Frequently asked Exam Questions on Medical Microbiology!
Exam Question # Q.1. What do you mean by Sterilization?
Ans. Micro-organisms are found at each and everywhere, causing contamination, decay and infection. In order to maintain healthy atmosphere we need to kill them.
So sterilization is the process of destruction, removal elimination and inactivation of all forms of microbes from culture media and body surfaces etc. the methods of sterilization employed, depends on the purpose for which it is carried out, the material which has to be sterilized and the nature of micro-organisms that are to be removed and destroyed.
Disinfection:
Disinfection is the process adopted for the destruction and removal of all forms of microbes, capable of giving rise to infection.
Sanitation:
It is the same process used as a synonym for disinfection, particularly with reference to the food production and catering lab, as well as the operation theatres.
Antisepsis:
Antisepsis is the term, associated with the sterilization, used to inhibit the growth of bacteria in wounds or injuries.
Chlorination:
Bromination (Halogenation) and decontamination are also same terms related to destroy and kill and remove all forms of micro-organisms from water, commodities, containers and culture media etc.
Pasteurization:
Pasteurization is also one specialized form of sterilization, associated with the milk and milk products, meant to destroy microbes from the above through rising temperature up to 68″C and cooling down through condensation and finally packing them.
Fumigation:
Fumigation is also one way to sterile (destroy microbes from the entire containers and spaces) through the introduction of fumes or gases. It efficiently removes and destroys all forms easily and rapidly from the hospital wards, goes downs, galleries, operation theaters and laboratories etc.
Exam Question # Q.2. What are the difference between Antiseptics and Disinfectants?
Ans. A wide range of chemicals used to destroy all forms of micro-organisms are termed as antiseptics and disinfectants, they should have following characteristics:
1. The antiseptics and disinfectants should have a wide spectrum of activity and be effective against all forms of micro-organisms i.e. vegetative spore, cystic and larval or oral form.
2. They should have high penetration power.
3. They should react in presence of organic matters.
4. They should always be effective in acidic as well as alkaline media.
5. They should not cause any considerable harm to our body, if applied.
6. They should be cheaper and easily available in the open market.
7. They should not be toxic if absorbed into circulation.
8. They should be compatible with other disinfectants.
Factors Influencing Antiseptics and Disinfectants:
The antiseptics and disinfectants are influenced by pH, temperature, concentration time of action nature of organism to be destroyed and presence of organic matter.
They have been divided into three groups:
1. High level disinfectants.
2. Intermediate level disinfectants and
3. Low level disinfectants.
1. High Level Disinfectants:
E.g. Gluteraldehyde, H2O2 and chlorine compounds. They are used to disinfect the equipment with plastic components which cannot be sterilized.
2. Intermediate Level Disinfectants:
E.g. Alcohols and phenolic compounds, these types of disinfectants are capable to destroy vegetative forms from the surfaces of equipment. So they are used to disinfect the equipment like laryngoscope, where contamination with spores is unlikely.
3. Low Level Disinfectants:
E.g. KMNO4, K2Cr2O7, spirit, they either destroy some forms of lower organisms or inactivate them. So they are used to disinfect stethoscopes, electrocardiogram electrodes etc.
Exam Question # Q.3. What are the Mode of Action of Disinfectants and Antiseptics?
Ans. 1. The High Level Disinfectants:
They have high penetration power, rupture the microbial cell wall and denature the nucleoprotein, and bring about complete destruction of vegetative form cystic form, spore from, eggs and larval forms of all types of micro-organisms i.e. Bacteria, Fungi, Protozoa and viruses. They have got vide spectrum of destruction of microbes being better bactericidal, fungal, protozoal and viricidal effects and less volatile effects.
Uses:
They are-used for preservation of tissues for histological examinations to sterile bacterial vaccines, to prepare toxoid from toxin and to kill bacteria and all forms.
2. The Intermediate Level Disinfectants:
They are of less penetration power and are efficient to kill only the vegetative forms by penetrating the cell wall of microbes. They do not destroy the nucleoprotein and cyst wall as well as the spore wall.
