staphylococcus
General features of Staphylococci
Gram+,- grape like clusters, grow well in culture media which contain broth or blood,they produce catalase, fac. anaerobes. the most virulent speciees:S.aureus, S. epidermidis, S.saprophyticus. nonmotile? nonspore forming. (extra points : differencation of S. aureus and S. epidermidis, S. saprophyticus.)
Classification of streptococci
1.hemolysis on blood agar(Alfa,Betta and nonhenolytic)
2.Cell wall antigen(group-specific carbohydrate or Lancefield antigen)A-U groups
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give morphological and culture charactheristic to N.gonococci
Gram- diplococci, nonmotile, nonsporforming, capsulated, Gonococci are aerobic. Optimal t for growth - 37 C, the optimal pH value is 7.2-7.4. Gonococci are demanding of nutrient media. Media containing blood,blood serum or ascitic fluid are used for their cultivation. On dense nutrient media, after 24 hours, gonococci form slightly cloudy or transparent colorless round colonies with smooth edges 1-3 mm in diameter.
Morphology
gram(-), oval or spherical cocci, 0,6-0,8 mm in size, arranged in pairs, non-motile, capsulated.
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Which of the following statements is correct?
A. Streptococci are catalase positive.
B. Growth of Streptococcus pneumoniae is not sensi- tive to optochin.
C. Streptococcus pyogenes is highly sensitive to baci- tracin.
D. Streptococci are obligate anaerobes.
E. Enterococcus faecalis is ẞ-hemolytic.
Correct answer = C. Streptococcus pyogenes is highly sensitive to bacitracin, and diagnostic disks with a very low concentration of the anti- biotic inhibit growth in culture.
All streptococci are catalase negative.
The growth of Streptococcus pneumoniae is inhibited by optochin.
Most streptococci are aerotolerant anaerobes, and grow fermentatively even in the presence of oxygen.
Enterococcus faecalis is y hemolytic (no hemolysis).
Koch’s Postulates
Koch theorized that a pathogen must be:
found in all cases of the disease examined
prepared and maintained in a pure culture
capable of producing the original infection, even after several generations in culture
retrievable from an inoculated animal and cultured again
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Culture characteristics
They are aerobes but growth is facilitated by 5-10% CO2, and high humidity. The optimum temperature for growth is 35-36°C and optimum pH 7.4-7.6.
On solid media, after incubation for 24 hours, the colonies are small (about 1 mm in diameter) trans- lucent, round, convex, bluish grey, with a smooth glistening surface and with entire edges. The colonies are typically lenticular in shape, butyrous in consistency and easily emulsifiable. Weak hemolysis occurs on blood agar. Smooth and rough types of colonies are found. Growth is poor in liquid media, producing a granular turbidity with little or no surface growth.
Blood agar, chocolate agar, Thayer-Martin medium and Mueller-Hinton starch casein hydrolysate agar are used to culture meningococci.
Lab diagnoses and epidemiology
specimens collection, Direct microscopy-Gram staining, culture. identification by biochemical tests, serologucal test
The mode of transmission may be by contact, direct or through fomites, by dust or airborne droplets.
the main source of infection are human and carriers.
Toxins of Streptococci
Hemolysins(Streptolysins O and S),Streptococcal pyrogenic exotoxin, Streptokinase(fibrinolysin), Deoxyribonucleases(streptodornase), Hyaluronidase and other enzymes
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Which one of the following media is most suitable for identifying Neisseria gonorrhoeae in a cervical swab?
A. Sheep blood agar
B. Chocolate agar
C. MacConkey agar
D. Thayer-Martin medium
E. Hektoen enteric agar
Correct answer = D. Thayer-Martin medium, which is composed of chocolate agar supple- mented with several antibiotics, suppresses the growth of nonpathogenic Neisseria and other normal and abnormal flora, but permits the growth of gonococcus.
Sheep blood agar sup- ports the growth of most bacteria, both gram- positive and gram-negative.
Chocolate agar provides the growth requirements for fastidious organisms such as Haemophilus influenzae or Neisseria gonorrhoeae, as well as for most other less-fastidious bacteria.
MacConkey agar supports most gram-negative rods, especially the Enterobacteriaeceae, but inhibits growth of gram-positive organisms and some fastidious gram-negative bacteria, such as Haemophilus and Neisseria species.
Hektoen enteric agar is also a selective medium often used to culture Salmonella and Shigella species.
Laboratory identification
Spesimen- from CSF and skin lesion, blood, nasopharyngeal swab, Culturing should be done in chocolate agar with increased CO2.
Serology (detection of antibodies to the polysaccharide antigen)
molecular diagnosis: PCR
additional tests: for differentiation all N.species -sugar utilization tests are used. N.meningitidis utilize both glucose and maltose, but N. gonorrhoeae uses only glucose.