Evaluation of Virulence Properties of Staphylococcus aureus Isolated from A Tertiary Level Hospital of Dhaka City

Abstract

Staphylococcus aureus is the most frequently isolated bacterium among both communityacquired

and nosocomial infections. It is the causal pathogen of a wide range of infectious diseases ranging from skin and soft tissue infections to toxin-mediated diseases and also poses antibiotic resistant. Methicillin resistant Staphylococcus aureus (MRSA) turns out to be fatal, because of multidrug resistance. Staphylococcus aureus produces many virulence factors, including toxins, immune-modulatory factors, and enzymes. In this study, investigations were done to evaluate the virulence factors. It was conducted in the laboratory of Department of Microbiology, Holy Family Red Crescent Medical College and hospital with the collaboration of the Department of Microbiology, Dhaka University. Samples were collected from both indoor and outdoor cases of HFRCMCH. In case of indoor patients, samples were taken from the ICU, NICU, dialysis units and post-operative wards. Staphylococcus aureus were isolated from clinical samples like blood, pus, wound swab from abscess. The organisms were identified by colonial morphology, microscopic examination and relevant biochemical test according to standard laboratory methods. Culture was done on blood agar, mannitol salt agar and nutrient agar media. After isolation and identification, virulent factors were assessed following the analysis of growth pattern and fermentation in Mannitol salt agar media; colonial pigmentation and hemolysis on blood agar plates were observed to identify the toxin haemolysin; biochemical tests like catalase, coagulase were also evaluated to identify the enzymes. 565 samples were collected from different patients. Among which 120 samples were positive for Staphylococcus aureus, which is 21.2%. In this trial, it was found that 68 isolates (56.7%) were impervious to Oxacillin. The majority of the MRSA isolates were multidrug resistant (MDR). 25.8%, 38.3%, 30.8%, 50%, 15%, 95%, 24.2%, 52.5%, 85%, 20.8% of positive samples were impervious to Amoxyclav, Cotrimoxazole,

Tetracyline, Ciprofloxacin, Ceftriaxone, Vancomycin, Gentamycin, Erythromycin, Azithromycin, Amikacin respectively. Whereas low degree resistance was shown towards Ceftazidime, Carbapenem. In determining the resistance of Staphylococcus aureus to methicillin PCR was done to identify mecA gene in the isolates. However, when amplifying a 533bp fragment, significant number of isolates were found to be mecA positive. Studying virulence factors could reveal a well to do pathway for the care and cure of the patients who have been suffering from nosocomial infections. Thus, the morbidity rate and sufferings of these group of people could be minimized up to a certain level by strict hygiene and preventative measures which are highly recommended to stop transmission.