Food Microbiology, Wageningen University & Research, Netherlands.
Food Microbiology, Wageningen University & Research, Netherlands.
Int J Food Microbiol. 2022 Feb 16;363:109518. doi: 10.1016/j.ijfoodmicro.2021.109518. Epub 2021 Dec 31.
It is well-established that Extended-spectrum beta-lactamase-producing (ESBL-) Escherichia coli challenge reliable detection of campylobacters during enrichment in Bolton broth (BB) following ISO 10272-1:2017. The overgrowth of Campylobacter by ESBL-E. coli in the enrichment medium BB can lead to false-negative detection outcomes, but the cause for the growth suppression is yet unknown. A plausible reason could be the competition-induced lack of certain growth substrates. Therefore, this study aimed to investigate whether campylobacters and ESBL-E. coli compete for the same medium components and whether this is the cause for the observed growth repression. The availability of possible growth substrates in BB was determined and changes in their extracellular concentration were measured over time during mono-culture enrichment of C. jejuni, C. coli or ESBL-E. coli as well as in co-culture enrichments of campylobacters and ESBL-E. coli. Comparative analysis showed lactate and fumarate utilization by C. jejuni and C. coli exclusively, whereas ESBL-E. coli rapidly consumed asparagine, glutamine/arginine, lysine, threonine, tryptophan, pyruvate, glycerol, cellobiose, and glucose. Both campylobacters and ESBL-E. coli utilized aspartate, serine, formate, a-ketoglutarate and malate. Trends in compound utilization were similar for C. jejuni and C. coli and trends in compound utilization were rather comparable during enrichment of reference and freeze-stressed campylobacters. Since final cell densities of C. jejuni and C. coli in co-cultures were not enhanced by the addition of surplus l-serine and final cell densities were similar in fresh and spent medium, growth suppression seems not to be caused by a lack of substrates or production of inhibitory compounds. We hypothesized that oxygen availability was limiting growth in co-cultures. Higher oxygen availability increased the competitive fitness of C. jejuni 81-176 in co-culture with ESBL-E. coli in duplicate experiments, as cell concentrations in stationary phase were similar to those without competition. This could indicate the critical role of oxygen availability during the growth of Campylobacter and offers potential for further improvement of Campylobacter spp. enrichment efficacy.
已有充分证据表明，根据 ISO 10272-1:2017，在 Bolton 肉汤（BB）中进行丰登时，产超广谱β-内酰胺酶（ESBL）的大肠埃希氏菌会对弯曲菌的可靠检测造成挑战。ESBL-E. coli 在富集培养基 BB 中过度生长会导致假阴性检测结果，但生长抑制的原因尚不清楚。一个合理的原因可能是竞争导致某些生长底物的缺乏。因此，本研究旨在调查弯曲菌和 ESBL-E. coli 是否竞争相同的培养基成分，以及这是否是观察到的生长抑制的原因。通过测定 BB 中可能的生长底物的可用性，并在单培养中测定 C. jejuni、C. coli 或 ESBL-E. coli 以及弯曲菌和 ESBL-E. coli 共培养富集过程中其胞外浓度随时间的变化，来确定 BB 中可能的生长底物的可用性。比较分析表明，C. jejuni 和 C. coli 仅利用乳酸盐和富马酸盐，而 ESBL-E. coli 则迅速消耗天冬酰胺、谷氨酰胺/精氨酸、赖氨酸、苏氨酸、色氨酸、丙酮酸、甘油、纤维二糖和葡萄糖。两种弯曲菌和 ESBL-E. coli 都利用天冬氨酸、丝氨酸、甲酸盐、a-酮戊二酸和苹果酸。C. jejuni 和 C. coli 富集过程中的化合物利用趋势相似，参考和冷冻应激弯曲菌富集过程中的化合物利用趋势也相当相似。由于在添加过剩 l-丝氨酸后 C. jejuni 和 C. coli 的共培养物中的最终细胞密度没有增加，并且新鲜和耗尽培养基中的最终细胞密度相似，因此生长抑制似乎不是由于缺乏底物或产生抑制化合物所致。我们假设氧气供应是共培养物中生长的限制因素。在重复实验中，较高的氧气供应增加了 C. jejuni 81-176 在与 ESBL-E. coli 共培养中的竞争适应性，因为在静止期的细胞浓度与没有竞争时相似。这可能表明氧气供应在弯曲菌生长过程中的关键作用，并为进一步提高弯曲菌属富集效率提供了潜力。
