It is possible to establish some components of the pathogen or particular metabolic products like toxins (poisons) relatively quickly. There is a whole range of laboratory methods for this. For example the laboratory technician mixes anti bodies against particular components of the pathogen, so called antigens in a sample. These antibodies are connected to visible materials, for example latex particles. If the specific antibodies attach themselves to the sought for antigens, a clotting is visible with the naked eye. Such quick tests can give valuable indications, but are also quite inexact and error-prone. The results are best interpreted in context with further microbiological tests.
A further method to obtain evidence of a pathogen is the cultivation of cultures. This examination needs more time. Even for germs which are easy to cultivate, the results of the culture can first be expected after approx. two days. Slowly growing germs, like the pathogen of tuberculosis or fungi take much longer, in certain circumstances several weeks until they can ultimately be defined. Some germs are not possible to cultivate using the usual methods.
Pathogen cultures (mainly bacteria and fungi)
From the culture, living pathogens from the sample should grow and multiply on the artificial breeding ground. (culture medium) These germs can then be exactly identified by the doctor using further investigation techniques and also their sensitivity to medicines can be tested (e,g, antibiotics).
The composition of the culture medium plays an important role for the diagnosis of the pathogen. Culture mediums contain water, nutrients, energy sources and trace elements as well as various materials, which germs need to be able to multiply. A gelling substance (agar-agar) gives the culture medium stability. The exact composition is determined by the requirements of the germ which is being sought:
• Most germs can grow on universal medium.
• Only particular germs can survive on selective medium.
• Indicator medium are coated with additives, which colour particular germs.
Selective- and indicator medium are used to identify pathogens from samples which contain other germs. For example smears of the skin and mucus membranes always contain the natural germ flora.
Doctors also use UV-C –light
Dosage, impact and risk-free use of UV-C – radiation
Which beams act as a bactericide?
The sun is adjudged to have healing qualities from time immemorial. But only in 1878, was it recognised by two researchers, Arthur Downes and Thomas P. Blunt, that microorganisms stopped multiplying under strong sunlight. After this discovery it still took a long time before a specific wavelength dependence with a maximum reaction for the range of 250-270 nm was realised, a portion of the UV-rays from the shortwave C-band (UV-C).
The key to an explanation has only existed since the 1950’s with the discovery of the structural composition of the DNA (Desoxyribonucleic acid) as a double helix by the researchers James Watson and Francis Crick.
The double helix structure of the DNA is based on a purine and pyrimidin pairing. These basic pairings are the porters of information of the DNA and these are differentiated between the four bases adenine, thymine, guanine and cytosine. The research of the following years concluded that the short wave and energy rich UV-C – radiation primarily created a photo chemical reaction with the thymine. This dimerisation (this means: two adjacent information carriers linked or glued).Through this molecular alteration the DNA becomes factually unusable for the essential biological process of transcription (preservation of the metabolism) and replication (cell division). Such an adequately damaged cell eventually dies.
Why does UV-C –radiation destroy germs?
In the inhibitory function of the UV-C –technology lies the primary difference to the chemical, mostly oxidative disinfection method. It is the central reason why a mutation based resistance development is not possible.
Connection between dosage and impact
The impact of the disinfection method based on UV-C – radiation is directly connected with the dosage used (= time x radiant energy / surface). High intensity over a short period of time or lower energy over a longer period of time are practically interchangeable und almost equivalent in the disinfection effect. The dosage as decisive parameter is indicated in µW*s/cm², often also as J/m².
The fundamental rule is: The simpler the microorganism structure is, the easier it is to disable them with UV-C – radiation. Therefore it is much easier to destroy viruses or bacteria (prokaryotic cells), than complex microorganisms like yeast or vegetative fungi (eukaryotic cells).
Fungi spores, whose DNA is protected by a pigmented cell wall and a concentrated cytoplasm, can only be disabled by an extreme dosage of UV-C.
Effect on humans
An increased radiation dose of UV-C –light causes skin redness (erythema) and painful eye infection (conjunctivitis).
For these reasons, the EU recommended limit (EU directive 2006-25-EG) of 6 mJ/cm², respectively. 60 J/m² daily exposure (at 253,7 nm) not be exceeded. It is important to take care with adequate protection!
