Antibiograms and molecular characterization of drug resistance of Mycobacterium abscessus complex from patients with multidrug-resistant pulmonary tuberculosis (MDR-TB) infection

• Main Author: Bongulto, Kenneth A.
• Format: text
• Language: English
• Published: Animo Repository 2019
• Subjects: Mycobacteria; Multidrug-resistant tuberculosis; Biology
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6182; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/13221/viewcontent/BONGULTO_KENNETH2.pdf
• Institution: De La Salle University

Mycobacterium abscessus complex isolates, comprised of 11 M. abscessus and 10 M. massiliense isolates from patients with multiple drug resistant pulmonary tuberculosis were characterized phenotypically and identified using mass_3210 sequencing. All isolates were acid fast bacilli and were non-photochromogens. Both subspecies grew in Ogawa media as early as the third day of incubation. There were two morphotypes of M. abscessus complex observed in the study: the moist and round – smooth colony; and the dry and waxier – rough colony. The majority of M. abscessus complex isolates were susceptible to amikacin, azithromycin, clarithromycin, and moxifloxacin (M. abscessus: 100%, 100%, 100%, and 81.8%, respectively; M. massiliense: 100%, 100%, 100%, 60%, respectively) as shown using the broth microdilution assay. Cefoxitin showed moderate in vitro activity against M. abscessus (63.6% were susceptible) and M. massiliense (50% were susceptible). Ciprofloxacin showed moderate in vitro activity against M. massiliense (60% were susceptible). However, 54.5% of the M. abscessus isolates were resistant to the drug. Doxycycline inhibited 72.7% of the total isolates, but was less effective against M. massiliensewhich showed a resistance rate of 60%. Inducible resistance to both azithromycin and clarithromycin was found in 27.3% of M. abscessus and 30% of the M. massiliense isolates on the 14th day of incubation. More so, 42.9% (9/21) of the M. abscessus complex isolates were found to be multidrug-resistant; 14.3% of which were M. abscessus isolates and 28.6% of which were M. massiliense isolates. Sequence analyses revealed that both macrolide-resistant M. abscessus and M. massiliense isolates had a T28 sequevar, indicating a functional erm(41) gene that resulted in inducible macrolide resistance. Interestingly, full-length erm(41) gene was found in the M. massiliense isolates. Moreover, sequence analysis of the rrl gene in these isolates revealed no point mutations in any region of the gene, indicating that their inducible resistance to the macrolides was due to the T28 sequevar in their erm(41) gene. On the other hand, Ala-83 was found in the gyrA QRDR of all fluoroquinolone-resistant isolates, while Arg-447 and Asn-464 were present in the gyrB QRDR of the resistant isolates. All substitutions are associated with resistance to the drug.