Induction of a specific humoral response by bacteriophages may impact the efficacy of phages as antibacterial agents in vivo. In our recent work we showed that T4 phage applied per os for a long period of time induced production of anti-phage antibodies in the gut and in the blood. Here we present results of a similar study with two staphylococcal bacteriophages: A3/R and 676/Z.
C57Bl6/J mice were treated with purified phage preparations in PBS, mixed with drinking water (1:1) to a final concentration of 4x109 pfu/ml continuously for 100 days. Control mice were given drinking water mixed with PBS. Then, phages were removed from the diet and the experiment was continued for the next 98 days. Blood was collected from mice and anti-phage antibody (IgG, IgA, IgM) levels in the plasma were tested using ELISA immunoassay.
We observed a marked increase in plasma IgG 22 days after the initiation of the treatment. IgG levels then continued to rise until day 36 and remained at high concentration also for the time after phages were removed from the diet. Interestingly, increase in IgG levels was not preceded by a marked IgM peak, only a slight increase in IgM levels was observed on day 22. Plasma IgA levels increased approximately 2-3 weeks later then IgG and reached their maximum 10-12 weeks after the initiation of phage treatment. Contrary to IgG, plasma IgA levels decreased overtime after phage treatment was terminated.
These data show that staphylococcal bacteriophages applied per os induced humoral response in vivo, interestingly, with a lower contribution of primary response but with a significant level of response in IgG and IgA.

This work was supported by the National Science Centre in Poland grant UMO-2012/05/E/NZ6/03314 and by the Wroclaw Centre of Biotechnology, programme The Leading National Research Centre (KNOW) for years 2014–2018.