Abstract
Purpose
Resistance to macrolide, lincosamide, and streptogramin B (MLS
B
) antibiotics in
Staphylococcus aureus
has emerged as a significant therapeutic challenge.
erm
gene–encoded ribosomal methylation is expressed either constitutively or inducibly, causing resistance to erythromycin and clindamycin with possible induction of clindamycin resistance during therapy.
msrA
‐mediated active drug efflux confers resistance to macrolides and streptogramin B while preserving clindamycin susceptibility. This study aimed to determine the antimicrobial susceptibility pattern of
S. aureus
isolates and correlate between the phenotypic and genotypic patterns of clindamycin resistance.
Methods
This cross‐sectional study was conducted from October 2022 to September 2023 at a tertiary care hospital laboratory. A total of 233 clinical isolates of
S. aureus
were included from exudate, blood, and bodily fluids. Antimicrobial susceptibility testing was performed using the Vitek 2 Compact system and interpreted according to CLSI 2022 and 2023 guidelines. Inducible clindamycin resistance was detected using the D‐test. Multiplex and uniplex PCR assays were performed for the detection of
ermA
,
ermB
,
ermC
, and
msrA
genes.
Results
Among 233
S. aureus
isolates, methicillin resistance was identified in 45.9% (107/233) isolates. The prevalence of constitutive MLS
B
(cMLS
B
), inducible MLS
B
(iMLS
B
), and MS phenotypes was 23.17%, 12.01%, and 10.3%, respectively. Overall clindamycin resistance was observed in 38.6% (90/233; 95% CI: 32.6%–45.0%). The
ermC
gene was detected in 30.47% (71/233) isolates, while
msrA
was identified in 9.44% (22/233), including 91.7% of isolates of the MS phenotype. Neither
ermA
nor
ermB
genes were detected. All isolates were susceptible to vancomycin, daptomycin, and tigecycline.
Conclusion
ermC
‐mediated MLS
B
resistance was present in 30.5% of isolates, with cMLS
B
(23.2%) being more common than iMLS
B
(12.0%). Routine D‐testing is essential to avoid clinical failure when using clindamycin for erythromycin‐resistant, clindamycin‐susceptible
S. aureus
. Also, 8 isolates were clindamycin resistant and susceptible to erythromycin, showcasing the diversity of the resistance profile of
S. aureus
toward MLS
B.