Gram negative bacteria and blood agar hemolysis

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SUMMARY

This discussion centers on the hemolytic properties of Gram-negative bacteria on blood agar, specifically sheep's blood agar. It establishes that while Gram-negative bacteria are generally considered gamma hemolytic, notable exceptions exist, such as pathogenic strains of E. coli associated with hemolytic uremic syndrome. The conversation highlights that hemolysis phenotypes are more critical for Gram-positive bacteria identification, particularly streptococci. Additionally, the importance of using mannitol salt agar (MSA) in conjunction with sheep's blood agar for accurate identification of Staphylococcus species is emphasized.

PREREQUISITES
  • Understanding of Gram-negative and Gram-positive bacterial classification
  • Knowledge of blood agar and its hemolytic properties
  • Familiarity with pathogenic E. coli and hemolytic uremic syndrome
  • Experience with mannitol salt agar (MSA) usage
NEXT STEPS
  • Research the hemolytic properties of E. coli on different blood agar types
  • Study the role of mannitol salt agar in differentiating Staphylococcus species
  • Investigate the clinical implications of hemolytic uremic syndrome caused by E. coli
  • Explore the identification techniques for Gram-negative bacteria using hemolysis phenotypes
USEFUL FOR

Microbiologists, clinical laboratory technicians, and healthcare professionals involved in bacterial identification and pathogenicity assessment will benefit from this discussion.

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I've looked all over and I can only find information on blood agar hemolyis for gram positive bacteria. Can I take this to mean that gram negative bacteria are generally gamma hemolytic? If so, are there any notable exceptions to this? One that I would guess is pathogenic E. coli, which cause hemolytic uremic (sp?) syndrome, but I was unable to find a direct connection to sheep's blood agar.
 
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Haemolysis phenotypes are more frequently used to described Gram-positive rather than Gram-negative because the haemolysis phenotype is often crucial for proper identification of the Gram-positive especially the streptococci. However, haemolysis can be observed in Gram-negative.

I've worked with a Gram-negative that was haemolytic but only with bovine blood. It didn't cause haemolysis in sheep's blood agar.

If you do a search with E. coli and haemolysis
or E. coli and hemolytic uremic syndrome on pubmed http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=escherichia coli haemolysis

you may find the information you are looking for.
 
I'm realizing now that mannitol salt agar is probabably an important to combine with sheep's blood agar. First if it grows on MSA you know it's probably Staphylococcus, then if it has beta hemolysis on the sheep's blood you know it's probably also pathogenic staph.
 

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