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Introduction
Introduction
Shigella flexneri is a pathogen, as it causes Shigellosis. This is an infectious disease that results in over a million deaths annually, most of which are in developing countries. The disease or infection can be prevented through sanitation efforts, which is the reason that it spreads rapidly throughout developing nations, which often lack proper food sanitation and infrastructure for sewage.
People study and are concerned about S. flexneri because it results in such a high number of deaths each year. Scientists are attempting to develop a vaccine that would be affordable to administer in developing nations because treating the bacteria with an antibiotic is not feasible in most nations where it spreads.
Taxonomy
Taxonomy
Domain: Bacteria
Kingdom: Eubacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacterales
Family: Enterobacteriacease
Genus: Shigella
Species: S. flexneri
Visualizing S. flexneri
Visualizing S. flexneri
Image One
Image One
Image one shows Shigella flexneri bacterium using a transmission electron microscope. These cells clearly appear to be rod shaped. These images were retrieved from a journal on the characterization/identification of fatty acids found in specific cell membranes. I was not able to find any information regarding how the cells were stained to create this color.
Image two
Image two
Image two shows Shigella flexneri under a microscope after performing a gram stain. Clearly, the rod-shaped cells have a bright pink color, meaning they did not retain the purple color of the crystal violet stain due to the thin layer of peptidoglycan in the cell wall. This indicates that the cells are gram negative.
Diagnostic Tests
Diagnostic Tests
Gram Stain
Gram Stain
The gram stain test is used to determine if a microbe is gram positive or gram negative. In the gram stain shown above, the bacteria appear pink because there is less peptidoglycan in the cell walls of gram-negative microbes. This means that Shigella flexneri is gram negative.
MacConkey Agar
MacConkey Agar
MacConkey agar is both selective and differential, so it is able to distinguish based on sugar lactose and bile accumulation. If a bacterium is positive for the test, meaning it in fact grows on the MacConkey agar, then the growth will appear red/pink as seen in the image. This means that Shigella flexneri can ferment lactose.
Glucose Fermenter
Glucose Fermenter
The glucose fermentation test determines a microbe’s ability to ferment carbohydrates. When a microbe is able to do so, it changes the color of the pH indicator to yellow by decreasing the pH and produces a (hydrogen or carbon dioxide). In the photo, the pH indicator is clearly yellow which shows a pH change that means the microbe is a glucose fermenter. This is what a tube would look like if the test was completed using Shigella flexneri.
Motility Test
Motility Test
The motility test is used to determine whether a microbe has the ability to move on its own (with a flagellum). The test uses SIM medium which allows the microbe to move throughout it if motile. When the inoculating needle is injected into the media, if the microbe is motile the color will diffuse throughout the media. In the image above, the color stays concentrated around where the needle was injected which suggests that the microbe cannot move and disperse throughout the media. This is what the test results would look like for Shigella flexneri because it is not motile.
L-arabinose
L-arabinose
The purpose of the L-Arabinose test is to determine whether a microbe can ferment arabinose. If so, it produces acidic end products, resulting in a color change of the media, but if not the media appear the same color. Since Shigella flexneri cannot ferment arabinose, there would be no color change in the indicator because the pH would not change, so it would remain orange like it is in the image above.
D-mannitol
D-mannitol
Mannitol salt agar can be used to test a microbe’s ability to ferment mannitol. When a microbe is positive for the test, meaning it can ferment mannitol, the pH of the byproduct causes the color of the methyl red indicator to change to yellow. This means an acid is formed. This is what the test would appear like for Shigella flexneri which is positive for the mannitol salt agar test.
