Energy-dependent efflux mediated by class L (tetL) tetracycline resistance determinant from streptococci

Abstract

The class L (TetL) tetracycline resistance determinant from streptococci specified resistance and an energy-dependent decreased accumulation of tetracycline in both Streptococcus faecalis and Escherichia coli. Using E. coli, we showed that the reduced uptake resulted from active efflux. The streptococcal class M determinant, known to render the protein synthesis machinery of S. faecalis resistant to tetracycline inhibition, did not alter tetracycline transport in either host.Tetracycline resistance (Tcr) determinants are widespread among gram-negative and gram-positive bacteria, both anaerobes and aerobes (10). The original source of these determinants is unknown, but recent studies have shown that previously identified determinants appear to have moved into new hosts. Of particular note, determinants with strong homology to class M (TetM), initially found among streptococci (3), have now been identified among newly appearing Tcr strains of Mycoplasma (17), Ureaplasma (16), Campylobacter (19), Gardnerella (15), Neisseria (14), and Clostridium (7) spp. The wide dispersal of this determinant can probably be attributed in part to its existence on transposon Tn916 originally described in Streptococcus faecalis (5). Two other streptococcal determinants, class L (TetL) and class N (TetN), have also been discovered (3).The mechanism of resistance specified by the class M determinant in S. faecalis occurs at the level of the target of tetracycline, namely, the protein synthesis machinery within the cell (2). The class L determinant, on the other hand, does not prevent the inhibition of protein synthesis in S. faecalis but rather decreases tetracycline uptake (2). The purpose of the present study was to determine the mechanism for this decrease in both S. faecalis and Escherichia coli as hosts.The naturally occurring plasmids pMV158 (class L) and pAM211 (class M) (2) were used in S. faecalis. In E. coli, we used pVB A15 (a hybrid of pMV158 with the E. coli cloning vector pVH2124 [3]) and pJI3 (a 5-kilobase HinclI region of the chromosomal class M determinant from Streptococcus agalactiae B109 containing the entire Tcr determinant cloned into the E. coli vector pACYC177 [3,8]). These plasmids were introduced into E. coli SK1592 (3) by transformation.The levels of resistance to tetracycline and minocycline expressed aerobically and anaerobically in S. faecalis and E. coli were assayed at 37°C by the gradient plate method on Penassay medium (Difco Laboratories) (4). In both genera, the class M determinant specified resistance to both tetracycline and minocycline, while the class L determinant, as previously reported for streptococci (2), expressed only resistance to tetracycline. In S. faecalis, Tcr mediated by class L on pMV158 varied (MIC, 50 to 100 ,ug/ml) in different experiments and that specified by class M on pAM211 was

Tetracyclines in veterinary medicine and bacterial resistance to them

“…Group 2 is represented by Tet(K) from Staphylococcus aureus (Mojumdar and Khan, 1988) and Tet(L) from Bacillus subtilis (McMurry et al, 1987). Primarily found in gram-positive bacteria, they were occasionally identified in gram-negative genera and also among anaerobes (Miranda et al, 2003;Roberts, 2003).…”

Characterization of the tetracycline resistance gene of plasmid pT181 of Staphylococcus aureus

“…The mechanism and genetic regulation of tetracycline resistance have been extensively studied in gram-negative species, specifically within the family Enterobacteriaceae (1,12,13,22,42). A number of studies have also been carried out on tetracycline resistance in gram-positive bacteria (4,9,10,15,16,25). Tetracycline resistance determinants identified within the streptococci and bacilli do not show significant homology with the determinants isolated from gram-negative bacteria at the DNA sequence level (5,15,26).…”

Tetracycline/H+ antiport and Na+/H+ antiport catalyzed by the Bacillus subtilis TetA(L) transporter expressed in Escherichia coli

“…The tet(L) genes encode transporters that export tetracycline in an energy-dependent fashion that has been presumed to be comparable to the cobalt-tetracycline/H ϩ antiport catalyzed by related products of the A to C classes of tet genes (13). The class A to C tet genes are found in plasmids and transposons of gram-negative bacteria, whereas class L tet genes have been found exclusively in plasmids of gram-positive bacteria except for the one chromosomal example in B. subtilis (20,21).…”