Thursday, October 22, 2009

22 - Runyon classification (of Nontuberculous Mycobacteria)

The Runyon classification of nontuberculous mycobacteria based on the rate of growth, production of yellow pigment and whether this pigment was produced in the dark or only after exposure to light.

It was introduced by Ernest Runyon in 1959.

On these bases, the nontuberculous mycobacteria are divided into four groups:


SLOWLY GROWING MYCOBACTERIA :

The first three groups are classified as "Slowly growing Mycobacteria".

Runyon I: Photochromogens
Runyon I organisms (photochromogens) are slow growing, and produce a yellow-orange pigment when exposed to light. Mycobacterium kansasii, Mycobacterium marinum, Mycobacterium simiae, Mycobacterium asiaticum.

Runyon II: Scotochromogens
Runyon II organisms (scotochromogens) are slow growing, and produce a yellow-orange pigment in light or in the dark. Mycobacterium scrofulaceum, Mycobacterium gordonae, Mycobacterium szulgai, Mycobacterium xenopi, Mycobacterium celatum, Mycobacterium flavescens.


Runyon III: Nonchromogenic
Runyon III organisms are slow growing, and do not produce pigment. Mycobacterium avium-intracellulare, Mycobacterium xenopi, Mycobacterium terrae, Mycobacterium paratuberculosis, Mycobacterium shimoidae, Mycobacterium genavense


Runyon IV: RAPID GROWERS : 

Runyon IV organisms are rapid growing for mycobacteria (colonies in 5 days). They do not produce pigment. Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium abscessus, Mycobacterium chelonae,   Mycobacterium thermoresistibile,  Mycobacterium peregrinum .

Some rapidly growing mycobacteria are considered "late-pigmenting".

21 - MacConkey agar



THE FIGURE ABOVE SHOWS LACTOSE FERMENTERS (TO THE LEFT) AND NON-LACTOSE FERMENTERS (TO THE RIGHT) ON MACCONKEY AGAR.

MacConkey (also McConkey) agar is a (differential) culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation.

It contains bile salts (to inhibit most Gram-positive bacteria, except Enterococcus and some species of Staphylococcus), crystal violet dye (which also inhibits certain Gram-positive bacteria), neutral red dye (which stains microbes fermenting lactose), lactose and peptone.

Alfred Theodore MacConkey developed it while working as a bacteriologist for the Royal Commission on Sewage Disposal.

Acting as a visual pH indicator, the agar distinguishes those Gram-negative bacteria that can ferment the sugar lactose (Lac+) from those that cannot (Lac-).

This medium is also known as an "indicator medium" and a "low selective medium". Absence of electrolytes serves to inhibit swarming by Proteus species.

LACTOSE FERMENTERS (LAC+) :

By utilizing the lactose available in the medium, Lac+ bacteria such as Escherichia coli, Enterobacter and Klebsiella will produce acid, which lowers the pH of the agar below 6.8 and results in the appearance of red/pink colonies.

NON-LACTOSE FERMENTERS  (LAC-) :

Non-Lactose fermenting bacteria such as Salmonella, Proteus species and Shigella cannot utilize lactose, and will use peptone instead. This forms ammonia, which raises the pH of the agar, and leads to the formation of white/colorless colonies.

SLOW LACTOSE FERMENTERS :

Some organisms ferment lactose slowly or weakly, and are sometimes put in their own category. These include Serratia and Citrobacter.

A variant, Sorbitol-MacConkey agar, (with the addition of additional selective agents) can assist in the isolation and differentiation of enteropathogenic E. coli serotypes such as E. coli O157:H7.

20 - Nagler's Reaction



At least 12 different toxins have been identified in strains of Cl. perfringens. One of these is the alpha-toxin, a lecithinase that hydrolyses the phospholipid lecithin (a component of cell membranes) to a diglyceride and phosphorylcholine.

