TABLE 2.

Spontaneous HSV mutation frequency as scored by plating efficiency using PCV and ACV^a

Virus type	Strain	n	Spontaneous mutation frequency				% Resistant virus
			PCV		ACV		PCV	ACV
			Mean	Range	Mean	Range
HSV-1	SC16	12	4.9 × 10−4	1.9–12.0	7.3 × 10−4	3.0–15.0	0.05	0.07
	484	10	2.9 × 10−5	0.1–0.5	2.7 × 10−5	0.1–0.5	0.003	0.003
	1123	10	7.1 × 10−5	0.3–0.9	5.1 × 10−5	0.1–0.8	0.007	0.005
	1761	10	2.9 × 10−4	2.0–4.0	2.6 × 10−4	2.2–3.2	0.03	0.03
	424	10	5.1 × 10−4	2.7–6.9	4.3 × 10−4	2.6–6.5	0.05	0.04
Mean			2.8 × 10−4		3.0 × 10−4		0.03	0.03
HSV-2	SB5	34	7.8 × 10−3	3.6–18.0	6.7 × 10−3	3.4–14.0	0.8	0.7
	333	12	6.9 × 10−3	1.6–12.5	6.3 × 10−3	1.7–11.0	0.7	0.6
	6757	20	3.5 × 10−1	230–520	2.1 × 10−1	170–280	35	21
	6652	10	9.1 × 10−3	6.5–11.0	7.7 × 10−3	5.7–11.5	0.9	0.8
	64C	10	1.9 × 10−2	10.0–48.0	1.4 × 10−2	8.0–23.0	1.9	1.4
	83D	10	6.1 × 10−3	3.3–9.0	5.1 × 10−3	1.3–8.0	0.6	0.5
Meanb			9.8 × 10−3		8.0 × 10−3		1.0	0.8

^an = total number of replicate wells from two independent experiments, except for viruses HSV-2 SB5 and 6757, which represent data from four independent experiments. Mean represents the mean frequency of mutation, the number of drug-resistant viruses per total number of viruses. Range represents the low and high frequency of resistance calculated from each test sample, the number of drug-resistant viruses per total number of viruses. Range values are expressed in 10⁻⁴ for HSV-1 and 10⁻³ for HSV-2. Percent resistant virus indicates percentage of drug-resistant viruses within the progeny virus mixtures, calculated directly from the spontaneous mutation frequency. Drugs were used at 3 μg/ml for HSV-1 and 8 μg/ml for HSV-2. 

^bThe HSV-2 mean was calculated without strain 6757 because this atypical isolate demonstrated an unusually high mutation frequency.