INFECTIOUS AGENTS - Bacteria Flashcards
What are the two most common bacterial morphologies seen in veterinary practice?
Cocci (spherical)
Bacilli (rod)
List the general structures that make up bacteria
Capsule
Cell wall
Cytoplasmic membrane
Cytoplasm
Flagella
Fimbriae/Pili
Chromosome
Ribosomes
Inclusion bodies
Plasmids
Not all bacteria have all of these structures
What is the structural difference between prokaryotic and eukaryotic ribosomes? What are the benefits of this structural difference to antibiotic targeting?
The difference in ribosome size allows antibiotic targeting of the prokaryotic ribosome without damaging eukaryotic ribosomes
What is the term used to describe bacteria that has been prevented from further growth?
‘Bacteria static’
What are the functions of bacteria capsules?
Protective outer surface of the bacterial cell
Anti-phagocytic
Hydrated to prevent dessication of the bacterial cell during transmission
Which component normally makes up bacterial capsules?
Acidic polysaccharides
Which species of bacteria has a capsule that is not made up of acidic polysaccharides?
B. anthracis (Anthrax) capsules are made up of poly D-glutamic acid
What are the functions of the bacterial cytoplasmic membrane?
Site of electron transport and oxidative phosphorylation
Synthesis of macromolecules
Sensitive to environmental changes allowing the induction of mitosis
What is the function of the bacterial cell wall?
Provides strength and rigidity to the bacterial cell
Protects the bacterial cell from osmotic lysis
What is the structure within the bacterial cell wall which provides the bacteria with strength and rigidity?
Peptidoglycan
(T/F) Free peptidoglycan in the bloodstream can cause shock
TRUE
Describe the structure of the bacterial chromosome
Usually a closed circle of double stranded DNA
What it the function of bacterial plasmids?
Bacterial plasmids often carry antibiotic resistance genes
Which protein makes up flagella?
The globular protein flagellin
How do flagella provide bacterial cells with motility?
Flagella are attached to the bacterial cell by a motor unit which carries out a rotating motion due to energy provided by an ion concentration gradient across the bacterial cytoplasmic membrane
What are the four terms used to describe bacterial flagella arrangement?
Monotrichous: single flagellum on one side of the bacterial cell
Ampitrichous: one or more flagella at each end of the bacterial cell
Lophotrichous: two or more flagella on each side of the bacterial cell
Petritrichous: flagella surrounding the bacterial cell
What is the function of fimbriae present on bacterial cells?
Fimbriae allow specific adhesion of bacterial cells to eukaryotic cells due to the presence of lectins on the fimbriae which bind to specific carbohydrate residues present on eukaryotic cell surfaces
(T/F) Fimbriae expression is not affected by environmental conditions
FALSE. Fimbriae are only expressed when in the body of an animal
What is the function of bacterial pili and how does this function aid bacterial virulence?
Pili are adapted fimbriae involved in conjugation (the swapping of genes or plasmids between Gram negative bacteria). Conjugation allows for the swapping of antibiotic resilience genes - contributing to bacterial virulence
What are bacterial endospores and why are they produced?
Endospores form within the bacterial cells in response to unfavourable survival conditions for the bacteria. These spores contain the bacterial DNA and are released from the cell when the bacteria are eventually lysed
Endospores are very difficult to kill
What can be used to kill endospores?
Autoclave
Why is Gram staining of bacteria so important?
Gram staining identifies Gram positive and Gram negative bacteria. This is important as Gram positive and Gram negative bacteria have different structures and thus different susceptibilities to antibiotics
What colour do Gram positive bacteria stain in a Gram stain?
Purple
What colour do Gram negative bacteria stain in a Gram stain?
Red
What are the differences between the structure of Gram positive and Gram negative bacterial cell walls?
GRAM POSITIVE: Thick peptidoglycan layer with the presence of teichoic and lipoteichoic acids
GRAM NEGATIVE: Thin peptidoglycan layer with an outer membrane external to the peptidoglycan layer
What makes up the outer membrane of Gram negative bacteria cell walls?
Lipopolysaccharides (LPS)
What is the function of the outer membrane of Gram negative bacteria cell walls?
The outer membrane acts as a barrier to antibiotics and other penetrating agents through the use of the lipopolysaccharides (LPS)
Which structural component of Gram negative bacteria causes septic shock if it gets into the bloodstream?
Lipid A (component of the lipopolysaccharides)
How do acid fast bacteria differ from most bacteria?
Resists decolourisation during Gram staining so instead harsher staining methods have to be used
What type of bacteria are mycobacteria?
Mycobacteria are acid fast bacteria
Why are mycobacteria such a significant public health concern?
Mycobacteria cause the zoonotic disease tuberculosis (TB)
How are mycoplasma bacteria resistant to beta-lactam antibiotics?
Mycoplasmas bacteria are resistant to beta-lactam antibiotics due to having no peptidoglycan in their cell wall
How does chlamydia differ from other bacteria?
