Microbiology of Pathogenic Factors

Are most microbes beneficial or pathogenic?

Most microbes are beneficial and exist as part of our body's normal flora, either having mutualistic or commensalistic with the host - as long as they remain where they should in the body

What are resident microorganisms?

Microorganisms that permanently colonize the host

What are transient microorganisms?

Microorganism that temporarily colonize the host. Can be due to different food consumed or being in a new environment (travelling to different countries - different flora)

What 4 factors determine the distribution of normal flora in the body?

1. Nutrients

2. Physical and Chemical Factors

3. Mechanical Factors

4. Host factors (Age, Nutritional status, Disability, Stress, Hygiene, Lifestyle, Geography, Occupation)

Thus, these factors result in different types of normal flora present across the body

How does nutrient affect distribution of normal flora in the body?

Body environment requires sufficient amount and type of nutrients.

Examples of nutrients may include secretions and excretions of cellular products and glands, and ingested food by the host

How does physical and chemical factors affect distribution of normal flora in the body?

The microorganism has to tolerate exposure to these factors , which include temperature, pH, O2, CO2, salt, sunlight

How does mechanical factors affect distribution of normal flora in the body?

The microorganism has to be able to tolerate enzymes or mechanical processes present in that area of the body. Examples include chewing, oral + GI enzymes, peristalsis for the GI tract, and mucous and ciliary action of the respiratory system

How do host factors affect distribution of normal flora in the body?

Age

-Older age = weaker microbiome

Nutrition

-Lower nutrition = weaker microbiome

Disability

-Immobility -> alterations in skin condition (moisture) -> different microbiome

Stress

-Increased stress = weaker microbiome

Hygiene

-Lack of hygiene = different microbiome

Lifestyle

-Lifestyle factors

Geography

-Different environment = different microbiome (Canada vs tropical country)

Occupation

-Different occupation = different microbiome (high varied exposure to microbiomes as a nurse compared to non hospital occupation)

Which areas in the human body contain significant normal resident flora?

-Upper respiratory tract

-Lower respiratory tract

-Lower digestive tract

-Urinary system

-Reproductive System

-Eyes and skin

Important to consider as nurse to not act as a vector, transporting normal flora to a place it does not belong

What is Microbial Antagonism?

Normal flora, including those that have a commensal relationship with the host, will have an indirect benefit to the host's health by competing with pathogenic microbes, preventing a possible infection

The microbes compete with pathogens by:

-Competing for nutrients

-Produce harmful substances to pathogen

-Manipulation of the host environment (altered pH and O2)

Note that an infection from the pathogenic microbe is still possible, especially if the balance between normal flora and the pathogenic microbes is altered

What are three mechanisms in which normal flora perform microbial antagonism?

-Normal flora compete with pathogens for limited nutrients

-Normal flora are able to produce substances that may be harmful to the pathogen

-Normal flora may manipulate the host environment by altering pH and O2 levels

How does E.coli act as a microbial antagonist?

E.coli produces bacteriocins which inhibit the growth of Salmonella and Shigella species, both of which are responsible for causing gastroenteritis (GI infections)

What are factors that can affect the normal flora vs pathogenic microbe balance?

Pathogen factors

-Huge exposure to pathogenic microbes

Normal Flora factors

-Age (weakened flora)

-Changes in hygiene (ineffective hygiene -> wiping butt to urethra because of MSK changes, resulting in introduction of flora in the urinary tract)

-Nutritional status (lack of nutrition = weakened flora)

-Antibiotic use (destroys normal flora)

How can antibiotic use lead to increased susceptibility to C. diff infections?

In a hospital environment, C.diff can be transferred via endospore and enter a patient's GI tract, where it lies dormant. A hostile environment caused by the presence of normal flora keeps the endospore in check by taking away nutrients and prevents it from converting into it's pathogenic form.

If the patient is given a large dose of antibiotics to treat an infection, the antibiotic can also destroy the normal flora in the GI as well, which can create an environment conductive for C. diff growth by increasing the amount of available nutrients, resulting in the endospore being converting into a pathogenic form and starting another infection

aka an opportunistic infection

What is antibiotic-mediated destruction?

Normal flora in the body being killed off due to high dosages of antibiotics, allowing potential pathogenic microorganisms to thrive due to the lack of microbial antagonism

What is an opportunistic infection?

An infection caused by a microorganism that typically does not cause harm to the human body, but due to an alteration in conditions or the environment, causes an infection

What are three factors that can cause an opportunistic infection?

-Movement of normal flora out of normal habitat

-Weakened immune system

-Change in composition of host normal floar

How can movement of normal flora out of it's normal habitat cause an opportunistic infection?

If normal flora is out of it's normal habitat (ex: GI flora in the urinary tract), it can result in an infection. This can be caused by improper hygiene (wiping butt to urethra), injury, and lack of IV + catheter care

How can E. coli cause an opportunistic UTI?

