factors Pathogenesis/Virulence Factors TTSS “Trigger” Mechanism/ Macropinocytosis Salmonella Multiple host and bacterial effectors function in concert to promote entry. “Trigger” Mechanism/ Macropinocytosis Salmonella TTSS injected proteins
Salmonella effectors contributing to cytoskeletal remodeling. SopE/E2: (→Cdc42 and Rac GEF) Induces membrane ruffling of host cells to promote entry. SopB: (→Inositol phosphatase) Generates PtdIns(3)P and Ins(1,4,5,6)P4 upon invasion. Promotes indirect Rho GTPase activation and macropinocytosis. SipA: →Induces actin bundling. Inhibits ADF-mediated and gelsolinmediated actin depolymerization. Potentiates the activity of SipC. SipC: Translocon component. Inserts into host cell membrane and promotes actin nucleation and bundling. Pathogenicity determinants Pathogenicity determinants Endotoxin/ LPS Invasome/Fimbriae (Adhesion) TTSS Multitude of specific virulence factors SipA, SipC…. Pathogenicity Islands Salmonella: Salmonella Pathogenicity Island (SPI); five identified (1040kbp size); SPI1 important for invasion of enterocytes encodes TTSS+ proteins isolation of Salmonella from stool or blood cultures is positive diagnosis of infection Use of Hektoen enteric (HE) and (XLD) media to enrich Salmonella and Shigella spp. (most other enterics do not grow Serotyping performed to trace origin of outbreak (O, H, Vi antigens) PulseField Gel Electrophoresis (PFGE) Diagnosis Diagnosis TSI TSI Comparison of human & feline isolates Comparison of human & feline isolates of S. typhimurium via PFGE
Restriction Enzyme1 Restriction Enzyme2 Conclusion: isolates are identical!! Patient got infected by cat. Reducing the risk of Salmonella Reducing the risk of enteritidis infection Keep eggs refrigerated. Discard cracked or dirty eggs. Wash hands and cooking utensils with soap and water after contact with raw eggs. Eat eggs promptly after cooking. Do not keep eggs warm for more than 2hours. Refrigerate unused or leftover egg containing foods. Avoid eating raw eggs (as in homemade ice cream or eggnog). Commercially manufactured ice cream and eggnog are made with pasteurized eggs and have not been linked with Salmonella enteritidis infections. Avoid restaurant dishes made with raw or undercooked, unpasteurized eggs. Restaurants should use pasteurized eggs in any recipe (such as Hollandaise sauce or caesar salad dressing) that calls for pooling of raw eggs. Treatment/Prevention Typhoid Fever Vaccination live attenuated vaccine polysaccharide subunit vaccine 75% of cases reported in US where acquired while traveling!! Treatment/Prevention Treatment/Prevention Typhoid Fever True for protection from all foodborn pathogens! Get vaccinated before traveling in high risk countries Treatment and control Gastroenteritis: Supportive therapy dehydration prevention balancing electrolytes Avoid antibiotics in gastroenteritis to prevent prolonged carrier state Enteric fever or septicemia ampicillin or trimethoprim/sulfamethoxazole or ciprofloxacin (antibiotic resistance; in vitro susceptibility testing!!)
S. typhi carried in gall bladder (gall stones); carrier state administer antibiotics remove gall stones (biofilm!) 85% cure of carrier state. ...
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- Fall '08