Department of microbiology microbial food technology group a diploma in quality assurance in microbiology diploma


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Introduction :

  • Neurotoxin is produced by Clostridium botulinum which causes disease called Botulism.

  • Death in infants is within 3 – 6 days & adults is 6 – 9 days.

  • Organism is Gram positive, anaerobes, gas forming rod shaped bacteria which occurs in soil.

  • Antigen are classified based on toxigenicity as A,B,C,D,E,F,G – 7 types.

  • Type A  Highly toxic to humans than B

  • Type B, F & G  Less toxic to man.

  • Type C  Cow, Cattle, other animals.

  • Type D  Cattle.

  • Type E  Fish and fish products.

Growth and toxin production :

  • The factors that influence the growth of organism are nutrient content of food [canned food, meat & fish], pH, temperature, oxidation - reduction potential, salt concentration, moisture content.

  • Contamination of food may be due to soil.

  • Toxin is produced at pH 4.5, Organism must autolyse or sporulate to produce toxin.

  • Non-proteolytic toxins are fully activated, These can be activated by binding with trypsin.

  • Medium must have glucose or maltose for growth & toxin production.

  • Medium should have nitrogen source, carbon source, casein and protein.

  • Temperature [350C], pH [acidic – toxin production, Neutral – growth, anaerobic environment.

  • Nacl inhibits the growth of the organisms.

Toxins :

  • Toxins are protein substances produced by the organism during the growth and it is thermolabile.

  • Denaturation of the toxin is at 800C for 5 – 6 mins [type A], 900C for 15 mins [type B].

  • Radiation is used for toxin denaturation because it sterilizes deeply.

  • Type A & B spores are highly heat resistant and the D valve is 1210C – 0.21 min – Type A, 1000C – 0.003 to 0.017 mins – Type E.

Foods involved :

  • Meat, string beans, sweet corn, beets, fish, asparagus, spinach, canned foods [ proteolytic – odor,

non-proteolytic – gas production].

Disease :

  • Incubation period [12 – 36 hrs], symptoms include nausea, vomiting, diarrhea, fatigue, dizziness, headache, constipation, double vision, difficult in swallowing & speaking, mouth dryness, throat constriction, swollen & coated tongue.

  • Temperature is normal or subnormal, involuntary muscles become paralyzed, paralysis spreads to the respiratory tract, heart & death results due to respiratory failure.

  • Symptoms are similar for type A,B,E poisoning but nausea, vomiting & urinary retention usually more severe with type E toxin.

  • Treatment [antitoxin administration, artificial respiration, keeping the patient isolated, maintaining the fluid balance in the body].

  • Neurotoxin ingested with food Neurotoxin passes through gut mucosa into blood stream

Toxin spreads throughout the body through bloodstream

Toxin binds to nerve at the junction This results in paralysis.

Conditions for outbreak :

  • Presence of the spores of type A, B, E.

  • A food in which the spores can germinate & the clostridia can grow & produce toxin.

  • Survival of the spores of the organism eg. Because of inadequate heating in canning or inadequate processing.

  • Environmental conditions after processing that will permit germination of the spores, growth & toxin production by the organism.

  • Insufficient cooking of the food to inactivate the toxin.

  • Ingestion of the toxin bearing food.

Prevention of outbreaks :

  • Use of approved heat processes for canned foods.

  • Rejection of all gassy [swollen] or otherwise spoiled canned foods.

  • Refusal even to taste a doubtful food.

  • Avoidance of foods that have been cooked, held & not well heated.

  • Boiling of a suspected food for atleast 15 mins.

  • Avoidance of raw or precooked foods.

  • To prevent botulism from smoked fish :

    1. good sanitation throughout production & handling.

    2. fish heated to atleast 820C – 30 mins in coldest part.

    3. fish be frozen immediately after packaging & kept frozen.

    4. all packaged be marked “ perishable – keep frozen”.

Infant botulism :

      • Infants --> predisposed constipation.

      • Weakness, lack of sucking, loss of head control, diminished gag reflex.

      • Death within 3 – 6 days.

      • Milk, canned food [cereals] may cause intoxication.

Through mother’s infection.

2.Discuss The Food Borne Infection Of Salmonellosis

Introduction :

  • Causes gastroenteritis, Gram negative rods, non-spore formers, non-lactose fermenting organisms, facultative anaerobes, ferments glucose to produce gas and belongs to Enterobacteriaceae family.

