Phenotypic and Genotypic Characterization of Linezolid Resistance Coagulase-negative Staphylococci Possessing cfr-Carrying Plasmid

The interplay between mobilome and resistome in Staphylococcus aureus

Antibiotic resistance genes (ARGs) in Staphylococcus aureus can disseminate vertically through successful clones, but also horizontally through the transfer of genes conveyed by mobile genetic elements (MGEs). Even though underexplored, MGE/ARG associations in S. aureus favor the emergence of multidrug-resistant clones, which are challenging therapeutic success in both human and animal health. This study investigated the interplay between the mobilome and the resistome of more than 10,000 S. aureus genomes from human and animal origin. The analysis revealed a remarkable diversity of MGEs and ARGs, with plasmids and transposons being the main carriers of ARGs. Numerous MGE/ARG associations were identified, suggesting that MGEs play a critical role in the dissemination of resistance. A high degree of similarity was observed in MGE/ARG associations between human and animal isolates, highlighting the potential for unrestricted spread of ARGs between hosts. Our results showed that in parallel to clonal expansion, MGEs and their associated ARGs can spread across different strain types sequence types (STs), favoring the evolution of these clones and their adaptation in selective environments. The high variability of MGE/ARG associations within individual STs and their spread across several STs highlight the crucial role of MGEs in shaping the S. aureus resistome. Overall, this study provides valuable insights into the complex interplay between MGEs and ARGs in S. aureus, emphasizing the need to elucidate the mechanisms governing the epidemic success of MGEs, particularly those implicated in ARG transfer.IMPORTANCEThe research presented in this article highlights the importance of understanding the interactions between mobile genetic elements (MGEs) and antibiotic resistance genes (ARGs) carried by Staphylococcus aureus, a versatile bacterium that can be both a harmless commensal and a dangerous pathogen for humans and animals. S. aureus has a great capacity to acquire and disseminate ARGs, enabling efficient adaption to various environmental or clinical conditions. By analyzing a large data set of S. aureus genomes, we highlighted the substantial role of MGEs, particularly plasmids and transposons, in disseminating ARGs within and between S. aureus populations, bypassing host barriers. Given that multidrug-resistant S. aureus strains are classified as a high-priority pathogen by global health organizations, this knowledge is crucial for understanding the complex dynamics of transmission of antibiotic resistance in this species.

Staphylococcus capitis: insights into epidemiology, virulence, and antimicrobial resistance of a clinically relevant bacterial species

SUMMARYStaphylococcus capitis is divided into two subspecies, S. capitis subsp. ureolyticus (renamed urealyticus in 1992; ATCC 49326) and S. capitis subsp. capitis (ATCC 27840), and fits with the archetype of clinically relevant coagulase-negative staphylococci (CoNS). S. capitis is a commensal bacterium of the skin in humans, which must be considered an opportunistic pathogen of interest particularly as soon as it is identified in a clinically relevant specimen from an immunocompromised patient. Several studies have highlighted the potential determinants underlying S. capitis pathogenicity, resistance profiles, and virulence factors. In addition, mobile genetic element acquisitions and mutations contribute to S. capitis genome adaptation to its environment. Over the past decades, antibiotic resistance has been identified for S. capitis in almost all the families of the currently available antibiotics and is related to the emergence of multidrug-resistant clones of high clinical significance. The present review summarizes the current knowledge concerning the taxonomic position of S. capitis among staphylococci, the involvement of this species in human colonization and diseases, the virulence factors supporting its pathogenicity, and the phenotypic and genomic antimicrobial resistance profiles of this species.

Molecular Characterization of Clinical Linezolid-Resistant Staphylococcus epidermidis in a Tertiary Care Hospital

Staphylococcus epidermidis (S. epidermidis) is part of the human skin flora but can also cause nosocomial infections, such as device-associated infections, especially in vulnerable patient groups. Here, we investigated clinical isolates of linezolid-resistant S. epidermidis (LRSE) collected from blood cultures at the University Hospital Münster (UHM) during the period 2020-2022. All detected isolates were subjected to whole genome sequencing (WGS) and the relatedness of the isolates was determined using core genome multilocus sequence typing (cgMLST). The 15 LRSE isolates detected were classified as multilocus sequence type (ST) 2 carrying the staphylococcal cassette chromosome mec (SCCmec) type III. All isolates showed high-level resistance for linezolid by gradient tests. However, no isolate carried the cfr gene that is often associated with linezolid resistance. Analysis of cgMLST data sets revealed a cluster of six closely related LRSE isolates, suggesting a transmission event on a hematological/oncological ward at our hospital. Among the included patients, the majority of patients affected by LRSE infections had underlying hematological malignancies. This confirms previous observations that this patient group is particularly vulnerable to LRSE infection. Our data emphasize that the surveillance of LRSE in the hospital setting is a necessary step to prevent the spread of multidrug-resistant S. epidermidis among vulnerable patient groups, such as patients with hematological malignancies, immunosuppression or patients in intensive care units.

