Identification and Characterization of a Vancomycin Intermediate-Resistant Staphylococcus haemolyticus Isolated from Guangzhou, China

Background

Staphylococcus haemolyticus is an opportunistic pathogen that belongs to coagulase-negative Staphylococci (CoNS). Increasing infection and multi-drug resistance cases caused by this strain have been reported and thus it poses a great health threat.

Methods

The third-generation sequencing technology was performed on a S. haemolyticus SH-1 isolated from a clinical sample to analyze the drug resistance genes, which included vancomycin resistance related genes. In addition, antimicrobial susceptibility tests, transmission electron microscopy and Triton X-100 stimulated autolysis were conducted to understand its biological characteristics.

Results

The study shows that this clinical isolate is a vancomycin intermediate-resistant strain. Genome comparison also revealed that WalK(N70K) and WalK(R280Q) mutations may contribute to the vancomycin resistant phenotype. Besides, S. haemolyticus SH-1 exhibit common features of thicker cell wall and decreased autolytic activity.

Conclusion

S. haemolyticus SH-1 with WalKR mutations shows typical characteristics of vancomycin resistant strains. Combining the genome features and biological properties, our findings may provide important information for the understanding of the molecular mechanism of S. haemolyticus to vancomycin intermediate-resistance.

Adaptations of Vancomycin-Intermediate Sequence Type 72 Methicillin-Resistant Staphylococcus aureus for Daptomycin Nonsusceptibility

In Korea, the major clonal type of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is sequence type 72 (ST72) with staphylococcal cassette chromosome mec (SCCmec) type IV (ST72-MRSA-IV). In this study, we used a previously well-characterized isogenic pair of ST72 vancomycin (VAN) susceptible-and VAN intermediate-MRSA strains (VSSA303 and VISA072) and several VSSA strains complemented with plasmids expressing single-point mutated genes (dprAG196C, femAF92C, vraRE127K, and vraSRE127K) identified in the VISA strain. Using the strain set, we assessed the (1) susceptibilities to daptomycin (DAP) and cationic antimicrobial peptides (CAMPs), (2) alterations in cell envelope phenotypes, such as cell wall autolysis, surface positive charge, and membrane potential (ΔΨ), (3) transcriptional expression profiles of genes involved in surface charge regulation and changes of ΔΨ, and (4) cytokine stimulation profiles in murine macrophages. The vraRE127K mutation could enhance surface positive charge through mprF- and dltABCD-independent mechanisms with thickened cell wall. However, none of the single-point mutated genes increased DAP resistance. The DAP nonsusceptible (DAP-NS) phenotype observed in VISA072 strain likely resulted from the combined effects of low ΔΨ and increased positive surface charge. These results suggest that physicochemical alterations in cell envelope are involved in the survival response of DAP-NS VISA072 in sites of infections.

High diversity in SCCmec elements among multidrug-resistant Staphylococcus haemolyticus strains originating from paediatric patients; characterization of a new composite island

PURPOSE

Staphylococcus haemolyticus has emerged as a highly antimicrobial-resistant healthcare-associated pathogen, in particular for patients admitted to neonatal intensive care. The objective of this study was to study the nature of SCCmec types among MDR-SH strains isolated from paediatric patients.

METHODOLOGY

S. haemolyticus strains (n=60) were isolated from paediatric patients. Antibiotic resistance patterns were established using the disk agar diffusion and micro-broth dilution methods. SCCmec typing was performed using whole-genome sequencing (WGS) and an additional PCR analysis.

RESULTS

All S. haemolyticus isolates demonstrated multidrug resistance. Using WGS, various novel mec types and combinations of SCCmec types were found, including a new composite island [SCCmec type V (Vd)+SCC cad/ars/cop] comprising 30 % of the strains. SCCmec type V was identified in 23 % of the isolates. A combination of the mecA gene enclosed by two copies of IS431 and absence of the mecRI and ccr genes was identified in 11 strains. In total, mecA regulatory genes were absent in all SH isolates used in this study.

