Klebsiella vaccine was prepared from strains of Klebsiella aerogenes with capsular types Kl, K36, K44 and K Cross (a type which cross-reacts in vitro with sera from many klebsiella capsular types). The vaccine was extracted by dialysis and ultrafiltration from capsular material released during growth of the bacteria in a five-day batch culture.
Mice given one dose of vaccine from K1a (l·0 μg/mouse) survived lethal intraperitoneal challenge of 11/11 homologous klebsiella strains four days after vaccination; 14 days after vaccination protection against the same challenge strains had declined to 5/11 strains. Vaccines from Kla, b, c, K3G, K44 and K Cross induced homologous protection and protected mice against different ranges of heterologous klebsiella capsular types.
The protective response of the mice was greatly enhanced by administering three doses of the vaccines. Vaccines from Kl, K36, K44 and K Cross protected mice against 14/20, 11/20, 10/20 and 9/20 homologous and heterologous klebsiella challenge strains respectively.
None of the klebsiella vaccines was toxic for mice at the immunizing dose (l·0 μg/mouse). Vaccine from K36 was the most lethal, killing mice at 103 immunizing doses. The least toxic vaccine was from K44, which killed mice at 104 immunizing doses.