IPC - Module 1

Question 1

What is a microorganism?

Answer 1

A Microorganism is:

An organism too small to be seen without the aid of a microscope.
Relatively simple in structure and often unicellular (single-celled).
Also called a “microbe”, “germ” or “bug”.
Some people in the medical community may use the slang term “bug” when referring to a microorganism. For example “What kind of bug does the patient have?” They are not referring to an insect in this case, but rather an infection causing microorganism.

Question 2

Groups of Microorganisms

Answer 2

The four groups of microorganisms are:

Protozoa
Fungi
Bacteria
Viruses

Question 3

Protozoa

Answer 3

Protozoa are unicellular creatures that move either by flagella or amoeboid motion. Each cell has a nucleus and is enclosed by a plasma membrane. Protozoa live in water and soil and feed on bacteria and small particles.

Some protozoa live in our bodies without causing any harm but a few are responsible for disease. Most people are familiar with Giardia infections, commonly called “beaver fever.” Giardia attach to the intestinal wall by two sucking discs resulting in diarrhea because the food cannot be broken down and absorbed properly. Giardia move by flagella. Some amoeba will also invade the intestinal wall and cause diarrhea. Occasionally they move into deeper tissue. These protozoa are usually picked up in warm countries with poor sanitation. The amoeba move by extension of pseudopods and do not have flagella

Question 4

Fungi

Answer 4

Fungi can be thought of as non-photosynthetic plants. Each cell has a nucleus and is enclosed by a rigid cell wall. The fungi are a very diverse group of microorganisms that can be simply divided into yeasts or molds

Yeasts are unicellular oval structures that reproduce by budding. Many types of yeast are used in the food and beverage industry for making breads and wines. They all look the same under the microscope. Some yeasts are capable of causing disease in humans with Candida being the most common. Candida may cause oral thrush, vaginal discharge, skin infections, pneumonia and even death.

Molds are multicellular structures that form visible clumps of growth. Bread and cheese molds are typical examples. The mold starts out with long tubular structures that eventually produce spores. These spores are visible as grey, blue – green or black growth. Human infections caused by the mold-type of fungi usually involve skin.

Athlete’s foot and ring worm are infections caused by this type of fungus.

Question 5

Bacteria

Answer 5

Bacteria are tiny unicellular organisms typically surrounded by a rigid cell wall. They do not have an organized nucleus but carry out all of the activities necessary for growth and reproduction.

Bacteria are ubiquitous which means that they are found just about everywhere there is moisture and nutrients. Many bacteria grow in or on humans and are an essential part of our body flora. However, many other bacteria cause infections.

Sore throat or “Strept throat” is caused by a type of bacteria called Streptococcus. Certain types of Staphylococcus cause skin abscesses called boils. Almost everyone has heard of food poisoning caused by the Salmonella from poultry. Figure 1.1.5 shows what bacteria look like under the microscope.

Question 6

Viruses

Answer 6

Viruses are even smaller than bacteria and have very simple structure. Viruses are unable to grow and reproduce on their own and must rely on a living host cell to replicate the viral parts. Animal, plant and bacterial cells all serve as host cells for viruses.

A number of human diseases are caused by viruses. Influenza and colds are viral infections that inflict discomfort on everyone at some point during their life. More serious viral infections include hepatitis, rabies and HIV.

Question 7

Treatment

Answer 7

Each group of microorganism, when causing an infection, requires a different drug for treatment. Protozoal infections are treated with antiprotozoal drugs, fungal infections are treated with antifungal drugs; bacterial infections are treated with antibiotics and viral infections are treated with antiviral drugs.

Question 8

Size of Microorganisms

Answer 8

Most microorganisms are measured in metric units called micrometers.

