Effect of surgical antimicrobial prophylaxis duration for colic surgery on complications and resistome

Based on human studies, surgical antimicrobial (AMD) prophylaxis (SAP) beyond 24 h is unnecessary and potentially detrimental.

To compare clinical and microbiological outcomes in patients receiving 24- or 72-h of SAP for colic surgery.

Prospective randomised clinical trial.

Horses that recovered from colic surgery were considered. Exclusion criteria were (1) age <2 years; (2) Miniature Horses, pony, and draught breeds; (3) azotaemia; (4) recent hospitalisation, colic surgery, or AMDs; (5) local AMD administration. Eligible horses were randomly assigned to receive SAP with potassium penicillin and gentamicin for 24- or 72-h. Clinical data and complications were compared between SAP groups. Admission and discharge faecal samples from a subset of horses (N = 49) underwent shotgun metagenomic sequencing on an Illumina platform. Host reads were filtered by aligning to reference genomes using the Burrows-Wheeler Aligner, and taxonomic classification was performed with kraken2. Sequencing reads were aligned to the Comprehensive Antimicrobial Resistance Database (CARD)5 and characterised using the AMR++ pipeline. The microbiome/resistome was characterised and compared between SAP groups over time.

One hundred and forty horses completed the study (24-h N = 71 and 72-h N = 69). The only clinical variable that was different between SAP groups was age (24-h median age 16 [IQR 9, 20] and 72-h 12 [6, 18] years, p = 0.03). There was no significant difference between groups for any complications including incisional infection (24-h 17 [95% CI 10-27]% and 72-h 16 [9-26]%, p = 0.9). Time was the main driver of changes in the microbiome/resistome: alpha diversity decreased while AMD resistance genes associated with administered AMD increased between admission and discharge. Discharge beta-lactam resistance genes were significantly higher in the 72-h than the 24-h group.

Single hospital, small numbers for complications, clinicians not blinded to SAP group.

SAP for 24-h is recommended for horses undergoing colic surgery.