Classification :

  • S. tyhi [ infect humans], S. typhimurium [infect animals].

  • Serotypes --> Somatic Ag [O], Capsular Ag [Vi], Flagellar Ag [H].

  • Temperature [370C – optimum, 450C – maximum, 6.7 – 7.80C - Minimum], pH [ neutral – optimum,

    1. – minimum, 9 - maximum].

  • Increased H2S  S. typphimurium, S. enteritis, decreased H2S  S. typhi.

  • Grows well in low acid foods [5.5 – 5.7].

  • Heat sensitive bacteria [ 660C – 12 mins, 600C – 78 to 83 mins].

  • D value [600C for 0.06 – 11.3 mins].

  • More concentration of bacteria can cause disease  atleast 100 sp.

  • Very less infective  S.pullorum, Highly infective  S.enteritis.

Sources of Salmonella contamination :

  • Humans [ Direct / Indirect, feces, handling, water contamination.]

  • Animals [Direct / Indirect] – Dogs, cattle, cat [feces, infection, infected animal meat contamination, poultry products – hen, chicken, meat & egg] due to improper processing, egg coated with fecal material. Increased refrigeration results in increased moisture & forms the pores & through this the organism enters.

  • Bakery products – sources through flies, cockroach, insects from infected to normal food.

Foods involved :

  • Bakery products, Meat, Chicken, Milk and milk products – cheese, egg and egg products, cream cakes, Bacon & ham.

Disease :

  • Incubation period [12 – 36 hrs]. Symptom includes gastrointestinal infection are nausea, vomiting, abdominal pain, diarrhea, headache, chills.

  • Other evidences are watery, greenish, foul-smelling stool, prostration, muscular weakness, faintness, moderate fever, restlessness, twitching, drowsiness.

  • Mortality is low [1%]. Diarrhea to death in 2 – 6 days.

  • Symptoms persist for 2 – 3 days, followed by uncomplicated recovery. Carriers – 0.2 to 5 %.

  • Organism ingested along with the food Organisms grows in the host gut Organism affects gut giving gastroenteritis

  • Bacterial cells ingested along with the food Cells invade the tissues & release endotoxin

Fever, vomiting , Diarrhea [fluid & electrolyte loss] --- It leads to loss of water & sodium ions

Conditions for outbreak :

  • Food must contain or become contaminated with the salmonella bacteria.

  • Good culture medium.

  • Viable organism must be ingested.

Prevention of outbreak :

  • Avoidance of contamination of food [diseased human beings, animals, carriers, contaminated eggs].

  • Destruction of the organisms in food by heat.

  • Prevention of the Salmonella growth in foods by adequate refrigeration or by other means.

  • In the prevention of contamination :

    1. care and cleanliness in food handling & preparation.

    2. Food handlers should be healthy & clean.

    3. Rats & other vermin & insects should be kept away from foods.

    4. Ingredients used in food should be free of Salmonella.

    5. Food should not be allowed to stand at room temperature for any length of time.



Organism :

  • Gram positive, non-motile, anaerobic, spore forming rods.

  • Temperature [43 – 470C], pH [ 5 – 9 ], D value [900C – 0.015 to .71 mins].

  • Organism growth is inhibited by 5% Nacl.

  • Toxins produced are A, B, C, D, E where A is infective and C is less infective.

Foods :

  • Raw foods, soil, sewage, animal feces, meat, fish, poultry.

Disease :

  • Incubation period [8-24 hrs].

  • Abdominal pain, diarrhea, gas, fever, nausea, vomiting are the symptoms.

  • Enterotoxin released in the gut during sporulation results in fluid accumulation in the intestine.

  • Toxin is heat labile [ 600C – 10 mins – inactivated].


1. Enterotoxin heat labile

2. Inactive at 60c for 10 min

3. Abdominal pain, diarrhoea with gas trouble, fever, nausea, vomiting.

  1. Mortality is low.

Conditions for outbreak :

  • Food contaminated with the organism.

  • Food is not maintained properly.

  • Inadequate cooling.

  • Food is consumed without reheating.

Cells sporulate & produce enterotoxin

Infective dose:

Large number of vegetative cells in a food are required to produce food poisoning. The minimum seems to be about 7 x 105/g of food ingested but numbers as high as 108 /g or greater may be required.

