Spread of Serratia marcescens Coharboring aac(6′)-Ib-cr, blaCTX-M, armA, and blaOXA-1 Carried by Conjugative IncL/M Type Plasmid in Korean Hospitals

The prevalence of aac(6')-Ib-cr and its associated genes and mobile elements was investigated in Serratia marcescens collected from 12 hospitals in Korea in 2005 and 2006. A total of 215 isolates (from 166 and 149 isolates collected in 2005 and 2006, respectively) were included in the study. Aac(6')-Ib-cr was detected in only two isolates collected in 2005 and in 12 isolates collected from three hospitals in 2006. All 12 isolates carried class 1 integron and coharbored bla(CTX-M) and armA. Bla(OXA-1) and ISCR1 were detected in 10 and 8 isolates, respectively. All 12 isolates carried IncL/M type plasmid and 6 of them also carried IncA/C type plasmid. Conjugal transfer was successful for 9 of 12 aac(6')-Ib-r, all 12 bla(CTX-M), 8 of 12 armA, and 6 of 10 bla(OXA-1). Of the 12 transconjugants, IncL/M type plasmid, IntI1, ISEcp1, and ISCR1 were detected in 12, 9, 12, and 8, respectively. The transferability of aac(6')-Ib-cr, armA, and bla(OXA-1) was 100% for isolates harboring ISCR1, against 25%, 0%, and 0%, respectively, for isolates not harboring ISCR1. Both clonal and horizontal transfer were demonstrated by pulsed-field gel electrophoresis and plasmid profile analysis, respectively. Stringent infection control practices and further investigation of association between mobile elements and resistance genes are warranted.