Antibiograms and Molecular Characterization of Drug Resistance of Mycobacterium abscessus complex from Patients with Multidrug-Resistant Pulmonary Tuberculosis (MDR TB) Infection

Abstract

In the Philippines, acid fast bacilli positive sputum samples commonly treated as TB due to Mycobacterium tuberculosis (MTB) complex. However, Mycobacterium abscessus (MAB) complex is often found in MTB cultures, or in patients confirmed negative for TB through sputum microscopy and culture. Hence, patients with MAB infections are mistakenly prescribed six-month anti-TB treatments. In this study, MAB complex isolates from MDRTB patients were identified and further sub-speciated using the mass 3210 gene. Antimicrobial susceptibility was tested using broth microdilution and resistance genes erm(41), rrs, rrl, gyrA, and gyrB were studied for mutations. Majority were susceptible to amikacin, azithromycin, clarithromycin, and moxifloxacin [MAB: 100%, 100%, 100%, 81.8%, respectively; M. massiliense (MAM): 100%, 100%, 100%, 60%, respectively]. 50% MAM and 63.6% MAB were susceptible to cefoxitin; 60% MAM and 45.5% MAB were susceptible to ciprofloxacin; 72.7% MAB, and 10%MAM were susceptible to doxycycline. Inducible resistance to azithromycin and clarithromycin was found in 27.3%MAB and 30% MAM. 42.9% MAB complex isolates were MDR. Macrolide resistant MAB and MAM had T28 sequevar, showing functional erm(41) responsible for inducible resistance. Unexpectedly, full length erm(41) was found in MAM. Therrl gene in these isolates showed no point mutations, indicating T28 sequevar as cause of inducible resistance. All fluoroquinolone resistant isolates showed Ala-83 in gyrA fluoroquinolone resistant-dependent region (QRDR) and Arg-447 and Asn-464 in gyrB QRDR. These are associated with resistance to the drug.