Uses:
These type of disinfectants and antiseptics are used to sterile the instruments which do not go in depth of tissues, instead they reach the internal organs like larynx etc.
3. The Low Level Disinfectants:
They do not even destroy all vegetative forms. They bring about dehydration in microbes that is why making them unconscious and inactivated.
Uses:
They are used to sterile the instruments and apparatuses which are never inserted into the tissues they always remain outside the tissue. The instruments like stethoscope, cardiogram electrodes are taken under sterilization by above disinfectants.
Exam Question # Q.4. How to Test Efficiency Working of Disinfectants?
Ans. Followings four methods/tests have been adopted for testing of disinfectants and antiseptics:
1. Rideal Walker test.
2. Chick Martin test.
3. Kelsey-Sykes test (capacity test).
4. In-use tests.
1. Rideal Walker Test:
In this test suspensions containing similar quantities of organisms are submitted to the action of varying concentration of phenol and of disinfectants to be tested. The dilution of the test disinfectant which sterilizes the suspensions in a given time is divided by the corresponding dilution of phenol.
This gives the phenol coefficient. The phenol coefficient of 1.0 means that the test disinfectants have been as effective as phenol. Higher the phenol coefficient more effective is the disinfectants.
2. Chick Martin Test:
In this test disinfectants acts in the presence of organic matter to simulate natural conditions. Organic matter in the form of dried yeast or feces is included.
3. Kelsey-Sykes Test (Capacity Test):
It gives a measure of capacity of a disinfectant to retain is activity when repeatedly used microbiologically. The standard organism (staph aureas, E. Coli. etc.) is added to the disinfectant in three successive lots at 0, 10 and 20 minutes.
These three lots are kept in contact with the disinfectant for 8 minutes. These three are transferred at 8, 18, 28 minutes respectively to a recovery medium. The efficiency of disinfectants is judged by its ability to kill bacteria.
4. In-Use Test:
The liquid phase of disinfectant solutions in actual use in hospital practices is examined quantitatively for viable organisms. A use dilution is then disinfectant is determined by its ability to inactive a known number of standard strain of a pathogenic staphylococcus on a given surface within a certain time. The result of such test is more useful than those of the phenol coefficient test and its modifications.
Exam Question # Q.5. Why Disposal of Contaminated need Proper Management?:
Ans. Waste and contaminated material include syringes, knives, blades and thermometer. This waste may be:
1. Household non-infected.
2. Infected waste.
In household non-infected waste these are no need to decontaminate them. While infected waste require proper management. Place in puncture proof container, containing 1% of bleach, prepared every morning and then finally dispose it off.
(i) All liquid bacterial cultures must be sterilized before disposal. Generally this should be achieved by autoclaving.
(ii) All autoclaving of waste MUST be carried out in a designated waste autoclave which has been performance-tested. Autoclaved liquid waste may be discharged to drains.
(iii) Plastic tubes, Universals and Petri dishes for autoclaving must be placed in double thickness, open autoclave bags and the bags contained in strong autoclavable plastic or steel containers to retain any liquids (especially molten agar) during autoclaving.
(iv) After autoclaving, drain off excess liquid and dilute with hot running water to drains, tie off the bags, attach a “Safe for Disposal” sticker to each bag, place them in a black bin bag, and take them to the skip in the basement.
(v) Contaminated syringes, needles and sharps are to be placed in Sharp safe containers and dealt with according to normal procedures.
Exam Question # Q.6. What are the Rules and Regulations for Waste Disposal?
Ans. (a) If the Material is Uncontaminated:
Uncontaminated carcasses or tissues are those that have not been exposed to fixative or other chemical agents originating from animals that have not been administered with drugs or other laboratory chemicals. Such material should be returned to the animal house for maceration in a plastic bucket or bag.
If the material cannot be returned immediately the bucket or bag should be labeled with the name of the user and stored in a designated fridge or cool room until this can be done. The bags should contain no swabs or disposable gloves or sharps.
(b) If the Material is Contaminated:
As disposal of contaminating chemicals, radioisotopes or micro-organisms is part of risk assessment.
