ABSTRACT
When Pst I-generated digests of genomic DNA from each of the type strains of 49 of the Vi phage types of Salmonella typhi were probed with a PCR-amplified IS200 gene probe, all strains were found to possess at least 11 IS200 elements carried on fragments in the range 24.2-1.2 kb. Fourteen fingerprints were identified but two patterns designated IS200Sty1 and IS200Sty2 predominated. In one strain, a plasmid-mediated IS200 element was identified. When IS200 fingerprinting was applied to epidemiologically-unrelated strains of S. typhi isolated in Ecuador, 3 patterns were identified in 10 strains belonging to 9 different phage types. It is concluded that Vi phage typing remains the method of choice for the primary differentiation of S. typhi but that IS200 fingerprinting may be of limited use in laboratories which do not have access to phage typing.
Subject(s)
DNA Fingerprinting/methods , DNA Transposable Elements/genetics , DNA, Bacterial , Genome, Bacterial , Salmonella typhi/classification , Salmonella typhi/genetics , Typhoid Fever/epidemiology , Typhoid Fever/microbiology , Bacteriophage Typing/methods , Ecuador/epidemiology , Evaluation Studies as Topic , Humans , Plasmids , Polymerase Chain Reaction/methodsABSTRACT
We examined 141 Salmonella typhi strains of known phage type isolated during ongoing epidemiologic studies in Santiago, Chile, and Lima, Peru. Plasmids were present in 12 (17%) of 70 S. typhi isolates from Santiago and 5 (7%) of 71 isolates from Lima; these plasmids were not associated with antimicrobial resistance. Identical 21 kilobase (kb) plasmids (as defined by restriction endonuclease digest pattern) were present in 13 of the 17 plasmid-containing isolates. Virtually identical digest patterns were identified when chromosomal DNA of selected strains from Santiago, Lima, and the United States was extracted and then digested with restriction endonucleases. The similarities among plasmids and chromosomal digest patterns emphasize the homogeneity and possible clonal origin of S. typhi isolates; these data also suggest that there is only a limited role for plasmid and chromosomal analysis as a substitute for phage typing in epidemiologic studies.