The isolation and identification ofMycobacterium aviumcomplex (MAC) recovered from Los Angeles potable water, a possible source of infection in AIDS patients

Los Angeles water was investigated as a possible source of Mycobacterium avium complex (MAC) infection in patients with AIDS. MAC consists of M. avium (MA), M. intracellulare (MI) and Mycobacterium X (MX) (positive for MAC by DNA probe but not MA or MI). The study included 13 reservoirs supplying 90% of the water to the City of Los Angeles, ten major hospitals and 58 dwellings. Water samples were filtered through 0.45 μm Millipore filters and decontaminated with either sodium hydroxide and/or oxalic acid and cetylpyridinium chloride. The decontaminated filters were placed on selective Middlebrook 7H10 medium and observed for growth at three and eight weeks. Coccobacillary acid‐fast bacilli were subcultured; Tween and nitrate negative isolates were identified by DNA hybridization probes. Eight morphotypes were observed and nontubercu‐lous mycobacteria (NTM) were recovered from 12 (92%) reservoirs, 54 (95%) homes, and ten (100%) hospitals. Twenty‐six (34%) of the NTM were probe positive for MAC. MA was isolated from 70% of hospitals, 9% of dwellings, and 15% of reservoirs. Serotyping and multilocus enzyme electrophoresis results demonstrate a genetic relatedness between some M[Agrave] water and MA clinical isolates.