Enhanced resistance to Pseudomonas aeruginosa infection in mice pretreated with OK-432.

The resistance to Pseudomonas aeruginosa infection in normal mice was markedly enhanced by intra peritoneal administration of streptococcal preparation, OK-432. OK432 reduced the mortality and enhanced the in vivo killing activity of peritoneal cells against P. aeruginosa infection in immunosuppressed mice treated with high doses of dexamethasone. A streptococcal preparation, OK-432, developed by 0 kamoto et al. 21), has been known to have potent antitumor activities in experimental animals11 ' 27l and humans13 ' 21l. Its stimulates the host defense mechanism in terms of activation of macrophages11l, lymphocytes13l, granulopoiesis9l and serum complement components15 ' 26l, and production of interferon17> and of serum antibody33l. It was proved that Mycobacterium bovis (BCG)4• 36l, Propionibacterium acnes (Corynebacterium parvum)12• 18> and OK-43213• 20 which are currently being used in cancer immunotherapy also enhance the resistance to experimental bacterial1• 19, 28 -ao and viral 61io, 14, 16l infections in animals. Among these, little is known of its enhanced resistance to bacterial infections in animals. In the present study, we examined the effect of this agent on P. aeruginosa infection in normal and dexamethasonetreated mice. OK-432 was donated by Chugai Pharmaceutical Co., Tokyo. As the challenge inoculum, P. aeruginosa PAO 3047 and Escherichia coli 81 were used in some experiments. These organisms were incubated at 37° C for 24 h in heart infusion broth. Bacterial cells were harvested by centrifugation, washed three times, and diluted in saline. Female ddY mice 4 to 5 weeks old were purchased from the Shizuoka Union for Experimental Animals, Shizuoka, Japan. Each animal was given intraperitoneally (i. p.) 1 or 5 KE (Klinische Einheit) of OK432 suspended in sterile physiological saline. Because 1 and 5 KE of OK-432 contain 2, 690 and 13, 450 units of penicillin G, respectively, equivalent amounts were added to each dose of saline inoculum administered to the control animals also. Ten mice each in the experimental and control groups were challenged i. p. with 0. 1 ml of serial 5-fold dilutions of P. aeurginosa (2. 8 x 108 /ml) or E. coli 81 (1. 2 x 107/ml) one day after injection with OK-432. The LD50 was determined by the method of Reed and Muench23l. Mortality data were recorded 7 days after challenge. As shown in Fig. 1, LD50 values for P. aeurginosa and E. coli increased about 12and 4-fold, respectively, as compared with those in control mice. Twenty mice in the experimental and control groups were administered i. p. with or without 1 or 5 KE of OK-432. At various time intervals for up to 14 days, mice were infected i. p. with 0. 1 ml of P. aeruginosa (4. 7-5.6x107 /ml), and survival was recorded 7 days after infection. As shown in Fig. 2, the enhanced resistance in mice was gradually reduced and completely lost 10 days (1 KE) and 14 days (5 KE) after administration of OK-432. However, the resistance in both experimental groups to infection was significantly enhanced for 5 days thereafter (P<O. 05). Study was made to determine whether or not