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

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 28day 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 ionizationtime 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 ϭ 0.01) or Middlebrook 7H11 agar (76.7% versus 47.4%; P ϭ 0.0001) alone, but it was not significantly different from that of an acidfast bacillus culture (AFC) which includes both MGIT and Middlebrook 7H11 agar (76.7% versus 63.9%; P ϭ 0.0647). RGM35 had significantly lower sensitivity than the MGIT system (49.6% versus 59.4%; P ϭ 0.0367) and AFC (49.6% versus 63.9%; P ϭ 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.

Evaluation of a novel rapidly-growing mycobacteria medium for isolation of Mycobacterium abscessus complex from respiratory specimens from patients with bronchiectasis

“…In conclusion, our study corroborates previous studies in patients with chronic pulmonary (bronchiectatic) disease where RGM medium shows potential for transitioning the current AFB sputum culture processing scheme into a less tedious, less time-consuming and more effective work flow with the expectation of enhanced recovery of NTM, especially the M. abscessus complex [4, 5, 6, 7, 11, 12].…”

“…The relatively high contamination rate observed in this study is partly attributable to the fact that 58% of samples (173/297) were from patients who had previously submitted samples that had led to contamination during routine culture for AFB. Although the number of patients and cultures in the current studies is less than some previous studies, our number of isolates of M. abscessus complex was higher than any study we are aware of to date [5, 6, 7, 12, 13].…”

Evaluation of a new culture medium for isolation of nontuberculous mycobacteria from environmental water samples

“…The presence of contamination by non-mycobacteria and the length of time required for NTM growth means there is a higher risk of NTM going undetected using typical environmental NTM testing methods. Current decontamination processes and selective media, such as 7H11, have also been shown to suppress the growth of some species of NTM [ 10 , 19 ]. Both clinical and environmental samples processed for NTM often require methods or media with high selectivity to restrict the growth of contaminants that are often present in the sample [ 16 ].…”

Nontuberculous mycobacteria isolated from specimens of pulmonary tuberculosis suspects, Northern Tunisia: 2002-2016

“…Another explanation would be that for decades, the Tunisian population has been massively vaccinated with BCG, at birth and at entry to school, a practice that could have contributed to reduce NTM infection rates [30]. Furthermore, we believe that the use of the classical decontamination protocol coupled to culture in Löwenstein-Jensen medium might not be optimal for NTM isolation [31,32].…”