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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 (Whooping cough)
Francisella tularensis (Tularemia)
Haemophilus ducreyi (Chancroid)
Mycobacterium tuberculosis (Tuberculosis)
Mycobacterium avium complex (NORD)
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)
0 / 13 complete
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Strep agalactiae (Group B Strep)
Streptococcus agalactiae p. , 135
Streptococcus agalactiae in p. 135
Streptococcus agalactiae as cause p. 135
β -hemolytic nature of p. 133
encapsulated bacteria p. 125
Gram-positive testing p. 132
immunodeficient patients p. 116
meningitis p. 177
in neonates p. 181
pneumonia p. 176
prophylaxis for p. 194
splenic dysfunction p. 96
With Streptococcus agalactiae sometimes called Strep agalactiae, strepto means a chain, coccus means round shape, and agalactiae literally means “no milk”.
So, Strep agalactiae refers to the round bacteria that grow in chains and that was previously known to infect cattle, resulting in reduced milk production.
Later on, Strep agalactiae was found to also be a human potential pathogen responsible for a number of infections that most commonly affect pregnant women and newborns.
Strep agalactiae are also called Group B Strep – GBS - in Lancefield classification developed by an American microbiologist Rebecca Lancefield.
Ok now, a little bit of microbe anatomy and physiology.
Strep agalactiae 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.
Now, a particular trait of Streptococcus species is that they are catalase negative, meaning they do not produce an enzyme called catalase.
This is unlike other common gram positive cocci, like Staphylococcus, which are catalase positive.
When cultivated on a medium called blood agar, Strep agalactiae colonies cause beta hemolysis, also called complete hemolysis.
That’s because Strep agalactiae makes a toxin called beta-hemolysin, that causes complete lysis of the hemoglobin in the red blood cells, making them blood agar change color from red to transparent yellow around the colonies.
However, other Streptococcus species, like Strep pyogenes, are also beta hemolytic.
So to identify Strep agalactiae specifically, the bacitracin test, the hippurate test, or the CAMP test can be done.
With the bacitracin test, a disk of bacitracin is added to the blood agar.
Strep agalactiae is bacitracin resistant, so the colonies remain intact, whereas Strep pyogenes is bacitracin sensitive, so the colonies die off.
With the CAMP test, Strep agalactiae is grown with Staphylococcus aureus on the same blood agar.
Both these bacteria are beta-hemolytic, but Strep agalactiae makes a substance called CAMP factor, which enhances the action of staphylococcal beta-hemolysin.
Streptococcus agalactiae, also known as group B streptococcus, is a gram-positive, beta-hemolytic, catalase-negative, and bacitracin-resistant bacterium, which can cause several infections in humans. Most frequently, Streptococcus agalactiae causes neonatal infections like pneumonia, sepsis, meningitis, and septic arthritis. It can also cause chorioamnionitis or cystitis in pregnant females. Treatment involves antibiotics like penicillin G or ampicillin, or Cefazolin and Vancomycin. To prevent Streptococcus agalactiae infections in neonates, intrapartum antibiotic prophylaxis can be administered to vaginally colonized pregnant females.
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