Distribution of Virulence Factors and Resistance Determinants in Three Genotypes of Staphylococcus argenteus Clinical Isolates in Japan

Abstract

Staphylococcus argenteus, a novel staphylococcal species independent of S. aureus, causes a wide spectrum of infectious diseases. As detection of this species from humans and animals has been increasingly reported worldwide, its growing virulence and drug resistance via external genetic determinants has become concerning. In this study, the prevalence and genetic characteristics of virulence factors and drug resistance determinants were investigated for 82 S. argenteus clinical isolates in Hokkaido, Japan, for a one-year period starting in August 2019. These S. argenteus isolates corresponded to 0.66% of the total number of S. aureus isolates collected in the same period. The most prevalent genotype was sequence type (ST) 2250 and staphylocoagulase (coa) genotype XId (45.1%, n = 37), followed by ST1223-coa XV (30.5%, n = 25) and ST2198-coa XIV (24.4%, n = 20). Panton-Valentine leukocidin genes (lukS-PV-lukF-PV) were identified in a single ST2250 isolate. Only ST1223 isolates had the enterotoxin gene cluster (egc-2), seb, and selw (detection rate; 100%, 60%, and 84%, respectively), while sec, sey, sel26-sel27, tst-1 were only detected in ST2250 isolates (detection rate; 10.8%, 100%, 67.6%, and 10.8%, respectively). ST2198 isolates harbored selx at a significantly higher rate (60%) than isolates of other STs. Although most of S. argenteus isolates were susceptible to antimicrobials examined, ST2198 showed higher resistance rates to penicillin, macrolides, and aminoglycosides than other STs, and it harbored various resistance genes such as blaZ, erm(C), msr(A), lnuA, and aac(6')-Ie-aph(2″)-Ia. Only one ST2250 isolate possessed SCCmec-IVc, showing resistance to oxacillin. blaZ was the most prevalent determinant of resistance in the three STs and belonged to two plasmid groups and a chromosomal group, suggesting its diverse origin. lnu(A) in ST2198 isolates was assigned to a major cluster with various staphylococcal species. The present study indicates that the prevalence of virulence factors and drug resistance profile/determinants differ depending on the lineage (ST) of S. argenteus.

Keywords: Japan; ST; Staphylococcus argenteus; enterotoxin; resistance gene; virulence factors.

Figure 1

Phylogenetic dendrogram of blaZ (a) and lnu(A) (b), constructed by the maximum likelihood method using MEGA X. The tree was statistically supported by bootstrapping with 1000 replicates, and genetic distances were calculated by the Kimura two-parameter model. Variation scale is provided at bottom. Percentage bootstrap support is indicated by values at each node (values <80 are omitted). Closed black and blue circles indicate S. argenteus isolates analyzed in the present study and strains available in the GenBank database, respectively. Inverted triangles denote genes of representative BlaZ protein sequence types (PS types) described previously [46], by which P (P1, P2)-, C-, and PC-groups were assigned as shown on the right (a). Cluster numbers 1–3 and subcluster 1a are shown on the right (b). The species name S. aureus was omitted (a), and GenBank accession numbers are shown in parenthesis followed by strain names.

Figure 1

Phylogenetic dendrogram of blaZ (a) and lnu(A) (b), constructed by the maximum likelihood method using MEGA X. The tree was statistically supported by bootstrapping with 1000 replicates, and genetic distances were calculated by the Kimura two-parameter model. Variation scale is provided at bottom. Percentage bootstrap support is indicated by values at each node (values <80 are omitted). Closed black and blue circles indicate S. argenteus isolates analyzed in the present study and strains available in the GenBank database, respectively. Inverted triangles denote genes of representative BlaZ protein sequence types (PS types) described previously [46], by which P (P1, P2)-, C-, and PC-groups were assigned as shown on the right (a). Cluster numbers 1–3 and subcluster 1a are shown on the right (b). The species name S. aureus was omitted (a), and GenBank accession numbers are shown in parenthesis followed by strain names.