Detection of Heteroresistant Vancomycin-Intermediate <i>Staphylococcus haemolyticus</i> Among Blood Isolates

<i>Staphylococcus haemolyticus</i> is frequently associated with infections in hospitalized patients and acts as a reservoir for antibiotic resistance genes. The widespread use of vancomycin in treating serious infections has led to the emergence of heteroresistance to vancomycin in certain <i>S. haemolyticus</i> isolates. This study aimed to determine the rate of heteroresistant vancomycin-intermediate <i>S. haemolyticus</i> (hVISH) among 166 blood isolates collected from patients admitted to Jawaharlal Institute of Postgraduate Medical Education and Research between January 2017 and June 2018. E-test was done to determine vancomycin minimum inhibitory concentration (MIC). Heteroresistance screening was performed using brain heart infusion agar containing 4 µg/mL vancomycin (BHIV₄). Confirmation of heteroresistance was performed by population analysis-profile area under curve (PAP-AUC) analysis. Whole-genome sequencing was performed on eight isolates. All isolates were vancomycin-susceptible by E-test, while 18.7% exhibited heteroresistance by PAP-AUC. The sensitivity, specificity, positive predictive value, negative predictive value, and kappa agreement of BHIV₄ with PAP-AUC were 64.5%, 97.8%, 87%, 92.3%, and 0.692, respectively. Mutational analysis of the eight isolates revealed variations in <i>vraSR</i>, <i>tcaRAB</i>, <i>walKR</i>, yyc<i>HIJ</i>, <i>rpoBC</i>, <i>lytSR</i>, <i>clpP</i>, <i>phoR</i>, PBP₄, <i>msrR</i>, <i>cmk</i>, and <i>mprF</i> operons, along with novel mutations in cell wall synthesis operons. The rate of hVISH isolation in our study is in agreement with other studies worldwide. As the sensitivity of BHIV₄ is only moderate, it may be prudent to consider alternate antibiotics if MIC of vancomycin approaches the breakpoint. Furthermore, our analysis revealed multiple mutations within glycopeptide resistance operons, providing a better understanding of the molecular mechanisms underlying heteroresistance in <i>S. haemolyticus</i> and its implications for antimicrobial therapy and surveillance strategies.