New ventures in the genotoxic and cytotoxic effects of macrocyclic lactones, abamectin and ivermectin.

Abamectin and Ivermectin are 2 closely related members of the Avermectin family of 16-membered macrocyclic lactones derived from the actinomycete Streptomyces avermectinius which exhibit extraordinary anthelmintic activity. They are used worldwide in veterinary and human medicine as well as in agriculture. In the present review we summarized the results published so far for estimating the genotoxicity and cytotoxicity exerted by both compounds in several cellular systems. Although both compounds do not induce in vitro and in vivo gene mutations in either bacterial or mammalian cells, there is no concrete evidence of a clear clastogenic effect exerted both in vitro and in vivo in mammalian cells. However, reports indicating that both anthelmintic agents are able to induce single DNA-strand breaks in vitro and inhibit cell growth either in vitro or in in vivo bioassays, are scarce. Taking into account the similarity of the genotoxicity and cytotoxicity exerted by both antibiotics, and that only Abamectin has been classified so far as a class II toxicity pesticide by the EPA, the necessity of reconsideration for a further hazard evaluation of Ivermectin by an international regulatory agency(ies) is strongly recommended.

In vitro genotoxic and cytotoxic effects of ivermectin and its formulation ivomec on Chinese hamster ovary (CHOK1) cells.

The effects of ivermectin (IVM) and its commercial formulation ivomec (IVM 1.0%) were studied on Chinese hamster ovary (CHO(K1)) cells by several genotoxicity [sister chromatid exchange (SCE) and single cell gel electrophoresis (SCGE)] and cytotoxicity [cell-cycle progression (CCP), mitotic index (MI), proliferative replication index (PRI), 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and neutral red (NR)] bioassays within the 1.0-250 microg/ml concentration-range. While IVM and ivomec did not modified SCE frequencies, they induced DNA-strand breaks revealed by SCGE. An enhancement of slightly damaged cells and a decrease in undamaged cells were observed in IVM-treated cultures with 5.0-50.0 microg/ml. In ivomec((R))-treated cells, while an increase in slightly damaged cells was induced with 5.0-50.0 microg/ml, the damaged and undamaged cells increased and decreased only with 50.0 microg/ml. Both compounds exerted a delay in CCP and a reduction in PRI when 25.0 microg/ml was employed whereas cytotoxicity was observed at higher concentration than 50.0 microg/ml. No MI alteration was observed with 1.0-10.0 and 1.0-5.0 microg/ml of IVM and ivomec, respectively. A concentration-related trend to an increase in MI was achieved within 1.0-10.0 microg/ml. An increase in the MI was induced in 10.0 microg/ml ivomec-treated cultures. A marked reduction of about 89% and 62% in regard to controls was observed with 25.0 microg/ml of IVM and ivomec, respectively. NR and MTT assays revealed a cell growth inhibition when 0.25-250.0 microg/ml of both compounds was employed. The results highlighted that IVM and ivomec exert both genotoxicity and cytotoxicity in mammalian cells in vitro, at least in CHO(K1) cells.

Susceptibility of Enterococcus faecalis to twelve antibiotics, time-kill assays, and high-level aminoglycoside resistance in a university hospital in Argentina.

A total of 201 Enterococcus faecalis strains isolated from different body sites were tested to (i) establish their antibiotic susceptibility pattern; (ii) determine the percentage of strains highly resistant (MIC greater than 2,000 micrograms/ml) to five aminoglycosides and (iii) know if the combination of penicillin or ampicillin plus an aminoglycoside is reliably synergistic for the strains with low-level resistance (MICs ranged from the break point of susceptibility for each aminoglycoside to 2,000 micrograms/ml). Erythromycin exhibited very poor activity with MIC90 greater than 128 micrograms/ml. Pefloxacin and norfloxacin had intermediate activity, inhibiting 50% of isolates at 4 micrograms/ml and 90% at 8 micrograms/ml. Trimethoprim-sulfamethoxazole (1:20) inhibited 94% of isolates at less than or equal to 2 micrograms/ml and 87.6% at less than or equal to 0.5 microgram/ml. Ampicillin, penicillin and piperacillin were the most potent agents studied. Ninety percent of strains were inhibited at 1 microgram/ml of ampicillin and 4 micrograms/ml of penicillin and piperacillin. The E. faecalis isolates were relatively or totally resistant to the aminoglycosides. Ninety six (47.8%) were highly resistant at least to one of them. High level resistance to streptomycin was found in 47.3% of all strains and was the most frequent resistance encountered; amikacin highly resistant strains were the less common and accounted for 4.5%. Low-level resistance to the aminoglycosides ranged from 50.2% (for streptomycin) to 94.5% (for amikacin). Thirty one E. faecalis isolates were selected for 24-time kill-assays. There was a good correlation between resistance to penicillin or ampicillin aminoglycoside synergy in all but 3 strains which were highly resistant. Among the strains with low-level resistance to the aminoglycosides, there was no synergy in 37 (63.8%) of 58 killing assays with each of the aminoglycosides combined with penicillin. These results demonstrate that the susceptibility to 2,000 micrograms/ml of the aminoglycoside does not assure the penicillin or ampicillin aminoglycoside synergism.

Susceptibility of Enterococcus faecalis to twelve antibiotics, time-kill assays, and high-level aminoglycoside resistance in a university hospital in Argentina.

A total of 201 Enterococcus faecalis strains isolated from different body sites were tested to (i) establish their antibiotic susceptibility pattern; (ii) determine the percentage of strains highly resistant (MIC greater than 2,000 micrograms/ml) to five aminoglycosides and (iii) know if the combination of penicillin or ampicillin plus an aminoglycoside is reliably synergistic for the strains with low-level resistance (MICs ranged from the break point of susceptibility for each aminoglycoside to 2,000 micrograms/ml). Erythromycin exhibited very poor activity with MIC90 greater than 128 micrograms/ml. Pefloxacin and norfloxacin had intermediate activity, inhibiting 50

of isolates at 4 micrograms/ml and 90

at 8 micrograms/ml. Trimethoprim-sulfamethoxazole (1:20) inhibited 94

of isolates at less than or equal to 2 micrograms/ml and 87.6

at less than or equal to 0.5 microgram/ml. Ampicillin, penicillin and piperacillin were the most potent agents studied. Ninety percent of strains were inhibited at 1 microgram/ml of ampicillin and 4 micrograms/ml of penicillin and piperacillin. The E. faecalis isolates were relatively or totally resistant to the aminoglycosides. Ninety six (47.8

) were highly resistant at least to one of them. High level resistance to streptomycin was found in 47.3

of all strains and was the most frequent resistance encountered; amikacin highly resistant strains were the less common and accounted for 4.5

. Low-level resistance to the aminoglycosides ranged from 50.2

(for streptomycin) to 94.5

(for amikacin). Thirty one E. faecalis isolates were selected for 24-time kill-assays. There was a good correlation between resistance to penicillin or ampicillin aminoglycoside synergy in all but 3 strains which were highly resistant. Among the strains with low-level resistance to the aminoglycosides, there was no synergy in 37 (63.8

) of 58 killing assays with each of the aminoglycosides combined with penicillin. These results demonstrate that the susceptibility to 2,000 micrograms/ml of the aminoglycoside does not assure the penicillin or ampicillin aminoglycoside synergism.