Salmonella Shigella (SS) agar is not autoclaved because it is a selective culture medium designed to isolate and differentiate Salmonella and Shigella species from other bacteria in clinical and environmental samples. Autoclaving could degrade key components of the medium, such as bile salts and certain nutrients, which are crucial for the selective growth of the target organisms. Instead, SS agar is typically sterilized using filter sterilization to maintain its effectiveness while preventing contamination.
Its color is red.
Salmonella and Shigella agar (SS agar) is both selective and differential. It is selective because it inhibits the growth of most gram-positive bacteria and non-enteric gram-negative bacteria, allowing for the isolation of Salmonella and Shigella species. Additionally, it is differential as it contains indicators that differentiate between lactose fermenters and non-fermenters, with lactose fermenters producing pink colonies and Salmonella and Shigella typically forming colorless colonies.
To differentiate between Salmonella enteritidis and Shigella sonnei, the triple sugar iron (TSI) agar test can be used. Salmonella enteritidis typically produces hydrogen sulfide (H2S), resulting in black colonies on TSI agar, while Shigella sonnei does not produce H2S and will not change the color of the agar. Additionally, biochemical tests such as urease and indole tests can further help distinguish between the two, as Shigella sonnei is urease negative and indole positive, while Salmonella enteritidis is urease negative and indole negative.
Shigella and the majority of salmonellae Clear, colorless, transparent Salmonella enteriditis ATCC 13076 Colorless with black center Salmonella typhi ATCC 6539 Colorless with black center Salmonella typhimurium ATCC 14028 Colorless with black center
MacConkey agar: Selective for Gram-negative bacteria, inhibits the growth of Gram-positive bacteria. Hektoen enteric agar: Selective for Gram-negative enteric pathogens, such as Salmonella and Shigella species. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar: Selective for Vibrio species, especially Vibrio cholerae. Cefsulodin-irgasan-novobiocin (CIN) agar: Selective for Yersinia species.
To differentiate a colorless colony on MacConkey agar, which indicates non-lactose fermenting bacteria, you would perform a series of biochemical tests. First, conduct a hydrogen sulfide (H2S) test; Salmonella typically produces H2S, resulting in black precipitate on triple sugar iron (TSI) agar, while Shigella does not. Additionally, you can perform an indole test; Shigella flexneri is indole positive, while Salmonella is usually negative. Confirmatory tests, such as serotyping or specific PCR assays, can further identify the organism.
Salmonella, Shigella, Yersinia, and Serratia are all gram-negative facultatively anaerobic rods.
salmonella
Salmonella, Shigella Organisms that ferment lactose display "nucleated colonies" - colonies with dark centers.
Mnemonic: KEE Klebsiella pneumoniae Enterobacter cloacae E. coli Shigella sonnei can ferment lactose, but only after prolonged incubation and so it is referred to as a '''''late-lactose fermenter'''''. Vibrio cholerae is also a late lactose fermenter.
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The biochemical test commonly used to identify Salmonella typhi is the Widal test. This test detects antibodies produced in response to a Salmonella typhi infection by measuring agglutination (clumping) reactions between the bacteria and specific antibodies in the patient's serum. Other tests like blood culture and polymerase chain reaction (PCR) can also be used for confirmation.