Performance of RGM Medium for Isolation of Nontuberculous Mycobacteria from Respiratory Specimens from Non-Cystic Fibrosis Patients

摘要

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 degrees C (RGM30) and 35 degrees 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 degrees 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.