Performance of RGM medium for isolation of nontuberculous mycobacteria from respiratory specimens from non-cystic fibrosis patients

Suwatchareeporn Rotcheewaphan, Oluwadamilola E. Odusanya, Christina M. Henderson, Dominic Stephenson, Kenneth N. Olivier, John D. Perry, Adrian M. Zelazny

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4 Citations (Scopus)

Abstract

A new selective medium for rapidly growing mycobacteria (RGM medium) was evaluated on respiratory specimens from non-cystic fibrosis patients and compared to the mycobacterial growth indicator tube (MGIT) system and Middlebrook 7H11 agar for the isolation of all nontuberculous mycobacteria (NTM). A total of 203 mucolyzed respiratory specimens collected from 163 patients were inoculated on RGM medium and incubated at both 30°C (RGM30) and 35°C (RGM35) over a 28-day period. N-Acetyl-L-cysteine-sodium hydroxide (NALC-NaOH)-decontaminated specimens were inoculated into MGIT and Middlebrook 7H11 agar and incubated at 35°C for 42 days. NTM were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) or gene sequencing. A total of 133 NTM isolates were recovered overall from 101 (49.8%) specimens collected from 85 (52.1%) patients by a combination of all culture methods. The sensitivity of RGM30 for the recovery of NTM was significantly higher than that of either the MGIT system (76.7% versus 59.4%; P 0.01) or Middlebrook 7H11 agar (76.7% versus 47.4%; P 0.0001) alone, but it was not significantly different from that of an acid-fast bacillus culture (AFC) which includes both MGIT and Middlebrook 7H11 agar (76.7% versus 63.9%; P 0.0647). RGM35 had significantly lower sensitivity than the MGIT system (49.6% versus 59.4%; P 0.0367) and AFC (49.6% versus 63.9%; P 0.0023). RGM medium was highly effective at inhibiting the growth of nonmycobacterial organisms in the respiratory specimens, with breakthrough contamination rates of 5.4% and 4.4% for RGM30 and RGM35, respectively.

Original languageEnglish
Article numbere01519-18
JournalJournal of Clinical Microbiology
Volume57
Issue number2
Early online date30 Jan 2019
DOIs
Publication statusPublished - 1 Feb 2019

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