Bengt Hellmark

Antibiotic susceptibility among Staphylococcus epidermidis isolated from prosthetic joint infections with special focus on rifampicin and variability of the rpoB gene

Staphylococcus epidermidis is the most important pathogen in infections related to implanted foreign materials, especially prosthetic joint infections (PJIs). The aim of this study was to investigate the antimicrobial activities of 16 antibiotics against S. epidermidis isolated from PJIs, with special focus on rifampicin and rpoB variability. Ninety-one per cent of the isolates were multiresistant (i.e. resistant to members of more than three classes of antibiotics). Thirty-nine per cent were resistant to rifampicin, associated with one or two single-nucleotide polymorphisms (SNPs) in rpoB. Using IsoSensitest agar with supplements, 61% were resistant to oxacillin, and using Mueller-Hinton II agar with supplement, 84% were resistant. Using the Etest, 58% were resistant to cefoxitin, and using the disk diffusion test, 91% were resistant. The mecA gene was detected in 85% of the isolates. Regarding recently available antibiotics, all isolates were susceptible to tigecycline and linezolid, and 97% were susceptible to daptomycin. In addition, two novel antibiotics, dalbavancin and ceftobiprole, were tested, although not yet available for routine use. The MIC(50) and MIC(90) values of these novel antibiotics were 0.032 and 0.047 mg/L and 0.5 and 1.5 mg/L, respectively. Among the other antibiotics, the rates of resistance varied between 0% (vancomycin) and 82% (trimethoprim-sulphamethoxazole). S. epidermidis strains causing PJIs often show multiresistance, including resistance to rifampicin, which is mainly caused by one or two SNPs. Some of the newer antimicrobial agents may provide alternatives for monotherapy or combination therapy with rifampicin. Detection of mecA is necessary before initiating treatment of infections due to S. epidermidis when it displays intermediate susceptibility to cefoxitin.

Comparison of Staphylococcus epidermidis isolated from prosthetic joint infections and commensal isolates in regard to antibiotic susceptibility, agr type, biofilm production, and epidemiology.

Staphylococcus epidermidis is the predominant bacterial species in the normal flora of the human skin and superficial mucosal membranes. However, it has also emerged as the most important pathogen in infections related to foreign-body materials, such as prosthetic joints and heart valves. The aims of this study were to characterise S. epidermidis isolated from prosthetic joint infections (PJI; n=61) and commensal isolates from healthy individuals (n=24) in regard to antimicrobial sensitivity, agr type, hld gene presence, biofilm production including presence of ica and aap genes involved in the biofilm formation process and epidemiology using both phenotypic (the PhenePlate-system) and genotypic [multilocus sequence typing (MLST)] methods. Among the PJI isolates, the majority (67%) were multidrug-resistant. Two major clusters of PJI isolates could be identified; 44% belonged to MLST sequence type (ST) 2, all but one were of agr type 1, and 31% were assigned ST215 and were of agr type 3. Of the commensal isolates, only one isolate was multidrug-resistant, and they were more molecular epidemiologically diverse with mainly MLST singletons and a maximum of 3 isolates assigned to the identical ST. Biofilm production was detected in 41% of the PJI isolates and 58% of the commensal isolates, with the aap gene (95%) more frequently detected than the ica genes (62%) in the biofilm-positive isolates. In conclusion, S. epidermidis isolated from PJIs and commensal isolates differed regarding antimicrobial sensitivity and molecular epidemiological typing using MLST, but not substantially in the distribution of agr types, biofilm production, or the presence of ica and aap genes.

First Three Neisseria gonorrhoeae Isolates with High-Level Resistance to Azithromycin in Sweden: a Threat to Currently Available Dual-Antimicrobial Regimens for Treatment of Gonorrhea?

Neisseria gonorrhoeae has developed resistance to all antimicrobials previously used for first-line treatment of gonorrhea (1).…

Simultaneous species identification and detection of rifampicin resistance in staphylococci by sequencing of the rpoB gene