One micrometer equals 1/1,000 of a millimeter. A portion of a metric ruler is shown in Figure 1.1.6, with the larger units being centimeters and the smaller units being millimeters. All microorganisms are smaller than 0.1 mm which equals 100 micrometers

Question 9

Size of Protozoa

Answer 9

15-20 Micrometers

Question 10

Size of Fungi

Answer 10

5-10 Micrometers

Question 11

Size of Bacteria

Answer 11

0.3 - 5 micrometers

Question 12

Size of Viruses

Answer 12

0.3 - 5 micrometers

Question 13

Shapes of Bacteria

Answer 13

Most disease-causing microorganisms found in the hospital setting are bacteria. Bacteria can be placed in three groups based on their shape. Their shape is maintained by the rigid cell wall.

Cocci (pleural), coccus (singular)
Spherical or round cells

Rods or bacilli (bacillus)
Rectangular shaped boxes

Spirilla (spirillum)
Curved or spiral shaped rods

Question 14

Gram Reaction of Bacteria
Gram Stain

Answer 14

Bacteria can be divided into two groups on the basis of a Gram stain. The stain has been used for over 100 years to stain bacteria and make them more visible when viewed under the microscope. Once the staining procedure is carried out, one group of bacteria appear dark bluish-black in color and are called gram positive. The other bacteria are a pink to red color and are called gram negative.

Question 15

Importance of Gram Reaction

Answer 15

Looking at the gram reaction and shape of bacteria is often the first step in identifying them in the laboratory. Bacteria can be divided into six groups, based on the gram reaction and the shape of the cells:
gram positive cocci
gram negative cocci
gram positive rods ( bacilli)
gram negative rods (bacilli)
gram positive spirilla
gram negative spirilla

The gram reaction determines the effectiveness of certain antibiotics. Penicillin G, for example, is quite effective in killing gram positive bacteria but is relatively ineffective against gram negative bacteria.
Gram stain results assist the physician in initial selection of an appropriate antibiotic.

The gram reaction determines the effectiveness of certain disinfectants as well. Some disinfectants are more effective against gram positive than gram negative bacteria.

Question 16

Bacterial Endospores

Answer 16

A small number of bacteria (a few Gram positive rods) are able to produce a special type of spore within the bacterial cell. These spores are typically called endospores to differentiate them from fungal spores borne on the ends of hyphae.

Bacterial cells that do not contain endospores are often referred to as vegetative cells. Even Gram positive rods that are able to form spores exist as vegetative cells when they are actively growing and multiplying.

Question 17

Sporulation

Answer 17

Sporulation takes place when certain nutrients are depleted. One copy of the genetic material and a tiny amount of cytoplasm is enclosed by a layer of insulating material and the whole structure is covered with several compact layers of spore coat.

Endospores may remain dormant for days, months and even years without nutrients or moisture. Many of the bacteria found in dust, cereals, grains and soil exist as endospores.

A “viable” endospore is able to germinate (grow) into a vegetative cell when moisture and nutrients are provided. One spore will germinate into one vegetative bacterium.

The spores are found ubiquitously (everywhere) in the soil and normally do not cause infections as they require special conditions to vegetate, such as lack of oxygen. Gangrene and tetanus result when spores are introduced deep into injured tissue where blood flow has been disrupted and oxygen levels are low. Unlike gangrene and tetanus, anthrax will grow in the presence of oxygen, but requires other pre-disposing conditions such as damaged tissue or inhalation in to the lungs.

Question 18

The significance of endospores in sterilization and disinfection:

Answer 18

Endospores are quite resistant to heat. Most vegetative bacteria are killed by exposure to moist heat at 60-80°C for 10 minutes, but spores will survive these high temperatures. Some spores are killed by boiling, but others require a temperature of 121°C for 12-15 minutes for destruction.

Endospores are more resistant to disinfectants than vegetative bacteria. Low level disinfectants may not kill endospores and high-level disinfectants require extended exposure times.

Endospores are also very resistant to destruction by cold (viable spores have been discovered in the intestines of mammoths found in Siberian glaciers).

Endospores are also resistant to ultraviolet light, acids, alkalis and detergents.

