Phenotypic Drug Susceptibility Patterns of Mycobacterium tuberculosis Isolates to First-Line Anti-Tuberculosis Drugs in South-Western Nigeria

Abstract

Drug-resistant tuberculosis (TB) undermines global TB control efforts, yet comprehensive phenotypic drug susceptibility data from South-Western Nigeria remain limited. Understanding local resistance patterns is essential for optimising treatment regimens and informing programmatic responses. This study aimed to determine the phenotypic susceptibility patterns of culture-confirmed Mycobacterium tuberculosis isolates to first-line anti-tuberculosis drugs among patients in South-Western Nigeria. Seventy-four GeneXpert MTB/RIF-positive sputum specimens from patients attending health facilities in Osun, Oyo, and Lagos States underwent mycobacterial culture on Löwenstein-Jensen medium. Culture-confirmed M. tuberculosis isolates were subjected to phenotypic drug susceptibility testing against rifampicin, isoniazid, and ethambutol using the proportion method. Of 74 GeneXpert-positive specimens cultured, 51 (68.9%) yielded M. tuberculosis. Among these 51 isolates, 36 (70.6%) demonstrated resistance to at least one first-line drug. Rifampicin resistance was detected in 27 isolates (52.9%), isoniazid resistance in 18 (35.3%), and ethambutol resistance in 13 (25.5%). Fifteen isolates (29.4%) met criteria for multidrug-resistant TB (MDR-TB), defined as combined rifampicin and isoniazid resistance. Analysis of the geographical distribution revealed that 74.1% of rifampicin-resistant, 77.8% of isoniazid-resistant, and 84.6% of ethambutol-resistant isolates originated from Osun State. Substantial resistance to first-line anti-tuberculosis drugs, particularly rifampicin, was detected among culture-confirmed M. tuberculosis isolates in South-Western Nigeria. The high prevalence of drug resistance and MDR-TB highlights the need for routine culture and drug susceptibility testing to guide individualized treatment and prevent treatment failure.