In vitro antimicrobial properties of azidothymidine (AZT)

In addition to the activity against a number of retroviruses, azidothymidine (AZT) has antibacterial activity against many bacteria. The effect of AZT on 224 bacterial species, including 25 strains of Salmonella spp. isolated from HIV-positive patients, was tested. AZT had no activity against all the strains of tested Gram-positive bacteria and Pseudomonas species (MIC > 128 micrograms/ml), whereas a different activity against Enterobacteriaceae (MIC range, 128 to 0.06 micrograms/ml) was found. In particular 76% of Salmonella spp. isolated from HIV-positive patients showed MICs > 1 microgram/ml, whereas similar MICs value were found in 50% of the Salmonella strains isolated from HIV-negative subjects. In addition, strains of Salmonella isolated from stools were more resistant to AZT when compared to strains isolated from blood even if this difference was not statistically significant. No correlation was found between length of therapy and Salmonella resistance to AZT in HIV-positive patients and a low incidence of Salmonella relapses in subjects treated with AZT was observed. The possibility that AZT may have an ancillary benefit in controlling some bacterial infections in AIDS patients is discussed.