Preston Broth and Bolton Broth plus clavulanic acid suppress ESBLs sufficiently in Campylobacter enrichment procedures

Hazeleger, W.C.; Zhang, J.; Jacobs-Reitsma, W.F.; Besten, H.M.W. den


The presence and increase of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae in food have become important factors that interfere with the isolation of Campylobacter, resulting in false-negative detection results. The ISO-protocol for detection of thermotolerant Campylobacter spp. in food and animal
feeding stuff s (ISO 10272-1, 2006) describes the use of Bolton broth (BB) which is mixed 10:1 with the food sample including a pre-enrichment step at 37°C to resuscitate sublethally damaged cells. Currently, the ISOprotocol is revised and a distinction is made between diff erent food samples, where the more selective Preston Broth (PB) is advised for samples in which high background fl ora such as ESBLs is suspected. However, detailed growth dynamics of Campylobacter and its competitors during enrichment remain unclear, while these would provide a solid base for further improvement of the enrichment procedure of ampylobacter. Therefore, growth kinetics were studied in detail using several strains of C. jejuni and ESBLs combined and separately in BB, PB and BB supplemented with clavulanic acid (BBc). Also, growth dynamics of ampylobacter and ESBLs in naturally contaminated chicken samples were evaluated. No signifi cant diff erences in growth kinetics were found using a pre-enrichment step of 4 h at 37°C compared to immediate enrichment at 41.5°C. Furthermore, the yields and often the growth rates of Campylobacter in co-culture with ESBLs were lower than in pure cultures, indicating severe suppression of Campylobacter by ESBLs. PB and BBc, however, successfully inhibited growth of ESBLs and are therefore a better choice as enrichment media for potentially ESBL-contaminated samples.