Molecular characterization of sporadically-occurring nosocomial methicillin-resistant Staphylococcus aureus isolates from Ireland

Abstract number: P1712

Kinnevey P., Shore A., Rossney A., Coleman D.

Objective: Ireland has a high prevalence of MRSA and the predominant strains from Irish hospitals since the 1970s have been well characterised. However, there are no published data on sporadically-occurring MRSA isolates from Ireland. This study aimed to undertake detailed molecular characterisation of representatives of such sporadically-occurring MRSA.

Methods: Forty-seven MRSA isolates recovered from patients in Irish hospitals between 2000 and 2006 with unfamiliar antibiogram-resistogram or pulsed-field gel electrophoresis typing patterns underwent spa and SCCmec typing. Representatives of each spa and SCCmec type combination underwent multilocus-sequence typing (MLST).

Results: The 47 MRSA isolates yielded 21 spa types; the most prevalent of which were t032 (10/47, 21%), t190 (5/47, 11%), t242 (5/47, 11%) and t008 (4/47, 9%). Thirty-one isolates (66%) harboured SCCmec II, III or IV, or previously described subtypes, while 26% (12/47) yielded additional SCCmec amplimers indicative of novel SCCmec I, II, IV and V subtypes. Four isolates (9%) harboured potentially novel SCCmec elements and failed to yield ccr and/or mec amplimers. The 33 spa and SCCmec type combinations identified belonged to 22 sequence types (STs), with ST8 predominating (8/33, 24%). Four STs were represented by more than one spa type: (a) ST8; t190, t064, t1209 and t008 (b) ST22; t032, t022 and t2951 (c) ST36; t012 and t018 (d) ST5; t109 and t242. Conversely, six spa types were represented by more than one ST; in three instances the STs belonged to the same clonal complex (CC) (a) t008; CC8 (ST8, ST983, ST985 and ST1337), (b) t242; CC5 (ST5 and ST1435), (c) t127; CC1 (ST1115 and ST1336) but in three instances the STs belonged to different CCs (a) t002; CC6 (ST979) and CC5 (ST930 and ST100) (b) t032; CC616 (ST984) and CC22 (ST22) (c) t018; CC30 (ST36) and CC731 (ST982). spa, SCCmec and MLST typing yielded 36 type combinations, belonging to 12 CCs, among the 47 isolates, with CC8 predominating (28%; 13/47), followed by CC22 (11/47, 23%), CC5 (10/47, 21%), CC1 (3/47, 6%), CC30 (2/47, 4%) and CC45 (2/47, 4%). Six CCs (CC731, CC6, CC862, CC779, CC361 and CC616) were represented by single isolates.

Conclusions: This study revealed extensive genetic diversity among Irish 'sporadic' nosocomial MRSA. The considerable variability within SCCmec of these isolates further highlights the diversity of SCCmec and represents a significant gene pool for recombination events with other SCCmec elements.