Molecular Characterization of Staphylococcus aureus and Coagulase-Negative Staphylococci Isolates at a Rural Hospital...

This study is aimed at identifying antimicrobial resistance (AMR) and virulence-encoded genes in Staphylococcus aureus and coagulase-negative staphylococci (CoNS) isolates from a rural hospital in Southern Malawi. S. aureus isolates were further characterized by typing of staphylococcal protein A (spa).

We conducted a cross-sectional study of 36 Staphylococcus isolates from clinical samples collected at Malamulo Hospital in Makwasa, Malawi. Antimicrobial susceptibility testing was performed using the disc diffusion method. Polymerase chain reaction (PCR) was used to detect AMR genes (mecA, ermA, ermB, ermC, tetK, tetL, tetM, and tetO) and virulence genes (PVL: lukS-PV, lukF-PV; splA, splB, splC, splD, splE, and splF). PCR also confirmed S. aureus isolates through the detection of nuc, spa, or coa genes. Spa typing of S. aureus isolates was performed by Sanger sequencing.

The 36 isolates were identified as 14 S. aureus and 22 CoNS species. The highest resistance among all isolates was against sulfamethoxazole/trimethoprim (n = 18, χ² = 2.338, df = 2, p = 0.311), penicillin (n = 15, χ² = 2.258, df = 1, p = 0.175), and tetracycline (n = 14, χ² = 1.190, df = 1, p = 0.314). One CoNS and three S. aureus isolates demonstrated phenotypic multidrug methicillin resistance. The tetK gene was significantly more prevalent among S. aureus compared with CoNS isolates (χ² = 10.227, df = 1, p < 0.01). No significant difference was found between S. aureus and CoNS in the detection of mecA (χ² = 1.063, df = 1, p = 0.547), tetL (χ² = 1.348, df = 1, p = 0.511), tetM (χ² = 0.110, df = 1, p = 1.000), or PVL genes (lukS-PV and lukF-PV) (χ² = 4.129, df = 1, p = 0.064). Spa typing identified seven spa types, with the most common type identified as t941 (n = 3).

This study reveals the presence of both multidrug-resistant CoNS and S. aureus strains with diverse spa types in rural Southern Malawi and highlights a role for molecular testing in surveillance and diagnostic testing.