MICROBIOLOGY - viruses, testing methods, sterilization, antimicrobials (IAS50, 51, 60(antimicrobial type part) Flashcards
Virus genetic material? What is the genetic material covered by
How can the covering be destroyed
DNA or RNA, enclosed in capsid
capsid can be destroyed by heat or bleach (NaOCl)
Some viruses have lipid envelope - where is it derived from and how can it be destroyed
Cell membrane of host cell (essentially a phospholipid bilayer)
destroyed by soap, alcohol, detergent
Define defective viruses and give an example
Defective viruses: those that do not contain all the genes that code for proteins for viral replication so have to depend on helper viruses
eg hepatitis D requires hepatitis B antigen as its own surface antigen but does not have the gene and cannot produce it on its own - so hep D can only coexist with hep B
Lytic cycle?
1) virus attaches onto cells at receptors
2) virus penetrates cells, injecting genetic material (RNA into cytoplasm, DNA into nucleus)
3) viral protein synthesis and nucleic acid replication
4) assembly of nucleic acid and viral proteins to new virions
5) release of virions from cell (may lead to cell death)
Synthesis of viral nucleic acids, viral proteins for DNA and RNA virus?
DNA virus: viral DNA self replicates > transcription to mRNA > translation to form new viral proteins
RNA virus:
positive sense RNA: RNA replicates itself, directly undergoes translation to form new viral proteins
negative sense RNA: RNA undergoes transcription to +ve sense RNA by RNA-dependent RNA polymerase > translation (original viral RNA replicates itself)
Retroviruses: 1) reverse transcription to proviral DNA > 2) transcription to viral mRNA by transcriptase > 3) translation to viral proteins (original viral RNA replicated)
How do viruses with latent cycle cause recurring infections
Eg herpesviruses: virus genome in circular episomes integrated into host chromatin - so when immune system immunity becomes lower (eg stress) virus travels down nervous pathways to trigger symptoms
How do oncogenic or retroviruses exert effect
Viral genome integrated into host genome
Eg: HIV virus infects CD4+ cells and injects its genome into the cells - infected CD4+ cells produce the virus and immune system becomes compromised - so immediately receive antiretroviral treatment for 4 weeks upon exposure to try eliminate infected cells and the affected genome)
How to classify viruses:
1) DNA or RNA
2) No. of strands OR for RNA: +ve or -ve sense
3) Enveloped or unenveloped
DNA viruses - classify them and give examples
DNA viruses:
1) Double stranded, enveloped: e.g. hepadnaviruses, herpesviruses, poxviruses
2) Double stranded, unenveloped: eg e.g. adenoviruses, papillomaviruses, polyomaviruses
1) Single stranded, unenveloped: e.g. parvoviruses
RNA viruses: classify them and give examples
+ve sense RNA:
Unenveloped: e.g. caliciviruses, picornaviruses
Enveloped: e.g. coronaviruses, flaviviruses, togaviruses
-ve sense RNA:
Enveloped: e.g. arenaviruses, bunyaviruses, filoviruses, orthomyxoviruses, paramyxoviruses, rhabdoviruses
both +ve and -ve:
Double capsid: Reoviruses
RNA via DNA (retroviruses): enveloped
Define: incubation period, period of infectivity
Incubation period: The time interval between virus entry and the commencement of disease symptoms
Period of infectivity: The time interval in which there is virus shedding; dependent on the virus
Compare pathogenesis: localized infections and systemic infections
Localized: The virus multiplies at the epithelial surface at or near its site of entry to the body
Systemic:
Initially, the virus multiples locally at the site of entry.
It then spreads by blood (viraemia; chronic: e.g. hepatitis B, HIV) or other means (e.g. along peripheral nerves) to distant sites and localizes in target organs (tissue tropism).
It may lead to organ damage and hence major diseases
Viral culture/transport medium components?
Live cell culture/infected animal
transport medium need: pH buffer, pH indicator, antibacterials, proteins to maintain virus stability
Which form of PCR for RNA viruses
reverse transcriptase PCR
Groups of viruses causing skin rash?
Herpesvirus, enterovirus, vaccine-preventable virus
Herpesvirus classification?
Symptoms/morphology/transmission method for each?
HSV1, HSV2, VZV, cytomegalovirus
HSV1: cold sores, usually transmitted via oropharyngeal secretions
● primary infection and reactivation most commonly orofacial lesions
HSV2: usually sexually transmitted
● primary infection and reactivation most commonly anogenital lesions
VSV: varicella zoster virus
■ airborne transmission
■ primary infection: chickenpox
■ reactivation: herpes zoster (shingles)
ABOVE 3 ALL LATENT IN SENSORY GANGLIA
Cytomegalovirus:
latent in Haematopoietic progenitor cells
causes Infectious mononucleosis like syndrome, congenital CMV disease
severe/disseminated reinfections (reactivations) in immunosuppressed but asymptomatic otherwise
Infectious mononucleosis viral causes?
