Efficacy of a synthetic antimicrobial peptidomimetic versus vancomycin in a Staphylococcus epidermidis device-related murine peritonitis model.

OBJECTIVES: Biofilm-forming Staphylococcus epidermidis is a prevalent cause of peritonitis during peritoneal dialysis. We compared the efficacy of a synthetic antimicrobial peptidomimetic (Ltx21) versus vancomycin in a murine model mimicking a device-related peritonitis. METHODS: Silicone implants, pre-colonized with an S. epidermidis biofilm, were inserted into the peritoneal cavity of BALB/c mice. Three groups (36 mice in each) with pre-colonized implants received intraperitoneal treatment with Ltx21, vancomycin or placebo. Mice were euthanized on day 3 (n = 12), day 6 (n = 12) or day 8 (n = 12) post-implantation. Controls were mice with sterile implants (n = 18) and mice without surgery (n = 6). Bacterial reductions in cfu were analysed from implants and peritoneal fluid (PF). Inflammatory responses in serum and PF were measured. RESULTS: Vancomycin resulted in a stronger reduction in cfu counts, both on pre-colonized implants and in PF, compared with Ltx21 and placebo. Complete bacterial clearance of the implants was not achieved in any of the groups. The implants pre-colonized with S. epidermidis 1457 resulted in a low-grade peritonitis. We observed, only on day 6, a significant increase in the PF leucocyte count in the group with pre-colonized implants compared with the group with sterile implants (P = 0.0364). CONCLUSIONS: Treatment with vancomycin or Ltx21 was not sufficient to achieve complete bacterial clearance of implants, underlining the difficulties of treating such infections. The low-grade infection may attenuate the inflammatory response and contribute to impaired bacterial clearance.

Core genome conservation of Staphylococcus haemolyticus limits sequence based population structure analysis.

The notoriously multi-resistant Staphylococcus haemolyticus is an emerging pathogen causing serious infections in immunocompromised patients. Defining the population structure is important to detect outbreaks and spread of antimicrobial resistant clones. Currently, the standard typing technique is pulsed-field gel electrophoresis (PFGE). In this study we describe novel molecular typing schemes for S. haemolyticus using multi locus sequence typing (MLST) and multi locus variable number of tandem repeats (VNTR) analysis. Seven housekeeping genes (MLST) and five VNTR loci (MLVF) were selected for the novel typing schemes. A panel of 45 human and veterinary S. haemolyticus isolates was investigated. The collection had diverse PFGE patterns (38 PFGE types) and was sampled over a 20 year-period from eight countries. MLST resolved 17 sequence types (Simpsons index of diversity [SID]=0.877) and MLVF resolved 14 repeat types (SID=0.831). We found a low sequence diversity. Phylogenetic analysis clustered the isolates in three (MLST) and one (MLVF) clonal complexes, respectively. Taken together, neither the MLST nor the MLVF scheme was suitable to resolve the population structure of this S. haemolyticus collection. Future MLVF and MLST schemes will benefit from addition of more variable core genome sequences identified by comparing different fully sequenced S. haemolyticus genomes.

[Coagulase-negative staphylococci--biofilm and antibiotic resistance]. / Biofilm og antibiotikaresistens hos koagulasenegative stafylokokker.

BACKGROUND: Coagulase-negative staphylococci (CoNS) may cause serious infections in immunocompromized patients. CoNS often display multiresistance to antibiotics, and biofilm production is the central virulence factor. Our aim was to investigate these factors in CoNS that colonize children with an increased risk of CoNS infections. MATERIAL AND METHOD: We collected CoNS isolates from intravasal catheters (n = 19) and the skin (n = 47) from 30 hospitalized neonates, and CoNS skin isolates from 20 children with cancer before (n = 20) and after (n = 18) six months of cancer treatment. We analyzed antibiotic resistance and biofilm production with phenotypic methods. We used PCR to detect genes that encode antibiotic resistance and biofilm formation. RESULTS: 11 of 19 (58 %) catheter isolates and 14 of 47 (30 %) skin isolates (p = 0.04) produced biofilm. We found an increasing prevalence of oxacillin resistance (20 % versus 67 %, p = 0.004) and gentamicin resistance (15 % versus 67 %, p = 0.003) after six months of cancer treatment. Biofilm positive CoNS isolates displayed higher levels of antibiotic resistance than biofilm-negative isolates. INTERPRETATION: Our results indicate that sick neonates and children hospitalized with cancer are colonized with pathogenic CoNS strains demonstrating virulence- and antibiotic-resistance patterns that are different from those found in CoNS in healthy people who are not hospitalized.