Author/Authors :
Sirichoat، Auttawit نويسنده Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand , , Wongthong، Sujintana نويسنده Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand , , Kanyota، Ratdawan نويسنده Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand , , Tavichakorntrakool، Ratree نويسنده Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand , , Chanawong، Aroonwadee نويسنده Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand , , Welbat، Jariya Umka نويسنده Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand , , Lulitanond، Aroonlug نويسنده Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand ,
Abstract :
Staphylococcus aureus, with reduced vancomycin susceptibility, is probably under the regulation of several genes and various express phenotypes. This study aimed to investigate the phenotypic differences between vancomycin-susceptible S. aureus (VSSA), vancomycin-intermediate S. aureus (VISA), and heterogeneous VISA (hVISA) isolates. 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. 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). 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.
