Phenotypic and Genomic Characterization of Rapidly Growing Non-Tuberculous Mycobacteria Isolated from Surgical Site Infections in a Tertiary Care Hospital of Dhaka

Author(s): Rafia Afreen Jalil, ABM Bayezid Hossain, Md. Manjur Alam, Abdullah Al Tarique, Nabila Khanduker, Samia Shihab Uddin, Imtiaz Ahmad, Mushfique Manjur, Shaila Akhtar, Nooriya Haque

Background: Chronic surgical site infections (SSIs) caused by rapidly growing non-tuberculous mycobacteria (RGM) are increasingly recognized, yet their epidemiology and antimicrobial profiles remain poorly defined.

Objective: The study aimed to isolate, identify, and characterize rapidly growing RGM from patients with SSIs, and to determine their antimicrobial susceptibility profiles using both phenotypic and molecular techniques.

Methods: In this cross-sectional study at Green Life Medical College & Hospital, Dhaka, 149 patients who developed SSI following laparoscopic or open surgery were evaluated over one year. Clinical specimens (wound swab, pus, and tissue) underwent culture on standard media. Bacterial and mycobacterial isolates were identified by colony morphology, biochemical assays, and GeneXpert MTB/RIF (to exclude M. tuberculosis). RGM species were further characterized by urea hydrolysis, citrate utilization, and susceptibility to Ciprofloxacin and Polymyxin B. Antibiotic susceptibility was assessed by disc diffusion and broth microdilution.

Results: Patients’ ages ranged from 22 to 80 years (mean 51.0±16.74 years); 54.36% were male. Most infections (67.79%) occurred following laparoscopic procedures, with symptoms typically onset at 2-5 weeks postoperatively. Of 149 samples, 84 (56.38%) yielded pathogens: non-tuberculous mycobacteria (17.45%) predominated, followed by Klebsiella spp. (15.44%), Staphylococcus aureus (10.06%) and Escherichia coli (7.38%). Among 26 RGM isolates, Mycobacterium abscessus comprised 80.77% and M. fortuitum 19.23%. Biochemically, all 26 were urea-positive and citrate-negative. Only 19.23% showed susceptibility to both Ciprofloxacin and Polymyxin B by disc diffusion. The broth microdilution method revealed 100% sensitivity of both species to Amikacin; M. fortuitum was uniformly susceptible to Ciprofloxacin, Meropenem, Clarithromycin, Doxycycline, and Linezolid. Conversely, M. abscessus exhibited high resistance to Ciprofloxacin (85.71%), Meropenem (100%), and Doxycycline (61.90%), while 61.90% remained susceptible to Clarithromycin and 76.19% to Linezolid. Both species were resistant to Trimethoprim-Sulfamethoxazole.

Conclusions: RGM, particularly M. abscessus, are significant SSI pathogens with diverse resistance profiles. Species-level identification and tailored antimicrobial susceptibility testing are essential for effective management.