In recent years, coagulase-negative staphylococci (CoNS) have been increasingly recognised as causative agents of various infections, especially in immunocompromised patients and related to implanted foreign body materials. In this study, rpoB sequencing was used for simultaneous species identification and detection of rifampicin resistance in clinical staphylococci isolates. Forty-nine (96%) out of 51 isolates, representing 17 different Staphylococcus species according to the initial phenotypic species identification, were identified to the species level using rpoB sequencing. Furthermore, the two remaining isolates were Kocuria sp. and Corynebacterium sp. respectively, according to 16S rRNA sequencing. Comparison with the phenotypic diagnostics also revealed that 8 (16%) of the 49 isolates differed regarding identified species. Discrepant analysis confirmed the result of the rpoB sequencing for all except 2 of these isolates, which could not be distinguished as single species using 16S rRNA sequencing. Regarding detection of rifampicin resistance, isolates obtained pre- and post-treatment with rifampicin were examined. These isolates comprised S. aureus (7 patients) and S. lugdunensis (1 patient). Rifampicin resistance was mainly detected following short-term treatment with rifampicin in combination with isoxazolyl-penicillin, or long-term treatment with rifampicin and ciprofloxacin. Each rifampicin-resistant isolate displayed an identical rpoB sequence as their corresponding rifampicin-susceptible isolates except for one (n = 6) or two (n = 1) nonsynonymous single nucleotide polymorphisms, or insertion of one codon (n = 1). In conclusion, rpoB sequencing is a rapid, objective and accurate method of species identification and simultaneous detection of rifampicin resistance in staphylococci.

Decreased susceptibility to chlorhexidine and prevalence of disinfectant resistance genes among clinical isolates of Staphylococcus epidermidis

Staphylococcus epidermidis is a versatile agent, being both a commensal and a nosocomial pathogen usually with an opportunistic role in association with implanted foreign body materials. Pre‐operative antiseptic preparation is an important strategy for reducing the risk of complications such as surgical site infection (SSI). Currently, the most widely used antiseptics are alcohols, quaternary ammonium compounds (QACs), and the bisbiguanide chlorhexidine. Occurrence of resistance to the latter agent has drawn increasing attention. The aim of this study was to investigate if decreased susceptibility to chlorhexidine among S. epidermidis was present in our setting, a Swedish university hospital. Staphylococcus epidermidis (n = 143), retrospectively collected, were obtained from prosthetic joint infections (PJI) (n = 61), post‐operative infections after cardiac surgery (n = 31), and the skin of the chest after routine disinfection prior to cardiac surgery (n = 27). In addition, 24 commensal isolates were included. Minimum inhibitory concentration (MIC) of chlorhexidine was determined on Mueller Hinton agar plates supplemented with serial dilutions of chlorhexidine. Five QAC resistance genes, qacA/B, smr, qacH, qacJ, and qacG, were detected using PCR. Decreased susceptibility to chlorhexidine was found in 54% of PJI isolates, 68% of cardiac isolates, 21% of commensal isolates, and 7% of skin isolates from cardiac patients, respectively. The qacA/B gene was present in 62/143 isolates (43%), smr in 8/143 (6%), and qacH in one isolate (0.7%). The qacA/B gene was found in 52% of PJI isolates, 61% of cardiac isolates, 25% of commensal isolates, and 19% of the skin isolates. In conclusion, decreased susceptibility to chlorhexidine, as well as QAC resistance genes, were prevalent among S. epidermidis isolates associated with deep SSIs.

Antibiotic susceptibility of Propionibacterium acnes isolated from orthopaedic implant-associated infections.

INTRODUCTION Prosthetic joint infections (PJIs) caused by Propionibacterium acnes account for a larger proportion of the total number of PJIs than previously assumed and thus knowledge of the antimicrobial susceptibility patterns of P. acnes is of great value in everyday clinical practice. MATERIALS AND METHODS Using Etest, the present study investigated the susceptibility of 55 clinical isolates of P. acnes, obtained from orthopaedic implant-associated infections of the knee joint (n = 5), hip joint (n = 17), and shoulder joint (n = 33), to eight antimicrobial agents: benzylpenicillin, clindamycin, metronidazole, fusidic acid, doxycycline, moxifloxacin, linezolid and rifampicin. Synergy testing was also conducted, in which rifampicin was combined with each of the remaining seven antibiotics. RESULTS All isolates (n = 55) were susceptible to most of the antibiotics tested, with the exception of 100% resistance to metronidazole, five (9.1%) isolates displaying decreased susceptibility to clindamycin, and one (1.8%) to moxifloxacin. None of the antimicrobial agents investigated were synergistic with each other when combined and nine isolates were antagonistic for various antimicrobial combinations. The majority of the antimicrobial combinations had an indifferent effect on the isolates of P. acnes. However, the combination of rifampicin and benzylpenicillin showed an additive effect on nearly half of the isolates. CONCLUSION Almost all P. acnes, isolated from orthopaedic implant-associated infections, predominantly PJIs, were susceptible to the antibiotics tested, with the exception of complete resistance to metronidazole. Synergy test could not demonstrate any synergistic effect but additive effects were found when combining various antibiotics. Antagonistic effects were rare.

