Microbiology Flashcards
Microbiology
Is the study of organisms that are too small and are not visible clearly to the naked eye or un-aided eye when they exist individually.
Microorganisms general size
Less than 0.1mm
Extremophiles
Some microorganisms are capable of inhabiting extreme environmental conditions that are unfavourable or even lethal for other organisms.
Thermophiles - condition
High temperatures
Psychrophiles - condition
Low temperatures
Acidophiles - condition
acid pH
Alkaliphiles - condition
basic pH
Halophiles - condition
require NaCl
Barophiles - condition
high pressure
High growth rate of microorganisms
Posses a high surface area to volume ratio due to their small size.
Flowing rate of materials in to the inside of the cells and exit of waste materials to the outside of the cells increases and results in high metabolic rate.
Average generation time or the time taken required to double the population of microorganisms is relatively less.
Basic 3 distinct shapes of bacteria
Rod shape - Bacillus
Spherical shape - Coccus
Spiral shape - Spirillum
2 morphological varieties found in virus according to the symmetry of protein coats
Icosahedral
Helical
4 major nutritional types seen among microorganisms
Chemoautotrophs
Chemoheterotrophs
Photoautotrophs
Photoheterotrophs
4 physiological groups of microbes
Obligate aerobes
Obligate anaerobes
Facultative anaerobes
Microaerophiles
2 types of nitrogen fixing microbes with examples
Free living - Azotobacter sp
Symbiotic - Rhizobium sp. with legume roots
Different forms of coccus bacteria
Coccus
Diplococcus
Streptococcus
Tetrad
Sarcinae
Straphylococcus
Coccus
Cells divide in 1 plane
Divided cells detach from each other after cell division
Diplococcus
Cells divide in 1 plane
Divided cells remain in pairs
Streptococcus
Cells divide in 1 plane
Divided cells remain attached in chain like patterns
Tetrad
Cells divide in 2 planes producing 4 cells remain attaches together
Sarcinae
Cells divide in 3 planes and remain attached in group of 8 cells
Straphylococcus
Cells divide in multiple planes and form grape like cluster of cells
Types of bacilli bacteria
Single bacillus - Single rod
Diplobacillus - Remain in pairs after cell division
Streptobacillus - Occurs in chain after cell division
Types of spiral bacteria
Vibrio - Bacteria look like curved rods
Spirillum - Helical shape, like a corkscrew and rigid body
Spirochete - Helical shape, flexile body
Photoautotrophs (source of energy, source of carbon and examples)
Light
CO2
Purple sulfur and green sulfur bacteria
Photoheterotrophs (source of energy, source of carbon and examples)
Light
Organic carbon
Purple non sulfur bacteria
Chemoautotrophs (source of energy, source of carbon and examples)
Inorganic chemicals
CO2
Nitrobacter, Nitrosomanas, Thiobacillus thiooxidans
Chemoheterotrophs (source of energy, source of carbon and examples)
Organic chemicals
Organic carbon
Most bacteria
Obligate aerobic
Require O2 for their survival
Generate energy by oxidative phosphorylation
Acetobacter sp.
Obligate anaerobic
Cannot survive in the presence of O2
Generate energy by fermentation
Clostridium sp.
Facultative anaerobic
Prefer to grow in the presence of O2 producing energy by oxidative phosphorylation
They can also grow in anaerobic environments using fermentation
Escherichia coli
Microaerophilic
Can grow only in O2 concentrations lower than those in air
Lactobacilus sp
Reproduction methods of bacteria
Mostly undergoes asexual reproduction - Binary fission, fragmentation or budding
Performs conjugation as a sexual method
Unicellular and colonial forms of Cyanobacteria
Majority of unicellular forms stay together by copious secretion of mucilage by daughter cells.
In colonial forms cells remain attached by walls or held in a common gelatinous matrix forming a colony of cells. Types - spherical, cubical, square or irregular shape.
