There are over 2,000 various groupings (serovars) that comprise S. enterica, each very closely related to each other making Salmonella Typhi a prime example of a serovar. Salmonella typhi is a gram negative bacterium that causes systemic infections and typhoid fever in humans. This rod-shaped, flagellated organism’s sole reservoir is humans. It has caused many deaths in developing countries where sanitation is poor and is spread through contamination of water and undercooked food. Eradication seems highly unlikely due to recent emergence of multi drug resistance strains. Salmonella Typhi strain Ct18 was originally isolated from a patient in a hospital in Vietnam. The chromosome sequence is 4,809,037 bp in length with a G+C content of 52.09%. The chromosome was sequenced though the method of shotgun sequencing with 97,000 shotgun reads. Since then, Salmonella typhi has undergone evolutionary change and has become resistant to antibiotics .
CELL STRUCTURE AND METABOLISM
Salmonella typhi is a rod-shaped, gram negative bacteria that contain features that separates itself from other types of bacteria which include: having 2 membranes ( and outer and an inner), periplasm, and a Lipopollysaccharide chain that consists of α-d-galactosyl-(1 → 2)-α-d-mannosyl-(1 → 4)-l-rhamnosyl-(1 → 3)-repeating units, and has short branches of single 3,6-dideoxyhexose residues .
Salmonella typhi has a complex regulatory system, which mediates its response to the changes in its external environment. Sigma factors, which are global regulators that alter the specificity of RNA polymerase, are examples of such regulation. Some sigma factors direct transcription to produce stress proteins, which increases the chances of the bacteria surviving environmental changes. RNA polymerase S is produced in response to starvation and changes in pH and temperature. It also regulates the expression of up to 50 other proteins and is also involved in the regulation of virulence plasmids.
In order to survive in the intestinal organs of its hosts where there are low levels of oxygen, Salmonella typhi has to be able to learn to use other sources other than oxygen as an electron acceptor. Therefore, Salmonella has adapted to grow under both an aerobic and anaerobic conditions.
Salmonella’s most common source of electron acceptors is nitrogen. Examples of other electron acceptors are: nitrate, nitrite, fumarate, and dimethlysulphoxide. Global and specific regulatory systems of anaerobic gene expression, like the ones mentioned above, are implemented to make sure that the most energetically favorable metabolic process is used. Evidence shows that the availability of oxygen is an environmental signal that controls Salmonella’s virulence.
Salmonella typhi is a food born pathogen and that is increasingly difficult to control. Salmonella’s ability to change its phenotype and genotype in response to environmental changes make it almost impossible to eradicate from the food chain. When a culture of Salmonella was transferred to higher temperatures (60 C), it took 60 minutes to maximize heat resistance. When the pH was lowered, acid resistance increased. The time taken to kill 90% was 4-14 minutes. Salmonella cells experience gradual changes which is why Salmonella thrives in undercooked meat. It is able to adapt to survive the cooking process and also has the ability to cross the gastric acid barrier (this is how they enter the human intestine). A high-fat matrix is protects Salmonella against these stressful environments .
Without prompt treatment, Salmonella Typhi infection can lead to liver damage, inflammation of the heart, holes in the gut, and internal bleeding.
Treatments antibiotics could be used: Ampicillin, chloramphenicol, trimethoprim- sulfamethoxazole, Amoxicillin and ciprofloxacin if not treated, takes 3 weeks ~ month to be cured only 10% - 30% of untreated cases Intravenous fluids and Electrolytes may be given there are increasing amount of antibiotic resistance, must be careful .
Transmission Salmonella Typhi – original bacteria that only lives in humans People with typhoid fever carry bacteria in their bloodstreams and intestinal Even when people recover from the fever they continue to carry the bacteria can be spread by food or drink that have been handled by people who owns Salmonella Typhi can also spread by the contaminated sewage that extends to water .
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