E.coli, which normally resides in the GI tract, can access the urinary tract through improper hygiene (potential due to MSK issues), resulting in a UTI

How can a weakened immune system cause an opportunistic infection?

Corticosteroid therapy, acquired immunosuppression, or antirejection meds can cause microorganisms, that do not have an effect on healthy patients, to cause an infection

How can Pneumocystis jirovecii cause pneumonia, despite it being a part of normal flora in the respiratory tract?

Weakening of the immune system can cause Pneumocystis jirovecii to be pathogenic in a patient - resulting in an infection

How can alteration in normal flora composition cause an opportunistic infection?

Antibiotic therapy can kill normal flora normally present in the human body, lowering the competition for pathogenic microorganisms to thrive and cause an infection in the body

What are the 6 processes in the pathogenesis of a microorganism?

1. Contact/Exposure

2. Adherence

3. Evasion of Host Defenses

4. Penetration of Host

5. Damage to Host Cells

6. Transmission

What is the contact/exposure phase of the pathogenesis of a microorganism?

The microorganism gains entry into the host through portals of entry (mucous membranes, skin, deposition)

What is the most common portal of entry in a human?

The respiratory tract

What are 3 portals of entry in a human?

1. Mucous membranes (conjunctiva of eye, respiratory tract, gastrointestinal tract, genitourinary tract)

2. Skin (Natural openings, breakdown, infection)

3. Direct deposition under mucous membranes or skin (injury, surgery, invasive procedures)

Which mucous membranes serve as portals of entry for microorganisms?

Conjunctiva (of eye), upper respiratory tract, gastrointestinal tract, genitourinary tract

How does skin serve as a portal of entry for microorganisms?

While skin is an almost impenetrable barrier, microorganisms can gain entry through natural openings in the skin (follicles, sweat gland ducts), as well as through injury, breakdown, dryness, and infection of the skin

How can microorganisms gain entry to the host through direct deposition beneath mucous membranes or skin?

Injuries (Punctures, wounds, cuts), surgery, and invasive procedures can allow microorganisms to penetrate the skin barrier and start and infection

What is the adherence phase of the pathogenesis of a microorganism?

Pathogen attaches to specific host tissues by forming adhesin receptor complexes, where the adhesin on the microorganism binds to surface receptors located on the cells of host tissue

What are three structures that act as adhesins for microorganisms to bind to host tissue?

Bacterial structures (fimbriae, flagella)

Adherence proteins (M proteins)

Glycocalyx (Capsule, Slime layer)

What are two bacterial structures that act as adhesins to host cell receptors?

Fimbriae (many short straight filaments)

Flagella (long filament for movement)

How does pyelonephriotgenic E. coli adhere to the epithelium of the urinary tract?

The p.fimbriae of the E.coli forms an adhesin receptor complex with galactose disaccharides on the surface of epithelial cells in the urinary tract, resulting in a UTI

It is the most common cause of a UTI (90% of cases)

What is an adherence protein that act as adhesins for microorganisms to bind to host tissue?

M proteins

How does streptococcus pyrogens adhere to epithelial cells?

M proteins are produced by streptococcus pyogenes (group A streptococcus) and appear as hair like projections on the bacterial cell surface. This protein allows the bacteria to bind to various epithelial host receptors, resulting in the capacity to cause many types of infections (cellulitis, Necrotizing encephalitis, strep throat)

What are two types of glycocalyx that act as adhesins to host cell receptors?

Capsule (Firm)

Slime layer (Loose, forms biofilms)

How does Neisseria meningitidis type B adhere to epithelial cells in the brain?

Neisseria meningitidis possesses a K1 capsule that is capable of binding to epithelial cells of the ventricles and vascular endothelium of the brain, resutling in meningitis

What are biofilms of bacteria?

Colonies of bacteria that adhere to living or non living surfaces due to a slime layer. A biofilm consists of many layers, making them highly resistant to the body's immune defenses, disinfectants, and antibiotics as it may only penetrate a few layers of the biofilm - with deeper layers remaining intact.

Thus surgical intervention is often required to treat a biofilm infection

What is the evasion phase of the pathogenesis of a microorganism?

Adhesin mechanisms and enzymes produced by the microorganism allow it to evade or become resistant to phagocytosis, allowing the microorganism to rapidly replicate and cause infectious symptoms

What are two adhesive bacterial structures that also act as mechanisms of evasion?

Capsule (Prevent phagocyte adherence)

Cell wall (M protein and Mycolic acid)

How does the bacterial capsule act as a mechanism of evasion?

The bacterial capsule helps the bacteria evade phagocytosis by preventing adhesion of phagocytes to the pathogen, increasing the virulence of the bacteria.

