Welcome to the Wonderful World of Microbiology and Infectious Disease!

What are Microbes?Microbes are living things that are too small to be seen with the unaided eye They include bacteria, fungi, protozoa and

microscopic algae.Typically we view microbes as harmful, causing diseases, but only a minority of all microbes is pathogenic (disease-producing).

BacteriaBacteria are microbes, which are single-celled organisms that are too small to be seen without a microscope.

They are considered to be prokaryotes, which means that their DNA is not enclosed by a membrane. Eukaryotic cells have a nucleus with a

membrane.Where can bacteria be found?

Bacterial Cell

Basic Bacterial Anatomy

Bacterial Cell Parts

Capsule – outer covering on some bacteria; protects the cell and makes it more pathogenic; considered a glycocalyx or sugar coat

Cell wall – semi-rigid structure that maintains the shape of the cell and protects the interior of the cell from changes in the outside environment The bacterial cell wall contains peptidoglycan.

Some bacteria have just a few layers of peptidoglycan while others have many.

Peptidoglycan is not found anywhere else in the biological world.

Bacterial Cell PartsPlasma membrane - thin structure inside the cell wall that surrounds the cytoplasm, serves as a selective barrier through which materials can enter and exit

Ribosomes - appear as small dots in the cytoplasm; they make proteins

Nucleoid – the area where the DNA is found in the cell The DNA strand is long, continuous and usually

circular Bacteria possess NO chromosomes.

Bacterial Cell Parts

Plasmids - small circular strands of DNA not connected to the main DNA strand

Cytoplasm - everything inside the plasma membrane; mostly made up of water

Pili – hair-like structures that allow bacteria to attach to other cells and transfer DNA (conjugation)

Flagella - long tails that help bacteria move

Shapes of Bacteria

Come in three main shapes

Bacillus (rod)

Coccus (sphere)

Spirillum (spiral)

Arrangements of BacteriaStraight chains of bacteria are referred to as strepto-

Two cells of bacteria are called diplo-A cluster of bacterial cells is known as staphylo-

Gram StainDeveloped by the Danish bacteriologist Hans Christian Gram in 1884

Classifies bacteria into two major groups: Gram-positive Gram-negative

Gram Stain

Gram StainThe crystal violet and iodine combine within the cytoplasm of the bacterial cells.

Gram-positive - The color does not get washed out from the alcohol wash and the cells remain purple. Have thicker layer of peptidoglycan in cell walls

that enables the cell to retain the crystal violetGram-negative - The color is washed out by the alcohol and is no longer visible. When the counterstain safranin is applied, the cells appear red. The crystal violet can be washed out because they

have a thinner layer of peptidoglycan

Gram-positive Gram-negative

Gram Stain

Gram-positive/Gram-negative Cell Walls

Normal Flora/MicrobiotaWe all live with a variety of microbes on and in us.

These microbes make up our normal flora and include fungi, protists, but mostly bacteria.

Our body is made up of 1013 cells and we harbor about 1014 bacteria. 10 times more bacterial cells than human cells!

They are in most cases beneficial to us because they protect our bodies from diseases by preventing the overgrowth of harmful microbes.

Normal Flora/MicrobiotaNormal flora can be found throughout our body localized in certain regions. Skin Eyes (conjunctiva) Nose and throat (upper respiratory system) Mouth Large intestine Urinary system Reproductive system

Factors that influence where normal flora/microbiota are found

Availability of nutrientsChemical and physical factorsDefenses of the hostAgeGender

Normal Flora/Microbiota of SkinMicrobes on our skin must be able to withstand secretions from the sweat and sebaceous glands that have antimicrobial properties.

Keratin, a protein found on the skin, acts as a resistant barrier and the low pH of the skin can also inhibit many microbes.

These factors prevent the microbes that are in direct contact with the skin from becoming permanent residents.

Staphylococcus epidermidisS. epidermidis is the most abundant inhabitant of the skin, especially the upper body.

Staphylococcus aureus The nose is one of the most common sites for S. aureus.

It is a leading cause of bacterial disease in humans. It can be transmitted from the nasal membranes of a carrier to a susceptible host (immunocompromised).

Propionibacterium acnes

Located on greasy areas of the skin, such as the forehead

Can become trapped in hair follicles and cause inflammation and acne

Different species of Propionibacterium can live on the sides of our nose and on our armpits.

SymbiosisThe relationship between the normal flora and the host is called symbiosis. Symbiosis - living together

Three types of symbiotic relationships 1. mutualism 2. commensalism 3. parasitism

Animal symbiosis (4:20)

MutualismWhere both the host and bacteria are thought to derive benefits from each other, it is referred to as being mutualistic. 

