Department of Veterinary Science, University of Pisa, Viale delle Piagge 2, Pisa, Italy.
Comp Immunol Microbiol Infect Dis. 2021 Jun;76:101656. doi: 10.1016/j.cimid.2021.101656. Epub 2021 Apr 22.
Teat-dipping is one of the most effective methods to prevent mammary infections in ruminants, including sub-clinical mastitis caused by coagulase-negative staphylococci (CoNS). Improper disinfectant application could expose microorganisms to sub-inhibitory concentrations leading to phenotypic variations. In this study, 12 chlorhexidine-digluconate (CHDG)-tolerant (of which 4 qac positive) and 12 benzalkonium chloride (BC)-tolerant (of which 7 qac-positive) CoNS isolates from ovine milk were exposed to sub-inhibitory concentrations of CHDG and BC, respectively. Changes in disinfectant susceptibility against BC and CHDG, antibiotic resistance against 12 antibiotics and biofilm production were then assessed for both groups. After CHDG stress, 67 % and 83 % of the CHDG-stressed isolates doubled their MICs for BC and CHDG, respectively and 2 qac-negative isolates showed a four-fold increase of their MBCs for CHDG. After BC stress, MICs for BC and CHDG doubled in 58 % and 83 % of the BC-stressed isolates, respectively, while one qac-positive isolate increased four-fold the MIC for BC. Cross-resistance to antibiotics was assessed by disc diffusion method. Some qac-positive isolates varied their resistance profile, while a blaZ-positive isolate showed a resistant phenotype against ampicillin only after the exposure to the disinfectant. As for qac-positive isolates, one CHDG-stressed and 2 BC-stressed increased their resistance to kanamycin and cefoxitin, respectively. The Congo Red Agar test was carried out to assess the in vitro slime production: all isolates were negative after stress. In conclusion, sub-inhibitory exposure to disinfectants may affect disinfectant and antibiotic susceptibility, the latter in particular for qac-positive isolates and those hosting unexpressed antibiotic resistance genes.
乳房浸渍是预防反刍动物乳房感染（包括由凝固酶阴性葡萄球菌（CoNS）引起的亚临床乳腺炎）的最有效方法之一。消毒剂使用不当可能会使微生物暴露于亚抑制浓度下，从而导致表型变异。在这项研究中，从绵羊乳中分离出 12 株对洗必泰葡萄糖酸（CHDG）（其中 4 株 qac 阳性）和 12 株对苯扎氯铵（BC）（其中 7 株 qac 阳性）具有耐受性的 CoNS 分离株，分别用亚抑制浓度的 CHDG 和 BC 处理。然后，评估两组对 BC 和 CHDG 的消毒剂敏感性变化、对 12 种抗生素的耐药性和生物膜产生情况。在 CHDG 应激后，CHDG 应激分离株中有 67%和 83%的分离株对 BC 和 CHDG 的 MIC 分别增加了一倍，2 株 qac 阴性分离株的 CHDG MBC 增加了四倍。在 BC 应激后，BC 应激分离株中有 58%和 83%的分离株的 BC 和 CHDG 的 MIC 分别增加了一倍，而 1 株 qac 阳性分离株对 BC 的 MIC 增加了四倍。通过药敏纸片扩散法评估交叉耐药性。一些 qac 阳性分离株的耐药谱发生了变化，而仅在暴露于消毒剂后，一株 blaZ 阳性分离株对氨苄西林表现出耐药表型。对于 qac 阳性分离株，1 株 CHDG 应激和 2 株 BC 应激分离株分别增加了对卡那霉素和头孢西丁的耐药性。通过刚果红琼脂试验评估体外粘液产生：所有分离株在应激后均为阴性。总之，亚抑制浓度的消毒剂暴露可能会影响消毒剂和抗生素的敏感性，特别是对于 qac 阳性分离株和那些携带未表达的抗生素耐药基因的分离株。