2 types of nitrogen fixing cyanobacteria
Free living - Nostoc sp.
Symbiotic - Anabaena-Azolla sp
Heterocyst and akinete of Cyanobacteria
Nitrogen fixation takes place in special cells called heterocyst. Nitrogen fixation is catalysed by the enzyme nitrogenase. Nitrogenase is sensitive to O2. Heterocyst carry thick cell wall to protect nitrogenase from O2
Akinete is a thick walled resting spore with stored food. Akinete is resistant to drought and high temperatures. They are able to survive during unfavourable environmental conditions although vegetative cells dries out.
Reproduction seen in Cyanobacteria
Reproduces only by asexual methods
Single unicellular forms and colonial non-filamentous types by simple cell division
Colonial unicellular and colonial filamentous by fragmentation
sp. meaning in microbiology
Species
Nutritional modes seen among fungi
Saprophytic (decomposers)
Parasitic (plant and animal pathogens)
Mutualistic (lichens and mycorrhizae)
Reproduction seen in fungi
Unicellular fungi reproduce asexually by fission or budding
Filamentous fungi asexually or sexually by producing spores
Pleomorphic meaning
Occurring in various distinct forms
Nutritional modes seen among protists
Photoautotrophic
Heterotrophic
Mixotrophic
Respiratory modes seen among protists
Aerobic
Anaerobic
Facultative anaerobic
Reproduction seen among protists
Reproduce sexually by gametes and asexually by fission
Mollicutes
Mollicutes are prokaryotes included in the domain Bacteria
Mycoplasma and phytoplasma are considered unique due to the absence of cell walls
Mycoplasma
Pleomorphic
Smallest prokaryotic group of microorganisms invisible under the light microscope
Do not contain flagella
Almost all mycoplasma are parasites of humans and animals
Reproduce by budding and binary fission and do not posses spores
Requires high amount of growth factors
Aerobes or facultative anaerobes
Phytoplasma
Similar in size to mycoplasma
Only can be seen under the electron microscope
Phytoplasma only infect plants and are generally present in the phloem sap
Cannot grow in artificial media
Transmitted mostly by leafhoppers
Reproduce in both leafhoppers as well as plant body
Reproduce by binary fission and budding
Posses aerobic or facultative anaerobic mode of respiration
Characteristic features of virus
Do not show any cellular organisation
Not considered as living organisms
Can only multiply with a host cell (obligate parasites)
Composition of viruses
Composed of a central core of nucleic acid and surrounded by a protein coat called the capsid which is made up of a fixed number of protein subunits called capsomeres
May have either DNA or RNA as their genetic material
Depends on the host cell’s protein synthesis machinery
Consists of reverse transcriptase enzymes for reverse transcribing RNA into DNA
4 types of morphological forms of virus and examples
Helical viruses- Long rigid or flexible rods e.g: Rabies virus
Icosahedron - Icosahedron symmetry e.g: Aden virus
Complex - Exhibits more than one form of symmetry with additional structures e.g: Bacteriophage
Enveloped viruses - Roughly spherical. Capsid covered by envelopes e.g: Herpes simplex virus
Bacteriophages
Are typical group of viruses that are capable of infecting bacteria
2 distinct multiplication mechanisms of viruses
Lytic cycle
Lysogenic cycle
Difference between lytic cycle and lysogenic cycle
Lytic cycle involves with the lysis of the host cell whereas the lysogenic cycle allows viral DNA incorporating into host DNA and multiply without causing lysis of the host cell
Steps of lytic cycle
Attachment
Penetration
Biosynthesis
Maturation
Release
Viroids
Consist only of short piece of RNA with no protective layer such as a protein coat
Can only multiply within a host cell
Do not contain any gene and only carry signals for their multiplication
Viroids infect plants, but no other life forms unto date
Prions
Are proteinaceous infectious particles.
