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.


OBJECTIVE
This study aimed to investigate the phenotypic differences between vancomycin-susceptible S. aureus (VSSA), vancomycin-intermediate S. aureus (VISA), and heterogeneous VISA (hVISA) isolates.


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.
Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Auttawit
A
Sirichoat
Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Sujintana
S
Wongthong
Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Ratdawan
R
Kanyota
Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Ratree
R
Tavichakorntrakool
Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Aroonwadee
A
Chanawong
Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
Jariya Umka
JU
Welbat
Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Aroonlug
A
Lulitanond
Coagulase; Methicillin-Resistant Staphylococcus aureus; Urease; Vancomycin