Topic 13 Microbial Infectivity Flashcards
(26 cards)
Terminologies
_ - organism being infected
_ - no disease - environmental microorganisms
_ _ - colonize host tissue - no disease
- Host
- Saprophytes
- Commensal organisms
Terminologies
_ - a microbe that is capable of causing disease
- _ pathogen - can cause disease in a host regardless of the host’s resident microbiota or immune system
- _ pathogen - can only cause disease in situations that compromise the host’s defenses, such as the body’s protective barriers, immune system, or normal microbiota
Pathogen
- Primary pathogen
- Opportunistic pathogen
Host factors affecting the growth and pathogenesis of bacteria
The disease outcome is heavily influenced by the interactions between the _ and the _
- _ _ - physical and chemical attributes of the host protect against microbial infection
- _ _ - results from a disturbance in the balance between bacterial virulence and host resistance
Factors affecting bacterial pathogenesis - HHAHCPP
host and microbes
- Host Resistance
- Bacterial Infectivity
Factors affecting bacterial pathogenesis - Host immune system, host genetics, age, host microbiota, coexisting infections, pathogen virulence, pathogen resistance
Terminologies
_ - invasion of the host by microorganisms, which then multiply in close association with the host’s tissues
- _ infection - confined to a small area of the body, typically near the portal of entry
- _ infection- infection becomes disseminated throughout the body
- _ infection - has noticeable signs and symptoms
- _ infections - infection is active, but does not produce any outward symptoms
- can still be contagious and may progress to clinical disease over time
LSCS
Infection
- Local infection
- Systemic infection
- Clinical infection
- Subclinical infection
Terminologies
_ - ability to produce a disease
- pathogenic or non-pathogenic
- qualitative term
_ - relative degree of pathogenesis (tissue damage)
- quantifies pathogenicity
- quantitative term
Pathogenicity
Virulence
Bacterial Mechanisms of Pathogenicity: How Microorganisms Cause Disease
P, N, A -> P -> D
Portals of entry, number of invading microbes, adherence -> penetration or evasion of host defenses -> damage to host cells/cytopathic effects
_ _
- contact with surfaces or objects
- ingestion of food or water
- inhalation of airborne bacterial particulates
- direct physical contact with individuals manifesting bacterial infections
Bacterial Exposure
Bacterial Mechanisms of Pathogenicity
1a. Portal of Entry
- _ _ - respiratory tract, gastrointestinal tract, conjunctiva, genitourinary tract
- _ - some microorganisms can gain entry through hair follicle and sweat glands
- _ - through a breach in the protective barriers of the skin and mucous membranes
- Mucosal surface
- Skin
- Parenteral
Bacterial Mechanisms of Pathogenicity
1b. Numbers of Invading Microbes
- _ - infectious dose; number of microbes required to produce infection in 50% of a sample population
- measures the _ of the microbe
- Bacillus anthracis - Portal of entry | _
- Skin - 10-50 endospores
- Inhalation - 10k-20k endospores
- Ingestion - 250k-1M endospores
- ID50
- measures the virulence of the microbe
Bacterial Mechanisms of Pathogenicity
1b. Numbers of Invading Microbes
- _ - lethal dose, amount of toxin or pathogen necessary to kill 50% in a population within a certain time period
- measures _ of a toxin
- Toxins | _
- Botulinum - 0.03 ng/kg
- Shiga toxin - 250 ng/kg
- Staphylococcal enterotoxin - 1350 ng/kg
- LD50
- measures potency of a toxin
Bacterial Mechanisms of Pathogenicity
1c. _
- Capability of pathogenic microbes to attach to the host cells
- _ (ligands) on the pathogen bind to receptors on the host cell
- Colonize and multiply at a rate faster than their removal
- Helps in penetrating the body tissue and cells
1c. Adherence
- adhesins
Bacterial Mechanisms of Pathogenicity
1c. Adherence
_
- _ - prevents phagocytosis
- _ and _ - thin, protein tubes originating from cytoplasmic membrane found in all Gram - bacteria (but not in many Gram + bacteria)
- p are typically longer and fewer in number than fimbriae
- _ - involved in bacterial adhesion and invasion by providing motility towards target cells and receptors, and by adhering to these targets
Adhesins
- capsule
- fimbriae and pili
- flagella
Bacterial Mechanisms of Pathogenicity
1d. _
- establishment of a colony of organism at a particular site
- important for pathogen survival and invasion to other sites
- _ - matrix enclosed microbial assemblies that produce a glycocalyx or extra polymeric substance (EPS), that allows the biofilm to attach to a surface
(biological or non biological)
- more resistant to host defenses/immune system or antibiotic treatments
1d. Colonization
- biofilm
Bacterial Mechanisms of Pathogenicity
2a. _ _ _ _
- ability of the pathogen to spread to other locations (cells, tissue or system) in the host
