Presence of ROB-1 β-lactamase correlates with cefaclor resistance among recent isolates of Haemophilus influenzae

beta-Lactamase production in Canadian isolates of Haemophilus influenzae has remained relatively constant (25-35%) over the last decade despite increasing cefaclor resistance (MIC greater than or equal to 32 mg/L). TEM (294/324, 90.7%) and ROB-1 (30/324, 9.3%) prevalence rates among 324 isolates of H. influenzae obtained from across Canada in 1997-1998 were similar (P > 0.05) to previously published reports. However, 66.7% (26/39) of cefaclor-resistant isolates were ROB-1-positive (P < 0.001) and the remaining four ROB-1-positive isolates were cefaclor-intermediate (MIC 16 mg/L). Susceptibilities to loracarbef (P < 0.001) and cefprozil were also reduced in the presence of ROB-1 while the activities of cefuroxime, cefotaxime, cefixime and imipenem were similar in both TEM- and ROB-1-positive isolates.