INF1 - E. BACTERIA AND PATHOGENICITY-COVERED Flashcards
what are prokaryotes
- no defined nucleus
- smaller (<1-2 microns)
- bacteria
what are eukaryotes
- defined nucleus a
- bigger (10-100+ microns)
- animals, plants, fungi, protozoa, algae
what is unique to bacterial cells compared to ours
peptidoglycan cell wall
what is peptidoglycan made of
- N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) pentapeptide (glycan monomer)
- D-alanine in postions 4 and 5
- additional pentaglycine sequence in some gram-+ve bacteria - attached to lysine at position 3
- glycan monomers transported across cytoplasmic by bacteoprenol
- monomers joined through glycosidic bonds by glycerotransferases to make polymer chains
- polymer chains cross linked through peptide bonds between third positions on one polymer and D-alanine of another chain by transpeptidases
describe the gram-positive cell wall
- 80-90% peptidoglycan
- gram stain dyes cell blue/purple
- teichoic acid embedded in wall which facilitates movement in to and out of bacterium (can stimulate inflammatory response)
- proteins embedded in the wall: adhesins help with adhesion to host cells and surfaces
- enzymes aid nutrient acquisition and can damage host cells and tissue
- permeable to most antibiotics some species sporulate (bacilli)
examples of gram-positive bacteria
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Clostridium difficile
describe the gram-negative wall
- 10-20% peptidoglycan
- gram dye stains cell pink
- has an outer membrane which is linked to peptidoglycan by lipoprotein anchor
- rich in lipopolysaccharide (endotoxin) which allows entry of molecules into cell (can stimulate strong inflammatory response)
- proteins like enzymes and adhesions
- impermeable to many antibiotics
- no sporulating bacteria
examples of gram-negative bacteria
- Escherichia coli
- Salmonella enterica
- Campylobacter jejuni
- Vibrio cholera
- Heliobacter pylori
- Chlamydia trachomatis
what does lipopolysaccharide consist of
lipid A
core region oligosaccharide and other molecules
O-polysaccharide tail (O antigen)
describe the acid-fast cell wall (mycobacterium tuberculosis)
- mostly made of mycolic acid (glycolipid) - Ziel-Neelson stain (red)
- small amount of peptidoglycan
- mycolic acids impede entry of molecules so slow growing bacteria but greater resistance to chemical agents and enzymes
- this is why you need antibiotics for months due to hard access across cell wall
differences between prokaryotic and eukaryotic cells
- fimbriae and pili in prokaryotic cells
- capsules and slime layers in some bacteria
(form biofilms: collection of micro-organisms surrounded by the slime they secrete and attached to an inert or living surface and hence antimicrobials can’t penetrate) - flagella in some bacteria
what are endospores
- formed by some gram+ve bacteria due to ‘starvation’ or adverse environment, can cause infection
- exist in state of dormancy, can persist for long periods
- highly resistant to extreme of temp, pH, desiccation, radiation, chemical agents (ie - antibiotics, disinfectants)
what is the microbiome
- bacteria in/on our body which don’t cause damage and can be beneficial or protective
- unique in everyone
- low virulence bacteria ie, low risk of causing disease
- reduce risk of colonisation by pathogenic bacteria
- disrupted by overuse/inappropriate use of antibiotics (we need antibiotic stewardship)
what is an infection
- any microorganism or toxin (ie produced by bacteria and contaminating foodstuff) capable of entering human body and causing harm
- via initial interaction/invasion of epithelial tissue (skin, eye, internal mucosa of airways, gut, genitourinary)
what is bacteraemia
presence of bacteria in blood
what is sepsis
systemic infection
host immune response to bacteria wall (LPS/teichoic acid)
what is a disease
recognisable systems/illness often with defined damage of injury to host tissues
what is pathogenicity
ability to cause disease
what are pathogenicity/virulence factors
features that enable attachment, colonisation, tissue invasion, production of toxins or enzymes etc
examples of pathogenicity factors
Enzymes
Adherence - pili/fimbriae, M protein, lipoteichoic acids
Toxins - exotoxins and endotoxins (released by damaged bacteria)
Resistance to antibiotics - prevent entry, degradation, modification/increased expression, efflux
Invasion of sterile body sites - invasions, enzymes, toxins or opportunistic wounds
Circulation - systemic infection, spread through host
Evasion of immune responses - capsule, enzymes, toxins
what is virulence
measure of ability to cause disease
what is infectiousness
ease of spread in a population, linked to pathogenicity and virulence
what is intoxication/food poisoning
ingestion of bacterial-derived toxin or in absence of infection (toxin contaminating food)
what do bacteria need apart from ability to cause infection
opportunity
- can minimise this by hygiene, social distancing, wound care, PPE etc
