Objectives: To determine the pattern and antimicrobial resistance genes of cephalosporin resistance in Shigella flexneri and Shigella dysenteriae over 9 years.
Methods: Isolates of Shigella (S. flexneri, n = 119 and S. dysenteriae, n = 24) were tested for resistance to ceftriaxone and cefepime by disc diffusion, for MIC by Etest and for extended-spectrum β-lactamase (ESBL) and AmpC production. The presence of antimicrobial resistance genes was investigated by PCR using specific primers for bla(TEM), bla(OXA-1), bla(CTX-M-15), bla(SHV) and bla(CMY-2) for all the isolates.
Results: Twenty (16.8%) S. flexneri isolates were resistant/intermediately susceptible to ceftriaxone/cefepime, while all S. dysenteriae were susceptible. In S. flexneri isolates, the MIC(50) values of ceftriaxone and cefepime were found to be 0.032 and 0.125 mg/L, respectively, while their MIC(90) values were 12 and 8 mg/L, respectively. The MIC(50) and MIC(90) for S. dysenteriae were below 1 mg/L for ceftriaxone; however, for cefepime the MIC(90) was found to be 4 mg/L. Of the 20 resistant/intermediately susceptible S. flexneri isolates, 9 were positive for ESBL production and 4 for AmpC production by phenotypic tests. All 20 isolates were found to be positive for bla(TEM), 10 for bla(CTX-M-15), 8 for bla(OXA) and 7 for bla(CMY-2); none was positive for bla(SHV).
Conclusions: We report a high level of cephalosporin resistance with high MICs and ESBL- and AmpC-mediated antibiotic resistance in Shigella from north India.