Clinical carbapenem-resistant Acinetobacter spp. in pet animals: an exploratory study

1. Introduction. Many studies have been performed on carbapenem-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex and only a few studies have been addressed on carbapenem resistance in not-ACB complex species. A. baumannii infections are an important concern in human and veterinary medicine, considering its ability to cause invasive infections and acquire multidrug resistance. Recently, colistin and carbapenem-resistant A. baumannii have increased worldwide with a reduction of antimicrobial efficacy, especially in case of coinfection with the pandemic SAR-CoV-2. To assess the frequency and the antimicrobial susceptibility of both ACB and not-ACB complex members, an epidemiological study on pet animals was carried out. 2. Materials and Methods. From 2018 to 2020, different clinical speciments from dogs, cats and horses were cultured and Acinetobacter spp. identified by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Susceptibility to a panel of 14 human and veterinary antimicrobials, belonging to 9 different categories, was assessed by Kirby-Bauer and E-test methods. 3. Results. From respiratory, enteric, genital, urinary, skin, joint-bone, and sistemic infections of clinically hospitalized and in-visit pet animals, 628 specimens were cultured and Acinetobacter strains (n=16, 2.5%) were identified. The same percentage (50%) of ACB complex members (A. baumannii, A. dijkshoorniae, A. pittii) and not-ACB complex members (A. lwoffii, A. courvalinii, A. johnsonii and A. bereziniae) was observed. The nosocomial origin was significantly represented (P=0.045) in not-ACB complex strains. All Acinetobacter spp. were sensitive to aminoglycosides and polymyxins. The same carbapenem-resistance (37.5%) was observed for both groups, involving A. baumannii and A. dijkshoorniae for the first group, A. courvalinii and A. bereziniae for the second one. ACB complex strains showed significant higher resistances for tetracyclines (P=0.021) and monobactams (P=0.007). 4. Discussion and Conclusions. Acinetobacter isolates belonging to the ACB and not-ACB complex are of particular concern in pet animals since these bacterial species are also associated with the nosocomial and in-visiting clinical settings. The two isolated multidrug-resistant A. dijkshoorniae strains represent the first identification in clinically infected dogs in Italy. Phenotypic antimicrobial resistance, in addition to the carbapenem resistance observed for ACB and not-ACB strains, can be considered a public health concern. In particular, not-ACB complex species, showing relevant resistance profiles, strengthen their role as zoonotic pathogens.