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Group : Laboratory Medicine

Subject : General Microbiology and Parasitology (Paper-II)

Q-1-a) Define microorganism. Compare between prokaryotic and eukaryotic cell. (Jan-2020).


They are small organisms and are either microscopic or submicroscopic creatures.

Differences between prokaryotic (bacteria) & eukaryotic (human) cell:

1. SizeSmallerLarger
2. Nucleus:     Nuclear membrane, Nucleoli Chromosome AbsentSinglePresent Multiple
3. Mitotic division NoYes
4. Membrane bound organelles (e.g. mitochondria)AbsentPresent
5. PlasmidPresentAbsent
6. Ribosome70S (30S+50S)80S (40S+60S)
7. Cell wall containing peptidoglycanYesNo.

Q-1-b) Write down the different stages of bacterial growth curve with their importance. (Jan-2020)

Bacterial growth curve : 

If a small number of bacteria is inoculated into a liquid nutrient medium and bacteria is counted of  frequent intervals and a graphical demonstration is produced by putting log number of cells along the Y-axis and time along the X-axis, then it is known as bacterial growth curve.

Phase of growth curve:

1. Lag phase or preparatory phase 

2. Log phase or exponential phase

3. Stationary phase 

4. Decline phase/Death phase

Description of each phase:

1.Lag Phase:

This is the time or period required for bacteria for adjustment in human body.


  •  No appreciable multiplication of bacteria occurs in this phase.
  • Metabolic activity increases. 
  •  Cell size may increase
  • Time requires 1-4 hours


Membrane acting antibiotics such as polymyxin, amphotericin-B can be used in this phase. Detergents, soaps and other surface acting agents act better in the lag phase.

2. Log Phase: 


  • Rapid cell multiplication & cell number increases in geometric process.
  •  Active synthesis of the cell wall occurs.
  •  Metabolic activity increase at a very high rate 
  • Time requires 1-4 hours.


  • Antibiotics act better at this phase as cell wall growth is very active during this phase.
  •  At this phase disease-producing capability of bacteria is highest, and if not treated the disease properly at this stage, dreadful conditions like septicaemia can result.

3. Stationary phase:


  • At this stage, multiplication rate & death rate of bacteria are equal, so net growth rate is zero.
  • Cell dies because of exhaustion of nutrients in the bacteria & accumulation of toxic products in themedium.
  •  Exotoxin production starts at this stage.
  •  Time requires – few hours to days.


  • Release of exotoxin starts. 
  • Spore forming bacteria starts formation of spores.
  • Cell wall acting antibiotics may be used. 
  • Gram positive bacteria may be transformed into Gram negative bacteria by erosion of

peptidoglycan layer.

4. Decline phase/Death phase:


  • The death rate is greater than the multiplication rate. 
  • Accumulation of toxic products occurs.
  • Time requires a few hours to days.


  • Exotoxin of C. diphtheria is produced in this phase.
  • Bacteria may develop L-forms, which are resistant to antibiotics. 
  • Sporulation starts in some bacteria.

Q-1-c) Name the blood borne parasite. Write down the Laboratory diagnosis of kala-azar. (Jan- 2020)

Blood borne parasite :

The blood borne parasites which can be found in the bloodstream of an infected person are called blood borne parasites. 

Name some blood borne parasite :

  • Leishmania donovani causes Kala-azar
  • Plasmodium species causes Malaria
  • Wuchereria bancrofti causes Filariasis 

Laboratory diagnosis of kala-azar:


 Leishmaniasis can be diagnosed by demonstration of the parasite (LD bodies) from the cutaneous, mucosal lesions and incase of visceral leishmaniasis from Bone marrow, Spleen or Lymph node aspirate. It can also be diagnosed by detection of antigen or antibody by immunological tests and isolation of the organism by culture if facilities are available. Nucleic acid techniques are also helpful.

Specimen collection:

 Aspiration of bone marrow, spleen, lymph nodes, buffy coat of blood.

Microscopic examinations:

  • Leishman (or Giemsa) stained smear.
  •  Findings: Amastigote form (LD bodies) in bone marrow, splenic aspirate and within blood monocytes.

