Antimicrobial Surveillance of Haemophilus influenzae in the United States during 2000-2001 Leads to Detection of Clonal Dissemination of a β-Lactamase-Negative and Ampicillin-Resistant Strain

Abstract

ABSTRACT A 2000-2001 U.S. Haemophilus influenzae surveillance study ( n = 1,434) detected nine (0.6%) β-lactamase-negative and ampicillin-resistant (BLNAR) isolates collected from two different hospitals. The MICs of ampicillin for all nine isolates were 4 μg/ml, with results being reproducible; and all nine isolates were susceptible to amoxicillin-clavulanate, cefuroxime, cefprozil, macrolides, and fluoroquinolones. Pulsed-field gel electrophoresis of genomic DNA following Sma I digestion demonstrated identical patterns for each of the nine isolates, suggesting intra- and interhospital dissemination of a BLNAR clone.