PRESTON AGAR BASE

Description

Preston Agar Base was described by Bolton and Robertson for isolation of Campylobacter species and is recommended by APHA. Isolation of Campylobacter species on selective agar medium is made both with or without selective broth enrichment. Direct plating without enrichment is adequate for fresh faecal samples, faecal contents or intestinal specimens as high numbers of the organisms may be anticipated. For the food samples enrichment is required. Preston Selective Supplement IV contains antibacterial and antifungal agents. Polymyxin B is active only against gram-negative bacteria and Proteus species are sometimes resistant. Trimethoprim usually inhibits Proteus species as well as other gram-negative bacteria. Rifampicin is also active against gram-negative organisms. Cycloheximide acts as antifungal agent. On Preston Agar Base thermotolerant Campylobacter species tend to produce moist, grey, flat spreading growth, which tends to coalesce. Occasionally some contaminating organisms may grow on this medium but they are usually restricted to the area of primary inoculum. These include Pseudomonas species, more resistant coliforms, Streptococcus species and yeasts.