To Örebro University

Background and objectives: Staphylococcus epidermidis is a major cause of prosthetic joint infections (PJIs). Multidrug resistant (MDR), hospital-adapted clones constitute most cases globally, though regional differences in lineage dissemination likely exist. The aim was to explore the population structure of S. epidermidis from PJIs in Sweden and France, with a focus on the presence of antimicrobial resistance (AMR).

Methods: This study included genome sequence data from 191 clinical S. epidermidis isolates collected from patients with PJI in central Sweden (2007-16; n = 138) and the Lyon region in France (2015-20; n = 53).

Results: Hospital-adapted lineages with a high burden of AMR dominated the cases in both countries. However, the ST2 lineage was significantly more prevalent in Sweden (43% versus 11% in France), while ST5 and ST87 were more common in France (55% versus 10% in Sweden). ST215 was only present in Sweden (25%). A significantly higher prevalence of streptogramin resistance genes [vat(B), vga(A), vga(B)] was found in French (26%) versus Swedish (2%) isolates. These genes were present in all ST87 isolates and in 20% of the French ST5 isolates. The erm(C) gene (resistance to streptogramin A, macrolides and lincosamides) was also more common in the French isolates (77% versus 55% of Swedish isolates), and so was the fusidic acid resistance gene fusB (France: 66%, Sweden: 39%).

Conclusions: This study highlights significant regional differences in S. epidermidis variants causing PJI. Despite similar MDR levels, certain AMR genes, particularly those related to streptogramin resistance, were significantly more prevalent among French isolates. This suggests that S. epidermidis undergoes local adaptation to region-specific antibiotic usage.

BACKGROUND: There is limited knowledge regarding how long prepared sterile goods can wait before becoming contaminated. We investigated whether surgical goods could be prepared the day before surgery and kept sterile overnight in the operating room, if protected by sterile covers.

METHODS: Sterile surgical goods for open-heart surgeries (n=70) were randomized to preparation on the morning of the operation or on the previous evening. Exposure time was the total time between preparation and use. Primary outcome was bacterial growth reported as colony forming units (cfu), isolated on 840 agar plates. The protocol was registered with ClinicalTrials.gov (NCT05597072).

RESULTS: When the agar plates were protected with sterile covers, exposure time had no impact (intervention group: 7 cfu, control group: 17 cfu). Without protection, longer exposure time was associated with more cfu (p=0.016). A total of 499 cfu were isolated, displaying 59 different types of bacteria including 13 resistant Staphylococcus epidermidis, 6 (46%) of which were multidrug resistant.

CONCLUSIONS: Sterile goods could wait in the operating room for at least 15 hours before use without increased risk of bacterial air contamination, if protected with sterile covers. However, if the goods were not covered, bacterial air contamination occurred over time.

PURPOSE: To describe the clinical characteristics of exogenous episodes of endophthalmitis from which Staphylococcus epidermidis was isolated by vitreous cultures. We also explored the genomic traits of these S. epidermidis isolates and their relatedness to S. epidermidis originating from carriers and from prosthetic joint infections in the same geographical region.

METHODS: S. epidermidis isolated from cases of exogenous endophthalmitis (n = 33) were genome sequenced. Clinical features were retrospectively collected from medical records. The isolates were compared with previously sequenced S. epidermidis isolates from the nares of healthy individuals (n = 151) and from prosthetic joint infections (n = 138).

RESULTS: The most common ophthalmological procedure preceding the endophthalmitis was a posterior segment surgery (76%; 25/33), mainly intravitreal injection (70%; 23/33). These patients displayed a significantly shorter time to symptoms compared to those with an anterior segment surgery (median 3 vs. 9 days; p < 0.001), and significantly less phenotypic methicillin resistance (8%, n = 2/25 vs. 50%, n = 4/8; p = 0.02). Most isolates of S. epidermidis originating from endophthalmitis cases did not belong to known healthcare-associated lineages and did not cluster with isolates from prosthetic joint infections. Rather, they were more similar to isolates from the nares of healthy individuals.

CONCLUSIONS: Genomic data suggest that the S. epidermidis isolated from the vitreous of Swedish cases of postsurgical endophthalmitis may originate from the commensal flora of the individual, and not from the healthcare facilities. The type of preceding surgical procedure (anterior vs. posterior segment) may influence both symptom delay and the presence or absence of methicillin resistance.

BACKGROUND: Staphylococcus epidermidis is a ubiquitous member of the healthy skin and mucous microbiota but is also an opportunistic pathogen responsible for various infections, often treated with antibiotics like rifampicin. Resistance to rifampicin in S. epidermidis arises primarily through nonsynonymous mutations in the rpoB gene.