Smaller this virus
Lack nucleic acid but can replicate with the help of host’s gene that encodes the prion protein
Found as disease causing agents in some birds and mammals
All these diseases are neurological diseases
Diseases caused by prions
All are neurological
Transmissible Spongiform Encephalopathies (TSEs) - Large vacuoles develop in the brain giving spongy like appearance
Mad cow disease (emerged in cattle)
Creutzfeldt-Jakob disease (CJD) is one of the human diseases caused by prions
Sterilisation
Process of removal or destruction of all forms of microbial life including endospores
2 types as physical and chemical
Physical methods of sterilisation
Moist heat sterilisation (done by denaturing proteins under high temperature and pressure)
Dry heat sterilisation - direct flaming, Incineration, Hot-air sterilisation
Pasteurisation
Boiling
Filtration
UV radiation
Moist heat sterilisation
Moist heat is used to sterilise culture media, heat stable reagents and laboratory equipments. E.g: autoclaving, pressure cookers
Dry heat sterilisation
Dry heat is used to sterilise glassware, Petri dishes, pipettes, inoculation loops and needles and scalpels
Types of pasteurisation
High temperature short-time (HTST) - 72 C , 15 s
Low temperature long time (LTLT) - 63 C, 30 min
Ultra high temperature (UHT) - 140 C, less than 5 s
Filtration
Used to sterilise heat stable liquids such as enzymes and some culture media. Pore size varies from 0.01micrometers to 0.45 micrometers
Major disadvantage of using UV radiation as a sterilisation method
Does not penetrate through solid surfaces and coverings such as paper, glass and textile
Chemical methods of sterilisation
Ethylene oxide kills microorganisms and endospores (highly penetrating)
Chlorine dioxide has been used to fumigate enclosed building areas contaminated endospores of Bacillus anthracis
What is used in water treatment prior to chlorination
Chlorine dioxide
Culture media description
Is a material prepared for providing nutrients and anchorage which are essential for the growth of microorganisms under laboratory conditions
Agar is used as a solidifying agent (agar solidifies at temperatures below 40 C). Before microbes are entered glassware and nutrient medium should be sterilised. Prior to observation microbes are stained once on the glass slide for better viewing. e.g: methylene blue, crystal violet and saffranin
Commonly used microbial culture media and their components
Nutrient agar - peptones, meat extract, NaCl, agar and distilled water. Used to culture bacteria.
Potato-dextrose agar (PDA) - Potatoes, glucose, agar and distilled water. Used to culture fungi.
How does humans get in contact with microorganisms for the 1st time
Generally humans are free of microbes at birth.
During the birth, newborn first gets in contact with the microbes present on the vagina of mother.
Usually these are Lactobacilli
Lactobacilli colonise the intestine of the new-born. These are called the normal microbiota
Microbes and diseases
it has been estimated that their are 1014 microbial cells for every 1013 body cells. Most of these microbes are not harmful or even beneficial. e.g: E.coli in low concentrations in the large intestine synthesise vitamin K and B and avoid colonisation of certain disease causing agents such as Salmonella typhi. Probiotics are live microbial cultures which and alleviate diarrhoea and prevent entry of Salmonella enteric during antibiotic therapy.
Most of these microbes colonise on inner surfaces of the body such as mucous membrane of nasal tract, throat, upper respiratory and intestinal and genitourinary tracts. Some are opportunistic (E.coli)
Pathogen
An organism or entity (non-living entities such as virus and prions) that is capable of causing disease.
Host
Organism with within which infected pathogens live on or in and multiply.
Pathogenicity
The ability of a pathogen to cause disease in the host by overcoming the defence of a host
Parasite
An organism or entity living on or in another living organism (host) and obtain nutrients and other resources from the host.
Characteristics of pathogenic microorganisms
Having optimal growth conditions(temperature) which corresponds to the body conditions of the host.
