Extended-spectrum β-lactamase (ESBL) production of Escherichia coli strains isolated from diarrheic pigs

Background: Extended spectrum beta-lactamases (ESBLs) are enzymes conferring resistance to the majority of beta-lactam antibiotics in many bacterial species, including Escherichia coli. Bacteria harboring these enzymes could be resistant to 3rd and 4th class cephalosporines and carbapenems, depleting the range of compounds available for treating serious human infections. Objectives: The authors of this study aimed to examine the ESBL production of 50 selected E. coli strains isolated between 2016 and 2022 in Hungary from cases of porcine diarrhea. Materials and Methods: Archived E. coli strains suspected to produce ESBL were selected based on results. The 50 strains tested in the study originated from 27 different farms, 28 were collected from suckling, 22 from weaned piglets. The phenotypic characterization of the strains was achieved using Micronaut-S beta-lactamases MIC plates. Results and Discussion: Phenotypic characterization of selected E. coli strains revealed the presence of ESBL production in 35 strains, two strains additionally produced AmpC cephalosporinase, and one strain only produced AmpC. ESBL producing strains were found on 20 of the 27 farms investigated. Many of the ESBL producing strains originating from cases of neonatal diarrhea did not possess any of the examined virulence factor genes, nor were they beta-hemolytic. ESBL producing strains from post weaning diarrhea cases on the other hand were all beta-hemolytic and had one or several virulence factor genes. ESBL producing strains are likely widespread, although with quite low frequency in the Hungarian swine production system, both among pathogenic and likely commensal groups of E. coli. Continuous monitoring of ESBL producing strains is warranted, possibly with the inclusion of ESBL selective media or other methods of identification in routine AST, especially in case of E. coli strains isolated from suckling piglets.