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The genome of Pseudomonas aeruginosa consists of a relatively large circular chromosome (5.5–6.8 Mb) that carries between 5,500 and 6,000 open reading frames, and sometimes plasmids of various sizes depending on the strain. [11] Comparison of 389 genomes from different P. aeruginosa strains showed that just 17.5% is shared.
It is designed to selectively isolate gram-negative and enteric (normally found in the intestinal tract) bacteria and differentiate them based on lactose fermentation. [1] Lactose fermenters turn red or pink on MacConkey agar, and nonfermenters do not change color. The media inhibits growth of gram-positive organisms with crystal violet and ...
TSI agar slant results: (from left) preinoculated (as control), P. aeruginosa, E. coli, Salmonella Typhimurium, Shigella flexneri The Triple Sugar Iron (TSI) test is a microbiological test roughly named for its ability to test a microorganism's ability to ferment sugars and to produce hydrogen sulfide. [1]
The colonies of lactose fermenters appear yellow. It is also used to culture possible Salmonella that may be present in a food sample. Most Salmonella colonies produce a black centre on it. Cetrimide agar is used for the selective isolation of the Gram-negative bacterium Pseudomonas aeruginosa.
Hektoen enteric agar (HEK, HE or HEA) is a selective and differential agar [1] primarily used to recover Salmonella and Shigella from patient specimens. HEA contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria.
Alternatively, oxidation-fermentation polymyxin-bacitracin-lactose (OFPBL) agar can be used. OFPBL contains polymyxin (which kills most Gram-negative bacteria, including Pseudomonas aeruginosa ) and bacitracin (which kills most Gram-positive bacteria and Neisseria species).
Microscopic image of gram-negative Pseudomonas aeruginosa bacteria (pink-red rods). Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. [1]
Shigella sonnei can ferment lactose, but only after prolonged incubation, so it is referred to as a late-lactose fermenter. During fermentation of the sugar, acid is formed and the pH of the medium drops, changing the color of the pH indicator. Different formulations use different indicators; neutral red is often used. For example, lactose ...