TABLE 4.

Frequencies of spontaneous mutation to rifampin or spectinomycin resistance in Chlamydia spp.a

StrainMutation frequency in presence of drug
Rif (200 ng/ml)Spc (300 μg/ml)
C. trachomatis L2
    Wild type1.55 × 10−7 ± 1.44 × 10−7<3.60 × 10−8
    L2R1NAc<2.40 × 10−8
C. psittaci 6BC
    Wild type7.34 × 10−7 ± 6.23 × 10−71.12 × 10−6 ± 1.70 × 10−6
    Wild type after three passagesb1.90 × 10−8 ± 0.7 × 10−84.48 × 10−5 ± 0.89 × 10−5
    BCR1NA2.23 × 10−7 ± 1.59 × 10−7
    BC0E17.54 × 10−8 ± 3.38 × 10−8NA
  • a The frequency of spontaneously resistant mutants was calculated as described in Materials and Methods. Data are means ± SD.

  • b Infectious particles from a single plaque were expanded during three developmental cycles to obtain a recent clonal population of C. psittaci 6BC.

  • c NA, not applicable.