OBJECTIVES: To investigate the prevalence of rpoB mutations and their association with phenotypic rifampicin resistance in clinical S. epidermidis isolates from Denmark, France, and Sweden.

METHODS: All clinical isolates (N = 942) were whole-genome sequenced to identify mutations in rpoB and subsequently linked to phenotypic rifampicin resistance based on antimicrobial susceptibility testing.

RESULTS: A total of 64 (6.8%) isolates were resistant to rifampicin. They carried all mutational changes in the rifampicin resistance-determining region (RRDR). Among 12 identified nonsynonymous mutations, 11 were exclusively observed in resistant strains, including novel mutations not previously described in S. epidermidis.

CONCLUSIONS: This study highlights the diverse genetic variants of rpoB associated with rifampicin resistance in clinical S. epidermidis isolates, including novel mutations. The strong correlation between mutational changes in RRDR and phenotypic resistance reinforces the role of rpoB mutations as a primary mechanism of resistance in clinical isolates.

Hematogenous prosthetic joint infections (PJIs) are primarily associated with Staphylococcus aureus, and there is a 30%-40% risk of contracting a hematogenous PJI following an S. aureus bacteremia. The aim of this study was to investigate whether identical strains of S. aureus were present in each patient from a cohort with both bacteremia and PJI and to explore the genomic differences between paired isolates obtained from blood cultures and tissue biopsies. All patients with a PJI and a temporally concomitant bacteremia due to S. aureus from 2005 to 2020 were included. Paired isolates of S. aureus from tissue biopsies and blood cultures were subjected to whole-genome sequencing. Twenty-four episodes of PJI were identified in 23 patients. All pairwise isolates from individual patients belonged to the same multilocus sequence type, clonal complex, and core genome multilocus sequence typing (cgMLST) complex type. The median number of single nucleotide polymorphisms (SNPs) in the conserved core genomes between the pairwise isolates was 3. In conclusion, identical cgMLST complex types and low levels of SNP differences between paired isolates of S. aureus from blood cultures and tissue biopsies suggest hematogenous seeding in all cases of PJI in this cohort.

Background: International guidelines for Staphylococcus aureus vertebral osteomyelitis recommend 6 weeks of treatment, including oral follow-up using antibiotics with high bioavailability such as a fluoroquinolone/rifampicin combination. Oral flucloxacillin is not recommended due to low bioavailability and scarce evidence. However, flucloxacillin as oral follow-up treatment is common practice in Sweden based on favourable clinical experience, good tolerability, few interactions, and low ecological impact. Our aim was to review a single-centre experience of S. aureus vertebral osteomyelitis, with focus on flucloxacillin treatment.

Methods: A single-centre retrospective cohort of patients with Staphylococcus aureus vertebral osteomyelitis (n = 40) was identified between 2010 and 2016. Patients were further stratified by antibiotic treatment strategy with focus on oral flucloxacillin therapy (n = 24). Primary outcomes were relapse or death within 12 months of treatment initiation, and antibiotic-related adverse effects during treatment.

Results: Methicillin-susceptible S. aureus (MSSA) caused 38 of the infections (95%), and five patients (13%) died, all in-hospital. Flucloxacillin was used for at least 75% of the oral treatment duration in 24 patients (60%). Median antibiotic treatment duration among these patients was 125.5 days (IQR 95-182), 109 days (IQR 76-149) of which comprised oral antibiotics. There were two relapses and two deaths among the patients treated predominantly with flucloxacillin, resulting in a composite clinical cure rate of 83% (20 of 24).

Conclusions: Prolonged oral flucloxacillin administration could be a potential treatment option for MSSA vertebral osteomyelitis. A prospective study of optimal treatment duration and dosing strategies for flucloxacillin in vertebral osteomyelitis is warranted.

BACKGROUND: Surgical site infection (SSI) and antimicrobial resistance are a worldwide problem affecting patient safety. It is lacking randomised controlled trials (RCT) regarding how the number of personnel in the operating room (OR) affects the air quality. We aimed to investigate the effect the number of personnel in the OR have on bacterial air contamination during the preparation of sterile surgical goods, to identify the species and antibiotic susceptibility of the bacteria isolated, and to describe the number of SSIs together with causative microorganisms.

