Salmonella Pathogenesis

Salmonella Salmonella One infect all types of domestic animals of the most prevalent agents causing foodborne disease-salmonellosis Classification is based on serology and phage susceptibility assays More than 2600 serovars S. enterica is divided into seven subspecies with group I causing disease in humans and other warmblooded animals :Typhimurium, Enteritidis, Choleraesuis, Dublin, Gallinarum, and Pullorum Examples Salmonella Salmonella Facultative are gram (-) motile rods aerobes Salmonella Resistant grow at an optimum of 37oC to heat if in foods with lower pH, or low water activity or in food with a high fat content Viability declines during frozen storage, especially if near the freezing point Optimum pH for growth of Salmonella is 6.5-7.5; may grow at a pH range of 4.5-9.0 and formic acid reduce the persistence of Salmonella in foods Succinic Salmonella Prevalence  Factors which favor the continued presence in the food chain   Ubiquity of salmonella in the environment Intensive husbandry practices in the meat, fish, and shellfish industries  Lack of microbiological control on animal feeds favors the continued prevalence of this pathogen in the food chain  Poultry products remain the main reservoir of salmonella  Eggs and egg products are also a concern since there is Transovarian transmission of the pathogen into the interior of the egg Salmonella Prevalence  Developed countries= more than 80% of the Salmonella cases occur individually rather than in outbreaks Large Salmonella Outbreaks   Foods linked to transmission include milk powder, raw milk, cheddar cheese, egg products, and liver pate Some fruits and vegetables have also been linked to outbreakscantaloupes, chocolate, mustard dressing    Infectious dose will vary, as few as 1 to 10 cells Foods with a high fat content may have a low infectious dose due to the organism being trapped in micelles which protect it against acidic ph Salmonella Prevalence    Food-borne infections account for 1.3 billion cases of acute diarrhea with 3 million deaths world-wide Salmonellosis in the U.S. is 40,000 cases annually Recent years a notable increase in cases related to a multi-drug resistant S. typhimurium DT104  Case-fatality and hospitalization rates due to this strain are twice that of other Salmonella infections Salmonella Pathogenesis Disease Disease depends on age of the host-more severe in newborns, infants, the elderly Disease oHost also depends on the serovar and type of host specific serovars: typhi, paratyphi, sendai cause disease only in humans oPullorum/gallinarum in poultry, dublin in cattle; choleraesuis serovars in pigs can also infect humans; typhimurium and enteritidis are the major serovars that cause disease in humans, cattle, poultry, sheep, pigs, horses, and wild rodents. Salmonellosis Salmonellosis Diarrhea, abdominal pain, vomiting and fever Bacteremia has been associated with highly invasive serovars such as choleraesuis or dublin clinical sequels include erythrema nodosum, meningitis, osteomielitis, septic arthritis, pnuemonia, choleocydtitis, endocarditis, pericarditis, and cystitis Other of infection is the establishment of a carrier state which lasts for 5-6 months. state is responsible for the spread of the bacterium to others, farms, food-handlers, and consumers. Carrier A complication Salmonella Invasion passes through the stomach and survives the acid pH by eliciting an acid tolerance response the distal ileum; portal of entry is the M-cell and it binds by means of fimbriae from the lpf operon or from the pcf operon Heritable Salmonella Colonizes phase variation mechanism Triggered by intestinal-derived signal Salmonella Invasion  Penetration and destruction of M-cell  Localized accumulation of cytoskeletal proteins such as actin, vinculin, vimentin, and ezrin at site of entry Formation of membrane ruffles occurs with every cell type examined   Recruitment of lymphoid cells and PMN   Secretion of large amount of fluid Leads to inflammation of the area Salmonella Invasion   Colonizes intestinal epithelial cells In vivo       Microvilli denuded transiently, membrane ruffling Bacterial penetration 1-2 h Cytosketetal rearrangements, 30-60 min Actin filament rearrangement No microtubule involvement Ca++ flux Distruption of tight junctions Causes depolarization of epithelial cells  In vitro   Salmonella Invasion island of 40kb has been identified which also contains a type III secretion system SPI Pathogenecity operon encoded type III secretion system operon InvA-C filamentous appendages appear upon cell contact and require a function type III secretion system by a shift from acidic to alkaline pH in the absence of eukaryotic cells; also activated by environmental conditions such as high osmolarity, low oxygen tension, DNA supercoiling, and alkaline pH oMore oActivated oFunctional than 15 proteins are inserted into the inner and outer membrane. Classes: inner and outer membrane proteins InvA, SpaP, SpaQ, SpaR, SpaS, InvG, InvH, PrgH, PrgK; an energizer of the system, the inner membrane ATPase InvC; secreted proteins with putative targets in the host cell known as effector proteins SipB, SipC, SptP, AvrA; other secreted proteins SipA; cytosolic chaperons which prevent premature degradation of secreted proteins SicA, SicP; transcriptional regulatory proteins InvF, HilA, and InvE Salmonella Invasion Other Invasion Factors is needed LPS is also required for invasion are also needed Motility Intact Fimbriae Host Factors for Invasions of host cell essential functions ruffling oActin Subversion cytoskeleton reorganization oMembrane oSignal oSopE