Figure 5. Pyocin S5 can afford protection against lethal P. aeruginosa infections in the presence of pyocin S5 antibodies.

(a) Bacterial counts were determined by CFU counts from homogenised lungs. Multiple doses of pyocin S5 (75 μg/dose) were administered intranasally three times, two weeks apart over four weeks. At thirteen weeks, mice were infected with P. aeruginosa P8 and treated with pyocin S5 (75 μg) or PBS intranasally 1 h post-infection. Bars represent Mean ± SEM of counts from 5 animals. *Denotes statistical significance for comparison of treatment versus control by a one-sided Mann-Whitney U test with Bonferroni correction applied. (b) Pyocin S5-specific IgG and IgA serum levels for mice repeatedly exposed to pyocin S5 or PBS (as described in a). The control group were immunized subcutaneously (S.C.) with pyocin S5 (75 ug/dose) in Freunds complete/incomplete adjuvant on three occasions, two weeks apart. No pyocin S5-specific IgA was detected in any of the animals tested. Bars represent Mean ± SEM calculated from the serum of 5 animals per group. (c,d) as for (a,b) except mice were repeatedly exposed to pyocin S5 via the intraperitoneal (I.P.) route prior to intranasal pyocin S5 or PBS treatment. The pyocin S5-specific IgG levels in (d) were very low in the pyocin S5 only group (1000-fold less than the Freunds complete/incomplete control group) and no pyocin S5-specific IgA was detected.