Isolation and identification from culture:

  •  NNN media (Novy, Mac Neal, Nicole).
  • Incubation- at 22° C.
  • Incubation time-1 to 2 weeks.
  • Findings- promastigote forms of parasites are found.

Serological tests:


For detection of antibody

  • ICT (ImmunoChromatographic Test)
  • DAT (Direct Agglutination Test)
  • IFAT (Indirect Fluorescent Antibody Test)
  • CFT (Complement Fixation Test)

For detection of antigen-

  • ELISA (Enzyme Linked ImmunoSorbent Assay)
  •  RIA (Radio Immuno Assay)


  • Aldehyde test for detection of high globulin.
  •  Antimony test.
  • Blood count-Decrease WBC. RBC, Platelet.

NA based techniques: 

PCR (Polymerase chain reaction).

Q-1-d) Draw and label a bacterial cell structure. (Jan-2020).

Q-1-e) Define toxin and toxoid. Give the difference between exotoxin and endotoxin. (Jan-2020)


Toxins are poisons, protein or conjugated protein produced by some higher plants, certain animals and pathogenic bacteria that is highly toxic to other living organisms. 


Toxoids are derivatives of bacterial exotoxins produced by chemically altering the natural toxin, or by engineering bacteria to produce harmless variants of the toxin.

 Difference between exotoxin and endotoxin are given below: 

                          Exotoxin                        Endotoxin
1.Excreted by living cells.1.Integral part of the cell wall of Gram-negative bacteria.Released on bacterial death and in part during growth.Release is not required for biologic activity.
2.Produced by both Gram-positive and Gram-negative bacteria.2.Produced only by Gram-negative bacteria.
3.Highly antigenic3.Weakly antigenic
4.Polypeptide in nature4.Lipopoly saccharide in nature.
5.Toxoid can be produced5.Toxoid is not produced.
6.Heat labile6.Heat stable
7.Usually do not produced fever in the host7.Usually produced fever in the host by release of interleukin-1,and other mediators.
8.Usually controlled by extra-chromosomal genes e.g-plasmid ,phage gene.8.Synthesis directed by chromosomal genes.

Q-2-a) Define and classify STD with example. (Jan-2020)

STD (sexually transmitted diseases):

STDs are a group of communicable diseases that are transmitted predominantly by sexual contact and caused by a wide range of bacterial, viral, protozoal & fungal agents and ecto-parasites.

Microorganisms causing STD:

ClassificationPathogenDisease or Syndrome

1. Neisseria gonorrhoeaeGonorrhea, PID, urethritis, neonatal, conjunctivitis
2. Treponema pallidumSyphilis
3. Haemophilus ducreyiChancroid
4. Chlamydia trachomatis5. Calymmato bacterium granulomatisPID, urethritis, neonatal conjunctivitis, granuloma inguinale

1. Herpes simplex virusGenital herpes
2. Hepatitis B virusAcute & chronic hepatitis, hepatocellular carcinoma
3. Hepatitis C virusAcute & chronic hepatitis, hepatocellular carcinoma
5. Human papilloma (HPV)Genital & anal warts
6. Molluscum contagiosum virusGenital Molluscum contagiosum
C.FungalCandida albicansVaginitis (Moniliasis)

Trichomonas vaginalisVaginitis
Giardia lambliaGiardiasis
Entamoeba histolyticaAmoebiasis

Sarcoptes scabieiScabies
Phthirus pubisPubic pediculosis

Q-2-b) Define immunological tests. Name different antigen-antibody reactions with example. (Jan-2020)

Immunological tests:

The tests used to detect antigen or antibody in serum or in other specimens is called immunological test.

Serological tests:

 The tests used to detect antigen or antibody in serum is called immunological test.

