Sakazakii DHL Agar, Granulated

Principle And Interpretation

Enterobacteriaceae have wide distribution. Many members form the normal gut and intestinal microflora in humans and animals. They are also found on plants and in soils and water (1). Some species occupy very limited ecological niches. They are a major component of the normal intestinal flora of humans but are relatively uncommon at other body sites. They account for nearly 50% of septicemia cases, more than 70% of urinary tract infections and a significant percentage of intestinal infections (2).

Sakazakii DHL Agar is modified Deoxycholate Agar (GM065/M065) as described by Sakazakii et al (3, 4). Sakazakii DHL Agar stands for Sakazakii Deoxycholate-Hydrogen sulphide-Lactose Agar. The medium is selective for the identification and isolation of Enterobacteriaceae due to inclusions of sodium deoxycholate. Sodium deoxycholate inhibits gram-positive bacteria and also prevents swarming growth of Proteus species. However due to the low concentration of sodium deoxycholate coupled with the nutritionally rich media, fastidious strains of Salmonella and Shigella are able to grow on this medium. Sulphur is released from thiosulphate or other sulphur-containing compounds in the form of sulphide. The H2S thus produced is detected by ferric ammonium citrate to form insoluble heavy metal sulphides that appear as a black precipitate (5). Proteus, Morganella, Rettgerella and Providencia colonies are surrounded by dark brown zones due to phenylalanine deamination. Phenylalanine is sourced from peptone that forms an iron complex with the ferric ions. The high concentration of sucrose in the medium permits the recovery of sucrose positive and lactose negative members of Enterobacteriaceae.