bla SED-1 beta-lactamase-producing Citrobacter sedlakii isolated from horses and genomic comparison with human-derived isolates.

The researchers aimed to identify Citrobacter sedlakii bacteria in horses that produce beta-lactamase, an enzyme that gives them resistance to certain antibiotics, and compare their genomic characteristics to similar bacterial isolates from humans.

Objectives

• The study aimed to detect and study Citrobacter sedlakii, a specific type of bacteria that can produce a compound called beta-lactamase, in horses. The production of beta-lactamase is significant as it enables bacteria to resist certain types of antibiotics, making bacterial infections harder to treat.
• The researchers also sought to compare these isolates from horses with those derived from humans, to understand any similarities, differences, and possible transmission pathways.

Methods and Results

• Nine C. sedlakii isolates were identified in horse feces, characterized, and compared to human-derived isolates using whole genome sequencing and phylogenomic methods.
• Of these nine isolates, seven were resistant to ampicillin, a common antibiotic. At least one isolate showed resistance to other antibiotics like ceftriaxone, gentamicin, meropenem, and streptomycin.
• All nine isolates carried a specific gene, blaSED-1 beta-lactamase, which confers resistance to ampicillin.
• Individual isolates were detected carrying the mcr-9 gene that confers resistance to colistin, and the aac(6′)-lid gene that confers resistance to aminoglycosides.
• Seven isolates contained genes that confer resistance to certain metals: copper, silver, and arsenic.
• Genomic studies showed that two isolates from horses were phylogenetically similar to two human-derived isolates from the NDARO database.

Conclusions

• This research yielded valuable information about the antimicrobial susceptibility of C. sedlakii in horses, a relatively unexplored area of knowledge.
• The identification of specific genes mediating resistance, like blaSED-1 beta-lactamase, also add to the understanding of how these bacteria resist certain antibiotics.

The implications of this study could be significant for practical measures to control disease spread in veterinary and possibly human medicine, subject to further studies. Antibiotic resistance is a critical public health issue, hence studies like these contribute key knowledge to combating the problem.