VTAH Final

20% - Chapters 2-4 & 80% - 5-9

is a standardized process where a series of tests are performed on the sample to determine the genus and species of the pathogen

bacterial identification

growing bacteria on specialized media. Media is a substrate allowing for the growth and cultivation of bacteria either on it or in it.

Culturing of bacteria

a method of introducing bacteria onto the media

inoculating the bacterial media

opportunity for the bacteria to grow. Typically, 48 hours

Incubating the sample

Will be identified by gram stain and biochemical tests

the cultivated bacteria

3 types of media to culture bacteria

Selective, Differential, and Enrichment Media

Encourage the growth of some bacteria and suppress other

Selective media

Used to distinguish a certain type of bacterial colony. Result is usually a color change.

Differential Media

Special nutrients to allow growth of a particular organisms.

Enrichment Media

Example of a Selective media

Mannitol Salt Agar (MSA)

Mannitol Salt Agar is selective to

Staphylococci and inhibitory to most other bacteria

Example of a Differential Media

Blood Agar

Displays a color change in the presence of bacteria that can lose (break down) red blood cells

Blood Agar

Example of Bacteria to use Blood Agar (differential media):

Streptococcus pyogens

Example of an enrichment media:

Chocolate Agar

Chocolate Agar

Contain the nutrients required to support the growth of a variety of bacteria and it does not suppress other bacteria.

Examples of Common Stains

Diff Quick, Gram Stain, and Acid-Fast Stain

A type of Romanowsky stain (I.e blood smear and cytology samples)

Diff Quick

Differential stain used to identify gram positive vs gram negative bacteria

Gram Stain

Crystal Violent, Gram’s Iodine, Ethyl alcohol, and Safranin

Reagents used for Gram Stain

It is used for bacteria that do not gram stain well (like Mycobacterium)

Acid-Fast Stain

Carbolfuchsin, Alcohol, and Methylene blue

Reagents used for Acid-Fast Stain

Acid Fast is used to identify:

Mycobacterium and Rhodococcus

Acid Fast Positive Bacteria will stain

Red

Acid Fast Negative Bacteria will stain

Blue

Examples of Biochemical Test

Catalase, Coagulase & Oxidase Test

Indicates the presence of catalase enzyme that some bacteria produce. This test helps in bacterial identification. Resulting in the formation of bubbles. Test help differentiate between Staphylococcus spp and Streptococcus spp.

Catalase Test

Catalase Test help differentiate:

Staphylococcus spp and Streptococcus spp

Indicates the presence of coagulase enzyme that some bacteria produce. Test differentiates Staphylococcus aureus and Staphylococcus epidermidis.

Coagulase test

Coagulase Test help differentiate between

Staphylococcus Aureus & Epidermidis.

In coagulase test, if the results are positive it is:

Staphylococcus Aureus

In coagulase test, if the results are negative it is:

Staphylococcus epidermidis

Used in microbiology to determine if a bacterium produces a certain Cytochrome C oxidase (catalyzes the biochemical process). + Test means it will turn purple or blue.

Oxidase Test

Oxidase test differentiate among members of:

Pasteurella, Pseudomonas, and Enterobacteriaceae

Positive Oxidase Test:

Pasteurella and Pseudomonas

Negative Oxidase test:

E.coli & Salmonella

The area where the antibiotic killed the bacteria.

Zone of inhibition

Common Fungal Stains

Lactophenol Cotton Blue & India Ink

Enables identification of fruiting heads and spores. Unique enough to identify genus and species of the fungus.

Microscopic Examination

Used to examine dermatophytes

Lactophenol Cotton Blue

Helps to identify Crytococcus neoformans

India Ink

Contains Sabouraud’s dextrose agar with various antibacterial and antifungal agents to retard the growth of contaminant organisms. Contains a pH indicator that a color change occur when it indicates a positive culture.

Dermatophyte Test Media (DTM)

A drug that kills microorganisms or inhibits its growth

Antimicrobial drugs

Example of antimicrobial drugs are:

Antibiotics & antifungals

The toxicity primarily affects the pathogen and not the host.

Selective toxicity

An antimicrobial that targets a wide range of pathogens (I.e ability to kill both gram-positive & gram-negative bacteria)

Broad Spectrum

An antimicrobial that targets a narrow range of pathogens (I.e. ability to kill only gram-negative bacteria)

Narrow Spectrum

This term is used to describe an antibiotic that inhibits bacterial growth. It does not kill the bacteria.

Bacteriostatic

This term is used to describe an antibiotic that causes the bacteria to die.

Bactericides

Classification of Antimicrobial Drug MOAs

Inhibition of cell wall synthesis, disruption of plasma membrane function, inhibition of protein synthesis, inhibition of nucleic acid synthesis, and inhibition of enzyme activity

Inhibits division and destabilizes the cell wall, leading to rupture & target prokaryotic cells

Inhibition of Cell Wall Synthesis

Cause an increase in permeability and loss of cytoplasm and cell contents. This only used topically. Targets gram negative bacteria.