Having structures to adhere to host cells and to protect against host’s defence mechanisms. e.g: capsule, pilli
produce toxins
Having enzymes for invasiveness such as phospholipase, lecithinase and hyaluronidase
Having DNase to alter host’s metabolic processes
Virulence
Is the degree of pathogenicity of the pathogen
Virulent factors
Certain genes of the pathogenic microorganisms express factors which gives them the ability to infect the host and cause diseases
Invasiveness
Is the ability of the pathogens to invade tissues by overcoming host’s defence mechanisms and multiply for colonising
Toxigenicity
Ability of microorganisms to produce biochemical substances known as toxins that disrupt the normal functions of cells. Toxins can be proteins or lipopolysaccharides which are known as biological poisons.
Endotoxins
Endotoxins are lipopolysaccharides
Thermo-stable toxins which are part of the microbial cell. Endotoxins gets released when the microbial cell dies and the cell walls are broken apart
All endotoxins cause the same symptoms regardless of the species of pathogen which includes chills,fever,weakness, generalized aches and sometimes shock and death
Endotoxins are produces only by gram-negative bacteria
e.g: Lipopolysaccharides of the cell walls of Salmonella typhi
Exotoxins
Produced inside bacterial cells as part of their growth and metabolism and are secreted to the surrounding after cell lysis
Exotoxins are proteins (thermo-liable), majority are enzymes (inactivated by boiling). Due to the catalytic nature only a small amount will be quite harmful
Commonly produced by gram-positive bacteria and few gram-negative bacteria
3 types as neurotoxins, enterotoxins and cytotoxins
3 types of exotoxins, characteristics and examples
Neurotoxins - interfere with normal transmission of nerve impulse. e.g: Clostridium tetani and Clostridium botulinum
Enterotoxins - stimulates cells of the gastrointestinal tract in a abnormal way. e.g: Vibrio cholera
Cytotoxins - kills host cells by enzymatic attack. e.g: Corynebacterium diphtheriae
Causative agent and affected organ of Chickenpox
Herpes virus (varicella-zoster)
Skin
Causative agent and affected organ of Rubella
Rubella virus
Skin
Causative agent and affected organ of Measles
Measles virus
Skin
Causative agent and affected organ of Conjunctivitis
Haemophilus influenza / Adenovirus
Eye
Causative agent and affected organ of Bacterial meningitis
Streptococcus pneumonia
Haemophilus influenza
Neisseria meningitis
Nervous system
Causative agent and affected organ of Tetanus
Clostridium tetani
Nervous system
Causative agent and affected organ of Rabies
Rabies virus
Nervous system
Causative agent and affected organ of Rheumatic fever
Streptococcus pyogenes
Cardiovascular system
Causative agent and affected organ of Tuberculosis
Mycobacterium tuberculosis
Respiratory system
Causative agent and affected organ of Influenza
Influenza virus
Respiratory system
Causative agent and affected organ of Pneumonia
Streptococcus pneumonia
Respiratory system
Causative agent and affected organ of Hepatitis
Hepatitis A virus
Digestive system
Causative agent and affected organ of Food poisoning
Staphylococcus aureus
Digestive system
Causative agent and affected organ of Cholera
Vibrio Cholera
Digestive system
Causative agent and affected organ of Typhoid
Salmonella typhi
Digestive system
Causative agent and affected organ of Leptospirosis
Leptospira interrogans
Urinary system
Causative agent and affected organ of Gonorrhea
Neisseria gonorrhoea
Reproductive system
Causative agent and affected organ of Genital herpes
Herpes simplex virus
Reproductive system
Causative agent and affected organ of AIDS
Human immunodeficiency virus
Immune system
Protists
Pleomorphic
Different locomotive structures such as pseudopodia, cilia or flagella
Photoautotrophs, heterotrophs or mixotrophs
Aerobes, anaerobes or facultative anaerobes
Symbiotic interactions with lichens
Sexually by gametes or asexually by fission
Phospholipase
Destroy animal cell membranes
Lecithinase
Hydrolyses the lecithin component of lipid in cell membranes
Hyaluronidase
Destroys body tissues by breaking down the hyaluronic acid which is cementing substances between cells
Antiseptics and disinfectants
Major difference is that antiseptics can be safely directly applied to the human body. Generally formulated as liquids and their effectiveness varies with concentration, duration of exposure, temperature and presence of organic matter.