CONCLUSION

A high diversity of SCCmec elements with the prevalence of a new composite island was determined among MRSH strains. The structure of the composite island represented by MDR-SH strains in this study, in combination with the presence of a restriction-modification system type III, is described for the first time in this study. The presence of an 8 bp direct repeat (DR) and the sequences flanking the DR may support the integration of the mecA gene complex as a composite transposon (IS431-mecA-IS431) independently from recombinase genes.

Teicoplanin resistance in Staphylococcus haemolyticus is associated with mutations in histidine kinases VraS and WalK

We investigated the genetic basis of glycopeptide resistance in laboratory-derived strains of S. haemolyticus with emphasis on differences between vancomycin and teicoplanin. The genomes of two stable teicoplanin-resistant laboratory mutants selected on vancomycin or teicoplanin were sequenced and compared to parental S. haemolyticus strain W2/124. Only the two non-synonymous mutations, VraS Q289K and WalK V550L were identified. No other mutations or genome rearrangements were detected. Increased cell wall thickness, resistance to lysostaphin-induced lysis and adaptation of cell growth rates specifically to teicoplanin were phenotypes observed in a sequenced strain with the VraS Q289K mutation. Neither of the VraS Q289K and WalK V550L mutations was present in the genomes of 121S. haemolyticus clinical isolates. However, all but two of the teicoplanin resistant strains carried non-synonymous SNPs in vraSRTU and walKR-YycHIJ operons pointing to their importance for the glycopeptide resistance.

The SAV1322 gene from Staphylococcus aureus: genomic and proteomic approaches to identification and characterization of gene function

Background

Bacterial two-component regulatory systems (TCRS) are associated with the expression of virulence factors and antibiotic susceptibility. In Staphylococcus aureus, 16 TCRS types have been identified. The histidine kinase/response regulator SAV1321/SAV1322 in the S. aureus shares considerable homology with the TCRS DesKR in Bacillus subtilis. However, a function for the SAV1322 locus has not yet been assigned.

Results

Deletion of the SAV1322 locus in S. aureus results in reduced growth when cultured under low (25 °C) and high (46 °C) temperature conditions. The sav1322 deletion mutant is more tolerant to oxidative stress in vitro and is less pathogenic in a murine infection model when compared with wild-type parent strain Mu50. Furthermore, the sav1322 mutant exhibits lower MICs for gentimicin, tetracyclines and glycopeptides, increased autolysis, and a thinner cell wall when compared with the wild-type strain. Microarray and proteomic analyses show that the expression of cell-wall-associated genes glmS and murZ are lower, and the expression of heat shock and stress-related genes (hrcA, ctsR, dnaK, dnaJ, grpE, clpB, and clpC) are higher in the sav1322 mutant when compared with the wild-type strain. In addition, the sav1322 mutant displays altered expression of proteins involved in carbohydrate/energy metabolism, cell wall metabolism, and stress or heat shock response, as well as other metabolic processes including lipid metabolism, amino acid biosynthesis, purine or pyrimidine metabolism, transcription, and protein biosynthesis.

Conclusions

The S. aureus SAV1322 locus plays a pronounced role in temperature adaptation, antibiotic resistance, and virulence by regulating a wide range of genes and proteins involved in metabolism and stress tolerance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0824-2) contains supplementary material, which is available to authorized users.

Variable number of tandem repeat profiles and antimicrobial resistance patterns of Staphylococcus haemolyticus strains isolated from blood cultures in children

Staphylococcus haemolyticus is a healthcare-associated pathogen and can cause a variety of lifethreatening infections. Additionally, multi-drug resistance (MDR), in particular methicillin-resistant S. haemolyticus (MRSH) isolates, have emerged. Dissemination of such strains can be of great concern in the hospital environment. A total number of 20S. haemolyticus isolates from blood cultures obtained from children were included in this study. A high prevalence of MDR-MRSH isolates with high MIC values to vancomycin was found and 35% of the isolates were intermediate resistant to vancomycin. Multilocus variable number of tandem repeats analysis (MLVF) revealed 5 MLVF types among 20 isolates of S. haemolyticus. Twelve isolates shared the same MLVF type and were isolated from different wards in a pediatric hospital in Iran. This is a serious alarm for infection control; i.e. in the absence of adequate infection diagnostics and infection control guidelines, these resistant strains can spread to other sectors of a hospital and possibly among the community.