Antibiotic susceptibility and genotypic profiles of clinical methicillin-susceptible (MSSA) and -resistant (MRSA) staphylococcus aureus isolates in Hospital Angkatan Tentera Tuanku Mizan, Kuala Lumpur

Staphylococcus aureus (S. aureus) causes infections in hospitals and communities, including in the military cohort, which imposes serious healthcare and operational burden. Monitoring its antibiotic susceptibility and genotypic traits is essential for effective treatment and infection control. This study assessed the antibiotic susceptibility profile and the distribution of pvl and mecA genes of methicillin-susceptible (MSSA) and -resistance S. aureus and (MRSA) isolates fromHospital Angkatan Tentera Tuanku Mizan (HATTM), Kuala Lumpur in 2019. Additionally, investigations on the staphylococcal chromosome cassette mec (SCCniec) type and spa type were performed on MRSA isolates.
All 5. aureus isolates were identified using standard bacteriological methods. The antibiotic susceptibility profile of the isolates was determined using the Kirby- Bauer method. Genotypic characterization of all isolates included the detection of the staphylococcal genus-specific 16S rRNA gene, the S. aureus species-specific gene (nuc), the methicillin resistance gene (znecA), and the virulence gene, Panton- Valentine leucocidin gene (pvl) using polymerase chain reaction (PCR). For SCCmec and spa typing, PCR or/and sequencing methods were employed. Descriptive analysis was conducted to compare the demographic data of the patients with the antibiotic susceptibility profiles and genotypic variables of the MSSA and MRSA isolates.
A total of 209 S. aureus isolates were obtained from various clinical samples including wound and pus, blood, tissue, bone, intravenous catheter, umbilicus swab, high vaginal swab, urine, nasal swab, tracheal aspirate, pleural fluid, throat swab, eye swab, and breast aspirate collected from patients admitted to HATTM. Of these, 123 isolates were MSSA and 86 isolates were MRSA. No vancomycin-intermediate or - resistant S. aureus (VISA or VRSA, respectively) was isolated. The MSSA isolates were commonly isolated from wound and pus specimens (55/123, 44.7%) and demonstrated low resistance to all antibiotics tested. Conversely, the MRSA isolates were mostly isolated from blood specimens (36/86, 41.9%), and exhibited complete resistance (86/86, 100%) to penicillin, ampicillin, and sulbactam/ampicillin. Both MSSA and MRSA were predominantly isolated from patients aged above 40 years old (84/123, 68.3%, and 71/86, 82.6%, respectively). In terms of acquisition, 193 (92.3%) isolates were from community-acquired infections, while 16 (7.7%) isolates were from hospital-acquired infections.
The 16S rRNA gene and nuc were detected in all S. aureus isolates (209/209, 100%). Only 42 of the 209 5. aureus isolates tested positive for pvl, mostly MSSA (35/42, 83.3%). There was a significant relationship between; 1) the methicillin susceptibility with patients’ age group (p = .020) and type of acquisition (p < .000); 2) the antibiotic resistance pattern with patients’ age group (p = .017); and 3) the presence of pvl with the patient's age group (p = .001) and isolation site (invasiveness) (p = .005). Most MRSA isolates were of SCCniec type IVh (65/86, 75.58%), spa type t032 (55/85, 63.95%), and 5paCC-t022 (66/85, 77.65%). The MRSA SCCmec type IVh- spa t032 type was associated with resistance traits to cefoperazone, azithromycin, erythromycin, and fusidic acid (p = .022, p = .015, p = .011, and p = .036, respectively).
This study highlights the importance of an effective infection control policy to prevent the dissemination of S. aureus virulent and resistance-related traits from the community to hospitals and vice versa and evident the persistence of the newly shifted MRSA strain in Malaysian clinical MRSA isolates.