Emergence and dissemination of a community-associated methicillin-resistant Panton-Valentine leucocidin-positive Staphylococcus aureus clone sharing the sequence type 5 lineage with the most prevalent nosocomial clone in the same region of Argentina

Abstract

Epidemiological surveillance for community-associated methicillin-resistant Staphylococcus aureus revealed prevalences of 33% and 13% in pediatric and adult patients, respectively, in Cordoba, Argentina, in 2005. This study describes for the first time the emergence and dissemination of the sequence type 5 (ST5) lineage as the most prevalent clone (89%) (pulsed-field gel electrophoresis type I-ST5-staphylococcal cassette chromosome type IVa-spa type 311) harboring the Panton-Valentine leukocidin and enterotoxin A genes.

FIG. 1.

(A) SmaI restriction patterns from representative CA-MRSA and CA-MSSA strains of each subtype and representative HA-MRSA strains of more prevalent subtypes were digitized, presented schematically (middle), and analyzed to calculate the Dice coefficient of correlation and to generate a dendrogram (left) by the unweighted-pair group method using average linkage clustering. Isolates differing by up to six fragments were considered to be subtypes of a given clonal type, and the similarity cutoff was 80%. Genotypes are denoted as subtype (PFGE)-ST (by MLST)-MRSA/MSSA-SCCmec type (right). Gs and Gr are representative strains of the A1 subtype showing susceptibility and resistance to gentamicin, respectively. Nc-8325 refers to the NCTC 8325 control strain. (B) PFGE DNA patterns of representative subtypes of the type I major clone, comparing MRSA (I1, I2, and I4) and MSSA (I5 and I6) strains isolated in Cordoba, Argentina, during 2006. White arrows indicate a single band of difference between I6 (CA-MSSA) and I2 (CA-MRSA) as well as between I5 (CA-MSSA) and I1 (CA-MRSA). The SCCmec IVa element was detected by PCR within the 190-kb band found in the CA-MRSA strains but not in the CA-MSSA-derived 150-kb band (data not shown). Subtypes are indicated at the top by numbers. L, DNA molecular size markers in kb (lambda DNA ladder; Promega). Nc, NCTC 8325 control strain. (C) Annual distribution of infections caused by CA-MRSA strains belonging to the type I clonal family from 2001 to 2006. n, total number of strains characterized as PFGE type I recovered in each year, as indicated. Each genotype was named as subtype (PFGE)-ST (by MLST)-SCCmec type-spa type. The more prevalent genotype among CA-MRSA strains is shaded in gray. (D). Proposed genetic events leading to the emergence of different CA-MRSA and HA-MRSA clones within the CC5 lineage in Cordoba, Argentina. Different HA-MRSA and CA-MRSA clones are indicated by boxes. Shaded and white boxes represent MSSA and MRSA, respectively. Full genotypes are given for the ST, SCCmec type, spaA repeats/RIDOM spa type, PFGE type or subtypes (I1 to I6), and presence of pvl and sea genes. Proposed evolutionary pathways are indicated by filled arrows. Strains diversification through the horizontal transfer of pvl and sea genes and SCCmec allotypes as well as minor changes detected in spa type (differs only by deletion or duplication of one repeat) and in the PFGE type/subtype are indicated next to the arrows. Dashed boxes indicate PVL-positive CA-MRSA and CA-MSSA clones derived from the ancestral MSSA PVL-negative clone (double-lined box). The new CA-MRSA clone that emerged and disseminated in this region is indicated by a double-dashed box. Dashed arrows represent the evolutionary pathway of MRSA clones already proposed (18).