Study on the drug resistance and pathogenicity of Escherichia coli isolated from calf diarrhea and the distribution of virulence genes and antimicrobial resistance genes

When the solution becomes the problem: a review on antimicrobial resistance in dairy cattle

Antibiotics' action, once a 'magic bullet', is now hindered by widespread microbial resistance, creating a global antimicrobial resistance (AMR) crisis. A primary driver of AMR is the selective pressure from antimicrobial use. Between 2000 and 2015, antibiotic consumption increased by 65%, reaching 34.8 billion tons, 73% of which was used in animals. In the dairy cattle sector, antibiotics are crucial for treating diseases like mastitis, posing risks to humans, animals and potentially leading to environmental contamination. To address AMR, strategies like selective dry cow therapy, alternative treatments (nanoparticles, phages) and waste management innovations are emerging. However, most solutions are in development, emphasizing the urgent need for further research to tackle AMR in dairy farms.

Antibiotic resistance profiling and phylotyping of human-diarrheagenic Escherichia coli pathotypes detected from diarrheic and non-diarrheic calves in Iran

BACKGROUND

Escherichia coli (E. coli) serves as a common indicator of gut microbiota and is utilized for monitoring antimicrobial resistance determinants in food-producing animals. This study aimed to investigate antimicrobial resistance patterns in virulence gene-positive E. coli isolates obtained from 340 healthy and diarrheic calves.

METHODS AND RESULTS

A total of 340 fecal swab samples were obtained from diarrheic (n = 170) and healthy (n = 170) calves for 12 months from different farms in Kerman, Iran. The samples were phenotypically analyzed to detect E. coli isolates and antibiotic resistance. Also, antimicrobial resistance genes, diarrheagenic E. coli pathotypes, and phylogenetic background were screened by PCR. Fifteen percent (51/340) of E. coli isolates were positive for at least one of the examined virulence genes (VGs); the prevalence of VGs in E. coli isolates from healthy calves (36/170; 21.17%) was higher than that in diarrheic cases (15/170; 8.82%). Out of the 51 VG-positive isolates, six pathotypes including Shiga toxin-producing E. coli (STEC; 27.45%), enterotoxigenic E. coli (ETEC; 23.52%), enterohemorrhagic E. coli (EHEC; 19.6%), necrotoxigenic E. coli (NTEC; 19.6%), enteropathogenic E. coli (EPEC; 15.68%), enteroinvasive E. coli (EIEC; 1.96%) and three hybrid pathotypes including ETEC/STEC, ETEC/EHEC, and STEC/EIEC were detected among the strains. Antimicrobial resistance (AR) was observed in 98.03% of the VG-positive isolates, which was the same for both healthy and diarrheic calves. The maximum prevalence rate of AR was found against trimethoprim/sulfamethoxazole (49.01%; 3/51), while the minimum prevalence rate was against gentamycin (5.88%; 25/51). Among the VG-positives, phylotype A was found to be the most prevalent followed by B1 and D phylotypes.

CONCLUSIONS

The prevalence of VG-positive E. coli isolates was higher in healthy calves compared to diarrheic cases. AR was widespread among VG-positive isolates. These findings suggest that calves may serve as potential reservoirs of antimicrobial-resistant hybrid pathotypes of E. coli.

Development of a bispecific Nanobody anti-F17 fimbria as a potential therapeutic tool

Pathogenic strains of Escherichia coli F17+ are associated with various intestinal and extra-intestinal pathologies, including diarrhea, and result in significant animal mortality. These infections rely on the expression of virulence factors, such as F17 fimbriae, for adhesion. F17 fimbriae form a protective layer on the surface of E. coli bacteria, consisting of a major structural subunit, F17A, and a minor functional subunit, F17G. Because of the evolution of bacterial resistance, conventional antibiotic treatments have limited efficacy. Therefore, there is a pressing need to develop novel therapeutic tools. In this study, we cloned and produced the F17G protein. We then immunized a camel with the purified F17G protein and constructed a VHH library consisting of 2 × 109 clones. The library was then screened against F17G protein using phage display technology. Through this process, we identified an anti-F17G nanobody that was subsequently linked, via a linker, to an anti-F17A nanobody, resulting in the creation of an effective bispecific nanobody. Comprehensive characterization of this bispecific nanobody demonstrated excellent production, specific binding capacity to both recombinant forms of the two F17 antigens and the E. coli F17+ strain, remarkable stability in camel serum, and superior resistance to pepsin protease. The successful generation of this bispecific nanobody with excellent production, specific binding capacity and stability highlights its potential as a valuable tool for fighting infections caused by pathogenic E. coli F17+ strain.