Low prevalence of mupirocin resistance among Staphylococcus aureus clinical isolates from a Chinese tertiary hospital

Mupirocin for Skin Infection: Clinical Experience from China

Mupirocin, an antibiotic produced by Pseudomonas fluorescens, is mainly used for the topical treatment of various skin and soft tissue infections caused by Staphylococcus (including methicillin-resistant Staphylococcus aureus) and Streptococcus around the world for decades. Nevertheless, the clinical application scope of mupirocin varies in different countries due to differences in their medical policies, prescription types, and drug resistance. According to the experience of Chinese doctors in the past few years, mupirocin presented low drug resistance rates, and could be used as a treatment option for various primary infections and secondary infections, with antibacterial effects in a broad application. In this review, we summarized the experience of mupirocin used in the Chinese population and discussed its clinical value to provide novel insights and inspiration for physicians.

Comparative efficacy of vancomycin in treating ST5 and ST764 methicillin-resistant Staphylococcus aureus infections in adult patients

IMPORTANCE

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that is resistant to multiple drugs and can cause serious infections. In recent years, one of the most widespread strains of MRSA worldwide has been the clonal complex 5 (CC5) type. Sequence type 5 (ST5) and ST764 are two prevalent CC5 strains. Although ST5 and ST764 are genotypically identical, ST764 is classified as a hybrid variant of ST5 with characteristics of community-associated MRSA (CA-MRSA). In contrast to ST5, ST764 lacks the tst and sec genes but carries the staphylococcal enterotoxin B (seb) gene. Vancomycin is commonly used as the first-line treatment for MRSA infections. However, it is currently unclear whether the genetic differences between the ST5 and ST764 strains have any impact on the efficacy of vancomycin in treating MRSA infections. We conducted a prospective observational study comparing the efficacy of vancomycin against ST5-MRSA and ST764-MRSA in five hospitals in China. There were significant differences in bacteriological efficacy between the two groups, with virulence genes, such as the tst gene, being a risk factor for bacterial persistence (adjusted odds ratio, 4.509; 95% confidence interval, 1.216 to 16.724; P = 0.024). In the future, it may be necessary to consider personalized vancomycin treatment strategies based on the genetic characteristics of MRSA isolates.

Phylogenetic analysis and virulence characteristics of methicillin-resistant Staphylococcus aureus ST764-SCCmec II: an emerging hypervirulent clone ST764-t1084 in China

Previous studies have shown that the increased prevalent ST764 clone in China, Japan, and other Asian areas. However, the knowledge of the genetic features and virulence characteristics of methicillin-resistant Staphylococcus aureus (MRSA) ST764 in China is still limited. In this study, we identified 52 ST764-SCCmec type II isolates collected from five cities in China between 2014 and 2021. Whole genome sequencing showed that the most common staphylococcal protein A (spa) types of ST764 in China were t002 (55.78%) and t1084 (40.38%). Virulence assays showed that ST764-t1084 isolates had high haemolytic activity and α-toxin levels. Of the critical regulatory factors affecting α-toxin production, only the SaeRS was highly expressed in ST764-t1084 isolates. Mouse abscess model indicated that the virulence of ST764-t1084 isolates was comparable to that of S. aureus USA300-LAC famous for its hypervirulence. Interestingly, ST764-t002 isolates exhibited stronger biofilm formation and cell adhesion capacities than ST764-t1084 isolates. This seems to explain why ST764-t002 subclone has become more prevalent in China in recent years. Phylogenetic analysis suggested that all ST764 isolates from China in Clade III were closely related to KUN1163 (an isolate from Japan). Notably, genomic analysis revealed that the 52 ST764 isolates did not carry arginine catabolic mobile element (ACME), which differed from ST764 isolates in Japan. Additionally, most ST764 isolates (69.23%) harboured an obvious deletion of approximately 5 kb in the SCCmec II cassette region compared to KUN1163. Our findings shed light on the potential global transmission and genotypic as well as phenotypic characteristics of ST764 lineage.

