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Background  Methicillin-resistant  Staphylococcus aureus  (MRSA)-bloodstream infections (BSI) are predominantly seen in the hospital or healthcare-associated host. Nevertheless, the interactions of virulence factor (VFs) regulators and β-lactam resistance in MRSA-BSI are unclear. This study aims to characterize the molecular relationship of two-component systems of VFs and the expression of the β-lactamase gene in MRSA-BSI isolates. In this study, 639 samples were collected from BSI and identified by phenotypic methods. We performed extensive molecular characterization, including  SCCmec  type,  agr  type, VFs gene profiles determinations, and MLST on isolates. Also, a quantitative real-time PCR (q-RT PCR) assay was developed for identifying the gene expressions.    Results  Ninety-one (91)  S. aureus  and 61 MRSA (67.0%) strains were detected in BSI samples. The presence of VFs and  SCCmec  genes in MRSA isolates were as follows:  tst  (31.4%),  etA  (18.0%),  etB  (8.19%),  lukS-PVL  (31.4%),  lukF-PV  (18.0%),  lukE-lukD  (16.3%),  edin  (3.2%),  hla  (16.3%),  hlb  (18.0%),  hld  (14.7%),  hlg  (22.9%),  SCCmecI  (16.3%),  SCCmecII  (22.9%),  SCCmecIII  (36.0%),  SCCmecIV  (21.3%), and  SCCmecV  (16.3%). Quantitative real-time PCR showed overexpression of  mecRI  and  mecI  in the toxigenic isolates. Moreover,  RNAIII and sarA  genes were the highest expressions of MRSA strains. The multi-locus sequence typing data confirmed a high prevalence of CC5, CC8, and CC30. However, ST30, ST22, and ST5 were the most prevalent in the resistant and toxigenic strains.    Conclusion  We demonstrated that although regulation of β-lactamase gene expressions is a significant contributor to resistance development, two-component systems also influence antibiotic resistance development in MRSA-BSI isolates. This indicates that resistant strains might have pathogenic potential. We also confirmed that some MLST types are more successful colonizers with a potential for MRSA-BSI.    Supplementary Information  The online version contains supplementary material available at 10.1186/s12866-021-02257-4.

bmc microbiology

Regulation of virulence and β-lactamase gene expression in Staphylococcus aureus isolates: cooperation of two-component systems in bloodstream superbugs