Prevention of outbreaks:

  1. Eat meat immediately after cooking.

  2. Cool cooked meats rapidly to 7ºC or below for storage and reheat to an internal T of above 70ºC before consumption.

  3. Store cooked chilled foods correctly and heat to an internal T of 70 C or above.

  4. Foods held hot before consumption should be maintained at 60 C or above.

  5. Avoid transferring spores from raw to cooked meat during boiling, slicing, mincing but not using common utensils and observing good hygiene.

  6. Adequate & rapid cooling of cooked foods.

  7. Reheating.

  8. Personal hygiene.

  9. Sanitation.

3.What is foodborne disease? 

Foodborne disease is caused by consuming contaminated foods or beverages.  Many different disease-causing microbes, or pathogens, can contaminate foods, so there are many different foodborne infections. 

In addition, poisonous chemicals, or other harmful substances can cause foodborne diseases if they are present in food.  More than 250 different foodborne diseases have been described. 

Most of these diseases are infections, caused by a variety of bacteria, viruses, and parasites that can be foodborne.  Other diseases are poisonings, caused by harmful toxins or chemicals that have contaminated the food, for example, poisonous mushrooms.  

These different diseases have many different symptoms, so there is no one "syndrome" that is foodborne illness.  However, the microbe or toxin enters the body through the gastrointestinal tract, and often causes the first symptoms there, so nausea, vomiting, abdominal cramps and diarrhea are common symptoms in many foodborne diseases. 

Many microbes can spread in more than one way, so we cannot always know that a disease is foodborne.  The distinction matters, because public health authorities need to know how a particular disease is spreading to take the appropriate steps to stop it. 

For example, Escherichia coli O157:H7 infections can spread through contaminated food, contaminated drinking water, contaminated swimming water, and from toddler to toddler at a day care center.  Depending on which means of spread caused a case, the measures to stop other cases from occurring could range from removing contaminated food from stores, chlorinating a swimming pool, or closing a child day care center. 

4.What are the most common foodborne diseases? 

The most commonly recognized foodborne infections are those caused by the bacteria Campylobacter, Salmonella, and E. coli O157:H7, and by a group of viruses called calicivirus, also known as the Norwalk and Norwalk-like viruses. 

Campylobacter is a bacterial pathogen that causes fever, diarrhea, and abdominal cramps.  It is the most commonly identified bacterial cause of diarrheal illness in the world.  These bacteria live in the intestines of healthy birds, and most raw poultry meat has Campylobacter on it.  Eating undercooked chicken, or other food that has been contaminated with juices dripping from raw chicken is the most frequent source of this  infection. 

Salmonella is also a bacterium that is widespread in the intestines of birds, reptiles and mammals.  It can spread to humans via a variety of different foods of animal origin.  The illness it causes, salmonellosis, typically includes fever, diarrhea and abdominal cramps.  In persons with poor underlying health or weakened immune systems, it can invade the bloodstream and cause life-threatening infections. 

E. coli O157:H7 is a bacterial pathogen that has a reservoir in cattle and other similar animals.  Human illness typically follows consumption of food or water that has been contaminated with microscopic amounts of cow feces.  The illness it causes is often a severe and bloody diarrhea and painful abdominal cramps, without much fever.   In 3% to 5% of cases, a complication called hemolytic uremic syndrome (HUS) can occur several weeks after the initial symptoms.  This severe complication includes temporary anemia, profuse bleeding, and kidney failure. 

Calicivirus, or Norwalk-like virus is an extremely common cause of foodborne illness, though it is rarely diagnosed, because the laboratory test is not widely available.  It causes an acute gastrointestinal illness, usually with more vomiting than diarrhea, that resolves within two days. 

Unlike many foodborne pathogens that have animal reservoirs, it is believed that Norwalk-like viruses spread primarily from one infected person to another.  Infected kitchen workers can contaminate a salad or sandwich as they prepare it, if they have the virus on their hands.  Infected fishermen have contaminated oysters as they harvested them. 

Some common diseases are occasionally foodborne, even though they are usually transmitted by other routes.  These include infections caused by Shigella, hepatitis A, and the parasites Giardia lamblia and Cryptosporidia.  Even strep throats have been transmitted occasionally through food. 

