Azithromycin Resistance in Shigella spp. in Southeast Asia.

Infection by spp. is a common cause of dysentery in Southeast Asia. Antimicrobials are thought to be beneficial for treatment; however, antimicrobial resistance in spp. is becoming widespread. We aimed to assess the frequency and mechanisms associated with decreased susceptibility to azithromycin in Southeast Asian isolates and use these data to assess appropriate susceptibility breakpoints. isolates recovered in Vietnam and Laos were screened for susceptibility to azithromycin (15 μg) by disc diffusion and MIC. Phenotypic resistance was confirmed by PCR amplification of macrolide resistance loci. We compared the genetic relationships and plasmid contents of azithromycin-resistant isolates using whole-genome sequences. From 475 available spp. isolated in Vietnam and Laos between 1994 and 2012, 6/181 isolates (3.3%, MIC ≥ 16 g/liter) and 16/294 isolates (5.4%, MIC ≥ 32 g/liter) were phenotypically resistant to azithromycin. PCR amplification confirmed a resistance mechanism in 22/475 (4.6%) isolates ( in 19 isolates and in 3 isolates). The susceptibility data demonstrated the acceptability of the (MIC ≥ 16 g/liter, zone diameter ≤ 15 mm) and (MIC ≥ 32 g/liter, zone diameter ≤ 11 mm) breakpoints with a <3% discrepancy. Phylogenetic analysis demonstrated that decreased susceptibility has arisen sporadically in Vietnamese isolates on at least seven occasions between 2000 and 2009 but failed to become established. While the proposed susceptibility breakpoints may allow better recognition of resistant isolates, additional studies are required to assess the impact on the clinical outcome. The potential emergence of azithromycin resistance highlights the need for alternative options for management of infections in countries where is endemic.