Dissemination of Methicillin-Resistant Staphylococcus aureus Sequence Type 764 Isolates with Mupirocin Resistance in China

Mupirocin, a topical antimicrobial agent, is an important component in the eradication of methicillin-resistant Staphylococcus aureus (MRSA) colonization. The molecular characteristics of 46 mupirocin-resistant MRSA (MR-MRSA) clinical isolates were analyzed by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec element (SCCmec) typing, spa typing, and analysis of virulence genes. All 26 MRSA isolates with low-level mupirocin resistance possessed a V588F mutation in ileS. Among 20 MRSA isolates with high-level resistance to mupirocin, all carried mupA; 2 isolates also possessed the V588F mutation in ileS, and 1 possessed the V631F mutation in ileS (isoleucyl-tRNA synthetase). The majority of MR-MRSA isolates were resistant to erythromycin, clindamycin, tetracycline, ciprofloxacin, and gentamicin, but the rates of resistance to rifampin and fusidic acid were 8.7% and 6.5%, respectively. Eight sequence types (STs) were found among the 46 MR-MRSA isolates, of which ST764 was the most prevalent (76.1%). The most frequent spa type identified was t1084 (52.2%). The SCCmec type most frequently found was type II (80.4%). The most common clone among low-level MR-MRSA isolates was ST764-MRSA-SCCmec type II-t1084 (23 isolates), while ST764-MRSA-SCCmec type II-t002 (9 isolates) was the most common clone among high-level MR-MRSA isolates. Additionally, all toxin genes except the seb gene were not identified among ST764 isolates. Among clonal complex 5 (CC5) isolates, immune evasion cluster (IEC)-associated genes (chp, sak, and scn) and seb were present in ST764 but absent in ST5, while sec, sel1, tsst-1, and hlb genes were identified in ST5 but absent in ST764. In conclusion, the spread of CC5 clones, especially a novel ST764-MRSA-SCCmec type II-t1084 clone with high-level resistance to mupirocin, was responsible for the increase in mupirocin resistance. These findings indicated that the emergence of the ST764 MR-MRSA clone involves a therapeutic challenge for treating serious MRSA infections. IMPORTANCE Mupirocin, a topical antibiotic that is commonly used for the nasal decolonization of MRSA and methicillin-sensitive Staphylococcus aureus in hospital settings and nursing homes, was introduced as a highly effective antibiotic against MRSA. Mupirocin acts by competitively binding isoleucyl-tRNA synthetase, thereby disrupting protein synthesis. This drug shows bacteriostatic and bactericidal activity at low and high concentrations, respectively. However, with the increase in mupirocin use, low-level and high-level resistance during nasal mupirocin treatment has been reported. In a previous study, the proportion of MRSA strains with high-level mupirocin resistance in a Canadian hospital increased from 1.6% in the first 5 years of surveillance (1995 to 1999) to 7.0% (2000 to 2004).

Prevalence and molecular characterization of methicillin-resistant Staphylococcus aureus with mupirocin, fusidic acid and/or retapamulin resistance

Background

The data on the prevalence of resistance to mupirocin (MUP), fusidic acid (FA) and retapamulin (RET) in methicillin-resistant Staphylococcus aureus (MRSA) from China are still limited. This study aimed to examine these three antibiotics resistance in 1206 MRSA clinical isolates from Eastern China. Phenotypic MUP, FA and RET resistance was determined by minimum inhibitory concentrations (MICs), and genotypic by PCR and DNA sequencing of the mupA/B, fusB-D, cfr, vgaA/Av/A_LC/B/C/E, lsaA-C/E and salA and mutations in ileS, fusA/E, rplC, and 23S RNA V domain. The genetic characteristics of resistance isolates were conducted by pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).

Results

Overall MRSA MUP, FA and RET resistance was low (5.1, 1.0 and 0.3%, respectively). MupA was the mechanism of high-level MUP resistance. All low-level MUP resistance isolates possessed an equivocal mutation N213D in IleS; of these, 2 reported an additional V588F mutation with an impact on the Rossman fold. FusA mutations, such as L461K, H457Q, H457Y and V90I were the primary FA mechanisms among high-level resistance isolates, most of which also contained fusC; however, all low-level resistance strains carried fusB. Except lsaE gene detected in one isolate, no other resistance mechanisms tested were found among RET-resistant isolates. Additionally, sixteen PFGE types (A-P) were observed, among which type B was the most common (49/76, 64.5%), followed by types E and G (4/76, 5.3% each) and types C and M (3/76, 3.9% each). All resistant strains were divided into 15 ST types by MLST. ST764 (24/76, 31.6%), ST630 (11/76, 14.5%), ST239 (9/76, 11.8%) and ST5 (7/76, 9.2%) were the major types. PFGE type B isolates with the aforementioned STs were mainly found in mupirocin resistant isolates.

Conclusions

MUP, FA and RET exhibited highly activity against the MRSA isolates. Acquired genes and chromosome-borne genes mutations were responsible for MUP and FA resistance; however, the mechanism for some RET-resistant isolates remains to be further elucidated. Also, the surveillance to MUP in MRSA should be strengthened to prevent elevated resistance due to the expansion of clones.