Influence of the beta-lactam resistance phenotype on the cefuroxime versus cefditoren susceptibility of Streptococcus pneumoniae and Haemophilus influenzae recovered from children with acute otitis media.
OBJECTIVE
To study the influence of resistance phenotypes (based on sentinel antibiotics: penicillin and amoxicillin with/without clavulanate) on the cefuroxime versus cefditoren susceptibility of Streptococcus pneumoniae and Haemophilus influenzae recovered from children with acute otitis media.


METHODS
Middle ear isolates (193 S. pneumoniae and 114 H. influenzae) received in the Spanish Reference Laboratory (Instituto de Salud Carlos III) were tested. Antimicrobial susceptibility to penicillin, amoxicillin with/without clavulanate, cefuroxime and cefditoren was determined by agar dilution using Mueller-Hinton agar supplemented with 5% sheep blood for S. pneumoniae and Haemophilus Test Medium for H. influenzae. Strains were classified according to penicillin susceptibility (S. pneumoniae) or beta-lactamase production (H. influenzae).


RESULTS
The decrease in penicillin susceptibility of S. pneumoniae (from the susceptible to the resistant category) decreased amoxicillin and cefuroxime susceptibility rates from 100% to 34% and 0%, respectively. All pneumococcal strains were inhibited by 0.5 mg/L cefditoren, including those from penicillin-resistant serotypes 14, 23F, 6B and 9V with higher amoxicillin versus penicillin MICs. Susceptibility rates of beta-lactamase-positive H. influenzae strains were 93.8% and 85.4% to amoxicillin/clavulanate and cefuroxime, respectively. Resistance to amoxicillin/clavulanate (MIC>or=8/4 mg/L) was 12.1% (8 out of 66) and 6.3% (3 out of 48) in beta-lactamase-negative and -positive strains, respectively. All H. influenzae strains were inhibited by <or=0.06 mg/L cefditoren.


CONCLUSIONS
Susceptibility to sentinel beta-lactams cannot predict activity of other members of the group. The addition of clavulanic acid to amoxicillin does not guarantee 100% coverage of H. influenzae, regardless of beta-lactamase production.
Fenoll
Asunción
A
Spanish National Reference Pneumococcal Laboratory, Instituto de Salud Carlos III, ctra. Majadahonda-Pozuelo Km. 2, 28220 Majadahonda, Madrid, Spain. afenoll@isciii.es
Aguilar
Lorenzo
L
Robledo
Olga
O
Giménez
María-José
MJ
Tarragó
David
D
Granizo
Juan-José
JJ
Gimeno
Mercedes
M
Coronel
Pilar
P
D000208:Acute Disease; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002444:Cefuroxime / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D002648:Child; D006193:Haemophilus influenzae / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010033:Otitis Media / Q000382:microbiology*; D010641:Phenotype; D013296:Streptococcus pneumoniae / Q000187:drug effects*; D018440:beta-Lactam Resistance / Q000235:genetics* / Q000502:physiology*; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; C073460:cefditoren; D001618:beta-Lactamases; D002444:Cefuroxime