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Microorganisms and Disease
Today we know that disease-causing microorganisms can be carried in water and that their presence in drinking water is a serious hazard to human health. But that knowl- edge is relatively new_._ In 1676 a Dutch scientist was able to see bacteria using a very primitive microscope, but it wasn’t until the mid and late 1800s that we began to understand that bacteria caused disease and that they can be carried in water_._ Micro- organisms that cause disease by transmission through contaminated water are called waterborne pathogens^23. One of the main jobs of water system operators is to control potentially pathogenic microorganisms. So it is important that they are familiar with the different types of microorganisms and their characteristics.
Microbiology
Definition Microbiology is the study of microorganisms, of small living things. Although some forms of organisms studied by microbiologists can be seen with the naked eye, most of the things that microbiologists are interested in require the use of a microscope to see clearly. Microorganisms of interest to the water industry include the following:
- Bacteria
- Protozoa
- Viruses^24
- Algae
- Fungi^25 What to Study To understand how to minimize growth and control pathogens, you must study the structure and characteristics of the microorganisms. In the sections to follow, we will look at size, shape, types, nutritional needs, and control of each of the major groups of microorganisms_._ We will also discuss some of the specific waterborne pathogens.
Bacteria
Most Common Microorganism Bacteria are among the most common microorganisms in water. Bacteria are primi- tive, single-celled organisms with a variety of shapes and nutritional needs. Size Range Bacteria range in size from 0.5 to 2 microns in diameter and about 1 to 10 microns in length. A micron is a metric unit of measurement equal to one-millionth of a meter or one-thousandth of a millimeter. Another way to visualize the size of bacteria is to consider that it would take about 1000 bacteria, lying side-by-side, to reach across the head of a straight pin. Three Shapes There are three general groups of bacteria based on their physical shape:
- Rod-shaped bacteria are called bacilli. - Spherical-shaped bacteria are called cocci.
- Spiral-shaped bacteria make up the third group.
Biological Characteristics of Water
(^23) Waterborne Pathogens – Bacteria, virus, and protozoa that cause disease and are carried by water. (^24) Virus – A submicroscopic organism that passes through filters capable of removing bacteria. (^25) Fungi – Non-chlorophyll-bearing plants that lack roots, stem, or leaves, that occur in water, sewage or sewage effluents, and that grow best in the absence of light.
Bacilli Cocci Spiral-shaped bacteria Within these three groups, there are many different arrangements. Some exist as single cells, others as pairs, as packets of four or eight, as chains, and as clumps. Food Requirements Most bacteria require organic food to survive and multiply. This food comes from plant and animal material that gets into the water where the bacteria exist. The bac- teria convert the food to energy and use the energy to make new cells. Some bacteria can use inorganics (such as iron) as an energy source. These bacteria can exist and multiply even where organic pollution is not present. Temperature Requirements Temperature affects the rate at which bacteria grow. The warmer the environment, the faster the rate of growth. Typically, for each increase of 10° C, the growth rate doubles. This means that bacteria will multiply more quickly when it is warm, and more chlorine may be required to obtain proper disinfection. pH Requirements pH affects bacteria growth. Most bacteria grow best at a neutral pH. Extreme acidic or basic conditions will inhibit growth. Other materials, such as metal ions (cop- per, lead, silver), and some organics, such as pesticides and herbicides, are toxic and inhibit bacterial growth. Oxygen Requirements Many bacteria are aerobic^26. They require free or dissolved oxygen in their aquatic environment. A few bacteria are anaerobic^27. They can exist and multiply in an environment that lacks dissolved oxygen. Some bacteria that are normally aerobic can switch to anaerobic. These adaptable bacteria are said to be facultative^28. One of the most troublesome bacteria in the water business is the iron bacteria, which is a facultative organism_._ The bacteria responsible for most of the biological treatment of wastewater are aerobic. (^26) Aerobic – A condition in which “free” or dissolved oxygen is present in the aquatic environment. (^27) Anaerobic – A condition in which “free” or dissolved oxygen is not pres- ent in the environment. (^28) Facultative – Microorganisms that can switch from aerobic to anaerobic growth or can grow in an anaerobic or aerobic environment.
