Microbiology Flashcards
Mycoplasma
Aerobic Gram positive acid-fast bacilli.
Mycobacteria are characterised by a waxy cell wall composed of glycolipids including mycolic acid, which renders them acid-fast.
Mycobacterium tuberculosis complex causes human and animal tuberculosis.
Mycobacterium avium complex causes superinfection in immunosuppressed individuals, classically in the setting of HIV/AIDS.
Mycobacterium ulcerans causes the Bairnsdale ulcer.
Clostridium
Anaerobic Gram positive bacilli capable of producing endospores.
Clostridium classically lives in soil.
Clostridium difficile causes pseudomembranous colitis.
Clostridium botulinum produces botulinum toxin and causes botulism in humans.
Clostridium tetani causes tetanus.
Clostridium perfringens causes gas gangrene.
Streptococcus
Gram positive cocci, many of which are facultative anaerobes.
Often included in normal human flora.
Streptococci are classified by their haemolytic properties.
Alpha haemolytic streptococci produce hydrogen peroxide that result in the oxidisation of iron in haemoglobin to green methaemoglobin. These include Streptococcus pneumoniae and Streptococcus viridans.
Beta haemolytic streptococci produce streptolysin, an exotoxin that results in complete lysis of red blood cells. Beta haemolytic streptococci are further subdivided into Lancefield groupings, the most clinically relevant of which are group A and group B.
Group A streptococci, namely Streptococcus pyogenes, cause both noninvasive and invasive infections. Noninvasive infections include pharyngitis, impetigo and scarlet fever. Invasive infections include toxic shock syndrome, necrotising fasciitis and pneumonia. Group A infections can be complicated by acute rheumatic fever and post-streptococcal glomerulonephritis.
Group B streptococci, namely Streptococcus agalactiae, cause meningitis and pneumonia in neonates and the elderly. Often colonise the female reproductive tract.
Staphylococcus
Facultative anaerobic Gram positive cocci.
Ubiquitous on normal human skin flora.
Staphylococci can be coagulase-positive or -negative.
Staphylococcus aureus is predominantly coagulase-positive, although some atypical forms do not produce coagulase.
Staphylococcus epidermidis is coagulase-negative.
Diphtheria
Corynebacterium diphtheriae is a Gram-positive rod with clubbed ends.
It is passed as an aerosol or through skin educates.
Characterised by an oropharyngeal fibrinosuppurative exudate. It releases an exotoxin that damages heart, nerves and other organs.
Diphtheria toxin blocks host protein synthesis by ADP ribosylation.
