Ability of Chromogenic Agar, MALDI-TOF, API 20E and 20 Strep Strips, and BBL Crystal Enteric and Gram-Positive Identification Kits to Precisely Identify Common Equine Uterine Pathogens

Abstract

Bacterial endometritis is a well-recognized cause of subfertility in mares. Clinicians rely on accurate identification of bacteria to determine if the isolate is pathogenic to develop a therapeutic plan. To determine the accuracy of bacterial identification systems, 25 isolates each of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Streptococcus equi subspecies zooepidemicus were evaluated by Matrix-assisted laser desorption/ionization–time of flight (MALDI-TOF), chromogenic agar, API bacterial identification system and BBL Crystal bacterial identification system. The gold standard for bacterial identification used in this study was DNA sequencing of 16S rDNA (ribosomal subunit). Chromogenic agar (96%) and MALDI-TOF (95%) identified a significantly greater number of bacterial isolates as compared with the BBL Crystal (86%) and API identification (38%) systems. The BBL Crystal system correctly identified a significantly great number of Gram-negative isolates (93% accurate) as compared with S. zooepidemicus isolates (75% accurate). In conclusion, MALDI-TOF and chromogenic agar were able to precisely identify both Gram-positive and Gram-negative equine uterine pathogens. Matrix-assisted laser desorption/ionization–time of flight systems are currently used in veterinary diagnostic laboratories; however, chromogenic agar can be incorporated into clinical practice to rapidly and accurately identify common equine uterine pathogens.