HP03 - Comparison of Bacteriological Culture with Molecular Methods for Identifying Bacteria in Liver Samples from Dogs

Abstract:
Background
Culture has traditionally been used to detect and identify bacteria. Results can take several days and some species of bacteria are fastidious. Molecular methods could allow results to be obtained more quickly and might allow detection of fastidious species.

Objective
To compare bacteriological culture with 16S rRNA gene next-generation sequencing (NGS) and qPCR for identifying bacteria in liver samples from dogs.

Animals
Liver biopsies obtained from 18 dogs presented for diagnostic workup of chronic liver disease.

Methods
Prospective cross-sectional study. Liver biopsies were macerated and plated on standard media for aerobic and anaerobic bacteriological culture. The same biopsy sample was transported overnight in an anaerobic container on ice packs for NGS and qPCR. For 10 dogs, negative controls were obtained by swabbing the macerator and culture broth (together, or separately) prior to sample processing.

Results
Seventeen samples had a negative bacteriological culture. One culture positive sample (Corynebacterium tuberculostearicum) was negative by molecular methods. Four of 18 samples (22%) were positive by molecular methods only; reported bacteria varied widely. Concordant negative results between bacteriological culture and molecular methods were obtained in 13/18 (72%) samples. In 5/10 (50%) negative controls, NGS detected E. coli DNA (10⁵ – 10⁷ copies/gram).

Conclusions and clinical importance
Concordant negative results from bacteriological culture and molecular methods were obtained in a majority of liver samples from dogs. However, the clinical relevance of bacterial DNA in liver samples from dogs remains uncertain as half of the negative controls were reported to contain bacterial DNA.