JOURNAL ARTICLE

Molecular epidemiology of sequential outbreaks of Acinetobacter baumannii in an intensive care unit shows the emergence of carbapenem resistance

Raffaele Zarrilli, Margherita Crispino, Maria Bagattini, Elena Barretta, Anna Di Popolo, Maria Triassi, Paolo Villari
Journal of Clinical Microbiology 2004, 42 (3): 946-53
15004037
The molecular epidemiology of multidrug-resistant Acinetobacter baumannii was investigated in the medical-surgical intensive care unit (ICU) of a university hospital in Italy during two window periods in which two sequential A. baumannii epidemics occurred. Genotype analysis by pulsed-field gel electrophoresis (PFGE) of A. baumannii isolates from 131 patients identified nine distinct PFGE patterns. Of these, PFGE clones B and I predominated and occurred sequentially during the two epidemics. A. baumannii epidemic clones showed a multidrug-resistant antibiotype, being clone B resistant to all antimicrobials tested except the carbapenems and clone I resistant to all antimicrobials except ampicillin-sulbactam and gentamicin. Type 1 integrons of 2.5 and 2.2 kb were amplified from the chromosomal DNA of epidemic PFGE clones B and I, respectively, but not from the chromosomal DNA of the nonepidemic clones. Nucleotide analysis of clone B integron identified four gene cassettes: aacC1, which confers resistance to gentamicin; two open reading frames (ORFs) coding for unknown products; and aadA1a, which confers resistance to spectinomycin and streptomycin. The integron of clone I contained three gene cassettes: aacA4, which confers resistance to amikacin, netilmicin, and tobramycin; an unknown ORF; and bla(OXA-20), which codes for a class D beta-lactamase that confers resistance to amoxicillin, ticarcillin, oxacillin, and cloxacillin. Also, the bla(IMP) allele was amplified from chromosomal DNA of A. baumannii strains of PFGE type I. Class 1 integrons carrying antimicrobial resistance genes and bla(IMP) allele in A. baumannii epidemic strains correlated with the high use rates of broad-spectrum cephalosporins, carbapenems, and aminoglycosides in the ICU during the study period.

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