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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Antibiotic Laboratory, Servicio de Bacteriología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
Silvia
S
García-Cobos
Margarita
M
Arroyo
María
M
Pérez-Vázquez
Belén
B
Aracil
Noelia
N
Lara
Jesús
J
Oteo
Emilia
E
Cercenado
José
J
Campos
D000328:Adult; D000668:Ampicillin Resistance; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002439:Cefotaxime / Q000494:pharmacology*; D002648:Child; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D005838:Genotype; D006192:Haemophilus Infections / Q000453:epidemiology / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000145:classification / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D008297:Male; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D017720:Molecular Epidemiology; D058885:Multilocus Sequence Typing; D020125:Mutation, Missense; D046915:Penicillin-Binding Proteins / Q000235:genetics; D013030:Spain / Q000453:epidemiology; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D046915:Penicillin-Binding Proteins; D015378:Imipenem; D001618:beta-Lactamases; D002439:Cefotaxime
PBP3; bacteraemia; β-lactams