Identification of Broad-Spectrum Beta-lactamase CTX-M-2, CTX-M-8, and Ampc-dependent CMY Genes in Shigella sonnei Isolated from Pediatric Diarrhea Specimens by Multiplex-PCR and Antibiotic Resistance Pattern Determination

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Background: Shigella species are one of the most common causes of bacillary dysentery and sometimes death especially in children and immune-compromised individuals. The diversity of disease-causing species and the emergence of drug resistance make it difficult to select the appropriate antibiotic to treat shigellosis. One of the important causes of resistance in Shigella isolates is the presence of genes encoding broad-spectrum beta-lactamase enzymes. The aim of this study was to determine the frequency of Shigella sonnei strains producing CTX-M-2, CTX-M-8, and CMY beta-lactamase genes by Multiplex PCR and to investigate their association with antibiotic resistance in S. sonnei strains. Materials & Methods: This descriptive cross-sectional study was conducted in a period of 6 months from the beginning of June to the end of October 2016. A total of 200 diarrhea specimens were collected from the patients with suspected shigellosis from the Children's Medical Center (Tehran). The antibiotic susceptibility testing was performed using disk diffusion method on Müller-Hinton agar in accordance with CLSI instructions. After DNA extraction, the presence of CTX-M-2, CTX-M-8, and Ampcdependent CMY genes was determined by Multiplex-PCR using specific primers. Results: From all the samples, 60 (30%) S. sonnei strains were obtained using standard microbiological and biochemical tests. Majority of the strains were resistant to erythromycin (26 strains, 43.3%) and cefepime (24 strains, 40%). The molecular test results showed that 40 (66.6%) and 33 (55%) of the strains carried the CTX-M-8 and CMY genes, respectively (P<0.05). The CTX-M-2 gene was not detected in any of the samples. Conclusion: The results indicate a high frequency of CMY gene among Shigella sonnei isolates and higher resistance of these strains was found against erythromycin and cefepime. Therefore, careful medical care and proper and timely use of appropriate antibiotics to prevent the spread of resistant isolates seems inevitable.