Species identification of Mycobacterium abscessus subsp. abscessus and Mycobacterium abscessus subsp. bolletii using rpoB and hsp65, and susceptibility testing to eight antibiotics

SummaryObjectivesTo separate Mycobacterium abscessus subsp. bolletii from Mycobacterium abscessus subsp. abscessus using species identification, and to investigate the in vitro activity of amikacin, cefoxitin, imipenem, levofloxacin, moxifloxacin, clarithromycin, azithromycin, and linezolid against Mycobacterium abscessus.MethodsSeventy M. abscessus isolates, previously identified by 16S rRNA sequencing, were further identified by comparative sequence analysis of rpoB and hsp65. Drug susceptibility testing was conducted using the microplate Alamar Blue assay in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines and interpreted using CLSI breakpoints.ResultsOf the 70 strains, 45 (64%) were M. abscessus subsp. abscessus and 25 (36%) were M. abscessus subsp. bolletii. The majority of M. abscessus isolates were susceptible to azithromycin, amikacin, linezolid, and imipenem (M. abscessus subsp. abscessus: 93%, 98%, 93%, and 73%, respectively; M. abscessus subsp. bolletii: 96%, 96%, 80%, and 68%, respectively). Approximately half of the M. abscessus isolates were moderately susceptible to cefoxitin and moxifloxacin (M. abscessus subsp. abscessus 53% and 49%; M. abscessus subsp. bolletii 72% and 68%). Nearly all the M. abscessus isolates were resistant to levofloxacin (M. abscessus subsp. abscessus 96%, M. abscessus subsp. bolletii 100%). Inducible clarithromycin resistance was found in M. abscessus. After 14 days of incubation, 83% M. abscessus subsp. abscessus and 36% M. abscessus subsp. bolletii were resistant to clarithromycin.ConclusionsUsing rpoB and hsp65, M. abscessus subsp. bolletii could be distinguished from M. abscessus subsp. abscessus. Amikacin and azithromycin showed excellent activity against M. abscessus in vitro. Imipenem, linezolid, cefoxitin, and moxifloxacin also showed good activity. Levofloxacin was inactive against M. abscessus. Although clarithromycin showed excellent activity against M. abscessus on day 3, inducible resistance occurred, and after 14 days clarithromycin showed little activity against M. abscessus subsp. abscessus, but still had good activity against M. abscessus subsp. bolletii.