Microbiology Flashcards
What are the three most common shapes of bacteria
cocci, bacili, and spiral
What are examples of cocci bacteria
staphylococcus (clump) and streptococcus (chain)
What are bacillus bacteria
rod shaped bacteria
What are fusiform bacteria
long slender rods
what type of bacteria is a curved rod
gram-negative pathogens such as vibrio cholerae
What are spores
single-celled reproductive units often produced by fungi, bacteria algae etc (inert structures resistant to physical and chemical challenge
what distinguishes gram -ve from gram +ve
their cell wall (-ve has a thin peptidoglycan layer with an outer membrane containing LPS and +ve has a thick peptidoglycan layer with no outer layer )
What colour does gram -ve stain
pink because it’s thin wall does not retain the stain/dye
Gram +ve stains pink, true or false?
false, it stains purple because it’s thin wall can retain the stain/dye
What are examples of gram-negative bacteria?
E.coli and salmonella
What is selective media?
The presence of one substance permits the growth of one colony over another
Give an example of selective media
mannitol sugar agar - salts allow preferential isolation of staphylococci
salmonella shigella - bile salts inhibit growth of coliforms
What is differential media?
media that selects for the growth of specific prokaryotes - clearly distinguishable colonies
what are examples of differential media
McConkay agar selects for gram -ve and inhibits gram +ve) and eosin methylene blue (allows for lactose fermenters such as e.coli)
Which bacteria is involved in hemolysis
streptococci
what is hemolysis
breakdown of RBCs causing the release of haemoglobin
What are the different types of hemolysis and examples of bacteria that perform this?
alpha - partial breakdown of RBCs, the colonies stain green (streptococcus pneumonia)
beta - full breakdown and release of haem in the RBCs so the colonies appear clear (streptococcus pyogenes) these are more virulent
gamma - no hemolysis occurs (enterococcus)
what antibody activity can you test in vitro
agglutination (have antibodies attached to a latex bead)
What DNA technology is useful in sequencing the genetic material of bacteria/viruses?
qPCR
What is MALDI-TOF
a type of mass spectrometry used to identify molecules/proteins based on their mass-charge ratio
What is a pathogen
harmful organism that produces pathology
What is meant by commensal/symbiosis
an organism part of the natural flora that has a mutualistic relationship
What is an opportunistic pathogen
one that causes infection upon opportunity such as immunocompromised individual
Give examples of protozoan derived diseases?
malaria and toxoplasma
give examples of fungal infections
aspergillus (moulds)
Give two examples of gram-negative cocci
Neisseria meningitis and gonorrhoeae
What are the three groups of enterobacteriaceae
ferment lactose rapidly, variable or slow lactose fermentation and another group that the majority do not ferment lactose
What are coliforms
gram-negative rod-shaped bacteria
what is the first-line antibiotic for coliforms (gram-negative) ?
gentamicin
what endotoxin causes sepsis from coliform infection?
LPS
What is sepsis?
host response to severe infection mediated by LPS /endotoxin from a bacteria
What is fever?
increase of the body temperature above 38 degrees
What are the four groups of gram-positive pathogens
streptococcus
enterococcus
staphylococcus
clostridia
What is the most common bacteria to cause UTIs
enterococci
Which gram-positive bacteria has spores central to its spread and ability to avoid antimicrobials?
clostridioles
Why are spores resistant to antibiotics
antibiotics generally need a cell to be metabolically active and spores are not
what is a facultative anaerobe
a bacteria that can switch between anaerobic and aerobic respiration
What are the two broad classes of antibiotics
beta-lactams and glycopeptides
What is the difference between bacteriostatic and bactericidal
bactericidal kills the bacteria and the former just inhibits the growth
What are 5 ideal factors of an antibiotic
minimal toxicity to the host (no adverse side effects)
kills the bacteria
oral administration
long half-life (not having to give multiple times throughout the day etc)
appropriate tissue distribution (pro drug)
what are beta-lactams
group of antibiotics that are analogues to d-ala-d-ala and bind to the penicillin-binding protein active site, therefore targeting the bacterial cell wall
what are the two main groups of beta-lactams
penicillins and cephalosporins
what do beta-lactams do
impairs the cell division by binding to the penicillin-binding protein
What are the limitations of penicillins?
