Bacterial Infection & Antimicrobial Resistance Flashcards
What is the first barrier of host defence?
The skin
What does the number and variety of microorganisms depend on?
Moisture
pH
Temperature
Salinity
Chemical wastes (urea and fatty acids)
Presence of other microbes
What are the three regions where different skin microbiota live?
Sebaceous sites
Moist sites
Dry sites
What are the normal skin microbiota?
Staphylococcus
Micrococcus
Diphtheroids
Malassezia furfur
Which is the most common skin microbiota?
Staphylococcus
What is the most common skin microbiota infection?
Acne Vulgaris
Is acne chronic or acute inflammation?
Chronic inflammation
What causes acne?
Propionibacterium acnes
What are the characteristics required for bacterial pathogenesis?
Route of entry
Adhesion
Colonisation & Invasion
Virulence factors
Survival
How is the skin abscess formation caused by staphylococcus aureus?
Bacterial entry & Adherence
Bacterial proliferation & PMNs influx
Abscess & pus formation
What is the infection triangle for disease?
Susceptible host
Virulent Pathogen
Favorable Environment
What is the infection triangle for less disease?
Susceptible host
Virulent Pathogen
Unfavourable Environment
What are examples of a susceptible host?
Burned skin or no defence
What are examples of virulent pathogens?
S. aureus
Virulence factors
What are examples of favourable environment?
Damaged tissue
Abundant nutrients for pathogen
Exposed wound
Lack of preventive measures
What is the bacterial growth cycle?
Bacteria divide by binary fission
Bacterial growth byproducts due to fermentation are acid, gas & various metabolites
What are the bacteria doubling time range?
Between 20 minutes (fast-growing) to more than 24 hours (slow growing bacteria)
When do bacteria start growing more rapidly?
When they establish their niche
What are the different stages of the bacterial growth cycle?
Lag phase
Log phase
Decline growth phase
Endogenous respiration phase
What happens in the lag phase?
No cell division occurs while bacteria adapt to their new environment
In which phase is there an exponential growth of the population, human disease symptoms usually develop?
The log phase
What is the stationary phase?
Reproductive and death rates equalize
What happens during the decline phase?
Accumulation of waste products and scarcity of resources causes population to die
What are the functions of the bacterial capsule (glycocalyx)?
Adhering layer of polysaccharides
Protects cells from the environment and allows them to attach to surfaces
Inhibits phagocytosis by immune cells
What is a capsule?
A thick layer of glycocalyx
What is a slime layer?
A diffuse layer of polysaccharides
What are pili?
Protein fibers extending from the surface of many bacteria that are used for attachment
What is the function of conjugation pili?
Transfer genetic material between cells
What is the function of the flagella?
Provide motility
What does a prokaryotic flagella contain?
Helical filament, a hook and a basal body
What is the bacterial cell wall?
A tough and protective external shell
What is the function of the cell wall?
Protects the cell from injury
Maintains the cell shape and water balance
Providing attachment sites
Countering effects of osmotic pressure
Essential for cell division
Antigenic determinants
Resistance of antibiotics
What does a ruptured bacterial cell wall mean?
Cell death
What is the structure of gram-negative bacteria cell wall?
Lipopolysaccharides also called endotoxins
What is the structure of gram-positive bacteria cell wall?
Thick peptidoglycan layer
What part of the bacteria represents a selectively permeable barrier?
The cell membrane
Which part of the bilayer form a permeability barrier? Why?
The hydrophobic fatty acid chain because they are negatively charged
What are the functions of the membrane proteins?
Cell wall synthesis
Energy metabolism
DNA replication
Sensation of stimuli
Molecule transport, and active transport
Where do ribosomes exist?
In cell cytoplasm
What is the function of ribosomes?
Protein synthesis
How is bacterial DNA organised?
With the nucleoid
How does the DNA of chromosomes usually exist as?
Single, circular chromosomes
What is the structure of DNA with a nucleoid?
Highly compacted
What do plasmids carry?
Nonessential but often useful information
What are the bacterial cell shapes?
Cocci, bacilli, coco bacilli, spiral
What kind of tests help identify the genus and the species of bacteria?
Colony morphology, biochemical tests and serological tests
How do antibiotics kill bacteria?
Cell wall (peptidoglycan synthesis)
Protein synthesis
Membrane integrity
Nucleic acid synthesis
Metabolic pathways
Which components of the cells are affected by antibacterials?
Membrane
Ribosomes
Metabolic pathways
Which antibiotics affect the cell wall?
β-lactams:
Penicilins
Cephalosporins
Carbapenems
Monobactams
Bacitracin
Glycopeptides
Which antibiotics affect the protein synthesis?
30s inhibitors:
Aminoglycosides
Tetracyclines
Tigecycline
50s inhibitors:
Chloramphenicol
Clindamycin
Linezolid
Macrolides
Streptogramins
Which antibiotics affect the membrane integrity?
