Algunos medios para cultivo de microbios.

Nutritive agar

CHARACTERISTICS General medium. No bacterial growth inhibitors. Final pH = 7.3±0.2. Color: light to medium amber, slightly opalescent.

COMPOSITION (g/L) Pluripeptone: 5 (source of C and N) Meat extract: 3 NaCl: 8 Agar: 15

PREPARATION Suspend in H~2O. Mix and let rest for 5 min. Heat gently while sahking and boil 1 to 2 min until its complete dissolution. Distribute and sterilize 15 min at 121 ºC.

Blood gelose base

CHARACTERISTICS Highly nutritious medium, fit for organisms with high nutrition needs. NaCl keeps osmotic balance. Final pH = 7.3±0.2. Color: amber (with blood, cherry red).

COMPOSITION (g/L) Heart muscle infusion: 375 Peptone: 10 NaCl: 5 Agar: 15 Optional: 5-10% blood. It adds some extra nutrients and allows detection of hemolysis.

EMB

CHARACTERISTICS || Medium for isolation of fast-growing Gram- bacilli with low nutrient needs. It allows development of all species from family Enterobacteriaceae, which includes Escherichia, Salmonella, Shigella, Yersinia, Proteus, Enterobacter, etc. pH = 7.2±0.2. It contains Gram+ growth inhibitors.

• Bacteria which use lactose and/or sucrose: dark center, blue periphery.
• Not using lactose or sucrose: colorless.
• E. coli: metallic green, blue-black center.
• Citrobacter: metallic look.
• Klebsiella pneumoniae: moldy, purple-rose, confluent.
• Proteus mirabilis: colorless.
• Candida: pink and pointy.
• Enterococcus faecalis: small, pointy, transparent.
• Salmonella typhimurium: colorless.
• Shigella flexneri: colorless.

COMPOSITION (g/L) || Peptone: 10 | Lactose: 5 | Sucrose: 5 | Dipotassium phosphate: 2 | Agar: 13.5 | Eosine: 0.4 | Methilene blue: 0.065

PREPARATION || Suspend in H~2O. Mix and let rest for 5 min | Heat gently while stirring, and boil 1 - 2 min until it disolves | Sterilize 15 min at 121 ºC | Cool down to 45 ºC and distribute while gently shaking.

Mac Conckey

CHARACTERISTICS Easy-growing gram- bacilli, aerobes or facultative anaerobes. pH = 7.1±0.2. pH lowers around the colony due to lactose fermentation. Non lactose fermentators yield colorless colonies. I contains gram+ growth inhibitors. Color: purple red.

E. coli: red with a turbid halo.

Klebsiella pneumoniae: pink, moldy.

Salmonella typhimurium: transparent.

Shigella flexneri: transparent.

Proteus mirabilis: transparent.

Enterococcus faecalis: tiny, colorless, opaque.

COMPOSITION (g/L) || Peptone: 17 | Pluripeptone: 3 | Lactose: 10 | Bile salt mix: 1.5 | NaCl: 5 | Agar: 13.5 | Neutral red: 0.03 | Violet crystal: 0.001

PREPARATION || Suspend in H~2O. Let rest for 5 min and mix. Heat gently and boil for 1 o 2 min until disolved. Sterilize 15 min in autoclave at 121 ºC.

Staphylococcus 110

CHARACTERISTICS || Selectivo medium for Staphylococcus. pH = 7.0±0.2. NaCl inhibits development of other species. Color: light amber, opalescent with precipitate.

COMPOSITION (g/L) || Yeast extract: 2.5 | Tryptein: 10 | Gelatin: 30 | Lactose: 2 | D-Manitol: 10 | NaCl: 75 | HK~2PO~4: 5 | Agar: 15

Salt and manitol

CHARACTERISTICS || Selective medium for Vibrio and Staphylococcus. pH = 7.4±0.2. Color: red.

S. aureus: yellow (it ferments manitol and lowers pH)

S. epidermidis: red (does not ferment manitol)

COMPOSITION (g/L) || Meat extract: 1 | Pluripeptone: 10 | D-Manitol: 10 | NaCl: 75 | Agar: 15 | Phenol red: 0.025

PREPARATION || Suspend in H~2O. Let rest for 5 min and mix. Boil for 1 to 2 min. Distribute and sterilize in autoclave 15 min at 121 ºC.

Salmonella Shigella

CHARACTERISTICS || Selective medium for Salmonella and some species of Shigella. pH = 7.0±0.2. Contains growth inhibitors for Gram+, coliforms and Proteus. Color: red to orange.

Salmonella typhimurium, Proteus mirabilis: transparent, black center (H~2S)

Shigella flexneri, S. sonnei: transparent

Escherichia coli: pink to red

Klebsiella pneumoniae: pink, creamy, moldy

Enterococcus faecalis: colorless, very little growth

Pseudomonas aeruginosa

COMPOSITION (g/L) || Pluripeptone: 5 | Meat extract: 5 | Lactose: 10 | Bile salt mix: 8.5 | Sodium citrate: 8.5 | Na~2S~2O~3: 8.5 | Iron citrate: 1 | Agar: 13.5 | Shiny green: 0.00033 | Neutral red: 0.025

PREPARATION || Suspend in H~2O. Let rest 5 min and mix. Boil 2 to 3 min. Do NOT sterilize in autoclave. Cool down to 45-50 ºC and distribute about 20 ml/dish. Dry medium surface for several minutes in the stove.

Sources