rapid excretion by the kidney
patients often allergic
resistance
What is a good broad antibiotic for primary care?
amoxicillin
How does beta lactam based resistance develop?
the production of beta lactamases by bacteria can degrade the drug
what is co-amoxiclav a combination of?
amoxicillin and clavulanic acid (a beta-lactamase inhibitor)
What is flucloxacillin?
this has had the structure altered so that beta lactamase cannot degrade it so allows it to persist and is useful for streptococci and staphylococci and replaced methicillin
works on gram positive
what is temocillin used for?
gram-negative organisms and used in IV in secondary care
What are cephalosporins?
broad-spectrum antibiotics that significantly affect the gut flora
Which of these is not an advantage of cephalosporins?
A broad spectrum
B reduced hypersensitivity
C a variety of spectrums and targets
D excreted rapidly in the urine
D
What are glycoproteins?
restricted to gram-positive because of the size of the cell wall in gram-negative - this binds to the d-alanine d-alanine (the substrate itself) preventing the cross-linking
important for resistant staph aureus
what are two examples of glycoproteins drugs?
vancomycin and teicoplanin
Name the three groups of protein synthesis inhibitors
aminoglycosides
tetracyclines
macrolides
What are the 6 components of a cell that serve as antibiotic targets
cell wall
ribosomes
DNA replication
DNA gyrases
metabolic pathways
cell membrane
What are aminoglycosides?
bacteriocidal
usually long half life
What is an example of an aminoglycoside?
gentamycin
What are the properties of gentamycin?
Must be given IV
inhibits protein synthesis by irreversible binding and kills the bacteria
mainly gram-negative aerobic organisms
side effects include damage to the kidney - must be monitored
What are tetracyclines?
bacteriostatic
broad spectrum
GI flora risk
What are macroslides?
bacteriostatic
intracellular pathogens
Often used in cases of penicillin allergy
very safe as has in increased rate of absorption
What is an example of a macroslide?
erythromycin
What is trimeprothim?
antibiotic that targets nucleic acids, primarily used in UTIs
Name the three types of antibiotics that target nucleic acids
Fluoroquinolones
metronidazole
trimeprothim
What are quinolones?
bind to the A subunit of DNA gyrase preventing replication
What is an example of quinolones?
ciprofloxacin - broad spectrum IV and oral
Which antibiotics are used for C.difficile
quinolones/ciprofloxacin
What does metronidazole target?
anaerobes (and parasites/protozoa)
What antibiotics target folic acid synthesis?
trimeprothim and sulphonamides
what is meant by empiric prescribing?
uncertainty of what is causing the infection so one prescribes what is most likely to have a positive effect without damaging the host
What is natural resistance?
the microorganism is more resistant to the the mode of action of the antibiotic
What are the four different ways of natural resistance?
target not present
target not accessible
developmental structure/state
metabolism
What is a biofilm?
A structured community of microbes that adhere to surfaces making them more resistant to environmental stress
What are persistor cells?
dormant non growing cells that downregulate their metabolism to tolerate antimicrobials
What is clinical resistance?
the tolerance gained by bacteria upon continual exposure to an antimicrobial/antibiotic
What causes clinical resistance?
mutation or gene transfer
How does resistance provide a selective advantage?
They are able to persist despite mechanisms to limit their survival so can go on to reproduce etc
What factors create resistance?
variation (HGT eg) and the selective pressure (antibiotic)
What are the three methods of horizontal gene transfer?
natural competence
bacteriophage (viruses or phages transfer bacterial DNA between cells)
bacteria conjugation (sex pili)
What bacterial infection engages in bacteriophage HGT
MRSA
Where is HGT most common and why?
in the gut because bacterial cells are present in close proximity
What are the mechanisms of AMR
altered permeability (changes to the outer membrane, reduced OmpF) and inactivation (beta-lactamases) and altered target site
Give three types of b lactamases
penicillinase
extended spectrum beta lactamase (ESBL)
carbapenemase (CPE)
Give an example of an altered target site
How does MRSA acquire its resistance?
Through multiple mechanisms;
HGT of a gene that alters the PBP which allows it to continue cell wall synthesis in the presence of a drug, it also has efflux pumps
What is a drug that can treat MRSA?
vancomycin
What antibiotic is used against VRE
daptomycin
