Gram ⊝ rod. Non-lactose fermenter, oxidase ⊝. Can invade the GI tract via M cells of Peyer patches. Flagellated. Produce H₂S, motile.

Salmonella typhi:- Human reservoir only- Can disseminate hematogenously- Virulence factor: Endotoxin, Vi capsule → extensive intracellular replication in macrophages → spread through lymphatics and RES.- Monocytic response- Causes typhoid fever (rose spots on abdomen, constipation, abdominal pain, fever)- Treat with ceftriaxone or fluoroquinolone- Oral vaccine contains live attenuated S typhi, IM vaccine contains Vi capsular polysaccharide- Carrier state with gallblader colonization

Salmonella spp:- Human and animals (poultry, eggs, pets, turtles)- Can disseminate hematogenously- Enterocolitis/gastroenteritis. Second most common bacterial cause after Campylobacter. 6-48 hour incubation; nausea and vomiting; only occasionally bloody, loose stools; fever; abdominal pain; myalgia; headache- Septicemia, osteomyelitis (in patients with sickle cell disease)- Inflammatory response marked by neutrophil infiltration (PMN response)- Antibiotics prolong duration, not indicated