SurveillanceAntibiotic susceptibility survey of blood-borne MRSA isolates in Japan from 2008 through 2011
Introduction
Staphylococcus aureus (S. aureus) is a leading cause of hospital- and community-associated infections. In the hospital, methicillin-resistant S. aureus (MRSA) is the highest risk of infection at surgical wounds, the lower respiratory tract and the cardiovascular system, and the second most common cause of health care-associated pneumonia and septicemia [1], [2], [3]. Infections caused by MRSA are worse than those caused by other pathogens due to the limited choices of available antibiotics and thus it is difficult to eradicate these strains. Moreover, the worst situation is that blood stream MRSA infection has a higher rate of mortality and must endure longer hospital stays [4].
Vancomycin has been the agent of choice for methicillin-resistant S. aureus (MRSA) infections as it provided efficacious and promising therapy [5]. Nevertheless, with the emergence of S. aureus strains having intermediate resistance towards vancomycin (vancomycin-intermediate S. aureus [VISA]), treatment options for patients infected with these strains have become limited [6]. Heterogeneous vancomycin-intermediate S. aureus (Hetero-VISA or hVISA) strains are also being reported more frequently worldwide [7]. These strains are interpreted as ‘susceptible’ to vancomycin using conventional MIC determination tests, but contain a sub-population of cells which can grow in the presence of >2 mg/L vancomycin [8], [9]. Another category of MRSA with reduced vancomycin-susceptibility, designated as BIVR, which is resistant to vancomycin only in the presence of β-lactam antibiotics was reported to be prevalent in Japan [10], and the combined phenotype of hVISA and BIVR was associated with a higher probability of mortality in patients with MRSA bacteremia [11]. Therefore, it is important to understand the current state of the prevalence of MRSA with reduced vancomycin-susceptibility from blood stream infections.
Here, we describe a current surveillance study of antibiotic susceptibility on the blood-borne MRSA strains collected from 11 university hospitals and 3 general hospitals covering from Tokyo-Nagoya-Osaka and Kyushyu regions of Japan isolated during a period from 2008 through 2010. The data were compared with the previous surveillance studies with non-bacteremic MRSA isolates studied in 2007 through 2009 by the same laboratory [12], [13], [14]. Our study also focused on determining the strains with reduced vancomycin susceptibility. Though information on MRSA epidemiology in Japan is growing [12], [13], [14], [15], significant gaps exist on the locality of sampling, availability of central laboratories to serve for characterizing MRSA, and availability of surveillance data. Our data presented here will provide information on the most recent trends in the emergence and dissemination of antibiotic resistant strains among the blood stream MRSA infections in Japan.
Section snippets
Participating hospitals and collection of bacterial isolate
Blood-borne MRSA strains were isolated during Jan. 2008 through May 2011 at 11 university hospitals and 3 general hospitals in Japan located Kanto, Kinki, Tokai and Kyushyu regions. Only one MRSA sample was collected from the same patient. All the blood-borne MRSA strains were primarily identified at the local participating hospitals. The clinical isolates were suspended in Micro-bank tubes (Asuka Junyaku, Tokyo, Japan) at the local hospitals, and delivered under frozen states to the
Results
The overall susceptibility profile of MRSA isolates to 14 antibiotics was shown in Table 1 and Fig. 1. As shown in Table 1, the MIC50, MIC90 and MIC ranges of 11 antibiotics including TEIC, VCM, ABK, MINO, MPIPC, IMP, CLDM, CPFX, LZD, CFX and MEPM were comparable with those of in non-bacteremic MRSA isolates studied in 2007 through 2009 by this Central Laboratory [12], [13], [14]. Those of the antibiotics that showed high MIC90 and MIC50 (16–32 μg/ml) were MINO, MPIPC, IPM, CLDM, CPFX, CFX and
Discussion
The bacteremic infections caused by the methicillin-resistant S. aureus are problematic due to the high mortality and only limited antibiotics are available for the treatment [24]. In this paper, we carried out nationwide surveillance of antimicrobial susceptibility of bloodborne MRSA isolates to ascertain resistance patterns in order to assist in the enforcement of infection control measures. Our major findings were that over 97% of the isolates were susceptible to teicoplanin, linezolid,
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