In addition to disease caused by direct infection, some foodborne diseases are caused by the presence of a toxin in the food that was produced by a microbe in the food.  For example, the bacterium Staphylococcus aureus can grow in some foods and produce a toxin that causes intense vomiting. 

The rare but deadly disease botulism occurs when the bacterium Clostridium botulinum grows and produces a powerful paralytic toxin in foods.  These toxins can produce illness even if the microbes that produced them are no longer there. 

Other toxins and poisonous chemicals can cause foodborne illness.  People can become ill if a pesticide is inadvertently added to a food, or if naturally poisonous substances are used to prepare a meal.  Every year, people become ill after mistaking poisonous mushrooms for safe species, or after eating poisonous reef fishes. 

5.How are foodborne diseases diagnosed? 

 The infection is usually diagnosed by specific laboratory tests that identify the causative organism.  Bacteria such as Campylobacter, Salmonella, E. coli O157 are found by culturing stool samples in the laboratory and identifying the bacteria that grow on the agar or other culture medium. 

Parasites can be identified by examining stools under the microscope.  Viruses are more difficult to identify, as they are too small to see under a light microscope and are difficult to culture.  Viruses are usually identified by testing stool samples for genetic markers that indicate a specific virus is present. 

Many foodborne infections are not identified by routine laboratory procedures and require specialized, experimental, and/or expensive tests that are not generally available. 

If the diagnosis is to be made, the patient has to seek medical attention, the physician must decide to order diagnostic tests, and the laboratory must use the appropriate procedures.  Because many ill persons to not seek attention, and of those that do, many are not tested, many cases of foodborne illness go undiagnosed. 

For example, CDC estimates that 38 cases of salmonellosis actually occur for every case that is actually diagnosed and reported to public health authorities

6.How are foodborne diseases treated? 

There are many different kinds of foodborne diseases and they may require different treatments, depending on the symptoms they cause. 

Illnesses that are primarily diarrhea or vomiting can lead to dehydration if the person loses more body fluids and salts (electrolytes) than they take in.  Replacing the lost fluids and electrolytes and keeping up with fluid intake are important. 

If diarrhea is severe, oral rehydration solution such as Ceralyte*, Pedialyte* or Oralyte*, should be drunk to replace the fluid losses and prevent dehydration.  Sports drinks such as Gatorade* do not replace the losses correctly and should not be used for the treatment of diarrheal illness. 

Preparations of bismuth subsalicylate (e.g., Pepto-Bismol)* can reduce the duration and severity of simple diarrhea.  

If diarrhea and cramps occur, without bloody stools or fever, taking an antidiarrheal medication may provide symptomatic relief, but these medications should be avoided if there is high fever or blood in the stools because they may make the illness worse. 

*CDC does not endorse commercial products or services

7.How do public health departments track foodborne diseases? 

Routine monitoring of important diseases by public health departments is called disease surveillance.  Each state decides which diseases are to be under surveillance in that state.

  In most states, diagnosed cases of salmonellosis, E. coli O157:H7 and other serious infections are routinely reported to the health department. 

The county reports them to the state health department, which reports them to CDC.  Tens of thousands of cases of  these "notifiable conditions" are reported every year.  For example, nearly 35,000 cases of Salmonella infection were reported to CDC in 1998.

However, most foodborne infections go undiagnosed and unreported, either because the ill person does not see a doctor, or the doctor does not make a specific diagnosis.  Also, infections with some microbes are not reportable in the first place. 
To get more information about infections that might be diagnosed but not reported, CDC developed a special surveillance system called FoodNet.  FoodNet provides the best available information about specific foodborne infections in the United States, and summarizes them in an annual report. 

 In addition to tracking the number of reported cases of individual infections, states also collect information about foodborne outbreaks, and report a summary of that information to CDC. 

About 400-500 foodborne outbreaks investigated by local and state health departments are reported each year.  This includes information about many diseases that are not notifiable and thus are not under individual surveillance, so it provides some useful general information about  foodborne diseases.  
8.What are foodborne disease outbreaks and why do they occur? 

An outbreak of foodborne illness occurs when a group of people consume the same contaminated food and two or more of them come down with the same illness. 

It may be a group that ate a meal together somewhere, or it may be a group of people who do not know each other at all, but who all happened to buy and eat the same contaminated item from a grocery store or restaurant. 

For an outbreak to occur, something must have happened to contaminate a batch of food that was eaten by a the group of people.  Often, a combination of events contributes to the outbreak. 

