Open AccessEvaluation of the Impact of Direct Plating, Broth Enrichment, and Specimen Source on Recovery and Diversity of Methicillin-Resistant Staphylococcus aureus Isolates among HIV-Infected Outpatients
Author(s) -
Sigrid K. McAllister,
Valérie Albrecht,
Gregory E. Fosheim,
H. Ken Lowery,
Philip J. Peters,
Rachel J. Gorwitz,
J. L. Guest,
Jeffery Hageman,
Rondeen Mindley,
Linda K. McDougal,
David Rimland,
Brandi Limbago
Publication year - 2011
Publication title -
journal of clinical microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.349
H-Index - 255
eISSN - 1070-633X
pISSN - 0095-1137
DOI - 10.1128/jcm.05323-11
Subject(s) - microbiology and biotechnology , staphylococcus aureus , methicillin resistant staphylococcus aureus , micrococcaceae , staphylococcal infections , agar , pulsed field gel electrophoresis , medicine , biology , bacteria , antibacterial agent , antibiotics , biochemistry , genetics , genotype , gene
We compared recovery ofStaphylococcus aureus and methicillin-resistantS. aureus (MRSA) from nasal and groin swab specimens of 600 HIV-infected outpatients by selective and nonselective direct plating and broth enrichment. Swabs were collected at baseline, 6-month, and 12-month visits and cultured by direct plating to mannitol salt agar (MSA) and CHROMagar MRSA (CM) and overnight broth enrichment with subculture to MSA (broth). MRSA isolates were characterized by pulsed-field gel electrophoresis (PFGE), staphylococcal cassette chromosomemec (SCCmec ) typing, and PCR for the Panton-Valentine leukocidin. At each visit, 13 to 15% of patients were colonized with MRSA and 30 to 33% were colonized with methicillin-susceptibleS. aureus (MSSA). Broth, CM, and MSA detected 95%, 82%, and 76% of MRSA-positive specimens, respectively. MRSA recovery was significantly higher from broth than CM (P ≤ 0.001) or MSA (P ≤ 0.001); there was no significant difference in recovery between MSA and CM. MSSA recovery also increased significantly when using broth than when using MSA (P ≤ 0.001). Among specimens collected from the groin, broth, CM, and MSA detected 88%, 54%, and 49% of the MRSA-positive isolates, respectively. Broth enrichment had a greater impact on recovery of MRSA from the groin than from the nose compared to both CM (P ≤ 0.001) and MSA (P ≤ 0.001). Overall, 19% of MRSA-colonized patients would have been missed with nasal swab specimen culture only. USA500/Iberian and USA300 were the most common MRSA strains recovered, and USA300 was more likely than other strain types to be recovered from the groin than from the nose (P = 0.05).