Chronic Superficial Infection in a Dog caused by Multidrug-Resistant Pseudomonas aeruginosa

Abstract

Background: Pseudomonas aeruginosa is a gram-negative aerobic bacterium and non-glucose fermenting, that usually
causes opportunistic infections in animals, including humans. It is rarely involved in primary disease. The antibioticresistant bacterial strains are mainly developed due to the inappropriate use of antibiotics, however treating P. aeruginosa infections can be difficult owing to their natural resistance to antibiotics. Furthermorer resistant microorganisms such as P. aeruginosa grow by developing biofilms. Inaccurate diagnoses and absence of adequate microbiological tests can cause difficulties in resolving cases. This report describes a case of chronic superficial infection in a bitch caused by multidrugresistant Pseudomonas aeruginosa (MDR-PA).
Case: A 6-year-old bitch Shih Tzu, initially presented with an exudative erythematous lesion in the snout region, which progressed to deep lesions, and spread to the back and limbs; furthermore, the animal always experienced a fever before new wounds emerged. Lesion samples, collected using a swab and processed at the Veterinary Microbiology Laboratory of the Federal University of Jatai (UFJ), revealed the presence of Pseudomonas aeruginosa. The isolate was multidrug-resistant and a carrier of TEM and ppyR genes. In the diffusion disk antibiogram, the isolate was found resistant to 14 different antibiotics belonging to 6 classes. Antimicrobial resistance was also tested using the minimum inhibitory concentration (MIC) test against imipenem, ceftazidime, ciprofloxacin, ticarcillin + clavulanic acid and aztreonam present in the MIC test strip. Treatment with amikacin and muporicin proved to be effective; however, owing to lesions extending to the face and palpebral involvement, the animal lost its eyeballs.
Discussion: Pseudomonas aeruginosa is frequently associated with nosocomial infections mainly affecting immunosuppressed patients. Among the antibiotics tested, the group with the highest number of ineffective antibiotics was beta-lactams, where sensitivity was only observed for ticarcillin and ceftazidime. Recent studies have demonstrated that ceftazidime can reduce biofilm volume, inhibit motility, and repress the expression of genes associated with bacterial adhesion in P. aeruginosa. Therefore, the production of biofilm in P. aeruginosa is an important virulence factor as it facilitates a stable environment for the microorganism, which protects the bacteria from contact with antimicrobials. In addition, prolonged exposure to a wide variety of antimicrobials creates an environment of selective pressure between microorganisms, facilitating the emergence of multidrug-resistant strains. Furthermore, it is now well recognized that low doses of antibiotics, administered during continuous and fluctuating treatments, can stimulate biofilm establishment and are partly responsible for biofilm-specific antimicrobial tolerance. The resistance profile of P. aeruginosa isolated from dogs varies considerably, and the presence of isolates with a possible biofilm production capacity represents a challenge for the interpretation of the antimicrobial susceptibility profile. Culture and antibiogram is fundamentally important, both clinically and in environmental monitoring, in addition to the use of antibiogram data for decision making in clinical treatment.

Keywords: antimicrobial resistance, susceptibility profile, MDR-PA, biofilm, exudative erythematous lesion