Although the host will eventually produce antibodies to counter the infection, this takes time and allows the bacteria to rapidly replicate

How does streptococcus pneumoniae evade host defenses?

Streptococcus pneumoniae possess a cell capsule, which results in pneumoniae or meningitis

How does the bacterial cell wall act as a mechanism of evasion?

Bacterial cell wall that contain M proteins or mycolic acid (Mycobacterium tuberculosis) helps resist digestion of the bacteria by phagocytes

How does streptococcus pyogenes evade host defences?

Streptococcus pyrogens possesses M proteins in the cell wall, which not only facilitates adherence of the bacteria, but also helps resist phagocytosis

Streptococcus pyrogens also possesses streptokinase, which digests the body's clots to infect deeper tissue

How does Mycobacterium tuberculosis evade host defences?

Mycobacterium tuberculosis possesses Mycolic acid in the cell wall, which helps the bacteria resist phagocytosis

What are bacterial enzymes that help the bacteria evade host defences?

Coagulase and kinase

How does coagulase help bacterial evasion of host defences?

Coagulase facilitates the conversion of fibrinogen into fibrin, forming a blood clot. Since phagocytes travel via the blood stream, the formation of a clot isolates the bacteria and prevents phagocytes from reaching the bacterial infection

What are coagulase positive and negative staphylococcus species?

Coagulase positive staph = staph species that have coagulase enzyme to form clots and protect it from the host's immune defenses (streptococcus aureus)

Coagulase negative staph = staph species that do not have coagulase enzyme (staphylococcus epidermis)

How does staphylococcus aureus evade host defenses?

Staphylococcus aureus possesses coagulase, which aids in the formation of blood clots that impairs phagocytes from reaching and killing the bacteria. It then releases kinase once it has replicated so that the infection can spread throughout the body

How does kinase help bacterial evasion of host defenses?

In the case of staphylokinase:

Once the staphylococcus aureus has been isolated from the hosts immune cells through formation of fibrin clots, it continually replicates. It then releases kinase, which digests these clots, and allows the bacteria to spread throughout the body

In the cause of streptokinase:

Digestion of clots made by the body allows streptococcus pyogenes to infect deeper tissue

What is a disseminated infection?

An infection that becomes systemic and spreads from it's original point to multiple organs throughout the body

Facultative intracellular bacteria, like nisseria gonorrhea, become disseminated by traveling on immune cells

How can facultative intracellular bacteria evade host defenses?

Facultative intracellular bacteria can survive inside of immune cells, protecting it from the immune cell, antibiotics, and allowing the bacteria to become disseminated and travel throughout the blood stream.

The bacteria does this through 4 mechanisms

1. Fuses with the phagocyte's lysosomes to evade phagosomes

2. Prevents fusion of phagosomes and lysosomes, preventing the phagocyte from releasing it's cytotoxins

3. Reducing effectiveness of toxic compounds within the lysosome

4. Producing cell walls that are resistant to lysosomal proteases

What are two enzymes that allow bacteria to penetrate host tissue?

Hyaluronidase (Between cells)

Collagenase (Collagen below tissue)

How does hyaluronidase allow bacteria to penetrate host tissue?

Hyaluronidase breakdown down polysaccharides that hold cells together, creating a small channel that allows the bacteria to pass through the cells

How does collagenase allow bacteria to penetrate host tissue?

Collagenase breakdown collagen fibers at the base of the tissue, allowing the bacteria to move deeper into the host, where there are less immune cells that can kill the bacteria

How does invasins allow bacteria to penetrate host tissue?

Invasins rearrange actin filaments of the cell membrane, resulting in membrane ruffling and producing ruffles - or folds - on the cell membrane. These folds allow the bacteria to "sink" into the cell and become engulfed

Which bacterial species produce invasins to penetrate the host cell?

Salmonella and E. coli species

What is the damage phase of the pathogenesis of a microorganism?

Once the bacteria has adhered to host tissue and evaded host defenses, the bacteria begins to damage host cells through appropriation of host nutrients, direct damage to cells - resulting in cell lysis, production of toxins, and causing hypersensitivity reactions

What are 4 mechanisms in which microorganisms can cause cell damage and disease?

1. Appropriation of host nutrients (Iron)

2. Direct damage to cells (Cell lysis)

3. Production of toxins (Endotoxins and exotoxins)

4. Hypersensitivity reactions (Allergies)

How do bacteria appropriate host nutrients to cause host cell damage?

Bacteria will "steal" iron, located on iron-transport proteins in the human host, as it is required for the growth of most pathogenic bacteria

The bacteria will do this using three mechanisms

1. Siderophores (greater affinity for iron)

2. Direct binding

3. Production of toxins that kill bacteria, causing release of iron

What are three mechanisms in which bacteria will sequester iron from host cells?

