Antimicrobial Resistance and Genetic Diversity of Staphylococcus Aureus from Surgical Site Infections at Two Hospitals in Accra

ABSTRACT 

Background: Surgical site infections (SSIs) are the most common healthcare-associated infections affecting surgical patients. Such infections are often caused by methicillin-susceptible as well as methicillin-resistant Staphylococcus aureus. Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to the entire class of beta-lactam antimicrobials; which are largely used in clinical medicine. Patients infected with MRSAs therefore have limited therapeutic options, and this may lead to prolonged periods of hospitalisation and high heath care cost. In Ghana, information on SSI as well as the occurrence and prevalence of MRSA and MSSA from such infections are scarce. Data on bacteria species recovered from SSI is key for effective surveillance and selection of appropriate antimicrobial therapy. This study therefore, investigated the proportions of MRSA and MSSA using phenotypic and molecular detection tools among patients diagnosed of surgical site infections in two hospitals.  

Aim: The aim of this study was to determine the antimicrobial resistance patterns and molecular characteristics of Staphylococcus aureus detected in patients with surgical site infections at the Korle-Bu Teaching Hospital and 37-Military Hospital in Accra. 

Method: This was a hospital-based cross-sectional study conducted from June to November 2018 at the Korle-Bu Teaching Hospital (KBTH) and 37-Military Hospital in Accra. Surgical patients diagnosed of SSI were recruited using the Centers for Disease Control (CDC) case definition for surgical site infection. Patient demographic data (age, sex, type of operation etc.) and wound swabs or aspirates were collected after receiving an informed consent. S. aureus was identified using colonial morphology, coagulase testing and the Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS). Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method; measured zone sizes were interpreted according the CLSI guidelines. Multiplex PCR was performed to detect mecA (methicillin-resistant gene), spa (S. aureus specific gene) and pvl (Panton Valentine Leukocidin toxin gene) in the S. aureus isolates. Libraries for illumina sequencing were prepared using the Nextera DNA Flex Library preparation kit. Whole genome sequencing was done with the MiSeq Illumina sequencer at Noguchi Memorial Institute for Medical Research (NMIMR). Genomes were assembled using an in-house pipeline; assembled sequences were then uploaded to the centre for genomic epidemiology website (http://www.genomicepidemiology.org/) to determine the spa types, sequence types and virulence gene content of the S. aureus isolates. 

Results: A total of 110 patients were recruited into the study, 34 (12.5%) were male and 76 (69.1%) were female. Patients between the ages of 25-44 years were highest in the number among the patients enrolled. Overall, 13 S. aureus isolates (11.8%; 13/110) were recovered and all were resistant to penicillin and susceptible to gentamicin and vancomycin. Cefoxitin resistance (4/13; 30.77%) was detected only in isolates from 37-Military Hospital. On the other hand, tetracycline (46.15%; 6/13) and norfloxacin (15.38%; 2/13) resistance was recorded at both hospitals. Sensitivity of isolates to linezolid (84.62%; 11/13), clindamycin (76.92%; 10/13), rifampicin (92.31%; 12/13), co-trimoxazole (92.31%; 12/13) and erythromycin (53.85%; 7/13) was very high. The four (30.76; 4/13) isolates resistant to cefoxitin (MRSA) and were also positive for mecA by PCR. The predominant S. aureus genotype found in the study was ST152t355. The four MRSAs detected belonged to ST152-t355 and ST5-t586 clone. Eight (61.53%; 8/13) isolates were positive for the Panton Valentine Leukocidin toxin. Twelve other virulence genes were detected with haemolysin A and B (hlgA and hlgB) being the most prevalent. 

Conclusion: S. aureus isolates recovered were genetically diverse. The detection of ST152 MRSA among surgical patients is particularly of interest; this global clone has also been reported in Central Europe, the Balkan, Switzerland and Denmark as a community acquired MRSA. Continuous surveillance may be required to monitor the spread of these pandemic clones in the hospital setting.