[The analysis of species identification and susceptibility testing of Mycobacterium abscessus].

OBJECTIVES: To evaluate the method of differentiating Mycobacterium abscessus subsp. abscessus (subsp. M. abscessus) from Mycobacterium abscessus subsp. massiliense (subsp. M. massiliense), and to investigate the activity of different antibiotics in vitro.

METHODS: Sixty Mycobacterium abscessus (M. abscessus) isolates previously identified by using 16S rRNA sequence, were identified by comparative sequence analysis of rpoB and hsp65, and were divided into subsp. M. abscessus and subsp. M. massiliense. Two subspecies' resistant proportions were compared by chi-square test. Finally the relationship between clarithromycin resistance and erm(41) was analyzed.

RESULTS: Of all the 60 M. abscessus isolates, 65% (39/60) belonged to subsp. M. abscessus, 35% (21/60) belonged to subsp. M. massiliense. 97% (38/39) subsp. M. abscessus and 95% (20/21) subsp. M. massiliense were susceptible to amikacin. 92% (36/39) subsp. M. abscessus and 95% (20/21) subsp. M. massiliense were susceptible to azithromycin. 74% (29/39) subsp. M. abscessus and 67% (14/21) subsp. M. massiliense were susceptible to imipenem. 46% (18/39) subsp. M. abscessus and 76% (16/21) subsp. M. massiliense were moderately susceptible to cefoxitin. 82% (32/39) subsp. M. abscessus were resistant to clarithromycin, and 95% (20/21) subsp. M. massiliense were susceptible to clarithromycin. Of all the 28 subsp. M. abscessus isolates which were sequenced suscessfully, 23 isolates were resistant to clarithromycin, and 22 isolates in them had T28 in erm(41), and the rest one had C28 in erm(41). However, all the 5 subsp. M. abscessus isolates which were susceptible to clarithromycin had C28 in erm(41).

CONCLUSIONS: M. abscessus can be divided into subsp. M. abscessus and subsp. M. massiliense by using rpoB and hsp65. Amikacin, azithromycin and imipenem showed excellent inhibition activity against M. abscessus in vitro. Cefoxitin also showed a good inhibition activity. Clarithromycin had a poor inhibition activity against subsp. M. abscessus, but a good inhibition activity against subsp. M. massiliense. Erm(41) was related to clarithromycin resistance.