If the material is contaminated with chemicals. This applies to carcasses or tissues which have been exposed to fixatives or any other laboratory chemicals, or in the case of animals, which have had pharmaceuticals or any other chemicals administered to them.
Material in this category (excluding radioactive waste) should be sealed in a bag with a tag identifying the user and placed in a yellow biohazard bag in a designated fridge or cool room until it can be deposited in the waste disposal.
The bag must be labeled with a yellow Clinical/Biological Waste label (obtainable from the safety office) or it will not be accepted by the disposal company. If difficulty is found in sticking the label to the bag a hole can be punched in a corner so that it can be attached with a bag tie.
On arrival at the waste disposal store the bag will be given a number by the technician in charge and the user will fill in a register indicating his or her name and a brief description of the contents of the bag (e.g. animal carcass, swabs, tissues, gloves etc.) opposite the number. The bag will then be collected by the safety office for incineration.
(i) If material is contaminated with toxic micro-organisms:
Such contaminated material should be placed in an autoclavable bag labeled with a tag identifying the user and sterilized before being placed in a yellow biohazard bag in a designated fridge or cool room until being deposited in the waste disposal store for incineration.
(ii) If the Material is contaminated with Radioactivity:
When the material is contaminated with radioisotopes alone, the maceration route for disposal may be used, subject to the following conditions:
1. The disposer must ensure that the total radioactivity and the concentration of radioactivity which will be present in the discharge from the macerator to drains.
2. The disposer must contact Joint Services to arrange a time for the disposal.
3. Disposers of radioactive tissues/carcasses (who must be registered radiation workers) must take the waste materials in a plastic jar or box fitted with a lid, and bearing a formal label showing the radiation trefoil, the radionuclide, the radioactivity present and the name of the disposer.
4. Transfer of the carcasses into the macerator must be carried out by the disposer.
5. Following disposal of the waste, the disposer must carry out a Radioactive Contamination Survey of the equipment.
6. The disposer must ensure that the Radioisotope Acquisition and Disposal Record booklet.
(iii) If the material is contaminated with radioactivity and non-radioactive toxic agents.
The hospitals are not authorized to transfer solid radioactive waste to other sites for incineration. Therefore, if it is anticipated that the material will be contaminated with radioisotopes and non-radioactive toxic agents (for which incineration would be the normal route), it is imperative that careful consideration is given to the provision of special disposal routes before the work begins. All proposed special disposal routes must be discussed with, and approved by, the Safety Committee members responsible for Chemical, Biological and Radiological matters.
(c) Good Laboratory Procedures:
1. Swabs contaminated with blood or tissue fluids should be autoclaved in double sealed bags (plus autoclave tape) and then internalized into a black bag before removal as industrial waste. It is the personal responsibility of the user to ensure that the material is adequately autoclaved, promptly removed after sterilization and subsequently disposed of in an appropriate fashion.
2. Areas used for animal dissections should be identified as a designated area in the room and scrubbed with vim, disinfectant and washed down with 80% ethanol. Empty cages should be returned immediately after use to the animal unit.
3. All workers who are handling animals should ensure that they have received the appropriate tetanus vaccination.
4. Equipment that has been inadvertently contaminated with animal or human waste must be immediately decontaminated. It is an absolute requirement before repair and maintenance procedures that we can specify the absence of any contaminating hazard.
Broken and uncontaminated or decontaminated glass should be placed in cardboard boxes clearly designated glass. Seal the box and place in skip.
Exam Question # Q.7. How to Diagnose Leprosy:
Ans. Examinations for Leprosy (Hansen’s Disease):
The laboratory diagnosis of Leprosy is made by:
1. Histology.
2. Examination of appropriate Ziehl-Neelsen-stained skin smears for AFB.
Bacilli are found in polar Lepromatous leprosy (LL), Borderline (BB) and its variants Borderline Lepromatous (BL). They are scanty in Borderline tuberculoid (BT) and are not found in polar tuberculoid (TT).
