Influence of the β-lactam resistance phenotype on the cefuroxime versus cefditoren susceptibility of Streptococcus pneumoniae and Haemophilus influenzae recovered from children with acute otitis media

• Published in: Journal of antimicrobial chemotherapy 2007-08, Vol.60 (2), p.323-327
• Main Authors: Fenoll, Asunción, Aguilar, Lorenzo, Robledo, Olga, Giménez, María-José, Tarragó, David, Granizo, Juan-José, Gimeno, Mercedes, Coronel, Pilar
• Format: Article
• Language: English
• Subjects: Acute Disease; amoxicillin resistance; Anti-Bacterial Agents - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; antimicrobial susceptibility; Bacterial diseases; beta-Lactam Resistance - genetics; beta-Lactam Resistance - physiology; beta-Lactamases - chemistry; beta-Lactamases - metabolism; Biological and medical sciences; Cefuroxime - pharmacology; Cephalosporins - pharmacology; Child; Ear, auditive nerve, cochleovestibular tract, facial nerve: diseases, semeiology; Ent and stomatologic bacterial diseases; Haemophilus influenzae - drug effects; Human bacterial diseases; Humans; Infectious diseases; Medical sciences; Microbial Sensitivity Tests; middle ear isolates; Non tumoral diseases; Otitis Media - microbiology; Otorhinolaryngology. Stomatology; paediatric isolates; Pharmacology. Drug treatments; Phenotype; Staphylococcal infections, streptococcal infections, pneumococcal infections; Streptococcus pneumoniae - drug effects
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkm209

Objectives 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 β-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 β-lactamase-positive H. influenzae strains were 93.8% and 85.4% to amoxicillin/clavulanate and cefuroxime, respectively. Resistance to amoxicillin/clavulanate (MIC ≥ 8/4 mg/L) was 12.1% (8 out of 66) and 6.3% (3 out of 48) in β-lactamase-negative and -positive strains, respectively. All H. influenzae strains were inhibited by ≤0.06 mg/L cefditoren. Conclusions Susceptibility to sentinel β-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 β-lactamase production.