<i>Acinetobacter baumannii</i> in blood-borne and central nervous system infections in intensive care unit children: molecular and genetic characteristics and clinical significance

Abstract

Acinetobacter baumannii is a representative of the peak priority nosocomial pathogens capable of causing infections with high mortality and economic treatment costs. The purpose of our study was to determine a role of A. baumannii in blood-borne and central nervous system infections in children. We conducted a retrospective study of A. baumannii associated cases of bacteremia and CNS infection in children. A. baumannii strains were isolated from 17 children followed up with surgical pathology (congenital heart defects 24%, abdominal pathology 29%, severe combined trauma 29%) and with somatic diseases accompanied by antibacterial and/or glucocorticosteroid therapy 18%. The minimum inhibitory concentrations of antibiotics were determined by the broth microdilution method. Carbapenemase genes were detected by real time polymerase chain reaction. Biofilm formation genes were determined by PCR. Biofilms were grown using flat-bottomed polystyrene tablets, followed by coloring, fixation, elution and detection. Population diversity was assessed by the multilocus sequence typing. About a quarter of cases of bacteremia and central nervous system infection caused by A. baumannii had an unfavorable outcome. Resistance to carbapenems, aminoglycosides, fluoroquinolones was more than 70%. Carbapenemases of the OXA-23 (24%) and OXA-40 (41%) groups were identified. The study of biofilm production showed that A. baumannii isolates formed biofilms of varying intensity: weak biofilms (59%), moderate (35%) and strong (6%). During determining the sensitivity to meropenem for biofilm and planktonic forms of cultures, it was determined that the minimum inhibitory concentrations of meropenem were significantly higher for biofilms than for planktonic forms. The minimum inhibitory concentrations of meropenem for plankton cells ranged from 0.5 to 512 mg/l. While in biofilms the same microorganisms had in vitro minimum inhibitory concentrations of meropenem within 128 to 512 mg/l and higher. All isolates bore biofilm formation regulating genes: bfmR, bap and katE. The ompA gene was found in 94% strains, and the csuA/B gene was found in 88%. The population pattern of A. baumannii isolated from blood and cerebrospinal fluid of children was represented by nine different sequence types. Most of the isolates were represented by genotypes: ST944Oxf, ST1550Oxf, ST1104Oxf belonging to the international clonal line ICL6, and ST450Oxf, ST2063Oxf and ST1102Oxf of the international clonal line ICL2. Blood-borne and central nervous system infections associated with A. baumannii have a great importance in clinical practice. This microorganism is able to persist for a long time on biotic and abiotic surfaces, has a wide natural and acquired antibiotics resistance.