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.

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