TABLE 1.

Effect of 1 h Caco-2 pretreatment with cytochalasin D or with calcium-free medium on S. sonnei and S. flexneri internalization, where centrifugation (2,000 × g for 10 min) has and has not been used to facilitate initial contact of bacteria with enterocytes

Shigella species	Treatment	Avg no. of log10 viable bacteria ± SEa
		Not centrifuged		Centrifuged
		Control	Cytochalasin	Control	Cytochalasin
S. sonnei	Cytochalasin	1.9 ± 0.1	2.0 ± 0.1	3.9 ± 0.2	3.2 ± 0.2b
	Calcium-free medium	2.3 ± 0.2	3.6 ± 0.1c	3.8 ± 0.2	4.6 ± 0.1c
S. flexneri	Cytochalasin	1.8 ± 0.1	2.0 ± 0.1	2.7 ± 0.1	2.9 ± 0.1
	Calcium-free medium	1.8 ± 0.1	3.6 ± 0.1c	2.8 ± 0.2	4.7 ± 0.1c

^aAverage of at least three separate assays, with a lower detection limit of 50 bacteria (1.7 log₁₀). Numbers of internalized shigellae consistently increased in control enterocytes that were centrifuged compared to control enterocytes that were not centrifuged (P < 0.01). 

^bSignificantly decreased compared to corresponding control enterocytes, P < 0.05. 

^cSignificantly increased compared to corresponding control enterocytes, P < 0.01.