Isolates of β-lactamase-negative ampicillin-resistant Haemophilus influenzae causing invasive infections in Spain remain susceptible to cefotaxime and imipenem

• Published in: Journal of antimicrobial chemotherapy 2014-01, Vol.69 (1), p.111-116
• Main Authors: García-Cobos, Silvia, Arroyo, Margarita, Pérez-Vázquez, María, Aracil, Belén, Lara, Noelia, Oteo, Jesús, Cercenado, Emilia, Campos, José
• Format: Article
• Language: English
• Subjects: Adult; Ampicillin Resistance; Anti-Bacterial Agents - pharmacology; beta-Lactamases - genetics; Cefotaxime - pharmacology; Child; Electrophoresis, Gel, Pulsed-Field; Female; Genotype; Haemophilus Infections - epidemiology; Haemophilus Infections - microbiology; Haemophilus influenzae - classification; Haemophilus influenzae - drug effects; Haemophilus influenzae - enzymology; Haemophilus influenzae - genetics; Humans; Imipenem - pharmacology; Male; Microbial Sensitivity Tests; Microbial Viability; Molecular Epidemiology; Multilocus Sequence Typing; Mutation, Missense; Penicillin-Binding Proteins - genetics; Spain - epidemiology
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkt324

The epidemiology of invasive Haemophilus influenzae has changed in recent years. β-Lactamase-negative ampicillin-resistant (BLNAR) invasive isolates have recently been described in Europe but their clinical significance is unclear. Our main goal was to determine whether invasive H. influenzae remains susceptible to β-lactam antibiotics indicated in the treatment of invasive infections. The antibiotic susceptibility of 307 invasive H. influenzae isolates to seven β-lactam antibiotics was determined by microdilution and interpreted by EUCAST and CLSI breakpoints. We also identified the bla genes, the amino acid substitutions in the transpeptidase domain of penicillin-binding protein 3 (PBP3), the molecular epidemiology of invasive BLNAR isolates by PFGE and MLST, and the time-kill curves of two isolates with PBP3 mutations conferring reduced susceptibility to aminopenicillins and cephalosporins. Of the invasive isolates, 86.6% were non-typeable and 62% were isolated from adults. Decreased susceptibility to β-lactams was due to the BLNAR genotype (gBLNAR; 19.2%) and to β-lactamase production (16.9%). Susceptibility rates to amoxicillin/clavulanic acid, cefotaxime, cefixime and imipenem were greater than 98%. Of 18 gBLNAR non-typeable isolates studied by MLST, 15 different STs were obtained. Amoxicillin and cefotaxime were bactericidal after 2 and 4 h of incubation, respectively. Invasive H. influenzae disease was mainly due to non-typeable isolates infecting adults, and the most common mechanism of β-lactam resistance was mutations in the transpeptidase domain of PBP3. The gBLNAR non-typeable isolates were genetically diverse. The majority of invasive H. influenzae remained susceptible to third-generation cephalosporins; amoxicillin and cefotaxime were bactericidal in two gBLNAR isolates.