Carbapenem-Resistant <i>Acinetobacter baumannii</i> from Serbia: Revision of CarO Classification

<div><p>Carbapenem-resistant <i>A</i>. <i>baumannii</i> present a significant therapeutic challenge for the treatment of nosocomial infections in many European countries. Although it is known that the gradient of <i>A</i>. <i>baumannii</i> prevalence increases from northern to southern Europe, this study provides the first data from Serbia. Twenty-eight carbapenem-resistant <i>A</i>. <i>baumannii</i> clinical isolates were collected at a Serbian pediatric hospital during a 2-year period. The majority of isolates (67.68%) belonged to the sequence type Group 1, European clonal complex II. All isolates harbored intrinsic OXA-51 and AmpC cephalosporinase. OXA-23 was detected in 16 isolates (57.14%), OXA-24 in 23 isolates (82.14%) and OXA-58 in 11 isolates (39.29%). Six of the isolates (21.43%) harbored all of the analyzed oxacillinases, except OXA-143 and OXA-235 that were not detected in this study. Production of oxacillinases was detected in different pulsotypes indicating the presence of horizontal gene transfer. NDM-1, VIM and IMP were not detected in analyzed clinical <i>A</i>. <i>baumannii</i> isolates. IS<i>Aba1</i> insertion sequence was present upstream of OXA-51 in one isolate, upstream of AmpC in 13 isolates and upstream of OXA-23 in 10 isolates. <i>In silico</i> analysis of <i>carO</i> sequences from analyzed <i>A</i>. <i>baumannii</i> isolates revealed the existence of two out of six highly polymorphic CarO variants. The phylogenetic analysis of CarO protein among <i>Acinetobacter</i> species revised the previous classification CarO variants into three groups based on strong bootstraps scores in the tree analysis. Group I comprises four variants (I-IV) while Groups II and III contain only one variant each. One half of the Serbian clinical isolates belong to Group I variant I, while the other half belongs to Group I variant III.</p>