Restrictive Streptomycin Resistance Mutations Decrease the Formation of Attaching and Effacing Lesions in Escherichia coli O157:H7 Strains

Streptomycin binds to the bacterial ribosome and disrupts protein synthesis by promoting misreading of mRNA. Restrictive mutations on the ribosomal subunit protein S12 confer a streptomycin resistance (Strr ) phenotype and concomitantly increase the accuracy of the decoding process and decrease the rate of translation. Spontaneous Strr mutants ofEscherichia coli O157:H7 have been generated forin vivo studies to promote colonization and to provide a selective marker for this pathogen. The locus of enterocyte effacement (LEE) ofE. coli O157:H7 encodes a type III secretion system (T3SS), which is required for attaching and effacing to the intestinal epithelium. In this study, we observed decreases in both the expression and secretion levels of the T3SS translocated proteins EspA and EspB inE. coli O157:H7 Strr restrictive mutants, which have K42T or K42I mutations in S12. However, mildly restrictive (K87R) and nonrestrictive (K42R) mutants showed slight or indistinguishable changes in EspA and EspB secretion. Adherence and actin staining assays indicated that restrictive mutations compromised the formation of attaching and effacing lesions inE. coli O157:H7. Therefore, we suggest thatE. coli O157:H7 strains selected for Strr should be thoroughly characterized beforein vivo andin vitro experiments that assay for LEE-directed phenotypes and that strains carrying nonrestrictive mutations such as K42R make better surrogates of wild-type strains than those carrying restrictive mutations.