In contrast to UV-A or UV-B – radiation, the penetration depth of UV-C – radiation in the human skin is very limited. The danger of skin cancer therefore can therefore, also when subjected to intensive UV-C – radiation (with unprotected body parts) be assessed as low. Scientific proof of the direct connection has not yet been found.
Risk free usage of UV-C
UV-C – radiation does not penetrate solid objects , also no window glass (borsilicate, duran) or
Transparent plastics (acrylic glass, polystyrene, etc.)!
As the visible wavelengths of light, the UV-C – rays move in straight lines and the quality of their intensity deteriorates clearly with increased distance from the source.
The further one is from the UV source, the less dangerous it is. For devices with sight protection strips or in fully enclosed cabinets there is never an immediate danger.
Should a direct sight or skin contact with an unenclosed UV-source be unavoidable, then simple measures like safety glasses or sun cream with a high protection factor are fully adequate.
Hygiene in hospitals: doctors use UV-C – light
For the control of dangerous hospital germs, US doctors also want to use UV-C – light. A test in clinic rooms showed that special lamps destroyed commonly present germs.
The fact that UV-C – light can eliminate bacteria, is not new knowledge, but in the face of increasing problems with antibiotic resistant germs, this knowledge is once again valuable. At a conference on the subject of hospital hygiene in San diego, California, the "IDWeek", doctors reported how effective UV-C – lamps can be in the struggle against the germs.
The scientists of Deverick Anderson from the Duke University in Durham have concretely examined how the radiation effects three commonly found hospital germs: Clostridium difficile, a bowel bacteria, that under certain circumstances can cause severe diarrhea, The genre acinetobacter, which can cause pneumonia or wound and urine infection in people with weakened immune systems and enterococci, which are resistant against the antibiotic vancomycin (VRE). They can lead to severe infections in patients in the intensive care unit.
99,80 - 100,00 percent less viable germs
Altogether the doctors selected 50 hospital rooms, in which patients with at least one of these infections previously were. There were some rooms in intensive care units and some rooms from other wards. The researchers collected samples from various surfaces in these rooms including the remote control, the toilet and the handles on the bed. Afterwards, in the middle of the room, they installed a lamp with eight UV-C – tubes installed on a central light and left the light in operation for 45 minutes. After this, they took renewed samples from the surfaces.
The number of viable germs on the surfaces was reduced drastically through the radiation treatment – it sank by around 98 percent, as reported by the scientists. Already in a previous study, a similar treatment showed that also the feared hospital germ MRSA can be combatted with UV-C – light, Anderson reported.
"We would naturally never propose that the rooms should be cleaned exclusively with UV-C – light ", stressed Anderson. Precisely when considering the increasing number of bacteria which are no longer affected by conventional antibiotics, the lamps could prove an important additional method in the hospital arsenal. The UV-C –disinfection has the advantage that no personnel are necessary and no additional chemicals need to be used. It is also not to be expected that the germs will become resistant against the treatment. Decisive is, that the lamps emit the shortwave UV-C - radiation, according to the doctors. UV-C – light has already been used for several years in laboratories and for the disinfection of air and liquids.
UV-C – light helps, to eliminate germs in hospital rooms
UV-C –light for fighting germs
Despite high hygiene standards, germs in hospitals are a serious danger for patients. To combat the pathogens, scientists have investigated the use of UV-C – light and achieved promising results.
UV-C - light makes germs harmless
Already for many years UV-C – light has been used for disinfection in laboratories. Now researchers from the Duke University in Durham, USA have investigated the application of UV-C – light against germs in hospital rooms for the first time. Hospital germs accumulate on various surfaces by frequent touching, for example the bed frame or the telephone. The researchers concentrated on the three most common hospital germs which cause, for example severe diarrhea, pneumonia and various wound infections.
The study supervisor, Deverick Anderson and his team installed lamps with shortwave UV-C radiation in 50 hospital rooms where infected patients previously were and radiated the rooms for 45 minutes.
The result: The UV-C –radiation made 98 percent of the hospital germs harmless.
