Abstract
In this study we aimed to characterize antimicrobial resistance in methicillin-resistant Staphylococcus aureus (MRSA) isolated from bloodstream infections as well as the associated genetic lineages of the isolates. Sixteen MRSA isolates were recovered from bacteremia samples from inpatients between 2016 and 2019. The antimicrobial susceptibility of these isolates was tested by the Kirby–Bauer disk diffusion method against 14 antimicrobial agents. To determine the macrolide–lincosamide–streptogramin B (MLSB) resistance phenotype of the isolates, erythromycin-resistant isolates were assessed by double-disk diffusion (D-test). The resistance and virulence genes were screened by polymerase chain reaction (PCR). All isolates were characterized by multilocus sequence typing (MLST), spa typing, staphylococcal chromosomal cassette mec (SCCmec) typing, and accessory gene regulator (agr) typing. Isolates showed resistance to cefoxitin, penicillin, ciprofloxacin, erythromycin, fusidic acid, clindamycin, and aminoglycosides, confirmed by the presence of the blaZ, ermA, ermC, mphC, msrA/B, aac(6’)-Ie-aph(2’’)-Ia, and ant(4’)-Ia genes. Three isolates were Panton–Valentine-leukocidin-positive. Most strains (n = 12) presented an inducible MLSB phenotype. The isolates were ascribed to eight spa-types (t747, t002, t020, t1084, t008, t10682, t18526, and t1370) and four MLSTs (ST22, ST5, ST105, and ST8). Overall, most (n = 12) MRSA isolates had a multidrug-resistance profile with inducible MLSB phenotypes and belonged to epidemic MRSA clones.
Highlights
Staphylococcus aureus is an opportunist human pathogen responsible for numerous types of infections, from skin infections, such as abscesses or infected wounds, to life-threatening conditions, such as endocarditis, osteomyelitis, or septicemia [1]
A total of 16 methicillin-resistant Staphylococcus aureus (MRSA) isolates were obtained from 103 hospitalized patients with bacteremia over the 3-year study period, corresponding to a patient incidence of 15.5%
The isolate categorized as ST5984 belonged to spa-type t1084, staphylococcal chromosomal cassette mec (SCCmec), and agr type II and presented resistance to penicillin, erythromycin, ciprofloxacin, and fusidic acid
Summary
Staphylococcus aureus is an opportunist human pathogen responsible for numerous types of infections, from skin infections, such as abscesses or infected wounds, to life-threatening conditions, such as endocarditis, osteomyelitis, or septicemia [1]. S. aureus has become an important cause of nosocomial infections, methicillin-resistant. S. aureus (MRSA), which is usually associated with a multidrug-resistance profile [3]. MRSA infections are difficult to treat and are a leading cause of morbidity and mortality, especially among hospitalized patients and humans with weakened immune systems [4]. Due to the increase of MRSA strains, macrolides, lincosamides, and streptogramin B (MLSB ) were often used to treat MRSA infections, which led to a subsequent cross-resistance to these antibiotics [5]. Different mechanisms are responsible for the MLSB resistance, the most common being the target modification mediated by the erm (erythromycin ribosome methylase) gene [6]. The predominant clonal complexes responsible for hospital infections in Portugal are CC22 and CC5, with the epidemic methicillin-resistant
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