Antigen-antibody reactions with examples of each type:

Name of Ag-Ab reaction                                       Example

1. Agglutination test
Slide agglutinationSerotyping of bacteriaBlood grouping
Tube agglutination
Widal test for enteric feverWeil-Felix test for rickettsial infection
Latex agglutinationHbsAg detection ASO titre (antistreptolysin-O titre) estimation
Particle agglutinationDetection of anti HIV antigen
HaemagglutinationTPHA for diagnosis of syphilis 

2.precipitation test
Tube precipitation testEstimation of antibody
Gel diffusionSingle radial diffusion: for estimation of antibody.Double gel diffusion: For identification of antigen.
CIE (counter immuno- electrophoresis)Detection of cryptococcus antigen in CSF. Detection of carcino-embryonic antigen (CEA).
3. Complement fixation test (CFT)CFT for kala-azar, CFT for filarial parasite, CFT for gonococcus

4. Others (immunoassay using labeled reagents)
Immuno-fluorescence (IF)- Detection of T & B cells,Detection of treponemal antibody in syphilitic patients
Enzyme-linked immunosorbent assay – . HIV antibody,Hepatitis-B panel (HbsAg, HbeAg, Anti-HBs,Anti-HBc)
Radio-immuno assay (RIA) – Detection of HbsAg.

Q-2-c) Define spore. Name five spore bearing organism with disease produced by them. Jan-2020


Spores are resistant stages of bacteria produced when bacteria are exposed to unfavorable environmental conditions and are highly resistant to heat,desiccation(dehydration),chemicals etc.

          Spore bearing organism                          Disease
Bacillus anthracisAnthrax
Bacillus subtilisFood poisoning (rare)
Clostridium TetaniTetanus
Clostridium perfringensGas gangrene
Clostridium BotulinumBotulism

Q-2-d) Define and classify sterilization. (Jan-2020)

Sterilization : 

Sterilization is the process by which all viable microorganisms including spores are killed or eliminated.

Classification of sterilization : 

  1. Physical 
  2. Chemical 
  3. Filtration 

A.Physical method : 

  1. Heat
    • High Heat
      • Dry Heat
        • Hot air oven 
        • Incineration
      • Moist Heat
        • Boiling
        • Steaming
          • With Pressure
            • Autoclave
          • Without Pressure
            • Tyndallization
            • Koch’s Steamer
        • Pasteurization
          • Holding Method
          • Flash Method
    • Low Heat
      • Water Bath
      • Vaccine Bath
  2. Radiation
    • X-ray
    • Gamma ray
    • UV ray

B.Chemical method : 

  1. Alcohols
  2. Phenols.
  3. Ethylene oxide
  4. Detergents
  5. Dettol
  6. Acids and alkalis
  7. Formaldehyde
  8. Glutaraldehyde
  9. Oxidizing agents

C.Filtration method : 

  1. Bark field
  2. Chamber land
  3. Membrane filter
  4. Hepa filter

Q-2-e) Write the principle and uses of hot air oven. (Jan-2020).

Ans: Hot air oven is the best apparatus for dry heat sterilization.It is a double walled metal chamber which is electrically heated.The fan or turbo blower fixed inside the chamber assists the uniform circulation of hot air.

Principle: Temperature needed in hot air oven is 160 degree celsius  for one hour.Spore are also killed at this temperature.To guard against temperature variations air should be made to circulate by a suitable fan.

Uses of hot air oven:

Hot air oven is used for sterilization of-

  1. Sterilization of glassware,such as all glass syringes,test tubes,petri dishes,pipettes,flasks and instruments like forceps,scissors,knives,scalpels etc.
  2. Sterilization of powders,fats,oils and greases which are impermeable to moist heat.
  3. Sterilization of cotton swabs.

Q-3-a) Define and classify culture media. Give the composition of chocolate agar media. (Jan-2020).

Media/Culture media:

Media may be defined as an artificial food for the cultivation of bacteria in the laboratory.

Classification of media:

A. On the basis of consistency:

1) Solid media: e.g. nutrient agar, blood agar, chocolate agar etc .

2) Semisolid media: e.g. soft agar media.

3) Liquid media: Peptone water, bile broth, sugar broth, Loeffler’s serum, Robertson’s cooked meat media etc.

B. On the basis of chemical/nutritional composition:

1) Simple/basal media: For general purpose. Example – nutrient broth, nutrient agar, peptone water, glucose broth etc.

