Penicillin-binding protein 2 genes of non-β-lactamase-producing, penicillin-resistant strains of Neisseria gonorrhoeae

Oligonucleotides that correspond to regions of the penicillin-binding protein 2 gene (penA) that differ between penicillin-sensitive and penicillin-resistant strains have been used as probes to classify the penA genes in a collection of penicillin-resistant gonococci isolated in Britain. 44/47 of those gonococcal strains that had minimal inhibitory concentrations of greater than or equal to 0.25 microgram benzylpenicillin per ml contained extensively altered penA genes which appeared to be very similar (or identical) to one or other of the two classes of altered penA genes that have been described previously. Since these two classes of altered penA genes are related, it appears that the great majority of the altered penA genes on non-beta-lactamase-producing penicillin-resistant gonococci have a clonal origin. The other three penicillin-resistant strains had altered penA genes that were different to those described previously. A crucial step in the development of the altered forms of PBP2 with decreased affinity for penicillin appears to have been the insertion of an extra codon within the transpeptidase domain of the penA gene. This insertion was found in the penA gene of all gonococci with minimal inhibitory concentrations of greater than 0.016 microgram benzylpenicillin per ml but was not found in any strains with minimal inhibitory concentrations of less than or equal to 0.016 microgram per ml.     

THE GROWTH OF SELECTED DESMID (DESMIDIALES,CHLOROPHYTA) TAXA AT DIFFERENT CALCIUM AND PH LEVELS

The growth of clonal isolates of Closterium moniliferum and Cosmarium granatum from hard waters and Triploceras gracile from an acid bog was examined at two different levels of calcium and pH. Low pH and low calcium favored the growth of Triploceras, whereas Closterium grew equally well at both calcium levels but preferred the higher pH. Cosmarium favored both high pH and a high calcium concentration. Each taxon was affected by an interaction of the parameters on the growth rates. The results from studies on these taxa do not completely support the generalizations generated by previous investigations on the chemical factors affecting the growth and distribution of desmids; the controlling influences may, therefore, involve a complex interaction of factors which are unique for individual taxa or groups of taxa.