Antimicrobial resistance patterns and prevalence of class 1 and 2 integrons in Shigella flexneri and Shigella sonnei isolated in Uzbekistan

BACKGROUND: Shigella is a frequent cause of bacterial dysentery in the developing world. Treatment with effective antibiotics is recommended for shigellosis, but options become limited due to globally emerging resistance. One of the mechanisms for the development of resistance utilizes integrons. This study described the antibiotic susceptibility and the presence of class 1 and 2 integrons in S. flexneri and S. sonnei isolated in Uzbekistan. RESULTS: We studied 31 isolates of S. flexneri and 21 isolates of S. sonnei isolated in Uzbekistan between 1992 and 2007 for the susceptibility or resistance to ampicillin (Am), chloramphenicol (Cl), tetracycline (Te), co-trimoxazole (Sxt), kanamycin (Km), streptomycin (Str), gentamicin (Gm), cefazolin (Czn), cefoperazone (Cpr), cefuroxime (Cur), ceftazidime (Ctz), nalidixic acid (NA) and ciprofloxacin (Cip). Am/Str/Cl/Te and Am/Str/Cl/Te/Sxt resistance patterns were found most frequently in S. flexneri. Single isolates were resistant to aminoglycoside, quinolones and cephalosporins. The resistance patterns were different in the two species. Integrons were detected in 93.5% of S. flexneri (29/31) and 81.0% of S. sonnei (17/21) isolates. In addition, 61.3% of S. flexneri (19/31) isolates and 19.0% of S. sonnei (4/21) isolates carried both classes of integrons. In 29.0% of S. flexneri (9/31) isolates, only class 1 integrons were identified. In S. flexneri isolates, the presence of class 1 integrons was associated with resistance to ampicillin and chloramphenicol. Only Class 2 integrons were present in 61.9% of S. sonnei (13/21) isolates. CONCLUSIONS: Our study documents antibiotic resistance among Shigella spp. in Uzbekistan. Ninety percent of Shigella strains were resistant to previously used antibiotics. Differences among S. flexneri and S. sonnei isolates in patterns of antimicrobial resistance to routinely used shigellosis antibiotics were observed. The majority of S. flexneri were resistant to ampicillin, chloramphenicol, tetracycline and streptomycin. Class 1 and 2 integrons were widely present in these Shigella strains. Resistance to ampicillin/chloramphenicol was associated with the presence of class 1 integrons. Though several mechanisms are possible, the resistance of Shigella isolates to ampicillin/chloramphenicol may be associated with the expression of genes within class 1 integrons.