Antimicrobial Resistance and Antimicrobial Activity of Staphylococcus lugdunensis Obtained from Two Spanish Hospitals

Abstract

Staphylococcus lugdunensis is a coagulase-negative-staphylococci (CoNS) that lately has gained special attention in public health as a human pathogen and also as a bacteriocin-producer bacteria. In this study, we characterized 56 S. lugdunensis isolates recovered from human samples in two Spanish hospitals. Antimicrobial susceptibility testing was performed and antimicrobial resistance and virulence genotypes were determined. Antimicrobial activity (AA) production was evaluated by the spot-on-lawn method against 37 indicator bacteria, including multidrug-resistant (MDR) isolates, and the presence of the lugD gene coding for lugdunin bacteriocin was analyzed by PCR. The antibiotic resistance detected was as follows (% resistance/genes detected): penicillin (44.6%/blaZ), oxacillin (1.8%/mecA on SCCmec-V), erythromycin-clindamycin inducible (7.1%/erm(C), msrA), tetracycline (5.3%/tetK), gentamicin and/or tobramycin (3.6%/ant(4')-Ia, acc(6')-aph(2″)), and fosfomycin (21.4%). A MDR phenotype was detected in 5% of isolates. Twenty-one of the S. lugdunensis isolates showed susceptibility to all 20 antibiotics tested (37.5%). The screening for AA revealed 23 antimicrobial producer (AP) isolates with relevant inhibition against coagulase-positive-staphylococci (CoPS), including both methicillin-susceptible and -resistant S. aureus. The lugD gene was detected in 84% of the 56 S. lugdunensis isolates. All of the AP S. lugdunensis isolates (n = 23) carried the lugD gene and it was also detected in 24 of the non-AP isolates, suggesting different gene expression levels. One of the AP isolates stood out due to its high antimicrobial activity against more than 70% of the indicator bacteria tested, so it will be further characterized at genomic and proteomic level.

Keywords: S. lugdunensis; antibiotic resistance; bacteriocins; coagulase-negative-staphylococci.

Figure 1

Number of antimicrobial producer (AP) isolates of each established antimicrobial categories (InterA-AP, IntraA-AP and RA-AP) that present high, medium and low antimicrobial activity (H-Act, M-Act and L-Act, respectively). * Statistically significant differences were observed (p ≤ 0.05).

Figure 2

Antimicrobial profile summary of the 9 high antimicrobial-producers S. lugdunensis isolates with a broad Interespecific Activity (InterA-AP). Abbreviations: CoPS, coagulase-positive Staphylococcus; CoNS, coagulase-negative Staphylococcus.

Figure 3

Antimicrobial resistance phenotype of the 56 S. lugdunensis isolates versus the 23 AP and the 33 non-AP S. lugdunensis isolates. Abbreviations: PEN, penicillin; OXA, oxacillin; FOS, Fosfomycin; ERY-CLIind, erythromycin-clindamycin inducible; TET, tetracycline; TOB, tobramycin; GEN, gentamycin; MUP, mupirocin. Non-statistically significant differences (p ≤ 0.05) were observed.