Phosphorylation and inactivation of aminoglycosidic antibiotics by E. coli carrying R factor

Destination of aminoglycoside antibiotics in the 'post-antibiotic era'

Aminoglycoside antibiotics (AGAs) were developed at the dawn of the antibiotics era and have significantly aided in the treatment of infectious diseases. Aminoglycosides have become one of the four major types of antibiotics in use today and, fortunately, still have an important role in the clinical treatment of severe bacterial infections. In this review, the current usage, modes of action and side effects of AGAs, along with the most common bacterial resistance mechanisms, are outlined. Finally, the recent development situation and possibility of new AGAs in the 'post-antibiotic era' are considered.The Journal of Antibiotics advance online publication, 25 October 2017; doi:10.1038/ja.2017.117.

Julian Davies and the discovery of kanamycin resistance transposon Tn5

This paper recounts some of my fond memories of a collaboration between Julian Davies and myself that started in 1974 in Geneva and that led to our serendipitous discovery of the bacterial kanamycin resistance transposon Tn5, and aspects of the lasting positive impact of our interaction and discovery on me and the community. Tn5 was one of the first antibiotic resistance transposons to be found. Its analysis over the ensuing decades provided valuable insights into mechanisms and control of transposition, and led to its use as a much-valued tool in diverse areas of molecular genetics, as also will be discussed here.

Enzymatic Adenylylation of Streptomycin and Spectinomycin by R-Factor-Resistant Escherichia coli

A resistance (R) factor- containing strain of Escherichia coli which is known to inactivate streptomycin by adenylylation has been shown to be spectinomycin resistant. An osmotic shockate of this strain catalyzes the formation of the biologically inactive spectinomycin adenylate, in which the adenylyl residue is probably attached to a d-threo methylamino alcohol moiety of spectinomycin. Both the streptomycin and spectinomycin adenylylating activities show the same temperature inactivation profile, and both are present in a protein fraction purified for the streptomycin inactivating enzyme. Mutants obtained from this strain which were sensitive to either spectinomycin or streptomycin were shown to lack both enzymatic activities when tested in vitro. Revertants of these mutants selected for recovery of either streptomycin resistance or spectinomycin resistance regain both activities. Therefore, we conclude that the inactivation of the two drugs is catalyzed by the same enzyme. Examination of a number of R factor-carrying strains has shown that those strains which are resistant to streptomycin and spectinomycin contain the adenylylating enzyme, whereas strains resistant to streptomycin but sensitive to spectinomycin inactivate streptomycin by phosphorylation.

Isolation of 8'-phosphate ester derivatives of amicoumacins: structure-activity relationship of hydroxy amino acid moiety

Two new compounds, 8'-phospho derivatives of amicoumacins A and B, were isolated from the culture broth of a strain of Bacillus pumilus together with amicoumacins A and B. Their structures were elucidated on the basis of spectroscopic methods and alkaline phosphatase treatments. Comparison of the antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) of these compounds suggested that C-8' hydroxyl and C-12' amide group of amicoumacin A played a critical role for anti-MRSA activity.

Semisynthetic aminoglycoside antibiotics: Development and enzymatic modifications

