Normal Flora of the Human Body

-many organs and sites in the healthy human host are free of microorganisms. These include the cerebrospinal fluid, blood, urinary bladder, uterus, fallopian tubes, middle ear, paranasal sinuses

and kidneys.

It is estimated that the adult human body is host to al least 100 trillion microbial cells at any time.

Normal Flora

-indigenous microorganisms, most of which are bacteria

-they inhabit the skin and some of the inner surfaces of the body (such as the skin,

mouth, nasopharynx, ears, intestinal tract, and lower urogenital tract)

-sex of the host may also influence the composition of the normal microbial flora

-species, no. of normal flora sometimes depends at particular ages of the host.

-members of the normal flora may also be thought of as the resident flora (those microbes regularly found in a given site at particular host age).

-are harmless they do not cause disease unless they become opportunistic pathogens (which

cause infections if tissue injury occurs at specific body sites or if the resistance of the body to infection is decreased)

Various Factors affect the nature and extent of the normal flora:

1. weather (inc T & humidity, inc density of skin microflora)2. age has an effect (young children has more varied microflora

and carry more G- bacteria, potential pathogens thanadults)

3. hospitalized patients (> no. Of pathogens and antibiotic-resistance organisms than normal people)

4. personal hygienic habits influence the resident microflora andunclean individuals have higher population densities)

Transient flora

-simply harbored for a short time by the human body

-may be present only for several hours, days, or weeks,and then disappear

Distribution and Occurrence of the Normal Flora

1. Blood, Body fluids, and tissues

-occasional microbes may cross protective epithelial barriers as a result of trauma, such

as tooth extraction and child birth

-microbes found in the bloodstream for a brief time such transient bacteremia may cause infection of damaged or abnormal heart valves leading to subacute bacterial endocarditis (inflammation of the membrane lining the heart and its valves)

2. Skin -1st line of defense

-several factors responsible for discouraging microbial growth on the skin:

1. dryness -102 to 104 bacteria per square centimeter)2. low pH- between pH 3 to 53. inhibitory substances- eg. Sweat

glands (lysozyme-enzyme that destroy the peptidoglycan of bacterial cell walls)

-sebaceous glands- secretes complex lipids which may be partially degraded by bacteria such as Propionibacterium acnes to produce long-chain fatty acids, such as oleic acid (highly inhibitory to other bacteria)

3. Eye – has conjunctiva(membrane lining the eyelids which continually washed by a flow of tears-tends to remove microorganisms (has lysozyme)

4. Respiratory tracta. Upper respiratory tractb. lower respiratory tract

5. Mouth- S. mutans (produces glucan that is formed only in the presence of sucrose)Dental plaque- aggregation of bacteria and organic matter on the surface of the teeth.-contains a very high number of bacteria, 108

cells per milligram

6. Gastrointestinal tracta. Stomachb. small intestinec. large intestine- has the largest microbial popn

7. Genitourinary tract

Effect of Normal Flora on the human hostThree approaches have been used to answer this

A. Use of germfree animals(helpful in understanding the fxns of NF of humans-germfree life (practical tools for solving problems of importance in biology and medicine)

-able to study the effects of microorganisms added to germfree animals

Gnotobiotic-animals that are raised in an environment with one or more known microorganisms

Germfree animals vs. Normal Animals

1. GA have underdeveloped immune system(making them unusually susceptible to infection if exposed to microorganisms). They lack antibodies to normal flora antigens, which often share similarity to the antigens of disease-causing microorganisms and confer partial protection against these pathogens.

3. GA require higher levels of B vitamins in their diet than do normal animals; they also require vit K, which normal animals do not require in their diet(this indicates that the normal flora makes a significant contribution to satisfying the vitamin requirements of the host).

