Microbiological virulence factors Flashcards
What are the classical characteristics of viruses?
Obligate intracellular parasites
Smaller, DNA or RNA
Metabolically inert
Use host cell synthetic machinery
What are the classical characteristics of bacteria?
Unicellular
Prokaryotic- nucleus not organised, double stranded circular DNA in cytoplasm
Rigid peptidoglycan cell wall
Binary fission
What are the classical features of fungi?
Eukaryotic
Rigid cell wall
Sexual and asexual replication
Unicellular yeast like or filamentous conidia/spore bearing forms
What are the classical features of parasites?
Eukaryotic
Unicellular protozoa or multicellular helminths
Many with intermediate hosts in complex life cycle
What is the cytoplasmic membrane of bacteria made of?
Proteins and phospholipids
What does the cytoplasmic membrane of bacteria not contain?
Sterols (only found in eukaryotes)
What is the function of the bacterial cell membrane?
Synthesise and export cell wall components
Respiration
Secretion of extracellular enzymes and toxins
Uptake of nutrients by active transport mechanisms
What is the function of bacterial cell wall?
Protective- rigid so can withstand osmotic and mechanical stress + provides barrier against certain toxic chemical and biological agents
Gives shape to the bacterium
Firm base for pili, fimbriae and flagella
Contains antigens- important in virulence and in host antibody production
What are the 2 different types of bacterial cell wall?
Gram positive
Gram negative
What are gram positive cell walls like?
2 layers
Peptidoglycan and teichoic acids
Inner plasma membrane and outer thick peptidoglycan layer
What are Gram negative cell walls like?
3 layers
Thin peptidoglycan layer
Outer plasma membrane containing lipopolysaccharide (LPS) and outer membrane proteins (OMP)
What is the bacterial capsule?
Mucoid polysaccharide layer
Consists of polymerised d-glutamic acid
What is the function of the bacterial capsule?
Anti-phagocytic activity anf prevents attack by complement
Adhesion
What is the capsule used for?
Laboratory diagnostic tests and used in vaccines
What are 2 of the main types of pili and what do they do?
Sex pili- transfer DNA by conjugation
Common pili- for attachment
What is the function of pili?
They are important in adhesion and anti-phagocytic activity
What is the function of flagella?
Motility
Give example of intracellular structures in bacteria?
Nucleoid
Ribosomes
Inclusion granules
Endospores
What are the basic requirements for bacteria in terms of nutrition?
Basic requirements- carbon, nitrogen, water and a source of energy
How is the fact that some bacteria require specific gases and growth factors used diagnostically?
Media can be developed for selective isolation and identification of particular bacteria
What are the classifying features of bacteria?
Shape- round, long, curved, pairs, clusters, chains etc Atmospheric requirement- requires oxygen, increased co2 and oxygen toxic Spore production (dangerous feature)
What are the main bacteria identification tests?
Enzyme production- Testing to see whether they produce certain enzymes such as: Urease Catalase Coagulase Oxidase
Toxin production:
Protein synthesis inhibitors
Haemolysins
Superantigens
What are the components of the Gram stain?
Stain 1= Methyl violet and lugol’s iodine (violet-blue)
Stain 2= Methyl red (pale pink-red)
What component of the Gram stain does both Gram positive and Gram negative bacteria take?
Gram positive- Stain 1 (violet blue)
Gram negative- Stain 2 (pale pink red)
How are Gram positive first classified?
Based on shape- rods or cocci
What are Gram positive bacteria differentiated based on after their shape?
How they aggregate and other biochemical test results
How do staphylococcus aggregate and how do they respond to catalase test?
In clusters (grapes) Catalase positive
How do streptococcus aggregate and how do they respond to catalase test?
In pairs/chains
Catalse negative
How are staphylococci differentiated?
Based on coagulase test
Positive- s.aureus
Negative- s.epidermidis and s.saprophyticus and others
What are streptococci differentiated based on?
Extent of haemolysis that they cause:
Alpha haemolytic- (must be further differentiated using optochin- toxic chemical)
Optochin sensitive- s.pneumoniae
Optochin resistant- viridans group
Beta haemolytic-
Group A- s. pyogenes
Group B- s.agalactiae
Group D- enterococci
Non-haemolytic
Streptococcus milleri
Anaerobic streptococci
What types of infection are caused by staphylococci?
Staphylococcus aureus- severe infection e.g. skin/soft tissue, endocarditis and osteomyelitis
Coagulase negative staphylococci- Skin commensals of low pathogenic potential and can infect prosthetic material causing line, pacemaker infections and endocarditis
What type of infection do group B strep tend to be associated with?
Neonatal infection because 1/3 of healthy women carry B strep in genital tracts and can be transferred to baby during delivery
What are the two groups of spore forming bacteria?
Bacillus sp.- bacillus cereus and bacillus anthracis
Clostridia sp.- clostridium perfringens, clostridium tetani, clostridium botulinum and clostridium difficile
What do endospores contain?
Bacterial DNA, cytoplasm, plasma membrane, peptidoglycan, little water, dipicolinic acid and keratin like coat
When are endospores formed?
In response to adverse environmental conditions
What are endospores resistant to?
Chemical inactivation
What is the function of endospores?
Protective- Survive drying, heat, dehydration and radiation
What is anthrax used as?
Chemical weapon
How is anthrax treated?
Ciprofloxacin
What is Hide Porter’s disease?
Cutaneous anthrax carried in contaminated animal hides, an occupational disease
Characterised by black eschars, oedema and swelling
What does the periplasm of gram-negative bacteria contain?
Enzymes with hydrolytic function
Enzymes that inactivate antibiotics
Oligosaccharides
What is haemophillus influenzae?
Gram negative cocco bacilli found in the nasal cavity that doesn’t cause much of a problem as most people are vaccinated
What does Gram negative outermembrane contain?
Phospholipids Lipopolysaccharide (LPS)
What is important about lipopolysaccharide?
It is toxic to humans and can cause fever and shock (endotoxin shock)
What does LPS consist of?
Lipid A (toxic component of endotoxin) Core polysaccharide O antigen (major surface antigen of Gram-negative cells)
How are a lot of gram negative bacteria differentiated?
Using another test- oxidase Oxidase negative- Coliforms e.g. E.coli, Klebsiella spp, Enterobacter spp, Seratia spp. Proteus spp. Oxidase positive- Pseudomonas spp.
