Introduction – Polymicrobial Infections
Polymicrobial infections can be defined as simultaneous or successive infections caused by two or more distinct microorganisms or genotypically different strains of the same pathogen in the same anatomical site. In human urinary tract infections (UTIs), 39% of urine cultures in elderly patients are suspected to exhibit polymicrobial infections1. Alarmingly, polymicrobial infections are not limited to UTIs, can cause infections at different sites, and even be caused by multiple bacteria of the same species. For example, a report that showed four genotypically distinct strains of the same bacterial species worked synergistically to create a flesh-eating polymicrobial infection2.
Similar studies/results have been reported in veterinary medicine showing companion animals carry bacteria and exhibit antimicrobial resistant (AMR) bacteria that are of importance to human health. A veterinary clinic in Singapore reported 45% of samples collected from companion animals were polymicrobial in nature and a high percentage were multi-drug resistant3.Two pathogenic bacterial species typically associated with companion animal infections are Escherichia coli (E. coli), the leading cause of UTIs, and Staphylococcus pseudintermedius (S. pseudintermedius), the primary agent of canine skin infections.
In this study, we assessed the MiQLab test for detection of subpopulations of AMR pathogens in mixed veterinary samples and compared it to Culture and Sensitivity Testing (C&ST) as well as indepth antimicrobial susceptibility testing (AST) considered gold standards for veterinary diagnostics. The MiQLab Bacterial and AMR Test can detect 10 common bacterial pathogens and 9 types of AMR markers that confer resistance to four classes of antimicrobials (Beta-lactams, Lincosamides, Sulfa-TMP, and Tetracyclines).
E. coli strains (AR-Bank #0019 and clinical isolate 18079740) and S. pseudintermedius strains (clinical isolates, 18031351 and 18079358) were inoculated from a bacterial stock into brain heart infusion (BHI) broth and grown overnight at 37ºC with shaking. The next day E. coli and S. pseudintermedius strains were respectively diluted (1 mL into 9 mL of filter sterilized (FS) beagle urine) and (1 mL into 9 mL of phosphate-buffered saline (PBS)), representing high concentration urine and skin control samples.
To generate 1:1,000 mixed culture samples, the strains with AMR genes were mixed at a 1,000-fold lower concentration than the strains without AMR genes, representing a subpopulation of AMR bacteria in the mixed sample. E. coli strains were mixed (18079740 (1:10) with ARB #0019 (1:10,000)) into FS beagle urine representing the mixed urine sample whereas S. pseudintermedius strains were mixed (18031351 (1:10) with 18079358 (1:10,000)) into PBS representing the mixed skin sample.
Individual and mixed culture samples were run on the MiQLab using the Bacterial and AMR Test V2. In parallel, samples were transferred to AMIES transport medium via swab (skin samples) or sterile transport container (urine samples) and shipped to two reference laboratories for C&ST (Figure 1). The turnaround time (TAT) was calculated, and results analyzed.
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