New Campylobacter screening method improve outbreak detection

porA gene seems to be a good indicator of the uniqueness of a specific strain.

In a new study, a team of California-based scientists shows that by targeting and analyzing a specific gene in Campylobacter jejuni, labs can screen dozens of isolates of the bacteria to find the handful most likely to be the source of an outbreak.

Unlike other enteric bacteria, such as E. coli O157:H7, Campylobacter is so diverse in a farm environment that many different strains can be present in just a few samples.

This genetic diversity makes it hard for scientists to link a human Campylobacter infection to its source, since the leading method of bacterial analysis — pulsed-field gel electrophoresis (PFGE) — is time-consuming and labor intensive, and therefore difficult to perform on more than a few isolates at a time.

For this study, researchers zeroed in on one gene in Campylobacter, called porA, which has been suggested to be a good indicator of the uniqueness of a specific strain.

The team collected samples from two different California dairies that were the sources of Campylobacter jejuni outbreaks linked to milk, and conducted porA sequencing on over 100 isolates found in cow feces and water runoff at these locations.

Campylobacter outbreaks are rare. The majority of Campylobacter infections occur as sporadic cases not linked to other illnesses; thus opportunities to study a Campylobacter outbreak are none too common.

Through porA analysis, the researchers narrowed this set down to a group of 8 most likely to match the outbreak strain.

At the second farm, which was ground zero for a 2007 Campylobacter outbreak raw milk that sickened 11 people, a total of 34 C. jejuni isolates were collected. These were narrowed down to a set of 17 likely candidates by porA sequencing. Using this screening method to prioritize isolates, knowing that it was going to be too expensive for the state to test many Campylobacter isolates using PFGE,” explained Jay-Russell.

The study was conducted by researchers at the University of California, Davis; the California Department of Public Health; USDA’s Agricultural Research Service and CDC’s Epidemic Intelligence Service. It appears in this month’s issue of the Journal of Clinical Microbiology.

Source:  Food Safety News