CMV, HIV, other herpesviruses
Enterovirus - name some examples and what diseases they cause that give skin rash symptoms
Enterovirus A71: Hand foot mouth disease
Parvovirus B19: erythema infectiosum (slapped cheek syndrome)
Name some vaccine-preventable viruses causing skin rash
How is mpox most commonly transmitted?
measles, mumps, rubella, mpox
mpox: MSM
Name 5 big groups of respiratory viruses?
Name 4 other groups of viruses that can also cause respiratory diseases?
Influenza A and B viruses, respiratory syncytial viruses, SARS-CoV-2, adenoviruses, rhinoviruses/enteroviruses
parainfluenza, HMPV (human metapneumovirus), MERS, other coronaviruses (eg HKU1, NL63, OC43, 229E)
SARS-CoV-2: how to test for it - for PCR, which genes are targeted?
why is it called coronavirus
What type of virus (based on genetic material classification) is it
What does transverse chest CT scan show for patients with viral pneumonia
Testing by RT-PCR, RAT
E (envelope), N (nucleocapsid protein), RdRp (polymerase)
Coronavirus because it has spikes on surface shaped like crowns
-ve sense RNA enveloped virus
focal ground glass changes
Respiratory syncytial viruses (RSVs):
Name 1 disease it can cause
What does it form in cell culture
Seasonality and peak?
Acute bronchiolitis (blockage of bronchioles) in young children
syncytium, multinucleated giant cells
All year seasonality, peak in summer
Influenza:
1) How many types? Which are more serious?
2) Structure (the 2 that make up naming of influenza viruses)? What are the components targeted by?
3) Define: drift and shift
1) 3 types, A/B/C, A and B more serious
2) H: hemagglutinin - for entry to cells (targeted by serum nAb)
N: neuraminidase for cell exit (target by antivirals)
(so HxNx)
3) Drift: slight mutations in existing influenza strains causing seasonal influenza
Shift: major changes, usually involving recombination with animal influenza, causing pandemics (eg avian H3Nx with human H2N2 leading to human H3N2)
Diseases caused by influenza?
Medication to treat influenza?
self-limiting URTI, LRTI, chronic illness exacerbation, encephalitis, myocarditis
In children taking aspirin: Reyes’ syndrome
Oseltamivir (NA inhibitor) / Zanamivir
Evolution of influenza A strain?
1918: H1N1 (Spanish flu) is formed by direct adaptation/mutation of bird viruses.
1957: H2N2 (Asian flu) is formed by bird-human viral genetic re-assortment.
1968: H3N2 (HK flu) is formed by bird-human viral genetic re-assortment.
1977: H1N1 (Russian flu) re-emerges.
2009: H1N1 is formed by bird-pig-human viral genetic re-assortment.
Influenza peak?
Vaccine recommendations to what high risk groups? Name some
What does vaccine increase to reduce infection risk?
By how much does antibody content decrease in 6 months however?
bimodal seasonality with higher winter than summer peak
eg: young children, elderly, people with chronic diseases, healthcare workers
Vaccination increases the HAI titre and significantly reduces the relative risk, but nAb would decrease by 4 folds in 6 months
Most significant disease adenovirus causes?
What other diseases can adenovirus cause?
Common cold
gastroenteritis, conjunctivitis, myocarditis
3 types of viruses that can cause viral pneumonia in young immunocompetent children?
RSV, influenza A/B, adenovirus
Name diseases caused by: rhinoviruses
which enterovirus is linked with acute LRTI
Common cold but sometimes asthma
Enterovirus D68
Which enterovirus causes infective myocarditis
What other viruses can cause myocarditis
Enterovirus B (Coxsackievirus B3), influenza, adenovirus
2 major types of viruses causing gastroenteritis?
2 more types of viruses that can cause gastroenteritis?
rotavirus, norovirus/sapovirus
astrovirus, enteric adenovirus
Rotavirus - most common in what type of people?
Structure?
Symptoms?
How can it be prevented
Children
non-enveloped virus, with spokes of wheel and double layer of shell
High fever, vomiting & loose stool
Babies: Milk curd with acid smell on napkin
oral live attenuated vaccine
Norovirus infection age demographic? Any vaccines available?
ALL ages, no
How are noroviruses, sapoviruses, astrovirus and enteric adenoviruses transmitted
morphology of astrovirus and enteric adenovirus?
fecal-oral route
astrovirus: 30nm, non-enveloped, star-like shape with 5-6 points
enteric adenovirus: 100nm, non-enveloped DNA virus, icosahedral
Diseases that can cause hemorrhagic fever? How are these transmitted?
