Array-based typing of community- and healthcare associated MRSA and occurrence of epidemic strains in eastern Saxony

Abstract number: 1733_801

Monecke S., Jatzwauk L., Weber S., Ehricht R.

Objectives: Objective of the study was to test a diagnostic microarray under routine conditions and to obtain insights into the epidemiology of Community- and Healthcare Associated MRSA (CA- and HA-MRSA) in eastern Saxony.

Methods: Multiplex linear DNA-amplification and subsequent microarray hybridisation were performed which allowed to detect 144 genes or distinct allelic variants simultaneously. All relevant exotoxins, antimicrobial resistance determinants, the allelic variants of agr, as well as staphylococcal exotoxin-like genes were included. Hybridisation profiles were used for assignment to epidemic strains. The study was performed in eastern Saxony including an university hospital, a long-term rehabilitation facility and three county hospitals. For the study of HA-MRSA, random samples from routine diagnostics as well as isolates from outbreak investigations were tested. Additionally, all cases were included in which PVL-positive CA-MRSA were suspected to be involved.

Results: Most prevalent HA-MRSA strains are South German EMRSA, New York/Japan Clone (``Rhine-Hessen EMRSA''), Berlin EMRSA, and EMRSA-15 (``Barnim Epidemic Strain''). Other strains are by comparison rather rare. Isolated cases of infections with PVL-negative ST1 and ST8 MRSA were detected. ST8 Hannover ERMSA which used to be very common in the 1990s virtually disappeared, and EMRSA 16 was completely absent.

CA-MRSA were not found prior to 2004. Still now, cases are rather sporadic. The most prevalent strain is the PVL-positive ST80-MRSA IV (four detected cases in 2004, one outbreak including four cases in 2005, two cases in 2006). First infections with PVL-positive ST8-MRSA IV (USA300, one case in 2005 and one in 2006) and ST30-MRSA IV (WSPP strain, one case in 2006) were also diagnosed. PVL-positive ST1-MRSA IV (USA400) were not detected yet.

Conclusions: The DNA-microarray proved to be a powerful tool for epidemiological monitoring and identification of epidemic strains. In contrast to other typing methods it facilitated the assessment of virulence and antibiotic susceptibility of a given isolate within a single experiment. In the region studied, the majority of HA-MRSA infections was caused by a few epidemic strains. Emerging strains (New York/Japan Clone as well as SCCmecIV strains EMRSA-15 and Berlin EMRSA) play a major role. PVL-positive CA-MRSA are still very rare, and the most important strain is ST80-MRSA IV.