Use of antimicrobials and resistance in bacteria isolated from blood cultures in a Danish county from 1992 to 1995

Detection of methicillin resistance in coagulase-negative staphylococci by cefoxitin disc diffusion and oxacillin Etest. A study of consecutive bacteraemia isolates

Coagulase-negative staphylococci (CoNS) are a significant cause of nosocomial bacteraemia and their susceptibility to beta-lactamase-stabile penicillins is unpredictable. To ensure appropriate antibiotic therapy reliable methods for detection of methicillin resistance (MR) are needed. The objectives of this study were to determine the frequency of MR in a set of CoNS from cases of monomicrobial bacteraemia and to evaluate two phenotypic assays for detection of MR, the 10 microg cefoxitin disk test on Iso-Sensitest agar using a semiconfluent inoculum and the oxacillin Etest. MR was determined by a commercial genomic mecA assay. Of 110 CoNS, 75 were mecA positive and 35 mecA negative. Using interpretive zone diameters R < 22 mm and S > or = 27 mm, the cefoxitin disk test had a sensitivity and specificity of 100%. A correct prediction was obtained for 86 isolates, while 23 were indeterminate (> or = 22 mm; <27 mm). Using CLSI's guidelines, sensitivity and specificity of the oxacillin Etest were 100% and 80%, respectively. A correct prediction was obtained for 102 isolates, while 7 mecA negative isolates were classified as resistant. Thus, the cefoxitin disk test and the oxacillin Etest performed with high accuracy and both seem to be suitable for routine use.

Different trends in antibiotic resistance rates at a university teaching hospital

OBJECTIVES

To investigate long-term trends in antibiotic resistance of common bacterial species isolated at a university hospital and in its intensive care units (ICUs).

METHODS

Levels of antibiotic resistance of common bacterial pathogens were investigated at the Karolinska Hospital during the 12-year period 1988-99. Resistance rates were analyzed for the entire hospital, as well as for ICUs combined.

RESULTS

At the Karolinska Hospital, we found increased ciprofloxacin resistance among Escherichia coli isolates, from 0% in 1991 to 11% in 1999. In the ICUs, the corresponding increase was from 0% to 4.8% during the same period. Co-trimoxazole resistance levels increased from 7.5% to 14%, with lower levels for the ICUs. For ampicillin, cefuroxime, and gentamicin, the levels of resistance were similar in the whole hospital and in the ICUs. Among Pseudomonas aeruginosa isolates, imipenem resistance was higher in the ICUs. For ciprofloxacin, resistance increased from 2.5% in 1991 to 13% in 1999 in the whole hospital, with similar figures for the ICUs.

CONCLUSION

The resistance rates at the Karolinska Hospital were still generally low, but were increasing for some antibiotic-microbe combinations. The results emphasize the importance of including all sectors of a hospital in resistance surveillance studies, and also the value of long surveillance periods.

Long-term antibiotic resistance surveillance of gram-negative pathogens suggests that temporal trends can be used as a resistance warning system

Antibiotic resistance among Gram-negative bacteria and antibiotic consumption were investigated at the Karolinska Hospital, Stockholm, Sweden over a 12-y period. The investigation showed an increase in ciprofloxacin resistance of Escherichia coli from 0% in 1991 to 7% in 1997 and to 11% in 1999. Resistance among Pseudomonas aeruginosa isolates to ciprofloxacin increased from 2.5% in 1991 to 9.0% in 1997 and to 13% in 1999. Resistance levels for norfloxacin showed the same high statistical significance in terms of the temporal trend. A more detailed analysis showed higher resistance against norfloxacin in specific wards. Relationships between antibiotic use and antibiotic susceptibility showed different patterns. The increased ciprofloxacin resistance of E. coli and P. aeruginosa during the study period was paralleled by an increased consumption of quinolones. During the 12-y study period the total use of cephalosporins increased 2.5-fold, while the levels of E. coli resistance to cefuroxime and cefotaxime remained stable. A third pattern was seen with trimethoprim-sulfamethoxazole, namely increasing resistance of E. coli as the use of trimethoprim-sulfamethoxazole declined. The analysis of resistance levels and antibiotic consumption in the present study suggests different mechanisms for the increased resistance. The significant trend of increased resistance to antibiotics over time constitutes an important warning system.