Molecular epidemiology of sequential outbreaks of Acinetobacter baumannii in an intensive care unit shows the emergence of carbapenem resistance.
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.
Dipartimento di Scienze Mediche Preventive, Università di Napoli Federico II, Naples, Italy. rafzarri@unina.it
Raffaele
R
Zarrilli
Margherita
M
Crispino
Maria
M
Bagattini
Elena
E
Barretta
Anna
A
Di Popolo
Maria
M
Triassi
Paolo
P
Villari
D000151:Acinetobacter Infections / Q000453:epidemiology*; D040981:Acinetobacter baumannii / Q000235:genetics; D015780:Carbapenems / Q000627:therapeutic use; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D004196:Disease Outbreaks; D024881:Drug Resistance, Bacterial; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008826:Microbial Sensitivity Tests
D015780:Carbapenems