Infectious Disease and Pathogenicity Flashcards
Cocci bacteria
Round and spherical
Bacilli
Rod shaped
Monococcus
Single round cell
Diplococcus
Paired cells
Staphylococcus
Grouped cells
Streptococcus
Chained cells
Bacteria cell components
Cell Wall Flagella Pilli/fimbriae Nucleoid Plasmids Cytoplasm Ribosomes Endospore Capsule
What is an endopsore?
Small, highly resistant, thick-walled, “resting” cells
Produced in response to environmental stressors
Formed when bacteria stops growing as environment cant support its growth
What are inclusion bodies?
Form in cytoplasm
Can be fat/iron/proteins
Protein aggregates
Site of viral multiplication
Gram negative bacteria
Outer and inner membrane
Thin layer of peptidoglycan
Gram positive bacteria
No outer membrane
Thick layer of peptidoglycan
What separates the outer and inner membrane in gram negative bacteria?
Periplasm
Smaller one in gram positive
Function of periplasmic space
Protein oxidation Folding Thin layer of peptidoglycan Quality control Contains enzymes involved in cell's metabolism
When are resistant spores formed?
In adverse conditions
Environmental stress e.g lack of nutrients, bad pH
Why do bacteria produce spores?
To produce a dormant and highly resistant cell to preserve the cell’s genetic material in times of extreme stress
The spores are resistant to UV/radiation/Biocides/ Gamma radiation
Layers of spore (innermost to outermost)
Core Inner membrane Germ cell wall Cortex Outer membrane Coat Exosporum
Function of exosporum?
adherence and biocide protection
Sequence of treatment
- Observance of patient- symptoms
- Sampling
- Laboratory observation and culture
- Identification tests
- Treatment e.g antibiotics
- Observation of population
- Preventing transmission
Definition of disease
A disturbance in the state of health wherin the body cannot carry out all its normal functions
Infectious disease definition
Infection caused by pathogenic micro-organisms
Infection definition
Invasion and multiplication of a pathogenic microbe within or on a host
Contamination
Presence of microbes in a location/environment
What is koch’s postulates?
4 criteria to establish a causative relationship between a microbe and disease
What are the 4 criterias of koch’s postulates?
- The specific causing agent must be seen in every disease
- The agent must be isolated from a diseased host and grown in pure culture
- The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
- The agent must be re-isolated from the diseased host and identified as identical to the specific disease causing agent
What diseases does koch’s postulates work for?
Plague
Anthrax
Cholera
Typhoid
When is koch’s postulates less evident in?
Condition is chronic
Condition has multiple causes
Conditions where pathogen can’t be grown outside of body (in-vitro)
No suitable animal model of infection
What conditions would koch’s postulates be less evident for?
Pneumonia
Wound infections
Septicaemia
Urinary Tract infections
What is normal flora?
Micro-organisms present on body surfaces covered by epithelial cells and are exposed to the external environment
Where in the body is normal flora found?
Gastrointestinal tract
Respiratory Tract
Genitourinary tract
Normal flora and host cell
They live in benign symbiosis with one another
Examples of normal flora
E.coli found in the intestines
Staphylococcus aureus in nostrils
Why can’t normal flora cause disease even if they are pathogenic?
They lack attachment to a suitable surface
When does normal flora become pathogenic?
When environment changes e.g environmental stress, hormonal levels, stress, climatic
e.g MRSA
6 stages of disease progression
1 and 2- transmission and exposure to disease
3 and 4- Adherence and invasion
5 and 6- Colonisation and Tissue Damage
What does successful exposure and transmission depend on?
Number of microbes- the more the better
Airborne- size, density, surface features
Waterborne- density, surface features, hydrophobicity
Contact- resistance to dessication, spore formation, adhesion
Vectors
Fomites
Distribution on host: into cuts , digestive system, genitourinary system, lungs
What does adherence and invasion depend on?
Adherence depends on host’s and microbe’s features
Invasion depends on breaking i surface layers or acitve procedures from microbe
Chemotaxis and motility Attachment via pilli/non-fimbrial adhesions
Penetrations of epithelia/cells via proteases
Anti-phagocytic capsules may allow survival stopping phagocyte entering microbe
Virulent bacteria can inject epithelium cells with molecules to change features of surface
What does colonisation and tissue damage depend on?
Growth of bacteria in host means host’s responses are avoided
Growth of microbe in host requires nutrients
There is limited nutrient availability in the host cell
Tissue damage caused by accumulation of toxins released by microbe
What defences does the host cell have?
- Physical barriers (e.g sebum on skin)
- Cellular defences (phagocytes, killer cells)
- Inflammation
- Complement System
- Immunity
What is the result of bacteria prolonging an immune response?
Chronic infection
3 characteristics of a pathogen
- Virulence
- Pathogenicity
- Virulence/Pathogenicity factor
Pathogenicity
Ability of a pathogen to produce an infectious disease in an organism
Virulence
Relative degree of damage caused by pathogen/ degree of pathogenicity of a pathogen
Virulence/Pathogenicity Factor
Microbial product/strategy that causes virulence/pathogenicity
Molecular determinants of pathogenicity
- Attachment to host tissues
- Production and delivery of various factors
- Replication and evasion of immunity
- Damage to host tissues
How do bacteria adhere to host?
Bacteria employ proteins such as adhesins which are normally found on ends of fimbriae/pilli
Adhesins can consist of glycocalyx
What do bacteria use to penetrate host?
Enzymes (proteases)
Capsules
Cell wall components
How do bacteria damage host cells?
Direct damage Endotoxins Exotoxins Toxins Hypersensitivity reactions (allergies)
What do pilli/fimbriae attach to on host cell?
Host cell glycoprotein receptors
Role of capsules in bacteria?
Prevent phagocytes attaching
Preventing phagocytosis
e.g streptococcus pneumoniae
What enzyme is released by bacteria to get into host cell?
Proteases
A few enzymes released by bacteria that harm eukaryotic cells
Coagulase
Collagenase
Haemolysins
Leukocydins
Which bacteria releases haemolysins?
Alpha haemolytic streptococci
Beta haemolytic streptococci
Difference between alpha and beta haemolytic streptococci?
Alpha- haemolysins released cause incomplete lysis of RBCs
Beta- haemolysins released cause complete lysis of RBCs
Which bacteria produces coagulase?
Staphylococcus aureus
Action of coagulase?
Causes blood to coagulate (clot)
Blood clot prevents phagocytes phagocytosing bacteria
Fibrinogen converted to fibrin= clot
What bacteria produces collagenase?
Clostridium perfringens
Action of collagenase?
Breaks down collagen in muscle tissue
Allowing bacteria to spread through muscle tissue
Action of leukocidins?
Pore forming exotoxins that kill leukocytes
Cause degranulation of lysosomes within leukocytes
Decreases host resistance
2 types of toxins released by bacteria
Endotoxins
Exotoxins
What bacteria are exotoxins mainly produced in?
Gram positive bacteria
How do exotoxins work?
Secreted by bacteria cell into surrounding medium
Mainly by gram positive bacteria
What are endotoxins part of?
Part of outer portion of cell wall in gram negative bacteria
How do endotoxins work?
Once bacteria dies and cell wall is broken down endotoxins are released
