Antimicrobial Resistance Patterns of ESBL-Producing Escherichia coli in Dogs from Thailand: Evaluation of Algal Extracts as Novel Antimicrobial Agents

<b>Background/Objectives:</b> Multidrug-resistant (MDR) bacteria, including extended-spectrum beta-lactamase (ESBL)-producing <i>Escherichia coli</i>, in companion animals pose a growing public health concern due to the close interactions between pets and humans. This study aimed to investigate antimicrobial resistance patterns and the prevalence of ESBL-producing <i>E. coli</i> isolated from healthy dogs in Thailand, as well as the potential of algal extracts obtained through ethanol extraction and enzymatic hydrolysis as alternative antimicrobial agents against these drug-resistant organisms. <b>Methods:</b> Antimicrobial susceptibility testing was performed on 43 <i>E. coli</i> isolates from healthy dogs. ESBL production was confirmed using standard phenotypic methods, and resistance genes were detected by PCR. The algal extracts were tested for antibacterial activity against MDR isolates. <b>Results:</b> Among the 43 <i>E. coli</i> isolates, 67.44% were classified as MDR, with high resistance rates observed for ampicillin (79.07%), tetracycline (65.12%), and ciprofloxacin (62.79%), highlighting significant antimicrobial resistance concerns. Of the MDR isolates, 31.03% (9/29) were confirmed as ESBL producers. Gene analysis revealed <i>bla</i>_TEM as the most prevalent gene (53.49%), followed by <i>bla</i>_CTX-M (9.30%), while <i>bla</i>_SHV was detected in a single isolate resistant only to ampicillin and was absent in all MDR strains. Ethanol extracts of <i>Haematococcus pluvialis</i> and <i>Caulerpa lentillifera</i> demonstrated inhibitory effects against MDR <i>E. coli</i>. <b>Conclusions:</b> MDR and ESBL-producing <i>E. coli</i> are prevalent in healthy dogs, posing a potential public health risk. Algal extracts from <i>H. pluvialis</i> and <i>C. lentillifera</i> show promise as alternative antimicrobials. Further research is necessary to optimize their efficacy and investigate their in vivo applications, including clinical and environmental settings.