Background/Objectives: Malassezia pachydermatis is a lipophilic yeast frequently associated with otitis externa and dermatological disorders in companion animals. This study aimed to evaluate the antifungal susceptibility of M. pachydermatis isolates from dogs and cats and to investigate the genomic determinants of reduced susceptibility. Methods: Susceptibility testing of 87 clinical isolates was performed using a modified CLSI broth microdilution method in Sabouraud dextrose broth supplemented with 1% Tween 80. The whole genome of ten representative isolates was sequenced and the genetic factors that are involved in drug resistance were investigated. Results: Ketoconazole, itraconazole, and terbinafine exhibited the highest efficacy, while miconazole and clotrimazole showed reduced activity. Whole genome sequencing revealed single nucleotide polymorphisms (SNPs) in genes that play a key role in the ergosterol biosynthesis pathway, particularly in ERG11 and ERG1. While some specific amino acid substitutions (e.g., K446R in ERG11) were found only in isolates with elevated MIC values, no direct correlation with resistance could be unequivocally established. Conclusions: Genomic analyses also uncovered chromosomal mutations and the heterozygosity of certain isolates, suggesting that complex, multifactorial mechanisms may drive the development of drug resistance. These findings highlight the importance of standardized susceptibility testing and further genomic investigations to promote effective antifungal therapy in veterinary medicine.

Background/Objectives: Pasteurella multocida is responsible for a wide variety of animal diseases worldwide, causing major economic losses. These infections are usually treated with antibiotics; however, the emergence of multidrug-resistant (MDR) strains is increasingly hindering. Understanding antibiotic resistance in P. multocida is important for effective treatment strategies and public health, as it impacts both animal and human welfare. Methods: In this study, the antibiotic susceptibility of 80 P. multocida isolates was evaluated by phenotypic (disk diffusion and broth microdilution) and genotypic analysis via whole-genome sequencing, with particular attention to the occurrence of MDR strains. The strains were tested against antibiotics from nine antimicrobial classes (penicillins, cephalosporins, aminoglycosides, tetracyclines, macrolides, fluoroquinolones, lincosamides, phenicols, and sulfonamides). Antimicrobial resistance gene (ARG) sequences and single-nucleotide polymorphisms (SNPs) were evaluated in paired reads using the Bacterial and Viral Bioinformatics Resource Center (BV-BRC) and the Comprehensive Antibiotic Resistance Database (CARD) via Resistance Gene Identifier (RGI), respectively. Results: Phenotypic results indicated that cephalosporins and phenicols were the most effective drugs against P. multocida; however, the majority of strains were also susceptible to fluoroquinolones and tetracyclines. In contrast, high resistance rates were observed to sulfamethoxazole and clindamycin. The most prevalent resistance genes were strA, sul2, and tetH, while none of the strains harbored the bla-_TEM or erm (42) genes. Conclusions: Of the two phenotypic methods, MIC values showed a stronger positive correlation with genotypic results, making it a more suitable method for determining antibiotic susceptibility. The phenotypic results for phenicols, tetracyclines, and fluoroquinolones showed a strong correlation with the detected resistance genes. In contrast, resistance to sulfamethoxazole, β-lactams, and macrolides remained genetically unexplained, suggesting the existence of additional resistance mechanisms to be explored.

Background/Objectives: The One Health approach is crucial for managing and controlling the spread of antimicrobial resistance. Frederiksenia canicola is a recently identified bacterial species that seems to be a component of the oral microbiota of dogs; however, its pathogenic nature is questionable. Methods: In this study, the antibacterial susceptibility of F. canicola isolates was determined using the disk diffusion and broth microdilution methods. Genome-wide comparative analyses were performed to identify the genetic factors driving virulence and antimicrobial drug resistance (e.g., virulence factors, antimicrobial resistance genes (ARGs) and prophage-related sequences). Results: Most of the F. canicola isolates lacked virulence-associated genes. F. canicola is likely resistant to clindamycin, lincomycin and neomycin, but susceptible to penicillin, erythromycin and enrofloxacin. Antimicrobial resistance genes were not found in the F. canicola genomes, but prophage-related sequences were identified, suggesting its potential in the transfer of genes associated with drug resistance between bacteria in the oral microbiome. Conclusions: F. canicola is presumably a commensal organism with low virulence potential, as evidenced by the absence of virulence-associated genes. As F. canicola can colonize a wide range of hosts, including humans, further investigation with a greater number of isolates is needed to better understand the role of F. canicola in disease development and the spread of drug resistance.