Background: Pseudomonas aeruginosa is a pathogen that causes infections in animals and humans, with veterinary implications including ear infections in dogs, respiratory diseases in cats, and mastitis in ruminants. In humans, it causes severe hospital-acquired infections, particularly in immunosuppressed patients. This study aimed to identify and assess the prevalence of specific virulence factors in Pseudomonas aeruginosa isolates. Methods: We analyzed 98 Pseudomonas aeruginosa isolates from various animal samples (dogs, cats, ruminants, fowl) from northeastern Poland in 2019–2022 for virulence-related genes (toxA, exoU, exoT, exoS, lasB, plcN, plcH, pldA, aprA, gacA, algD, pelA, endA, and oprF) by PCR and assessed biofilm formation at 48 and 72 h. Genomic diversity was assessed by ERIC-PCR. Results: The obtained results showed that all strains harbored the pelA gene (100%), while the lowest prevalence was found for pldA (24%) and exoU (36%). Regardless of the animal species, strong biofilm forming ability was prevalent among the strains after both 48 h (75%) and 72 h (74%). We obtained as many as 87 different genotyping profiles, where the dominant one was profile ERIC-48, observed in four strains. Conclusions: No correlation was found between presence or absence of determined genes and the nature of infection. Similarly, no correlation was found between biofilm-forming genes and biofilm strength. The high genetic diversity indicates challenges for effective prevention, emphasizing the need for ongoing monitoring and research.

Staphylococcus aureus is one of the aetiological agents of mastitis in dairy cattle. Their biofilms are relevant for human and veterinary medicine. It has been shown that some antibiotics at low concentrations can stimulate the production of biofilms, but there is little information on the effects of low concentrations of nisin, which is considered a therapeutic agent and has been added to food products for years as a biopreservative. In our study, we used Staphylococcus aureus strains (n = 28) isolated from dairy cattle. The MIC of nisin were determined using the broth microdilution method. Based on the minimum inhibitory concentration (MIC) results, the following concentrations were selected for further analyses: nisin at 39, 19, 9 IU/mL; nisin in combination with tetracycline at 39 IU/mL + 0.06 μg/mL, 18 IU/mL + 0.06 μg/mL, and 9 IU/mL + 0.06 μg/mL; and tetracycline alone at 0.06 μg/mL. The biofilm-forming capacity was determined via crystal violet staining in 96-well plates, icaD gene expression was determined using the 2−ΔΔCt method, and microscopic evaluation was carried out using scanning electron microscopy. Results: The MICs were 156 IU/mL (46%) and 312 IU/mL (43%) for most strains. Due to large statistical deviations, there were no statistically significant changes in the biofilm-forming capacity or icaD gene expression despite a visible increasing trend. Despite the absence of statistically significant differences, it was observed that for all concentrations analysed biofilm formation was noticeably greater for both nisin alone and for tetracycline and its mixtures than for untreated cells. Conclusions: In our opinion, the effects of nisin, especially at low concentrations, on biofilm structure show a certain worrying trend that may pose a future threat.

Pseudomonas aeruginosa is an opportunistic pathogen of clinical significance in both human and veterinary medicine. In human healthcare, it is primarily associated with multidrug-resistant hospital-acquired infections. In companion animals, it commonly causes chronic and difficult-to-treat infections of the ears, wounds, and respiratory tract. This study aimed to evaluate the impact of sub-inhibitory concentrations of commonly used antiseptics in veterinary practice on the biofilm-forming ability of P. aeruginosa strains of animal origin. Ten P. aeruginosa strains of animal origin (dogs, cats) isolated from clinical samples as a primary cause of infection, were selected for analysis. Antibiotic susceptibility of the tested strains was determined using the disk diffusion method in accordance with EUCAST and CLSI guidelines. The minimum inhibitory concentrations for two antiseptics: Octenisept and Polisept Vet Wound Irrigation Silver Pro were determined using the microdilution method. Subsequently, the effects of 1/4 and 1/8 MIC concentrations on biofilm formation and its early structure were assessed. Additionally, we evaluated the impact of a short-term exposure to MIC concentrations of tested agents on mature P. aeruginosa biofilms. Fluorescence microscopy was employed to visualize differences in biofilm architecture after 48 h of exposure to the antiseptics in 1/4 MIC concentrations. All analyzed strains were resistant to amoxicillin–clavulanic acid, tetracycline, and trimethoprim/sulfamethoxazole. The minimum inhibitory concentration values were 0.00625% for Octenisept (Schülke & Mayr, Norderstedt, Germany) and 1.25% for Polisept Vet Wound Irrigation Silver Pro (JM Sante Pharma, Sosnowiec, Poland). Exposure to sub-inhibitory concentrations (1/4 and 1/8 MIC) significantly affected biofilm formation in a time-dependent manner. A marked stimulation of biofilm production was observed after 48 h of incubation, whereas this effect was less pronounced after 24 h. In contrast, the analyzed antiseptics did not affect the structure of preformed biofilm after 24 h of exposure. Fluorescence analysis demonstrated similar proportions of live and dead cells between groups; however, the total number of cells differed substantially, with more than a twofold increase observed under the tested conditions. Sub-inhibitory concentrations of antiseptics were found to stimulate biofilm formation in P. aeruginosa strains. Given the potential for low concentrations of antiseptics to occur in the environment, further research and close monitoring of this phenomenon are necessary.

Bovine mastitis remains one of the most economically important diseases in dairy cattle, with Staphylococcus aureus being a major etiological agent, partic

Introduction: The virulence of Yersinia ruckeri , the causative agent of enteric redmouth disease in salmonids, is influenced by multiple factors, including flagellar gene expression. This study investigates the role of fliC gene expression in the pathogenicity of Y. ruckeri and its impact on the immune response of infected rainbow trout ( Oncorhynchus mykiss ). Material and Methods: Using two virulent strains differing in fliC expression, clinical symptoms, mortality rates and key immune parameters were evaluated. Ninety farmed rainbow trout with average body weight of 110.5 ± 24.1 g and average length of 20.7 ± 1.9 cm were used. Allocation was made of 10 fish each to a control group, a low-dose group challenged with one strain, a high-dose group challenged with that strain, and low- and high-dose groups challenged with the second strain, and each challenge group was duplicated. Results: Fish infected with the fliC -repressed strain exhibited more severe symptoms, higher mortality rates and a weaker immune response regardless of infectious dose compared to those infected with the fliC -expressing strain. The lack of an active fliC gene was associated with a lower gammaglobulin level, decreased respiratory burst and suppressed T-cell proliferation. However, increased potential killing activity was noted for that strain. Conclusion: These findings clearly demonstrate the dual role of the fliC gene in the pathogenicity of Y. ruckeri and host immune modulation in rainbow trout.