phenotypic characteristics of vancomycin-non-susceptible staphylococcus aureus

Background: staphylococcus aureus, with reduced vancomycin susceptibility, is probably under the regulation of several genes and various express phenotypes. objectives: this study aimed to investigate the phenotypic differences between vancomycin-susceptible s. aureus (vssa), vancomycin-intermediate s. aureus (visa), and heterogeneous visa (hvisa) isolates. materials and methods: a total of 130 methicillin-resistant s. aureus (mrsa) isolates were studied, including 49 vssa, 28 hvisa, and 5 visa isolates from blood cultures and 48 isolates (two vssa, six hvisa, and 40 visa) derived in vitro (laboratory-induced/sub-passaged). their phenotypes were examined using a coagulase tube test, colony spreading on soft agar, and urease activity. the sccmec and agr typing were performed using multiplex pcr. results: most of the mrsa isolates were sccmec iii-agr i (84.5%), followed by sccmec ii-agr ii (11.8%). the average plasma coagulation time of vancomycin-non-susceptible isolates was longer than that of the susceptible isolates (12 vs. 2.6 hours). four hvisa (p = 0.023) and nine visa (p < 0.001) isolates yielded a negative coagulase test after 24-hour incubation. the percentage of vssa isolates showing non-spreading colonies (accessory gene regulator (agr) dysfunction) was significantly lower than in the visa group (p = 0.013), but no significant difference was found between vssa and hvisa. the visa group showed higher urease activity than that of the vssa and hvisa groups (p = 0.002). conclusions: there were diverse phenotypic changes among vancomycin-non-susceptible s. aureus isolates. this may be due to the variety of related regulatory systems. the diversity of phenotypic expression may result in its misidentification in routine laboratory checks.