Sequence Type 5 (ST5) as a Possible Predictor of Bacterial Persistence in Adult Patients with Methicillin-Resistant Staphylococcus aureus Pneumonia Treated with Vancomycin

Vancomycin remains the mainstay of treatment for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. This study assessed risk factors for vancomycin failure in 63 patients with MRSA pneumonia through detailed clinical, microbiological, pharmacokinetic/pharmacodynamic, and genetic analyses of prospective multicenter studies conducted from February 2012 to July 2018. Therapeutic drug monitoring was performed during vancomycin treatment, and the 24-h area under the curve (AUC(0–24)) was calculated. All baseline strains were collected for MIC determination, heterogeneous vancomycin-intermediate S. aureus (hVISA) screening, and biofilm determination. Whole-genome sequencing was performed on the isolates to analyze their molecular typing and virulence and adhesion genes. Clinical signs and symptoms improved in 44 patients (44/63, 69.8%), with vancomycin daily dose (P = 0.045), peak concentration (P = 0.020), and sdrC (P = 0.047) being significant factors. Isolates were eradicated in 51 patients (51/63, 81.0%), with vancomycin daily dose (P = 0.009), cardiovascular disease (P = 0.043), sequence type 5 (ST5; P = 0.017), tst (P = 0.050), and sec gene (P = 0.044) associated with bacteriological failure. Although the AUC(0–24)/MIC was higher in the groups with bacterial eradication, the difference was not statistically significant (P = 0.108). Multivariate analysis showed that no variables were associated with clinical efficacy; ST5 was a risk factor for bacterial persistence (adjusted odds ratio, 4.449; 95% confidence interval, 1.103 to 17.943; P = 0.036). ST5 strains had higher frequencies of the hVISA phenotype, biofilm expression, and presence of some adhesion and virulence genes such as fnbB, tst, and sec than non-ST5 strains. Our study suggests that ST5 is a possible predictor of bacterial persistence in MRSA pneumonia treated with vancomycin. IMPORTANCE Few studies have simultaneously examined the influence of clinical characteristics of patients with pneumonia, the vancomycin pharmacokinetic/pharmacodynamic (PK/PD) index, and the phenotypic and genetic characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains. We assessed risk factors for vancomycin failure in patients with MRSA pneumonia by analyzing these influences in a prospective multicenter study. Sequence type 5 (ST5) was a possible predictor of bacterial persistence in adult patients with MRSA pneumonia (adjusted odds ratio, 4.449). We found that this may be related to ST5 strains having higher levels of vancomycin heterogeneous resistance, biofilms, and the presence of adhesion and virulence genes such as fnbB, tst, and sec.