Epidemiological typing of MRSA isolates from blood cultures taken in Irish hospitals participating in the European Antimicrobial Resistance Surveillance System (1999–2003)

Abstract

Between 1999 and 2003, meticillin-resistant Staphylococcus aureus (MRSA) isolates recovered from blood cultures in Irish hospitals that participate in the European Antimicrobial Resistance Surveillance System were investigated by epidemiological typing using antibiogram-resistogram (AR) typing, biotyping, and DNA macrorestriction digestion using SmaI followed by pulsed-field gel electrophoresis (PFGE). PFGE patterns were assigned five-digit pulsed-field type (PFT) numbers, and PFTs of apparently related patterns were abbreviated to two-digit PFT groups (PFGs). AR and PFGE typing results were combined to produce AR-PFG types. Representative isolates of each AR-PFG type recovered in 2002 were typed by multilocus sequence typing and staphylococcal cassette chromosome (SCC) mec analysis. Isolates from 1999 and 2000 were also typed by phage typing. The extent to which epidemiological types of MRSA from blood cultures could be extrapolated to the total MRSA population was investigated by comparing results obtained with isolates from the total MRSA population versus those obtained with blood cultures during three study periods. Over the 5 years from 1999 to 2003, 1,580 blood culture isolates from 1,495 patients were analysed. Typeability and discriminatory indices were as follows: AR typing, 1 and 0.97; phage typing, 0.29 and 0.89; PFGE, 0.99 and 0.95; AR-PFG typing, 1 and 0.95. The most frequently occurring AR-PFG types were 06-01, 07-02, 13-00, and 14-00 and were exhibited by 57, 7, 14, and 12% of isolates, respectively. During the study period, the distribution of AR-PFG type changed markedly, with the prevalence of one type (AR-PFG 06-01) increasing by 880%, from 22% (39/181) in 1999 to 80% (343/430) in 2003. Investigation of whether epidemiological types among blood culture isolates of MRSA were representative of the total MRSA population showed that there was no significant difference in most instances. MLST and SCCmec typing showed that AR-PFG types 06-01, 07-02, 13-00, and 14-00 were ST22-MRSA-IV, ST36-MRSA-II, ST8-MRSA-IID, and ST8-MRSA-IIE, respectively.

Emergence of Hospital- and Community-Associated Panton-Valentine Leukocidin-Positive Methicillin-Resistant Staphylococcus aureus Genotype ST772-MRSA-V in Ireland and Detailed Investigation of an ST772-MRSA-V Cluster in a Neonatal Intensive Care Unit

“…In 1989 the most frequently occurring strain was ST239-MRSA-III, while in 1993 this had changed to ST8-MRSA-II (31,37). The most recent change in strains occurred in 1998, when the frequency of ST22-MRSA-IV had increased, and this strain now accounts for 80% of MRSA bloodstream infections investigated in the NMRSARL under the European Antimicrobial Resistance Surveillance Network (EARS-Net; previously EARSS) in 2003 (32). Although the predominant MRSA strain causing bloodstream infections has not changed since 1998, the proportion of S. aureus isolates that are resistant to methicillin fell from 41.9% in 2006 to 24.3% in 2010 (4).…”

“…All MRSA isolates were characterized by a biotyping method that investigated hydrolysis of urea, hydrolysis of Tween 80, and pigment production, all as described previously (32).…”

“…DNA macrorestriction digestion analysis followed by pulsed-field gel electrophoresis (PFGE) was performed on all MRSA isolates as described previously (33). Banding patterns were analyzed using the GelCompar software package (version 4.1; Applied Maths, Belgium) (32), and the final interpretation of the differences between PFGE patterns was performed as recommended by Tenover et al (44).…”

Evaluation of the IDI-MRSA assay on the SmartCycler real-time PCR platform for rapid detection of MRSA from screening specimens

“…LoD assays were performed on four MRSA isolates that exhibited a range of oxacillin minimum inhibitory concentrations (MIC) and were representative of strains currently or recently prevalent in Ireland [5,6]. These isolates comprised: (1) ST22-MRSA-IV, MIC >256 mg/l; (2) ST22-MRSA-IV, MIC 32 mg/l; (3) ST8-MRSA-IID, MIC >256 mg/l; (4) an isolate with an MIC of 4.0 mg/l that was mecA-positive by PCR and expressed PBP2a but for which multilocus sequence typing (MLST) data and SCCmec-typing results were unavailable.…”

“…LoDs for both culture methods were calculated on the basis of growth of >1 colony on a single subculture medium or ≥1 colony on more than one subculture medium and were expressed as the average of the counts obtained with the four isolates. [5,6]. Details of these isolates are summarised in Table 1.…”