2) Special media:

i) Enriched media: e.g. blood agar medium, Lowenstein-Jensen medium.

 ii) Enrichment media: e.g. Tryptic soya broth.

iii) Selective media: e.g. Mac Conkey’s agar, blood tellurite agar.

iv) Indicator/ differential media: e.g. blood agar, Mac Conkey’s agar.

 v) Transport media: e.g. Stuart medium, Carry-Blair medium.

vi) Storage media: e.g. egg-saline medium.

C. On the basis of oxygen requirement:

  • Aerobic media.
  • Anaerobic media.

Composition of chocolate agar media:

  • Nutritious agar
  • Sterile defibrinated blood

It is heated blood agar media.( This medium is prepared by heating 10% sterile blood in molten nutrient agar which is then allowed to cool.Heating causes rupture of the red blood cells to liberate nutrient to the media).

Q-3-b) Define pathogenicity and virulence. Write down the virulent factors of bacteria. (Jan-2020)


Pathogenicity means ‘the capability or power of a pathogen to cause disease’.


Virulence means ‘the degree or measure of pathogenicity of a given pathogen to cause disease’.

Virulence factors for bacterial pathogenicity:

1. Adherence factors: 

  • Pilli: in case of Neisseria gonorrhoeae
  • Capsule
  • Glycocalyx

2. Invasion of host cells and tissues:

  • Enzyme: e.g. hyaluronidase of Streptococcus pyogenes. 
  • By breaking mucous membrane – N. gonorrhoeae.
  • Through intact mucous membrane-Shigella.

3. Antiphagocytic factors:

  • Capsule 
  • Pilli
  •  Protein A
  •  Coagulase enzyme

4. Enzymes:

  • Tissue degrading enzymes: Hyaluronidase, Lecithinase etc.
  •  IgA protease: Produced by S. pneumoniae, N. meningitidis, H. influenzae etc.

5. Toxins:

  • Exotoxins: Enterotoxin, tetanospasmin, botulinum toxin, pyogenic toxin etc.
  • Endotoxins: It is the constituent of the cell wall of Gram-negative bacteria and responsible for fever, shock, leukopenia, hypoglycemia, hypotension, DIC etc.

 6. Others: M-protein of Streptococcus pyogenes: interfere with ingestion by phagocytes.

Q-3-c) Define immunity. What are the beneficial harmful effects of immunity. (Jan-2020)

Immunity: Recently, Immunity is defined as-

“ all those physical mechanisms that endow the animal with the capacity to recognize materials as foreign to itself and to neutralize, eliminate or metabolize them.”

Beneficial effects of immunity:

a) Prevention of many diseases by vaccination, eg-measles vaccine, polio vaccine etc. 

b) Following clinical & sub-clinical infections, there is production of immunoglobulins which gives

protection to the host. The majority of the beneficial effects are unseen.

Harmful effects of immunity:

  1. Hypersensitivity conditions like asthma,rheumatic fever,glomerulonephritis etc.

      b) Autoimmune diseases like rheumatoid arthritis, SLE (Systemic lupus erythematosus),    autoimmune haemolytic anaemia etc.

Q-3-d) What are the types of antibiotic sensitivity test? Write down the indicators of doing sensitivity test. (Jan-2020)

Types of sensitivity test:

  1. Disk diffusion
  2. Drug dilution or broth dilution method (it is better, because the concentration of drug required for treatment can be known by this process).

Indicators of doing sensitivity test:

  • The size of the effect that is being studied.
  • The variability of the data.
  • The desired level of confidence in the results.
  • The resources available for conducting the test.

Here are some specific examples of when a sensitivity test might be used:

  • To determine the effect of a new drug on a disease.
  • To assess the impact of a change in policy on a population.
  • To evaluate the accuracy of a model.
  • To design a clinical trial.
  • To optimize a manufacturing process.

Indication of doing sensitivity test:

An antibiotic sensitivity test is indicated in the following situations:

  • To determine the most effective antibiotic to treat a bacterial infection.
  • To monitor the response to antibiotic treatment.
  • To identify bacteria that are resistant to antibiotics.
  • To help guide the development of new antibiotics.

