In vitro susceptibility of Haemophilus influenzae to cefaclor, cefixime, cefetamet and loracarbef.
The susceptibility of 2,212 Haemophilus influenzae isolates cultured in UK clinical laboratories in 1991 was determined for four orally-administered beta-lactam drugs. These isolates included 1,893 ampicillin-susceptible, 191 beta-lactamase-positive and 128 ampicillin-resistant, beta-lactamase-negative Haemophilus influenzae. While 150 (6.8%) isolates were resistant to cefaclor (MIC > or = 16 mg/l) and 85 (3.8%) to loracarbef, all were inhibited by < or = 2 mg/l cefetamet and < or = 1 mg/l cefixime and were therefore susceptible to these agents. Ranges and modes of inhibition zone diameters and MICs indicated that the susceptibility of a variable proportion of the 191 beta-lactamase-positive isolates to cefaclor, loracarbef and cefetamet was reduced compared with the fully susceptible population. In contrast, a major reduction in susceptibility to all four antimicrobial agents was seen among the 128 ampicillin-resistant (MIC 1-64 mg/l) beta-lactamase-negative isolates such that these accounted for 53% and 67% of the total number of organisms resistant to cefaclor and loracarbef respectively. In addition, 23 of 25 isolates inhibited only by > or = 1 mg/l cefetamet and all eight inhibited only by > or = 0.5 mg/l cefixime showed this type of resistance to ampicillin. Results indicate the importance of detecting non-beta-lactamase-mediated resistance to ampicillin and any concomitant diminished susceptibility to other beta-lactam drugs.
Williams
J D
JD
Department of Medical Microbiology, London Hospital Medical College, UK.
Powell
M
M
Fah
Y S
YS
Seymour
A
A
Yuan
M
M
D000668:Ampicillin Resistance; D002433:Cefaclor / Q000494:pharmacology; D020682:Cefixime; D002439:Cefotaxime / Q000031:analogs & derivatives / Q000494:pharmacology; D015296:Ceftizoxime / Q000031:analogs & derivatives / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology*; D006193:Haemophilus influenzae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D012044:Regression Analysis
D002511:Cephalosporins; C054920:loracarbef; C047444:cefetamet; D002433:Cefaclor; D020682:Cefixime; D015296:Ceftizoxime; D002439:Cefotaxime