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Methicillin-resistant Staphylococcus aureus in acute otitis externa?.

ABSTRACT: ObjectiveOtologic methicillin-resistant Staphylococcus aureus (MRSA) infection has historically been rare, but given the rise in community-acquired MRSA carriage and infection at other body sites, prevalence rates may be changing. The goal of this study was to determine the prevalence of MRSA in recent otologic cultures from patients with acute otitis externa (AOE).Study designRetrospective review of an institutional microbiologic database.MethodsA retrospective analysis was performed on serial culture isolates taken from the ear at a quaternary care hospital from January 2014 to April 2016. The causative pathogen and antibiotic sensitivity was determined by culture isolation and end point mean inhibitory concentration (MIC) testing. Medical records were reviewed to document patient characteristics, chronicity of infection, symptomatology, and previous treatments.ResultsOver the study period, 173 patients were diagnosed with AOE and underwent otologic cultures of the ear. Fifty-three (30.6%) of cultures grew S.aureus (SA). Of SA infections, 15 (28.3%) were identified as MRSA. MRSA patients were typically older than patients with methicillin-sensitive SA (MSSA) (mean age 46.7 ± 17.9 vs 29 ± 19.4, P = 0.003) and had more medical comorbidities (4 vs 1.7, P = 0.001). Compared to patients with MSSA, patients with MRSA were significantly more likely to have had prior ototopical antibiotic exposure (37% vs 73%, P = 0.019).ConclusionContemporary ear culture isolates at quaternary care center show higher rates of MRSA compared to historical reports in the literature. Clinicians should consider ear cultures to identify MRSA AOE.Level of EvidenceIV.

SUBMITTER: Duarte MJ

PROVIDER: S-EPMC6284227 | biostudies-other | 2018 Dec

REPOSITORIES: biostudies-other

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Project description:Methicillin resistant Staphylococcus aureus (MRSA) infection is becoming refractory to existing antibiotic therapy owing to the inherent ability of S. aureus to develop rapid resistance and is considered a major threat to public health. We found that a natural isolate of Bacillus pumilus from the Columbia River Estuary produces a strong anti-MRSA compound, amicoumacin A. As amicoumacin A has been reported to exhibit anti-microbial, anti-inflammatory, and anti-ulcer activities, we sought to uncover its mechanism of action. Genome-wide transcriptome analysis of S. aureus COL in response to amicoumacin A showed alteration in the expression of genes involved in several cellular processes including cell envelope turnover, cross-membrane transport, virulence, metabolism, and general stress response. The most highly induced gene was lrgA, encoding an antiholin-like product, which has been shown to be induced in response to a collapse of membrane potential. In order to gain further insight into the mechanism of action of amicoumacin A, a whole genome comparison of wild-type COL and amicoumacin A-resistant mutants isolated by serial passage method was carried out. Single point mutations resulting in codon substitutions were uncovered in several distinct genes: ksgA, RNA dimethyltranferase; fusA, elongation factor G; dnaG, primase, ; lacD, tagatose 1,6-bisphosphate aldolase, ; and SACOL0611, encoding a putative glycosyl transferase gene. Based on these results, a candidate approach was undertaken to recreate the same amino acid substitution individually in FusA and KsgA, each of which resulted in two-fold resistance towards amicoumacin A. The fusA gene is known as the site for fusidic acid- resistant mutations; however the codon substitutions in EF-G that cause amicoumacin A resistance and fusidic acid resistance occur in separate domains and do not bring about cross resistance. Taken together, these results suggest that amicoumacin A might cause perturbation of the cell membrane and lead to energy dissipation. Decreased rates of cellular metabolism including protein synthesis and DNA replication in resistant strains might allow cells to compensate for membrane dysfunction and thus increase cell survivability.

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Methicillin-resistant Staphylococcus aureus in acute otitis externa?.

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