Asma Rahman^1,, S.M. Shamsuzzaman¹, Nigha Zannat Dola¹, Modina Ansary Nabonee¹

Citrobacter freundii, being an opportunistic pathogen is evolving as an important cause of nosocomial infection along with multidrug resistance, leading to a high mortality rate. The emerging range of high antibiotic resistance and the need to prevent infections has led to the development of alternative therapeutic molecules. Immune prophylaxis is considered a safe approach against the pathogen. This study was carried out to see the protective effectiveness of antibodies caused by oral formalin inactivated whole cell vaccine against multidrug resistant C. freundii. In this study, MDR C. freundii was separated from various clinical samples and used for the oral immunization of 9 Swiss albino mice. Seven days following immunization with the third dose of vaccine, the mice were challenged orally with live C. freundii and witnessed for 14 days. Blood from the tail was drawn 14 days after each booster, and lastly, cardiac puncture was done 14 days post challenge. Total antibodies that bind with antigen and functional antibodies having bactericidal activity were assessed by ELISA and serum bactericidal antibody (SBA) assay, respectively. In this study, 14 days after post challenge, 100% survival rates were seen among the immunized mice. ELISA showed all serum from the pre- and post-challenge immunizations had considerably greater optical density values of IgG in comparison to the control mice. On the other hand, SBA assay showed 100% bactericidal activity of the immunized mouse sera using 50% and 25% guinea pig complement following incubation for 3 hours at 1:10 serum dilution. In this study, formalin inactivated oral immunization with MDR C. freundii produced protective antibodies in Swiss albino mice. Safe and tolerable formalin inactivated oral whole cell vaccines may be the most effective and practical way of preventing enteric diseases.

citrobacter freundii, formalin, immunization, oral