Dengue virus, ebola virus, yellow fever, hantavirus
Dengue and yellow fever: mosquito-borne arboviruses
ebola: bloodborne and transmitted by bodily fluids
hantavirus: transmitted by rodent contact
Dengue fever symptoms?
Clinical presentations:
Mosquito bites, fever and chills, fine blanchable rash over the whole body
Low Hb, WBC and platelet counts in blood tests
Hemorrhagic fever in repeated infections, skin blisters and blood in vomit/feces/lungs
Hantavirus symptoms?
Renal infections
CNS infections?
Meningitis, encephalitis, meningoencephalitis
Viruses causing CNS infections?
Japanese encephalitis virus, herpesvirus, enterovirus, rabies
Japanese encephalitis virus symptoms Diagnosis?
Clinical presentations:
Confusion; brief, involuntary, irregular limb twitching; cannot recognize people
MRI: Bilateral thalamic hyperintense signal (implying inflammation in hippocampus)
CSF: Increased WBC & protein
Diagnosis: Acute meningoencephalitis
Other viruses that can cause acute meningoencephalitis?
Herpesvirus, enterovirus, rabies, Zika virus
Zika virus symptoms?
fetal microcephaly - leads to severe mental retardation when fetus infected during pregnancy
Rabies: fatality and any medication available?
Fatal BUT vaccine and prophylaxis available
Cancer-causing viruses?
HPV, EBV, HBV/HCV
What diseases do each cancer-causing virus cause?
HPV: cervical cancer, oropharyngeal cancer
EBV: nasopharyngeal carcinoma
HBV/HCV: hepatocellular carcinoma
Can Hepatitis D exist as an infection on its own
NO - needs co-infection with hep B
Name 1 prion disease
Creutzfeld-Jakob disease (due to misfolding of PrP protein)
Laboratory test for disease diagnosis: what can be tested?
Diagnosis by microbial factors:
visualization (miscroscopy, staining, by microbial morphology)
culture
Detect specific microbial components (eg proteins, lipids, DNA/RNA)
By host factors:
Antibody response
Lymphocyte activation by specific microbial antigen
Basic principle of electron microscopy in diagnosis?
Transmission electron microscopy - negative staining, for viruses of size 20-300nm
Using samples with viral load of >10^6 viral particles/mL
Samples:
stool (viral gastroenteritis)
Vesicle fluid - (HSV, VZV, mpox - the rash viruses)
Kidney tissue, urine (polyoma virus infection)
Serum (ONLY for parvovirus B19/hep B since viral load high only in these 2 cases)
Negative staining: background darkly stained (using eg phosphotungstic acid or uranyl acetate), viruses relatively unstained except for characteristic surface features
Electron beam shot thru specimen, scattered, backscattered and absorbed electrons analyezed
Images generated based on e- density
ONLY IDENTIFIABLE UP TO FAMILY LEVEL - NOT TO GENUS/SPECIES
What can gram stain differentiate
Gram +ve and -ve bacteria, Candida (appears gram positive)
Which stain used to test for acid-fast bacteria
Name 1 fluorescent stain
Ziehl-Neelsen stain
immunofluorescent stain (apple-green fluorescence)
Functions for (and any particular bacteria tested by): (Just remember which bacteria is tested by which agar)
Blood agar
Chocolate agar
MacConkey agar
Thayer-Martin agar
Bordet-Gengou agar
Lowenstein-Jensen agar
Blood agar: supportive agar to detect hemolysis (esp strep)
Chocolate agar: Basically heated blood agar, lyses RBC inside to release nutrients, especially for Haemophilus influenzae
MacConkey agar: used to differentiate between lactose fermenters (E. coli, pink) and non-fermenters (clear) - USED ESPECIALLY TO DIFFERENTIATE SHIGELLA, SALMONELLA
TM agar: Used to test for Neisseria gonorrheae (additional nutrients to support its growth, antimicrobials to suppress growth of other microbes)
BG agar: Used to test for Bordetella pertussis (Additional nutrients and higher blood concentration)
LJ agar: Used to test for Mycobacterium and Nocardia - egg based medium, malachite inside suppresses growth of other bacteria
If clear result given for MacConkey agar which other agar can differentiate Salmonella - and what morphology on that agar?
XLD agar - black colonies
Which agar to test for Vibrio cholerae?
TCBS agar - cholerae gives YELLOW colonies
other vibrios appear blue/green
Color of E. coli on CHROMID agar?
Red
SELDOM ASKED but just in case - what does CLED agar test for?
