Bacteriophage is being explored as a diagnostic tool

Bacteriophage is being explored as a diagnostic tool ...

Tuberculosis (TB) is a fatal infectious disease that killed 1.5 million people worldwide in 2020. Developing countries are particularly affected, and treatment, particularly in children and adolescents, can be difficult. The mycobacteria that cause TB can also infect cattle and have a significant effect on farming. PBD Biotech has developed a diagnostic test for TB that uses bacteriophage technology alongside qPCR to identify live, disease-causing pathogens.

Dr. Tomas Richardson, a research and development manager at PBD Biotech, spoke to him to discuss how Actiphage technology can assist in the future of TB diagnosis.

Katie Brighton (KB): Could you explain what bacteriophages are, and what of their various uses?

Phage (or bacteriophage to give them their full name) are viruses that infect and replicate within bacteria as part of their natural lifecycle. During that process, the bacteria cell is typically destroyed and its contents and DNA are released.

I believe there is a greater appreciation of phage, and viruses more broadly, as a research tool as well as in more applied settings. In recent years, phage have been developed as a tool for managing antibiotic-resistant bacterial infections. In addition, phage has been suggested as a tool for improving the gut microbiome''s functionalization, where they can be utilized to develop orthologous circuits and systems.

How has PBD Biotech exploited the use of bacteriophage technology in the development of a novel diagnostic test?

TR: Critically, phage exhibit host specificity and infect live bacteria of a given species or group. PBD Biotech has combined phage technology (to detect only viable mycobacteria) with traditional target DNA methods to develop a highly sensitive and specific novel diagnostic assay, which is currently in clinical trials to assess its effectiveness for detection of Mycobacterium tuberculosis (TB). According to WHO figures, 1.5 million people died worldwide from TB in 2020 and millions more are carriers of the disease

The causative properties of TB are called mycobacteria, and this property is subject to an unusually thin waxy cell wall. However, this vulnerability renders mycobacteria recalcitrant to DNA extraction and PCR detection. TB diagnosis is also extremely challenging, mainly because of the remarkably slow growth rates that they exhibit. For example, fast-growing bacteria like Escherichia coli grow and replicate with a doubling time of up to 20 minutes, whereas mycobacteri

Especially in early disease and in children, human TB diagnostics often depend on sputum from the lungs to detect infection. However, almost half of people with pulmonary TB have unable to produce sputum. Actiphage is capable of detecting mycobacteria from blood samples, which are generally less effective to measure. Hopefully, this method may be particularly effective in determining when a human or animal is likely to develop infectious symptoms.

KB: The Actiphage assay is also capable to detect TB in cattle. What advantage does this combination have over current testing methods?

TR: In 2021, more than 40,000 cattle were culled due to bovine TB in the United Kingdom. The disease is a serious concern for farmers and the environment, thus it is a burden to taxpayers. The current primary screening test for bovine TB is the SICTT, which measures the immune response of the cattle. A veterinarian injects small quantities of avian and bovine tuberculin into the animals skin at two different locations to obtain the results. Three days later, a more severe local

The SICTT test is thought to have a 5090 percent tolerance. It takes three days to produce a result, requires at least two vet visits, and cannot distinguish between infected and vaccinated cattle, thus preventing the use of vaccination as a tool for biological control. Despite the relatively small sensitivity of the SICTT method, it also misses a significant proportion of carriers, leaving a reservoir of disease within herds.

Actiphage detects the presence of a living pathogen at very low levels. It can therefore help identify carriers of the disease before they become infectious so that they may be removed from the herd. A fact that Actiphage detects the pathogen rather than the immune response, also signifies that it may be used as a DIVA assay to isolate infected with Vaccinated Animals, which is potentially extremely beneficial in the fight against bovine TB.

Is the Actiphage assay to destroy and detect certain bacteria?

TR: Although phage are capable of infecting and destroying bacteria, there are currently no intentions to develop Actiphage into an antibacterial therapy. However, there is possibility to utilize phage to address mycobacteria seen in the so-called incipient disease, resulting in a phase of TB infection in which the previously active disease gradually becomes active.

Is it possible to see the testing outside of cattle being performed? How about diagnosing different diseases?

TR: Absolutely. Other people are TB-positive, bovine TB, and Johnes disease in cattle (which are caused by Mycobacterium tuberculosis, M. bovis, and M. avium subspecies paratuberculosis respectively). Actiphage is currently in clinical trials to detect human TB.

What are the future plans/priorities for you and your organization, out of your objective to achieve the World Organization for Animal Health (WBO) validation?

TR: While bovine TB is a notifiable disease, OIE validation is certainly a critical step towards international recognition of Actiphage as an effective diagnostic. However, the technology can also be used without OIE validation for the diagnosis of Johnes disease. This is important as current diagnostic tests struggle to detect the causative agent (M. avium subspecies paratuberculosis).

I think that PBD Biotech will be more focusing on diagnosing and combating human tuberculosis. Human TB is second only to COVID-19 as a fatal infectious disease worldwide. As such, working with partners to develop a highly effective human diagnostic with the potential to identify latent TB infections is going to be a priority.

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