Molecular Epidemiology of Sequential Outbreaks of Acinetobacter baumannii in an Intensive Care Unit Shows the Emergence of Carbapenem Resistance

Abstract

The molecular epidemiology of multidrug-resistant Acinetobacter baumannii was investigated in the medicalsurgical 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 ␤-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.

Prevalence of Metallo-β-lactamases Encoding Genes Among Pseudomonas aeruginosa Strains Isolated From the Bedridden Patients in the Intensive Care Units

“…Results were interpreted according to the CLSI criteria. The intermediate level of antibiotic susceptibility was considered resistance (13,15).…”

Safety Assessment of Transgenic Organisms, Volume 4

“…Several studies have identified that previous antibiotic treatment was the only risk factor for A. baumannii acquisition (Zarrilli et al, 2004;Carbonne et al, 2005). Hence an appropriate use of antibiotic is critical to reduce the emergence of new multi-drug resistant strains (Coelho et al, 2004;Jain and Danziger, 2004).…”

“…Different integron types have been recognized on the basis of the sequence of the integrase gene. Class 1 integrons were the most common integrons found in Gram-negative bacteria such as Acinetobacter, especially in A. baumannii isolates (Gallego and Towner, 2001;Da Silva et al, 2002;Houang et al, 2003;Poirel et al, 2003;Segal et al, 2003;Nemec et al, 2004;Zarrilli et al, 2004; Abbott et al, 2005). Class 1 integrons have also been found in Acinetobacter strains of environmental origin (Petersen et al, 2000).…”

Carbapenem Resistant Acinetobacter Baumanii Versus MRSA Isolates in ICU in Clinical Center Skopje

“…Dissemination by airborne or other routes can seed environmental reservoirs which either can start [6] or prolong outbreaks [7,8]. In institutions where outbreaks occur in ICUs, a common contaminated object in the environment can often be identified as the source.…”