transduciton pathways (substances of the SpI-1 encoded system) stimultes actin reorganization by increasing GDP/GTP nucleotide exchange in several GTPases oStimulates production of proinflammatory cytokines as IL-8, and activates transcriptional factors Proliferation within Nonprofessional Phagocytes Salmonella Salmonella proliferates in membrane-bound vacuoles containing vacuole fuses with host compartments containing lysosomal-membrane glycoproteins and bypasses compartments of the endocytic route SPI-2 is required for intracellular proliferation within epithelial cells findings suggests that macrophages and specialized epithelial cells allow Salmonella to proliferate intracellularly Recent Proliferation within Nonprofessional Phagocytes  Although non-growing, remain viable for periods of 1014 days Salmonella have been shown to reduce their metabolic rate to perpetuate with the host cell The PhoPQ system is involved in preventing growth of intracellualr Salmonella; phoP mutants grow actively in non-permissive cells First example of a bacterial-mediated mechanism that prevents its own proliferation in a specific host cell     Long persistance of Salmonella within non-phagocytic cells could be linked to Salmonella derived reactive arthirits, chronic infections, or carrier asymptomatic Proliferation within Professional Phagocytes Active membrane ruffling and macropinocytosis occurs upon ingestion of Salmonella by phagocytic ells Trafficking route used by Salmonella within a cultured macrophage is different than within epithelial cells Fusion of the endosome with mature lysosomes seems to occur Nevertheless that compartment does not behave as a conventional mature lysosomal since there is no processing of lysosomal enzymes contained within triggers bacterial response for survival and replication within these cells Salmonella Acidification may exist within two populations; one activity growing and the other static but not viable Proliferation within Professional Phagocytes Salmonella is also able to trigger apoptosis of the infected macrophage Products involved in triggering apoptosis are: SPI-1 oxygen regulated protein (OrgA), OmpR/EnvZ, SPI-1 secreted proteins such as InvJ, SpaO SipB, SipC, and SipD Induced apoptosis may destroy phagocytic cells before they process antigen and activate T-cells may react to infection with Salmonella and program it’s own death to avoid excessive release of immune mediators Macrophage Survival within Phagocytic cells  Proteins involved in DNA repair are needed such as RecA and RecBC for survival Increased levels of SodA (Mn dependent) results in increase survival within macrophages in vitro but not for survival in the mouse model Increased levels ot SodC (Zn2+-Cu2+) results in increased survival in the mouse model but not in macrophages in vitro SlyA is a transcriptional regulator involved in Salmonella survival by giving it resistance to toxic oxidative products     Sap proteins are required for antimicrobial peptide resistance Salmonellosis PhoP-PhoQ Two regulatory System component system=pair of proteins, one of which, the sensor, underoges a change in response to a change in the environment and communicates this change, usually in the form of a phosphate to another protien, response regulator, which then causes the appropriate cellular response Sensing extracellular signals such as limiting amounts of Mg2+ and mild acidic pH Salmonellosis  PhoQ is a inner membrane integral protein capable of binding Mg2+ and Ca2+ Upon binding PhoQ auto-phosphorylates and transfers the phosphate to PhoP, a cytosolic protein Phosphorylated PhoP acts then as a transcriptional regulator or at least 40 genes o   Some virulence genes are activated as pag and others repressed such as prg Virulence traits linked to this regulatory system include:(1) bacterial survival within macrophages, epithelial cell (2) resistance to cationic antimicrobial peptides, (3) invasion of epithelial cells, (4) control of Ag presentation by bacteriainfected macrophage, (5) resistance to bile acids o Salmonellosis PmrAB Two regulatory system component system bacterial resistance to polymixin and other LPS-binding antimicrobial peptides Auto-regulated Controls of these genes is dependent on low pH or Mg2+ limitation Expression Salmonellosis  OmpR/EnvZ regulatory system   Two component system Senses changes in external medium osmolarity OmpR is the transcriptional regulator EnvZ is its cognate membrane sensor o   Controls expression of major outer membrane proteins:OmpC and OmpF Salmonellosis o High osmolarity favors expression of OmpC while low osmolarity shifts the expression to PmpF OmpF mutants are avirulent in the mouse typhoid model OmpCF mutants are attenuated in the in vivo model when administered orally but not interperiotoneally o o Salmonellosis RpoS (katF) Sigma factor regulatory factor in starved bacteria Important High levels of this protein in cells that are reaching stationary phase Needed Needed for survival in stationary phase also for nutrient stresses in Salmonella such as carbon, nitrogen, or phosphate starvations Increased Required in intracellular bacteria for virulence Salmonellosis Roles of a Salmonella virulence plasmid (60-80 kb) Needed for the production of systemic disease; cured strains are unable to produce systemic disease in the mouse typhoid system retain capacity for colonization the intestinal tract and spreading to target tissues and organs Spv Mutants operon control of the RpoS sigma factor Under play a role in signaling between intracellular Salmonella and the host cell Only Protein synthesized in intracellular bacteria