TABLE 1.

LD₅₀s and in vitro characterization of avirulent mutants

Mutant	LD50 (log10)		Growth in LB brotha		Leakiness (7.5 h)b	Resistance to:		Cell invasion		Survival in J774 cellsa
	i.p.	i.g.	1.5 h	4 h		DOCc	NRSd	CHO cellsa	Caco-2 cellsa
CL13	6.34	>11.81	++	++	−	++	++	++	++	−
CL79	4.65	>11.90	+	+	+	+++	+	+	+	+
CL230	>7.23	>9.52	++	+	−	+	−	−	−	+
CL448	6.68	>11.81	+	++	+++	−	−	++	++	+
CL98	<4.00	8.90	++	++	−	++	+	+++	++	++
CL238	<4.00	>9.05	++	++	−	++	++	++	++	++
CL287	<4.00	>9.13	++	++	−	+++	++	++	+	++
CL288	<4.00	>10.11	++	++	−	+++	+/++	++	+	++
CL401	<4.00	>8.35	+	++	+	+	+/++	+	+	+
CL500	<4.00e	>9.95	++	++	−	++	++	++	++	++
CL547	<4.00e	>11.87	++	++	−	++	+	+	+	+
CL554	<4.00e	>9.99	++	++	−	++	++	++	++	++
14028	<1.00f	5.78f	++	++	−	++	++	++	++	++

^a++, comparable to the wild-type level; +, <50% of the wild-type level; −, <10% of the wild-type level. 

^bMembrane leakiness was scored qualitatively by comparing the zones of clearing around colonies with that for the wild type. 

^cIn most cases there was growth of the inoculum in sodium deoxycholate (DOC), and scores were based on the level of growth observed. −, inoculum killed; +, <50% of wild-type growth; ++, growth comparable to wild-type growth; +++, growth rate exceeding wild-type growth by >50%. 

^dScores were based on both survival and growth of the original inoculum in normal rabbit serum (NRS), compared with those of the parental strain. −, <10% of the inoculum survived; +, <50% of the inoculum survived; +/++, the inoculum grew by <50%; ++, the inoculum grew by >50%. Comparison of the resistances of mutants to normal and heat-treated sera revealed that CL230, CL448, and CL98 are complement sensitive while CL79 and CL547 appear sensitive to a different serum component. 

^eBetween 3 and 4. 

^fMean for three experiments.