 Here are some specific examples of when an antibiotic sensitivity test might be ordered:

  • A patient with a urinary tract infection (UTI) who has not responded to initial antibiotic treatment.
  • A patient with a serious infection, such as sepsis, who needs to be started on antibiotics immediately.
  • A patient with a known history of antibiotic resistance.
  • A patient who is taking an antibiotic for a long period of time.
  • A patient who is pregnant or breastfeeding.

Q-3-e) Draw and label stages of E.H. Write down the intestinal and extra intestinal lesion of E.H. (Jan-2020)

A. Intestinal lesions:

  • Acute intestinal lesions-Ulcers
  • Chronic intestinal lesions-Scar, ulcers

B.Extra intestinal or metastatic lesions:

  • Amoebic liver abscess
  • Amoebic lesions at other sites like lung.pleura,pericardium.

Q-4-a) Define and classify microscope. Mention the different parts of compound microscope. (Jan-2020)


The microscope is a magnifying instrument by which small objects that can not be seen by the naked eye become visible under it.

Classification of microscope:

1.Simple microscope

2.Compound/light microscope

There are many types of light microscope,such as-

  1. Bright field microscope
  2. Dark field microscope
  3. Phase contrast microscope
  4. Polarizing microscope
  5. Fluorescence microscope

3.Electron microscope

a)Transmission electron microscope

b)Scanning electron microscope

Parts of compound Microscope : 

  1. Mechanical parts 
  2. Optical parts 

1. Mechanical parts:

  1. Base (পদদেশ ) 
  2. Pillar (স্তম্ভ) 
  3. Arm (বাহু/তল ) 
  4. Body tube (দেহ নল) 
  5. Coarse adjustment screw 
  6. Fine adjustment Screw 
  7. Draw tube (টানা নল)
  8. Stage(মঞ্চ)   
  9. Slide clip
  10. Slide Screw 
  11. Stage screw 
  12. Condenser Screw

2. Optical parts :

  1. Eyepiece
  2. Objective 
  3. Condensar 
  4. Mirror 
  5. Objective lens 
  6. Diaphragm 

Microscope Objective are four (4) types :

  1. Scanner : 4x : Histo & Cytopathological Slide দেখা হয়।
  2. Low (dry) : 10x : Balancing of magnification and working distance.
  3. High (dry) :  40x : Blood cell, Urine Slide, Stool slide দেখা হয়।
  4. Oil immersion :100x : Bacteria দেখা হয়।

Q-4-b) Write down the name of five common helminth found in Bangladesh with disease produced by them. (Jan-2020)

1. Ascaris Lumbricoides/RoundwormAscariasis
2. Ancylostoma duodenale/HookwormAncylostomiasis
3. Enterobious Vermicularis/PinwormEnterobiasis
4. Taenia saginata/Beef tapewormTaeniasis
5. Trichuris Trichiura/WhipwormTrichuriasis
6. Taenia solium/Pork tapewormTaeniasis

Q-4-c) Define dysentery. Write down the difference between acute amoebic and acute bacillary dysentery. (Jan-2020)


Dysentery is an infection of the intestines that causes diarrhea that may contain blood or mucus. Other possible symptoms include abdominal pain, nausea and vomiting, and fever. Dysentery can occur as a result of bacterial or parasitic infections.

TraitsAcute amoebic dysenteryAcute bacillary dysentery
A. Naked eyeMucus and altered blood mixed with stoolMucopurulent flakes mucus and blood mixed intimately.
B. ReactionAcidAlkaline
C. Microscopic
Cellular exudateScantyPlenty
Pus cellFewPlenty
Red cellIn rouleauxDiscrete
MacrophagesVery rarePresent
Trophozoites of E.histolyticaPresentAbsent
Charcotleyden crystalMay be presentAbsent
BacteriaNumerous,motileFew non-motile
D. Bacteriological Culture

E.coli and other normal floraShigella

Q-4-d) Write down the five RNA & DNA viruses with disease produced by them. (Jan-2020)

