REGIONAL DIFFERENCES IN BETA-LACTAMASE AND AMPICILLIN AND CEFPROZIL RESISTANCE IN HAEMOPHILUS-INFLUENZAE IN THE UNITED-STATES

This study tracks regional differences in resistance of Haemophilus in fluenzae to ampicillin and the second-generation cephalosporin cefproz il as well as the role of beta-lactamase. Isolates were gathered from 12 regions of the United States, and culture specimens were tested by standard methods for beta-lactamase production, serotype, and suscepti bility to ampicillin and cefprozil. A total of 1240 isolates were obta ined, for an average of 103 per region. Beta-lactamase was produced by 35.7% of the isolates, which were thus ampicillin resistant; 63.8% we re beta-lactamase negative, ampicillin susceptible; 0.4% were betalact amase negative, ampicillin resistant; and 0.1% were beta-lactamase neg ative, ampicillin intermediate. Overall, 36.1% of the H. influenzae st rains were not susceptible to ampicillin. Conversely, beta-lactamase p roduction had a minimal effect on susceptibility to cefprozil, as only 4.3% of the strains were resistant to this drug. The number of beta-l actamase-positive strains of H. influenzae by serotype (type b, non-ty pe b, nontypeable) was nearly identical. Beta-lactamase production by geographic region varied from 26.9% to 48.6%, indicating significant r esistance in H. influenzae throughout the country. The in vitro activi ty of cefprozil against most ampicillin-resistant beta-lactamase-posit ive strains of H. influenzae suggests that an oral cephalosporin may b e useful in the treatment of infections due to beta-lactamase-producin g H. influenzae.