1. Siderophores - molecules released by bacteria which have a greater affinity for iron than host iron-transport proteins. The siderophore with the iron will then be taken back up by the bacteria through siderophore receptors on the bacteria

2. Direct binding to host iron-binding proteins (Tug of war for iron)

3. Producing toxins that kill host cells, causing release of iron, which is then sequestered by the bacteria

What are siderophores?

Molecules released by bacteria which have a greater affinity for iron than host iron-transport proteins. The siderophore with the iron will then be taken back up by the bacteria through siderophore receptors on the bacteria

How does bacteria directly damage tissue to cause host cell damage?

Bacteria (and viruses) rapidly replicate in the host cell. In order to be released from the host cell, the host cell is ruptured, killing the cell and allowing the pathogen to spread to other tissues in greater numbers

How do bacterial toxins cause host cell damage?

Bacteria can produce toxins which alter normal metabolism of cells. Upon release, these toxins can inhibit cellular protein synthesis, destroy blood cells and blood vessels, and disrupt nervous system function.

Toxins can include exotoxins (A + B toxins, membrane disrupting toxins, superantigens) and endotoxins (lipid A)

What are exotoxins?

Toxins that are actively produced inside of a bacteria and are secreted into the surrounding environment, or released from cell ylsis.

These toxins are often soluble and can transport throughout the blood stream to affect the body's tissues.

The toxin itself is usually the major cause of symptoms from the bacteria (botulism + staphylococcal food poisoning)

Include A+B toxins, membrane disrupting toxins, and superantigens

What causes symptoms from botulism and staphylococcal food poisoning?

Effect of exotoxins released by the bacteria

What are A-B toxins?

A type of exotoxin that consists of an A and B polypeptide

The A polypeptide is the active part of the toxin that results in changes in intracellular function - causing damage

The B polypeptide facilitates binding of the toxin to the host cell

What is the A polypeptide of an A-B toxin?

Active enzyme component of the toxin, results in change in intracellular function that causes host cell damage

What is the B polypeptide of an A-B toxin?

Binding component of the toxin, facilitates binding of the toxin to the host cell

How does the Bordetella pertussis cause alter the function of respiratory epithelial cells?

Bordetella pertussis releases A-B toxins which increase cAMP in respiratory epithelial cells, causing increased mucous production and coughing

What are membrane disrupting toxins?

A type of exotoxin that kills the host cell by forming protein channels or disrupting the phospholipid layer of the cell membrane

What are superantigens?

A type of exotoxin that provokes a huge immune response due to directly stimulating T cell activation and producing inflammatory cytokines, such as IL2 and TNFa, which causes disseminated intracellular coagulation and shock

What occurs during normal antigen immune activation compared to superantigen immune activation?

Normally, antigens will be presented by APCs to T-cells, which causes proliferation of T cells, and production of antibodies and cytokines.

Superantigens skip the APC presenting step and directly stimulate T-cells to proliferate and release excess IL-2, which causes release of TNFa. Excess release of TNF can lead to disseminated intracellular coagulation and septic shock

How do superantigens activate the immune system?

Superantigens skip the APC presenting step of T-cell activation and directly stimulate T-cells to proliferate and release excess IL-2, which causes release of TNFa. Excess release of TNF can lead to disseminated intracellular coagulation and septic shock

What two conditions can bacterial release of TNFa cause?

TNFa release from superantigens and endotoxin lipid A can lead to disseminated intracellular coagulation and septic shock

Which gram type of bacteria possess endotoxins?

Only gram negative bacteria due to possessing lipid A on the outer membrane

What are endotoxins?

Toxins, specifically lipid A, present on the outer membrane of gram negative bacteria which are released from the death of the bacteria.

Release of Lipid A causes macrophages to release high concentrations of IL-1, resulting in symptoms of chills, fever, weakness, and generalized aches, as well as increased production of TNFa, which can result in disseminated intracellular coagulation and septic shock

What are symptoms caused by release of Lipid A?

Release of IL-1 from macrophages causes same signs and symptoms regardless of the gram-negative bacteria.

General symptoms include chills, fever, weakness, and generalized aches

What is a significant difference between symptoms produced by endotoxins and exotoxins?

A fever will not be a symptom of an exotoxin, unless if it is a superantigen

A fever will ALWAYS be a symptom of an endotoxin

What is the transmission phase of the pathogenesis of a microorganism?

Once it has replicated enough, microorganisms leave the body through specific portals of exit in secretions, excretions, discharges, or shed tissue. Typically the portals of exit are very similar to the portals of entry and include:

-Respiratory tract

-Gastrointestinal tract

-Genitourinary tract

-Skin, Conjunctiva, Blood

What are portals of exit of bacteria?

Similar to portals of entry, include:

-Respiratory tract

-Gastrointestinal tract

-Genitourinary tract

-Skin, Conjunctiva, Blood