Disruption of Plasma Membrane Function

Target bacterial ribosomes. Target can be non-specific ribosomes can cause toxicity in animals. (I.e Nephrotoxicity or Ototoxic)

Inhibition of Protein Synthesis

Without synthesis of nucleic acids, the bacteria will die

Inhibition of Nucleic Acid Synthesis

Enzymes are required for bacterial growth, replication, and maintenance. Sulfa antibiotic drugs inhibit different enzymes and together they target multiple pathways.

Inhibition of Enzyme Activity

Mechanism of Action that are Bactericidal:

Inhibition of Cell Wall Synthesis, Disruption of Plasma Membrane Function, Inhibition of Nucleic Acid Synthesis, Inhibition of Enzyme Actovity.

Mechanism of Action that are Bacteriostatic:

Inhibition of Protein Synthesis

Methods of Resistance:

Altered Target, Enzyme degradation, and Efflux

Bacteria possessing an altered target will be resistant to antibiotics that can no longer bind to their intended target and exert their effect.

Altered Target

Bacteria possesses enzymes capable of degrading particular antimicrobials, rendering the antimicrobial ineffective against the bacterium. Example: Enzyme Beta-lactamase

Enzyme Degradation

Bacteria that possesses channels within their cell wall that are capable of actively exporting antimicrobials and other compounds out of the cell. Example, gram-negative and mycobacteria possesses efflux pumps.

Efflux

Random, genetic DNA mutation that are beneficial to the bacteria.

DNA mutations

Enables resistance bacteria to pass on plasmids that carry antimicrobial resistance to bacteria that do not have the resistance.

Conjugation

When bacteria die, they released DNA that can be picked up by a nearby bacteria.

Transformation

Bacterial DNA transferred from one bacteria to another inside of virus. Bacteriophages a virus that infects bacteria.

Transduction

Microorganisms which normally reside in a host without causing any infection or disease. AKA normal microflora

Commensals

Microorganisms capable of causing disease in its host.

Pathogen

Microorganism capable of causing disease when it is introduced into a site of the body where it does not normally reside or have access.

Opportunistic Pathogen

Resume of a successful pathogen:

The pathogen must be able to enter, to attach to some tissues within the body, multiply, spread, damage and avoid the immune defenses of the host.

The process by which a disease or disorder develops. It includes the origination and maintenance of the disease.

Pathogenesis

What are the first line of defense?

Skin, mucin, & secretory immunoglobulin A (IgA)

4 Defense Properties of Skin

Relatively dry, low pH, skin cells contain lysosomes and antimicrobial peptides, and the removal of bacteria from the external surface when the skin cells are naturally shed.

A group of mucoproteins found in various substances of the body such as saliva and gastric juices. Also forms a protective barrier that limits exposure and prevents the adhesion of pathogens.

Mucin

Immunoglobulins prevent microbial pathogens and toxins from traversing the skin.

Secretory Immunoglobulin A (IgA)

What are the second line of defense?

Phagocytes, Inflammatory Response, the complement system

Eating machines to the immune system, ability to engulf and removed pathogens and debris, are attracted to the chemical trail.

Phagocytes

examples of phagocytes:

Eutrophication, macrophages, and monocytes

A complex system of proteins the act in concert to help eliminate infectious microorganisms. Causes lysis of foreign and infected cells, phagocytosis and inflammation of surrounding tissues.

The complement system

Inflammatory response generated by complement enhances of body’s ability to combat pathogens, and activates clotting to prevent the spread of the pathogen.

Inflammation

Adaptive Immunity is considered to be

3rd line of defense

Has the ability to recognize pathogens, but can also kill them in store vital information pathogen it has two parts: humoral immunity and cell meditated immunity.

Adaptive Immunity

Defines as a process where an animal is given antibodies

Passive Immunity

Immunity after being exposed to an infection.

Active Immunity

Injection of preformed antibodies

Artificially acquired

Passive artificially example:

Immune serum given by Injection

Passive immunity example:

Mother to fetus via placenta

Characteristics of Fungi

Fungi are Eukaryotic, have plant-like cell walls, fungi can be unicellular or multicellular, fungi have a nucleus and organelles, strict aerobes and slow growing.

A type of fungal that is oval to spherical, single cell fungi, reproduce asexually by budding

Yeasts

Type of fungal that are multicellular filamentous fungi, threadlike filaments are called hyphae, molds can reproduce asexually or sexual, spores act as reproductive bodies of fungi

Molds

Fugal Routes: Superficial

Skin

Fungal Route: Deep

Subcanteous

Systemic Mycoses

Systemic Tissue → Internal

Fungal Transmission

Direct contact, Damp/Wet Environment, & Contact with fomites

Infects only the cutaneous (skin), Fungi invades the epithelial cells of the skin and mucous membranes, The most common form of fungal disease in animals

Superficial Fungal Disease

Example of Superficial Fungal Disease

Dermatophytes & Malassezia

True or false: Dermtophytes are Zoonotic.

True

Microsporum canis is known as

Ringworm

It invades the top layer of the skin (stratum corneum)

Lesion can be itchy (pruritic)

Secondary bacterial infections with staphylococcus

Transmission: Damp environment, direct contact, fomites

Microsporum canis (Ringworm)

Also invades the stratum corneum

Clinical signs like M canis. In dogs the infection is more severe.

Trichophyton mentagrophytes