Objective  To examine the infectivity of human adenovirus type 55 (HAdV-55) in human intestinal cells.

  Methods  Caco-2 cells were cultured in vitro, and infected with HAdV-3, 7, 14 and 55. The expression of viral proteins in infected cells was detected with immunofluorescence method. The intracellular and supernatant viral DNA levels were determined with fluorescent quantitative PCR at different points of time. The level of infectious virus particles in the supernatant of Caco-2 cells was determined with adenovirus sensitive HEp-2 infection assay.

  Results  Immunofluorescence assay showed positive result for the expression of HAdV-55 virus protein in Caco-2 cells 48 h post infection. HAdV-3, 7, 14, and 55 showed sustained replication and proliferation in Caco-2 cells. The level of viral DNA in infected cells and the supernatant increased with the infection time, and the viral DNA level of HAdV-55 was significantly higher than those of HAdV-3, 7 and 14. The infectious virus particles of HAdV-55 in Caco-2 supernatant were more than those of HAdV-3, 7 and 14, showing statistically significant difference (P<0.05). Caco-2 cells were infected with low doses of virus (1×TCID₅₀), and the cytopathic effect (CPE) of HAdV-55 infection wells was more significant than that of HAdV-3, 7 and 14 infection wells.

  Conclusion  This study found that human intestinal cells were susceptible to HAdV-55, and the infection level was higher than that of other common respiratory infections caused by adenovirus types 3, 7 and 14.