Division of Medical Microbiology, Faculty of Medicine and Health Sciences, Stellenbosch University and NHLS, Tygerberg Hospital, Francie van Zijl Drive, PO Box 241; Cape Town, Tygerberg, 8000, South Africa.
National Health Laboratory Service, Tygerberg Hospital, Cape Town, South Africa.
Antimicrob Resist Infect Control. 2020 Mar 14;9(1):47. doi: 10.1186/s13756-020-00707-8.
Antimicrobial resistance is an increasingly serious problem in public health globally. Monitoring resistance levels within healthcare and community settings is critical to combat its ongoing increase. This study aimed to describe the rates and molecular mechanisms of mupirocin resistance in clinical Staphylococcus aureus isolates from Tygerberg Hospital, and to describe its association with strain types.
We retrospectively selected 212 S. aureus isolates which were identified from blood samples and pus swabs during the years 2009-2011 and 2015-2017. The isolates were identified using conventional microbiological methods and genotyping was done using spa typing. Cefoxitin (30 μg) disc diffusion and the two disc strategy (5 μg and 200 μg) were used to determine susceptibility to methicillin and mupirocin, respectively. Isolates with high-level resistance were screened for the plasmid mediated genes mupA and mupB by PCR, and sequencing of the ileS gene was done for all isolates exhibiting low-level resistance to describe the mutations associated with this phenotype. Chi-square test was used to assess the associations between mupirocin resistance and S. aureus genotypes.
Of 212 S. aureus isolates, 12% (n = 25) were resistant to mupirocin, and 44% (n = 93) were methicillin resistant. Strain typing identified 73 spa types with spa t045 being the most predominant constituting 11% of the isolates. High-level mupirocin resistance was observed in 2% (n = 5), and low-level resistance in 9% (n = 20) of the isolates. The prevalence of high-level mupirocin resistance amongst MRSA and MSSA was 4 and 1% respectively, while the prevalence of low-level mupirocin resistance was significantly higher in MRSA (18%) compared to MSSA (3%), (p = 0.032). mupA was the only resistance determinant for high-level resistance, and the IleS mutation V588F was identified in 95% of the isolates which showed low-level resistance. A significant association was observed between spa type t032 and high-level mupirocin resistance, and types t037 and t012 and low-level resistance (p < 0.0001).
The study reported higher rates of low-level mupirocin resistance compared to high-level resistance, and in our setting, mupirocin resistance was driven by certain genotypes. Our study advocates for the continuous screening for mupirocin resistance in S. aureus in clinical settings to better guide treatment and prescribing practices.
抗微生物药物耐药性是当前全球公共卫生领域日益严峻的问题。在医疗保健和社区环境中监测耐药水平对于遏制耐药性的持续上升至关重要。本研究旨在描述来自泰格尔伯格医院临床金黄色葡萄球菌分离株中莫匹罗星耐药的发生率和分子机制，并描述其与菌株类型的关系。
我们回顾性选择了 212 株金黄色葡萄球菌分离株，这些分离株是在 2009-2011 年和 2015-2017 年期间从血液样本和脓液拭子中鉴定出来的。使用常规微生物学方法鉴定分离株，并使用 spa 分型进行基因分型。使用头孢西丁（30μg）纸片扩散法和双纸片法（5μg 和 200μg）分别测定对甲氧西林和莫匹罗星的敏感性。对高水平耐药的分离株进行质粒介导基因 mupA 和 mupB 的 PCR 筛选，对所有表现出低水平耐药的分离株进行 ileS 基因测序，以描述与该表型相关的突变。使用卡方检验评估莫匹罗星耐药与金黄色葡萄球菌基因型之间的关系。
在 212 株金黄色葡萄球菌分离株中，有 12%（n=25）对莫匹罗星耐药，有 44%（n=93）对甲氧西林耐药。菌株分型鉴定出 73 种 spa 型，spa t045 是最主要的型别，占分离株的 11%。高水平莫匹罗星耐药的分离株占 2%（n=5），低水平耐药的分离株占 9%（n=20）。MRSA 和 MSSA 中高水平莫匹罗星耐药的发生率分别为 4%和 1%，而 MRSA 中低水平莫匹罗星耐药的发生率明显高于 MSSA（18%对 3%）（p=0.032）。mupA 是高水平耐药的唯一耐药决定因素，95%表现出低水平耐药的分离株中存在 ileS 突变 V588F。spa t032 与高水平莫匹罗星耐药显著相关，而 spa t037 和 t012 与低水平耐药显著相关（p<0.0001）。
本研究报告的低水平莫匹罗星耐药率高于高水平耐药率，在我们的研究环境中，莫匹罗星耐药是由某些基因型驱动的。本研究主张在临床环境中持续筛查金黄色葡萄球菌中的莫匹罗星耐药性，以更好地指导治疗和处方实践。
