Nalidixic acid surrogate test for susceptibility to ciprofloxacin in Salmonella. Revisiting the question

J Med Microbiol. 2018 Jul;67(7):965-967. doi: 10.1099/jmm.0.000755.

Abstract

We investigated the reliability of nalidixic acid (NA) susceptibility as a marker of ciprofloxacin susceptibility in Salmonella, analysing 302 stool isolates. NC53 of the MicroScan system was used for NA susceptibility tests and the E-test was used for ciprofloxacin susceptibility tests. Among the isolates, 178 (58.9 %) were serogroup B, 74 (24.5 %) were serogroup D, 27 (8.9 %) were serogroup C and 23 (7.6 %) were from other minor serogroups. Globally, susceptibility to NA correctly predicted the susceptibility of Salmonella to ciprofloxacin, with a sensitivity of 81.5 %, a specificity of 97.6 %, and positive and negative predictive values of 88 and 96 %, respectively. However, there were differences among the serogroups in terms of sensitivity (P<0.001) and positive predictive values (P=0.013). NA is a reliable marker for serogroup D, but not for serogroups B or C. According to these findings, NA susceptibility measured with the MicroScan system can be used as a marker of ciprofloxacin resistance in some serogroups in our setting.

Keywords: Salmonella; ciprofloxacin; enteritis; nalidixic acid; stools.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Ciprofloxacin / pharmacology*
  • Drug Resistance, Bacterial / drug effects
  • Feces / microbiology
  • Humans
  • Microbial Sensitivity Tests
  • Nalidixic Acid / analogs & derivatives
  • Nalidixic Acid / pharmacology*
  • Salmonella / drug effects*
  • Salmonella Infections / drug therapy
  • Salmonella Infections / microbiology*
  • Serogroup

Substances

  • Anti-Bacterial Agents
  • Nalidixic Acid
  • Ciprofloxacin