Aarris Mia, Hertz Frederik Boëtius, Nielsen Karen Leth, Sato Alexander, Johansen Helle Krogh, Westh Henrik, Kemp Michael, Ellermann-Eriksen Svend, Løbner-Olesen Anders, Frimodt-Møller Niels, Charbon Godefroid
Department of Clinical Microbiology, Rigshospitalet, 2100 Copenhagen, Denmark.
Department of Immunology & Microbiology, University of Copenhagen, 2200 Copenhagen, Denmark.
Antibiotics (Basel). 2025 Apr 29;14(5):449. doi: 10.3390/antibiotics14050449.
BACKGROUND/OBJECTIVES: is a leading cause of bacteraemia in Danish hospitals. Approximately 70% of clinical isolates are penicillin-resistant, which is predominantly due to -mediated β-lactamase production.
A collection of 489 strains derived from bacteraemia were cultured and their genomes sequenced.
From this collection, 71% of isolates were methicillin-susceptible (MSSA) harbouring . While most isolates contained the gene belonging to the well-characterised A, B, C and D variants, three strains (1%) produced a BlaZ protein characterised by having threonine residues on both positions 128 and 216 and, therefore, belonged to neither of the established variants. We named this variant, variant F. We report that clinical isolates expressing variant F were resistant to oxacillin. The β-lactamase production phenotype in isolates carrying either of the A, B, C or D variants was only weakly discernible on MIC gradient strip and disk diffusion tests. When the β-lactamases were expressed either from a T7 promoter or from their endogenous promoters in , variant F was significantly better at degrading ampicillin than variant A. We also showed that variant F conferred oxacillin resistance when expressed in an isogenic strain, while variant A did not. Finally, we demonstrated that the F variant threonine 216 played a role in the enzyme's superior activity.
Our findings demonstrate that the new F variant of BlaZ is sufficient to render a BORSA strain, which is superior in the degradation of common anti-staphylococcal β-lactam antibiotics, such as benzylpenicillin, cloxacillin, and oxacillin. It is sensitive to β-lactamase inhibitors and rapidly degrades nitrocefin. We provide a genetic explanation for the borderline oxacillin-resistant (BORSA) phenotype.
背景/目的：在丹麦医院中，[具体细菌名称未给出]是菌血症的主要病因。大约70%的临床分离株对青霉素耐药，这主要是由于[具体机制未给出]介导的β-内酰胺酶产生。
培养了489株源自菌血症的菌株，并对其基因组进行测序。
在这个菌株集合中，71%的分离株对甲氧西林敏感（MSSA）且携带[具体基因未给出]。虽然大多数分离株含有属于特征明确的A、B、C和D变体的[具体基因未给出]基因，但有三株（1%）产生的BlaZ蛋白在第128位和第216位均具有苏氨酸残基，因此不属于已确定的任何一种[具体基因未给出]变体。我们将这种变体命名为变体F。我们报告称，表达变体F的临床分离株对苯唑西林耐药。在MIC梯度条试验和纸片扩散试验中，携带A、B、C或D变体之一的分离株的β-内酰胺酶产生表型仅微弱可辨。当β-内酰胺酶从T7启动子或其在[具体宿主未给出]中的内源启动子表达时，变体F在降解氨苄青霉素方面比变体A显著更好。我们还表明，变体F在同基因[具体菌株未给出]菌株中表达时赋予苯唑西林耐药性，而变体A则没有。最后，我们证明F变体的苏氨酸216在该酶的卓越活性中起作用。
我们的研究结果表明，BlaZ的新F变体足以使[具体菌株未给出]成为BORSA菌株，该变体在降解常见的抗葡萄球菌β-内酰胺抗生素（如苄青霉素、氯唑西林和苯唑西林）方面更具优势。它对β-内酰胺酶抑制剂敏感，并能快速降解头孢硝噻吩。我们为苯唑西林临界耐药（BORSA）表型提供了遗传学解释。
