Heterogeneity of Staphylococcus epidermidis in prosthetic joint infections: time to reevaluate microbiological criteria?

Prosthetic joint infection (PJI) is a feared and challenging to diagnose complication after arthroplasty, with Staphylococcus epidermidis as the major pathogen. One important criteria to define PJI is the detection of phenotypically indistinguishable microorganisms with identical antibiotic susceptibility pattern in at least two different samples. However, owing to phenotypical variation within genetic clones and clonal variation within a phenotype, the criteria may be ambiguous. We investigated the extent of diversity among coagulase-negative staphylococci (CoNS) in PJI and characterised S. epidermidis isolates from PJI samples, specifically multiple S. epidermidis isolates identified in individual PJI patients. We performed a retrospective cohort study on 62 consecutive patients with PJI caused by CoNS from two hospitals in Northern Sweden. In 16/62 (26%) PJIs, multiple S. epidermidis isolates were available for whole-genome analyses. Hospital-adapted multidrug-resistant genetic clones of S. epidermidis were identified in samples from 40/62 (65%) of the patients using a combination of pulsed-field gel electrophoresis and multilocus sequence typing. Whole-genome sequencing showed the presence of multiple sequence types (STs) in 7/16 (44%) PJIs where multiple S. epidermidis isolates were available. Within-patient phenotypical variation in the antibiotic susceptibility and/or whole-genome antibiotic resistance gene content was frequent (11/16, 69%) among isolates with the same ST. The results highlight the ambiguity of S. epidermidis phenotypic characterisation as a diagnostic method in PJI and call for larger systematic studies for determining the frequency of CoNS diversity in PJIs, the implications of such diversity for microbiological diagnostics, and the therapeutic outcomes in patients.

Molecular and Phenotypic Characterization of Multidrug-Resistant Clones of Staphylococcus epidermidis in Iranian Hospitals: Clonal Relatedness to Healthcare-Associated Methicillin-Resistant Isolates in Northern Europe.

The aim of the study was to investigate the molecular epidemiology of Staphylococcus epidermidis in Iranian hospitals and to compare the genotypes with a previously characterized collection of >1,300 S. epidermidis isolates of nosocomial and community origin from Northern Europe, Australia, and USA. In total, 82 clinical S. epidermidis isolates from three Iranian hospitals were examined by multilocus sequence typing, pulsed-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome mec (SCCmec) typing. In addition, antimicrobial susceptibility, the presence of the ica operon, and the predilection to biofilm formation were assessed. Three predominant PFGE clones were found. The PFGE patterns of the most common sequence type (PFGE type 040-ST2) showed 80% similarity to multidrug-resistant S. epidermidis (MDRSE) clinical isolates from eight hospitals in Northern Europe. The second most common (PFGE 024-ST22) showed an unique PFGE pattern, whereas the third most predominant genotype (PFGE 011-ST5) proved indistinguishable to the PFGE Co-ST5 identified in five hospitals in Northern Europe. In conclusion, the study documented the dissemination of three MDRSE clones within and between hospitals in Iran and revealed an intercontinental spread of two clonal multidrug-resistant lineages (ST2 and ST5) in the hospital environment. Isolates of the predominant clones were significantly more frequently associated with multidrug-resistance and biofilm formation compared to nonclonal isolates. Further studies are needed to explore and characterize the genetic traits that enable these successful MDRSE clones to persist and disseminate worldwide in the healthcare settings.

Screening for inhibition of Vibrio cholerae VipA-VipB interaction identifies small-molecule compounds active against type VI secretion.

The type VI secretion system (T6SS) is the most prevalent bacterial secretion system and an important virulence mechanism utilized by Gram-negative bacteria, either to target eukaryotic cells or to combat other microbes. The components show much variability, but some appear essential for the function, and two homologues, denoted VipA and VipB in Vibrio cholerae, have been identified in all T6SSs described so far. Secretion is dependent on binding of an α-helical region of VipA to VipB, and in the absence of this binding, both components are degraded within minutes and secretion is ceased. The aim of the study was to investigate if this interaction could be blocked, and we hypothesized that such inhibition would lead to abrogation of T6S. A library of 9,600 small-molecule compounds was screened for their ability to block the binding of VipA-VipB in a bacterial two-hybrid system (B2H). After excluding compounds that showed cytotoxicity toward eukaryotic cells, that inhibited growth of Vibrio, or that inhibited an unrelated B2H interaction, 34 compounds were further investigated for effects on the T6SS-dependent secretion of hemolysin-coregulated protein (Hcp) or of phospholipase A1 activity. Two compounds, KS100 and KS200, showed intermediate or strong effects in both assays. Analogues were obtained, and compounds with potent inhibitory effects in the assays and desirable physicochemical properties as predicted by in silico analysis were identified. Since the compounds specifically target a virulence mechanism without affecting bacterial replication, they have the potential to mitigate the virulence with minimal risk for development of resistance.