- _ - bacteria in the bloodstream
- can quickly spread to locations throughout the host
- _ - massive systemic shock which can result in septic shock and death
2a. Invasion or Immune Evasion
- Bacteremia
- Septicemia
Bacterial Mechanisms of Pathogenicity
2b. Evasion of Host the Host Defense
MRM
- Modulation of cell surface structures
- Release of enzymes or proteins that inhibit host immunity
- Mimicry of host molecules
Bacterial Mechanisms of Pathogenicity
2c. _ _
- modulate their cell surfaces
- pathogen alters its surface antigens or display of new antigens to escape attack by antibodies and immune cells
- e.g. Streptococcus pneumonia
- there are _ different serotypes of S. pneumoniae- all differ in the structure of their capsular polysaccharides
- display of new antigens are not recognized by immune response formed in response to previous infection
2c. Antigenic Variation
- 84 different serotypes
Bacterial Mechanisms of Pathogenicity
2d. _
- used in adhesion but also aid in immune evasion by preventing ingestion by phagocytes
- Examples:
- N. meningitidis - its physical “cloak,” or polysaccharide capsule, helps protect the bacteria from many of the body’s defenses by hiding it from the immune system
- the capsule of certain strains of E. coli and that of N. meningitidis serotype B contains polysaccharides that are structurally similar to polysaccharide found on the surface of some mammalian cells (Molecular mimicry)
2d. Capsules
Bacterial Mechanisms of Pathogenicity
2e. _ _ _
- _ _ - resists phagocytosis
- Streptococcus pyogenes
- _ _ - waxy lipid, resists digestion
- Mycobacterium tuberculosis
2e. Cell Wall Components
- M protein
- Mycolic acid
Bacterial Mechanisms of Pathogenicity
2f. Enzymes
- _ - digest polysaccharides that holds the cell together
- _ - forms a fibrin shield around the bacteria
- _ - breaks down collagen, allowing bacteria to spread throughout the tissue
- - - hydrolyze beta lactam ring of penicillin and
cephalosporin, thus inactivating the antibiotic
Enzymes and toxins that harm eukaryotic cells
CCDEHHH ILLPPPS
- Hyaluronidase
- Coagulase
- Collagenase
- Beta-lactamase
- Coagulase, collagenase, Deoxyribonuclease, Elastase and alkaline protease, Hemolysins, Hyaluronidase, Hydrogen peroxide and ammonia, Immunoglobulin A protease, Lecithinase or phospholipase, Leukocidins, Porins, Protein A, Pyrogenic Exotoxin B, Streptokinase
Bacterial Mechanisms of Pathogenicity
3a. Damage to Host Cells/_ _
1. _ _ _ _ _ - can invade deeper tissues, causing direct damage
- can trigger immune response resulting to inflammation
2. _ _ _ - endotoxin and exotoxin
3a. Cytopathic effet
1. Direct damage to colonized area
2. Production of toxins
Bacterial Mechanisms of Pathogenicity
3b. _
- produced by some bacterial pathogens in the form of substances that are poisonous to the host
- produces fever, cardiovascular problems, diarrhea, shock
- two categories: _ and _
- _ - organism’s ability to make toxins
- _ - presence of toxins in the host’s blood
- _ _ (BoNT) - a potent neurotoxin
- produced by the bacterium Clostridium botulinum, which can cause the disease botulism
- _ _ - produced by Clostridium tetani, causes the disease tetanus, characterized by muscle spasms and rigidity
3b. Toxins
- two categories: Exotoxins and Endotoxins
- Toxigenicity
- Toxemia
- Botulinum Toxin
- Tetanus Toxin
Bacterial Mechanisms of Pathogenicity
3b. Toxins
- _ - proteins produced inside pathogenic bacteria
- most commonly from G+ bacteria
- secreted following lysis
- _ - lipid portions of LPS that are part of the outer membrane of the cell wall of G- bacteria
- released when the bacteria die and cell wall breaks apart
- Exotoxin
- Endotoxin
Bacterial Mechanisms of Pathogenicity
3b. Toxins
Exotoxins | Endotoxins
Bacterial Source
Relation to Microorganism
Chemistry
Fever producing
Immunology (Relation to antibodies)
Lethal dose
Representative disease
Bacterial Mechanisms of Pathogenicity
3b. Toxins
Exotoxins | Endotoxins
Bacterial Source - G+ | G-
Relation to Microorganism - metabolic product of growing cell | present in LPS of outer membrane of cell wall and released with the destruction of cells or during division
Chemistry - protein, usually with 2 parts (AB) | lipid portion (lipid A) of LPS of outer membrane LPS
Fever producing - No | Yes
Immunology (Relation to antibodies) - can be converted to toxoid to immunize against toxin; neutralize by antitoxin | Not easily neutralized by antitoxin therefore effective toxoids cannot be made to immunize against toxin
Lethal dose - small | considerably larger
Representative disease - gas gangrene, tetanus, botulinum, diptheria, scarlet fever | typhoid fever, UTIs, meningococcal meningitis
Bacterial Mechanisms of Pathogenicity
3b. Toxins
Functional Types of Exotoxins
- _ - affects cells (Diphtheria toxin)
- _ - affects GIT (Cholera toxin)
- _ - affects nervous system (Tetanus toxins)
- Cytotoxins
- Enterotoxins
- Neurotoxins
