Analysis of antibiotic resistance genes in Neisseria gonorrhoeae strains with decreased sensitivity to ceftriaxone from Shenzhen city

Abstract

Objective To analyze the relationship of penA, ponA, porB and mtrR gene mutations with the reduced sensitivity to ceftriaxone in N. gonorrhoeae isolates from Shenzhen city. Methods A total of 296 clinical isolates of N. gonorrhoeae were collected in Shenzhen city from 2009 to 2011. The agar dilution method was used to estimate the sensitivity of these N. gonorrhoeae to ceftriaxone. Totally, 53 strains with reduced sensitivity to ceftriaxone (minimum inhibitory concentration (MIC) : 0.06-0.50 μg/ml) were identified, and 53 strains with high sensitivity to ceftriaxone were randomly selected from the remaining strains and served as the control group. PCR was performed to amplify the penA, ponA, porB and mtrR genes from the 106 isolates followed DNA sequencing. Results The mosaic structure of the penicillin-binding protein 2 (PBP2) gene (penA gene) was found in only one isolate with a ceftriaxone MIC of 0.125 0 μg/ml. Amino acid sequence analysis of the remaining 105 isolates yielded 16 different amino acid patterns. The MICs of ceftriaxone were relatively high (0.062 5 μg/ml) in N. gonorrhoeae strains harboring the amino acid patterns ⅩⅢ, ⅩⅧ or ⅩⅩⅩⅧ, but relatively low (0.008 0 μg/ml) in those harboring the amino acid pattern Ⅱ. No significant differences were observed in the frequency of mtrR, porB or ponA gene mutations between N. gonorrhoeae isolates with reduced sensitivity to ceftriaxone and those with high sensitivity (all P > 0.05) . Conclusions The mosaic structure of PBP2 may be not the primary reason for reduced sensitivity of Neisseria gonorrhoeae to ceftriaxone in Shenzhen, while different amino acid patterns produced by various mutations in amino acid residues at positions 500-580 in the non-mosaic PBP2, together with mtrR, porB and ponA mutations, may play more important roles in the reduced sensitivity. Key words: Neisseria gonorrhoeae; Ceftriaxone; DNA mutational analysis; Microbial sensitivity tests; Drug resistance, microbial