Características microbiológicas de cepas de Acinetobacter baumannii resistentes ao imipenem isoladas de pacientes internados em Unidade de Terapia Intensiva, e descrição clínico-epidemiológica dos portadores

Abstract

The increasing frequency of carbapenem-resistant Acinetobacter baumannii (CRAB) represents a clinical and epidemiological challenging, with demands better understanding of this pathogen. Areas of special interest are A. baumannii resistance mechanisms and potencial alternatives to antimicrobial treatment, as well as, the dissemination routes of this bacteria. Over the last 20 years, the improvement of molecular techniques brought a greater comprehension about the phenomenon of resistance acquisition and clonal distribution of A. baumannii. This study aimed to assess the enzymatic mechanisms involved in the carbapenem resistance presented by A. baumannii, and the genetic similarity pattern of CRAB strains, isolated from 56 patients attending a medical and coronary intensive care unit. Additionally, the clinical and epidemiological characteristics of this population were described. This was a cross-sectional study, involving 56 patients colonized or infected by CRAB strains, admitted in one of the intensive care of a university hospital, between December 2009 and December 2010. According to a protocol of the Infectious Diseases Service of our hospital, the strains of CRAB included in this study were conserved in temperature of -20 degree since the time of its original identification. 43 (76.8%) out of the 56 were recovered and underwent further microbiological phenotypic and genotypic studies. As results, the mean age of the 56 patients was 61 years (SD: ±15.1), and 58.9% were male. The main reason for ICU admission was medical condition (71.4%), and infection was the most frequent diagnosis (66.1%). The majority of patients (80.4%) had risk factors for CRAB colonization, predominantly use of invasive devices (87.5%) and previous antibiotics therapy (77.6%). From the 56 isolates, 70% represented were colonization by CRAB. The median APACHE II score at ICU admission was 15 (1-32), and the hospital mortality was 59.0%. Among the 56 CRAB strains studied, 43 (76.8%) were evaluated by quantitative ST (susceptibility test) for imipenem, tigecycline and polymyxin B), expression of metallo--lactamases, expression of oxacilinases and clonal distribution by ERIC-PCR. Resistance to imipenem (MIC 16g/ml) by agar dilution method was confirmed in 25 (58.1%) of the 43 strains evaluated. Ten (23.3%) strains were resistant to tigecycline (MIC> 2g/ml) and three were resistant to polymyxin B (MIC 4g/ml). The 43 strains were blaOXA-51 gene, confirming its identification as Acinetobacter baumannii, 22 (51.2%) carried blaOXA-23 gene, 8 (18.6%) and expressed blaOXA-143 gene. 14 (82.4%) out of the 17 isolates susceptible to imipenem by agar dilution method did not express any of the enzymes studied. None of the strains studied showed the presence of metallo--lactamases. The ERIC-PCR identified 15 distinct clones of Acinetobacter baumannii with predominance of six clusters, based on 90% similarity. Top sum up, we concluded that: (i) the studied patients had moderate clinical severity score, and had a high prevalence of risk factors for colonization or infection by CRAB strains; (ii) CRAB strains studied showed predominantly multidrug resistance pattern, with the prevalence of polymyxin B resistance was high; (iii) as suggested in some others studies, the expression of metallo--lactamases is not a common resistance mechanism of CRAB strains in Brazil, while most strains showed blaOXA-23 gene, and some carried blaOXA-143 gene (iv) the genetic pattern of these endemic strains was polyclonal.