The Effects of Citrobacter freundii Isolated from Cattle on the Immunological and Histopathological Changes in Mice

Abstract

Citrobacter species are opportunistic invasive bacterium and possible zoonotic pathogens that can cause infections in both humans and animals. A study was conducted in Baghdad City to isolate and identify Citrobacter freundii bacteria from cattle feces and to identify them by a different method, including biochemical testing, PCR analysis, VITEK 2, and sequencing of 16S rRNA, as well as assessing the immune response to the injection of the mice with C. freundii antigens. Thirty Swiss mice were divided into three general groups, injected with KWCA and SWCA immunized killed and sonicated with whole cell antigen. Immune response evaluation was done through the DTH-skin test and TAT. The results showed that the biochemical test revealed 20 isolates, comprising 20% of C.freundii. Vitek 2 results confirmed the positive selection of C.freundii isolates, equivalent to 97%, while 16S rRNA sequencing subjected the isolated bacteria to 99.74% similarity with GenBank references. This result registered one isolate of C. freundii in GenBank by accession number (OR766039). TAT results: The positive control and the second group (SWCA) have indicated an antibody titer of 1280. The first group KWCA has indicated 320. DTH results: The diameter of induration increases from 24 h to 48 h followed by a decrease at 72 h. KWCA results for 24 h, 48 h, and 72 h are 2.46 ± 0.001mm, 3.78± 0.008 mm, and 3.1± 0.0008 mm, respectively. The SWCA has an induration of 3.2± 0.576 mm, 4.08± 0.07 mm, and 3.35± 0.06 mm for 24 h, 48 h, and 72 h, respectively. The statistical difference is P<0.05. The Histopathological alterations indicated changes in both groups. The impact level is similar in all groups, from mild to moderate. In conclusion, the study observed that SWCA and KWCA promoted humoral and cellular immune responses.