Instructions for Preparation of Skin Smears:
These are best performed by experienced staff. The nodule of plaque is cleaned with ether or any suitable disinfectant. The skin is gripped tightly between thumb and forefinger of the left hand to exsanguinate the lesion. An incision, 5 mm long and 3 mm deep, is made in the skin between the fingers of the left hand with a small bladed scalpel, the pressure on the fingers being maintained.
The base of the wound is scraped several times in the same direction, so that tissue fluid and pulp collects on the blade and this is smeared on a labelled glass slide. There should be minimal blood on the specimen. Smears from ear lobes are made in the same manner. The incision is made along the lateral edge of the pinna, the latter being compressed between thumb and forefinger.
6-8 smears are made from each patient. The sites are recorded and it is preferable to repeat smears from the same site when repeat specimens are taken later. Slides should be heat fixed if there is a delay in reading in the laboratory.
Smears from Nasal Secretions:
These smears are essential in deciding whether a patient is infectious. They are always positive in untreated (LL), some (BL) and negative in all cases of (BB), (BT), and (TT). The patient is requested to blow into a tissue and smears are made with a scalpel onto glass slides (2-3).
Reporting Conventions:
Bacterial Index (BI) and Morphological Index (MI).
The BI is an index of the bacillary load in the patient.
This is expressed on a semi-logarithmic scale as given below:
BI Interpretation:
1+ 1 to 10 bacilli per 100 high power (oil immersion) fields
2+ 1 to 10 bacilli per 10 high power fields
3+ 1 to 10 bacilli per high power field 4+ 10 to 100 bacilli per high power field
5+ 100 to 1000 bacilli per high power field
6+ >1000 bacilli per high power field
Reference may be made to the term ‘globi’ in some reports. These are clumps of bacilli and are generally found in LL. The clumps are derived from micro-colonies in macrophages. MI interpretation. The MI is an index of viability of the bacilli. Solid bacilli are deemed to be viable while fragmented or granular bacilli are considered to be non-viable.
Two hundred discrete bacilli are evaluated if possible. The MI is equal to the percentage of viable bacilli. Note that pauci-bacillary lesions may not be assessable for the MI. The MI in untreated multi-bacillary leprosy usually ranges between 25 and 75 and should decline to 0 after 4 to 6 months of effective modern chemotherapy.
Exam Question # Q.8. What Precautions to be taken for Collecting Culture Samples?
Ans. The accuracy and quality of result of observation of any microbiological sample upto a large extent depends upon the modes of collection of samples.
The following points should be remembered in collecting the specimen for the microbial examination:
1. The sample should be collected prior to administration of antibiotics and if the sample is taken after that the concerned laboratory should be informed for it.
2. There are of lesion in case of superficial infection, should be well cleaned and sterilized by any prescribed surface active agent.
3. Investigating material should be collected from where the suspected organism is most likely to be found and with as little external contamination as possible.
4. Factors involved in successful isolation of causative agent should be considered well and taken into account as the greater number of causative agents is during the acute infection which is the right time of collection of specimen. So in accordance with the situation and must probability of availability of microbes, sample should be collected.
5. Specimen should be of a quality sufficient enough to permit complete examination and the remaining part of it should be kept in sterile container for further procedures if necessary.
6. For each type of examination and the specimen, the patient should be informed well in time.
7. Arrangement should be made for prompt delivery of specimens to the other laboratory which is located at a considerable distance.
8. All records of the sample, from collection upto the result must be recorded in the register maintained for the purpose.
9. The laboratory should be provided with sufficient clinical information to guide the microbiologist in the selection of suitable media and appropriate techniques. There should be close co-operation and frequent consultation among a technician, nurse and the microbiologist.
10. The following points must be kept in mind at the time of sample collection front the patient suspected to have anaerobic infection:
(i) Avoidance of contamination of sample with normal flora.
(ii) Avoidance of contact of sample with oxygen.
(iii) Avoidance of refrigeration of sample collected.
(iv) Immediately start the process of investigation.
(v) In case of suspicion on investigation due to delay, a transport medium should be used.
11. The containers equipment, environment and the clothings of investigator all must be well sterilized.
12. The aspirates should be collected in the container having tied them with coke or cotton plug and the sample should directly be induced into them with the help of needle without removing the lid or coke or cotton plug.
