Fig 3.

Phenotypic silver resistance. (A) Killing of bacteria by AgNO₃. OD₆₀₀ was measured after incubation (16 h, 36 ± 1°C, room air) of the indicated strains in LB medium supplemented with increasing amounts of AgNO₃. E. coli strains DH5α and DH5α(pMG101) served as negative (AgNO₃ MIC, 50 μM) and positive (AgNO₃ MIC, 600 μM) controls, respectively. Two sil PCR-positive strains (244 and 373) as well as three sil PCR-negative strains (114, 501R3, and E6) were included. Symbols in the key are labeled with the strain name, genetic cluster, and PCR results. Clinical outbreak strain 373 of genetic cluster I (22) was positive in all sil PCRs and showed an AgNO₃ MIC of 600 μM. Both strains 501R3 and E6 yielded negative PCRs with all sil genes and had AgNO₃ MICs equal to or below 50 μM. (B) Growth of strains on LB agar containing rising concentration of AgNO₃. The positions of the strains on the plates are depicted on the left.