Comparative analysis of naturally occurring L-amino acid osmolytes and their D-isomers on protection of Escherichia coli against environmental stresses.

Adaptation to high salinity and low or high temperature is essential for bacteria to survive. Accumulation of exogenous osmolytes is one of the ways that helps bacteria to survive under such extracellular stress. We have analysed the capability of various L-amino acids and their D-isomers to act as osmolytes and thus enable Escherichia coli cells to survive under various stress conditions. E. coli cells were grown in the presence or absence of L- and D-proline, alanine, serine and lysine under salt, heat and cold stresses. Of the various amino acids tested, L-proline, closely followed by L-serine turned out to be highly protective against environmental stresses. L-proline provided excellent protection (95%) against salt stress, followed by cold (60%) and heat (40%) stresses. D-amino acids on the other hand, proved to be highly inhibitory under stress conditions. Thus L-amino acids were found to be growth protectants under stress while their D-isomers were inhibitory during stress as well as normal conditions.

Intrafamilial Clustering Of HbsAg and HBV DNA Among The Families Of Carriers.

To find out the clustering of HBV carriers within a family, 50 HBsAg carriers were studied. The distribution of HBsAg was found to be high (33%) among the offspring of HBsAg negative father and positive mother when compared to positive father and negative mother (16%) or where both the parents were HBsAg negative (31%0. The frequency of HBV DNA was also found to be high among the offspring of HBV DNA negative father and HBV DNA positive mother (25%). Male infection leading to a clustering of HBsAg carrier families.

Detection of hepatitis Β virus in blood samples negative for surface antigen, by DNA probe hybridization assay.

A DNA hybridization assay was developed using a cloned hepatitis Β viral genome to detect the presence of infectious virions in human serum. The merit of this assay was to put in evidence virus particles in 7 out of 133 sera that were negative for surface antigen (HBsAg) using routine serological methods. The usefulness of this assay was confirmed by actual visualization of the virus under electron microscope. Some serum samples although positive for surface antigen, did not give a hybridization signal by dot blot assay and might indicate cases of acute hepatitis.