Bacterial infections in companion animals involve multiple body systems and are commonly encountered in veterinary practice. This retrospective study aimed to describe bacterial species recovered from canine and feline clinical samples submitted to a private veterinary diagnostic laboratory in Thailand and to evaluate their antimicrobial susceptibility and multidrug-resistance profiles. A total of 212 clinical records from 2023-2025 were reviewed. After exclusion of incomplete records, duplicate entries, culture-negative cases, and records lacking antimicrobial susceptibility testing results, 131 bacterial isolates were included in the final analysis, comprising 44 isolates from dogs and 87 from cats. Sample types included wound and abscess swabs, nasal discharge, urine, pleural fluid, abdominal fluid, ear swabs, blood, feces, and prostate gland abscesses. Wound and abscess samples were the most common submissions (49.62%). The most frequently isolated bacteria were Escherichia coli (21/131, 16.03%), Pseudomonas aeruginosa (18/131, 13.74%), Klebsiella pneumoniae/Klebsiella spp. (17/131, 12.98%), Staphylococcus pseudintermedius (10/131, 7.63%), and Staphylococcus aureus (10/131, 7.63%). Antimicrobial susceptibility varies across bacterial species and drug classes. Among the isolates tested, aminoglycosides and meropenem showed comparatively favorable in vitro activity, whereas lower susceptibility was observed for cephalexin, doxycycline, and several β-lactam agents. Multidrug-resistance was most prominent among Gram-negative isolates, particularly Enterobacter cloacae, Pseudomonas aeruginosa, Acinetobacter spp., Klebsiella pneumoniae, and Escherichia coli. These findings provide laboratory-based data from a veterinary diagnostic setting in Thailand and support the value of culture-based antimicrobial selection and ongoing local antimicrobial resistance surveillance.