A contaminated food may be left out a room temperature for many hours, allowing the bacteria to multiply to high numbers, and then be insufficiently cooked to kill the bacteria. 

Many outbreaks are local in nature.  They are recognized when a group of people realize that they all became ill after a common meal, and someone calls the local health department. 

This classic local outbreak might follow a catered meal at a reception, a pot-luck supper, or eating a meal at an understaffed restaurant on a particularly busy day. 

However, outbreaks are increasingly being recognized that are more widespread, that affect persons in many different places, and that are spread out over several weeks. 

For example, a recent outbreak of salmonellosis was traced to persons eating a breakfast cereal produced at a factory in Minnesota, and marketed under several different brand names in many different states. 

No one county or state had very many cases and the cases did not know each other. 

The outbreaks was recognized because it was caused by an unusual strain of  Salmonella, and because state public health laboratories that type Salmonella strains noticed a sudden increase in this one rare strain.  

In another recent outbreak, a particular peanut snack food caused the same illness in Israel, Europe and North America.  Again, this was recognized as an increase in infections caused by a rare strain of Salmonella

  The vast majority of reported cases of foodborne illness are not part of recognized outbreaks, but occurs as individual or "sporadic" cases. 

It may be that many of these cases are actually part of unrecognized widespread or diffuse outbreaks.  Detecting and investigating such widespread outbreaks is a major challenge to our public health system. 

This is the reason that new and more sophisticated laboratory methods are being used at CDC and in state public health department laboratories. 

9.List out the information centers for food safety and foodborne diseases? 

  • National Food Safety Initiative 

  • CDC's Food Safety Initiative home page 

  • U.S. Food and Drug Administration 

  • U.S. Food Safety and Inspection Service (FSIS) 

  • U.S. Environmental Protection Agency 

  • Role of the federal agencies in food safety 

  • Gateway to government food safety information 

  • Partnership for Food Safety Education/Fight BAC!TM 

  • Food Safety Training and Education Alliance 

  • Foodborne Illness Information Center 

  • National Food Safety Education Month 

  • Travelers' Health 


The procedure to be followed in testing the samples of food or specimens from human source upon receipt in the laboratory will depend on the type of food and the information available about the outbreak of food illness.

The first act in most laboratories is to make a microscopic examination of a preparation of the food stained by the Gram’s method. The smear is made from liquid or from the sediments from homogenized, centrifuged food.

The microscopic examination may give a clue to the causative if the sample has been properly refrigerated.

Preventive measures:

To keep foods as free as possible from contamination which pathogenic agents by selection of uncontaminated foods, by adequate pasteurization or other heat processing, by avoiding contamination from infected food handlers or carriers, and by generally good sanitary practice throughout the handling, preparation and serving of foods.

To eliminate opportunities for the growth of pathogens, toxigenic or infectious, in foods by adjustment of the composition, by prompt consumption after preparation, and by adequate refrigeration of perishable foods if they must be hold for any considerable time, keeping foods warm for long periods is especially to be avoided.

To reject suspected foods

To educate the public better concerning the causes and prevention of food borne illness and the dangers involved.


Employee health standards:


The food industry sanitarian is concerned which specific aseptic practices in the preparation, processing, and packaging of the food products of a plant and the health of cleanliness and sanitation of plant and the health of employee.

Food and plant sanitation:

Specific duties in connection which the food products may involve quality control and storage of raw products, the provision of a good water supply; prevention of the contamination of the foods at all stages during processing from equipment, personnel, & the vermin; and supervision of packaging and ware housing of finished products.

The supervision of cleanliness and sanitation of plant and premises includes not only the maintenang of clean and well sanilized surfaces of all equipment toughing the foods but also generally goods house keeping in and the plant and adequate treatment and disposal of wastes.

Employee health standards:

Duties affecting the health of the employees include provision of a potable water supply, supervision of matters of personal lygiene, regulation of sanitary facilities in the plant and in plant operated of plant lighting, heating and ventilation. The sanitarian may also participate in training employees in sanitary practices.

For the most part, sanitarians concern themselves chiefly with general aspects of sanitation, making inspections, consulting with personnel responsibless for details of canitation and executives directing such work, and training personnel in sanitation.



