Bacteriocins of indigenous clinical staphylococci: screening and charcterization

Staphylococcin [a class of bacteriocin] production was studied in 250 clinical isolates of staphylococci. 7% of the isolates exhibited intra - isolate and broad - range antagonistic activity. Crude bacteriocin preparations were not inactivated after prolonged thermal exposure [80°C] and were stable in the pH range of 5.4 - 10. The preparations also resisted the action of trypsin [a proteolytic enzyme], lysozyme [a glycolytic enzyme] and lipase [a lipolytic enzyme]. However, one of the extracts [Staphylococcin AB201] was sensitive to heat and trypsin. All the preparations retained their bioactivity after prolonged [16 weeks] refrigeration and freezing. Attempts to induce bacteriocin production [with UV, 0.5% mannitol and 2% yeast extract] and to elute cell bound bacteriocin [with 0.1M, 1M and 5M NaCl and 0.05M EDTA] were unsuccessful. The bacteriocinogenic determinants in the staphylococcal isolates were cured by heating [44°C] and ethidium bromide [300 micro g/mL], suggestive of their plasmid- borne location

Tools for genetic engineering

Genetic Engineering refers to the alteration of cellular DNA by means and methods other than normal sexual or mutational phenomena. Thus, this technology involves techniques in which DNA may be cut, rejoined, its sequence determined, or a segment altered in sequence to suit an intended use. For example, a DNA fragment may be isolated from one organism, spliced into other DNA fragment [the vector], and put into a bacterium or other organism. Many identical copies can thus, be made of the original DNA fragment. There are atleast two basic objectives of genetic engineering technology viz. to learn about the ways, the nature works and to make use of this knowledge for practical purposes. The two basic tools that are used in genetic engineering technology i. e. the "Vectors" or "Vehicles" [e. g. plasmids, cosmids, shuttle vectors and transposons] and "Restriction Enzymes" [e. g. restriction endonucleases] are being discussed at length

nitrosoguanidines mediated adaptive repair in pseudomonas syringae

Adaptive repair activity has been demonstrated in wild type cells of Ps. syringae. MNNG mediated [adapted] cells resisted more than the nonadapted cells. Treatment of the cells with protein synthesis inhibiting antibiotic chloramphenicol at a concentration of 100 micro gml -1 during adaptation prevented the enhanced resistance to killing effects of MNNG. However, such an effect was not demonstrated when the cells were treated with chloramphenicol during the MNNG challenge treatment of the adaptive cells. It is, therefore, evident that adaptive repair in Ps. syringae is mediated as a result of the induced synthesis of enzymes