Question 19

Growth of Bacteria - Binary Fission

Answer 19

Almost all bacteria reproduce by a process called binary fission

Question 20

Generation Time

Answer 20

Generation Time is the time it takes for binary fission to occur. This is the time it takes for the population to double. For example:

One bacterium becomes two bacteria
Forty bacteria become eighty bacteria
Generation time is not the same for all bacteria and is also affected by temperature and available nutrients. Rapidly growing bacteria under ideal conditions have a generation time of 15-30 minutes.

The generation time is related to the rate at which bacteria cause disease. The bacteria responsible for gas gangrene have a very short generation time, believed to be about 8 minutes. Once infection is established in human tissue, a whole limb may be destroyed in a day. The bacteria responsible for tuberculosis, on the other hand, have a long generation time (12-24 hours) and take weeks to produce disease

Question 21

Generation time & colonies

Answer 21

The generation time also determines the amount of time required for bacteria to form visible growth on culture media. A colony is a visible mass of bacteria that develops on the surface of a solid culture medium after a period of time and represents all the descendants of a single bacterial cell. The culture medium provides necessary nutrients for bacterial growth. Rapidly growing bacteria will form colonies within 18-24 hours.

Question 22

Bacterial Growth Curve

Answer 22

Bacteria do not go on growing at their maximum generation time forever. There would be no room for anything else on the surface of the earth if they did. If one cell divided every 20 minutes for 24 hours, there would be 1 x 1021 cells with a mass of 4,000 tons. Fortunately, reproduction is curtailed due to lack of nutrients, space and the build up of toxic waste products. The maximum number of bacteria possible is about 1 x 109 per mL or gram.

When bacteria are introduced into a new medium or environment, they go through four specific phases of growth. These phases make up the bacterial growth curve,

Question 23

4 stages of bacteria growth curve

Answer 23

1. Lag Phase
   When bacterial cells are placed in a new environment, there is little or no increase in numbers for a short period of time. This time is necessary for the cells to adapt to the new environment. The lag phase is usually a few hours but may be much shorter or much longer in some situations.

The lag period for bacteria in food is considered to be about two hours. This allows foods to be left out on a serving table for that long without much worry of bacterial growth and possible food poisoning.

2. Log Phase
   This is a period of maximum growth of bacteria. All the cells are dividing at a constant rate.
3. Stationary Phase
   The bacteria eventually exhaust their supply of nutrients and stop growing and multiplying. Even if nutrients are not used up, the end products of bacterial growth may accumulate and prevent further growth. The number of live bacteria stays constant during this period.
4. Death Phase (also called the Phase of Decline)
   Eventually the bacterial cells start to die and the number of live cells decreases. In some cases, most of the bacteria die in a short period of time but in other cases, some live bacteria can linger for weeks, months or even years. The bacteria that can survive the longest are those that form spores.

Question 24

The Growth Curve Related to Infection

Answer 24

Growth curves are plotted using laboratory cultures but the same sequence of events often takes place when a microorganism invades a host:

There are usually no disease symptoms for a period of time immediately following introduction of the microorganism into the host. This represents the incubation period of the disease, also called the lag phase of the growth curve.

This is followed by the onset of symptoms which may be fever, sore throat, swollen lymph glands, rash, vomiting or diarrhea depending on the infectious microbe involved. This is the acute stage of the disease and corresponds to the log phase. With the assistance of the patients defenses and medical intervention, most patients recover in this phase. However, if these fail, the patient dies during this acute stage.

The stationary phase follows, which is a period of time during which the symptoms are no worse but there is also no sign of recovery.

Finally the symptoms subside and recovery is on the way. This is the death phase (phase of decline) – death of the microorganism, not the host. The convalescent period of the disease covers the time needed for complete recovery. Recovery time will vary with different diseases, and infectious microorganisms often continue to be discharged during this period.

Question 25

Viral Characteristics

Answer 25

Viruses are very different from bacteria. Two of the most distinguishing characteristics are:

They are obligate intracellular parasites and only multiply when inside a living host cell. They have no ability to reproduce when outside the host cell. Viruses cannot multiply in the non-cellular environment and do not grow in foods, water, bacterial culture media or medications.

They contain a single type of nucleic acid, either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). All other forms of life contain both types of nucleic acid.