Example: E. coli synthesizes vitamin K and some B vitamins that are absorbed into our blood stream. The large intestine, in return, provides nutrients needed by the bacteria.

CommensalismCommensalism - where one organism benefits and the other is unaffected

Many of the bacteria that make up our normal flora are commensals.

These include the bacteria that are on the surface of our eyes (conjunctiva) and skin and some bacteria in the ear that live on secretions and sloughed-off cells.

ParasitismParasitism -when one organism benefits at the expense of the other organism

In some situations normal flora can make us sick. This can occur when the normal flora leave their habitat.

Example: When E. coli leave their habitat of the large intestine and gain access to other body parts, such as the urinary bladder, lungs or spinal cord, they can cause infections such as urinary tract infections, pulmonary infections, meningitis and abscesses.

NutrientsBacteria can colonize only where they can be supplied the right nutrients.

These nutrients can come from excretory products of the cells, substances in body fluids and dead cells, and food in the gastrointestinal tract.

Chemical and Physical Factors that Affect Bacterial Growth

TemperaturepHAvailable oxygen and carbon dioxideSalinitySunlight (UV rays)

Mechanical Factors that Affect Bacterial Growth

Certain areas of the body have different mechanical factors that can affect normal flora from colonizing.

These include: Chewing action of teeth Tongue movements Flow of saliva and digestive secretions in

gastrointestinal tract Muscular movements of throat, stomach, intestines

These mechanical factors can trap or dislodge microbes.

How do Bacteria Make us Sick? It’s not the bacteria themselves that make us sick;

it’s what they produce that makes us sick. Bacteria produce substances called toxins that

cause illness and disease. There are two types of toxins: exotoxins and

endotoxins Exotoxins are proteins that are secreted by

bacteria and are products of their metabolism. Generally produced by Gram-positive bacteria Some of the deadliest substances known (C. botulinum toxin) Disease examples: food “poisoning”, TSS, tetanus, botulism,

diphtheria, gas gangrene

Endotoxins are components of the bacterial cell wall (lipopolysaccharides). Generally found in Gram-negative bacteria Disease examples: no specific diseases; cause fever,

hemorrhaging, shock, miscarriage, coma, death

Defenses of HostThe body has many defenses against microbes that include: Activated cells that kill microbes Cells that inhibit growth Prevent adhesion to cell surfaces Neutralize toxins that microbes produce

These defense mechanisms are helpful in fighting pathogens.

BiofilmsMasses of microbes attached to a surface; increases pathogenicity (involved in 70% of infections)The “slime” is made primarily of polysaccharides with some DNA and proteins.

The microbes are connected to each other, enabling them to chemically communicate with each other, transfer DNA, and share nutrients.

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BiofilmsBecause of the complex chemical composition of the slime, biofilms are resistant to immune systems, disinfectants, and antibiotics (about 1000 times more resistant).

Significant problem on internal medical devices such as catheters, stents, and mechanical heart valves; also problematic on contact lenses

When microbes grow in biofilms, they communicate with each other.

Examples: plaque, pool algae, shower scumBacterial communication (15:00)

Biofilms – Progression of Growth

Virus CharacteristicsViruses contain DNA or RNA, but not bothPossess a protein coatSome viruses have surface spikesMost viruses infect only specific types of cells in one host

Host range is determined by specific host attachment sites and cellular factors

First isolated and studied in 1935 (tobacco mosaic virus)

Phage therapy and oncolytic viruses

Are Viruses Alive??Viruses are inert outside a host cell = nonliving

They have few or no enzymes of their own, so they need their host cells’ enzymes.

However, once they enter a cell, their nucleic acids become active and they start multiplying.

They cause infection and disease just like living pathogens.

They could be considered:a very complex mixture of chemicals, ora very simple living organism

Viral StructureVirion - a complete, fully-developed, infectious viral particle composed of nucleic acid and surrounded by a protective protein coat (capsid)

Capsomere – protein subunit of a capsid; can be used to identify a particular virus

Envelope – lipid, protein, and carb complex covering capsid; many times contains parts of host membrane Used to help virus enter host cell

Spike – carb-protein complex projecting from envelope; can be used to ID virusUsed to attach virus to host cell and clump cells together

Viral Anatomy

Relative Sizes of Viruses

How do Viruses Reinfect?Why do we get influenza more than once?

The surface proteins (spikes) of many viruses, like influenza, can easily mutate.

Although you may have produced antibodies to one influenza virus, the virus can mutate and infect you again.

