Lecture 8 _ BMMS3001BacteriologyMycologyLabManual2017.pdf

S aureus is coagulase positive demonstrated 2

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Colonies on solid media are round, and sometimes with golden yellow pigments. S. aureus is coagulase positive (demonstrated). 2. Staphylococcus epidermidis on blood agar Cultures of S. epidermidis are rarely pigmented. The organism is coagulase negative (demonstrated). 3. Streptococcus pyogenes on blood agar and Gram smear Streptococcus pyogenes are Gram-positive spherical cells, characteristically arranged in chains. The organism produces soluble hemolysins that result in beta-hemolysis (complete disruption of erythrocytes) on blood agar. Sensitivity to bacitracin is shown. 4. Streptococcus pneumoniae on blood agar and Gram smear The pneumococci are gram positive diplococci, often lancet-shaped and arranged in chains. They are alpha-hemolytic on blood agar. Sensitivity to optochin is shown. 5. Enterococcus faecalis on blood agar This group of bacteria vary in their hemolytic reaction; most strains are non-hemolytic, but alpha- and beta hemolytic strains are found.
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6 B. Gram negative cocci Neisseria gonorrhoeae on Thayer-Martin agar and Gram smear of urethral discharge The typical Neisseria organism is Gram-negative cocci, usually occurring in pairs. Individual cocci are kidney-shaped. Thayer-Martin agar containing antibiotics favors the growth of Neisseriae by inhibiting many other bacteria.
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7 Aerobic Gram Positive and Gram Negative bacilli A. Gram positive rods Three common aerobic Gram-positive rods are shown here with different clinical significance. 1. Corynebacterium diphtheriae on tellurite agar and Gram smear Different culture media are used for primary isolation and differentiation. Tellurite agar is both a selective and differential agar to inhibit the oral flora and to reveal different morphologies of the subspecies of C. diphtheriae . Loeffler medium is another differential medium to show the characteristics of the organism and allow development of metachromatic granules for microscopic demonstration. On Gram staining, the bacteria appear as Gram-positive club shape organisms arranged in palisades (Chinese characters). Albert stain is a special stain to demonstrate metachromatic granules for the identification of the organism at the subspecies level. The Elek plate is to demonstrate the production of diphtheria toxin by a pathogenic strain. Some C. diphtheriae are non-toxigenic and do not cause systemic disease. However once they acquire the toxin gene, they are equally able to induce disease. The vaccination programme in Hong Kong is very effective and diphtheria is virtually unknown here. Why do we need to study this organism? The other Corynebacterium spp . generally called diphtheroids can be found on the skin and are usually reported as contaminants. Do you know any disease for which they may be responsible? 2. Bacillus on blood agar and Gram smear Gram smear, a typical appearance of Gram-positive organisms, being large, straight and round- or square-ended rods and are spore-forming organisms.
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8 They can be found in the environment and contaminate specimens, wasting a lot of resources if specimens are not taken carefully enough.
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  • Fall '14
  • MauriceK.S.Tse

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