A 42-year-old loggerhead sea turtle named Shelly suffered from a chronic bacterial shell infection for four years, which eventually became resistant to most antimicrobials. Through a combination of bacteriophage and antibiotic treatment, scientists were able to achieve significant improvement in the animal's condition.*

In 2014, a female sea turtle—a member of the endangered species Caretta caretta —was diagnosed with a bacterial shell infection (Septicemic Cutaneous Ulcerative Disease, or SCUD). The disease manifested itself as loss of pigmentation, lesions, and localized softening of the shell. The causative agent, the gram-negative bacterium Citrobacter freundii , was isolated from the lesions and proved resistant to most antimicrobials. Treatment of such infections is difficult because medications poorly penetrate the shell tissue, which is essentially bone.

To treat the turtle's shell infection , it was decided to use bacteriophages, as they are highly specific and do not disrupt the normal intestinal microflora, which plays a critical role in the animal's digestion. Ten different bacteriophages specific to C. freundii were isolated from wastewater, and a series of phage cocktails were created from them in various combinations.

High-titer phage cocktails (10^12 PFU/ml) were administered in various forms and via various routes. The animal also received various antibiotics simultaneously, orally and subcutaneously. Phage cocktails were administered intravenously (into the jugular vein), topically with a contact time of at least 20 minutes (phage cocktails in solution form were injected into trepanation holes in the shell and into pockets under the shell, or sprayed onto the shell surface), and added to the water in which the animal lived.

Before, during, and after the course of phage therapy, the turtle underwent blood tests (general, biochemical, immune markers), cultures of the infectious agent were cultured, and its sensitivity to antibiotics was determined.

As a result of treatment , most of the lesions on the shell disappeared: new epithelium appeared, pigmentation returned, and the soft spots hardened. Despite the relief of the turtle's symptoms, pathogenic bacteria—not only C. freundii but also Enterococcus faecalis and Pseudomonas aeruginosa —periodically reappeared in the shell tissue. Interestingly, C. freundii cultures isolated before the start of phage therapy were multidrug-resistant , while cultures isolated at week 35 of treatment were susceptible to most antimicrobials.

Thus, phage therapy helped alleviate the clinical manifestations of SCUD in a 42-year-old sea turtle, with no observed side effects. The combined use of phages and antibiotics resulted in increased antibiotic sensitivity of the causative bacteria.

* Greene W, Chan B, Bromage E, Grose JH et al. The Use of Bacteriophages and Immunological Monitoring for the Treatment of a Case of Chronic Septicemic Cutaneous Ulcerative Disease in a Loggerhead Sea Turtle Caretta caretta. J Aquat Anim Health, 2021; 33:139-154. https://doi.org/10.1002/aah.10130