Clinical and Microbiological Aspects of β-Lactam Resistance in Staphylococcus lugdunensis

Abstract

Antimicrobial susceptibility results from broth microdilution MIC testing of 993 Staphylococcus lugdunensis isolates recovered from patients at a tertiary care medical center from 2008 to 2015 were reviewed. Ninety-two oxacillin-susceptible isolates were selected to assess the accuracy of penicillin MIC testing, the penicillin disk diffusion test, and three ␤-lactamase tests, including the cefoxitin-induced nitrocefin test, penicillin cloverleaf assay, and penicillin disk zone edge test. The results of all phenotypic tests were compared to the results of blaZ PCR. The medical records of 62 patients from whom S. lugdunensis was isolated, including 31 penicillinsusceptible and 31 penicillin-resistant strains, were retrospectively reviewed to evaluate the clinical significance of S. lugdunensis isolation, the antimicrobial agents prescribed, if any, and the clinical outcome. MIC testing revealed that 517/993 (52.1%) isolates were susceptible to penicillin and 946/993 (95.3%) were susceptible to oxacillin. The induced nitrocefin test was 100% sensitive and specific for the detection of ␤-lactamase compared to the blaZ PCR results, whereas the penicillin disk zone edge and cloverleaf tests showed sensitivities of 100% but specificities of only 9.1% and 89.1%, respectively. The penicillin MIC test had 100% categorical agreement with blaZ PCR, while penicillin disk diffusion yielded one major error. Only 3/31 patients with penicillin-susceptible isolates were treated with a penicillin family antimicrobial. The majority of cases were treated with other ␤-lactams, trimethoprimsulfamethoxazole, or vancomycin. These data indicate that nearly all isolates of S. lugdunensis are susceptible to narrow-spectrum antimicrobial agents. Clinical laboratories in areas with resistance levels similar to those described here can help promote the use of these agents versus vancomycin by effectively designing their antimicrobial susceptibility reports to convey this message.KEYWORDS Staphylococcus, antimicrobial resistance, beta-lactams, lugdunensis S taphylococcus spp. are normal skin flora inhabitants and, in some cases, opportunistic human pathogens (1). The coagulase-negative staphylococci (CoNS) are typically less virulent than Staphylococcus aureus in healthy human hosts. One exception is Staphylococcus lugdunensis, which may exhibit increased virulence compared to that of other CoNS (2). Infections associated with S. lugdunensis can include skin and soft tissue infections, native valve endocarditis, urinary tract infections, and prosthetic device infections (2).Isolates of CoNS, in particular Staphylococcus epidermidis, that harbor the mecA gene can have oxacillin MICs in the 0.5-to 2.0-g/ml range, which is much lower than the oxacillin MICs observed in mecA-positive isolates of S. lugdunensis and S. aureus (3-7). As such, the Clinical and Laboratory Standards Institute (CLSI) recommends that

Comparative Genome Analysis of Staphylococcus lugdunensis Shows Clonal Complex-Dependent Diversity of the Putative Virulence Factor, ess/Type VII Locus

“…Fosfomycin resistance-associated gene was highly conserved among the 21 strains while the distribution of penicillin and fusidic acid resistance genes was variable between isolates. This finding is in accordance with the results of McHardy et al (2017). who showed that the blaZ gene was detected in 39.1% of oxacillin-susceptible S. lugdunensis isolates.…”

“…S. lugdunensis exhibits a highly conserved antibiotic susceptibility to most anti-staphylococcal antibiotics, which may be related to these different barriers against the integration of foreign DNA (Higaki et al, 1999; McHardy et al, 2017). Indeed, only one plasmid carrying an antibiotic resistance gene ( tetK ) was identified in a newly sequenced genome.…”

Tailoring Antimicrobial Susceptibility Testing to Individual Species of Coagulase-Negative Staphylococci: Next Up, Staphylococcus epidermidis

“…The need for individualized AST methods and breakpoints for CoNS species was first shown with S. lugdunensis. S. lugdunensis isolates positive for mecA were found to have oxacillin MICs of Ն4 g/ml consistent with the higher breakpoint set for S. aureus (8)(9)(10). This is not surprising, given that S. lugdunensis, while classified as CoNS, behaves clinically in a manner similar to that seen with S. aureus (2).…”

Management and Prevention of Central Venous Catheter-Related Infections in the ICU

“…17 Of note, Staphylococcus lugdunensis should be treated in a similar manner to S. aureus. 167 For enterococcal CR-BSI, ampicillin is the first choice for ampicillin-susceptible strains, vancomycin for those which are ampicillin resistant, and daptomycin or linezolid for vancomycin-resistant (VRE) strains. 168 The role of combination therapy for treating enterococcal CR-BSI without endocarditis is unresolved, especially for VRE.…”