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C. K. Hesje, C. M. Sanfilippo, W. Haas, T. W. Morris; Contribution of Hospital-Acquired (HA) and Community-Acquired (CA) Methicillin-Resistant Staphylococcus aureus (MRSA) to Ocular Infections. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2414.
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Methicillin-resistant Staphylococcus aureus (MRSA) strains are commonly classified as hospital-acquired (HA) or community-acquired (CA). Typical HA isolates are characterized by a high level of multi-drug resistance and the SCCmec type II resistance genes. CA isolates are generally susceptible to most drugs, are often of SCCmec type IV, and frequently carry the Panton-Valentine leukocidin (PVL) genes. This study determined the presence of traits characteristic for HA and CA strains in ocular MRSA isolates.
Fifty recent ocular isolates, consisting of 35 MRSA and 15 methicillin-susceptible S. aureus (MSSA) comparator strains, were characterized. Minimum inhibitory concentration (MIC) testing was done according to current CLSI guidelines. Detection of the PVL-encoding genes and determination of the SCCmec type was done by PCR, while spa typing was performed by DNA sequencing.
Of the 35 MRSA isolates tested, 22 were of SCCmec type II, 12 of SCCmec type IVa, and 1 was of SCCmec type IVb. Nine (25.7%) of the 35 isolates tested positive for PVL and 31 (88.6%) isolates were resistant to ciprofloxacin (CIP). MRSA isolates of SCCmec type II lacked the PVL genes and had CIP MIC50 values of 256 ug/ml (range 32-256). Most (81.8%) of these isolates were of spa type t002. SCCmec type IV isolates were frequently of spa type t008, possessed the PVL genes (69.2%), and had CIP MIC50 values of 16 ug/ml (range 0.12-64). In the 15 MSSA control isolates, 3 (20%) tested positive for PVL and 6 (40%) were CIP resistant (MIC50 values of 0.5 ug/ml, range 0.12-256). Similar to their MRSA counterparts, the 5 MSSA isolates of spa type t002 lacked the PVL genes and showed high levels of CIP resistance. The remaining 10 MSSA were of diverse genetic background and 90% were CIP-susceptible.
Of the 35 ocular MRSA isolates studied here, 22 isolates met the criteria for HA-MRSA and 9 fit the definition of CA strains, indicating that both subgroups are well capable of infecting the eye. The results further suggest that ocular isolates mirror traits that are found in strains from other sites of colonialization or infection.
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