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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.

Francisella tularensis is an intracellular bacterium and as such is expected to encounter a continuous attack by reactive oxygen species (ROS) in its intracellular habitat and efficiently coping with oxidative stress is therefore essential for its survival. The oxidative stress response system of F tularensis is complex and includes multiple antioxidant enzymes and pathways, including the transcriptional regulator OxyR and the H2O2-decomposing enzyme catalase, encoded by katG. The latter is regulated by OxyR. A deletion of either of these genes, however, does not severely compromise the virulence of F tularensis and we hypothesized that if the bacterium would be deficient of both catalase and OxyR, then the oxidative defense and virulence of F tularensis would become severely hampered. To test this hypothesis, we generated a double deletion mutant, Delta oxyR/Delta katG, of F tularensis LVS and compared its phenotype to the parental LVS strain and the corresponding single deletion mutants. In accordance with the hypothesis, Delta oxyR/Delta katG was distinctly more susceptible than Delta oxyR and Delta katG to H2O2, ONOO-, and O-2(-), moreover, it hardly grew in mouse-derived BMDM or in mice, whereas Delta katG and Delta oxyR grew as well as F tularensis LVS in BMDM and exhibited only slight attenuation in mice. Altogether, the results demonstrate the importance of catalase and OxyR for a robust oxidative stress defense system and that they act cooperatively. The lack of both functions render F tularensis severely crippled to handle oxidative stress and also much attenuated for intracellular growth and virulence.

Conclusions Patients with symptomatic perforations of the nasal septum had a high prevalence of S. aureus in the nasal mucosa. Pulsed field gel electrophoresis (PFGE) analysis revealed a high genetic heterogeneity of S. aureus among both patients and controls. This indicates that presence of different strains of S. aureus can maintain a chronic inflammation in symptomatic nasal septal perforations. Objective The purpose of this study was to investigate the microbial flora around nasal septal perforations in patients having severe symptoms regarding bleeding, obstruction, and crustation associated with their perforation. Methods Twenty-five patients with untreated symptomatic nasal septal perforations were included. For culture, swabs around the perforations were collected. Bacteria were identified with standard laboratory techniques including a MALDI-TOF mass spectrometer. Epidemiological analysis was done using PFGE protocols. Bacteriological data were compared with data from a healthy control group. Results Staphylococcus aureus was present in the mucosa surrounding the nasal perforation significantly more often (p < 0.0001) in the patients (88%) compared to a control group (13%). Corynebacterium spp. and Propionibacterium spp. were significantly more frequently identified in the control group. The PFGE analysis of S. aureus strains revealed a high genetic heterogeneity and no specific S. aureus genotypes were associated with septal perforation.

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.

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 alpha-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 A(1) 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.