The food sanitation is concerned directly or indirectly with the adequate treatment and disposal of wastes from the industry. Solid and concentrated wastes ordinarily are kept separate the watery wastes and may be used directly for food, feed fertilizers, or other purpose; may first be concentrated dried, or fermented (ex: pea vine silage);or may be carted away to available land as unusable waste.


Care is taken to keep out of the waste waters as much wasted liquid or solid food material as possible by taking precautions to avoid introduction into the watery waste of drip, leakage, overflow, spillage, large residues in containers, foam, frozen on and food dust during the handling and processing of the food.

I t is recommended that sewage of human origin be kept separate from other plant waters because of the kept separate from other plant waters because of the possible presence of human intestinal pathogens.

Such sewage may be turned in to a municipal system.

Wastes from food plants ordinarily contain a variety of organic compounds, which range from simple and readily oxidizable kinds to those which are complex and difficult to decompose.

The strength of the sewage or food waste containing organic matter is expressed in terms of biochemical oxygen

demand ( BOD), which is the quantity of O2 used by aerobic microorganisms and reducing compounds in the

Stabilization of decomposable matter during a selected time at a certain temperature.

A period of 5 days at 20oC is generally used, and results are expressed as 5 days BOD.

Wastes from a food plant to be emptied into a body of water must either be so greatly diluted by that water must be treated first to reduce the oxidizable compounds to a harmless level.

Preliminary treatments of food- plant wastes by chemical means may be employed, but most systems of treatment and disposal depend on

1. Screening out of large particles.

2. Floating of fatty and other floating materials

3. Sedimentation of as much of the remaining solids

4. Hydrolysis, fermentation and putrefaction of complex organic compounds and finally

5. Oxidation of the remaining solids inn the water to a point where they can enter a municipal sewage treatment and disposal systems.


Dilution, by running waste waters into a large body of water.

Irrigation, in which wastewaters are sprayed onto shallow artificial ponds (with or without treatments)

Use of trickling filters; made of crushed rock, coke, filter tile, etc.,

Use of the activated- sludge method, in which wastewater is inoculated heavily with sludge from a previous reaction.

Use of anaerobic tanks of various kinds, where settling, hydrolysis, putrefaction and fermentation take place.





Some food borne disease outbreaks are not caused by bacteria or their toxins but results from mycotoxins, viruses, rickettsiae, parasitic worms, or protozoa or from the consumption of food contaminated with toxin substances.

10.Write a detailed account on mycotoxins and the key management steps to prevent mycotoxin contamination.


Mycotoxins are fungal metabolites. Some are highly toxic to many animals potentially toxic to human beings. Recent concern is related to their carcinogenic properties and their presence in many food items.


The fungi include the moulds, yeasts, blights, rusts and mushrooms.

Many fungi are useful. Some are edible. Ex: Mushrooms and single cell protein from yeast.

Other is widely used in industrial and food fermentation.

Ex: Aspergillus oryzae is used in the production of soy sauce, miso and sake and moulds take part in the ripening of certain cheese.

Some mushrooms are harmful or poisonous to humans, but in contrast, moulds have generally been regarded as harmless.

Many fungi can be isolated from plants, including Alternaria, Rhizopus, Fusarium, Cladosporium, Helminthosporium and Chaetomium.

The two predominant genera of fungi in stored products are probably Penicillium and Aspergillus, members of which produce mycotoxins.

The syndrome resulting from the ingestion of toxin in a mold- contaminated food is referred to as mycotoxicosis.


Aflatoxins are produced by certain strains of A.falvus and A. parasiticus.


The two major metabolites or aflatoxins have been designated B, and G1 because they fluoresce Blue(B1) and Green (G1).B2 and G2 are the dihydroderivatives of B1 and G1.


Aflatoxin B1, the most toxic of the aflatoxins, is toxic to various animals. Many of the other aflatoxin have been shown to be toxic or carcinogenic to different species of fish, mammals and poultry.


  • Many foods will support the growth of toxigenic strains if inoculated, including various dairy products, bakery products, fruit juices, cereals and forage crops.

  • In most cases, the growth of a toxigenic strain and the elaboration of aflatoxin occurs following harvesting or formulation of the product.

  • Peanuts, cottonseeds, and corn, however, differ significantly in that these products are susceptible to fungal invasion, growth and mycotoxin production before harvesting.

  • The contamination and potential for aflatoxin production in these crops is related to insect damage, humidity, weather conditions.