Antiseptics - ethanol, isopropanol, chloroxylenol
Disinfectants - phenol, hypochlorites (Na and Ca)
Microbes which are not destroyed by antiseptics or disinfectants
Polio virus, tuberculosis bacterium, spores of bacteria and fungi
Various actions shown by antibiotics
Inhibition of cell wall synthesis - Penicillin
Inhibition of protein synthesis - Erythromycin, Tetracycline
Disrupting plasma membrane - Daptomycin
Inhibition of DNA/RNA synthesis - Rifampin
Vaccines
Is a suspension of weakened pathogen or fractions of organisms that are used to induce immunity
Live attenuated viruses
Contains the live but weakened pathogen. Mimics an an actual infection and provides lifelong immunity. Booster vaccination is not needed. e.g: MMR, Chickenpox
Inactivated vaccines
Pathogen is inactivated or killed and requires booster doses. e.g: Rabies, influenza, polio and cholera
Subunit vaccines
Contains only the antigenic fragment of the pathogen that can induce immunity in the recipient. Types as toxoid vaccines and recombinant vaccines. Subunit vaccines requires repeated booster doses.
Toxoid vaccines contain the inactivated toxin derived from pathogens. e.g: Diphtheria and tetanus
Recombinant vaccines are made using genetic engineering. e.g: Hepatitis-B vaccine
E.g of using microbes in the early periods
Babylonian and Sumerian civilisations used yeast to make alcohol in 6000 BC
Advantages of using microbial processes over chemical processes
Simple nutritional requirements are sufficient for their growth.
Able to convert a wide range of raw materials
Able to convert cheap raw materials into industrially important products
Due to their high growth rate, raw materials can be converted to products within a short period of time
Growth conditions can be controlled to obtain desired end products
Reactions can be carried out a low temperatures, energy and pressure
Gives higher yield with higher specificity
Basic principles of microbial metabolic processes
Microbial cells are used as end products. e.g: single cell proteins
Microbial metabolic products are used as end products. e.g: primary end products - alcoholic beverages, secondary end products - antibiotics
Microbial metabolic processes are used as end products. e.g: bioremediation, metal extraction and retting
GM microbes are used to produce end products. e.g: commercial enzymes, vaccines and hormones
Single cell proteins
Microbial cells grown in large scale as food supplements and are rich in proteins. E.g: Yeast, Chlorella sp and Spirulina sp
alcoholic beverages
Yeast oxidises simple sugars such as sucrose derived from sugarcane into ethanol and CO2.
Production of vinegar
- Alcoholic fermentation - sugar is fermented by S.cerevisiae. Ethanol is subjected to acetic acid fermentation
- acetic acid fermentation - Ethanol undergoes incomplete oxidation to produce acetic acid. Highly aerobic and involves Acetobacter sp and Gluconobacter sp
Dairy products
Lactic acid producing bacteria converts lactose sugar in milk into lactic acid. e.g: L.bulgaricus, L.lactis and S.thermophillus
organic acids
Citric acids - sucrose fermented by Aspergillus niger
Metal extraction
Some metals from ores are extracted with the help of microbes (leaching). e.g: extraction of Cu from low grade Cu ore which other extraction methods are unprofitable, Thiobacillus ferrooxidans recovers Cu from ores that contain Fe and S (about 70%), Uranium and gold can also be leached.
Retting
Is the process of loosening fibres from woody stems or other plant materials such as coir. Pectinases facilitate loosening.
Residues which are not digested naturally
Residues of pesticides such as heavy metals, insecticide DDT, herbicide 2,4-D
Bioremediation
Technology that applies of living organisms to remove, degrade or detoxify pollutants.
