Ciprofloxacin resistance in non-typhoidal Salmonella serotypes in Scotland, 1993-2003

To determine the levels of resistance to ciprofloxacin among non-typhoidal salmonellae in Scotland.

Etest strips were used to determine the ciprofloxacin MICs for nalidixic acid-resistant salmonellae isolated from humans during 1993-2003.

The percentage of nalidixic acid-resistant salmonellae isolated from human infection in Scotland has increased from 1.4% in 1993, to 8.8% in 1998 and 21.3% in 2003. Of 493 strains of nalidixic acid-resistant Salmonella tested, a single isolate of Salmonella Typhimurium RDNC was resistant to ciprofloxacin at the NCCLS breakpoint of 4 mg/L. Eleven isolates were resistant at the Scottish Salmonella Reference Laboratory breakpoint of 0.5 mg/L, while 466 isolates (94.5%) had reduced susceptibility with MICs of > or =0.125 mg/L and <0.5 mg/L.

These results show that very few non-typhoidal isolates of Salmonella in Scotland that are resistant to nalidixic acid are also resistant to ciprofloxacin at the NCCLS recommended breakpoint of 4 mg/L. The majority of isolates examined, however, do show reduced susceptibility at 0.125 mg/L. This confirms the necessity for continuing antimicrobial surveillance of resistance to this important antibiotic.