TABLE 2.

Effect of Ers treatment on the antibiotic resistance of stationary-phase Legionella^a

Antibiotic	Concn (μg/ml)	JR32			dotA mutant
		% Survival		Ers/Stat	% Survival		Ers/Stat
		Stat	Ers		Stat	Ers
Gentamicin	100	1.75 × 10−3 ± 1.2 × 10−3	0.73 ± 0.41	420	0.041 ± 0.0042b	0.87 ± 0.06	21
Erythromycin	100	19 ± 2	46 ± 16	2.4	2.5 ± 0.9	12 ± 6	4.8
Rifampin	100	54 ± 0.5	69 ± 16	1.3	0.74 ± 0.04	70 ± 11	95

^aBacteria in the stationary phase (Stat) or following Ers treatment after the stationary phase (Ers) were resuspended in phosphate-buffered saline at a concentration of 1 × 10⁸ to 5 × 10⁹ CFU/ml, incubated at 37°C for 40 min with the concentration of antibiotic indicated, and then titrated on CYE plates. The titer obtained compared to titer before antibiotic treatment is expressed as the percent survival; the values are means ± standard deviations.

^bThe higher level of survival of the stationary-phase dotA mutant than of stationary-phase strain JR32 is attributable to the kanamycin resistance element in dotA::Tn903, which conveys a low level of gentamicin resistance.