2. GA are vulnerable not only to pathogenic bacteria but also to non-pathogenic ones. This is bec immunologic priming (a buildup of resistance to pathogens) has not occured under the protection of maternal antibodies soon after birth

B. Use of antimicrobial agents.(If the balance that occurs between the NF and the human host is altered by use of antimicrobial agents, the effects are useful in understanding the role of the normal flora).-examples:

1. treating the skin of humans with antibacterial agents, such as hexachlorophene, suppresses colonization by the normal G+ microbes and promotes growth and clinical infection by G- rods and other microorganisms notnormally able to cause infection

2. hospital patients receiving antibiotics may lose much of the normal flora of the large bowel, leading to pseudomembrane colitis-a severe disease caused by excessive growth of toxin-producing strains of anaerobic spore-forming bacterium, Clostridium difficile, which normally is absent or is only a minor component of the normal flora.

3. The yeast Candida albicans , a minor component of the normal flora may multiply dramatically following antibiotic therapy(since it is EUCARYOTE, resistant to antibacterial antibiotics)

C. albicans can cause diarrhea and superficial fungal infections in the mouth, vagina or anal area

C. Knowledge of certain characteristics of the normal flora that inhibit the growth of other microbes. These characteristics suggest that normal flora organisms may help to discourage the growth of microorganisms that are not part of the indigenous flora.

Characteristics of Normal Flora Organisms-these properties may include physical characteristics such as:

1. Adherence to host cells-many species of the normal flora can adhere to the surface of host epithelial cells, the tissue cells that cover body surfaces.-allows the bacteria to multiply while they avoid removal by the flushing effects of surface fluids and peristalsis(a progressive wave of contraction that forces contents toward an opening)eg. Streptococcus salivarius –adheres mainly to the surface of the tongueStreptococcus mutans –selectively binds to the smooth enamel surface of the teeth-desquamation, a phenomenon that affects microbial adherence (detachment of host epithelial cells from body surfaces and replacement of the lost cells by new cells)- in body sites like intestinal tract

2. Production of antimicrobial substances

- some resident microorganisms produce metabolic products that can inhibit other microbes.eg. In the large intestine-certain anaerobic bacteria produce organic acids such as acetic, lactic, or butyric acid as metabolic waste products (these inhibit the growth of other bacteria)

-some strains of skin staphylococci produce antibiotics that inhibit a wide variety of other bacteria

Microbiology of Food and Milk

Microorganisms are intimately associated with the availability, the abundance, and the quality of food for human consumption. Food items are easily contaminated with microorganisms in nature,during handling and processing.

Significance of Microorganisms in Food1. The numbers and kinds of microorganisms present in food

reflect the quality and safety of the food2. Some may cause food spoilage3. Some must be kept out, removed, inhibited or killed to

Prevent spoilage of food.4. Some can cause food poisoning or foodborne infections5. Some can produce certain food products by fermentation6. Some can be produced in large quatities as a food or feed

Supplement7. Contaminating microorganisms create special problem for

Food service industry as more “ready to serve” and “fast-food” products become available.

Food is particularly susceptible to microbial contamination and it serveas a growth medium for the contaminating microorganisms

*International, federal, state, country agencies routinely inspect and regulate food production. Standard procedures have been developed for the microscopic and cultural examination of foods.

-Food and Agricultural Organization(FAO), World Health Organization (WHO),United Nations International Children Emergency Fund (UNICEF)

-Bureau of Food Administration and Drugs (BFAD)

-follows the Compendium of Methods for the Microbiological Examination of Foods and Standard Methods for the Examination of Dairy Products

-results from the microbiological examination of foods provide:1. information on the quality of the raw food2. cleanliness of the conditions under which the food was

processed

3. And the effectiveness of the method of preservationIn the case of spoiled foods, it is possible:

1. to identify the microorganism responsible for the spoilageand its source

2. as well as the conditions which permitted the spoilage to occur. Then corrective measures can be instituted to prevent spoilage in the future.

A. Microscopic Techniques1. Gram stain technique2. Breed Smear- used to make a direct microscopic count of microorganisms in milk(the total number of microorganisms per milliliter of milk can be calculated)3. Howard mold-counting slide- has a chamber that holds a measured amount of specimen.

- used to enumerate mold fragments in food products such as fruits, juices and vegetables.(when the mold counts obtained exceed certain limits, the product is of poor quality or has been processed in an unsanitary manner.

