Abstract
Campylobacter is well recognized as the leading cause of bacterial foodborne diarrheal disease worldwide, and is routinely found in meat originating from poultry, sheep, pigs, and cattle. Effective monitoring of Campylobacter contamination is dependent on the availability of reliable detection methods. The method of the International Organization for Standardization for the detection of Campylobacter spp. in food (ISO 10272-1:2006) recommends the use of Bolton broth (BB) as selective enrichment medium, including a pre-enrichment step of 4–6 h at 37°C to revive sublethally damaged cells prior to incubation for 2 days at 41.5°C. Recently the presence of abundantly growing extended spectrum β-lactamase producing Enterobacteriaceae (ESBL bacteria) has become one of the most important factors that interfere with the isolation of Campylobacter, resulting in false-negative detection. However, detailed growth dynamics of Campylobacter and its competitors remain unclear, where these would provide a solid base for further improvement of the enrichment procedure for Campylobacter. Other enrichment broths, such as Preston broth (PB) and BB plus clavulanic acid (BBc) have been suggested to inhibit competitive flora. Therefore, these different broths were used as enrichments to measure the growth kinetics of several strains of Campylobacter jejuni and ESBL bacteria separately, in co-culture and of strains in chicken samples. The maximum cell numbers and often the growth rates of Campylobacter in mixed culture with ESBL bacteria were significantly lower than in single cultures, indicating severe suppression of Campylobacter by ESBL bacteria, also in naturally contaminated samples. PB and BBc successfully diminished ESBL bacteria and might therefore be a better choice as enrichment medium in possibly ESBL-bacteria contaminated samples. The efficacy of a pre-enrichment step in the BB ISO-procedure was not supported for cold-stressed and non-stressed cells. Therefore, omission of this step (4–6 h at 37°C) might be advised to obtain a less troublesome protocol.
Highlights
Campylobacteriosis is the most commonly reported zoonosis in the European Union showing an increasing trend over the period of 2008–2014, and the occurrence of thermotolerant Campylobacter in broiler meat remains high at 38.4% in 2014 (European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2015)
Growth rates of C. jejuni in BB plus clavulanic acid (BBc) (Figures 2A,B) and Preston broth (PB) (Figures 2C,D) were similar to growth in Bolton broth (BB) (P > 0.05), some lag time was observed in BBc
Selectivity of BB is based on the addition of four antibiotics; vancomycin, trimethoprim, amphotericin B, and cefoperazone, where the latter two are used in the isolation plate in the International Organization for Standardization (ISO)-protocol for detection of Campylobacter (ISO, 2006)
Summary
Campylobacteriosis is the most commonly reported zoonosis in the European Union showing an increasing trend over the period of 2008–2014, and the occurrence of thermotolerant Campylobacter in broiler meat remains high at 38.4% in 2014 (European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2015). Broilers are often contaminated with extended spectrum β-lactamase producing Enterobacteriaceae (ESBL bacteria; Bortolaia et al, 2010; Depoorter et al, 2012; Dierikx et al, 2013; Kawamura et al, 2014; Olsen et al, 2014). The presence of these ESBL bacteria in food has become an important factor interfering with the isolation of Campylobacter, resulting in false-negative detection, since abundantly growing ESBL bacteria hamper the isolation of Campylobacter colonies (Jasson et al, 2009). Strong scientific evidence for better isolation of the pathogen using a pre-enrichment step at 37◦C is scarce (Humphrey, 1986, 1989)
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