13. Some bacteria e.g. meningococcal in CSF are quite sensitive to low temperatures and require immediately culturing.
14. The clinical material likely to contain abundant microbial flora may be kept at 4°C in refrigerator for delay e.g. urine, faeces etc. where the viability is preserved and overgrowth is checked.
Exam Question # Q.9. What are the Steps of Processing of Clinical Samples in Laboratories?
Ans. It may be divided into four steps i.e.:
1. Collection and recording of sample.
2. Microscopic examination including staining.
3. Culture of collected specimen.
4. Serology or and
5. Skin test.
1. Collection and Recording of Sample:
The sample should be collected on per the instructions, written above and it should be recorded in register for the name, age, sex of patient name of sample, investigations to be carried out, amount (quantity) of sample etc. the container should also be having the same and necessary information’s including the registration number over the container.
2. The sample collected should immediately be undertaken for microscopic examinations directly or after staining as the case may be. It must be stained with Ziehl Neelsan, GIEMSA or grams stain.
3. Culture:
The specimen collected should immediately be cultured and isolated and the concerned studies like biochemical tests. Pathogenicity or toxigenecity tests etc. should be carried out.
4. Hematology and Serology:
Of the sample collected should also be performed for RBC, ESR, Hb, TLC, DLC, Widal test, Agglutination, precipitation, flocculation, and test as per the specimen.
5. Skin Test:
The skin test like dermal test (Montoux) direct KOH preparation is taken for microscopic examination. In case of fungal (mycotic) infection.
Exam Question # Q.10. How to Collect Naso-Pharyngeal Aspirate?
Ans. (i) A nasopharyngeal aspirate is required for the diagnosis of viral infections such as influenza, parainfluenza and respiratory syncytial virus (RSV). It is also the preferred type of specimen for the diagnosis of Bordetella pertussis infections by PCR and culture.
(ii) Operator must observe standard precautions and wear appropriate personal protective equipment.
(iii) Attach a mucus trap to the suction system and the appropriately sized catheter, leaving the wrapper on the suction catheter.
(iv) Turn on the suction and adjust the pressure.
(v) Without applying suction, insert the catheter into the nose, directed posteriorly and towards the opening of the external ear. The depth of insertion necessary to reach the posterior pharynx is equivalent to the distance between the anterior naris and external opening of the ear.
(vi) Apply suction and slowly withdraw the catheter using a rotating movement. The catheter should remain in the nasopharynx for no longer than 10 seconds. The trap should be kept upright.
(vii) If necessary rinse the catheter with a small volume of sterile 0.9% saline solution to ensure adequate specimen volume.
(viii) Disconnect suction and seal mucus trap with tubing.
Exam Question # Q.11. How to Diagnose Bordetella pertussis?
Ans. Cause-Whooping Cough:
Several tests are available to test for Bordetella pertussis. Culture is considered the gold standard because it is the only 100% specific method for identification. Other tests that can be performed include polymerase chain reaction (PCR) and serology.
Culture:
Since culture has excellent specificity, it is particularly useful for confirming pertussis diagnosis when an outbreak is suspected. Many other respiratory pathogens have similar clinical symptoms to pertussis and co-infections do occur. Furthermore, obtaining isolates from culture allows for strain identification and antimicrobial resistance testing.
Identifying which strain of B. pertussis is causing disease is of public health importance. Culture is best done from nasopharyngeal (NP) specimens collected during the first 2 weeks of cough when viable bacteria are still present in the nasopharynx. After the first 2 weeks, sensitivity is decreased and the risk of false-negatives increases rapidly.
CDC and FDA have developed a serologic assay that has been extremely useful for confirming diagnosis, especially during suspected outbreaks. Many State Public Health Labs have included this assay as part of their testing regimen for pertussis. Commercially, there are many different serologic tests used in United States with unproven or unknown clinical accuracy.
A blood test for antibodies to the bacterium is the preferred test for the diagnosis of Lyme disease. However, if a person has central nervous system symptoms, such as meningitis, then IgM, IgG, and Western blot testing may sometimes performed on CSF.
