Carbapenem-Resistant Acinetobacter baumannii from Serbia: Revision of CarO Classification

Abstract

Carbapenem-resistant A. baumannii present a significant therapeutic challenge for the treatment of nosocomial infections in many European countries. Although it is known that the gradient of A. baumannii prevalence increases from northern to southern Europe, this study provides the first data from Serbia. Twenty-eight carbapenem-resistant A. baumannii 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 A. baumannii isolates. ISAba1 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. In silico analysis of carO sequences from analyzed A. baumannii isolates revealed the existence of two out of six highly polymorphic CarO variants. The phylogenetic analysis of CarO protein among Acinetobacter 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.

The Acinetobacter Outer Membrane Contains Multiple Specific Channels for Carbapenem β-Lactams as Revealed by Kinetic Characterization Analyses of Imipenem Permeation into Acinetobacter baylyi Cells

“…In this context, other authors have reported the existence of insertion sequence (IS)-mediated disruptive events affecting carO (frequencies ranging from 3 to 14%) among epidemiologically related carbapenem-resistant A. baumannii clinical isolates in which the overproduction of diverse OXA enzymes represented the main mechanism of resistance (20-22, 26, 30, 31, 34, 49). It is worth noting that the simultaneous sequencing of Omp33/36 and OprD (21) or the sequencing of Omp33/36 (31) or OprD (49) of the isolates analyzed in the cited reports indicated no disruptive events affecting the corresponding genes. This suggests that while the complete loss of CarO can be tolerated by A. baumannii under carbapenem selection pressure, the simultaneous loss of CarO and OprD/OccAB1 may result in unattainable fitness costs in a situation compatible with a proposed role of the latter OM protein as a channel for multiple growth substrates (33) or with the ensuing defects in the barrier permeability functions of the OM (e.g., see Fig.…”

“…The identification of such channels has remained elusive, and a number of OM proteins, including CarO (13)(14)(15), the Omp33/36 protein (16), and a 43-kDa protein designated OprD (17), have been proposed as candidates on the basis of their loss in carbapenem-resistant Acinetobacter baumannii clinical strains. However, both the role of these OM proteins in carbapenem uptake and the contribution of their loss or mutation to the carbapenem-resistant phenotype, particularly in strains displaying another mechanism(s) of resistance, have been the subjects of controversies (3,15,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34).…”

Acinetobacter: an underrated foodborne pathogen?

“…Nevertheless, one of the main reasons why A. baumannii attracts considerable attention in the clinical arena is its prodigious ability to acquire and accumulate genetic determinants that confer resistance to antibiotics, resulting in infections caused by strains displaying the MDR phenotype [25]. Of particular concern are illnesses associated with Acinetobacter expressing resistance to broad-spectrum antibiotics of the carbapenem group, since there are few therapeutic options available for the treatment of such infections [25][26][27].…”

“…Of particular concern are illnesses associated with Acinetobacter expressing resistance to broad-spectrum antibiotics of the carbapenem group, since there are few therapeutic options available for the treatment of such infections [25][26][27]. The prevalence of carbapenem-resistant bacteria has been increasing in countries worldwide, including Brazil.…”

The Outer Membrane Proteins OmpA, CarO, and OprD of Acinetobacter baumannii Confer a Two-Pronged Defense in Facilitating Its Success as a Potent Human Pathogen

“…CarO is classified into two sub-groups; CarOa and CarOb; of which CarOb exhibits a two-fold greater specificity for IMP ( Catel-Ferreira et al, 2011 ). However, there has been a recent call to rethink the CarO classification system based on phylogenetic analysis ( Catel-Ferreira et al, 2011 ; Novovic et al, 2015 ). So far, at least six polymorphic variants of CarO have been reported to co-exist in A. baumannii populations with varied specificities to imipenem, highlighting the importance of the protein.…”