Department of Animal Science, College for Agricultural Sciences, Federal University of Paraiba (UFPB), Rod. PB079 Km12, s/n, 58397-000, Areia, PB, Brazil.
Department of Animal Science, College for Agricultural Sciences, Federal University of Paraiba (UFPB), Rod. PB079 Km12, s/n, 58397-000, Areia, PB, Brazil; Department of Veterinary Pathology, Sao Paulo State University (UNESP), Via de acesso Prof. Paulo Donato Castellane s/n, 14884-900, Jaboticabal, SP, Brazil.
Comp Immunol Microbiol Infect Dis. 2021 Dec;79:101697. doi: 10.1016/j.cimid.2021.101697. Epub 2021 Aug 28.
Methicillin resistance mediated by the mecA gene in Staphylococcus aureus, also known as "true MRSA", is typically associated with high oxacillin MIC values (≥8 mg/L). Because non-mecA-mediated oxacillin resistant S. aureus phenotypes can also cause hard-to-treat diseases in humans, their misidentification as methicillin-susceptible S. aureus strains (MSSA) can compromise the efficiency of the antimicrobial therapy. These strains have been refereed as Borderline Oxacillin-Resistant S. aureus (BORSA) but their characterization and role in clinical microbiology have been neglected. Considering the increasing importance of livestock-associated methicillin-resistant S. aureus ST398 (LA-MRSA) as an emerging zoonotic pathogen worldwide, this study aimed to report the genomic context of oxacillin resistance in porcine S. aureus ST398 strains. S. aureus isolates were recovered from asymptomatic pigs from three herds. Oxacillin MIC values ranged from 4 to 32 mg/L. MALDI-TOF-confirmed isolates were screened for mecA and mecC by PCR and genotyped by means of PFGE and Rep-PCR. Seven isolates were whole genome sequenced. None of the isolates harbored the mecA gene or its variants. Although all seven sequenced isolates belonged to one sequence type (ST398), two different spa types (t571 and t1471) were identified. All isolates harbored conserved blaZ gene operon and no mutations on genes encoding for penicillin-binding-proteins were detected. Genes conferring resistance against other drugs such as aminoglycosides, chloramphenicol, macrolide, lincosamide and streptogramin (MLS), tetracycline and trimethoprim were also detected. Isolates also harbored virulence genes encoding for adhesins (icaA; icaB; icaC; icaD; icaR), toxins (hlgA; hlgB; hlgC; luk-PV) and protease (aur). Pigs can serve as reservoirs of non-mecA-mediated oxacillin-resistant ST398 strains potentially pathogenic to humans. Considering that mecA has been the main target to screen methicillin-resistant staphylococci, the occurrence of BORSA phenotypes is probably underestimated in livestock.
金黄色葡萄球菌中 mecA 基因介导的耐甲氧西林（methicillin resistance mediated by the mecA gene in Staphylococcus aureus, 也称为“真正的耐甲氧西林金黄色葡萄球菌”，通常与高苯唑西林 MIC 值（≥8mg/L）相关。由于非 mecA 介导的苯唑西林耐药金黄色葡萄球菌表型也可能导致人类难以治疗的疾病，因此将其错误鉴定为甲氧西林敏感金黄色葡萄球菌（methicillin-susceptible S. aureus strains, MSSA）可能会影响抗菌治疗的效果。这些菌株被称为边界耐苯唑西林金黄色葡萄球菌（Borderline Oxacillin-Resistant S. aureus，BORSA），但其特征和在临床微生物学中的作用一直被忽视。考虑到与牲畜相关的耐甲氧西林金黄色葡萄球菌 ST398（livestock-associated methicillin-resistant S. aureus ST398，LA-MRSA）作为一种全球新兴的人畜共患病病原体的重要性日益增加，本研究旨在报告猪源 ST398 金黄色葡萄球菌耐苯唑西林的基因组背景。从三个牛群中的无症状猪中分离出金黄色葡萄球菌。苯唑西林 MIC 值范围为 4 至 32mg/L。通过 MALDI-TOF 确认的分离株通过 PCR 筛选 mecA 和 mecC，并通过 PFGE 和 Rep-PCR 进行基因分型。对 7 个分离株进行了全基因组测序。没有分离株携带 mecA 基因或其变体。尽管所有 7 个测序分离株均属于一个序列型（ST398），但鉴定出了两个不同的 spa 型（t571 和 t1471）。所有分离株均携带保守的 blaZ 基因操纵子，未检测到青霉素结合蛋白编码基因的突变。还检测到赋予对其他药物（如氨基糖苷类、氯霉素、大环内酯类、林可酰胺类和糖肽类、四环素类和磺胺类）耐药性的基因，以及检测到耐甲氧西林金黄色葡萄球菌的四环素和甲氧苄啶耐药基因。分离株还携带编码黏附素（icaA；icaB；icaC；icaD；icaR）、毒素（hlgA；hlgB；hlgC；luk-PV）和蛋白酶（aur）的毒力基因。猪可以作为非 mecA 介导的耐苯唑西林 ST398 菌株的储主，这些菌株对人类具有潜在的致病性。鉴于 mecA 一直是筛选耐甲氧西林葡萄球菌的主要靶标，因此在牲畜中可能低估了 BORSA 表型的发生。
