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One hundred and sixty viridans group streptococci (VGS) and 26 Gemella spp. resistant to erythromycin were studied to detect macrolide lincosamide and streptogramin B (MLS(B)) phenotypes and to investigate resistance rates to other antibiotics. The M phenotype was most prevalent in both bacterial groups (59.6% in VGS, 69.2% in gemellae) and the iMLS(B) phenotype was found least often (9.3 and 13.9%, respectively). All isolates with M phenotype had the mef(A/E) gene, being prevalent the mef(E) subclass. cMLS(B) and iMLS(B) strains contained the erm(B) gene, alone or in combination with the mef(A/E) gene. Thirteen isolates were intermediately resistant to quinupristin/dalfopristin and 11 strains showed low susceptibility to telithromycin. Linezolid was active against all the isolates tested and tetracycline resistance was the major one in VGS (41.6%) and Gemella spp. (46.2%).

Voriconazole and posaconazole are two new triazoles with broad-spectrum antifungal activity. The in vitro activity of these agents was compared with that of fluconazole against 113 clinical isolates of Candida spp. exhibiting a wide range of MICs for fluconazole (or =0.125 to64 mg/l). They included 22 C. albicans isolates, 22 C. glabrata, 20 C. tropicalis, 15 C. dubliniensis, 13 C. parapsilosis, 13 C. krusei, 4 C. lusitaniae, 3 C. guilliermondii and 1 C. famata. MICs were determined by broth microdilution test performed according to the National Committee for Clinical Laboratory Standards' M27-A document. Voriconazole and posaconazole were quite active against all Candida spp. isolates, with MIC(90) of 0.25 and 0.5 mg/l, respectively. Fluconazole MIC(50) and MIC(90) were 1 and 32 mg/l. Voriconazole and posaconazole showed in vitro activity against fluconazole-susceptible and -resistant Candida isolates. Higher voriconazole and posaconazole MICs were observed in isolates exhibiting higher fluconazole MICs (/=16 mg/l) than in those of fluconazole-susceptible isolates (MIC(90) for voriconazole and posaconazole in the fluconazole-resistant isolates were 0.5 mg/l versus 0.06 mg/l for voriconazole and 0.25 mg/l for posaconazole in the fluconazole-susceptible strains). C. dubliniensis was the most susceptible species, and voriconazole the most active antifungal agent against all Candida spp. tested.

The stability of dactimycin to aminoglycoside-modifying enzymes produced by 341 bacterial clinical isolates has been studied. Enzymatic activities were measured by the phosphocellulose binding assay. The results demonstrated that dactimicin was stable to the following enzymes: (i) AAC(3)-II,-III,-IV and -V. (ii) AAC(2'); (iii)AAC(6')-I and -II;(iv) ANT(2"); (v)ANT(4'); (vi) APH(3')-I,-II,-III and -IV. In contrast, dactimicin was only inactivated by two enzymes, AAC(3)-I and the bifunctional AAC(6')/APH(2"). This staphylococcal enzyme modified and inactivated dactimicin by acetylation but not by phosphorylation, suggesting the possibility of a second target amino group, such as 6'-NH2, in addition to the C4 amino group, which is the target for AAC(3)-I.

We studied the association of MLS resistance genes (erm(B) and mef(A) with others non-MLS resistance genes: tet(M) (tetracycline and minocycline), catpC194 (chloramphenicol) and aph3'-III (kanamycin) in order to know how is selected the multiresistant in Streptococcus pneumoniae. The tet(M) and catpC194 genes were present very often in the pneumococci with the erm(B) gene but the aph3'-III was found only in four strains. Tn1545 was nearly always the responsible for the dissemination of these genes. In contrast, mef(A) was not associated with tet(M) and and catpC194 and is disseminated in a different conjugative transposon. The linkage of multiple antibiotic resistance genes on the same mobile element is of importance for public health, because the use of one antibiotic selects for the transposon which carries multidrug resistance genes.

In Streptococcus pneumoniae, resistance to macrolide, lincosamide and streptogramin type B (MLS(B)) antibiotics is mediated by erm(B) and mef(A) determinants. Tetracycline resistance is always associated with resistance to minocycline and is due to the presence of the tet(M) gene. The erm(B) determinant is predominant. We demonstrated that the erm(B) gene could be present with mef(A), which is of streptococcal origin, and msr(A), which is of staphylococcal origin, this being an example of genetic promiscuity. The tet(M) determinant was associated with pneumococci harboring the erm(B) gene, while it was not associated with the strains harboring the mef(A) gene. This association is due to the fact that, in most of the cases, erm(B) and tet(M) reside in the same chromosomal conjugative transposon.