Department of Medical Microbiology, Immunology, and Cell Biology, Southern Illinois University School of Medicine, USA.
Interfaculty Institute of Microbiology and Infection Medicine, University of Tübingen, Germany.
Infect Genet Evol. 2024 Jan;117:105545. doi: 10.1016/j.meegid.2023.105545. Epub 2023 Dec 29.
Staphylococcus aureus are gram-positive bacteria responsible for a wide array of diseases, ranging from skin and soft tissue infections to more chronic illnesses such as toxic shock syndrome, osteomyelitis, and endocarditis. Vancomycin is currently one of the most effective antibiotics available in treating patients infected with methicillin-resistant S. aureus (MRSA), however the emergence of vancomycin-resistant S. aureus (VRSA), and more commonly vancomycin-intermediate S. aureus (VISA), threaten the future efficacy of vancomycin. Intermediate resistance to vancomycin occurs due to mutations within the loci of Staphylococcal genes involved in cell wall formation such as rpoB, graS, and yycG. We hypothesized the VISA phenotype may also arise as a result of the natural stress occurring within S. aureus biofilms, and that this phenomenon is mediated by the RecA/SOS response. Wildtype and recA null mutant/lexAG94E strains of S. aureus biofilms were established in biofilm microtiter assays or planktonic cultures with or without the addition of sub-inhibitory concentrations of vancomycin (0.063 mg/l - 0.25 mg/L ciprofloxacin, 0.5 mg/l vancomycin). Efficiency of plating techniques were used to quantify the subpopulation of biofilm-derived S. aureus cells that developed vancomycin-intermediate resistance. The results indicated that a greater subpopulation of cells from wildtype biofilms (4.16 × 10 CFUs) emerged from intermediate-resistant concentrations of vancomycin (4 μg/ml) compared with the planktonic counterpart (1.53 × 10 CFUs). Wildtype biofilms (4.16 × 10 CFUs) also exhibited greater resistance to intermediate-resistant concentrations of vancomycin compared with strains deficient in the recA null mutant (8.15 × 10 CFUs) and lexA genes (8.00 × 10 CFUs). While the VISA phenotype would be an unintended consequence of genetic diversity and potentially gene transfer in the biofilm setting, it demonstrates that mutations occurring within biofilms allow for S. aureus to adapt to new environments, including the presence of widely used antibiotics.
金黄色葡萄球菌是一种革兰氏阳性细菌，可导致多种疾病，从皮肤和软组织感染到更慢性疾病，如中毒性休克综合征、骨髓炎和心内膜炎。万古霉素是目前治疗耐甲氧西林金黄色葡萄球菌（MRSA）感染患者最有效的抗生素之一，然而，万古霉素耐药金黄色葡萄球菌（VRSA）的出现，更常见的是万古霉素中介金黄色葡萄球菌（VISA），威胁着万古霉素的未来疗效。万古霉素的中介耐药性是由于参与细胞壁形成的葡萄球菌基因的基因座（如 rpoB、graS 和 yycG）发生突变所致。我们假设 VISA 表型也可能是由于金黄色葡萄球菌生物膜内自然发生的应激引起的，而这种现象是由 RecA/SOS 反应介导的。在生物膜微量滴定或浮游培养物中建立了野生型和 recA 缺失突变体/lexAG94E 金黄色葡萄球菌生物膜的野生型和 recA 缺失突变体/lexAG94E 菌株，加入或不加入亚抑制浓度的万古霉素（0.063 mg/l - 0.25 mg/L 环丙沙星，0.5 mg/l 万古霉素）。采用平板计数技术定量测定从万古霉素中介浓度（4 μg/ml）中分离出具有万古霉素中介耐药性的生物膜衍生金黄色葡萄球菌细胞的亚群。结果表明，与浮游对照（1.53 × 10 CFUs）相比，来自野生型生物膜的更大亚群细胞（4.16 × 10 CFUs）从万古霉素中介浓度中出现（4 μg/ml）。与 recA 缺失突变体（8.15 × 10 CFUs）和 lexA 基因（8.00 × 10 CFUs）缺陷株相比，野生型生物膜（4.16 × 10 CFUs）对中介浓度的万古霉素也表现出更高的耐药性。虽然 VISA 表型是生物膜环境中遗传多样性和潜在基因转移的意外后果，但它表明生物膜内发生的突变使金黄色葡萄球菌能够适应新的环境，包括广泛使用的抗生素的存在。
