Prevalence, Antimicrobial Resistance and Phenotypic Detection of Virulence Factors of Non-fermenting Gram-negative Bacilli Isolated from Canine Clinical Infections

Abstract

Non-fermenting gram-negative bacteria (NFGNB) are increasingly implicated in persistent and multidrug-resistant infections in companion animals, prompting the present investigation to assess their prevalence, identification, antimicrobial resistance, virulence attributes, and genomic characteristics in canine clinical infections, with particular emphasis on Pseudomonas and Acinetobacter species. A total of 402 clinical samples collected from dogs with diverse clinical conditions were processed for bacteriological examination, of which 332 samples (82.6%) yielded bacterial growth, and 73 isolates (21.7%) were identified as NFGNB.  Samples were processed using standard microbiological techniques. Isolation was performed through enrichment in nutrient broth, followed by culture on nutrient agar and MacConkey agar. Among these, Pseudomonas spp. Constituted 19.0% (63/332), Acinetobacter spp. 2.7% (9/332) and Sphingomonas spp. 0.3% (1/332) with otitis and wound infections representing the major sources. Cultural and biochemical characterisation showed that all NFGNB produced non-lactose-fermenting colonies on Macconkey agar; in the oxidative–fermentative (of) test, both Pseudomonas and Acinetobacter isolates demonstrated oxidative utilisation of glucose without fermentation, supporting their classification as non-fermenters. Phenotypically, all pseudomonas isolates were motile and oxidase- and catalase-positive, whereas Acinetobacter isolates were non-motile and oxidase-negative; hemolytic activity was observed in 93.7% (59/63) of Pseudomonas isolates, while none of the Acinetobacter isolates exhibited hemolysis, and biofilm formation was detected in 63.5% of Pseudomonas and 33.3% of Acinetobacter isolates. Antimicrobial susceptibility testing demonstrated a high burden of multidrug resistance, with Pseudomonas spp. showing resistance to cephalothin (57.14%), cefotaxime (53.97%), ceftazidime (52.38%), imipenem (34.92%), meropenem (19.05%), and colistin (30.16%), while Acinetobacter spp. exhibited marked resistance to oxacillin (88.89%), co-trimoxazole (77.78%), cefotaxime (66.67%), ceftazidime (66.67%), imipenem (44.44%), and meropenem (33.33%).