TABLE 1.

Kinetic analyses of C. jejuni 81-176 entry into INT407 cells^a

Post-infection time (min)	Indirect viable count assay		Direct visualization AO-CV assay
	Invasion efficiency (%)	Avg. no. of inter-nalized bacteria/ averaged/host cell	% INT407 cells infected	Avg. no. of inter-nalized bacteria/ infected host cell
10	0.12 ± 0.04	0.18 ± 0.03	10.33 ± 3.51	1.22 ± 0.00
30	0.67 ± 0.24	0.80 ± 0.17	22.00 ± 3.46	1.85 ± 0.17
60	0.93 ± 0.16	1.13 ± 0.05	51.00 ± 5.57	1.93 ± 0.12
90	1.36 ± 0.17	1.72 ± 0.13	66.33 ± 5.57	2.02 ± 0.18
120	1.42 ± 0.18	1.76 ± 0.29	68.00 ± 3.73	2.13 ± 0.23

^aYoung INT407 cells were infected with C. jejuni 81-176 at an MOI of ∼200 for various times. The infected host cells were washed with EBSS and incubated for an additional 2 h with fresh medium containing 100 μg of gentamicin per ml; then internalized bacteria were enumerated by indirect bacterial count or observed directly via microscopic analysis of stained, infected monolayers by the AO-CV method as detailed in Materials and Methods. Invasion efficiency represents the percentage of the inoculum internalized by the end of the assay. Total bacteria internalized per well at each time point was divided by 10⁵ monolayer cells or the actual number of infected host cells to determine the number of internalized bacteria per host cell or number of internalized bacteria per infected host cell, respectively. The direct visualization method was used to enumerate the actual percentage of host cells containing internalized bacteria. Results shown are the mean ± SE of at least three separate assays.