Medical Microbiology: Analysis of Vibrio Cholerae Infection Case

This essay presents a detailed analysis of a medical microbiology case involving a 20-year-old male patient, RP, who presented with symptoms of watery diarrhea, abdominal pain, and cramps, leading to a diagnosis of infective gastroenteritis. The essay focuses on the evaluation of Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) agar results to identify the causative agent of the infection. The diagnostic procedures for cholera, including the string test and serogroup O1 antisera agglutination test, are explained in detail. The isolate was identified as Vibrio cholerae, a Gram-negative bacterium responsible for cholera, contracted through the fecal-oral route, often via contaminated water or food. The essay discusses the implications of the test results, the importance of fluid replacement therapy and antibiotic treatment, and preventive measures. The patient's travel history to Mumbai and exposure during the rainy season highlights the environmental factors contributing to the transmission of the disease. The essay emphasizes the role of sanitation, safe water, and hygiene in preventing cholera outbreaks and the significance of early diagnosis and appropriate treatment to manage the infection effectively. The essay also references several medical microbiology resources.

Running head: MEDICAL MICROBIOLOGY
Medical Microbiology
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1MEDICAL MICROBIOLOGY
The essay analyzes the case of RP, a 20 years old male patient with complaints of watery
diarrhea, abdominal pains and cramps. The review of the patient’s detail and his travel history
revealed infective gastroenteritis. The main purpose of the essay is to evaluate the TBS agar
results to find out the causes of infection in patients. The procedures used for diagnostics testing
of cholera and implications of the test results have been provided.
The isolate in the present case is Vibrio cholerae, which is a Gram-negative, facultative
bacterium responsible for causing the disease cholera in humans. These are asporogenous,
motile, curved or straight rods. When humans ingest the microorganism, it causes severe diarrhea
accompanied with vomiting and nausea. The primary connection between the microorganisms
and human is through water where there is an absence of proper water purification system. The
growth of the organism can be noted in TCBS agar, and the organism gives positive results for
Oxidase test and String test. Further, agglutination is observed with serogroup O1 antisera
(Gillespie 2014).
Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) Agar is widely used for the selective
isolation of Vibrio cholera from different specimens. The different components are sucrose,
dipeptone, sodium citrate, sodium thiosulphate, sodium chloride, yeast extract, ox bile, sodium
cholate, ferric citrate, bromothymol blue, thymol blue and agar. Sodium citrate and thiosulphate
inhibit growth of Enterobacteria. Ox bile and sodium cholate is responsible for inhibition of
gram-positive bacteria. Bromthymol Blue and Thymol Blue are pH indicators. Fermentation of
sucrose makes bromothymol blue turns yellow. thiosulfate acts as a sulfur source. Yeast
extract and peptone are sources of nitrogen, vitamins, and amino acids. Sodium chloride provides
optimum growth and metabolic activity of halophilic Vibrio spp. Agar acts as a solidifying agent
(Murray, Rosenthal and Pfaller 2015).

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If the results of the string test for identification of V. cholerae are positive, it is to be
understood that the cells of the bacteria have been lysed due to sodium deoxycholate or Sodium
taurocholate and the DNA has been released from the cells, leading to a viscous mixture. The test
is done by placing a drop of 0.5% aqueous solution of sodium deoxycholate on the slide mixing a
small bacterial growth culture from the MacConkey agar into the drop. A mucoid “string” is
noticed when one draws the inoculation loop away from the suspension if positive result is
achieved. In case of negative result, there is no appearance of string (Ford 2014).
Serogroup O1 organisms are the causal agents of cholera outbreaks. The serogroup
antisera is the agent that can be subdivide strains of Vibrio cholerae into various subtypes like
Ogawa, Inaba and Hikojama. The serogroup antisera test is based on the principle of
agglutination. Serogroup O1 antisera are set of antisera, which is absorbed with different strains
of Vibrio cholera. The main procedure surrounding the test includes taking V. cholerae strains
from broth cultures after confirming the organism by their morphological features and
emulsifying it with Vibrio cholerae antiserum. Next, the culture plates are observed for antigen-
antibody ineterctions. This test is interpreted by detecting agglutination process in the sample. A
positive interaction is indicated by signs of macroscopic agglutination, whereas a negative
interaction is denoted by absence of agglutination. Macroscopic agglutination also suggest that
one or more antigen of the V. cholera are specified by the antiserum (Baranova, Levinson and
Mantis 2018).
The isolate being serogroup O1 positive is identified when agglutinations are observed
with serogroup O1 antisera. In case of RP, serogroup O1 positive result was found thus
confirming that one or more antigens were present in Vibrio cholera strain and serotype O1 is
responsible for causing diarrhea in patient. These findings will have implications in deciding the

