Searching for a Bacteriophage Lysin to Treat Corynebacterium bovis in Immunocompromised Mice

Establishing the Median Infectious Dose and Characterizing the Clinical Manifestations of Mouse, Rat, Cow, and Human Corynebacterium bovis Isolates in Select Immunocompromised Mouse Strains

Corynebacterium bovis (Cb), the cause of hyperkeratotic dermatitis in various immunocompromised mouse strains, significantly impacts research outcomes if infected mice are used. Although Cb has been isolated from a variety of species, including mice, rats, cows, and humans, little is known about the differences in the infectivity and clinical disease that are associated with specific Cb isolates. The infectious dose that colonized 50% of the exposed population (ID50 ) and any associated clinical disease was determined in athymic nude mice (Hsd:Athymic Nude-Foxn1 nu ) inoculated with Cb isolates collected from mice (n = 5), rat (n = 1), cow (n = 1), and humans (n = 2) The same parameters were also determined for 2 of the mouse isolates in 2 furred immunocompromised mouse strains (NSG [NOD. Cg-Prkdcscid Il2rgtm1Wjl /Sz] and NSG-S [NOD. Cg-Prkdcscid Il2rgtm1Wjl Tg(CMV-IL3, CSF2, KITLG)1Eav/MloySzJ]). To determine the ID 50, mice (n= 6/dose; 3 of each sex) were inoculated topically in 10-fold increments ranging from 1 to 10 8 bacteria. Mice were scored daily for 14 days for the severity of clinical signs. On days 7 and 14 after inoculation, buccal and dorsal skin swabs were evaluated by aerobic culture to determine infection status. The mouse isolates yielded lower ID50values (58 to 1000 bacteria) than did the bovine (6460 to 7498 bacteria) and rat (10,000 bacteria) isolates. Human isolates did not colonize mice or cause disease. Mouse isolates produced clinical disease of vary- ing severity in nude mice. Despite significant immunodeficiency, furred NSG and NSG-S mice required a 1000- to 3000-fold higher inoculum for colonization than did athymic nude mice. Once colonized, clinically detectable hyperkeratosis did not develop in the haired strains until 18 to 22 d after inoculation, whereas athymic nude mice that developed clinically detect- able disease showed hyperkeratosis between 6 and 14 d after inoculation. In conclusion, there are significant differences in Cb's ID 50, disease course, and severity of clinical signs between Cb isolates and among immunodeficient mouse strains.

Phage Therapy as a Focused Management Strategy in Aquaculture

Therapeutic bacteriophages, commonly called as phages, are a promising potential alternative to antibiotics in the management of bacterial infections of a wide range of organisms including cultured fish. Their natural immunogenicity often induces the modulation of a variated collection of immune responses within several types of immunocytes while promoting specific mechanisms of bacterial clearance. However, to achieve standardized treatments at the practical level and avoid possible side effects in cultivated fish, several improvements in the understanding of their biology and the associated genomes are required. Interestingly, a particular feature with therapeutic potential among all phages is the production of lytic enzymes. The use of such enzymes against human and livestock pathogens has already provided in vitro and in vivo promissory results. So far, the best-understood phages utilized to fight against either Gram-negative or Gram-positive bacterial species in fish culture are mainly restricted to the Myoviridae and Podoviridae, and the Siphoviridae, respectively. However, the current functional use of phages against bacterial pathogens of cultured fish is still in its infancy. Based on the available data, in this review, we summarize the current knowledge about phage, identify gaps, and provide insights into the possible bacterial control strategies they might represent for managing aquaculture-related bacterial diseases.