What is a vaccination?Influenza viruses – (notice the spikes)

Virus video (3:38)

History of Vaccination (4:30)

Multiplication of Bacteriophages (Lytic Cycle)

A virus must invade and take over a host cell in order to multiply; it needs the host cell’s enzymes and nucleic acids.

Attachment Phage attaches by tail fibers to host cell receptors

Penetration Phage lysozyme (enzyme) opens cell wall; DNA is injected into cell

Biosynthesis Production of phage DNA and proteins; no complete phages yet; step when host cell is taken over

Maturation Assembly of phage Release Phage lysozyme breaks cell wall

and “baby” phages are released to wreak more havoc

Lytic Cycle of a Bacteriophage (a)

Attachment

Penetration

Biosynthesis

Lytic Cycle of a Bacteriophage (b)

Maturation

Release

Lytic/Lysogenic CyclesLytic cycle: Phage causes lysis and death of host cell

Lysogenic cycle: Prophage DNA (inserted phage DNA) incorporated in host DNAHost cell does not dieEvery time host divides, so does the prophage DNA.

Lysis of E. coli

Lytic/Lysogenic Cycles

Viruses and CancerAlmost anything that alters cellular DNA (oncogenes) has the potential to make normal cells cancerous.

Several types of cancer are known to be caused by viruses (~10% of all cancers).

Relationship between viruses and cancer first demonstrated in 1908 (chicken leukemia)

Oncoviruses – viruses that transform normal cells into cancerous cells.

Transformed cells have increased growth, loss of contact inhibition, and viral-specific T antigens (antigens that disrupt the normal cell cycle).

The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

Latent/Persistent Viral InfectionsLatent Viral Infections

Virus remains in asymptomatic host cell for long periods Cold sores, shingles, oncogenic viruses Many remain latent in nervous tissue Can be reactivated by immunosuppression

Persistent Viral InfectionsDisease progresses over a long period; generally fatal; disease presents years later

Often caused by another virusMeasles and fatal encephalitis; HBV and liver cancer; human papillomavirus and cervical cancer

Plant Viruses and Viroids• Plants are generally

protected by cell wall• Plant viruses enter

through wounds or via insects that suck plant’s sap

• Viruses can multiply inside insect cells, then get passed to plant

• Viroids• Viroids are infectious

pieces of RNA (potato spindle tuber disease)

• Responsible for millions of $ in crop damage

tobacco mosaic virus

Prions Infectious proteins first explained in 1982 Inherited and transmissible by ingestion, transplant, and surgical instruments; can be spontaneous as well

Treated with proteases or NaOH and autoclaveMost resistant to chemical biocides because when altered, they’re extremely stable and resistant to denaturation

Many are believed to be inherited (the case with the five human prion diseases)

PrPC: normal cellular prion protein; on cell surface

PrPSc: scrapie protein; accumulates in brain cells forming plaques (plaques used for postmortem diagnosis; don’t appear to be cause of cell death)

Prions

Microscopic "holes" are characteristic in prion- affected brain tissue sections, causing the tissue to develop a "spongy" appearance.

Prions

Section of a normal brainSection of brain affected by Creutzfeldt-Jakob disease

Prions (1:40) Fatal Familial Insomnia (9:55)

QUIZ TIME!!!

Bacteria can be found in the shape of _____.A. spheresB. rodsC. spiralsD. all of the above

Shapes of Bacteria

Identify each basic shape.

Because they have no nucleus or organelles, bacteria are considered to be _____.

The pili of a bacterial cell are used for _____.A. protection from macrophagesB. making proteinsC. movementD. transferring DNA to other bacteria (conjugation)

You will never find ______ in a bacterial cell.A. a nucleusB. a cell wallC. a ribosomeD. DNA

What is the carb covering of the bacterial cell that protects it from the outside environment?

A. plasma membraneB. capsuleC. cell wallD. pili

Normal flora are bacteria that cause disease.TrueFalse

Normal flora can only be found on our skin.TrueFalse

Spherical bacteria are called ________.

Rod-shaped bacteria are called ________.

Spiral bacteria are called _______.

When both the host and bacteria receive benefits from each other it is considered to be _____.

A. parasitismB. commensalismC. mutualism

Bacteria arranged in a straight chain are referred to as _________.

Bacteria arranged in a cluster are referred to as ________.

Two side-by-side cells of spherical bacteria are called ________.

Bacterial cells will burst at the end of the _____ cycle.

Cancer-causing viruses are called _____.

_____ are masses of a variety of microbes sticking to a surface.

The carb-protein structure that enables viruses to attach to host cells:A. capsuleB. glycocalyxC. spikeD. pili

Infectious proteins are called:A. viroidsB. bacteriophagesC. prionsD. normal flora