Researchers have suggested ways to improve the analysis to aid in source attribution and Campylobacter outbreak investigations.
The standard method for Campylobacter detection is via culture, although feasibility limitations usually result in selecting or characterizing only one isolate per sample.
Taking only a few isolates may lead to an underestimate of Campylobacter diversity on epidemiologically relevant sources such as chicken meat, and infection-associated populations may be overlooked.
Multiple combinations of culture methods were used to recover and sequence Campylobacter from 45 fresh retail chicken samples purchased in Norwich in 2021, selecting up to 48 isolates per sample.
Scientists said the choice of isolation method could affect the recovery of Campylobacter from chicken samples, potentially hampering source attribution and outbreak investigation. They added that an optimized culture approach and selecting multiple isolates per sample were essential for full recovery.
Most samples are positive
The study, published in the journal Epidemiology and infectionassessed the diversity of isolates recovered and determined the potential impact on source attribution and outbreak investigation.
Campylobacter is the most common cause of bacterial food poisoning, with an estimated 500,000+ cases each year in the UK. However, reported outbreaks are rare and most cases are thought to be sporadic.
Resampling-based simulations were used to assess the impact of Campylobacter sequence type (ST) diversity on outbreak detection.
Scientists used three enrichment broth conditions, two types of agar plates and two temperatures, resulting in twelve different combinations of culture methods.
Campylobacter was recovered from 39 of 45 samples, although only one was positive across all broth, temperature, and plate combinations. Only two samples were culture positive in all combinations of broth and temperature.
Fifteen samples were positive for more than one Campylobacter species. Campylobacter jejuni was identified in 36 samples, Campylobacter coli in 17 samples and 14 samples contained both species. One sample contaminated with Campylobacter jejuni was also positive for Campylobacter lari.
A lack of outbreaks
The presence of multiple Campylobacter reports may indicate numerous contamination events throughout the meat processing chain.
Sixty-two different STs were identified among the three Campylobacter species, of which 14 were novel. Positive samples contain 1 to 8 sequence types.
The simulation showed that up to 87 isolates per sample would be needed to detect 95 percent of the observed ST diversity, and that 26 isolates would be needed to reach the average probability of detecting a random ST outbreak of 95 percent. reaches.
Extensive sampling of isolates from food samples involved in outbreaks is not commonly done.
“This could be a possible reason why the majority of Campylobacter cases are considered sporadic; if the source contains multiple strains, cases exposed to the source may be infected with different strains that appear epidemiologically unrelated,” researchers said.
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