Incidence of quinolone resistance over the period 1986 to 1998 in veterinary Salmonella isolates from Germany

A total of 24,591 nonhuman salmonella strains isolated in Germany between 1 986 and 1998 were examined for their resistance to nalidixic acid by an aga r diffusion method. The rate of resistance (inhibition zone, less than or e qual to 13 mm) ranged from 0.2% in 1986 to a peak of 14.8% in 1990. Between 1991 and 1998 the MICs for nalidixic acid-resistant strains ranged from mo re than 256 mu g/ml for nalidixic acid to between 0.25 and 128 mu g/ml for enrofloxacin. In the early 1990s a particularly high incidence of fluoroqui nolone resistance (49.5%) was seen among isolates of Salmonella enterica se rotype Typhimurium (Salmonella Typhimurium) definitive phage type 204c that mainly originated from cattle. Among isolates from poultry an increase in the incidence of nalidixlic acid resistance to a peak of 14.4% was observed in 1991. This peak was due to the presence of specific resistant serotypes , mainly serotypes Hadar, Saintpaul, Paratyphi B (D-tartrate positive; form erly serotype Java) and New-port. Such strains exhibited a decreased suscep tibility to enrofloxacin (MIC, 1 mu g/ml). Among isolates from pigs the pea k incidence of resistance was reached in 1993, with 7.5% of isolates resist ant to nalidixic acid and enrofloxacin. The study demonstrates an increase in the incidence of strains that are resistant to nalidixic acid and that h ave decreased susceptibility to enrofloxacin after the licensing of enroflo xacin. In addition, the number of other serotypes that exhibited nalidixic acid resistance or reduced enrofloxacin susceptibility increased among the total number of isolates investigated between 1992 and 1998.