Ljv. Piddock et al., Evidence for an efflux pump mediating multiple antibiotic resistance in Salmonella enterica serovar Typhimurium, ANTIM AG CH, 44(11), 2000, pp. 3118-3121
The mechanism of multiple antibiotic resistance in six isolates of Salmonel
la enterica serovar Typhimurium recovered from a patient treated with cipro
floxacin was studied to investigate the role of efflux in the resistance ph
enotype. Compared to the patient's pretherapy isolate (L3), five of six iso
lates accumulated less ciprofloxacin, three of six isolates accumulated les
s chloramphenicol, and all six accumulated less tetracycline. The accumulat
ion of one or more antibiotics was increased by carbonyl cyanide m-chloroph
enylhydrazone to concentrations similar to those accumulated by L3 for all
isolates except one, in which accumulation of all three agents remained app
roximately half that of L3, All isolates had the published wild-type sequen
ces of marO and marR, No increased expression of marA, tolC, or soxS was ob
served by Northern blotting; however, three isolates showed increased expre
ssion of acrB, which was confirmed by quantitative competitive reverse tran
scription-PCR. However, there were no mutations within acrR or the promoter
region of acrAB in any of the isolates.