TABLE 3.

Diversity of Listeria species and L. monocytogenes allelic types isolated from soil and water samples collected from spinach fields previously identified as being at high or low risk for L. monocytogenes isolation

Sampling site	Event typea	Listeria spp.b		L. monocytogenes
		No. of allelic types	Shannon-Weiner index	No. of allelic types	Shannon-Weiner index
Low-risk field	—	18	2.4	7	1.2
	Irrigation	4	0.84	2	0.33
	Rain	16	2.5	6	1.4
High-risk field	—	21	2.0	7	1.1
	Irrigation	8	1.1	4	0.53
	Rain	18	2.2	6	1.2
Surface water	—	14	0.85	6	0.99
	Irrigation	4	0.67	3	0.39
	Rain	12	1.1	5	0.60

^aEvent type (i.e., irrigation or rain event) that initiated sample collection. — indicates information for all samples collected from the high-risk field, the low-risk field, or surface water regardless of the event type that initiated collection. The number of allelic types is not a simple summation of the numbers of ATs found following irrigation and rain events, as some ATs may have been found following events of both types.

^bListeria spp. including L. monocytogenes.