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Bacterial structure and functions
Bacillus anthracis (Anthrax)
Bacillus cereus (Food poisoning)
Corynebacterium diphtheriae (Diphtheria)
Clostridium botulinum (Botulism)
Clostridium difficile (Pseudomembranous colitis)
Clostridium tetani (Tetanus)
Streptococcus agalactiae (Group B Strep)
Streptococcus pyogenes (Group A Strep)
Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)
Legionella pneumophila (Legionnaires disease and Pontiac fever)
Salmonella typhi (typhoid fever)
Yersinia pestis (Plague)
Vibrio cholerae (Cholera)
Bordetella pertussis (Pertussis/Whooping cough)
Francisella tularensis (Tularemia)
Haemophilus ducreyi (Chancroid)
Gardnerella vaginalis (Bacterial vaginosis)
Coxiella burnetii (Q fever)
Ehrlichia and Anaplasma
Rickettsia rickettsii (Rocky Mountain spotted fever) and other Rickettsia species
Borrelia burgdorferi (Lyme disease)
Borrelia species (Relapsing fever)
Treponema pallidum (Syphilis)
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With Bacteroides fragilis, ‘bacter-’ means rod, ‘-oides’ means shape and ‘fragilis’ means fragile.
So, Bacteroides fragilis is a Gram-negative, rod-shaped bacterium.
Although it's generally considered a rod-shaped, its can range from a sphere to a rod shape, so it’s considered a pleomorphic bacterium.
Now, a little bit more about this microbe. For starters, Bacteroides fragilis is Gram-negative, which means that it has a thin peptidoglycan cell wall that can't readily retain purple dye when Gram stained.
Additionally, it's a non-spore-forming and non-motile bacteria.
It’s also an obligate anaerobe, meaning that it can only live without oxygen.
Another fact is that it’s bile resistant and seems to like bile, which makes sense since it lives in the colon.
So, not only can it grow anaerobically in blood agar, but it can also readily grow in bile esculin agar, also known as Bacteroides Bile Esculin.
After 48 hours of incubation at 35°C Bacteroides fragilis forms dark colonies with brown-black halos due to the hydrolysis of esculin.
From there, it can travel to virtually any organ in the body.
Alternatively, it can slip into the sterile peritoneal cavity accompanied by aerobic bacteria like E. coli, which are also part of the normal gut flora - so peritoneal infections are usually considered “polymicrobial” infection, to reflect that there’s more than one culprit.
Bacteroides fragilis is a Gram-negative, anaerobic rod-shaped bacterium, commonly found in the human gastrointestinal tract living as normal flora. However, it can cause illness when there is a disruption of the mucosal surface, either by trauma or surgery, causing the spread of Bacteroides fragilis to the bloodstream or surrounding tissues, causing infections such as sepsis, abscesses, and peritonitis. Symptoms vary depending on the site of the infection but can include fever, distended and tender abdomen, and abscesses.
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