Prevalence, biofilm formation, and mass spectrometric characterization of linezolid-resistant Staphylococcus capitis isolated from a tertiary hospital in China

OBJECTIVES

Linezolid-resistant Staphylococcus capitis (LRSC) has become a new challenge for clinical anti-infective therapy. The present study aimed to investigate the trends of LRSC prevalence in a tertiary hospital of China 2017-2020. The resistance mechanisms, virulence genes, biofilm formation, and mass spectrometric characteristics of LRSC isolates were also analysed.

METHODS

This study retrospectively analysed the antibiotic resistance trends of coagulase negative staphylococci (CoNS) isolated from clinical samples collected between 2017-2020. Antimicrobial resistance profiles were tested by micro-broth dilution and the E-test method. Antimicrobial resistance genes and virulence genes were detected by polymerase chain reaction, and dru-typing sequences were obtained by Sanger sequencing. Crystal violet staining in 96-well plates was used to detect biofilm formation ability. Mass spectrometric characterization of LRSC was analysed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) coupled with ClinProTools.

RESULTS

The linezolid resistance rate in 3575 CoNS clinical strains was 1.6%, wherein the great majority of was LRSC (91.1%, n = 51/56), with a resistant rate of 15.5% (n = 51/328) in all S. capitis isolates. In this study, 48 out of the 51 LRSC strains and 54 of 277 linezolid-susceptible S. capitis (LSSC) strains were enrolled. G2576T, C2104T, T2130A, C2163T, and T2319C mutations in the 23S rRNA V region and acquisition of cfr were the main linezolid resistant mechanisms in LRSC. The biofilm-forming ability of LRSC was more potent than LSSC, with a higher detection rate of bap (P < 0.05). Eleven mass spectrometric peaks of interest were identified by using MALDI-TOF MS and ClinProTools, which were differently distributed between LRSC and LSSC strains, with the area under the receiver operating characteristic curve of more than 0.8, especially for 5465.37 m/z.

CONCLUSIONS

Linezolid resistance was mediated by mutations in the 23S rRNA V region and presence of the cfr gene in LRSC strains. LRSC strains have stronger biofilm-forming ability than LSSC strains, which maybe associated with the adhesion-related gene of bap. Further, linezolid-resistant and linezolid-susceptible S. capitis could be rapidly identified with mass spectrometric characterization. To the best of our knowledge, this study is the first to document the biofilm formation ability of LRSC and the potential usefulness of MALDI-TOF MS for the discrimination of LRSC and LSSC.

Analysis of pathogen distribution and antimicrobial resistance at infected sites in plastic surgery

OBJECTIVE

By analyzing the distribution and drug resistance of common pathogen in different sites in plastic surgery to provide reference for clinicians to choose the best antibacterial treatment plan.

METHODS

Pathogens of postoperative infection in plastic surgery from January 2011 to December 2021 were retrospectively analyzed to determine the species and quantity, and to access the trend of each pathogen's detection rate. The antibiotic sensitivity and distribution characteristics of common pathogens were studied in conjunction with the site of infection.

RESULTS

A total of 1709 bacterial strains were detected, including 1244 gram-positive bacterial strains and 465 gram-negative bacterial strains. The main pathogen of perineum was Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), while Staphylococcus aureus (S. aureus) was the most common pathogen in the other infected sites. The detection rate of methicillin-resistant S. aureus (MRSA) and methicillin-resistant coagulase-negative staphylococcus (MRCNS) was on the rise from 2011 to 2021. No S. aureus and coagulase-negative staphylococcus (CoNS) strains were resistant to vancomycin. The sensitive rate of S. aureus from all parts and CoNS from all sites except lower limbs and mandible was higher than 80% to linezolid. The resistance rate of S. aureus and CoNS in all parts to penicillin, clindamycin, and erythromycin was high. The susceptibility rate of CoNS in lower mandible was high to gentamicin.

CONCLUSIONS

Staphylococcus aureus was the primary pathogen of gram-positive bacteria in all site of plastic surgery except perineum, followed by CoNS. The distribution and drug resistance of pathogen in different infection sites were different. We should formulate more accurate and reasonable antibacterial programs according to drug resistance results of various parts to reduce the emergence of resistant strains and effectively prevent and control infection.

An 11-year linezolid-resistant Staphylococcus capitis clone dissemination with a similar cfr-carrying plasmid in China

Linezolid resistance has represented a global concern with its wide dissemination among nosocomial pathogens in recent years. One hundred and two linezolid-resistant Staphylococcus capitis (LRSC) were constantly isolated from 2011 to 2021, which demonstrated single clonal dissemination in a Chinese tertiary hospital. A structurally similar cfr-carrying plasmid was identified among 90 isolates. A chromosomal cfr was located beside a Tn4001-like transposon and ISEnfa4 in one strain (LR95). The loss of cfr-carrying plasmid was observed in 11 isolates and the in vitro passage experiments. Conjugation experiments demonstrated the horizontal transferability of the cfr-carrying plasmid into Staphylococcus aureus RN4220. Both cfr-positive LRSC and S. aureus showed no significant differences in growth rates, while only the former displayed competition defect, suggesting this plasmid imposed a certain fitness cost on LRSC. Hence, ongoing measurements are supposed to be adopted to control the spread of these antimicrobial-resistant bacteria.