Plasmidos

Mutation Research, 264 (1991) 119-125 © 1991 Elsevier Science Publishers B.V. All rights reserved. 0165-7992/91/$03.50 ADONIS 0165799291000923

119

MUTLET 0541

Decreased resistance to antibiotics and plasmid loss in plasmid-carrying strains of Staphylococcus aureus treated with ascorbic acid
Carlos F. Amfibile-Cuevas 1, Rosa Maria Pifia-Zentella 2 and Maria Elena Wah-Laborde a1Departamento de Microbiologla, LUSARA, 08930 Mexico, D.F. and 2Departamento de Ciencias de la Nutrici6n y de los Alimentos, Universidad lberoamericana, 01210 Mexico, D.F. (Mexico)

(Accepted 5 July 1991)

Keywords." Ascorbic acid; Plasmid loss; Antibiotic resistance

Summary
The effect of ascorbic acid on plasmid-coded antibiotic resistance in Staphylococcus aureus was investigated. Several strainsof S. aureus were cultured in the presence of 1 mM ascorbate for 6 h. This treatment induced an increased loss of resistance markers in 4 o f 6 strains tested, and agarose gel electrophoresis showed this disappearance of plasmid DNA in ascorbate-induced susceptible colonies. The presence of ascorbate induced a 50-75% decrease in minimal inhibitory concentrations of different antibiotics forresistant strains. When ascorbate is added, formerly subinhibitory concentrations of penicillin or tetracycline have an increased inhibitory effect on resistant strains and even induced the death of 25-93% of the intial population. These results suggest that ascorbate can induce the loss of several plasmids of S. aureus, and that the levels of antibiotic resistance are also affected by the presence ofthis compound.

L-Ascorbic acid (vitamin C) has been found to be capable of modifying the properties of DNA (McCarty, 1945). Ascorbate can inactivate several phages by induction of single-strand breaks in their D N A (Murata and Kitagawa, 1973; Murata et al., 1971, 1986), and can induce multiple breaks in the chromosomes of repair-deficient mutants of Escherichia coli (Van Sluys et al., 1986a).This ef-

Correspondence: Dr. C.F. Am~ibile-Cuevas, (present address) Laboratory of Toxicology, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115 (U.S.A.), Tel: (617) 432-3490; Fax: (617) 432-1780.

fect was initially attributed to the generation of hydrogen peroxide (H202) a n d / o r hydroxyl free radicals (HO - ), but this does not seem to be clear. E. coli x t h A , anH202-hypersensitive mutant (Demple et al., 1983), is not sensitive to ascorbate treatment (Van Sluys et al., 1986b). A sequencespecific breakage following treatment with ascorbate, unlikely to be randomly generated by oxygen radicals, has been observed in phage DNA (Kobayashi et al., 1988). Most in vivo tests fail to detect mutagenic or carcinogenic activity for ascorbic acid (Douglas et al.,1984; Norkus et al., 1983). It seems that ascorbate

120 TABLE 1
S. aureus STRAINS

Strain DIM 152 DIM162 DIM260 RN11 RN794 RN2424

Plasmid N.C. N.C. N.C. p1258 pI55cl pTl81

Relevant phenotype (Sm,Tm,Spc,Amk) r (Tm,Spc,Amk) r (Tm,Spc,Amk) r Pcr,Em r Pc r Tc r

Reference B. Baca, unpublished* B. Baca, unpublished B. Baca, unpublished Peyru et al., 1969 Peyru et al., 1969 lordanescu andSurdeanu, 1980

Amk, amikacin; Era, erythromycin; Pc, penicillin; Sin, streptomycin; Spc, spectinomycin; Tc, tetracycline; Tin, tobramycin. N.C., not characterized. * From Universidad A u t 6 n o m a de Puebla (Mexico). DIM strains were clinically isolated, and aminoglycoside resistance was found to be plasmid-mediated.

can damage only small and unprotected D N A molecules, especially circularcovalently closed forms (cccDNA) which depend for their efficient replication and transcription on the maintenance of their supercoiled state. This laboratory has previously reported the elimination of penicillinase plasmids of S. aureus after a 6-h treatment with 1 mM ascorbate (Amfibile-Cuevas, 1988). The possibility that the elimination of bacterial resistance determinants could be of some...