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Contact-haemolysin production by entero-invasive Escherichia coli and shigellae
K Haider1, M J Albert, A Hossain
1Laboratory Sciences Division, International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh.
Abstract:
Entero-invasive Escherichia coli (EIEC) and shigellae were tested for contact-haemolysin (CH) with red blood cells (RBCs) of guinea-pig, rabbit, rat, mouse, monkey, man, sheep and chicken; all bacteria showed the best lysis with guinea-pig RBCs. The best culture medium for CH activity of shigellae was tryptic soy broth, and for EIEC it was casamino acid-yeast extract broth with 1 mM CaCl2. CH production by all species was best at the slightly alkaline pH which is optimal for growth; it was also dependent on the presence of a large (140-Mda) plasmid. Pre-treatment of bacteria with homologous antisera inhibited CH activity. Various treatments of bacterial cells and RBCs suggested that CH may be a protein molecule, and that a chitotriose-like moiety may serve as CH receptor. RBCs that were incubated with bacteria at 4 degrees C, or with heat-killed bacteria at 37 degrees C, were not lysed; also, isolated cell-surface components (lipopolysaccharide and outer-membrane protein) did not lyse RBCs. This suggests that metabolically active cells are required for CH activity. Production of CH by both EIEC and shigellae is consistent with a common mechanism for the virulence of these organisms.
Insights
Entero-invasive Escherichia coli (EIEC) and shigellae produce contact-haemolysin (CH) using metabolically active cells. This virulence factor, dependent on a large plasmid, is inhibited by antisera and requires specific conditions for optimal activity.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Entero-invasive Escherichia coli (EIEC) and shigellae are significant human pathogens.
- Contact-haemolysin (CH) is a virulence factor implicated in bacterial infections.
- Understanding the mechanisms of CH production is crucial for developing targeted interventions.
Purpose of the Study:
- To investigate the production and characteristics of contact-haemolysin (CH) in EIEC and shigellae.
- To identify optimal conditions for CH activity and its dependence on bacterial factors.
- To elucidate the nature of the CH molecule and its receptor on red blood cells (RBCs).
Main Methods:
- Testing CH activity of EIEC and shigellae against various animal and human RBCs.
- Optimizing culture media, pH, and temperature for CH production.
- Investigating the role of a 140-Mda plasmid and bacterial surface components in CH activity.
- Assessing the effect of pre-treatment with homologous antisera and bacterial cell viability on CH lysis.
Main Results:
- Guinea-pig RBCs exhibited the highest susceptibility to lysis by CH from both EIEC and shigellae.
- Optimal CH production was observed in specific broths (tryptic soy for shigellae, casamino acid-yeast extract for EIEC) at a slightly alkaline pH.
- CH activity was dependent on a large plasmid and required metabolically active bacterial cells, with evidence suggesting CH is a protein molecule and a chitotriose-like moiety acts as the receptor.
Conclusions:
- CH production by EIEC and shigellae is a common virulence mechanism.
- Metabolically active bacteria are essential for CH activity.
- The findings provide insights into the molecular basis of EIEC and shigellae pathogenesis.