chapter 12.3 case study, Virulence of cholera toxin gene-positive Vibrio cholerae non-O1/non-O139 strains isolated from environmental water in Kolkata, India

aim

hypothesis

presence of ctx gene in non-O1 and non-O139 strains will increase pathogenicity of these non-toxic strains

background

Vibrio cholerae: pathogen causing acute diarrheal disease-  “cholera”

V. cholerae serogroups O1 and O139 can produce cholera toxin(CT) and cause disease

1. Serogroups: classification of microorganisms based on shared surface antigens that trigger an antibody response

2. Cholera toxin: exotoxin produced by Vibrio cholerae 

Non-O1 and Non-O139 V. cholerae strains often don’t have the cholera toxin gene ctx gene and therefore don't cause outbreaks

The researchers identified 3 non-O1 and non-O139 strains that had the ctx gene and establish an infection

recall// pathogenicity: ability to cause disease

Are the researchers using the right terminology? Are they thinking of pathogenicity or virulence?

1. Pathogenicity: ability of a microbe to cause disease (qualitative)

2. Virulence: degree of harm cause by a pathogen (quantitative)

step 1: rabbit intestine with V. cholerae or buffer injected in diff locations

PBS: clean buffer solution, control

N16961: toxic strain of V. cholerae (O1 or O139, has ctx gene)

no1, 2, 3: (non O1, O139, has ctx gene)

A: non-toxic strain (non O1, O139, does not have ctx gene)

Cholera toxin causes accumulation of water in interesting, intestinal cells cant absorb water → diarrhea

If a strain secretes cholera todin, we should see fluid accumulation in the gut

step 1: volume of fluid accumulated

Which of the strains of “”non-toxic” V. cholerae  causes accumulation of fluid in the intestine?

Which strains of “non-toxic” V. cholerae are actually non-toxic/ non-pathogenic

Which strain of “non-toxic” V. cholerae is the most virulent?

step 2:

Which non-toxic strain can express and secrete cholera toxin?

Does the data in fig 1 correlate with the data in fig 2?

Do you think strain No1 would be likely to cause disease in humans based on the information in thsi slide? (graph of fig 2)

conclusion

• No1 “non-toxic” strain is theoretically pathogenic (encodes a virulence factor, cholera toxin), REMEMBER// strains that are non-O1 and non-O139 are considered “nontoxic”

• No1 likely has a toxin gene and produces toxins at 25C

Hypothesis was presence of ctx gene in non-O1 and non-O139 strains will increase pathogenicity of these non-toxic strains

• Evidence for this is mixed