Description
Salmonella and Shigella are gram-negative, facultatively anaerobic, non-sporulating rods in the family Enterobacteriaceae. They are widely distributed in animals affecting mainly the stomach and the intestines. Shigella is the causative agent of bacterial diarrhoea and the faecal-oral route usually transmits the disease. Human Salmonella infections are most commonly caused by ingestion of food, water or milk contaminated by human or animal excreta. Arizona group was originally named Salmonella Arizonae. It has been found mainly in reptiles and birds and occasionally in human patients with diarrhoea or septicemia. These organisms are difficult to differentiate biochemically from Escherichia coli, one of the most commonly recovered bacteria in clinical laboratory. B.C.P-D.C.L.S Agar (Bromo Cresol Purple – Deoxycholate – Citrate – Lactose-Sucrose Agar) is the modification of the original formulation of Leifson, which was later, modified by Hajna and Damon. It allows easy isolation of Salmonella, Shigella and Arizona organisms from a mixed culture by differentiating between lactose-negative, sucrosepositive coliforms. It also inhibits all gram-positive bacteria and most of the Proteus species along with some strains of S. dysentriae. Larger amount of the material can be inoculated into an enrichment medium followed by inoculation onto an agar plate, thereby, facilitating the isolation of Salmonella, when present only in small numbers. On incubation, Salmonella multiply rapidly, while E.coli and most other bacteria are inhibited. After enrichment, the enriched culture is plated onto a differential agar medium. B.C.P.-D.C.L.S. is a useful modification of D.C.A. (Deoxycholate Citrate Agar) that contains both lactose and sucrose. Some coliforms ferment sucrose more readily than lactose. Sucrose fermenting and lactose non-fermenting strains, e.g. some strains of Proteus and E.coli, form colonies distinguishable from the pale colonies of Salmonella and Shigella, which do not ferment sucrose, on this medium. Hence the number of false positive cultures requiring biochemical testing is reduced and the efficiency of isolation of Salmonella and Shigella is increased. B.C.P.-D.C.L.S. Medium is unsuitable for the isolation of Yersinia species, which are sucrose positive. Non-selective media should be inoculated along with this media. The medium can be directly inoculated with the test specimens. Alternatively, the sample can be enriched in GN Broth, Hajna, Tetrathionate Broth, or Selenite Broth, and subsequently isolated on B.C.P.-D.C.L.S. Agar. A less inhibitory medium should be run in parallel to B.C.P.-D.C.L.S.