2. Culture techniquesa. Plate culture techniques- used to determine a specimen’s total microbial

population or to count some particular group of microorganismsb. standard plate count- for counting bacteria in milk

Microorganisms in Fresh Foods1. Meats- low level of surface contamination(inner tissues are sterile)

- microbial counts of 100 to 100,000 per gram surfaces of beef carcasses - microbial counts on hamburger may reach 5 x 106 to 1 x 107 per gram of

sample2. Poultry- freshly dressed poultry has bacterial flora on the surface(from bacteria

present on live birds and from organisms introduced during killing, defeathering and evisceration. -under good sanitary conditions (bacterial count is frm 100 to 1000 bacteria

per square cm of skin surface) while less sanitary, bactl count increased by

100-fold or more.3. Eggs –inside of a freshly laid eggs is usually free of microorganisms

-cracks in the shell result in contamination and spoilage

Some examples of bacterial spoilage in eggs are:a. Green rots: caused by green-pigmented Pseudomonas species that can grow at 0o C.b. Colorless rots: Caused by species of Pseudomonas, Acinetobacter, Alcaligenes and coliforms. Various kinds of odors may develop.c. Black rots: caused by Proteus species which turn eggs black. Usually indicative of storage at temperatures above recommended level

*bacteria of the genus Salmonella have periodically been a major problem, causing food poisoning from contaminated egg products.

4. Fruits and Vegetables –occurs in various stages of development (bacteria, viruses & fungi)

-the more tissues are invaded the greater the likelihood of spoilage

-contamination may also depend on postharvest handling used

eg. Mechanical handling(produce breaks in the tissue) -pH of fruits are relatively low 2.3 lemons, 5.0 for bananas -pH range for vegetable is slightly higher (pH 5.0 to 7.0)

making vegetables more susceptible than fruits to attack by bacteria

5. shellfish and Finfish- microorganisms found reflects the microbial quality of the watersfrom where they harvested

-if the water is sewage polluted, the seafood is potentially capable of transmitting pathogenic microbeseg. Marine bacterium, Vibrio parahaemolyticus (gastroenteritis epidemics in USA)

6. Milk- microbes contaminate via the teat canal from the outside

General Principles of Food Preservation1. Asceptic Handling and Processing2. High Temperatures

a. Boiling

-microbes from freshly drawn milk ranges between several hundred and several thousand per milliliter. (highest in milk taken during the initial stages)

how? From the time it leaves the cow’s udder

into retail containersPotential source of added contamination: milking equipment, the personnel, and the air in the environment

-under sanitary conditions with strict sanitary practices produce milk with a low bacterial count and good keeping qualityMilk -described as “most nearly perfect food”

- excellent medium for growth of microorganisms-has great susceptibility to microbial spoilage

*Canning- 100 C for high-acid foods to 121 C for low acid foods (does not guaranteeSterile prodts bec of spores of Clostridium botulinum (caused food poisoning)

B Steam under pressurec. PasteurizationD sterilization -300 F (148.9 C) for 1 to 2 s3. Low temperatures

a. Refrigerationb. freezing (-32 C)-quick freeze method (most satisfactory)

4. Dehydration5. High osmotic pressure

a. In concentrated sugarb. with salt brine

6. Chemical additivesa. Organic acids (benzoic, sorbic,acetic, lactic & propionic acid)b. substances developed during processing(smoking)c. substances contributed during microbial fermentation(acids)

7. Radiationa. UVb. ionizing radiation

Pasteurization of milk-original time-temperature relationships determined with M. tuberculosis (regardedas the most heat-resistant pathogen likely to occur in milk, it is destroyed whenexposed to 140 F (60 C) for 10 min. Thus pasteurization was set to 143 F (61.6 C) for 30 min but it was discovered that Coxiella burnetii (causative agent of Q fever transmitted by milk, can survive in milk heated to 143 F for 30 min)

Two methods for Commercial pasteurization of milk:1. the low-temperature holding (LTH) method or vat pasteurization

- holds the milk at 145 F (62.8 C) for 30 min2. the high-temperature short-time (HTST) method

- exposes milk to a temperature of 161 F (71.7) for 15 sec*after pasteurization, the finished product shld be stored at low T to retard growth of microbesThat survive pasteurizationTo test if particular batch of milk has been pasteurized, phosphatase test is done.

