Enterobacteriaceae: Salmonella PDF

Enterobacteriaceae: Salmonella Dr Lone, DVM, PhD, DACVM  Salmonella spp. Genus: Salmonella, gram negative rod of family Enterobacteriaceae Three species: S. enterica, S. bongori, S. subterranea Subspecies of S. enterica (based on biochemical tests) - enterica (subspecies...

Enterobacteriaceae: Salmonella Dr Lone, DVM, PhD, DACVM  Salmonella spp. Genus: Salmonella, gram negative rod of family Enterobacteriaceae Three species: S. enterica, S. bongori, S. subterranea Subspecies of S. enterica (based on biochemical tests) - enterica (subspecies I) warm-blooded animals - salamae (subspecies II) cold-blooded animals - arizonae (subspecies IIIa) cold-blooded animals - diarizonae (subspecies IIIb) cold-blooded animals - houtenae (subspecies IV) cold-blooded animals - indica (subspecies VI) cold-blooded animals  Salmonella nomenclature LPS O-antigen, flagella vary considerably within a subspecies – more than 2600 serotypes in S. enterica ssp. enterica alone Salmonella enterica subsp. diarizonae S. entericaa subsp. diarizonae serotype 60:k:z will be written S. IIIb 60:k:z for all salmonellae except S. enterica ssp. enterica. S. enterica susb. enterica serotype 6,7:c:1,5 (S. I 6,7:c:1,5) is written as S. enterica ssp. enterica serotype Choleraesuis. How do you write S. enterica ssp. enterica serotypes – First mention: S. enterica ssp.enterica ser. Typhimurium, or S. enterica ser. Typhimurium on second mention you can simply write Salmonella Typhimurium – Paty attention: serotype name always begins with capital letter and is not italicized  Salmonella nomenclature (cont’d) Flagellar phase variation Phase variation: a reversible genetic rearrangement, to switch between expression of fliC (phase 1) and fljB (phase 2), and flpA (phase 3, rare and often plasmid encoded) a mechanism that is utilized by a number of important bacterial pathogens (McQuinston et al., 2004) is inhibitor, not part of flagellum Salmonella nomenclature (cont’d) 1, 2, 12 are individual epitopes on the LPs molecule of this serotype 99% infections in warm- blooded animals  Pathogenesis Pathogenesis depends on host factors, strain, and infectious dose. Key target: M cells in the distal small intestine and upper large bowel. Mechanism: Adhesion, invasion, and intracellular survival.  Pathogenesis (cont’d) 1. Adhesion: - Fimbriae (Pef, Agf, Lpf) bind to M cells. (plasmid-encoded fimbriae (Pef), aggregative fimbriae(Agf), long polar fimbriae (Lpf)) 2. Invasion: - SPI-1 effectors (SipA, SopB, SopE) trigger membrane ruffling. (SPI-1 : Salmonella pathogenicity island -1) - Salmonella enters epithelial cells via actin cytoskeleton rearrangement. 3. Intracellular Survival: - SPI-2 effectors allow survival within macrophages. - Formation of Salmonella-containing vacuole (SCV) enables replication.  Pathogenesis (cont’d) Adhesion and preparing to invade Pathogenesis (cont’d) SIF: Salmonella induced filaments  Pathogenesis (cont’d) The type III secretion system encoded in the Salmonella pathogenicity island- 2 (SPI-2) facilitates intracellular growth of nontyphoidal Salmonella interfering with the maturation of Salmonella-containing vacuoles along the degradative pathway. also protect Salmonella against the antimicrobial activity of reactive oxygen species (ROS) synthesized by the phagocyte NADPH oxidase 2 (NOX2).  Pathogenesis (cont’d) Intracellular survival strategies evade immune system: – PhoP/PhoQ system regulates survival in macrophages. This is TCS Bacteria adapt to changes in their environment using a mechanism known as the two-component regulatory system (TCS) (also called “two- component signal transduction system” or “two-component system”). It comprises a pair of at least two proteins, namely the sensor kinase and the response regulator.  Pathogenesis (cont’d) TCS DNA (chromosome)  Pathogenesis (cont’d) Growth in acid pH Antimicrobial peptide resistance Host Immune Response to Salmonella Inflammatory response mediated by cytokines like IL-8. Neutrophil recruitment and epithelial cell damage. Pathogenesis Pathogenesis (cont’d)  Clinical Manifestations Gastroenteritis: Most common, characterized by diarrhea and abdominal pain. – Non-typhoidal salmonellosis Septicemia: Occurs in severe cases, leading to systemic spread. – Typhoidal salmonellosis Host-specific infections: Salmonella can cause abortions in ruminants and horses Disease caused by some common serotypes Laboratory Diagnosis of Salmonella Samples: Fecal samples for enteric form, blood cultures for systemic disease. Culture Media: - MacConkey agar (lactose non-fermenting colonies). - XLD agar (black-centered colonies due to H2S production). Serotyping: Determination of O and H antigens. Molecular methods: PCR for detection and identification.  Laboratory diagnosis Host-adapted salmonellae from pigs & poultry don’t’ tolerate Selenite, Tetrathionate, Brilliant green agar  Treatment and Control Treatment: - Supportive care for gastroenteritis. - Antibiotics – Antimicrobial susceptibility test – for systemic infections (e.g., ampicillin, enrofloxacin) Control: - Good hygiene and biosecurity measures. - Vaccination with modified live vaccines New topic