Inducible Clindamycin Resistance in Gram-positive Cocci Isolated from Clinical Specimens of Patients with Bacterial Infections at a Tertiary Hospital in Tanzania

Abstract

Background: Clindamycin is a reserved antibiotic used to treat infections caused by Gram-positive cocci; however, increasing bacterial resistance threatens its effectiveness. Routine antimicrobial susceptibility testing may fail to detect inducible macrolide-lincosamide-streptogramin B (iMLS B) resistance, which requires the double disc diffusion (D-test) for accurate identification. Therefore, this study aimed to use the D-test to determine the prevalence of inducible clindamycin resistance among Gram-positive cocci isolates from patients with bacterial infections at a tertiary hospital in Tanzania.
Methods: A cross-sectional study was conducted among patients presenting with bacterial infections at Muhimbili National Hospital (MNH) in Tanzania from April to August 2022. Convenience sampling was used to include all eligible clinical specimens yielding Gram-positive cocci during the study period. All Gram-positive cocci isolated from the participants’ clinical specimens were subjected to antimicrobial susceptibility testing (AST) using the Kirby-Bauer disc diffusion method, and the D-test was performed to phenotypically detect iMLS B resistance. Demographic variables (age and sex), clinical specimen types, bacterial species, and antimicrobial resistance profiles were collected from patients’ records and laboratory results. Data were analyzed using Stata® Statistical Software version 15.1 (StataCorp LLC, College Station, TX, USA). Descriptive statistics were used to summarize the data, while the Chi-square test was used for analysis of categorical variables. A p-value < 0.05 was considered statistically significant.
Results: A total of 246 Gram-positive cocci isolates from clinical specimens were analyzed. The majority were Coagulase-negative Staphylococci (CoNS) 64.6%, followed by Staphylococcus aureus 30.1%. The prevalence of inducible clindamycin resistance was 25.2% (95% Confidence Interval (CI) [20.2%-30.9%]). Among the Staphylococcus aureus and CoNS isolates, 39.2% (95% CI [28.9%-50.6%]) and 20.8%(95% CI [15.2%-27.7%]) exhibited the iMLS B resistance phenotype, respectively. In addition, 63.5% of Staphylococcus aureus isolates were phenotypically confirmed as methicillin-resistant Staphylococcus aureus (MRSA), and 44.7% of these isolates demonstrated the iMLS B resistance phenotype. Furthermore, 75.6% (95% CI [69.9%-80.6%]) of the Gram-positive bacterial isolates were multidrug-resistant (MDR).
Conclusions: The present study demonstrated that a substantial proportion of Gram-positive cocci isolates exhibited iMLS B resistance, and the prevalence of MDR was high. These findings highlight the importance of incorporating the D-test into routine antimicrobial susceptibility testing to guide appropriate antibiotic therapy for infections caused by Gram-positive cocci. Furthermore, the results provide baseline evidence for future surveillance studies and support the need for strengthened antimicrobial stewardship programs and continued research to monitor and control antibiotic resistance in resource-limited settings.