title: Evaluation of RGM Medium for Isolation of Nontuberculous Mycobacteria from Respiratory Samples from Patients with Cystic Fibrosis in the United States.
abstract: A novel selective agar (RGM medium) has been advocated for the isolation of rapidly growing mycobacteria from the sputa of cystic fibrosis (CF) patients. The aim of this study was to compare RGM medium toBurkholderia cepaciaselective agar (BCSA) and a standard acid-fast bacillus (AFB) culture method for the isolation of nontuberculous mycobacteria (NTM) from patients with CF. The applicability of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for the identification of NTM isolated on RGM medium was also assessed. Respiratory samples (n= 869) were collected from 487 CF patients and inoculated directly onto RGM medium and BCSA. Cultures were incubated at 30°C and examined for up to 28 days. A subset of 212 samples (from 172 patients) was also cultured by using a mycobacterial growth indicator tube (MGIT) and on Lowenstein-Jensen medium following dual decontamination. By using a combination of all methods, 98 mycobacteria were isolated from 869 samples (11.3%). The sensitivity of RGM medium (96.9%) was significantly higher than that of BCSA (35.7%) for the isolation of mycobacteria (P< 0.0001). The sensitivity of RGM medium was also superior to that of standard AFB culture for the isolation of mycobacteria (92.2% versus 47.1%;P< 0.0001). MALDI-TOF MS was effective for the identification of mycobacteria in RGM medium. RGM medium offers a simple and highly effective tool for the isolation of NTM from patients with CF. Extended incubation of RGM medium for 28 days facilitates the isolation of slow-growing species, including members of theMycobacterium aviumcomplex (MAVC).
authors.affiliation: Pathology and Laboratory Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina, USA.|Infectious Diseases, Department of Medicine, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand.
authors.forename: Rongpong
authors.identifier: 0000-0002-1622-1209
authors.initials: R
authors.lastname: Plongla
authors.affiliation: Microbiology Department, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
authors.forename: Clair L
authors.initials: CL
authors.lastname: Preece
authors.affiliation: Microbiology Department, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
authors.forename: John D
authors.initials: JD
authors.lastname: Perry
authors.affiliation: Pathology and Laboratory Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina, USA Peter.Gilligan@unchealth.unc.edu.|Clinical Microbiology-Immunology Laboratories, UNC Health Care, Chapel Hill, North Carolina, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Gilligan
mesh_terms: D000362:Agar / Q000737:chemistry*; D003470:Culture Media / Q000737:chemistry*; D003550:Cystic Fibrosis / Q000382:microbiology*; D006801:Humans; D009165:Mycobacterium Infections, Nontuberculous / Q000175:diagnosis* / Q000382:microbiology; D009170:Nontuberculous Mycobacteria / Q000302:isolation & purification*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013183:Sputum / Q000382:microbiology*; D014481:United States
chemical_list: D003470:Culture Media; D000362:Agar
keywords: culture; cystic fibrosis; mycobacterium; rapid grower; selective medium