Recovery of thermophilic campylobacters from pond water and sediment and the problem of interference by background bacteria in enrichment culture

Abstract

The aim of this study was to address problems in the determination of thermophilic campylobacters in turbid pond water and sediment. Thirty sets of three samples of pond water (volumes 10, 100, 1000 ml) or sediment (0.1, 1.0, 5.0 ml) were examined for the presence of thermophilic campylobacters. The different volumes of pond water were processed by membrane filtration followed by selective enrichment. The samples of sediment were subjected directly to selective enrichment. Presumptive isolates were confirmed by Gram stain, cell morphology, presence of oxidase and catalase, growth under microaerobic but not aerobic conditions, and PCR. Confirmed Campylobacter species were recovered only from 10 and 100 ml samples of water and from 0.1 and 1.0 ml samples of sediments. The 1000 ml samples of water and 5.0 ml samples of sediment never gave positive isolates. PCR indicated that the confirmed isolates were all either Campylobacter jejuni or C. coli. Enrichment cultures from 1000 ml filtrations contained the highest number of background bacteria. It is suggested that the processing of large volumes of turbid environmental water samples or of sediment is counterproductive and may not yield positive Campylobacter cultures. This is probably due to antagonistic effects of large numbers of background bacteria out-competing campylobacters during the enrichment stage. Pilot studies to establish appropriate volumes of pond water or sediment samples should be undertaken before routine determination of campylobacters is begun.