Viruses possess a protein coat that surrounds the nucleic acid. Some viruses also have an envelope composed mainly of lipids that surrounds the coat while others have spikes protruding from the lipid envelope. Lipid viruses are generally easier to inactivate with disinfectants. Hepatitis B is an exception, as it is an enveloped virus that is quite resistant to destruction. It may still be infective in dried body fluids for seven days.

Question 26

Multiplication of Animal Viruses

Answer 26

In order for a virus to multiply in a host, it must attach to complementary receptor sites on the surface of the host’s cells. For the adenoviruses that cause colds, the complementary sites are located on epithelial cells of the respiratory tract, while the virus that causes AIDS attaches to receptor sites of specific white blood cells called lymphocytes.

Once attachment has taken place, the virus is taken into the host cell by endocytosis during which the cell’s membrane folds inward forming a vesicle containing the virus. As the host cell attempts to destroy the contents of the vesicle, the outer protein coat is digested and the nucleic acid is released inside the host cell.

The stage is now set for replication of new viral material using the enzymes and metabolic pathways of the host cell. The viral nucleic acid carries the genetic coding for new viral material and directs the synthesis of viral parts. Most DNA viruses replicate DNA in the nucleus of the cell and replicate proteins in the cytoplasm. The proteins move to the nucleus and are joined with the DNA, ready for movement out of the host cell. Lipids and other viral components may be added as the virus particle is released from the host cell.

Question 27

Influenzae A

Answer 27

Influenzae A viruses are responsible for pandemic flu outbreaks, which often rapidly spread world-wide and cause a great number of deaths. They are dangerous because they mutate quickly and often. Individuals do not have immunity to them and it is difficult to produce appropriate vaccines in time to protect large numbers of people. Examples of influenza A (H1N1) virus outbreaks include the 1918 Spanish flu epidemic, the Asian flu (H2N2) outbreak in 1957-58 and the Hong Kong flu (H3N2) of 1968-69. The spring of 2009 saw an outbreak of H1N1 swine flu.

Question 28

Influenza B and C

Answer 28

Influenza B and C Viruses cause local outbreaks. They are generally less severe with a lower mortality rate than Influenza A virus outbreaks.

Question 29

Colds

Answer 29

Colds are not caused by flu viruses. The majority are caused by rhinoviruses. Symptoms of the common cold include sneezing, runny nose, nasal congestion, scratchy or sore throat, coughing, headache and fatigue.

Influenza symptoms are more severe with rapidly rising fever, chills, body and muscle aches.

Question 30

Effects of Viruses on Host Cells

Answer 30

Infection of a host cell with virus usually kills the host cell by:
-Lysis of the cell when it fills with virus particles
-Diversion of the cell’s metabolic pathways to the manufacture of viral particles
-Destruction of the virus-infected cell by the lymphocytes of the cellular immune system. -This may be destructive to the host if the cells are vital for survival, as sometimes happens with liver cells infected with hepatitis B virus.

A few viruses are able to alter the nucleic acid of the host cell in such a way that the cell is transformed into a tumor cell. These viruses are called oncogenic viruses. Hepatitis B is considered an oncogenic virus because it is associated with liver cancer.

Question 31

Control of Viruses

Answer 31

Antibiotics have no effect on viral replication. This is because antibiotics are directed against metabolic pathways of bacteria. Since viruses have no metabolic activities of their own, antibiotics provide no antiviral activity.

Many drugs that would inhibit replication of viruses cannot be used because they would destroy the host cells. However, there are a few useful antiviral drugs. Acyclovir is well-known as a control measure for genital herpes and Zidovudine (ZDV) is useful in controlling the rate of replication of the AIDS virus and was the first drug approved to treat HIV in the late 1980’s. It was formerly called Azidothymidine or AZT.

Research into antiviral agents is especially active today, not only for treating AIDS patients but also treatment of COVID-19. Paxlovid is an antiviral used to treat mild to moderate COVID-19 in adults that are at high risk for hospitalization/death.

Immunization is also effective for many viral diseases.