Types of virus (RNA virus)Name of virusDisease
OrthomyxovirusesInfluenza A, B, c virusInfluenza
RhabdovirusesRabies virusRabies
Toga virusesRubella virusRubella
RetrovirusesHuman immunodeficiency viruses (HIV)AIDS
Types of virus (DNA virus)Name of virusDisease
pox virusesVariola,VacciniaSmallpox

Herpes viruses
Herpes simplex virus type 1 and 2Infections of mouth,eyes,central nervous system genitalia
Varicella zoster virusChicken pox
Herpes zosterSkin lesions
CytomegalovirusSalivary gland disease
HepadnavirusesHepatitis-B virusHepatitis

Q-4-e) Write down the life cycle of A.D (Ancylostoma duodenale). (Jan-2020)

Life cycle of Ancylostoma duodenale:

  • Infective form: Filariform larva
  • Portal of entry: Skin
  • Migration: Through lungs.
  • Site of location: Small intestine.

Life cycle:

(a) Host: Man is the only definitive host. No intermediate host.

(b) Stages: The various stages of life cycle are described below:

Stage-1: Passage of eggs from the infected host: The eggs, containing segmented ova with four blastomeres, are passed out in the faeces of the human host.

Stage-2: Development in soil: Egg→ Rhabditiform larvae → Molts twice → Filariform larva (infective stage).

Stage-3: Entrance into a new host: by penetration of skin, after cast off their sheaths.

Stage-4: Migration: Filariform larva in subcutaneous tissue→ Migrates through lymphatics or small venules →Venous circulation → Right heart→→ Pulmonary circulation → Alveolar space → Migration to bronchioles→ Trachea→ Larynx→ Epiglottis→ Pharynx → Swallowed in small intestine, during migration or on entering the esophagus, a third moulting occurs.

age-5: Localization and lying of eggs: The growing larva settle down into small intestine → Fourth moulting occurs→ Sexual maturation of larva→ Adult worm→→ Female adult worm lay egg→ The cycle is repeated→ Time interval skin penetration and appearance of egg in faeces is about 6 weeks.

Q-5-a) Write short note on vaccine. (Jan-2020)


Vaccines are immuno-biological substances which are introduced to the body of a person or other animals to produce immunity against a specific disease.

Types of vaccines: Vaccines may be–

1. Live attenuated vaccine:


  • BCG vaccine (for tuberculosis).
  • Typhoid oral.
  • Plague.


  •  Oral polio vaccine.
  • Yellow fever. 
  •  Rubella
  •  Mumps
  • Influenza


  • Epidemic Typhus.

2. Inactivated or killed vaccine:


  • Pertussis vaccine (for whooping cough).
  •  Cholera vaccine.
  •  Typhoid vaccine. 
  • Plague vaccine.


  • Salk vaccine (Polio).
  • Rabies.
  • Influenza. 
  • Hepatitis B.

3. Toxoids:


  • Tetanus toxoid-Tetanus.
  •  Diphtheria toxoid – Diphtheria.

4. Extracted cellular fractions:

  • Meningococcal vaccine. 
  • Pneumococcal vaccine.

5. Combination.

  • DPT-Diphtheria, Pertussis, Tetanus. 
  • MMR-Measles, Mumps, Rubella.
  • DT.
  • DP.
  • DPT with typhoid vaccine. 
  • DPTP (DPT + inactivated polio).

6. Recombinant vaccine: 

More recent preparations are subunit vaccine and recombinant vaccine, eg recombinant hepatitis-B vaccine.

Q-5-b) Write short note on Malarial Parasite. Jan-2020


Malaria is an infectious disease caused by plasmodium and transmitted by the bite of female anopheles mosquito, characterized by-fever, anemia, splenomegaly etc.

Therapeutic malaria:

Malarial infection has been artificially induced for the curative treatment of neurosyphilis. Plasmodium vivax is used for this purpose. This is called therapeutic malaria.