Molecular Diagnostics
Molecular Diagnostics
Primers:
Primers:
intI1L: ACA TGT GAT GGC GAC GCA CGA
intI1R: ATT TCT GTC CTG GCT GGC GA
Thermal Melting Point:
Thermal Melting Point:
intI1L: 56.3°C
intI1R: 53.8°C
GC Content:
GC Content:
intI1L: 57%
intI1R: 55%
Sequence:
>NR_026331.1 Shigella flexneri strain ATCC 29903 16S ribosomal RNA, partial sequenceTGGCTCAGATTGAACGCTGGCGGCAGGCCTAACACATGCAAGTCGAACGGTAACAGGAAGCAGCTTGCTGTTTCGCTGACGAGTGGCGGACGGGTGAGTAATGTCTGGGAAACTGCCTGATGGAGGGGGATAACTACTGGAAACGGTAGCTAATACCGCATAACGTCGCAAGACCAAAGAGGGGGACCTTCGGGCCTCTTGCCATCGGATGTGCCCAGATGGGATTAGCTAGTAGGTGGGGTAACGGCTCACCTAGGCGACGATCCCTAGCTGGTCTGAGAGGATGACCAGCCACACTGGAACTGAGACACGGTCCAGACTCCTACGGGAGGCAGCAGTGGGGAATATTGCACAATGGGCGCAAGCCTGATGCAGCCATGCCGCGTGTATGAAGAAGGCCTTCGGGTTGTAAAGTACTTTCAGCGGGGAGGAAGGGAGTAAAGTTAATACCTTTGCTCATTGACGTTACCCGCAGAAGAAGCACCGGCTAACTCCGTGCCAGCAGCCGCGGTAATACGGAGGGTGCAAGCGTTAATCGGAATTACTGGGCGTAAAGCGCACGCAGGCGGTTTGTTAAGTCAGATGTGAAATCCCCGGGCTCAACCTGGGAACTGCATCTGATACTGGCAAGCTTGAGTCTCGTAGAGGGGGGTAGAATTCCAGGTGTAGCGGTGAAATGCGTAGAGATCTGGAGGAATACCGGTGGCGAAGGCGGCCCCCTGGACGAAGACTGACGCTCAGGTGCGAAAGCGTGGGGAGCAAACAGGATTAGATACCCTGGTAGTCCACGCCGTAAACGATGTCGACTTGGAGGTTGTGCCCTTGAGGCGTGGCTTCCGGAGCTAACGCGTTAAGTCGACCGCCTGGGGAGTACGGCCGCAAGGTTAAAACTCAAATGAATTGACGGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGATGCAACGCGAAGAACCTTACCTGGTCTTGACATCCACGGAAGTTTTCAGAGATGAGAATGTGCCTTCGGGAACCGTGAGACAGGTGCTGCATGGCTGTCGTCAGCTCGTGTTGTGAAATGTTGGGTTAAGTCCCGCAACGAGCGCAACCCTTATCCTTTGTTGCCAGCGGTCCGGCCGGGAACTCAAAGGAGACTGCCAGTGATAAACTGGAGGAAGGTGGGGATGACGTCAAGTCATCATGGCCCTTACGACCAGGGCTACACACGTGCTACAATGGCGCATACAAAGAGAAGCGACCTCGCGAGAGCAAGCGGACCTCATAAAGTGCGTCGTAGTCCGGATTGGAGTCTGCAACTCGACTCCATGAAGTCGGAATCGCTAGTAATCGTGGATCAGAATGCCACGGTGAATACGTTCCCGGGCCTTGTACACACCGCCCGTCACACCATGGGAGTGGGTTGCAAAAGAAGTAGGTAGCTTAACCTTCGGGAGGGCGCTTACCACTTTGTGATTCATGACTGGGGTGAAGTCGTAACAAGGTASequence:
Disease and Treatment
Disease and Treatment
Infection occurs in the stomach of the host. It has the ability to penetrate the epithelial lining via the follicular associated epithelium. S. flexneri enters M cells inside the epithelial layer and uses them as a means of transport across the impermeable epithelial membrane. Once inside the intraepithelial pocket, the cells are engulfed by macrophages but are able to invade the killing mechanisms through IpaB-mediated lysis. Apoptosis of the macrophage occurs shortly after and the bacteria is released into the sub-mucosa.
The two most common types of antibiotics used to treat shigellosis are ciprofloxacin and azithromycin. However, in most developing nations where the disease results in the most deaths, antibiotics are not used because they are too expensive. Also, there are many strains of Shigella flexneri that have developed a resistance to these commonly used antibiotics. For this reason, scientists are working to develop a vaccine for the disease. Although no vaccines have been released for field use, the most recent efforts have been to develop a live vaccine that can be administered orally and will activate effectors of mucosal immunity. A vaccine is made possible thanks to the serotype immunity that is developed.
References
References
Lan R, Reeves PR. 2002. Escherichia coli in disguise: molecular origins of Shigella. Microbes and Infection 4:1125–1132.
Shigella flexneri infection: pathogenesis and vaccine development | FEMS Microbiology Reviews | Oxford Academic.
Pan J-C, Ye R, Meng D-M, Zhang W, Wang H-Q, Liu K-Z. 2006. Molecular characteristics of class 1 and class 2 integrons and their relationships to antibiotic resistance in clinical isolates of Shigella sonnei and Shigella flexneri. Journal of Antimicrobial Chemotherapy 58:288–296.
Lingfa L. Isolation And Characterization Of Fatty Acids Present In The Cell Membrane Of Acidithiobacillus Ferrroxidans. VIT University.
Image 2 was retrieved from https://www.jfmed.uniba.sk/fileadmin/jlf/Pracoviska/ustav-mikrobiologie-a-imunologie/ENTEROBACTERIACEAE__CAMPYLOBACTER__HELICOBACTER.pdf
About the Researcher
About the Researcher
Name: Blake Simmons
Sophomore
Major: Microbiology
Hobbies: golfing, freediving, surfing
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