Tại sao pH của môi trường vi sinh sau khi pha khác với pH ghi trên nhãn? (Why do I get a different pH from the one stated on the products label?)

 There are a number of reasons that can influence the pH. One is "overheating". Inadequate or unsuitable water may be another reason. pH-determiantion may have done incorrectly also. Lastly, a contamination from the container itself may have contributed to changing the pH.

 
Overheating may happen because of:
• Excess sterilization
• Heterogeneous mixing
• Repeated re-melting
• Improper storage
Make sure that the heating time and temperature are not exceeded and work under ambient conditions.
 
Unsuitable Water
As to the water, the following should be taken into consideration:
The purified water used should show a conductivity of less than 15 µS and a pH of between 5.5 and 7.7. De-ionisers are being regenerated with acids and alkalis and residue of this HCl in the purified water may cause the pH of the medium to drop. Water, when not fresh, may have absorbed CO2 from the atmosphere.
 
pH-Determination
Culture media composition is adjusted to give the right pH after reconstitution and sterilization. Should the medium be supplemented, the pH limits apply to the complete medium. The adjustment should not be done prior to autoclaving.
 
Reasons for obtaining a different pH reading may be due to:
• pH measurement at temperature out of the specifications (10°-37°C)
o Allow the medium to cool, and check again at specific temperature
• Improper electrode
o Agar products, at ambient temperature, will be in solid form and require the use of a flatbottomed pH probe, in order to facilitate measurement. The use of temperature compensation is not recommended. We suggest a combined electrode with following specifications:
o pH range : 2.0 to 11.0
o Working temperature range : 0.0 to 80°C
o Reference electrolyte : polymerized and without AgCl
o Diaphragm : open
o Expected life : 4 to 6 months or depending on the use.
• Broths are liquid and we recommend pH probes that are resistant to proteins and with fast readings, like the ones of triple ceramic diaphragm and greater sensitive membrane surface area with the following specifications:
o pH range : 0.1 to 12.0
o Working temperature range : 0.0 to 100oC
o Reference system : crystals of Ag / AgCl encapsulated, CRISOLYT-G electrolyte
o Diaphragm : 3 types of ceramics
o Expected life : 1 year or more if used correctly.
• Electrode used is not properly calibrated
Please re-calibrate the pH meter with Scharlau pH buffer solutions
Temperature compensation
We do not recommend the use of temperature compensation.
 
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“Chứng nhận Phù hợp an toàn” là gì? (What is a "Certificate of Suitability"?)

The Certificate of Suitability assures the buyer for the absence of BSE.

The Certificate of Suitability is granted by the Committee of European Directorate for the Quality of
Medicines (EQDM) of the European Pharmacopoeia.
It is granted to manufacturers of raw materials only and given for every single raw material and not to the company.
For this, the raw material company has to be ISO 9000 or GMP certified.
Every time any raw material or process is changed, or after its validity period, the manufacturer has to again apply for a renewal.
BSE should be of no concern, since culture media are not ingested. However, in the pharmaceutical industries, sterility validation of the filling machines have to be done periodically. This is done by passing broth media through the filling machinery (aseptic media fill experiments). Thus, if these media are contaminated with BSE, it could be transmitted to humans or animals through the medicines.
 
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Bệnh BSE là gì? (What is the BSE disease?)

BSE is the abbreviation of a disease called Bovine Spongiform Encephalitis, also called Transmissible Spongiform Encephalitis or Mad Cow Disease, which is mainly contracted by cattle.

In sporadic cases sheep have also been infected.
Originated in the U.K. and then got spread to several other European countries.
This disease is not found in Australia, New Zealand and USA.
The prions causing this disease can get into the culture media through the raw materials of bovine origin, like meat peptones, meat extracts, proteose peptone, bile and bile extracts, etc.
Note, that Casein peptone is made from milk and milk is devoid of BSE prions. For converting milk into casein an enzyme is required, which is of non-bovine origin. Hence BSE free certification is not required for Casein peptone.
Upon its alarming threat, the media manufacturers in Europe have started using raw materials of bovine origin from Australia, New Zealand and USA.
 
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Những rủi ro nào khi tôi làm việc với môi trường vi sinh? (What risks am I exposed to when working with culture media?)

The majority of culture media are harmless. Only some media, that contain selective agents like sodium azide or bi-selenite, can be regarded somewhat toxic and require to work with a safety mask.

The main threat may come from the manipulation of pathogenic micro-organisms. Protect yourself by working under laminar air flow cabinets and use glasses, masks and gloves.
 
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Những rủi ro nào khi tôi làm việc với môi trường vi sinh? (What risks am I exposed to when working with culture media?)
  • The majority of culture media are harmless. Only some media, that contain selective agents like sodium azide or bi-selenite, can be regarded somewhat toxic and require to work with a safety mask.
  • The main threat may come from the manipulation of pathogenic micro-organisms. Protect yourself by working under laminar air flow cabinets and use glasses, masks and gloves.
 
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Tôi có nên dùng lò vi sóng để đun sôi môi trường vi sinh không? (Should I use the Microwave oven for boiling the media?)

There is an increasing tendency to use this technique for heating or boiling media more rapidly.

We do not recommend this technique as such, because :
  • It is based on the principle of collision of the molecules (especially water molecules) and thereby generating a tremendous heat within a very short period of time.
  • The point at which the medium starts boiling is difficult to observe.
  • Rapid heating may not dissolve the medium uniformly and may cause overheating.
  • Uncontrolled heating may lead to the decomposition of the nutrients and also to spillage.
  • Hence, gradual and monitored heating with conventional heating devices is our recommendation to boil media.
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What are the possible causes for a loss of growth promotional or differential properties?

 

  • Overheating.
  • Repeated melting-overheating.
  • Inadequate or improper mixing.
  • Disturbance of the formula by the inoculum itself (addition of inhibitors or excessive electrolytes during inoculation)
Please also check the expiry date on the bottle and the general aspect of the medium in dry form. Humidity may degrade peptones contained in the formula. Contact with air may have oxidized any of the supplements. Exposure to sunlight may have altered the colour of the medium. Make sure each bottle is properly closed after each use and stored in a dry place guarded from direct sunlight.
 
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Đệm là gì? (What are buffers?)

Buffers are chemical substances, which contribute to keeping specific solutions within a tight range of pH, even if acids or bases are added to them.

There are various types of buffers.
The main types included in the formulas of culture media are phosphate and chloride salts of potassium and sodium.
 
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