Antibiotic resistance profiles of clinical Acinetobacter species other than A. baumannii in animals

Acinetobacter baumannii is one of the most clinically significant and difficult to treat ‘ESKAPE’ pathogens emerged in veterinary medicine as well as in human medicine. Despite the clinical relevance of members of the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex, pathogenic not ACB species have been reported from food and food-producing animals. As data on antimicrobial resistance regarding Acinetobacter, both ACB complex members and not, are still scarce in veterinary medicine, an epidemiological study was carried out in order to evaluate the prevalence of Acinetobacter infections and the antibiotic resistance profiles in animal isolates. Since 2018, from clinically infected dogs, cats and horses, different samples were cultured and analyzed by MALDI-TOF/MS. Susceptibility of each strain to a panel of 16 antibiotics (9 classes) was evaluated by Kirby-Bauer and E-test methods (EUCAST, 2020). Isolates that exhibited intermediate sensitivity were considered resistant to the antibiotic. Pandrug-resistant (PDR), extensively drug-resistant (XDR) and multidrug-resistant (MDR) isolates were defined as suggested by Magiorakos et al. (2012). Out of 628 bacteriological examinations, 16 (2.5%) resulted positive for strains belonging to Acinetobacter genus. In particular, 2.3%, 1.9%, and 3% were isolated from both visiting and hospitalized dogs, cats and horses, respectively. Members of ACB-complex accounted for 50% of isolates and in not ACB complex strains the nosocomial origin was significantly represented (P=0.045) (Table 1). All strains resulted sensitive to aminoglycosides and polymyxins (Figure 1). The ACB complex harboured 37.5% of extensively drug resistant (XDR) and 100% of multidrug-resistant (MDR) isolates, while not ACB complex harboured 37.5% of XDR and 75% of MDR isolates. Overall, carbapenem-resistance was associated with resistance to all the beta-lactams, both for MDR ACB and not ACB complex. Acinetobacter strains belonging to ACB complex showed a significant highest resistance to tetracyclines (P=0.021) and macrolides (P=0.007). To our knowledge, this report represents the first identification of MDR A. dijkshoorniae in clinically ill dogs in Italy. Our results emphasize the role of not ACB complex species as important zoonotic pathogens and as potential reservoirs of clinically relevant resistance profiles.