Novel dihydrofolate reductases isolated from epidemic strains of trimethoprim/sulfamethoxazole-resistant Shigella sonnei.
Two strains of trimethoprim-resistant Shigella sonnei bearing R plasmids pBH600 and pBH700 each elaborated a dihydrofolate reductase (DHFR) and were moderately resistant to trimethoprim (minimum inhibitory concentrations, 128 and 256 micrograms/ml, respectively). Neither plasmid hybridized to probes for DHFR types I, II, or III. The trimethoprim resistance genes from the R plasmids resided on a 1600-base pair (bp) PstI fragment of pBH600 and an 1800-bp PstI fragment of pBH700. Isoelectric focusing showed distinct isoelectric points for the enzymes coded for on pBH600 (5.3) and pBH700 (5.6-5.7). Trimethoprim-resistant S. sonnei from 10 locations in nine states were examined. Isolates from 8 locations hybridized only to a pBH700-derived probe and one isolate hybridized to a pBH600-derived probe. These two trimethoprim resistance genes appear novel. The gene on plasmid pBH700 codes for an enzyme that seems widespread among S. sonnei isolates in the USA.
Barg
N L
NL
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee.
Hutson
F S
FS
Wheeler
L A
LA
Thomson
C J
CJ
Amyes
S G
SG
Wharton
M
M
Schaffner
W
W
D000668:Ampicillin Resistance; D015139:Blotting, Southern; D002702:Chloramphenicol Resistance; D015342:DNA Probes; D004269:DNA, Bacterial / Q000032:analysis; D004196:Disease Outbreaks; D004405:Dysentery, Bacillary / Q000453:epidemiology / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009657:North Carolina / Q000453:epidemiology; D009693:Nucleic Acid Hybridization; D011815:R Factors; D012764:Shigella sonnei / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D013714:Tennessee / Q000453:epidemiology; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000302:isolation & purification*; D014296:Trimethoprim Resistance / Q000235:genetics; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology*
D015342:DNA Probes; D004269:DNA, Bacterial; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D013762:Tetrahydrofolate Dehydrogenase