ABSTRACT
Many of the resistance mechanisms of enterobacteria to antimicrobial agents are well understood; nevertheless several aspects remain unsolved, particularly with regard to prediction of clinical response. The resistance pattern observed in the antibiogram of a specific organism should be the sum of the natural resistance pattern, characteristic of the species, plus the acquired resistance. In enterobacteria the principal mechanism of resistance to beta lactams and aminoglycosides is enzyme production, Each enzyme recognizes one or more specific beta lactam or aminoglycoside, as a substrate. This translates as a specific resistance phenotype that allows one to infer the enzyme(s) implicated. Enzyme resistance is not, however, the only mechanism of resistance to these agents; often the pattern observed is multifactorial. Resistance to quinolones is due to point and sequence mutations which may be selected by initially active fluoroquinolones and cause a stepwise increase of resistance.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacterial Proteins/physiology , Drug Resistance, Multiple, Bacterial , Enterobacteriaceae/drug effects , Microbial Sensitivity Tests , Acetyltransferases/antagonists & inhibitors , Acetyltransferases/classification , Acetyltransferases/genetics , Acetyltransferases/physiology , Anti-Bacterial Agents/classification , Anti-Bacterial Agents/metabolism , Bacterial Proteins/antagonists & inhibitors , Bacterial Proteins/classification , Bacterial Proteins/genetics , Chromosomes, Bacterial/genetics , DNA Gyrase/genetics , DNA Topoisomerases/genetics , Drug Resistance, Multiple, Bacterial/genetics , Enterobacteriaceae/enzymology , Enterobacteriaceae/genetics , Enzyme Inhibitors/pharmacology , Gene Expression Regulation, Bacterial , Kanamycin Kinase/antagonists & inhibitors , Kanamycin Kinase/classification , Kanamycin Kinase/genetics , Kanamycin Kinase/physiology , Phenotype , R Factors , Substrate Specificity , beta-Lactamase Inhibitors , beta-Lactamases/classification , beta-Lactamases/genetics , beta-Lactamases/physiologyABSTRACT
We have developed a positively selectable marker for the green alga Chlamydomonas reinhardtii using the Streptomyces hygroscopicus aminoglycoside phosphotransferase gene (aph7"). Its expression is controlled by C. reinhardtii regulatory elements, namely, the beta2-tubulin gene promoter in combination with the first intron and the 3' untranslated region of the small subunit of ribulose bisphosphate carboxylase, rbcS2. C. reinhardtii cell-wall deficient and wild-type strains were transformed at rates up to 5 x 10(-5) with two constructs, pHyg3 and pHyg4 (intron-less). Transformants selected on plates with 10 microg/ml hygromycin B exhibited diverse levels of resistance of up to 200 microg/ml that were stably maintained for at least seven months; they contained two to five copies of the construct integrated in their genomes. Transcription of the chimeric aph7" gene, correct splicing of the rbcS2 intron, and polyadenylation of the transcripts have been verified by sequencing of RT-PCR products. Average co-transformation rates using pHyg3 and a second selectable plasmid were about 11%. This advocates the hygromycin-resistance plasmid, pHyg3, as a new versatile tool for the transformation of a broad range of C. reinhardtii strains without the sustained need for using auxotrophic mutants as recipients.
