Point-of-care (POC) molecular diagnostics test patients (i.e., pets in veterinary medicine) for pathogens in-clinic or at the site, as opposed to outsourcing tests to a typical reference laboratory. This greatly decreases the turnaround time (TAT) for results and gives both clinician and patient more confidence in the prescribed course of treatment.
In veterinary medicine, the difference between molecular testing and culture and sensitivity testing (C&ST) is particularly noteworthy. The average TAT for reference laboratory tests ranges from three to five days while having accessible, on-site qPCR in the clinic can reduce this to as little as a couple of hours.
Reducing the TAT for pathogen detection in a veterinary setting is helpful for several reasons:
- Aids in initial diagnosis through rapid detection.
- Allows clinicians to prescribe antimicrobials based on results, rather than empirically.
- Can lead towards better wellbeing for the pet and reduce the cost of care for the owner.
- Decreases antimicrobial-resistant (AMR) pathogen emergence because of a higher treatment certainty.
- Promotes antimicrobial stewardship.
Current Problems with Culture and Sensitivity Testing
Previously, the most effective way to detect pathogens and antibiotic resistance factors in veterinary medicine was through outsourcing. Clinical samples were collected on-site and sent to a reference laboratory, which would conduct one or more culture and sensitivity tests.
The TAT on this process, from collection to clinical result, was an average of three to five days.
What are Culture and Sensitivity Tests?
The C&ST is a two-fold, stepwise process aimed at identifying the pathogen causing the bacterial infection and determining the pathogen’s AMR.
- The “culture” in C&ST is very straightforward, consisting of diluting and plating the sample of interest on a specialized, bacterial growth-promoting (high nutrient) medium in a petri dish. The dishes are then incubated at a specific temperature to induce bacterial growth, which is observed through colony formation.
- After incubation, isolated colonies are analyzed by both morphological and biochemical tests in order to identify the pathogen, as set by the Clinical Laboratory and Standards Institute (CLSI) Subcommittee on Veterinary Antimicrobial Susceptibility Testing (VAST). After the disease-causing pathogen is isolated, it can be tested for AMR.
Figure 1 is an example of a typical C&ST workflow performed by a reference laboratory.
Culture and Sensitivity Testing in Veterinary Diagnostics
In veterinary medicine, the two techniques normally used to determine antibiotic resistance and susceptibility are the broth dilution and the disk diffusion assay. Both tests determine if the bacteria of interest are growing (antibiotic resistant) or not growing (antibiotic sensitive), as they are challenged by multiple classes of antibiotics.
The biggest disadvantage with using these tests for identifying antibiotic resistance or susceptibility is that they need ample time to work. Although C&ST is accurate, it is very time-consuming.
Poor Treatment Outcomes, Increased Antimicrobial Resistance
The large TAT between shipping a sample and identifying the pathogen forces a clinician to make treatment decisions prematurely. This is the number one disadvantage for relying on C&ST, as it can cause over or under treatment to occur.
- Over treatment results from making treatment decisions empirically and prescribing a broad-spectrum antimicrobial where a de-escalation of therapy is required.
- Under treatment can produce unsuccessful antimicrobial therapy or pathogen clearance that leads to therapy escalation.
Both instances put the health of the pet at risk and will result in higher cost for the owner as alternative antimicrobial therapy is prescribed. Furthermore, over or under treatment contributes to increased AMR rates.
Advantages of Point-of-Care Molecular Testing
Recent advancements in molecular diagnostics reduce TAT for pathogen detection to as little as one hour, avoiding the consequences of relying on C&ST reference labs. The most advantageous approach uses a rapid molecular diagnostic method known as real-time or quantitative Polymerase Chain Reaction (qPCR).
During qPCR, the pathogen’s DNA is amplified so the pathogen of interest can be quantified and identified in real time. Further, qPCR detects AMR markers associated with the pathogen. In molecular diagnostics, qPCR is considered the gold standard for its high sensitivity and specificity, low contamination risk, and ease of use.
Molecular Diagnostics at Point-of-Care
The real stride for pathogen and AMR detection in veterinary medicine is performing rapid diagnostics using qPCR at the POC, as outlined in Figure 2.
Conducting tests on samples in-clinic reduces the TAT normally associated with C&ST, further increasing the speed at which clinicians obtain results. The usual TAT for C&ST takes days, while Rapid Point-of-Care Molecular Testing possesses the power to identify pathogen(s) and/or AMR marker(s) in as little as ~2 hours.
Faster, Better Treatment Decisions and Reduced AMR
Getting pathogen testing results within hours instead of days both aids in the initial diagnosis and removes the pressure to use empirical therapy. Clinicians can prescribe targeted treatments, for known pathogens, and have confidence in the efficacy of those treatments.
Bringing molecular diagnostics into the point-of-care clinical toolkit has the benefit of promoting antibiotic stewardship and supporting efforts to slow the rise of AMR bacteria in veterinary medicine.