摘要

食物链被认为在将共生细菌和有益细菌的抗生素抗性传播给病原体方面发挥重要作用。嗜热链球菌是一种乳酸菌，作为乳品工业的起始者具有重要意义。该研究报告了16种代表性抗微生物剂对源自生乳的41种嗜热链球菌的最小抑制浓度（MIC）。发现显示对四环素（7），红霉素和克林霉素（2）以及链霉素和新霉素（1）有抗性的菌株。 PCR扩增鉴定了所有四环素抗性菌株中的tet（S），以及两种红霉素/克林霉素抗性菌株中的ermB。杂交实验表明每个抗性基因位于具有相似遗传组织的染色体中。对抗四环素（St-2和St-9），两种对红霉素/克林霉素（St-5和St-6）有抗性的抗生素抗性菌株和对链霉素/新霉素（St-10）经受基因组测序和分析。在St-2和St-9中分别在3.2和3.7kbp的小重叠群中鉴定tet（S）基因，侧接截短拷贝的插入序列（IS）元件。类似地，St-6和St-5中的ermB分别在1.6和28.1kbp的重叠群中发现。序列分析和最大重叠群的比较显示它含有三个片段（21.9,3.7和1.4kbp长），与来自粪肠球菌的非共线序列pRE25高度同源。这些片段含有ermB基因，其是具有转移起点（oriT）的转移模块加上15个编码参与缀合的蛋白质的开放阅读框，以及用于质粒复制和分离的模块。通过短的IS相关序列分离同源序列，类似于在链球菌物种中发现的整合和接合元件（ICE）的遗传组织。在St-10中未见到提供氨基糖苷类抗性的基因。在该菌株中对RsmG甲基转移酶中的四个菌株特异性氨基酸取代进行评分;这些可能与其链霉素/新霉素抗性有关。在酸奶制造和储存条件下，没有检测到来自嗜热链球菌的tet（S）或ermB向德氏乳杆菌的转移。目前的结果有助于表征嗜热链球菌中的抗生素抗性谱，为获得的抗性的遗传基础提供证据并深化其转移能力。

The food chain is thought to play an important role in the transmission of antibiotic resistances from commensal and beneficial bacteria to pathogens. Streptococcus thermophilus is a lactic acid bacterium of major importance as a starter for the dairy industry. This study reports the minimum inhibitory concentration (MIC) of 16 representative antimicrobial agents to 41 isolates of S. thermophilus derived from raw milk. Strains showing resistance to tetracycline (seven), erythromycin and clindamycin (two), and streptomycin and neomycin (one) were found. PCR amplification identified tet(S) in all the tetracycline-resistant strains, and ermB in the two erythromycin/clindamycin-resistant strains. Hybridisation experiments suggested each resistance gene to be located in the chromosome with a similar genetic organization. Five antibiotic-resistant strains -two resistant to tetracycline (St-2 and St-9), two resistant to erythromycin/clindamycin (St-5 and St-6), and one resistant to streptomycin/neomycin (St-10)- were subjected to genome sequencing and analysis. The tet(S) gene was identified in small contigs of 3.2 and 3.7 kbp in St-2 and St-9, respectively, flanked by truncated copies of insertion sequence (IS) elements. Similarly, ermB in St-6 and St-5 was found in contigs of 1.6 and 28.1 kbp, respectively. Sequence analysis and comparison of the largest contig showed it to contain three segments (21.9, 3.7, and 1.4 kbp long) highly homologous to non-collinear sequences of pRE25 from Enterococcus faecalis. These segments contained the ermB gene, a transference module with an origin of transfer (oriT) plus 15 open reading frames encoding proteins involved in conjugation, and modules for plasmid replication and segregation. Homologous stretches were separated by short, IS-related sequences, resembling the genetic organization of the integrative and conjugative elements (ICEs) found in Streptococcus species. No gene known to provide aminoglycoside resistance was seen in St-10. Four strain-specific amino acid substitutions in the RsmG methyltransferase were scored in this strain; these might be associated to its streptomycin/neomycin resistance. Under yogurt manufacturing and storage conditions, no transfer of either tet(S) or ermB from S. thermophilus to L. delbrueckii was detected. The present results contribute toward characterisation of the antibiotic resistance profiles in S. thermophilus, provide evidence for the genetic basis of acquired resistances and deepen on their transference capability.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5744436/