METHODS: This RCT used an intervention group in which two individuals prepared the surgical goods and a control group in which five individuals prepared the goods. Bacteria were isolated on aerobic and anaerobic plates, and bacterial growth was measured as colony forming units (CFU). All isolates were typed, and types known to cause SSI were tested for susceptibility to eight antibiotics. Data were analysed with the Mann-Whitney U test, the chi-square test, or Fisher's exact test.

RESULTS: Results were based on 69 open-heart surgeries and 414 plates. When sterile surgical goods were prepared with two personnel, the median CFU was 2 with an IQR of 2, compared with five personnel, the median CFU was 5, with an IQR of 5 (p < 0.001). The 272 CFU represented 45 different bacterial species, with 38 species isolated in the control group and 21 in the intervention group. The most frequently isolated bacteria were Cutibacterium acnes (82/272, 30%), and Staphylococcus epidermidis (36/272, 13%). Of the 36 S. epidermidis isolates, 11 (31%) were drug-resistant, including three multidrug-resistant. One patient in the control group was infected by Staphyloccocus aureus and Staphylococcus lugdunensis, neither of which was isolated during the preparation of sterile goods. One patient in the intervention group developed an SSI caused by C. acnes, Corynebacterium kroppenstedtii, and S. epidermidis. C. acnes and S. epidermidis were isolated during the preparation.

CONCLUSIONS: Minimising the number of personnel in the OR during preparation of sterile surgical goods is important to reduce the bacterial load.

TRIAL REGISTRATION: Prospectively 15 May 2022 at FoU Sweden (275659) and retrospectively 22 October 2022 at ClinicalTrials.Gov (NCT05597072).

INTRODUCTION: Dalbavancin is a lipoglycopeptide with an exceptionally long half-life that allows simplified administration, which may be of value in long-term treatment of bone and joint infections, such as prosthetic joint infections (PJIs). The objective was to determine trough (Cmin) values of dalbavancin during long-term PJI treatment according to the recommendation of the Swedish National Guidelines for Bone and Joint Infections: a loading dose of 1,500 mg on day 1 and another 1,500 mg on days 8-14, followed by day 28 administration of 1,000 mg every two weeks or 500 mg per week. PATIENTS/

METHODS: Twelve patients with PJI treated with at least six doses of dalbavancin were prospectively followed up, serum samples were collected, and renal function was investigated. Dalbavancin concentrations were measured using ultra-high pressure liquid chromatography coupled with unispray tandem mass spectrometry (UHPLC-MS/MS).

RESULTS: The median serum concentration (Cmin) 14 days after the first 1,500 mg dose was 36.3 mg/L (range: 6.6-62.4 mg/L). The median trough value at the date of the last given dose (1,000 mg) after a total of 6-7 doses was 53.6 mg/L (range: 32.0-97.5 mg/L). Three patients showed a tendency towards successive accumulation of dalbavancin during treatment. None of the patients showed any significant impairment in renal function.

CONCLUSIONS: Therapeutic drug monitoring during long-term dalbavancin treatment is recommended to avoid the risk of accumulation and unnecessarily high trough levels. In many cases, such monitoring can allow the dosing interval to be extended.

Local delivery of antibiotics as prophylaxis for prosthetic joint infections (PJIs) is frequently used during total hip replacement surgery. Morselized bone allograft impregnated with vancomycin and tobramycin (TobraVanc) could provide effective prophylaxis against bacteria commonly associated with PJIs. In this study, the concentrations of antibiotics released by bone allograft impregnated with TobraVanc were determined by using an in vitro bioassay system entailing measuring inhibition zone diameters caused by antibiotic-impregnated bone chips cast in agar against standard curves. The concentrations were determined in samples of TobraVanc-impregnated bone graft taken before and after the application of the bone graft in the patients undergoing acetabular revision surgery. Antibiotic-impregnated bone grafts, sampled prior to application in the patient, delivered antibiotics in the concentration ranges of 730-9,800 mg/L for tobramycin and 1,300-11,000 mg/L for vancomycin. Samples taken after application in the patient released lower concentrations of tobramycin (490-1,900 mg/L; P < 0.01) and vancomycin (3,000-5,100 mg/L; P < 0.05); however, these concentrations remained well above the tobramycin minimum inhibitory concentrations (MICs) for investigated, highly tobramycin-resistant Staphylococcus epidermidis strains (MICs > 256 mg/L). At the tested concentrations, bone graft material mixed with TobraVanc delivered antibiotics in potent concentrations above the MICs for bacteria causing PJIs. Clinical trials are needed to evaluate the efficacy and risk of TobraVanc-impregnated bone graft as a prophylactic agent for patients undergoing hip replacement surgery.