Functions - remediate soil and water contaminated with oil spills, toxic metal waste, hazardous organic wastes
Decompose wastewater from food processing and chemical plants
Nature, distribution and role of soil microorganisms
Soil provides an adequate physical and chemical environment for the growth of microorganisms in terms of space and nutrients such as minerals, water, decaying organic matter and gases such as O2, CO2 and N2. Depth of soil leads to diversity between soil microbes.
Top few cm hv the largest community of microbes. Majority of soil microflora includes bacteria and others such as fungi, algae, protozoa and actinomycetes. Soil microbes are important in decomposing and recycling of materials in biogeochemical cycles
Mineralization
Is the decomposition of plant and animal residue by using extracellular enzymes of bacteria and fungi.
Mineralization helps to remove plant and animal debris from the earth’s surface allowing other organisms to live. And recycles minerals which are found in limited quantities on earth.
Carbon cycle
All organisms contains large amount of carbon in their bodies as cellulose, starch, fat and proteins
1st step of the carbon cycle is the fixation of atmospheric CO2 by autotrophs and are made available for chemoheterotrophs and protozoans
Part of the C fixed in autotrophs and heterotrophs are released back into the atmosphere as CO2 through respiration and made available again for autotrophs
Another part of C fixed in chemoheterotrophs is released as faeces which is later decomposed by soil microbes
Rest of C fixed remain in organisms until they die and when they are dies it is decomposed and released back into the atmosphere
Microbes of carbon cycle consumes more than 80% of the methane produced in ocean beds before reaching the atmosphere
Ammonification
More than 90% of the organic nitrogen of soil exists as proteins. Proteins of dead plants and animals are decomposed by extracellular proteolytic enzymes and are converted to amino acids. These amino acids are taken into microbial cells and undergoes ammonification where the amino groups of amino acids are converted to ammonia and are further converted ammonium once they dissolve in soil water.
Nitrification
Process of converting ammonium ions to nitrate by nitrifying bacteria
NH4+ is converted NO2- by Nitrosomans
NO2- is converted NO3- by Niitrobacter
Denitrification
In the absence of O2 certain microbes reduce nitrates to N2. Occurs frequently in water-logged areas (pseudomonas sp) NO3-, NO2-,N2O,N2
Nitrogen fixation
Process of converting N2 to NH4+
Anaerobic bacteria fixing N2
Clostridium sp
Rhizosphere
Symbiotic interaction between plant roots and soil surrounding the root surface for about few mm. This micro-ecological zone is the most bio-diverse and dynamic habitat on earth. Microbes within the rhizosphere competes for space, nutrients and water of which bacteria are the most common (psedomonas,bacillus and Agrobacterium) Both pathogenic and symbiotic fungi inhabit the rhizosphere
Mycorrhizae
Symbiotic relationship between fungi and plant roots. Almost all land plants are associated with 1 or more mycorrhizal fungi. These fungi increases the surface area over which nutrients and water can be absorbed by the plants, reaches to small pores within soil and increases the uptake of immobile nutrients such as P,Zn,Cu
Microbes in improving soil quality
Involved in the formation of stable soil aggregates such as fungal filaments, actinomycetes filaments and polysaccharide gums produced by bacteria
Major criteria of indicator organisms of water quality
Should be present consistently in the human faecal matter in large amounts. e.g: coliforms
Coliform bacteria
Bacteria which are aerobic or facultative anaerobic, gram negative, non-endospore forming and rod shaped which ferments lactose to gas within 48 hours in a lactose broth at 35 C
Water borne diseases
Typhoid, paratyphoid, cholera, gastroenteritis and dysentery
Steps of urban water treatment
Sedimentation and coagulation
Filtration
Disinfection
Sedimentation and coagulation
If the water is turbid it is allowed to stand in large reservoirs for a holding period to allow settling of particle matter at the bottom. Enhanced by adding alum (aluminium potassium sulphate) which produces a sticky polysaccharide.
