Characterization and Antimicrobial Susceptibility of Actinomycetes from TB Smear Negative and Retreatment Patients in Nairobi, Kenya

Abstract

Actinomycetes are opportunistic pathogens in immunosuppressive patients. Pulmonary actinomycetes infections display symptoms that mimic Mycobacteria tuberculosis and can be misdiagnosed and treated as pulmonary TB. Actinomycetes can be co-infection with tuberculosis leading to delayed or inappropriate treatment. This study aimed to identify and determine antimicrobial susceptibility profiles of Actinomycetes from the sputum of TB smear negative and re-treatment patients referred to TB reference facilities in Kenya. Sputum specimens were collected and direct smears stained with Gram’s reagents. Culture was done on Mueller Hinton agar and incubated at 35°C for two weeks. Identification was done using phenotypic and biochemical procedures. Confirmation of the isolates was done using Polymerase Chain Reaction. A total of 52/385 (14%) Actinomycetes were isolated and subjected to antimicrobial susceptibility testing using broth microdilution method to determine the Minimum Inhibitory Concentration. Nine antibiotics were tested which included: Amikacin, Amoxicillin/Clavulanic acid, Ceftriaxone, Ciprofloxacin, Clarithromycin, Linezolid, Doxycycline, Trimethoprim-Sulfamethoxazole and Gentamycin. Staphylococcus aureus (ATCC 25923) was used as a control. Most of the isolates were susceptible to the test antibiotics. However, four isolates showed multidrug resistance to Ceftriaxone and Clarithromycin with resistance of 11.5% and 26.9% respectively. Gentamycin and Ciprofloxacin showed the highest susceptibility of 100% and 98.1% respectively. The findings of this study confirm that Actinomycetes are significant pathogens in TB smear-negative cases. Although most antibiotics were susceptible, resistance to few antibiotics was observed; hence, there is a need for proper screening of TB smear-negative cases to detect infections by Actinomycetes and also conduct the antimicrobial susceptibility test to determine which antibiotic is effective.