    • Patulin:

Produced by Penicillium expansum

    • Ochratoxin

Produced by Asperillus ochraceus

    • Luteoskyrin

Produced by Penicillium islandicum

    • Roquefortine

Produced by P. roqueforti


  • Quality of foods and food products may be defined as the degree of excellence of the various characteristics that influence consumer acceptance as well as consumer safety.

  • The selection of a particular food by a discerning consumer is made by the judgment of all the physical senses that is, tough, smell, taste and hearing.

  • Consumer safety requires the evaluation of food quality with respect to nutritional quality, hygienic condition and keeping storage.



The stated chief purposes of microbiological criteria for foods are to give assurance:

    1. That the foods will be acceptable from the Public health standpoint that is will not be responsible for the spread of infectious disease or for food poisoning.

    2. That the foods will be of satisfactory quality

    3. The foods will have keeping qualities that should be expected of the product.

    4. Sampling for tests is a problem since the lack of homogeneity in most foods makes location, size and number of samples significant.

    5. Standards usually are based on total numbers of organisms, numbers of organisms, numbers of indicator organisms or numbers of pathogens.


  • It may be necessary to carry out a microbiological examination of a food for one or more of a number of reasons.

  • Escherichia coli is a natural component of the human gut flora and its presence in the environment, or on foods, generally implies some history of contamination of faecal origin.

  • Traditional the group chosen has been designated the coliforms- those organisms capable of fermenting lactose in the presence of bile at 37C.

  • This will include most strains of E. coli but also includes organisms such as Citrobactor and Enterobactor.


. When examining foods, the possibility of detecting the presence of microorganisms by looking at a sample directly under the microscope should not be missed.

. A small amount of material can be mounted and teased out in a drop of water on a slide, covered with a cover slip, and examined.


The full microbiological examination usually requires that individual viable propagules are encouraged to multiply in liquid media or on the surface, or with in the matrix, of a medium solidified with agar.



1. Plate count agar Aerobic mesophilic count

2. Mac Conkey broth MPN of coliforms in water

3. Brilliant Green/Lactose/ Bile broth MPN of coliforms in food

4. Violet red/ bile/Glucose agar Enumeration of Enterobacteriaceae.

5. Crystal violet /Azide / Blood agar Enumeration of faecal Streptococci.

6. Baird- Parker agar Enumeration of S. aureus

7. Vassiliadis broth Selection enrichment of Salmonella.

8. Thiosulfate / bile/ citrate/ Sucrose agar Isolation of Vibrios

9. Rose Bengal/ Chloramphenicol agar Enumeration of moulds and yeasts

10. Mac Conkey agar E. coli


Plate counts-

  • It has already been suggested that to count microorganisms in a food sample by direct microscopy has a limited sensitivity because of the very small sample size in the field of view at the magnification needed to see microorganisms, especially bacteria.

  • In a normal routine laboratory the most sensitive methods of detecting the presence of a viable bacterium is to allow it to amplify itself to form a visible colony.

  • This forms the basis of the traditional pour plate and spread plate and most probable number counts.


    • .Cultural methods are relatively labour intensive and require time for adequate growth to occur.

    • . Many food microbiologists also consider that the traditional enumeration methods are not only too slow but lead to an over dependence on the significance of numbers of colony forming units.

    • . A number of methods have been developed which aim to give answer of redox to as “Rapid methods”.

1. Dye- reduction test:-

      • A group of tests which have been used for some time in the dairy industry dependent on the response of a number of redox dye to the presence of metabolically active microorganisms.

      • They are relatively simple and rapid to carry out at low cost.

      • The redox dyes are able to take up electrons from an active biological system and this results in a change of colour.

2. Immunological methods:-


3. DNA/RNA methodology:-

PCR method

11.Write an account on idli fermentation and the micro organisms involved in the fermentation.



The idli , also romanized "idly" or "iddly" and plural "idlis", is a savory cake popular throughout South India. The cakes are usually two to three inches in diameter and are made by steaming a batter consisting of fermented black lentils (de-husked) and rice. The fermentation process breaks down the starches so that they are more readily metabolized by the body.

Most often eaten at breakfast or as a snack, idlis are usually served in pairs with chutney, sambar, or other accompaniments. Mixtures of crushed dry spices such as milagai podi are the preferred condiment for idlis eaten on the go.

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