Increase in Nalidixic Acid Resistance among Salmonella enterica Isolates Recovered from Patients in Tehran, Iran

Nalidixic acid resistance rate is increasing amongst S. enterica isolates worldwide. We described here an increase in nalidixic acid resistance among S. enterica isolates recovered in Tehran, in Iran. The study included all Salmonellaisolates recovered from clinical cases in Tehran, Iran during 2006 and 2009. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute. The statistical analysis was performed using SPSS.

One hundred thirty eight S. enterica isolates were collected; of those, 89 (64%) were resistant to nalidixic acid. The percentage of isolates resistant to nalidixic acid was 59% (19/32) in 2006, 64% (34/53) in 2007, and 67% (36/53) in 2008. The most common multidrug resistance phenotype amongst nalidixic acid-resistant isolates was resistance to doxycycline, kanamycin, neomycin, streptomycin, sulfamethoxazole, and tetracycline. We found nalidixic acid resistance is increasing amongst nontyphoidal S. enterica isolates in our study. Over the past 3 years, there has been a significant increase in the proportion of nalidixic acid resistant S. enterica. Continued surveillance of antimicrobial resistance among S. enterica is needed to mitigate the increasing prevalence of nalidixic acid resistance among Salmonella.