Useful additional measures
The researchers emphasise that the radiation with UV-C –light should in no way replace the current disinfection measures. With the increasing number of resistant pathogens where current antibiotics are ineffective, UV-C –lamps can prove to be an ‘additional weapon’ to combat the germs.
A particular advantage of the UV-C – lamps is that their use does not require either personnel or chemicals!
Evidence of infectious agents (germ evidence)
Bacteria, viruses and fungi can cause serious illness. To be able to successfully treat such infections, doctors often identify the germ in the laboratory.
From Dr. med. Dagmar Schneck, updated on 03.06.2014.
One can breed bacteria cultures with culture mediums Panthermedia/Andreas T.
Stomach pain, diarrhea, fever – we can have such and other ailments if we are infected with pathogens. How does the doctor find the correct treatment for these ailments? On many occasions it is possible with a comprehensive questioning and physical examination, often supplemented by various blood tests, to obtain an impression of the illness and to decide on a suitable therapy. To be able to decide on the most effective medicine, the doctor must often know exactly, which pathogen has caused the symptoms. A wrong diagnosis is not only ineffective but can also be harmful.
How can the doctor identify pathogens?
Doctors identify the pathogens through the investigation of body fluids, stool samples or wound swabs. First indications are often evident from observation under the microscope. Laboratory analysis can sometimes identify the germ itself, sometimes their components, their metabolic products or also disease causing poisons (toxins) which can produce several types of bacteria. It is often possible to breed bacteria and fungi as ‚cultures‘ using various culture mediums". Doctors identify virus infections from particular antibodies. Antibodies are defence materials, which the body produces against elements of pathogens (so-called antigens).
When is an evidence of germs necessary?
A germ evidence serves on the one hand, with acute illness, to find a diagnosis. The germ evidence can also be important for people without illness if, for example in a food processing factory the workers need to be tested for salmonella. Or if it needs to be tested whether particular patients who are to be registered in hospital bring resistant bacteria with them. Also when several people in a community institution suffer from the same symptoms, the germ evidence can help to find the route of the infection.
Prerequisite for the germ evidence: a suitable sample
Many germs are identifiable with the appropriate examination samples. Examples of samples are wound swabs, stool samples, body fluids like urine, spinal fluid, secretions from the airways and a special type of blood test (blood cultures). These samples must not be contaminated with other germs from the surroundings. Therefore precautions must be made when extracting the samples and the preservation in suitable receptacles. The samples should also be sent quickly to the investigating laboratory so that the result is not falsified by long preservation times or inappropriate conditions. The most samples are taken by trained medical specialists. Some samples can also be extracted by patients, for example stool samples or the first daily urine.
Which samples are necessary to identify the pathogen is dependent upon the illness of the patient. Pathogens for infection of the urinary tract can be found in a urine sample, for a meningitis the germs can be found in the spinal fluid. For serious infection of the heart circulation system, like an inflammation of the heart valves, blood poisoning by serious organ infection or an infected vessel catheter, the germs can possibly be found in the blood. Also the time at which a sample is taken is important. The chances of identifying germs in the blood are at their best when the blood is taken shortly before or after an acute fever thrust.
Investigation steps in the microbiological laboratory: microscopy, quick tests, cultures
Many investigation tests are carried out in the laboratory, With the optical microscope, the sample can be examined when it is still fluid and hasn’t been used. This is the so called native preparation.
In addition the laboratory staff often produce dried preparations coloured with various dyes (e.g. the gram stain and further special colourations).It often possible to radically limit the spectrum of possible pathogens using this examination. The doctor can often recognise the presence of bacteria, fungi and parasites using the optical microscope. Viruses are too small to be identified in this way. Although typical changes in body cells are visible in the samples, which give an indication of a particular virus. The results of a microscopic analysis is often available inside one hour.
Important instruments for defining germs:
The microscope photo disc/RYF
Most cultures are „bred“ in a heat cabinet for about 48 hours. If the doctor suspects slow growing germs as the pathogens (e.g. legionella, mycobacteria or fungi), then longer breeding times are possible, partly up to several weeks. Longer breeding time are also usual for blood cultures.
Formation here: Pneumococci
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