The critical resistance mechanisms of aminoglycoside antibiotics in bacteria of clinical importance are the enzymatic N-acetylation, O-phosphorylation, and O-nucleotidylation that generally result in the inactivation of aminoglycosides. To overcome such resistance mechanisms, dibekacin (3',4'-dideoxykanamycin B) was developed as the first rationally designed semisynthetic aminoglycoside, based on the enzymatic 3'-O-phosphorylation of kanamycin. Subsequently, amikacin, netilmicin, and isepamicin were developed by introducing (S)-4-amino-2-hydroxybutyryl (AHB), ethyl, and (S)-3-amino-2-hydroxypropionyl side chains into the 1-amino group of kanamycin, sisomicin, and gentamicin B, respectively. These side chains are believed to block the access of a variety of aminoglycoside-modifying enzymes to their target sites. The latest semisynthetic aminoglycoside of clinical use in Japan is arbekacin (1-N-AHB-dibekacin), which has been extensively used since its approval as an anti-methicillin-resistant Staphylococcus aureus (MRSA) agent in 1990. Although it has several possible modification sites for aminoglycoside acetyltransferases (AACs), arbekacin-resistant MRSA strains that have emerged in the past 8 years have been those with a low or moderate level of resistance, due to a bifunctional enzyme, AAC(6')/APH(2"), at low incidence. To overcome AAC(6')/APH(2")-dependent arbekacin-resistant MRSA strains, 2"-amino-2"-deoxyarbekacin and its 5-epiamino derivative have been already synthesized. However, simulative modification studies using AACs from aminoglycoside-producing Streptomyces strains have revealed that AAC(3) and AAC(2') converted arbekacin to 3"-N-acetyl and 2'-N-acetyl derivatives, respectively, which retain high antibiotic activity. By contrast, the same acetylations of amikacin (3"-N-) and dibekacin (3-N-) resulted in their inactivation. Thus, these new findings confirmed the steric hindrance effect of the 1-N-acyl side chain and illuminated the novel aspect of arbekacin distinct from the other semisynthetic aminoglycosides, indicating that MRSA strains cannot be arbekacin-resistant even if they have acquired the aac(3) or aac(2') gene.

TmrB protein, responsible for tunicamycin resistance of Bacillus subtilis, is a novel ATP-binding membrane protein

tmrB is the gene responsible for tunicamycin resistance in Bacillus subtilis. It is predicted that an increase in tmrB gene expression makes B. subtilis tunicamycin resistant. To examine the tmrB gene product, we produced the tmrB gene product in Escherichia coli by using the tac promoter. TmrB protein was found not only in the cytoplasm fraction but also in the membrane fraction. Although TmrB protein is entirely hydrophilic and has no hydrophobic stretch of amino acids sufficient to span the membrane, its C-terminal 18 amino acids could form an amphiphilic alpha-helix. Breaking this potential alpha-helix by introducing proline residues or a stop codon into this region caused the release of this membrane-bound protein into the cytoplasmic fraction, indicating that the C-terminal 18 residues were essential for membrane binding. On the other hand, TmrB protein has an ATP-binding consensus sequence in the N-terminal region. We have tested whether this sequence actually has the ability to bind ATP by photoaffinity cross-linking with azido-[alpha-32P]ATP. Wild-type protein bound azido-ATP well, but mutants with substitutions in the consensus amino acids were unable to bind azido-ATP. These C-terminal or N-terminal mutant genes were unable to confer tunicamycin resistance on B. subtilis in a multicopy state. It is concluded that TmrB protein is a novel ATP-binding protein which is anchored to the membrane with its C-terminal amphiphilic alpha-helix.

R factor-mediated resistance to aminoglycoside antibiotics in Pseudomonas aeruginosa

Conjugal transferability of drug resistance was examined, in eleven Pseudomonas aeruginosa strains which were isolated in Frankfurt. Four R factors were demonstrated from three strains using P. aeruginosa as recipients but they were nontransferable to Escherichia coli K12. Two R factors, i.e., Rms146 and Rms147, mediated resistances to tetracycline (TC), streptomycin (SM), sulfanilamide (SA), kanamycin (KM), lividomycin (LV), gentamicin C complex (GM) and 3', 4'-dideoxykanamycin B (DKB). They mediated the formation of aminoglycoside-inactivating enzymes, i.e., SM phosphotransferase, SM adenylyltransferase, KM and LV phosphotransferase l, and GM and DKB 6'-N-acetyltransferase. TC resistance conferred by these R factors was due to impermeability of the drug. P. aeruginosa Ps 142 carried two kinds of R factor in one cell, Rms148 (SM) and Rms149 (SM-SA-GM-CPC) (CPC, carbenicillin). Rms148 (SM) was transferable at a high frequency of 10-1 and mediated the formation of SM phosphotransferase. Rms149 mediated the formation of drug-inactivating enzymes, ie., GM 3-N-acetyltransferase and beta-lactamase, but did not inactivate SM. SM resistance was probably due to impermeability of the drug.

