Staphylococcus aureus agrGenotypes with Enterotoxin Production Capabilities Can Resist Neutrophil Bactericidal Activity

Abstract

Staphylococcus aureus pathogenicity is mainly due to the production of a number of secreted and cell surface-associated proteins under the regulation of the agr gene. A region of the agr gene was used to subgroup S. aureus strains according to restriction fragment length polymorphisms. Additionally, strains were subtyped according to the coagulase gene in order to strengthen discriminatory power. Virulence capabilities of agr genotype subgroups were evaluated using an in vitro neutrophil bactericidal assay, which showed that prevalent genotypes were significantly better at evading this primary host defense. Multiplex PCR was then used to detect enterotoxin genes among the genotype subgroups in order to determine possible virulence candidates that enable strains to combat neutrophil killing. The prevalent genotype strains were found to possess higher production capabilities for enterotoxin A than did low-prevalence strains. The significance of enterotoxin A production capabilities in affecting pathogenicity of S. aureus strains was evaluated and found to have a profound effect on neutrophil killing abilities. The use of a large epidemiological database as a tool for subgrouping strains with varying degrees of pathogenicity has allowed the identification of relevant and previously undefined virulence factors that affect a pathogen's capability to overcome host immune defenses.Staphylococcus aureus is a gram-positive bacterium that has remained a persistent pathogen, causing such infections as endocarditis, meningitis, and toxic shock syndrome in humans. S. aureus also is the leading cause of intramammary infections (mastitis), especially in dairy animals, from whose milk it is frequently isolated (38). Neutrophils are the principle line of defense during the initial stages of mastitis, and the ability of these cells to phagocytize and kill invading bacteria is critically related to the establishment of new intramammary infections (26). Therefore, any bacterially derived component that may compromise neutrophil function would constitute an important virulence factor in the pathogenesis of S. aureus mastitis. Although a number of different virulence factors involved in the pathogenesis of S. aureus mastitis have been identified (38), the differential expression of these factors as it relates to field strain prevalence of S. aureus genotypes has not been investigated. A better understanding of the epidemiology of S. aureus mastitis as it pertains to virulence will provide insight concerning important host-pathogen interactions during the pathogenesis of disease.Subtyping is an important tool for epidemiologic investigation of bacterial infections. In the past decade, numerous molecular techniques such as multilocus enzyme electrophoresis, phage typing, plasmid DNA restriction patterns, random amplified polymorphic DNA ribotyping, and coagulase genotyping have proved useful in identification and comparison of S. aureus isolates in epidemiological studies (7,21,29,35,36). However, very few studies have identified S. au...

Analysis of the Genetic Variability of Genes Encoding the RNA III-Activating Components Agr and TRAP in a Population of Staphylococcus aureus Strains Isolated from Cows with Mastitis

“…tions within groups were also found (20,25,28,29). In this work, we identified 14 different agr restriction types among the analyzed strains.…”

Prevalence of agr Specificity Groups among Staphylococcus aureus Strains Colonizing Children and Their Guardians

“…S. aureus was isolated (one strain per subject) from 96 of 275 (35%) children and from 64 of 225 (28%) guardians (13). agr specificity groups were identified by PCR amplification of the hypervariable domain of the agr locus using oligonucleotide primers specific for each of the four major specificity groups (obviating the need for restriction fragment length polymorphism analysis commonly employed in previous studies [7,10,14]). A forward primer, pan-agr (5Ј-ATGCACATGGTGCACATGC-3Ј), corresponding to conserved sequences from the agrB gene, was used in all reactions (Fig.…”

Comparative Analysis of agr Locus Diversification and Overall Genetic Variability among Bovine and Human Staphylococcus aureus Isolates

“…This type of bacterial interference is unusual, because it affects the expression of a subset of genes rather than inhibiting growth. Diverse works have noted the existence of distinct agr alleles, as defined with agr restriction fragment length polymorphism, within agr groups both in clinical S. aureus isolates that originated with humans and in those from cows (2,15,16,19,24,29). In a recent study, one of us identified 12 distinct agr alleles in an epidemiologically unrelated collection of bovine mastitis isolates.…”