Antimicrobial resistance and prevalence of CvfB, SEK and SEQ genes among Staphylococcus aureus isolates from paediatric patients with bloodstream infections

Abstract

Staphylococcus aureus (S. aureus) is one of the most frequently isolated pathogens in neonatal cases of early and late-onset sepsis. Drug resistance profiles and carriage of toxin genes may affect the treatment and outcome of an infection. The present study aimed to determine the antimicrobial resistance patterns and frequencies of the toxin-associated genes conserved virulence factor B (CvfB), staphylococcal enterotoxin Q (SEQ) and staphylococcal enterotoxin K (SEK) among S. aureus isolates recovered from paediatric patients with bloodstream infections (BSIs) in Guangzhou (China). Of the 53 isolates, 43.4% were methicillin-resistant S. aureus (MRSA), and resistance rates to penicillin, erythromycin, clindamycin, trimethoprim/sulfamethoxazole, tetracycline, and ciprofloxacin of 92.5, 66.0, 62.3, 13.2, 20.8 and 1.9% were recorded, respectively. However, no resistance to nitrofurantoin, dalfopristin/quinupristin, rifampicin, gentamicin, linezolid or vancomycin was detected. Resistance to erythromycin, clindamycin and tetracycline in the MRSA group was significantly higher than that in the methicillin-susceptible S. aureus (MSSA) group. No significant differences in antimicrobial resistance patterns were noted between two age groups (≤1 year and >1 year). The proportion of S. aureus isolates positive for CvfB, SEQ and SEK was 100, 34.0 and 35.8%, respectively, with 24.5% (13/53) of strains carrying all three genes. Compared with those in MSSA isolates, the rates of SEK, SEQ and SEK + SEQ carriage among MRSA isolates were significantly higher. Correlations were identified between the carriage of SEQ, SEK and SEQ + SEK genes and MRSA (contingency coefficient 0.500, 0.416, 0.546, respectively; P<0.01). In conclusion, MRSA isolated from the blood of paediatric patients with BSIs not only exhibited higher rates of antimicrobial resistance than MSSA from the same source, but also more frequently harboured SEK and SEQ genes. The combination of the two aspects influenced the dissemination of MRSA among children. The present study clarified the characteristics of BSI-associated S. aureus and enhanced the current understanding of the pathogenicity and treatment of MRSA.

Keywords: Staphylococcus aureus; antimicrobial resistance; bloodstream infections; conserved virulence factor B; methicillin-resistant Staphylococcus aureus; paediatric patients; staphylococcal enterotoxin K; staphylococcal enterotoxin Q.

Figure 1.

Electrophoresis of SEK, CvfB and SEQ PCR amplicons on a 2% agarose gel. Lanes: 1, negative control for SEK; 2–6, SEK PCR products from five different isolates of MRSA; 7, negative control for CvfB; 8–12, CvfB PCR products from the same isolates as those in lanes 2–6; 13, negative control for SEQ; 14–18, SEQ PCR products from the same isolates as those in lanes 2–6. PCR, polymerase chain reaction; CvfB, conserved virulence factor B; SEK, staphylococcal enterotoxin K; SEQ, staphylococcal enterotoxin Q.