Question 32

Microorganisms

Answer 32

too small to be seen without the aid of a microscope
<0.1 mm
usually unicellular
also called “germs”, “microbes“, “bugs”

Question 33

Groups of Microorganisms

Answer 33

In order of decreasing size:

Protozoa: unicellular animals; move - flagella or ameboid motion;
e.g., microbe Giardia that causes “beaver fever“

Fungi: primitive plants
yeasts – unicellular

e.g., Candida – oral “yeast” infections, yeast vaginitis, skin infections, yeast diarrhea following antibiotic therapy

molds – multicellular
e.g., microbe that causes ringworm and athlete’s foot

Bacteria: unicellular; no organized nucleus; rigid cell wall
e.g., causative agent of Strept throat, Staph infections, Salmonella infections

Viruses: a bit of DNA or RNA surrounded by protein coat and sometimes lipid coat; grow only in other living cells; e.g. influenza virus, mumps, measles, rubella

Question 34

Size of Microbes

Answer 34

unit of measurement = micrometer = 1/1000 mm

Question 35

Gram Reaction of Bacteria

Answer 35

Bacteria stained with gram’s staining procedure, appear dark blue (gram positive) or red (gram negative); determined by cell wall structure
∴ possibilities: gram + cocci; gram - cocci, gram + rods, gram - rods, gram + spirilla, gram – spirilla

Why the gram reaction is important:
first step in identifying bacteria (look at shape and gram/color reaction)
determines effectiveness of antibiotics
determines effectiveness of disinfectants

Question 36

Shapes of Bacteria

Answer 36

round = cocci
(coccus)

rectangular = rods/bacilli
(bacillus)

spiral/curved = spirilla
(spirillum)

Question 37

Bacterial Endospores

Answer 37

Only a few bacteria (some gram positive bacilli such as tetanus, gangrene, botulism, anthrax) can form these under adverse conditions (too dry, too cold, lack of nutrients).

Spores vegetate (start growing) when growth conditions become good

Spores resist drying, heat and disinfectants (i.e. hard to kill)
heat: may take 121°C to kill
disinfectants: require high level disinfectant and long exposure time

Question 38

Bacterial Growth

Answer 38

Reproduce by binary fission:

Binary Fission

Time for this to occur (for population to double) = generation time = 15-30 minutes for rapidly growing bacteria, under ideal conditions (enough food, H20, correct temperature)

In lab, grow bacteria on culture media

Colony = visible mass of bacteria that forms on surface of solid culture media; usually takes 18-24 hours to form from 1 original cell; each colony is a clone - all descendants of a single bacterial cell.

Question 39

Viral Characteristics

Answer 39

Distinctive features:
metabolically inert - can multiply only in living host cells
contain DNA or RNA, not both
have protein coat that surrounds nucleic acid ± lipid envelope
Strangely, lipid viruses are generally easier to destroy than those with only a protein coat. (exception Hepatitis B – lipid virus survives 7 days on surfaces)

Question 40

Multiplication of Animal Viruses

Answer 40

Attachment to complementary site on host cell membrane

Penetration

Viral nucleic acid → nucleus: takes command of host cell and directs synthesis of new viral components

Synthesis of viral components:
nucleic acid - in nucleus
protein coat - in cytoplasm
Assembly of viral components

Release from host cell

Question 41

Effects of Viruses on Host Cell

Answer 41

Usually host cell dies (lysis; diversion of metabolic pathways; destroyed by host’s own lymphocytes)

Host cell may be transformed into tumor cell

Question 42

Control of Viruses

Answer 42

Antibiotics have NO effect

Antiviral drugs : acyclovir; ZDV etc

More and more anti virals being developed. Problem is that viruses are inside host cells – have to develop drugs which will destroy viruses without destroying host cells.

Question 43

Breakdown of Microorganisms

Type - Description - Treatment

Answer 43

Protozoa – Giardia & Amoeba – Anitiprotozoal

Fungi – Yeasts & Molds – Antifungal

Bacteria – about 1 micrometre in size – antibiotic
Viruses – reproduce inside living cells – antiviral