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

Abstract

Nontuberculous mycobacteria (NTM) are waterborne pathogens commonly found in building water systems where they are a primary concern to vulnerable patient populations and can cause severe disease. The recovery of NTM from environmental samples can be a laborious undertaking and current pre-treatment methods and selective media lack sensitivity. We explored the use of the highly selective Rapidly Growing Mycobacteria (RGM) medium for culturing NTM from environmental water samples compared to existing methods. In total, 223 environmental water samples, including potable and non-potable water, were cultured for NTM using three culture media. In addition to direct culture on RGM medium, each sample was cultured on Middlebrook 7H10 medium and Mitchison 7H11 medium after pre-treatment with 0.2M KCl-HCl. Additionally, 33 distinct species of NTM were inoculated onto RGM medium and 7H10 medium in parallel to directly compare their growth. The use of RGM medium alone without pre-treatment provided a sensitivity (91%) comparable to that offered by culture on both 7H10 and 7H11 with acid pretreatment (combined sensitivity; 86%) with significantly less overgrowth and interference from other organisms on RGM medium. The average concentration of NTM observed on RGM medium alone was comparable to or greater than the NTM concentration on either medium alone or combined. Thirty-three species were examined in parallel and all tested strains of 27 of these species successfully grew on RGM medium, including 19 of 21 from the CDC’s healthcare-associated infections species list. RGM medium was successful at recovering environmental NTM without a pre-treatment, greatly reducing labor and materials required to process samples. Simplification of culture processing for environmental NTM will allow for a better assessment of their presence in building water systems and the potential for reduced exposure of susceptible populations.

A New Culture Method for the Detection of Non-Tuberculous Mycobacteria in Water Samples from Heater–Cooler Units and Extracorporeal Membrane Oxygenation Machines

“…NTM Elite agar’s effectiveness in inhibiting non-AFB contamination is in keeping with a report by Alexander et al [ 19 ], showing that RGM medium generates much fewer samples with non-AFB growth (0.4%) than any other medium tested. In our study, however, we observed overgrowth in 9% of samples, which is somewhat higher than that reported by Alexander and co-workers.…”

“…Recent evidence has shown that protocols based on rapidly growing mycobacterium (RGM) media can be highly effective in recovering NTM from potable and non-potable water samples [ 19 ]. More specifically, RGM medium alone, without pre-treatment, has been shown to afford higher sensitivity (~91%) and lower overgrowth of contaminating water-borne microorganisms compared to standard media.…”

Recovery of Mycobacteria from Heavily Contaminated Environmental Matrices

“…Yield can be affected of course by the decontamination method due to sensitivity of some mycobacterial species to a decontamination agent [ 66 ]. Cultivation may be (and will be in further work) refined by using special cultivation media (e.g., RGM) [ 67 ]. For detection of mycobacteria by standard qPCR in these samples, the specificity was not high, perhaps unsurprisingly, as this method was primarily designed for less microbially loaded samples.…”

Antituberculosis Activity and Iron Chelation Ability of Brazilin Isolated from Caesalpinia Sappan L.

“…Purnanamasari et al [14] compared with the culture method, the Rema method had 80% sensitivity, 100% PPV (positive predictive value), and 97% NPV (negative predictive value). The feasibility study of the medium as a primary isolation media for mycobacteria, using MB BACT and Middlebrook 7h10 (MB7H10) and LJ medium, showed that the medium LJ was better and specific than the medium Middlebrook 7 H10 [15]. Antimicrobial susceptibility testing (AST) of Mtb has customarily been performed by the agar technique of proportion using the Lowenstein-Jensen (LJ) medium as bacterial culture medium by including the concentration the drug that has been suspended into the LJ medium.…”