Bacteriophage are viruses that target a bacterial host for infection. Their specificity is often constrained not only by a particular species, but can also be restricted to infect only a specific strain of that particular species.
Despite this specificity, use of bacteriophage as a means to fight infectious bacteria has remained somewhat limited. Phage were discovered around the same time as antibiotics, but the ease of antibiotic administration and efficacy against a host of different bacterial types gave antibiotics an edge (a competitive advantage, if you will). Studies on phage have continued in some parts of the world (largely Russia and eastern Europe), where you can receive phage therapy of resistant bacterial infections. Phage study in most of the western world has been limited to basic science, with little translation or application (yet – ongoing clinical trials may change that).
One application that has been approved in the U.S. is phage treatment of refrigerated ready-to-eat meats (think hot dogs and lox). These items can harbor harmful bacteria such as Listeria monocytogenes, which causes ~1600 annual food poisoning hospitalizations in the U.S. annually (and probably many more that remain unreported). Treating meat and poultry products with a cocktail of phages that target 170 strains of L. monocytogenes is an FDA-approved means of keeping the food chain safe from contamination.
In a report released today, scientists described a new type of bacteriophage that targets the bacterium Cronobacter sakazakii. Previously known as Enterobacter sakazakii, C. sakazakii is also a potent source of foodborne illness. While much less common than Listeria infection, C. sadazakii is arguably more serious: outbreaks are often associated with powdered infant formula, and aren’t killed in formula preparation.
Infants, because of their still-developing immune systems, are particularly susceptible to infections in general. Exposure to C. sakazakii can lead to food poisoning that can quickly become systemic, leading to meningitis. Mortality with this rare but serious disease is as high as 40% – so, clearly, it’s a bacterium to avoid.
The newly described bacteriophage, CR5, showed high antibacterial activity against C. sakazakii when tested in media or in infant formula. Merely 10 hours after treatment, there were no remaining bacteria.
Treating formula with bacteriophage may therefore be an effective protective measure, particularly given that formula may not contain any antibiotics. However, current recommendations are that formula be reconstituted (from powder or liquid concentrate) immediately before use, and any excess be discarded – I’m not sure that a 10-hour incubation will be approved by the WHO. Nevertheless, the discovery toward CR5 is a step toward eliminating terrible C. sadazakii infection in the best possible way – prevention before infection ever occurs.
-- Julie Wolf