This study aimed to identify and characterize lactic acid bacteria strains with antimicrobial activity against Proteus mirabilis, a gram-negative bacterium associated with Parkinson’s disease, Crohn’s disease, and nosocomial infections. Among the 987 lactic acid bacteria strains isolated from various sources, strain no. CHK903 showed high antimicrobial activity against P. mirabilis. Phylogenetic tree analysis based on the 16S rRNA gene and scanning electron microscope analysis identified the selected strain as the rod-shaped Weissella cibaria. The culture supernatants of W. cibaria CHK903 showed antimicrobial activity against some pathogens. Two antimicrobial compounds with molecular weights 189 and 365 Da were partially purified from the culture supernatants of W. cibaria CHK903 using Biogel P2 gel permeation column chromatography. The culture supernatants of W. cibaria CHK903 also showed significant antibiofilm properties, inhibiting biofilm formation by 90% and removing pre-formed biofilms by 60%. These findings suggest the potential therapeutic use of W. cibaria CHK903 as a natural antimicrobial against P. mirabilis-related infections.

Resistance to extended-spectrum cephalosporin in Enterobacteriaceae is increasingly prevalent in South Korea. This study aims to explore the distribution of AmpC genes in Proteus mirabilis isolated from stray and hospital-admitted companion animals in South Korea. AmpC β-lactamases hold clinical significance due to its potential to facilitate antimicrobial resistance to cefoxitin, cefazolin, and most penicillins. A total of 163 bacterial isolates belonging to the Enterobacteriaceae family were collected from dogs (n = 158) and cats (n=5). Of them, 134 isolates were from hospital-admitted animals, while 29 isolates from stray animals. Boronic acid tests and antimicrobial susceptibility tests were conducted for an initial screening to detect AmpC β-lactamase resistant P. mirabilis. Gene-specific PCRs were conducted to identify the type of AmpC genes, which include six groups (MOXM, CITM, DHAM, ACCM, EBCM, and FOXM), in the resistant isolates. The boronic acid disk tests revealed 45 (27.6%) positive isolates out of 163 isolates tested. Of these 45 isolates, six were determined to harbor the EBCM gene, 13 for CITM, one for FOXM, and one for DHAM by single detection PCR. No isolates carried for ACCM or MOXM. Thus, a total of 21 out of 163 isolates (12.9%) were demonstrated to possess AmpC genes. No isolates contain more than one group of AmpC gene family. A significantly higher percentage of P. mirabilis was found to possess AmpC genes compared to past studies. Therefore, the increasing trend in antimicrobial resistance in P. mirabilis indicates a dire need to monitor antimicrobial prescription in the veterinary field.