Occasionally, PCR (polymerase chain reaction) testing is performed on a sample because it is a more sensitive way of detecting an infection with B. burgdorferi. This method is useful in detecting the infection in samples such as fluid collected from a joint. It looks for the genetic material (DNA) of B. burgdorferi in the joint fluid (synovial fluid).
Very rarely, a sample, such as a skin biopsy, may be cultured to grow the bacterium.
Lyme disease testing is ordered when a person has symptoms suggestive of an infection with B. burgdorferi and lives in or has visited a region where deer ticks or black legged ticks are common, especially when the person has recently been bitten by a tick.
Some symptoms of Lyme disease may include:
(i) A characteristic “bulls-eye” rash that spreads from the site of the bite
(ii) Fever, chills
(iii) Headache
(iv) Fatigue.
If left untreated, Lyme disease may progress to cause:
(i) Intermittent joint pain
(ii) Meningitis
(iii) Facial paralysis (Bell’s palsy)
(iv) Weakness and numbness in the arms and legs
(v) Memory problems
(v) Less commonly, heart problems such as irregular heartbeat and eye inflammation.
IgM and IgG tests are ordered first. Western blot testing is ordered as a follow-up test when the first tests are positive or indeterminate. Acute and convalescent samples may be ordered several weeks apart to look for changes in antibody levels.
When someone does not have typical symptoms or a history of a tick bite and has not been in a region where Lyme disease is prevalent, then the doctor may rule out other causes for the person’s symptoms before suspecting and testing for Lyme disease.
Interpretation of Test Result:
A healthy adult who has never been exposed to the B. burgdorferi bacterium will not have any antibodies.
If a person’s IgM, IgG, and Western blot tests are positive, then it is likely that the person has Lyme disease. If the person’s antibody concentrations rise over time, then it is likely that the person has an active B. burgdorferi infection.
If someone tests positive for only the IgM antibody, then the person may have a very recent infection or a false positive test result.
If an IgM result is not detectable but the IgG and Western blot tests are positive, then it is likely that the person tested either has a later stage infection or had an infection at some time in the past.
If all tests are negative, then either the person’s symptoms are due to another cause or the antibody levels are too low to detect at that time; retesting a few weeks later may be needed to confirm or rule out infection.
If PGR testing is performed and the result is positive, then it indicates a recent infection with B. burgdorferi. If the PCR test result is negative, then no infection is present or the levels of DNA are too low to detect.
Exam Question # Q.12. How to Diagnose Corynebacterium Diptheriae?
Ans. Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria. It is also known as the Klebs-Loffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834 – 1912) and Friedrich Loffler (1852 – 1915).
Four subspecies are recognized: C. diphtheriae mitis, C. diphtheriae intermedins, C. diphtheriae gravis, and C. diphtheriae belfanti. The four subspecies differ slightly in their colonial morphology and biochemical properties, such as the ability to metabolize certain nutrients, but all may be toxigenic (and therefore cause diphtheria) or non-toxigenic.
Throat swabs, nasopharynx and skins swabs are the common specimen for laboratory diagnosis.
In order to accurately identify C. diphtheriae, a Gram stain is performed to show gram- positive, highly pleomorphic organisms with no particular arrangement. Special stains like Albert’s stain is used to demonstrate the metachromatic granules formed in the Polar Regions. The granules are called as polar granules, Babes Ernst Granules, Volutin, etc.
An enrichment medium, such as Loffler’s medium, is used to preferentially grow C. diphtheriae. After that, use a differential plate known as tellurite agar, which allows all Corynebacteria (including C. diphtheriae) to reduce tellurite to metallic tellurium. The tellurite reduction is calorimetrically indicated by brown colonies for most Corynebacteria species or by a black halo around the C. diphtheriae colonies.
Elek’s test for toxogenicity is used to determine whether the organism is able to produce the diphtheria toxin or not.
Isolation of Organism:
The second throat swab should be used to culture on different media e.g. Loffler’s serum slope agar and blood tellurite agar etc. the organism are grow best at 37°C and growth is examined after 24 hours and 48 hours. The colonies are subjected to gram and Albert’s staining and biochemical test done.
