Comparative efficacy of vancomycin in treating ST5 and ST764 methicillin-resistant Staphylococcus aureus infections in adult patients

This study compared the impact of sequence type 5 (ST5) and ST764, on the efficacy of vancomycin treatment in methicillin-resistant Staphylococcus aureus (MRSA) infections. From July 2012 to June 2020, a prospective observational study was conducted in five hospitals in China, enrolling 90 patients with MRSA infections, including 44 patients with ST5-MRSA and 46 patients with ST764-MRSA infections. All strains were subjected to minimal inhibitory concentration (MIC) determination, biofilm expression, heterogeneous vancomycin-intermediate S. aureus (hVISA) screening, and whole-genome sequencing. Vancomycin therapeutic drug monitoring was conducted, and the 24-hour area under the curve (AUC(0-24)) and AUC(0-24)/MIC values were calculated. ST5-MRSA shows elevated hVISA/VISA presence, increased biofilm formation, and higher presence of virulence genes like tst, sec, and sel. ST764-MRSA expresses seb, aiding infection in elderly patients in the community. Additionally, patients with ST764 infections exhibit higher vancomycin AUC(0-24)/MIC values, and fewer tracheotomies compared to ST5. Clinical signs and symptoms improvement were observed in 27 (61.4%) and 33 (71.7%) patients in the ST5 and ST764 groups, respectively (P = 0.372). On the other hand, 28 (63.6%) and 39 (84.8%) patients had laboratory-confirmed bacterial eradication in two groups, respectively (P = 0.029). Multivariate analysis showed that the virulence genes, such as the tst gene, were a risk factor for bacterial persistence (adjusted odds ratio, 4.509; 95% confidence interval, 1.216 to 16.724; P = 0.024). Our study showed that vancomycin was less effective in treating ST5-MRSA infection compared to ST764-MRSA infection, in part because ST5-MRSA is healthcare-associated MRSA while ST764-MRSA carries genetic characteristics of community-associated MRSA.