May 15, 2002 (CIDRAP News) – The most common cause of foodborne Salmonella infection—Salmonella enterica serotype Enteritidis—became increasingly resistant to the first-generation quinolone antibiotic nalidixic acid between 1995 and 2000, according to the results of national surveillance in Denmark.
Kåre Mølbak and colleagues randomly selected and tested 2,546 S Enteritidis isolates from the 13,334 S Enteritidis infections recorded in Denmark over the 6-year period, according to the report in the May issue of Emerging Infectious Diseases. Overall, 3.2% (82 of 2,546) of the isolates were resistant to nalidixic acid, but resistance increased from 0.8% (3 of 384 isolates) in 1995 to 8.5% (31 of 366) in 2000.
Resistance was significantly more common in isolates from patients with a history of foreign travel than in those from patients with infections acquired in Denmark—8.9% versus 2.4% (P<.0001), the report says. Resistance was more common in isolates from patients returning from European countries (other than Scandinavia) than in those from patients who had traveled to Africa or Asia. The researchers also found that resistance was more common in phage types often associated with infections from imported poultry products than in phage types usually associated with Danish layer hens.
Resistance to antibiotics other than nalidixic acid was infrequent, the report states. The investigators do not report resistance to fluoroquinolones, but they say resistance to nalidixic acid has been linked with reduced efficacy of fluoroquinolones such as ciprofloxacin.
"Our data support concerns that the current pattern of quinolone use in food animals leads to increasing quinolone resistance in S Enteritidis and that action should be taken to limit this use," the authors state. Citing several reasons, they contend that the use of nalidixic acid or fluoroquinolones in humans is not likely to contribute much to the increasing quinolone resistance in S Enteritidis.
Mølbak K, Gerner-Smidt P, Wegener HC. Increasing quinolone resistance in Salmonella enterica serotype Enteritidis. Emerg Infect Dis 2002;8(5)