No 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.

Enterobacter species, members of Enterobacteriaceae family that belong to the ESKAPE group, were expressed as the principal rise of nosocomial resistant infections. This study was aimed to test the antibacterial activity of ascorbic acid on Enterobacterclinical strains. Four Enterobacter strains were collected and identified by both biochemical and MALDI-TOF methods. Antibiotic susceptibility testing of commercially available antibiotics was performed using disc diffusion method. Antibacterial activity of ascorbic acid was tested by using agar well diffusion and broth microdilution methods. The collected strains were identified as three strains Enterobacteraerogenes and one strain Enterobacter cloacae. High resistance rates toward both cefotaxime and nalidixic acid were obtained by disc diffusion method. By well diffusion, 100 mg/ml and 50 mg/ml concentrations of ascorbic acid were found to be effective. While by using microbroth dilution, concentrations of 1.5, 3.125 and 6.25 mg/ml of ascorbic acid were detected as minimum inhibitory concentrations. Our results demonstrated a good antibacterial activity of ascorbic acid on Enterobacter strains and further studies on ascorbic acid/antibiotics combinations are in need.