Microbiology Flashcards
difference between sterilisation and disinfection?
disinfection is reducing or eliminating harmful microorganisms to levels considered safe (some bacteria, spores and viruses remain), whilst sterilisation is getting rid of all microorganisms (even spores)
describe fungi
higher plant like organisms
describe bacteria
small, single celled prokaryotes
describe viruses
v small obligate parasites, non-living
are the ribosomes different in prokaryotes and eukaryotes?
yes
They are 70S in prokaryotes (e.g. bacteria) and 80S in eukaryotes e.g. humans
Gm+ve and Gm-ve bacteria both have peptidoglycan layer in their cell wall. What’s the difference?
Gm+ve have a thick multi layer and Gm-ve have a single layer
Which Gm bacteria contain lipopolysaccharide in their outer membrane?
Gm-ve
LPS are endotoxins, and are released on cell lysis. They can lead to disseminated intravascular coagulation and septic shock
Which Gm bacteria contain lipopolysaccharide in their outer membrane?
Gm-ve
LPS are endotoxins, and are released on cell lysis. They can lead to disseminated intravascular coagulation and septic shock
which type of prokaryote (psycrophiles/ thermophiles/ mesophiles) grows at body temperature?
mesophiles
psycrophiles grow at low temp, thermophiles grow at high temp
can strict anaerobes survive in the presence of O2?
no - they die
can facultative anaerobes grow in presence of O2?
yes, but they grow better with O2 - but can grow without O2
can aerotolerant anaerobes grow in presence of O2?
yes, they tolerate it
what are the 4 phases of the bacterial growth curve?
- lag phase
- exponential
- stationary
- decline
biofilm
microorganisms sticking to each other and the cells adhering to a surface e.g. catheter
what are some organisms that don’t gram stain well, and why don’t they?
- mycobacterium TB (has a lipid rich/ waxy cell wall that doesn’t take up the stain)
- treponema pallidum (spirochaete that causes syphilis, an STI)
selective media?
the presence of specific substances permits growth of one organism over another
differential media?
incorporates chemicals that give visible changes and allow identification
how can Streptococci be differentiated?
Which type of haemolysis occurs
example of a protozoan disease?
malaria
what shape are Gm-ve cocci?
diplococci
Relevant species are:
-Neisseria meningitides
-Neisseria gonorrhoeae
describe coliforms
Gm-ve bacilli that look like E coli on Gm film and when cultured on blood agar
What is the 1st line antibiotic for treatment of coliform infection?
gentamicin
why do patients with coliform infection become v unwell quickly (hint: Gm-ve)
due to the endotoxin released when the bacteria die
what do endotoxins (LPS) cause to happen in the body when they are released?
- bind to macrophages, B cells and other cells that stimulate release of acute phase cytokines
- cytokines travel to brain (anterior hypothalamus)
- effects of sepsis
- PG E released, increasing thermal set point
- body shivers = fever
what happens in sepsis?
- small vessels become leaky and lose fluid into tissues
- lower blood volume requires heart to work harder to maintain oxygenation
- poor tissue perfusion means blood supply to less essential organs is shut down to try to maintain supply to brain
- clotting system activated causing clots in tiny blood vessels - using up all clotting factors and increasing risk of haemorrhage
5 ways infection can spread? (5 Is)
inhalation ingestion inoculation mother to Infant intercourse
which areas of the hand are most frequently missed during handwashing?
thumb and finger tips
orange waste bags are for what waste?
clinical waste
black bin bags are for what kind of waster?
domestic waste
what are precautions against infection via droplet inhalation?
single room
gloves, apron, mask
eye protection
vaccination
what are airborne microorganism precautions?
negative pressure room
gown, gloves, apron, eye protection, filter mask
vaccination
disinfection methods?
cleaning - hot water and detergent, rinse and dry
heat
ultrasound
chemicals
sterilisation methods?
heat (autoclave kills by coagulating and denaturing enzymes and proteins)
chemicals
radiation
filtration
what are some antibiotic targets?
cell wall protein synthesis bacterial DNA (replication) DNA gyrases metabolic pathways
why don’t glycopeptides (e.g. vancomycin) work on Gm-ves?
they are too large to get across the outer membrane of Gm-ves
what’s a common use for rifampicin?
in combination therapy for mycobacteria
what are antibiotics that we try to avoid using? (hint: the 4 Cs)
cephalosporins co-amoxiclav ciprofloxacin clindamycin (these are broad spectrum and are particularly associated with increased risk of Clostridium difficile infection)
persistor cells are resistant to antimicrobials. True/ False?
False
They are TOLERANT (very slow growth, dormant)
what are three ways in which bacteria can acquire new genes which may confer resistance?
transformation
transduction
conjugation
what are the three mechanisms of resistance?
altered antibiotic binding site
destroy the antibiotic (e.g. B-lactamases)
increased efflux of antibiotic from bacteria cell (before it has time to act)
what is ESBL (extended spectrum B-lactamase) resistant to?
all penicillins
extends to third generation cephalosporing and monobactams
what are prion proteins?
infectious proteins that have no DNA or RNA
responsible for mad cow disease
cannot be reliably removed by sterilisation or disinfection - surgical instruments have to be destroyed after use
why do some bacteria make us ill?
they produce toxins
exotoxins from mainly Gm+ves (produced inside cell and exported from it)
endotoxins from mainly Gm-ves (part of Gm-ve cell wall)
the toxins interact with cells of the immune system causing release of cytokines - leading to sepsis and septic shock
what is serology?
detection of antibodies in blood
how long does a TB culture take to come back?
4-12 weeks
do viruses contain DNA/ RNA?
either one (never both)
what does adenovirus infection usually infect?
respiratory system
what does Herpes simplex virus usually infect?
a type can cause oral herpes (cold sores) and another type can also cause genital herpes
what is the pathogenesis of viral infection?
cell death due to lysis or hijacking of cell machinery
cell death due to immune system (cytotoxic T cells)
causes cell proliferation (can lead to cancer)
what are examples of virally induced cancer?
HPV - cervical cancer
Hep B and Hep C - hepatocellular cancer
Epstein Barr virus - lymphoma
Herpes type 8 - Kaposi’s sarcoma
do Ig play a role in immunity against viruses?
yes
what is chronic infection by viruses?
when the virus remains active for years (e.g. HIV, Hep C). These patients remain asymptomatic but infectious for decades before getting life threatening complciations
how can viruses be detected?
PCR
antigen detection
mass spectrometry
