CORRELATION BETWEEN MUTATIONAL PROFILES IN FLUOROQUINOLONE RESISTANCE GENES (gyrA AND grlA) AND PHENOTYPIC ANTIBIOTIC SUSCEPTIBILITY IN CLINICAL ISOLATES OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA)
DOI: http://dx.doi.org/10.30970/sbi.2002.881
Abstract
Background. Methicillin-resistant Staphylococcus aureus (MRSA) is recognized as a highly significant multidrug-resistant pathogen that can lead to severe fetal infections in both humans and animals. Fluoroquinolones (FQs) are considered among the antibiotics of choice used to manage MRSA infections. This study addresses rising fluoroquinolone resistance that limits treatment options. Resistance mechanisms typically involve mutations in the gyrA and grlA genes, which encode the drug’s targets. Objective: the aim of this research is to identify the genetic basis for resistance in clinical MRSA isolates. Specifically, the research focused on investigating the distribution of mutations in the gyrA and grlA genes responsible for fluoroquinolone resistance in MRSA isolates obtained from different clinical sources and assessing the correlation of these mutations with phenotypic antibiotic resistance.
Materials and Methods. Fifty MRSA isolates collected from various clinical specimens (burn, wound, nose, throat, urine, skin, ear, and operating room samples) were used in the study. Bacteriological methods and PCR detection of the nuc gene confirmed the identification of the isolates. Then, all of the isolates were tested against seven different antibiotics (methicillin, ciprofloxacin, levofloxacin, norfloxacin, ofloxacin, lomefloxacin, and nalidixic acid) using the disk diffusion method and Minimum Inhibitory Concentration (MIC) tests. Twelve isolates exhibiting antibiotic resistance were selected for direct sequence analysis of the gyrA, grlA, and mecA gene regions. The relationship between mutations and resistance was analyzed statistically.
Results. All isolates (100 %) carried the mecA gene, and no mutations were detected in this gene. The prevalence of fluoroquinolone resistance was 24 % (12 isolates). Sequence analysis revealed mutations at eight different positions in the gyrA gene (two missense, one deletion, and five silent) and seven different positions in the grlA gene (three missense, one silent, and three insertions). Statistical analysis revealed a significant positive correlation between mutant isolates in the gyrA and grlA genes and fluoroquinolone resistance (p < 0.0001). A significant correlation was also found between nalidixic acid resistance and the presence of mutations (p < 0.009).
Conclusion. The findings of this study indicate that a major mechanism of fluoroquinolone resistance in clinical MRSA isolates is the accumulation of mutations in the gyrA and grlA genes, which encode target enzymes, and that these mutations are strongly associated with high-level phenotypic resistance. It has been confirmed that methicillin resistance Are rely to the presence of the mecA gene and does not require a mutation in the gene itself. These results provide deeper insight into the underlying mechanisms of antimicrobial resistance.
Materials and Methods. Fifty MRSA isolates collected from various clinical specimens (burn, wound, nose, throat, urine, skin, ear, and operating room samples) were used in the study. Bacteriological methods and PCR detection of the nuc gene confirmed the identification of the isolates. Then, all of the isolates were tested against seven different antibiotics (methicillin, ciprofloxacin, levofloxacin, norfloxacin, ofloxacin, lomefloxacin, and nalidixic acid) using the disk diffusion method and Minimum Inhibitory Concentration (MIC) tests. Twelve isolates exhibiting antibiotic resistance were selected for direct sequence analysis of the gyrA, grlA, and mecA gene regions. The relationship between mutations and resistance was analyzed statistically.
Results. All isolates (100 %) carried the mecA gene, and no mutations were detected in this gene. The prevalence of fluoroquinolone resistance was 24 % (12 isolates). Sequence analysis revealed mutations at eight different positions in the gyrA gene (two missense, one deletion, and five silent) and seven different positions in the grlA gene (three missense, one silent, and three insertions). Statistical analysis revealed a significant positive correlation between mutant isolates in the gyrA and grlA genes and fluoroquinolone resistance (p < 0.0001). A significant correlation was also found between nalidixic acid resistance and the presence of mutations (p < 0.009).
Conclusion. The findings of this study indicate that a major mechanism of fluoroquinolone resistance in clinical MRSA isolates is the accumulation of mutations in the gyrA and grlA genes, which encode target enzymes, and that these mutations are strongly associated with high-level phenotypic resistance. It has been confirmed that methicillin resistance Are rely to the presence of the mecA gene and does not require a mutation in the gene itself. These results provide deeper insight into the underlying mechanisms of antimicrobial resistance.
Keywords
MRSA, fluoroquinolone resistance, mutation analysis, sequence analysis, antibiotic resistance
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