Antimicrobial susceptibility and molecular subtyping of 55 Turkish Bacillus anthracis strains using 25-loci multiple-locus VNTR analysis

Abstract

Anthrax, which is caused by the bacterium Bacillus anthracis, is one of the oldest documented infectious diseases in both livestock and humans. The differentiation of B. anthracis strains is difficult because of their highly homogeneous genomes. We used multiple-locus variable-number tandem repeat analysis (MLVA) with 25 markers to genotype 55 B. anthracis isolates from 16 distinct regions of Turkey. The antimicrobial susceptibility of the isolates was investigated using the agar dilution method. An eight-loci MLVA assay revealed six unique genotypes (G(K)13, G(K)27, G(K)35, G(K)43, G(K)44, and G(K)61). However, the 25-loci MLVA was more discriminatory, revealing the presence of ten genotypes instead of six. The additional genotypes resulted from the split of four subtypes: G(K)35 (b and c), G(K)43 (a and f), G(K)44 (d and e), and G(K)61 (i and j). All of the Turkish B. anthracis isolates were susceptible to ciprofloxacin, levofloxacin, tigecycline, linezolid, and vancomycin. One isolate was resistant to penicillin and to doxycycline. A total of 34 isolates were susceptible, 20 isolates were partially susceptible, and one isolate was resistant to erythromycin. None of the isolates exhibited susceptibility to cefotaxime. A total of 53 isolates were susceptible to gentamicin, and two were resistant. The genotypes G(K)35 (n=24), G(K)44 (n=13), and G(K)43 (n=10) were the most prevalent in 10, 6, and 5 regions, respectively, of the total 16 provinces. The B. anthracis isolates collected from these regions implied that the movement of B. anthracis is a result of the increased transportation of livestock and the resultant cross contamination.