Trends in nalidixic acid resistance in nontyphoidal Salmonella isolated from 1999 to 2002: decreased susceptibility to 6 fluoroquinolones.
We determined the resistance to nalidixic acid and 6 fluoroquinolones of 771 nontyphoidal Salmonella strains isolated from humans between 1999 and 2002. A total of 22 different serotypes were identified among the Salmonella isolates, the most common being Salmonella Enteritidis (79%) and Salmonella Derby (8%). Resistance to nalidixic acid increased from 38% in 1999 to 43% in 2002. This resistance was not homogeneous among the different serotypes, with the highest percentage of resistant isolates belonging to Salmonella Hadar (79%) followed by Salmonella Enteritidis (46%). Reduced ciprofloxacin susceptibility (minimal inhibitory concentrations [MICs] from 0.12 to 0.5 microg/mL) was observed in 300 (39%) Salmonella. In our study, the nalidixic acid-resistant strains had an MIC90 at least 4-fold higher than the susceptible ones for all the fluoroquinolones tested, thus showing that resistance to nalidixic acid is an indicator of low-level resistance to all fluoroquinolones.
Rodriguez-Avial
Iciar
I
Servicio de Microbiología, Hospital Clínico San Carlos, 28040 Madrid, Spain. iciaravial@hotmail.com
Rodriguez-Avial
Carmen
C
López
Olga
O
Picazo
Juan J
JJ
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology*; D012475:Salmonella / Q000187:drug effects* / Q000302:isolation & purification; D012480:Salmonella Infections / Q000382:microbiology
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D009268:Nalidixic Acid