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appropriate treatment option for patient. O1 serogroup of Vibrio cholera strain has the potential
to cause epidemic cholera as it contains two major virulence factors, cholera toxin and the toxin-
coregulated pilus. After this identification, the transmission of the organism can be controlled by
initiating antibiotic therapy for patients. As the patient was complaining of watery diarrhoea,
fluid loss should be controlled in patient. This can be done by fluid replacement therapy and
giving electrolyte to patient. Antibiotics like tetracycline are particularly found useful in
treatment because it has the potential to shorten the period of infection and reducing duration of
hospital stay too. In addition, fluid replacement therapy will favor quick recovery of patient from
the infection (Dangbé et al., 2017).
The Vibrio cholera organism is likely to have been contracted through fecal-oral route
and by consuming contaminated food or water. The patient RP had went to India to visit a friend
and it was raining badly there. Although he drank only bottled water and ate restaurant foods
only, however he was tempted by street foods only. Hence, it can be said that rainy season and
presence of environmental contamination might be the cause of transmission of the cholera
bacteria. RP had visited Mumbai and Mumbai has many peri-urban slums regions, which are
regions most prone to cholera transmission. Secondly, rainy season also disrupts water and
sanitation systems thus increasing the risk of cholera transmission. Cholera is water borne
disease and patient was exposed to infection due to contamination of food and water during the
rainy season. Rain and flood increases risk of contamination and increases cholera ooutbreaks
during the rainy season (Roobthaisong et al. 2017).
The infection could have been prevented if the patient had access to adequate sanitation,
safe water and basic hygiene needs. If he had not take seafood during that time and developed
interest in eating street foods, the disease could have been prevented. Hence, when the patient

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was travelling to Mumbai, he should have taken simple precautions to avoid getting cholera.
These precautions includes drinking only boiled water or chlorine treated water, eating
thoroughly cooked foods, avoiding undercooked or raw fished and avoiding street foods. Taking
these simple precautions would have saved the patient from infection (Davies, Bowman and
Luby, 2017).
As cholera was the main cause of behind diarrhea and stomach upset in patient, the
patient could be treated by use of antibiotics and intravenous fluids. Antibiotics are useful when
the aim is to reduce the duration of infection particularly in severely ill patients. In addition
rehydration techniques like replacing lost fluids with oral rehydration salts could have reduced
severity in patient (Davies, Bowman and Luby, 2017).
The essay gave an insight into the diagnostic procedure and microbiological techniques
used to detect cholera infection in patient. Based on evaluating of O1 antisera results and string
test, the essay developed understanding regarding interpretation of results for diagnosis of
diarrhea. The methods to prevent and treat such infection in patients were also discussed.

5MEDICAL MICROBIOLOGY
References
Baranova, D.E., Levinson, K.J. and Mantis, N.J., 2018. Vibrio cholerae O1 secretes an
extracellular matrix in response to antibody-mediated agglutination. PloS one, 13(1),
p.e0190026.
Dangbé, E., Békollé, D., Irépran, D. and Perasso, A., 2017. Impact of hygiene, famine and
environment on transmission and spread of cholera. Mathematical Modelling of Natural
Phenomena, 12(2), pp.4-21.
Davies, H.G., Bowman, C. and Luby, S.P., 2017. Cholera–management and prevention. Journal
of Infection, 74, pp.S66-S73.
Ford, M., 2014. Medical microbiology. Oxford University Press.
Gillespie, S.H., 2014. Medical microbiology illustrated. Butterworth-Heinemann.
Murray, P.R., Rosenthal, K.S. and Pfaller, M.A., 2015. Medical microbiology. Elsevier Health
Sciences.
Roobthaisong, A., Okada, K., Htun, N., Aung, W.W., Wongboot, W., Kamjumphol, W., Han,
A.A., Yi, Y. and Hamada, S., 2017. Molecular Epidemiology of Cholera Outbreaks during the
Rainy Season in Mandalay, Myanmar. The American journal of tropical medicine and
hygiene, 97(5), pp.1323-1328.