Chlamydia bacteria are obligate intracellular pathogens (i.e. cannot grow outside of eukaryotic cells). This is due to their inability to produce their own ATP so have to take ATP from the host eukaryotic cell
Describe the two stage lifecycle of chlamydia bacteria
- The infectious form of chlamydia bacteria, known as the elementary bodies, exit the host cell and bind to other cell membranes. These elementary bodies are internalised by the cell into a vacuole where they replicate and become a reticular body
- These reticular bodies are the replicating form of the chlamydia bacteria which eventually break back down into elementary bodies, lyse the vacuole and eventually lyse the host cell, exiting the cell to repeat the life cycle again
Which stage of the chlamydia bacteria lifecycle directly contributes to the bacterial pathology?
The lysing of the host cell by the elementary bodies causes inflammation, directly contributing to the bacterial pathology
(T/F) Bacterial growth is the increase in the size of each individual bacterium
FALSE. Bacterial growth is the increase in the number of cells, not the size of each individual bacterium
Describe briefly how bacteria replicate
Bacteria replicate by binary fission, producing two identical daughter cells. These daughter cells may or may not separate after replication
Give two examples of bacteria which don’t separate after replication
Streptococci
Staphylococci
Describe the ways in which bacterial growth can be measured in liquid and/or solid media
- Turbidity: the absorbance of light or light scatter through the use of a spectrophotometer or nephelometer (fluid becomes more cloudy as the bacteria grow)
- Count particles: count bacteria under the microscope or through the use of an electronic particle counter
- Viable counts: bacteria grown in broth and then transferred onto solid media
What does ‘generation time’ mean in terms of bacterial growth?
The time taken for the bacterial population to divide and double
Describe the stages of a bacterial growth curve
Lag phase: time where the bacteria are adjusting to their environment
Log phase: exponential growth of bacteria
Stationary phase: nutrient depletion causing the rate of bacterial growth to be balanced out by the rate of bacterial death
What is the optimal temperature for the growth of pathogenic bacteria?
Most pathogenic bacteria are mesophiles meaning they have an optimal growth temperature of approximately 37°C
What is the optimal pH for the growth of pathogenic bacteria?
Most pathogenic bacteria are neutrophiles meaning they have an optimal growth pH of approximately 7
What is an obligate aerobe in terms of pathogenic bacteria?
Obligate aerobe’s can only grow in the presence of O2
What is a facultative anaerobe in terms of pathogenic bacteria?
Facultative anaerobe’s can grow with or without O2
What is a microaerophile in terms of pathogenic bacteria?
Microaerophile’s prefer less O2 and more CO2 to grow
What is an obligated anaerobe in terms of pathogenic bacteria?
Obligated anaerobe’s can only grow without the presence of O2 (O2 is toxic to these bacteria)
How does the optimal growth temperature and pH for many fungi differ from that of bacteria?
Both the optimal growth temperature and pH for fungi are much lower
Most pathogenic bacteria and fungi are chemoheterotrophs. What does this mean?
Microbes which use organic chemical substances as sources of energy
What is the purpose of streaking clinical samples across an agar plate?
Clinical samples are streaked across the agar plate to dilute the bacteria in order to grow individual colonies to allow identification of the bacteria
Why is enrichment media often used when growing bacteria on agar plates?
Many bacteria require complex substances in order to grow
Give three examples of enrichment media
Blood agar
Serum agar
Chocolate agar (heated blood)
Agar can be selective and differential. Describe what this means
Selective: contains substances which allow certain types of bacteria to grow, and inhibit the growth of other bacteria
Differential: contains substances used to differentiate closely related bacteria or groups of bacteria
Which group of bacteria is MacConkey agar used to cultivate?
Enteric bacteria
How is MacConkey agar selective and differential to enteric bacteria?
Selective: contains bile salts which inhibit the growth of non-enteric bacteria
Differential: contains lactose and neutral red indicator so bacteria which metabolise lactose produce acid and stain pink
How does the cultivation of fungi differ from the cultivation of bacteria?
More complex enrichment agar is required (often keratin)
More acidic agar required
What is the name of the agar used to cultivate fungi?
Sabourauds agar or Dextrose and peptone agar
Define sterilisation
Sterilisation is the killing or removal of all living organisms in or on a substance or object
Define disinfection
Disinfection is the killing of most microorganisms on a substance or object (kill enough to not cause disease)
Define sterile technique
Sterile techniques are procedures carried out in the absence of living things
Define aseptic technique
Aseptic techniques are procedures performed in a way to prevent contamination with infective microorganisms
What are the four main methods of sterilisation?
Irradiation (radiation)
Heat (dry and moist heat)
Filtration
Chemicals
What should ionising radiation (irradiation) be used to sterilise?
Disposable plastics and surgical materials
What would be an example of dry heat sterilisation?
Hot air oven
What should a hot air oven be used to sterilise?
Glassware
What would be an example of moist heat sterilisation?
Autoclave
List six factors which affect disinfection
Period of exposure
Concentration
Temperature
pH
Organic matter
Number of bacteria present
