Report

High Mutation Frequencies Among Escherichia coli and Salmonella Pathogens

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Science  15 Nov 1996:
Vol. 274, Issue 5290, pp. 1208-1211
DOI: 10.1126/science.274.5290.1208

Figures

  • Fig. 1.

    Agarose gel analysis of long PCR products from the mutS region of E. coli strains W3110, EC536, and EC503 (29). 3′ primers at a fixed site in rpoS (R3) were paired with 5′ primers at a site in fhlA (F2), at the beginning of mutS (S8), or at its end (L119). Primer sets were designed to amplify products of 12,045 bp (F2-R3; lanes B, E, and H); 10,668 bp (S8-R3; lanes C, F, and I); and 8477 bp (L119-R3; lanes D, G, and J), based on E. coli K12 sequence (10). Lanes A and K, 1-kb ladder (Gibco BRL).

Tables

  • Table 1.

    Rifampicin-resistant mutants in isolates of E. coli and S. enterica. Cultures were grown in BHI broth overnight at 37°C; LB medium was used for plating, including selection for rifampicin resistance (100 μg/ml). Putative mutators displayed at least a 50-fold increase in mutation frequency as compared with control levels. Mutator percent is the number of mutator phenotypes per number of isolates examined times 100.

    StrainNumber of isolates
    Total analyzedPutative mutatorMutator (%)
    E. coli
    O157:H712052 (1.7)
    Other serotypes2031 (5.0)
    ECOR collection7211 (1.4)
    S. enterica
    S. enteritidis1511 (6.7)
    Other serovars106143 (2.8)
    SARC collection1621 (6.2)
  • Table 2.

    Mutation frequency of hypermutable clones. Frequencies ± SD represent three to seven determinations from independent cultures. EC536 and SL12 served as controls for E. coli and S. enterica, respectively (27).

    IsolateMutants per 108 cells
    RifRSpcRNalR
    EC5361.2 ± 0.40.2 ± 0.10.5 ± 0.2
    EC503114 ± 2231 ± 8403 ± 41
    EC535119 ± 2335 ± 7300 ± 57
    DEC5A425 ± 15026 ± 2195 ± 110
    ECOR48441 ± 45SpcR177 ± 57
    S. enteritidis (SL12)2 ± 0.83 ± 0.20.8 ± 0.7
    S. enteritidis (C396)782 ± 10170 ± 25745 ± 163
    S. berta (SL78)738 ± 28930 ± 3148 ± 13
    S. halmstad (SL58)704 ± 265338 ± 73481 ± 269
    S. arizonae (S2978)798 ± 320407 ± 83199 ± 95
    S. infantis (SL101)981 ± 449172 ± 40113 ± 18
  • Table 3.

    Suppression of mutator activity by plasmid clones containing wild-type mut genes (28). Positive complementation is signified by >97% suppression of the mutator phenotype as assessed by spontaneous mutagenesis to rifampicin resistance. Percentage of suppression ± SD represents three or more determinations from independent cultures, except for S. typhimurium TW541, a known mutS-defective strain, which is the average of two experiments.

    IsolatepGW1899 (mutH+)pGW1842 (mutL+)pGW1811 (mutS+)pGT26 (uvrD+)pBR322*
    EC50356.4 ± 11.239.0 ± 7.697.3 ± 1.019.1 ± 11.940.2 ± 8.1
    EC53555.5 ± 10.038.2 ± 31.798.6 ± 0.644.2 ± 6.643.4 ± 17.9
    DEC5A44.2 ± 22.755.0 ± 4.099.3 ± 0.360.5 ± 12.862.1 ± 6.9
    ECOR4830.6 ± 18.626.6 ± 13.697.9 ± 1.946.0 ± 14.7ND
    S. enteritidis C39646.7 ± 10.832.2 ± 9.198.9 ± 1.043.8 ± 14.7ND
    S. berta SL7899.3 ± 0.646.4 ± 17.643.3 ± 8.861.6 ± 12.5ND
    S. halmstad SL5850.4 ± 16.732.6 ± 8.499.2 ± 0.255.6 ± 8.0ND
    S. arizonae S297837.3 ± 9.445.5 ± 5.738.3 ± 17.998.5 ± 2.1ND
    S. infantis SL10139.9 ± 19.050.9 ± 4.599.4 ± 0.818.6 ± 14.4ND
    S. typhimurium TW54160.069.199.433.737.3
    • * pBR322-transformed isolates were used to determine the extent of nonspecific suppression by vector DNA alone.

    • Salmonella typhimurium TW541 contains a Tn10 insertion in the mutS gene and was used to distinguish complementation and nonspecific suppression.

    • ND, no determination.