Environments polluted with excessively high levels of antibiotics released from manufacturing sites can act as a source of transferable antibiotic resistance (AR) genes to human commensal and pathogenic bacteria. The aim of this study was to evaluate AR of bacteria isolated from the Sava river sediments (Croatia) at the discharge site of effluents from azithromycin production compared to those from the upstream site and isolates collected in Croatian hospitals. A total of 228 environmental strains of azithromycin-resistant bacteria were isolated and identified, with 124 from the discharge site and 104 from the upstream site. In addition, a total of 90 clinical, azithromycin-resistant streptococcal and staphyloccocal isolates obtained from the Croatian Reference Center for Antibiotic Resistance Surveillance were analyzed. PCR screening of isolates on 11 relevant macrolide-resistance genes (MRGs) showed that discharge isolates had greater detection frequencies for 4 gene targets (ermB, msrE, mphE and ermF) compared to upstream isolates. Among clinical isolates, the most frequently detected gene was ermB, followed by msrD, mefE and mefC. The discharge site demonstrated a greater abundance of isolates with co-occurence of two different MRGs (predominantly msrE-mphE) than the upstream site, but a lower abundance than the clinical sources (most commonly msrD-mefE). The simultaneous presence of three or even four MRGs was specific for the discharge and clinical isolates, but not for the upstream isolates. When MRG results were sorted by gene mechanism, the ribosomal methylation (erm) and protection genes (msr) were the most frequently detected among both the discharge and the clinical isolates. Following sequencing, high nucleotide sequence similarity was observed between ermB in the discharge isolates and the clinical streptococcal isolates, suggesting a possible transfer of the ermB gene between bacteria of clinical and environmental origin. Our study highlights the importance of environmental bacterial populations as reservoirs for clinically relevant macrolide-resistance genes.

从生产场所释放的抗生素水平过高污染的环境可能成为人类共生和致病细菌可转移抗生素抗性（AR）基因的来源。这项研究的目的是评估与从上游站点和克罗地亚医院收集的分离株相比，从阿奇霉素生产废水的排放点从萨瓦河沉积物（克罗地亚）分离的细菌的AR。总共分离并鉴定了228株耐阿奇霉素的环境菌株，其中124个来自排放位点，104个来自上游位点。此外，还分析了从克罗地亚抗生素耐药性监测参考中心获得的90株临床，对阿奇霉素耐药的链球菌和葡萄球菌分离株。erm B，msr E，mph E和erm F）与上游分离物相比。在临床分离株中，最常检测到的基因是erm B，其次是msr D，mef E和mefC。出院位点显示，与两种不同MRG（主要是msr E -mph E）同时出现的分离株相比，其分离度更高。上游部位，但比临床来源的丰度低（最常见的是MSR D- mefE）。对于出院和临床分离株，三个或什至四个MRG的同时存在是特定的，但上游分离株不是。当按基因机制对MRG结果进行分类时，在出院和临床分离物中，核糖体甲基化（erm）和保护基因（msr）最为常见。测序后，观察到排放分离株中的erm B与临床链球菌分离株之间存在高核苷酸序列相似性，这表明erm B基因可能在临床和环境起源的细菌之间转移。我们的研究强调了环境细菌种群作为临床上相关的大环内酯类耐药基因的储库的重要性。