Review Continued
- Although some bacteria can use inorganic chemicals as an energy source, most bacteria require _________________ chemicals as a food source.
- Bacteria that require an environment with free or dissolved oxygen are said to be:
- Bacteria that require an environment without free or dissolved oxygen are said to be:
- Bacteria that can exist in an environment with or without free or dissolved oxygen are said to be:
- Some bacteria produce _________________, which are strong, resistant resting stages that make them more resistant to disinfection.
- Three waterborne diseases caused by bacteria:
Protozoa
Definition and Size Protozoa are one-celled animal-like organisms with a fairly complex cellular struc- ture. The protozoa are the giants of the microbial world. They are many times larger than bacteria and range in size from 4 to 500 microns. The larger ones can almost be seen with the naked eye. Groups of Protozoa The major groups of protozoa are based on their method of locomotion or movement:
- Amoebas move about by a streaming or gliding action. The shape of an amoeba changes as they sort of ooze from place to place. - Ciliates are covered with short hair-like projections, called cilia, which beat rapidly and propel the ciliate through the water. Most ciliates are free-swim- ming, although some are attached to floating material or basin walls. - Flagellates have one or more long whip-like projections, called flagella, which propel the free-swimming organisms. - Suctoria are attached organisms, similar to attached ciliates, but have ten- tacles rather than cilia. - Sporozoa are non-mobile and are simply swept along with the current of the water.
Amoeba Giardia lamblia Cyst, form Giardia lamblia Trophozoite, form Suctoria Stalked Ciliate Free-swimming Ciliate Food Requirements Protozoa use organics for food. In fact, bacteria are among their favorite prey. Proto- zoa are mostly aerobic or facultative in regards to oxygen requirements. In the same manner as bacteria, pH, toxic materials, and temperature affect their rate of growth. Life Cycle Most protozoa have a complex life cycle in which they alternate between an active growth phase, when they are called trophozoites, and a resting stage, called cysts. Cysts are extremely resistant structures that protect the organism from destruction when it encounters harsh environmental conditions. Resistance to Chlorine Because of their relative complexity and ability to form the extremely resistant cysts, protozoa require higher disinfectant concentrations and longer contact time to control them. In fact, some types of protozoa may be almost completely resistant to disinfec- tion by chlorination.
Elaborate irregular shapes Need for a Host There are almost as many kinds of viruses as there are types of other living organ- isms. Viruses exist that can invade virtually every kind of living cell: animals, plants, insects, fish, and even bacteria. After they invade their specific host, they take over the machinery of the host and force it to make more viruses. The host cell is then destroyed, and hundreds of new viruses are released into the environment. Disinfection Because they lack sensitive cellular machinery and because they have relatively tough capsids and envelopes, viruses are hard to destroy by normal disinfection practices. Increased disinfectant concentration and contact time must be used to ef- fectively destroy viruses by chlorine disinfection. Waterborne Diseases Waterborne viruses can cause three diseases:
- Hepatitis
- Viral gastroenteritis
- Poliomyelitis Review
- ________________ are many times smaller than bacteria and are considered to be intracellular parasites.
- Viruses lack internal cell mechanisms, so they must have a(n) ________________ cell in which to multiply.
- Three waterborne diseases caused by viruses:
Algae
Description Algae are a form of aquatic plants. Although in mass they are easily seen by the naked eye, many are microscopic as single cells. They exist as microscopic, single- celled forms and also as huge, multicellular forms, such as marine kelp. They oc-
cur in fresh and polluted water, as well as in salt water. Since they are plants, they are capable of using energy from the sun in the process called photosynthesis. They grow only where there is light, and they grow better where there is bright sunlight, as opposed to cloudy weather. They usually grow near the surface of the water because light cannot penetrate very far through the water. Algae are classified by their color:
- Green algae contain green chlorophyll and are found mostly in fresh water. This form is the green roadside ditch algae, and the type that grows on clari- fier and basin walls.
