Dissemination of methicillin-resistant Staphylococcus aureus USA300 sequence type 8 lineage in Latin America

Abstract

Background: Methicillin-resistant Staphylococus aureus (MRSA) is an important nosocomial and community-associated (CA) pathogen. Recently, a variant of the MRSA USA300 clone emerged and disseminated in South America, causing important clinical problems.

Methods: S. aureus isolates were prospectively collected (2006-2008) from 32 tertiary hospitals in Colombia, Ecuador, Peru, and Venezuela. MRSA isolates were subjected to antimicrobial susceptibility testing and pulsed-field gel electrophoresis and were categorized as health care-associated (HA)-like or CA-like clones on the basis of genotypic characteristics and detection of genes encoding Panton-Valentine leukocidin and staphylococcal cassette chromosome (SCC) mec IV. In addition, multilocus sequence typing of representative isolates of each major CA-MRSA pulsotype was performed, and the presence of USA300-associated toxins and the arcA gene was investigated for all isolates categorized as CA-MRSA.

Results: A total of 1570 S. aureus were included; 651 were MRSA (41%)--with the highest rate of MRSA isolation in Peru (62%) and the lowest in Venezuela (26%)--and 71%, 27%, and 2% were classified as HA-like, CA-like, and non-CA/HA-like clones, respectively. Only 9 MRSA isolates were confirmed to have reduced susceptibility to glycopeptides (glycopeptide-intermediate S. aureus phenotype). The most common pulsotype (designated ComA) among the CA-like MRSA strains was found in 96% of isolates, with the majority (81%) having a < or =6-band difference with the USA300-0114 strain. Representative isolates of this clone were sequence type 8; however, unlike the USA300-0114 strain, they harbored a different SCCmec IV subtype and lacked arcA (an indicator of the arginine catabolic mobile element).

Conclusion: A variant CA-MRSA USA300 clone has become established in South America and, in some countries, is endemic in hospital settings.

Figure 1

Pulsed field gel electrophoresis (PFGE) of CA-like MRSA isolate representatives of the ComA pulsotype from different countries. Lane 1, S. aureus NCTC 8325; lane 2, Col-177 (Colombia); lane 3, HUV-01 (Colombia); lane 4, CA-12 (Colombia); lane 5, C609 (Colombia), lane 6, V2125 (Venezuela); lane 7, E403 (Ecuador); lane 8, USA300-0114 strain; lane 9, USA300 varrying SCCmec IVb (Nebraska); lane 10, USA400 (N. Dakota); lane 11, S. aureus NCTC 8325.