Molecular Analysis of Bacterial Cytolysins

Abstract

Results of molecular and pathogenic studies of three different bacterial hemolysins (cytolysins) are presented. These exoproteins derive from the two gram-negative bacteria Escherichia coli and Aeromonas hydrophila and from the gram-positive pathogen Listeria monocytogenes. The hemolysin of E. coli is determined by an 8-kilobase (kb) region that includes four clustered genes (hlyC, hlyA, hlyB, and hlyD). This hemolysin determinant is part either of large transmissible plasmids or of the chromosome. The genes located chromosomally are found predominantly in E. coli strains that can cause pyelonephritis and/or other extraintestinal infections. A detailed analysis of the chromosomal hly determinants of one nephropathogenic E. coli strain revealed the existence of specific, large chromosomal insertions 75 kb and lOO kb in size that carry the hly genes but that also influence the expression of other virulence properties, i.e., adhesion and serum resistance. The direct involvement of E. coli hemolysin in virulence could be demonstrated in several model systems. The genetic determinants for hemolysin (cytolysin) formation in , A. hydrophila (aerolysin) and L. monocytogenes (listeriolysin) are less complex. Both cytolysins seem to be encoded by single genes, although two loci (aerB and aerC) that affect the expression and activity of aerolysin have been identified distal and proximal to the structural gene for aerolysin (aerA). Cytolysin-negative mutants of both bacteria were obtained by site-specific deletion and/or transposon mutagenesis. These mutants show a drastic reduction in the virulence of the respective bacteria.

Enterohemolysin production is associated with a temperate bacteriophage in Escherichia coli serogroup O26 strains

“…In contrast to other hemolysins and cytolysins (10,11,14), production of the enterohemolysin described here is associated with a temperate bacteriophage. Synthesis of enterohemolysin in E. coli JM83(pEO19) and its derivatives was found to be lethal for the bacterial host, which is in contrast to molecularly cloned a-hemolysin.…”

Actinobacillus pleuropneumoniae hlyX gene homology with the fnr gene of Escherichia coli

“…This property was localized to a segment of approximately 850 bp by deletion analysis. From the size of the region of DNA which encoded the hemolytic activity and the physiochemical properties of that hemolytic activity, it was apparent that the A44 plasmid did not encode the major 105-kDa hemolysin of A. pleuropneumoniae nor did it encode a hemolysin resembling other known hemolysins or toxins (3). To gain some insight into the nature of the A44-encoded hemolysin, the region conferring the hemolytic activity was sequenced.…”

Characterization of monoclonal antibodies against the Escherichia coli hemolysin

“…Nicaud et al (21) have reported that HlyC activation involves neither phosphorylation nor glycosylation of HlyA. HlyA hemolytic and cytotoxic activity is sensitive to phospholipase and lipase treatment (3,4). However, it has not been established that HlyC activity involves either a covalent or noncovalent association of phospholipid to HlyA.…”