- Euglenoids are single-celled, green-pigmented algae that resemble protozoa. They have flagella, but are considered algae because they carry out photosyn- thesis.
- Diatoms are golden-brown, single-celled forms that have a hard silica shell. The shells of millions of dead diatoms are mined commercially and known as diatomaceous earth.
- Cyanobacterium is bluish-green in color and undergoes photosynthesis. It was formerly called blue-green algae, but is now classified as a type of bacte- ria. Euglenoids Blue-green Diatoms Euglenoids Blue-grean Diatoms Problems Caused by Algae Although algae are not considered to be waterborne pathogens, they do cause some problems with water operations. They grow easily on the walls of basins and troughs, and heavy growth can cause plugging of screens and intakes. Algae release chemicals that can cause taste and odor problems in drinking water. Control of Algae Algae in raw water supplies can be controlled with chlorine and potassium permanga- nate. In raw water reservoirs, algae blooms are often controlled with copper sulfate.
Fungi
Description Fungi are of relatively minor importance to the water business. Fungi are non- photosynthetic organisms that grow as multicellular, filamentous, mold-like forms or as single-celled, yeast-like organisms. Fungi must have organic material as a food source.
- Disinfection means the destruction of pathogenic microorganisms, but does not necessarily mean complete destruction of all life forms. Operators may sterilize glassware in the laboratory, but the addition of chlorine to treated water is a disinfection process, not sterilization. Microorganisms can be controlled by manipulating their environment (such as ap- plying heat or changing the pH), by limiting or removing their food supply, or by subjecting them to damaging chemical or physical processes. Microbial growth is slowed considerably by refrigeration, by lowering the tempera- ture. Microbial growth can also be optimized by adjusting the temperature to one that favors a particular microorganism. Higher temperatures may be sufficient to sterilize an environment. Raising the pH with lime creates conditions in which most bacteria do not grow_._ Limiting sunlight prevents photosynthetic algae from growing_._ Know- ing the environmental factors that affect the growth of microorganisms help imple- ment strategies for control. Limiting the food supply can control the growth of microorganisms. Since many bacteria and most protozoa require organic matter for food, removing organics from the water and keeping surfaces and basins clean and free from organic matter limit growth. The removal of minerals, such as iron, from water can also discourage the growth of bacteria that use minerals as a food source_._ Keeping pipes and tanks clean and free or organic sediment can help control growth in the distribution system. A variety of chemicals and physical processes can be used to control microorganism growth. Chlorine, bromine, and iodine are well-known for their use as water disinfec- tants. Ozone is also an effective water disinfectant. Other chemicals, such as alcohol, formaldehyde, hydrogen peroxide, hexachlorophene, and certain heavy metals (silver and mercury) can be used to control growth_._ Some of these are strong and can only be used on inanimate objects. Others can be used to control microbial growth on skin and in eyes. Physical processes such as filtration, ultraviolet light, and gamma radia- tion are also effective. Practicing good personal hygiene is an easy and effective way to control microorgan- ism growth and to prevent the transmission of waterborne pathogens. Hand-washing is the most important practice_._ Washing hands after using the bathroom and before handling food and drinking water significantly reduces waterborne disease transmis- sion_._ Coughing into the crook of an elbow, instead into hands, can also help prevent transmission. Proper handling and disposal of human waste, and carefully cleaning up afterwards, is also important. Water system operators must practice personal hy- giene conscientiously to avoid contaminating equipment and water supplies.
Indicator Microorganism
To be sure that the water supplied to consumers is free of pathogens, operators must routinely sample and test the water for indications of the presence or absence of pathogens_._ It is beyond the capacity of treatment plant labs to directly test for any of the pathogenic microorganisms_._ But operators and technicians can test for bacte- ria called indicators, organisms whose presence indicates the possible presence of pathogens and whose absence means that the water is free of pathogens_._ The indica- tors used are a bacterial group known as total coliforms_._ As a group, coliforms live in the intestines of warm-blooded animals, as well as in the soil, in natural water, and on vegetation.
