Development of a Selective Differential Agar for Isolation and Enumeration of Campylobacter spp.

Abstract

Direct plating is an effective technique for isolation and enumeration of Campylobacters from a variety of sample types; however, distinguishing Campylobacters from non-Campylobacter contaminants that frequently grow on many existing agars is difficult. In this study, it was determined that exposing Campylobacters to low levels (200 mg/liter) of triphenyltetrazolium chloride (TTC) was not inhibitory to growth yet was sufficient to give a deep-red to magenta color to the colonies. The new agars (Campy-Line agar [CLA] and Campy-Line blood agar [CLBA]) are translucent. The contrast of deep-red colonies on a translucent background greatly facilitates Campylobacter isolation and makes enumeration on light boxes or by electronic means possible. Direct plating of broiler carcass rinse samples (n = 20) was compared on Campy-Cefex agar and CLA. Recovery of Campylobacter populations was not significantly different between the agars (P < 0.05); however, enumeration was much less labor intensive with the CLA. No contaminants were observed on the CLA, whereas the Cefex agar supported the growth of approximately 14 contaminating (non-Campylobacter) CFU/ml. In a separate trial, recovery of Campylobacters from carcass rinses (n = 25) was similarly compared on Cefex, CLA, and CLBA. Again, recovery of Campylobacters was not significantly different between the agars (Pearson correlation coefficient = 0.988), whereas about nine contaminating (non-Campylobacter) CFU/ml were observed on Cefex agar and none on CLA or CLBA. Although some contaminants can still grow on CLA and CLBA and can present red colonies, most of these contaminants are easily distinguished from Campylobacter by differences in colony morphology.