This is the first video on salmonella typhi and is focusing on an Introduction, classification, biochemical tests, route of transmission, and pathophysiology.
Salmonella is a genus of rod-shaped (bacillus), Gram-negative bacteria of family Enterobacteriaceae. Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon. Salmonellae are a medically important pathogen for both humans and animals. Salmonella species are non-spore-forming, facultative anaerobes [capable of generating ATP with oxygen ("aerobically") when it is available, or when oxygen is not available, using other electron acceptors or fermentation (anaerobically), predominantly motile with cell diameters between about 0.7- 1.5μm, lengths from 2-5μm, and peritrichous flagella (all around the cell body).
Genome sizes of Salmonella vary among serovars with ranges from 4460 to 4857 kb. Salmonellae form a complex group of bacteria consisting of two species; S. enterica and S. bongori, six subspecies; enterica, salamae, arizonae, diarizonae, houtenae, and indica and include more than 2,579 serovars, based on biochemical and genomic modifications.
The Cycle of Contamination
The main niche of Salmonella serovars is the intestinal tract of humans and farm animals. It can also be present in the intestinal tract of wild birds, reptiles, and occasionally insects. Feedstuff, soil, bedding, litter, and fecal matter are commonly identified as sources of Salmonella contamination in farms. As Salmonella colonizes the gastrointestinal tract, the organisms are excreted in feces from which they may be transmitted by insects and other animals to a large number of places and are generally found in polluted water. Salmonellae do not originate in water; therefore their presence denotes fecal contamination. Humans and animals that consume polluted water may shed the bacteria through fecal matter continuing the cycle of contamination.
Typhoidal Salmonella: S. typhi and S. paratyphi
Non-Typhoidal Salmonella (NTS): S. typhimurium and S. enteritidis
Typhoid or Enteric fever
Caused by: a. Salmonella typhi b. Salmonella paratyphi (A, B, C)
Lives only in humans
The transmission is Fecal-oral route. Most people in developed countries pick up typhoid bacteria while they're traveling and they can spread it to others through the fecal-oral route. If you eat food that has been handled by someone who has typhoid fever and who hasn't washed carefully after using the toilet, you can become infected.
In developing countries, where typhoid fever is established, most people become infected by drinking contaminated water. The bacteria may also spread through contaminated food and through direct contact with someone who is infected. Sometimes people can be chronic carriers (asymptomatic). Recent studies estimate that there are approximately 10–20 million cases of typhoid per year, resulting in 100,000–200,000 deaths.
Biochemical Identification of Salmonella typhi
Gram-Negative rods
Catalase negative: Do not produce catalase enzyme
Capsule, spores, and Gas negative
Motile
Oxidase negative [Do not produce cytochrome c oxidase]
Produces H₂S gas; has cysteine desulfhydrase and are able to remove the sulfhydryl and amino groups from cysteine, yielding hydrogen sulfide, ammonia, and pyruvic acid. Thus formed H₂S gas, which is colorless, combines with H₂S indicators (iron, bismuth or lead) present in the medium producing insoluble, heavy metal sulfides that appear as a black precipitate.
facultative anaerobes
Pathophysiology
One of the main characteristics that distinguish S. typhi from NTS is the production of a polysaccharide capsule named the Vi antigen. The Vi capsule inhibits phagocytosis and confers serum resistance likely by shielding the O‐antigen from antibodies. The genes encoding the Vi capsule are present within Salmonella Pathogenicity Island (SPI)‐7.
The atp and fur genes are involved in the acid tolerance response of Salmonella