Although some total coliforms are pathogenic, most are not, and harmless coliforms are normal inhabitants of all human intestinal systems_._ So if coliforms are found in a water sample, there is a possibility that it has been contaminated by human feces_._ On the other hand, since coliforms are always found in human feces, if no coliforms are found in a water sample, it is safe to conclude that it has not been contaminated with human feces. If total coliforms are found in a water sample, the sample is further tested for a more restrictive group of coliforms called fecal coliforms or for E. coli , a specific coliform bacterium_._ The tests for fecal coliforms and E. coli are more sensitive, but more difficult to run, so they are used to confirm the results of the total coliform test_._ Their presence is a stronger indication of fecal contamination that could contain waterborne pathogens. The Safe Drinking Water Act’s Total Coliform Rule specifies the frequency and procedures for sampling and testing for coliforms. Analytical laboratories running coliform tests on drinking water samples for compliance purposes must be certified by the Alaska Department of Environmental Conservation (ADEC). Review
- A disease that can be passed from one person to another is said to be:
- The majority of _____________ – borne diseases are transmitted through the “feces – water – mouth” route.
- _____________ means the complete destruction of all organisms or cells.
- _____________ means the control of pathogenic microorganisms.
- Manipulating a microorganism’s _____________ is one way of controlling it.
- Limiting a microorganism’s _____________ supply is another way of controlling it.
- Three chemicals, other than chlorine, that can be used to control microorganisms:
- Practicing good personal _____________ is an easy and effect way to control microor- ganism growth and to prevent the transmission of waterborne pathogens.
- A(n) _____________ is an organism whose presence indicates the possible presence of pathogens.
- The Total Coliform Rule specifies how often water systems must sample and test for _____________ bacteria.
- The absence of total coliform in a drinking water sample means the water is _____________ to drink.
8. The destruction of pathogenic microorganisms is called:
A. Sterilization B. Disinfection C. Sanitization D. Autoclaving
9. Protozoa that move with the aid of long, whip-like tails are classified as:
A. Amoeba B. Ciliates C. Flagellates D. Sporozoa
10. Protozoa that move with the aid of short, hair-like bristles are classified as:
A. Amoeba B. Ciliates C. Flagellates D. Sporozoa
11. The tough, resistant resting stage of the life cycle of protozoa is called a:
A. Capsid B. Cyst C. Spore D. Seed
12. Which of the following is a protozoal waterborne disease?
A. Polio B. Giardiasis C. Hepatitis D. Typhoid fever
13. Which of these microorganisms are considered obligate, intracellular parasites
because they lack system to reproduce on their own? A. Bacteria B. Protozoa C. Viruses D. Fungi
14. Which of the following is a viral waterborne disease?
A. Polio B. Giardiasis C. Cholera D. Typhoid fever
15. Which of the following is considered a form of aquatic plant because it is photo-
synthetic? A. Algae B. Protozoa C. Viruses D. Fungi
16. Diatoms belong to which group of microorganisms?
A. Algae B. Protozoa C. Viruses D. Fungi
17. Cyanobacterium , now classified as a bacteria, used to be classified with which
group of microorganisms? A. Algae B. Protozoa C. Viruses D. Fungi
18. Algae, in raw water reservoirs, can be controlled with which chemical?
A. Sodium hypochlorite B. Calcium oxide C. Copper sulfate D. Soda ash
19. Diseases that can be passed from one person to another are said to be:
A. Deadly B. Vectors C. Transmissible D. Toxic
20. Which of the following activity would not be considered a means of controlling
microorganisms by manipulating their environment? A. Adding lime to raise pH B. Refrigeration C. Filtration D. Limiting exposure to sunlight
21. Which of the following is not used as a chemical means for controlling microor-
ganisms? A. Bromine B. Alcohol C. Alum D. Hydrogen peroxide
