Occurrence and current frequency of CTX-M-type β-lactamases from a regional hospital in the South West of England

two serovars, a higher resistance to ciprofloxacin than to nalidixic acid was observed (Table 1). This might indicate that nalidixic acid is a more precise indicator for low fluoroquinolone resistance than ciprofloxacin. A Danish study has shown failures of treatment with ciprofloxacin for infection with Salmonella Typhimurium DT104, with an MIC value below the CLSI breakpoint. Similar failures of treatment might be observed for Salmonella Hadar and Salmonella Virchow if the CLSI breakpoint for ciprofloxacin is used. This is of great concern, since ciprofloxacin is often the drug of choice when treating invasive Salmonella infections. Twelve Salmonella Hadar and one Salmonella Newport isolate were resistant to cefalotin (Table 1). When tested phenotypically for extended-spectrum b-lactamase (ESBL) activity using the Etest (cefotaxime and ceftazidime with and without clavulanic acid), all isolates were ESBL negative. Prevalence of antimicrobial resistance varies greatly among less frequent Salmonella serovars isolated in Denmark, and some serovars show a higher level of resistance than others.