Polymixin B
Daptomycin
Which antibiotics affect the nucleic acid synthesis?
Fluroquinolones
Metronidazole
Rifamycins
Which antibiotics affect the metabolic pathways (folate)?
Sulfonamides
Trimethoprim
What are the antimicrobial resistance mechanisms?
Efflux pump
Blocked penetration
Inactivation of enzymes
Target modification
Which antibiotics are affected by efflux pumps in antimicrobial resistance?
Fluoroquinolones
Aminoglycosides
Tetracyclines
β-lactams
Macrolides
Which antibacterial are affected by blocked penetration?
β-lactams
tetracyclines
fluroquinolones
Which antibacterials are affected by the inactivation of enzymes?
β-lactams
aminoglycosides
macrolides
rifamycins
What do target modifications (mutation) affect?
fluoroquinolones
rifamycins
vancomycin
β-lactams
macrolides
aminoglycosides
Which organelles affected by target modifications?
Ribosomes & DNA
What is DNA gyrase?
Essential bacteria enzyme responsible for replication
How do fluoroquinolones affect the DNA gyrase?
They attach to it, blocking bacteria DNA replication leading to cell death.
How does antibiotic resistance occur?
Population of bacteria
Bacteria divide, and one cell undergoes a mutation
Cell with gene conferring resistance to antibiotic
Only resistance cell survives
Bacterium divides many times
What are the mechanisms of antibiotic resistance?
Intrinsic or acquired
Where does acquired resistance come from?
Genetic methods –> chromosomal methods or extra chromosomal methods
What are the chromosomal methods of antibiotic resistance?
Mutations
What are the extra chromosomal methods of antibiotic resistance?
Plasmids
How does antibiotic resistance happen from one bacteria to the rest?
Lots of germs, and only a few drug-resistant
Antibiotics kill bacteria causing the illness, as well as good bacteria protecting the body from infection.
The drug-resistant bacteria are allowed to grow and take over.
Some bacteria give their drug-resistance to other bacteria, causing more problems.
What kind of bacteria does an antibiotic kill?
Both bacteria that cause the disease and good bacteria that protect the organism
What are the mechanisms of antibiotic antibiotic resistance gene transfer?
Transformation
Transduction
Conjugation
What is antibiotic resistance gene transfer transformation?
Donor cell releases DNA including antibiotic-resistant genes to the recipient cell
What is the antibiotic resistance gene transfer transduction?
Phage-infected donor cell releases phage onto the recipient cell
What is a phage?
Small virus that affects bacteria
What is the antibiotic resistance gene transfer conjugation?
Transposon from the donor cell is transported to the recipient cell.
What are the three fundamental mechanisms of antimicrobial resistance?
Enzymatic degradation
Alteration of bacterial proteins
Changes membrane permeability to antibiotics
In which ways do bacteria produce enzymes that inactivate the antibiotics?
Inactivation of β-lactams
Inactivation of chloramphenicol
Inactivation of aminoglycosides
Which bacteria inactivate the β-lactams?
S. aureus, N. gonorrhoea, H. influenza
How do bacteria inactivate the β-lactams?
They produce β-lactamase which cleaves β-lactam ring
How is chloramphenicol inactivated?
By chloramphenicol acetyltransferase
Which kind of bacteria have a higher resistance to chloramphenicol and why?
Gram -ive because the enzyme chloramphenicol acetyltransferase is present
How are aminoglycosides inactivated?
Inactivated by acetyl, phospho, and adenylyl transferases which are present in both kinds of bacteria
Which antibiotic is altered in such a way that it binds to 50s r-RNA and prevents movement along m-RNA?
Erythromycin
How does altered tetracycline interfere with antibiotic targets?
Tetracycline interferes with the t-RNA anticodon reading of m-RNA
Which antibiotic is altered in such a way where it is responsible for the change of shape of 30s r-RNA and causes m-RNA to be read incorrectly?
Streptomycin
What is the function of the efflux pump?
It recognises the antibiotic and kicks it out.
In the disc diffusion method what is measured?
Zone of inhibition in mm
How is bacterial sensitivity categorised in the disc diffusion method?
Sensitive, Intermediate and Resistant
It depends on the diameter of the zone of inhibition, the greater the zone the more effective the antibiotic
What does the e-testing method determine?
The minimum inhibitory concentration in μg/ml
What does a low MIC indicate?
The antibiotic is working and a lower dose is required to reach the target effect.
Which are the ESKAPE pathogens?
E: enterococci
S: staphylococcus aureus
K: klebsiella
A: acinetobacter
P: pseudomonas aeruginosa
E:enterobacter
What are ESAKPE pathogens?
They are the pathogens that carry and spread the antibiotic resistance
What might cause antibiotic resistance?
Over-prescription
Misuse of antibiotics
Antibiotics used in agriculture
Poor infection control
Poor hygiene
Lack of rapid lab tests
