Efficient isolation of campylobacters from stools: what are we missing?

The past three decades have witnessed the rise of campylobacter enteritis in humans from virtual obscurity to notoriety, with present isolation rates superseding those of other enteric pathogens such as Salmonella spp. and Shigella spp. in most developed countries. Unlike the salmonellae and other enteric pathogens, most (∼ 99%) clinical reports concerning campylobacter are sporadic, and campylobacter enteritis outbreaks are rare. Although campylobacters are not completely new to applied bacteriology, they have largely evaded traditional techniques used for the isolation of pure cultures, apart from single isolations that were free from competing organisms. Until the development of a selective medium by Skirrow, 1 2 these organisms were known mainly by veterinarians as animal pathogens, which were responsible for a wide variety of disorders in cattle, sheep, and pigs. 3 Since the development of more sophisticated isolation techniques, the true disease potential of these organisms has become apparent and today campylobacteriosis is regarded as a zoonosis, which is capable of being transmitted to humans by a wide range of domestic animals. 3 There have been several reports describing the inability of selective media to recover certain species of campylobacter, especially the catalase weak or negative organisms, from faecal specimens. 4 5 In addition, there are large epidemiological differences between rates of infection with campylobacters between Northern Ireland and the rest of the UK; however, no data exist with regard to the rates of isolation of the atypical campylo-bacters from stool specimens locally. Therefore , it was the aim of our study to evaluate the efficacy of recovery of clinically relevant campylobacters from faecal specimens in Northern Ireland, using direct plating and differential filtration techniques. One hundred and eighty six faecal specimens from an equal number of patients with acute gastroenteritis were examined for the presence of Campylobacter spp. over the peak seasonal period, May to June. Faecal specimens were obtained from family practitioners in the community and were examined within 24 hours of receipt. Two isolation methods were compared for their efficacy in recovering viable organisms, namely: (1) direct plating of faeces on to two selective media at two different incubation temperatures (37°C and 42°C); and (2) differential filtration on non-selective medium incubated at 37°C. For both treatments , 0.5 g faeces was emulsified in 0.1% (wt/vol) peptone water. For direct plating, 10 µl of faecal suspension was inoculated on to both modified CCDA agar (Oxoid Ltd, Poole, Dorset, UK), containing …