Characterization of SCCmec elements in methicillin‐resistant Staphylococcus epidermidis isolated from blood cultures from neonates during three decades

Svensson K, Hellmark B, Söderquist B. Characterization of SCCmec elements in methicillin‐resistant Staphylococcus epidermidis isolated from blood cultures from neonates during three decades. APMIS 2011; 119: 885–93.

In vitro antimicrobial synergy testing of coagulase-negative staphylococci isolated from prosthetic joint infections using Etest and with a focus on rifampicin and linezolid.

In recent years, coagulase-negative staphylococci (CoNS) have been increasingly recognised as causative agents of various infections, especially in immunocompromised patients and related to implanted foreign body materials. CoNS, and especially Staphylococcus epidermidis, transform into a stationary growth phase and produce biofilm when involved in a foreign body infection, making them difficult to eradicate with antimicrobials. Rifampicin has the ability to penetrate biofilm, but resistance may develop rapidly. To reduce the emergence of resistance, rifampicin should be combined with additional antimicrobials, of which several different ones have been proposed, including the relatively new class of antimicrobials, oxazolidinones, represented by linezolid. Thirty-seven CoNS isolates from patients with prosthetic joint infection were investigated by synergy testing using Etest. Nine antimicrobial combinations, based on either rifampicin or linezolid, were tested. For 16 (43%) of the isolates, a synergistic (n = 5), additive (n = 14) and/or antagonistic (n = 11) effect were identified. In conclusion, Etest is an objective and easily performed in vitro method for antimicrobial synergy testing. However, each isolate requires testing for the specific combination considered for treatment.

Long-term molecular epidemiology of staphylococcus epidermidis blood culture isolates from patients with hematological malignancies

Staphylococcus epidermidis is an important cause of bloodstream infections in patients with hematological malignancies. Knowledge of the long-term epidemiology of these infections is limited. We surveyed all S. epidermidis blood culture isolates from patients treated for hematological malignancies at the University Hospital of Örebro, Sweden from 1980 to 2009. A total of 373 S. epidermidis isolates were identified and multilocus sequence typing, staphylococcal chromosome cassette mec (SCCmec) typing and standard antibiotic susceptibility testing were employed to characterize these isolates. The majority of the isolates 361/373 (97%) belonged to clonal complex 2, and the 373 isolates were divided into 45 sequence types (STs); Simpsons Diversity Index was 0.56. The most prevalent STs were ST2 (243/373, 65%) and ST215 (28/373, 8%). Ninety three percent (226/243) of the ST2 isolates displayed either SCCmec type III or IV. ST2 and 215 were isolated during the entire study period, and together these STs caused temporal peaks in the number of positive blood cultures of S. epidermidis. Methicillin resistance was detected in 213/273 (78%) of all isolates. In the two predominating STs, ST2 and ST215, methicillin resistance was detected in 256/271 isolates (95%), compared with 34/100 (34%) in other STs (p<0.001). In conclusion, in this long-term study of patients with hematological malignancies, we demonstrate a predominance of methicillin-resistant ST2 among S. epidermidis blood culture isolates.

Sequence types of Staphylococcus epidermidis associated with prosthetic joint infections are not present in the laminar airflow during prosthetic joint surgery

Molecular characterization of Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) has demonstrated a predominance of healthcare‐associated multi‐drug resistant sequence types (ST2 and ST215). How, and when, patients acquire these nosocomial STs is not known. The aim was to investigate if sequence types of S. epidermidis associated with PJIs are found in the air during prosthetic joint surgery. Air sampling was undertaken during 17 hip/knee arthroplasties performed in operating theaters equipped with mobile laminar airflow units in a 500‐bed hospital in central Sweden. Species identification was performed using MALDI‐TOF MS and 16S rRNA gene analysis. Isolates identified as S. epidermidis were further characterized by MLST and antibiotic susceptibility testing. Seven hundred and thirty‐five isolates were available for species identification. Micrococcus spp. (n = 303) and coagulase‐negative staphylococci (n = 217) constituted the majority of the isolates. Thirty‐two isolates of S. epidermidis were found. S. epidermidis isolates demonstrated a high level of allelic diversity with 18 different sequence types, but neither ST2 nor ST215 was found. Commensals with low pathogenic potential dominated among the airborne microorganisms in the operating field during prosthetic joint surgery. Nosocomial sequence types of S. epidermidis associated with PJIs were not found, and other routes of inoculation are therefore of interest in future studies.