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Lymphatic system anatomy and physiology
Immunodeficiencies: T-cell and B-cell disorders: Pathology review
Immunodeficiencies: Phagocyte and complement dysfunction: Pathology review
Autoimmune hemolytic anemia
Systemic lupus erythematosus
Immune thrombocytopenic purpura
Rheumatic heart disease
Streptococcus pyogenes (Group A Strep)
Streptococcus agalactiae (Group B Strep)
Clostridium botulinum (Botulism)
Clostridium tetani (Tetanus)
Bacillus anthracis (Anthrax)
Corynebacterium diphtheriae (Diphtheria)
Salmonella typhi (typhoid fever)
Vibrio cholerae (Cholera)
Bordetella pertussis (Pertussis/Whooping cough)
Legionella pneumophila (Legionnaires disease and Pontiac fever)
Yersinia pestis (Plague)
Francisella tularensis (Tularemia)
Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)
Rickettsia rickettsii (Rocky Mountain spotted fever) and other Rickettsia species
Treponema pallidum (Syphilis)
Borrelia burgdorferi (Lyme disease)
Mycobacterium tuberculosis (Tuberculosis)
Plasmodium species (Malaria)
Trypanosoma cruzi (Chagas disease)
Respiratory syncytial virus
COVID-19 (Coronavirus Disease 19)
Human parainfluenza viruses
Human herpesvirus 6 (Roseola)
Epstein-Barr virus (Infectious mononucleosis)
Herpes simplex virus
Varicella zoster virus
Hepatitis C virus
Yellow fever virus
West Nile virus
Anatomy of the eye
Anatomy and physiology of the teeth
Anatomy and physiology of the ear
Anatomy of the pharynx and esophagus
Anatomy of the lymphatics of the neck
Anatomy of the oral cavity
Anatomy of the orbit
Anatomy of the nose and paranasal sinuses
Lung volumes and capacities
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Staphylococcus epidermidis p. , 133
Gram-positive testing p. 132
in vivo biofilm production p. 127
normal flora p. 175
nosocomial infection p. 182
osteomyelitis p. 177
urease-positive p. 125
vancomycin for p. 187
Evode Iradufasha, MD
Robyn Hughes, MScBMC
Staphylococcus epidermidis or simply Staph epidermidis can be broken down into staph which means grapes, coccus which means round shape, and epidermidis referring to the superficial layer of the skin.
So, Staphylococcus epidermidis are round bacteria that tend to live clustered together as if they were grapes, and they are part of the skin normal flora even though they may also be found living on the mucosa of the gut.
Now, a little bit of microbe anatomy and physiology.
Staph epidermidis has a thick peptidoglycan cell wall, which takes in purple dye when Gram stained - so this is a gram-positive bacteria.
It’s non-motile and doesn’t form spores, and also, it’s a facultative anaerobe, meaning that it can survive in both aerobic and anaerobic environments.
Staph epidermidis is catalase positive, so it makes an enzyme called catalase.
We can use this to differentiate Staph epidermidis from other gram positive cocci, like streptococci and enterococci, which are catalase negative.
To test for this, a few drops of hydrogen peroxide are added to the colony of the suspected bacteria.
So, if catalase is present, like in staph epidermidis, it makes the hydrogen peroxide dissociate into water and oxygen, causing the mixture to foam.
Staph epidermidis is also urease positive, meaning it produces an enzyme called urease that dissociates urea into carbon dioxide and ammonia.
This can be tested by transferring a pure sample of bacteria from the culture to a sterile tube containing a mixture of “urea agar” broth and phenol red. Then, the mixture is incubated.
So, with Staph epidermidis, urease does it’s thing, making urea dissociate into carbon dioxide and ammonia.
Ammonia then makes the mixture change color from orange-yellow to bright pink.
This doesn’t happen with urease negative Gram-positive cocci, like Streptococcus pneumoniae or Enterococcus faecalis.
Furthermore, unlike many other Staphylococcus species, Staph epidermidis and its close relative, Staph saprophyticus, are both coagulase negative, meaning they don’t produce an enzyme called coagulase.
Testing for coagulase is done by transferring a colony of the suspected bacteria in test tube containing fibrinogen-rich plasma.
Coagulase-positive bacteria, like Staph aureus, convert the soluble fibrinogen into sticky fibrin, which then visibly clumps up.
With coagulase negative species, like Staph epidermidis or Staph saprophyticus, the fibrin doesn’t clump up.
Staphylococcus epidermidis is a round, gram-positive, catalase-positive, coagulase-negative, and urease-positive bacteria, which is normally part of the normal human flora, especially on the skin and mucosa. While S. epidermidis is generally harmless, it can cause opportunistic infections in people with weakened immune systems.
S. epidermidis is known to cause skin infections such as impetigo or cellulitis, but it's best known to contaminate and make biofilms on indwelling medical devices. From there, it can then get into the blood and cause severe infections, mostly in newborns. Treatment relies on antibiotics like Vancomycin and removing and replacing the infected medical device with a new, clean one.
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