Phosphatase –an enzyme present in raw (unheated) milk and body tissues that is destroyed by adequate pasteurization-by testing for the absence of this enzyme, you can determine whether milkhas been properly pasteurized

Disodium phenyl phosphatase phenol + phosphatePhoshate (substrate) (enzyme in raw milk) (end-products)

Microbial Spoilage of food- produce changse in appearance, flavor, odor, and other qualities of food

1. Putrefaction:Protein foods + proteolytic microbes amino acids + amines + ammonia +

hydrogen sulfide2. Fermentation:

Carbohydrate foods + saccharolytic microbes acids + alcohols + gases

3. Rancidity:Fatty foods + lipolytic microbes fatty acids + glycerol

Foods produced by Microorganisms*fermented foods remains one of the most common methods of food preservationin the world

-in production of cheese and fermented milks (starter cultures=cultures of specificmicroorganisms are deliberately added to the food to initiate the fermentation)

Fermented vegetables (cabbage, cucumbers and olives)-involves series of stages:

1. Initiation stage- microbes present on the vegetables begin to grow(aerobic, facultative

and anaerobic microbes. Then production of lactic acid by streptococci and lacto-bacilli lowers the pH and inhibits further growth of undesirable Gram- and spore-Forming bacteria.2. Primary fermentation stage

-lactic acid bacteria and fermentative yeasts predominates (fermentation continues)3. Secondary fermentation

-fermentative yeasts which are acid-tolerant, utilize any residual fermentable carbohydrate4. Postfermentation stage

- microbial growth, particularly molds and oxidative yeasts may occur on surface of the fermented product

Fermented Dairy Products-microorganisms play the key role in producing a product with a desirable

flavor, aroma and physical appearancea. Fermented milks – fermented foods made from milk such as sour cream and

yogurt (lactic acid bacteria are the most commonly used starter cultures for the prepn of these foods)

1. addition of starter culture to pasteurized milk2. incubation at a T favorable for the growth of starter culture microorganisms

3. The principal product is lactic acid along with diacyl(lesser amnts of buttery-Flavored cpd)

Production of Cheese-bacteria convert curd (casein in milk) into the desired cheese

Manufacture of cheese includes the following steps:1. curd is separated from whey (liquid portion of curdled milk)

-precipitation of the casein is caused by addition of the enzyme rennin to the milk or by lactic acid produced when milk undergoes lactic acid Fermentation

2. adjustments are made to the curd-adding salt-removing a specific amount of moisture-inoculating with a particular microorganism if required-shaping the curd into a desired size and form

3. incubation of the curd under conditions which favor the growth of the desired microorganismsTwo types:1. Unripened cheeses-curd which has not been fermented by microorganisms

Eg. Cottage and cream cheese

2. Ripened cheeses-result from the growth of bacteria or molds in or on the curd during a

prescribed incubation period-may be classified as:a. Hardb. semi-softc. soft

Microbial Cells as Food-Single Cell Protein (SCP)-cells of bacteria, yeasts and algae produced in massive quantities can

be used as food for animals as well as for humans-attractive as food sources bec they can be grown on industrial wastes

or by-products and yield a large crop that is rich in protein(called single-cell protein)= can be used as food substitute or supplement

Microbiology of Water

Drinking water of most communities and municipalities comes from surfacesources-rivers, streams and lakes

Water can be perfectly clear, odorless and tasteless and yet be unsafe to drink.Contaminants that pollute water are classified into three categories:1. chemical2. physical 3. biological

Water maybe:a. Potable – water that is safe to drink is free of disease-producing

microorganisms and chemical substances harmful to healthb. Non-potable-must be purified before it can be used for human con-

sumption-purification method vary depending on the source of water and amount of water needed