Detection of non-tuberculous mycobacteria in hospital water by culture and molecular methods

Non-tuberculous mycobacteria (NTM) are emerging pathogens in immunocompromised patients. Therefore, it is important for hospitals to consider tap water as a source for these infections. Aim of the study was to establish highly sensitive and specific techniques to detect and identify NTM in hospital drinking water. A Mycobacterium genus-specific 16S rDNA-based real-time LightCycler PCR assay with internal inhibition control and a M. xenopi-specific PCR were developed. Ninety-three water samples from 53 taps from 4 hospitals were investigated. NTM were cultured from 21 of 49 (43%) cold and 32 of 44 (73%) warm water samples. M. chelonae, M. flavescens, M. frederiksbergense, M. gordonae, M. moriokaense, M. mucogenicum, M. vaccae, and M. xenopi were identified with molecular methods. All 93 water samples were positive in the genus-specific PCR. M. xenopi DNA was detected in 40 of 44 (91%) warm and 33 of 49 (67%) cold water samples including 45 of 65 (69%) M. xenopi culture-negative samples. In conclusion, selective culture followed by molecular identification methods enabled detection of rare species of NTM in hospital drinking water and may be used in further studies investigating the epidemiology of NTM in water samples. The real-time PCR assays have a high sensitivity and allow rapid quantification of mycobacterial DNA in water samples.