Downloaded from www.microbiologyresearch.org by IP: 54.166.228.43 On: Tue, 06 Sep 2016 15:13:31 Microbiology (1999), 145, 1317-1324 Printed in Great Britain Colony morphotypes on Congo red agar segregate along species and drug susceptibility lines in the Mycobacterium avium-in tracellulare comp I ex Gerard A. Cangelosi, Christine 0. Palermo, Jean-Pierre Laurent, April M. Hamlin and William H. Brabant Author for correspondence: Gerard A. Cangelosi. Tel: + 1 206 284 8846. Fax: + 1 206 284 0313. e-mail : cangelos@u.washington.edu Seattle Biomedical Research Institute, 4 Nickerson St, Seattle, WA 98109, USA Isolates of the Mycobacterium avium-intracellulare complex (MAC) have long been known to segregate into transparent, opaque and rough colony morphotypes that differ from each other in clinically important parameters including drug susceptibility and virulence. Here the authors report additional morphotypic variation that occurs on two levels: interspecific (between M. avium and M. intracellulare) and intraspecific (within individual M. avium isolates). Clinical isolates of M. avium grown on Congo red (CR) plates formed red, pink or mixed (red and white) opaque colonies, while M. intracellulare isolates formed purely white opaque colonies. A quantitative CR binding assay showed that this interspecific differential applies to transparent as well as opaque colony variants; however, it was less pronounced among laboratory reference strains than among recent clinical isolates. Opaque colonies of M. avium isolates with 'mixed' phenotypes segregated into stable opaque red and white variants with shared IS1245 banding patterns (intraspecific segregation). White segregants of M. avium were more flocculent and significantly more resistant to ciprofloxacin and rifamycin drugs than were red segregants. Thus, cultivation on CR agar revealed a previously unknown multi- drug resistant colony morphotype of M. avium. Keywords : Mycobacterium avium-intracellulare complex (MAC), AIDS, phenotypic switching, antibiotic resistance, pre-rRNA INTRODUCTION The Mycobacterium avium-intracellulare complex (MAC) is responsible for common opportunistic in- fections of immunodeficient individuals, especially AIDS patients with low CD4' cell counts. Most AIDS- associated MAC infections involve the species M. avium, while non-AIDS-associated infections involve M . avium and M . intracellulare at approximately equal frequencies. In contrast to the primary mycobacterial pathogens Mycobacterium tuberculosis and Myco- bacterium leprae, which are transmitted from person to person, MAC infections are normally acquired from environmental sources (Guthertz et al., 1989; Grange, 1991 ; Inderlied et al., 1993 ; Peloquin, 1997; Swanson et al., 1998; Von Reyn et al., 1994). Most MAC isolates segregate into smooth transparent (SmT), smooth opaque (SmD or SmO) and sometimes rough colony type variants. Transparent variants pre- dominate in fresh clinical isolates but opaque variants are usually also present. Opaque variants grow faster in vitro and usually predominate after several passages. Clones switch back and forth between opaque and transparent morphotypes, but conversion to the rough morphotype involves well-characterized chromosomal deletions and is irreversible. All three morphotypic variations are known or presumed to involve cell envelope structures (Inderlied et al., 1993; Belisle et al., .................. .,. ........................................................................................................................ Abbreviations: CR, Congo red; HMC, Harborview Medical Center; MAC, Mycobacterium aviurn-intracellulare complex; RCRB, relative Congo red 1993 ; Belisle & Brennan, 1994 ; Prinzis et a/., 1994). The MAC is intrinsically resistant to Most antibiotics used to treat tuberculosis and leprosy. Drugs such as binding. ~~ 0002-3208 0 1999 SGM 1317