The activity of the alpha-toxin can be demonstrated by growth on agar containing egg yolk (as a source of lecithin): an opaque zone representing insoluble diglyceride, becomes evident around colonies of Clostridium perfringens (the Nagler reaction). The activity of alpha-toxin is inhibited by anti-alpha-toxin antibody (generated by vaccination with alpha-toxoid).

The photograph provided above shows a nutrient agar plate enriched with egg yolk. Anti a-toxin was spread over half of the plate (left half) and a heavy inocula of Cl. perfringens and Cl. sporogenes were streaked across the plate at right angles to the anti alpha-toxin boundary.

Note the opaque zone on the upper right half, around the colonies of clostridium perfringens, due to insoluble diglyceride formed as a result of action of lecithinase (alpha toxin) on the lecithin of egg. THIS IS THE NAGLER'S REACTION.

The upper left half does not show this phenomenon because of presence of anti alpha toxin .antibodies.

19 - Schuffner's dots



Fine, round, uniform red or red-yellow dot's (as coloured with Romanovsky stains) characteristically observed in erythrocytes infected with Plasmodium vivax and P. Ovale, but not ordinarily found in P. Malariae and P. Falciparum infections.

Tuesday, October 6, 2009

18 - Bacteria That Cause Disease in Humans - Major categories and groups

I. Gram-negative eubacteria that have cell walls  
   Group 1: The spirochetes Treponema
Borrelia
Leptospira
  Group 2: Aerobic/microaerophilic, motile helical/vibroid gram-negative bacteria Campylobacter
Helicobacter
Spirillum
  Group 3: Nonmotile (or rarely motile) curved bacteria None
  Group 4: Gram-negative aerobic/microaerophilic rods and cocci Alcaligenes
Bordetella
Brucella
Francisella
Legionella
Moraxella
Neisseria
Pseudomonas
Rochalimaea
Bacteroides (some species)
  Group 5: Facultatively anaerobic gram-negative rods Escherichia (and related coliform bacteria)
Klebsiella
Proteus
Providencia
Salmonella
Shigella
Yersinia
Vibrio
Haemophilus
Pasteurella
  Group 6: Gram-negative, anaerobic, straight, curved, and helical rods Bacteroides
Fusobacterium
Prevotella
  Group 7: Dissimilatory sulfate- or sulfur-reducing bacteria None
  Group 8: Anaerobic gram-negative cocci None
  Group 9: The rickettsiae and chlamydiae Rickettsia
Coxiella
Chlamydia
  Group 10: Anoxygenic phototrophic bacteria None
  Group 11: Oxygenic phototrophic bacteria None
  Group 12: Aerobic chemolithotrophic bacteria and assorted organisms None
  Group 13: Budding or appendaged bacteria None
  Group 14: Sheathed bacteria None
  Group 15: Nonphotosynthetic, nonfruiting gliding bacteria Capnocytophaga
  Group 16: Fruiting gliding bacteria: the myxobacteria None
II. Gram-positive bacteria that have cell walls  
  Group 17: Gram-positive cocci Enterococcus
Peptostreptococcus
Staphylococcus
Streptococcus
  Group 18: Endospore-forming gram-positive rods and cocci Bacillus
Clostridium
  Group 19: Regular, nonsporing gram-positive rods Erysepelothrix
Listeria
  Group 20: Irregular, nonsporing gram-positive rods Actinomyces
Corynebacterium
Mobiluncus
  Group 21: The mycobacteria Mycobacterium
  Groups 22–29: Actinomycetes Nocardia
Streptomyces
Rhodococcus
III. Cell wall-less eubacteria: The mycoplasmas or mollicutes  
   Group 30: Mycoplasmas Mycoplasma
Ureaplasma
IV. Archaebacteria  
  Group 31: The methanogens None
  Group 32: Archaeal sulfate reducers None
  Group 33: Extremely halophilic archaebacteria None
  Group 34: Cell wall-less archaebacteria None
  Group 35: Extremely thermophilic and hyperthermophilic sulfur metabolizers None

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