Abstract
Staphylococcus aureus is an important human pathogen that causes serious antibiotic-resistant infections. Its population structure is marked by the appearance and dissemination of successful lineages across different settings. To begin understanding the population structure of S. aureus causing ocular and otolaryngology infections, we characterized 262 isolates by antimicrobial sensitivity testing and multilocus sequence typing (MLST). Methicillin-resistant S. aureus were subjected to SCCmec typing and Panton-Valentine leukocidin (PVL) screening. Although we detected a high level of genetic diversity among methicillin-sensitive (MSSA) isolates, (63 sequence types—STs), the population was dominated by five lineages: ST30, ST5, ST8, ST15 and ST97. Resistance to penicillin, erythromycin and clindamycin was common among the major MSSA lineages, with fluctuations markedly impacted by genetic background. Isolates belonging to the predominant lineage, ST30, displayed high rates of resistance to penicillin (100%), erythromycin (71%), and clindamycin (63%). Overall, 21% of the isolates were methicillin-resistant (MRSA), with an apparent enrichment among otitis and orbital cellulitis isolates (>40%). MRSA isolates belonged to 14 STs grouped in 5 clonal complexes (CC), however, CC5 (56.1%) and CC8 (38.6%) dominated the population. Most CC5 strains were SCCmec type II, and resembled the hospital-adapted USA100 clone. CC8 strains were SCCmec type IV, and 86% were positive for the PVL toxin, common features of the community-acquired clone USA300. CC5 strains harboring a SCCmec type IV, typical for the USA800 clone, comprised 15.5% of the population. USA100 strains were highly resistant to clindamycin, erythromycin and levofloxacin (100%), while USA300 strains were frequently resistant to erythromycin (89%) but displayed lower rates of resistance to levofloxacin (39%) and clindamycin (17%). Our data demonstrate that the ocular and otolaryngology S. aureus populations are composed of strains that are commonly resistant to clinically relevant antibiotics, and are associated with the major epidemic clonal complexes of both community and hospital origins.
Highlights
Staphylococcus aureus is a prevalent community-acquired pathogen as well as a leading cause of nosocomial infection [1, 2]
Presence or absence of the Panton-Valentine Leukocidin (PVL) toxin gene was determined by direct PCR amplification of the LukS-PV-lukF-PV genes using GoTaq Green Master Mix (Promega) and previously described primers [24]. In this cross-sectional study, we evaluated the molecular epidemiology and antimicrobial resistance profile of 262 S. aureus isolates recovered between January and December, 2014 from patients seen at the Massachusetts Eye and Ear (Table 1)
Despite the ordinary community origins of our collection, we found moderate to high rates of resistance to clinically important antibiotics that are often used for treatment of infections affecting the eye and upper respiratory tract, such as penicillin ( 78%), erythromycin ( 41%) and clindamycin ( 32%)
Summary
Staphylococcus aureus is a prevalent community-acquired pathogen as well as a leading cause of nosocomial infection [1, 2]. Antimicrobial resistance surveillance studies of ocular and otolaryngology isolates have been performed previously on a local [15,16,17,18] or nationwide scale [7, 19], but molecular typing to characterize population structure is not a common component of those studies. To fill this gap, we sought to investigate the molecular epidemiology of S. aureus isolated from eye, ear, and sinus infections treated at a tertiary care center in New England. We used antimicrobial resistance testing and sequence typing to determine the population structure of the S. aureus reservoir in this setting, and to determine whether the major genetic lineages display varying rates of resistance to clinically relevant antibiotics
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