Evolution of multidrug-resistant Acinetobacter baumannii isolates obtained from elderly patients with respiratory tract infections.
OBJECTIVE
To study the evolution between 1999 and 2002 and mechanisms of antibiotic resistance in a multidrug-resistant Acinetobacter baumannii clone predominant in isolates from elderly patients with respiratory tract infections.


METHODS
Susceptibility to antimicrobials was determined using an agar dilution method. Bacterial clones were identified by PCR-fingerprinting and PFGE with ApaI. Carbapenemases were detected by phenotypic tests; by PCR with primers specific for bla (OXA-40), bla(IMP), bla(VIM-1) and bla(VIM-2); and by hybridization with DNA probes. Class 1 integrons were detected using PCR.


RESULTS
In 1999 isolates were grouped into two main genotypes: clone I (33%) and clone II (55%). These were also detected in 2002 with a different distribution: clone I (69%), clone II (22%). Resistance to amikacin, meropenem and imipenem increased significantly in clone I over this time, whereas clone II was not affected. In 2002, the incidence of bla(OXA-40) rose to 91% in clone I isolates with some also harbouring bla(VIM-2) and bla(IMP) genes. Different class 1 integrons were detected ranging in size from 550 to 1200 bp. No relationship was found between carbapenemases and class 1 integrons.


CONCLUSIONS
In elderly patients, a single clone became predominant among A. baumannii isolates, coinciding with an increase in antibiotic resistance rates. The majority of isolates harboured the bla(OXA-40) carbapenemase gene and some of them also harboured bla(VIM-2) and bla(IMP) genes. The presence of class 1 integrons also increased over time.
Canduela
Miren J
MJ
Dpto. Inmunología, Microbiología y Parasitología, Facultad de Medicina y Odontología, Universidad del País Vasco, Bilbao, Spain.
Gallego
Lucía
L
Sevillano
Elena
E
Valderrey
Cristina
C
Calvo
Felícitas
F
Pérez
Julia
J
D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D019143:Evolution, Molecular; D005260:Female; D006801:Humans; D032023:Integrons / Q000235:genetics; D008297:Male; D008826:Microbial Sensitivity Tests; D009693:Nucleic Acid Hybridization; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012141:Respiratory Tract Infections / Q000382:microbiology*; D001618:beta-Lactamases / Q000032:analysis / Q000235:genetics
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D015252:Deoxyribonucleases, Type II Site-Specific; C038485:GGGCCC-specific type II deoxyribonucleases; D001618:beta-Lactamases