Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) strains are widespread globally. Besides their virulence factors, the co-occurrence of antimicrobial and metal resistance has been reported. This study was designed to evaluate the antibiotic resistance and resistance phenotypes, investigate the occurrence of virulence factors, and detect heavy metal tolerance among MRSA strains. Antibiogram profiling was done as recommended by CLSI instructions. Resistance phenotypes were detected by D test, followed by characterization of enzymatic activities and biofilm formation assay. Antibacterial activity of different heavy metals was tested, and predictable synergistic assay was performed. Among MRSA strains collected, high resistance to ampicillin and amoxicillin/clavulanate (100%) and high susceptibility to clindamycin (70%) were obtained. Resistance phenotypes were detected as S, constitutive MLSB, inducible MLSB, and MS by percentages of 10%, 30%, 30% and 30% respectively. Virulence factors like lipolytic (50%) and hemolytic (70%) activity, and biofilm formation ability (100%) were detected. High resistance towards potassium and magnesium was observed. MTC of 500 ppm was detected for all isolates in case of cobalt and iron. In case of zinc and copper, MTC was detected as 500 ppm except for one isolate which was highly resistant, and 500 ppm for all isolates except for two isolates which were highly sensitive respectively. Magnesium in different concentrations (500 and 2000 ppm) showed synergistic activity with erythromycin and clindamycin. Results reveal high heavy metal tolerance among antibiotic resistant MRSA strains, in addition to the presence of virulence factors. Upcoming studies must be focused on the combination of sub-inhibitory concentration of different heavy metals with the available antibiotics.
Highlights
Staphylococcus aureus is a bacterial pathogen, which is considered as one of the most common agents in a variety of human infections including skin, soft tissue as well as eye[1]
Results presented in Table (1) showed that high resistance to ampicillin and amoxicillin/clavulanic by percentages of 100% was obtained
Different resistance phenotypes were detected as constitutive Macrolide-LincosamideStreptogramin B (MLSB), inducible MLSB, S, and MS by percentages of 10%, 30%, 30% and 30% respectively (Fig. 1)
Summary
Staphylococcus aureus is a bacterial pathogen, which is considered as one of the most common agents in a variety of human infections including skin, soft tissue as well as eye[1] Those bacterial species shows some virulence factors which are tightly regulated specially during bacterial growth and pathogenesis process 2. Bacterial biofilm formation ability always allow more advantages for bacterial cell survival compared to planktonic growth, including protection from shear stress, disinfectants, and antibiotics by its special structure[5,6,7] This mode of bacterial growth induces cellular dormancy associated with multidrug tolerance, and nonheritable phenotype that differs from classic mechanisms of antibiotic resistance[8,9]
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