Screening of potential pathogenic Citrobacter freundii

Objective To screen potential pathogenic Citrobacter freundii. Methods The adhesion of C. freundii on HEp-2 cells was tested by using 36 C. freundii strains isolated from Suixian county, Henan province, and lactate dehydrogenase (LDH) released induced by C. freundii was detected after co-cultured with HEp-2 cells for 10 hours. Moreover, the adhesion and cytotoxicity were compared among C. freundii 74, C. freundii 72, enteroaggregative E. coli (EAEC) strain 042 and 17-2, enteropathogenic E. coli (EPEC) strain 2348/69 and E. coli strain HB101. Results Sixteen C. freundii strains showed little adhesion, with indexes 1; 18 C. freundii strains showed intermediate adhesion, with adhesion indexes ranged from 1 to 100; C. freundii 65 and C. freundii 74 showed the strongest adhesion, with adhesion indexes 100. After 10 hours co-culturing with HEp-2 cells, 35 C. freundii strains, except C. freundii 74 (24%), showed low LDH releasing, similar to that induced by positive control HB101 (5.02%). It suggested that all the isolates, except C. freundii 74 were likely to be non-cytotoxic. C. freundii 74 showed an aggregative adherence pattern similar to that of EAEC 042,the LDH releasing induced by C. freundii 74 was higher than C. freundii 72, 2348/69 and HB101 (P0.01), but lower than EAEC17-2. Conclusion As a potential pathogen, C. freundii 74 showed the strongest adhesion and cytotoxicity.