TABLE 3.

Influence of the cloned tonB gene on antibiotic resistance in P. aeruginosa^a

Strain	Plasmid	Diam (mm) of zone of inhibitionb
		CAR	CEF	NOR	CIP	ERY	NOV	TET
PAO6609	pMMB206	23	20	28	26	26	18	17
PAO6609	pQZ04	19	16	25	23	20	15	14
K1032	pMMB206	20	20	30	18	20	15	11
K1032	pQZ04	20	20	29	18	20	15	10

^aFilter discs impregnated with the indicated antibiotics were overlaid on agar plates inoculated with the MexAB-OprM⁺ strain PAO6609 and the MexAB-OprM⁻ strain K1032 carrying plasmid pMMB206 or pMMB206::tonB (pQZ04). Following incubation overnight, the diameter of the circle of growth inhibition was measured. The reported values are representative of the values from two experiments. 

^bAntibiotic abbreviations were as described in the legend to Table 2. The amounts of antibiotic spotted onto the filter discs in 2 to 10 μl were as follows: for PAO6609, carbenicillin, 160 μg; cefepime, 5 μg; norfloxacin, 5 μg; ciprofloxacin, 2.5 μg; erythromycin, 2,560 μg; novobiocin, 1,280 μg; and tetracycline, 80 μg; for K1032, carbenicillin, 2.5 μg; cefepime, 1.25 μg; norfloxacin, 1.25 μg; ciprofloxacin, 0.3 μg; erythromycin, 160 μg; novobiocin, 80 μg; tetracycline, 2.5 μg.