Confirmation of toxigenicity:
Two normal giving pig are taken one of them is protected with an adequate does of antitoxin which is injected about 12 hours before the test. For test, broths are incubated with (injected) suspension of 18 hours growth of bacilli in loeffter’s serum slope if the strains are toxigenicity. The unprotected animal will die with 96 hours.
The loxiginicty can also be detected by immuno diffusion technique
Antimicrobial Susceptibility Testing:
There is no need for routine antimicrobial susceptibility testing. The organism is sensitive to penicillin and orythroncycin.
(i) Encapsulated (Capsule could be demonstrated during growth in infected animals)
(ii) Non-motile
(iii) Spores are formed in culture, dead animal’s tissue but not in the blood of infected animals.
(iv) Spores are oval and centrally located.
(a) Spores remain viable in soil for decades.
(b) In World War II in Scotland spores were exploded.
(c) Survived for > 40 years and were eradicated in 1987
(d) Changing environmental conditions (temp, rain etc.) help in survival and multiplication.
(e) Obligate pathogen
(i) Zoonotic
(ii) Aerosolized
(iii) Vectorial (flies)
(iv) Contaminated soil
(v) Contaminated food
(vi) Contaminated fomites (primarily wool and hides)
Composed of poly peptide of a high molecular weight consisting of D-glutamic acid.
2. Polysaccharide Somatic Antigen:
Composed of N-acetulglucoseamine and D-galactose
This toxin appear to be responsible for signs and symptoms characteristic of anthrax. Accumulation of the toxin in tissue and its effect on the central nervous system results in death by respiratory failure and anoxia.
1. Cutaneous Anthrax:
(i) Painless necrotic black-based ulcerating papule
(ii) May complicate by septicemia.
(iii) Most common
(iv) Caused by Bacillus anthracis infection of the skin.
2. Gastrointestinal Anthrax:
(i) Gastrointestinal necrosis and hemorrhage, abdominal pain, vomiting and bloody diarrhea
(ii) 50% mortality if untreated.
(iii) Caused by ingestion of “Bacillus anthracis” infection of the Gl-tract
3. Pulmonary Anthrax:
(i) Severe hilar lymph node necrosis and mediastinal hemorrhage.
(ii) 100% mortality if untreated.
(iii) Caused by inhalation of “Bacillus anthracis” infection of the lungs.
Blood Agar and Nutrient Agar are commonly used to cultivate the bacilli. Plates are incubated aerobically at 37°C.
Colonies have irregular borders and are non-hemolytic.
They are described as “Medusa head’ or “Comet tail”.
Specimen Collection and Laboratory Diagnosis:
Caution:
Laboratory safety is very important when working with any materials suspected of containing Bacillus anthracis.
Samples are collected depending on the site affected:
1. Swab samples from cutaneous lesions and blood cultures.
2. Sputum and blood for pulmonary anthrax.
3. Gastric aspirate, feces and blood for enteric anthrax.
Made from clinical samples, show large gram positive bacilli in long chains “Bamboo-like appearance”.
Purple bacilli with red capsule.
Experimental animals are injected intraperitoneally by a suspension of the test organism “Suspected B. anthracis culture”.
(i) The animal dies in 48-96 hours due to respiratory failure.
(ii) Large number of typical bacilli can be found in the blood and tissue of spleen of the infected animal.
1. Carbohydrate fermentation test-
2. Gelatine liquefaction test – Negative after 7 days. Growth has a characteristic appearance of an inverted pine tree.
3. Nitrate reduction test – Positive
4. Starch hydrolysis test – Positive
5. Voges-Proskauer test – Positive
6. Sensitivity to penicillin – Sensitive
7. Lysis by gamma phages – Positive. This test accurately differentiates B. anthracis from other bacillus species.
(i) Ciprofloxacin
(ii) Narrow spectrum penicillins
(iii) For penicillin-sensitive patients, tetracycline, erythromycin, chloramphenicol and streptomycin may be given as alternative drugs.