Filtration
Water is sent through beds of fine sand. Protozoan cysts are removed by the surface absorption onto the sand particles. Removes about 99% of bacteria. Some water treatment plants uses activated carbon for the removal of toxic chemicals.
Disinfection
Done through chlorination or by ozone. O3 is highly reactive and kills microorganisms by oxidation. O3 method is the preferred method as it leaves no taste or odour and has little residual effect.
Primary treatment of waste water
large floating materials are screened out
removal of sand
removal of oil and grease
solid matter is allowed to settle in sedimentation tanks
sludge collected and removed
No biological activity is used here and through this step about 25%-35% of organic matter is removed
Secondary treatment of waste water
Waste water is aerated to facilitate growth of aerobic bacteria and rapid microbial oxidation. Activated sludge system or the trickling filter method is used.
In activated sludge vigorous aeration is done mechanically and in tricking filter, waste water is slowly sprayed onto a bed of rocky material and allowed trickle. Microbes grow on the filter bed and oxidises organic matter. (75%-95%) Finally water is disinfected
Sludge remaining from both the treatments are sent to an anaerobic sludge digester and the organic matter in sludge is converted to CH4 and CO2 by anaerobic decomposition. Digested sludge can be used as a fertiliser.
Adverse effects of discharging large amounts of waste water
Dissemination of pathogenic microbes
Water pollution due to accumulation of biodegradable materials and their decomposition products
Decomposition which cause large consumption of O2 in water which affects aquatic organisms
Anaerobic decomposition leading to bad smells
Importance of recycling solid wastes
Improper disposal of waste can create breeding sites for mosquitoes, insects and rats which acts as vectors of diseases such as dengue, chickungunya and leptospirosis
creates social problems due to bad smell due to anaerobic decomposition of waste
accumulation of CH4 can cause explosions and fires
transmission of water borne diseases such as typhoid, paratyphoid, cholera, gastroenteritis and dysentery
ground water can be polluted due to leachate of waste (liquid pass through waste)
Solid waste management
Sorting and recycling
Degradation/ decomposition of organic matter (composting)
Sanitary. land fillings
Food spoilage
Growth of microorganisms on food changes the physical, chemical and biological components of food making it unfit for consumption
Chemical changes taking place in food
Putrefaction
Fermentation
Rancidity
Putrefaction
Proteins in the food source are broken down by proteolytic enzymes secreted by proteolytic microorganisms into amino acids, amines, ammonia and H2S
Fermentation
Complex carbohydrates are broken down into simple carbohydrates by amylase and then the simple carbohydrates are converted into food acids, alcohol and gases by saccharolytic enzymes
Rancidity
Lipids present in the food source is converted into fatty acids and glycerol by lipolytic enzymes
Physical changes taking place in food
Softening of food
Pigmentation
Ropiness
Slime or gum formation
Toxin accumulation
External factors influencing food spoilage
temperature of storage
R.H of environment
presence and concentration of gases in the environment
Internal factors influencing food spoilage
pH - most microbes grow best at pH 7, however holds and yeast grow over a wide range (2-10) and bacteria from 5-7
moisture content - high moisture containing food such as meat and fish are spoiled by bacteria and low moisture containing food are spoiled by molds and yeast.
nutrient content - nutrient rich food are easily spoiled
biological structure - outer covering of fruits, egg shells
Food borne pathogens
Typhoid - Salmonella typhi
Cholera - Vibrio cholera
Food poisoning - Staphylococcus aureus
Dysentery - Shigella
Botulism - Clostridium botulinum
Aflotoxins - Aspergillus flavus
Effects of food spoilage
Food borne infections - microbes enters into the human body through spoiled food and they grow and replicate producing toxins. Symptoms will be developed after some time. e.g: typhoid, cholera and dysentery
Food intoxications - Indigested spoiled food contains toxins. Symptoms are rapid. e.g: aflatoxins, botulism and food poisoning
Viruses also cause food borne illnesses
