Affiliation:
1. Department of Infectious Diseases, St. George's Hospital Medical School, London SW17 0RE, United Kingdom
Abstract
ABSTRACT
Staphylococcus aureus
strains often carry in their genomes virulence genes that are not found in all strains and that may be carried on discrete genetic elements. Strains also differ in that they carry one of four classes of an accessory gene regulator (
agr
) locus, an operon that regulates virulence factor expression and that has been proposed to be a therapeutic target. To look at their distribution among hospital strains, we investigated 38 methicillin-sensitive
S. aureus
isolates, classifying the isolates by
agr
class and screening them for the presence and restriction fragment length polymorphisms (RFLPs) of 12 core and 14 accessory virulence genes. Twenty-three (61%) were
agr
class I, 10 (26%) were
agr
class II, and 5 (13%) were
agr
class III. None were
agr
class IV. The
S. aureus
strains had distinguishable RFLP profiles, although clusters of isolates with clearly related core gene profiles were found among our strains, including all five
agr
class III strains, two sets of six strains within
agr
class I, and six strains within
agr
class II. Within these clusters there was evidence of horizontal acquisition and/or loss of multiple accessory virulence genes. Furthermore, two isolates from the same patient were identical except for the presence of the
sea
gene, indicating that movement of mobile elements may occur in vivo. Several strong correlations with the carriage of virulence genes between strains were seen, including a positive correlation between
tst
and
agr
class III and negative correlations between
tst
and
lukE-splB
and between
lukE-splB
and
seg-sei
. This suggests that the core genome or the presence of accessory genetic elements within a strain may influence acquisition and loss of other elements encoding virulence genes.
Publisher
American Society for Microbiology
Cited by
144 articles.
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