Antibacterial activity of lividomycin toward R factor-resistant strains of Escherichia coli

Forty-eight R factors conferring resistance to both kanamycin (KM) and streptomycin (SM) were demonstrated from 1,270 Escherichia coli strains of clinical origin. Among these R factors isolated, 42 also conferred resistance to the new antibiotic lividomycin (LV). Extracts of E. coli ML1410 carrying one such factor (R(M81)) inactivated LV as well as KM and SM. But extracts of E. coli ML1410 carrying an R factor (R(M82) or R(M83)) sensitive to LV could not inactivate LV. LV inactivation required both adenosinetriphosphate (ATP) and Mg(2+). Inactivated LV was reactivable by alkaline phosphatase. Isotopic studies with labeled ATP and elemental analysis of the reaction product indicate that it is a monophosphorylated derivative of LV.

Microbial transformation of antibiotics: phosphorylation of clindamycin by Streptomyces coelicolor Müller

Addition of clindamycin to whole-cell cultures of Streptomyces coelicolor Müller resulted in the loss of in vitro activity against organisms sensitive to clindamycin. Incubation of such culture filtrates with alkaline phosphatase generated a biologically active material identified as clindamycin. Fermentation broths containing inactivated clindamycin yielded clindamycin 3-phosphate, the structure of which was established by physical-chemical and enzymatic studies. Clindamycin was phosphorylated by lysates and partially purified enzyme preparations from S. coelicolor Müller. These reactions require a ribonucleoside triphosphate and Mg(2+). The product of the cell-free reactions was identified as clindamycin 3-phosphate.

Aminoglycoside antibiotics: inactivation by phosphorylation in Escherichia coli carrying R factors

R-factor strains which are streptomycin-resistant and spectinomycin-sensitive have been found to inactivate streptomycin by a new mechanism. The 3'-OH group of the 2-deoxy-2-methylamino-l-glucopyranosyl moiety is phosphorylated.

Resistance factor-mediated streptomycin resistance

Resistance (R) factor-mediated streptomycin (Sm) resistance differs from classical, high-level, chromosome-borne Sm resistance in its dominance over sensitivity and in the level of its effectiveness (in Escherichia coli approximately 25 mug/ml versus >2,000 mug/ml). In addition, an R factor-containing strain, unlike high-level Sm-resistant bacteria, showed an inoculum effect with respect to its level of Sm resistance. Crude extracts of this strain destroyed the inhibitory activity of Sm and bluensomycin (Blue) on in vitro protein synthesis. The ribosomes from this strain proved to be sensitive to Sm in vitro. The requirements for in vitro inactivation of Sm (and Blue) were determined to be: extract, adenosine triphosphate or deoxyadenosinetriphosphate, and Mg(++). Chromatographic techniques with radioisotopes revealed the formation of an inactivated form of Sm containing adenosine (or deoxyadenosine), phosphate, and Sm in equimolar amounts. The adenylate moiety is coupled to the streptobiosamine residue, rather than to the streptidine ring, of the Sm molecule. The adenylating enzyme, which is not induced by Sm, is located in the periplasmic space of the R factor-containing strain.

Inactivation of kanamycin, neomycin, and streptomycin by enzymes obtained in cells of Pseudomonas aeruginoa

Ten strains of Pseudomonas aeruginosa were disrupted and centrifuged. The supernatant fluids from centrifugation at 105,000 x g contained enzymes inactivating kanamycin, neomycin, and streptomycin in the presence of adenosine triphosphate. Kanamycin-inactivating enzyme was precipitated with ammonium sulfate at 66% of saturated concentration, and the inactivated kanamycin was shown to be kanamycin-3'-phosphate in which the C-3 hydroxyl group of 6-amino-6-deoxy-d-glucose moiety was phosphorylated. This is identical with kanamycin inactivated by Escherichia coli carrying R factor. Streptomycin-inactivating enzyme was precipitated with ammonium sulfate at 33% of saturated concentration.