Epidemiologic distribution of the arginine catabolic mobile element among selected methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolates

Abstract

We tested 214 Staphylococcus aureus isolates for the arcA locus of the arginine catabolic mobile element (ACME). All USA300 SCCmec IVa isolates, but no isolates containing other SCCmec subtypes, were arcA positive. arcA was also detected in selected methicillin-susceptible USA300 and methicillin-resistant USA100 isolates. DNA sequence analysis confirmed the integration of ACME in orfX.

FIG. 1.

SmaI-digested chromosomal DNA from S. aureus isolates USA300-0114 (mecA positive, arcA positive) (lane 1), USA300-0283 (mecA negative, arcA positive) (lane 2), and USA300-0020 (mecA negative, arcA negative) (lane 3), analyzed by BioNumerics, version 4.1. Relative band sizes (in kilobases) and the position of the SmaI fragment containing mecA and arcA are indicated.

FIG. 2.

Diagram of a portion of the published USA300 chromosomal sequence (GenBank accession number CP000255) showing ACME, SCCmec, and orfX (5). The numbers above the diagram are reference positions in the published USA300 genome sequence that indicate the junctions between adjacent chromosomal sequences and ACME, ACME and SCCmec, and SCCmec and orfX. Shaded arrows indicate the locations of the primers (AcmeR, located at 58109 to 57914, and Xsau325, located at 34189 to 34036) used to amplify the ACME-orfX junction in two methicillin-susceptible, arcA-positive USA300 isolates. The DNA sequences of the 333-bp ACME-orfX junction regions from the two isolates were identical and showed sequence homology to ACME (left-hand box) (sequence includes the 15-bp repeat DR_ACME-R [bracketed and boldfaced]) and orfX (right-hand box) (sequence does not contain DR_SCCmec-R), but no SCCmec sequences were detected. The numbers in the boxes indicate the reference positions in the USA300 genome sequence (5).