Malarial parasites:

  • Plasmodium vivax
  • Plasmodium falciparum 
  • Plasmodium ovale
  •  Plasmodium malariae

Definition/diagnosis of severe malaria:

  • Fever or history of fever within last 48 hours and
  •  One or more of the following features of severity:
  • A change of behavior, confusion or drowsiness. 
  • Altered consciousness or coma (cerebral malaria). ).
  • Generalized convulsions (<2 episodes in 24 hours)
  •  Hypoglycemia (<2.2 mmol/L or <40 mg/dl).
  • Acidosis 
  •  Difficulty in breathing or acute pulmonary oedema and adult respiratory distress syndrome 
  • Oliguria or acute renal failure (< 17 ml/hour or < 400 ml/24 hours and 0.3 ml/kg/hour in children) 
  • Severe anaemia (haematocrit 15%; Hb <5p/dl).
  • Fluid and electrolyte disturbance. 
  • Circulatory collapse or shock (algid malaria).
  • Haemoglobinuria 
  • Jaundice (clinical).
  • Bleeding tendency or abnormal bleeding.
  • Severe prostration, i.e. extreme weakness for which the patient cannot walk, stand or without assistant & in case of small child unable to eat.
  •  Severe vomiting.
  • Hyper parasitaemia, and
  • Presence of asexual form of P. falciparum in Blood Slide Examination (BSE) or positive rapid diagnostic test (RDT) for P. falciparum.

Q-5-c) Write short note on Laboratory hazards. (Jan-2020)

)There are many different types of laboratory hazards, but they can be broadly classified into three categories: 

  1. Chemical hazard
  2.  Biological hazard and
  3.  Physical hazard.
  • Chemical hazards are caused by chemicals that can be harmful to human health or the environment. They can be corrosive, flammable, toxic, or explosive. Some common chemical hazards include acids, bases, solvents, and heavy metals.
  • Biological hazards are caused by microorganisms such as bacteria, viruses, and fungi. These microorganisms can cause disease or infection. Some common biological hazards include HIV, SARS-CoV-2, and anthrax.
  • Physical hazards are caused by physical agents such as electricity, radiation, and moving machinery. These hazards can cause burns, cuts, injuries, or even death. Some common physical hazards include lasers, high voltage, and sharp objects.

It is important to be aware of the different types of laboratory hazards and to take appropriate safety precautions to avoid them. Some general safety precautions include:

  • Reading and following all safety labels and procedures.
  • Using personal protective equipment (PPE) as required.
  • Working in a well-ventilated area.
  • Handling chemicals and biological materials carefully.
  • Reporting any hazards to your supervisor immediately.

Q-5-d) Write short note on: Tyndallization. (Jan-2020)


Tyndallization is a sterilization procedure by intermittent heating at 100°C.


Principle of tyndallization:

Heating for 1 hour at 100°C, then incubation in a suitable media at room temperature for successive 3 days. Incubation induces germination of spores, which are killed by heating.

Heating for 30 minutes at 100°C→ Vegetative form bacteria are destroyed but spores remain→ Incubation for overnight at room temperature (37°C)→ Generation of spores → Second time heating, for 30 minutes at 100°C→ Vegetative form of bacteria are destroyed but few spores remain → Again incubation for overnight at room temperature (37°C) → Germination of few spores→ 3rd time exposure→ All the organism including spores are destroyed.


Sterilization of culture media containing egg,serum, sugar & gelatin.

Q-5-e) Write short note on: Pasteurization. Jan-2020


Pasteurization may be defined as the process by which milk is heated upto such a temperature & for such a period of time to destroy the microorganisms within the milk without altering the composition, flavor color & nutritive value of milk.


1. Holding method – 63°C for 30 minutes

2. Flash method-72°C for 15 seconds.

3. HTST method – High temperature for a short time.


The sterilization/killing of organisms of milk & milk products causes milk borne diseases.

Bacteria removed by pasteurization:

  • Mycobacterium bovis
  • Salmonella
  • Escherichia coli
  • Brucella abortus

Advantages of pasteurization over the boiling:

 Boiling causes destruction of many nutrients & flavour of the milk, but pasteurization preserves all the quality of the milk.

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