Differentiate between lactose fermenters and lactose non-fermenters (similar to MacConkey)
lactose fermenters: yellow
lactose non-fermenters: blue
Name 4 stains/inks used to test for fungi
Name 2 specific agars that can grow fungi besides differential media
India ink - test for Cryptococcus neoformans (gives halo appearance)
Gram stain (Candida)
KOH smear: Aspergillus - KOH smear can see fungal features (eg hyphae) but not enough to determine genus/species
Fluorescent stain
Sabouraud agar, blood agar
The gold standard for viral diagnosis?
Viral culture in cell line
Name 2 possible appearances of cytopathic effect (CPE) of cells
Cell shrinkage, detachment (form plaques)
What samples can be used to make viral culture in cell line?
Also what to do after the culture has been made?
What other tests can the cultured viruses be used in
Respiratory swabs (including eye conjunctival swabs), urine, vesicle fluid
And then:
Use electron microscopy to confirm if the virus morphology is compatible with the suspected virus (confirming if CPE is caused by the suspected virus)
Virus neutralization test: run the virus with serum of patient (containing neutralizing antibodies) recovering from infection
Antiviral susceptibility test: test which drugs can inhibit the virus from inducing CPE in cell line
Specific antibody test: Use the virus in cell line as antigen to test for the presence/absence of an antibody using immunofluorescence
3 assays to detect viral antigen?
1) immunofluorescence assay
2) Enzyme immunoassay
3) Immunochromatographic assay / lateral flow assay / RAT
Mechanisms for:
1) immunofluorescence assay
2) Enzyme immunoassay (for which antigens)
3) Immunochromatographic assay / lateral flow assay / RAT
Immunofluorescence assay
Direct: Viral Ag binds to virus-specific Ab with fluorescent indicator
Indirect: Viral Ag binds to virus-specific Ab, which itself binds to anti-mouse Ab with fluorescent indicator (usually apple green)
The background is commonly stained dark red
Enzyme immunoassay: (for polysaccharide, protein antigens)
use of corresponding antibody (capture Ab)
if antigen is present, it would bind to the antibody
when second antibody (Primary Ab, aka detection Ab) is added, it would bind to the antigen (if present)
Biotin labelled antibody attaches to Primary Ab
an anti-immunoglobulin enzyme (Streptavidin-HRPO) is attached to the Biotin-labelled antibody, which breaks down an added substrate to form a product of different colour (enzymatic color reaction)
OD value produced can be read by spectroscopy
RAT:
■ When the sample is added to the test kit, the Ag travels up to the control line. The test is invalid if there is no colour at the control line.
■ Colouration at the test line implies the presence of Ag for the microbe under testing (e.g. N (nucleocapsid) Ag of viruses).
■ RAT is a rapid but non-sensitive point-of-care test.
■ A negative result usually implies that the patient is non-infectious, even if infected.
Some examples of RAT (give 3) and name advantages and disadvantages of RAT
COVID-19 RAT, HBV serum sample test kit, influenza RAT
advantage: Rapidly obtainable results, easy to perform, fair correlation with infection
disadvantage: less sensitive than PCR
Uses for PCR?
can identify pathogens that are slow/hard to grow
replication of a DNA sequence much faster than growing pathogen
Which form of PCR for DNA and RNA viruses? especially which system’s viruses?
DNA: PCR
RNA: RT-PCR (reverse transcription PCR)
respiratory viruses
How many cycles for PCR tests to be sensitive?
50-60 cycles
For the primers and immunofluorescent probe how many base pairs
And what sequence are they based on
20bp
based on a unique 100bp sequence only found in the viral genome
Function of real time PCR and multiplex PCR?
1 major disadvantage of multiplex PCR?
Rt-PCR: relative quantification of viral nucleic acid in samples
multiplex PCR: simultaneous detection of multiple viruses
CANNOT quantify nucleic acid
Advantages and disadvantages of PCR?
Advantages:
* Results available rapidly, high sensitivity and specificity.
- Disadvantages:
- special equipment and expertise, cannot differentiate between residual nucleic acid and viable viruses
After PCR what to do to confirm presence of viral genetic material
1 disadvantage of conventional PCR? Then which method of PCR can remedy this weakness?
Gel electrophoresis
Cannot quantify amount of viral nucleic acid - real time PCR (qPCR/ Rt-PCR)
Minimum limit for detection for real time PCR?
200 bacterial gene fragment copies/ 200 live bacteria per mL of blood
Steps for real time PCR?
Basically the same as normal PCR (95c DNA denature, 50-60c add primer, 72c add DNA polymerase)
A fluorescent reporter is bound to the strand (on a probe) and fluorescent signal (of reporter) inhibited by a quencher.
When the amplification by the polymerase (with 5’ exonuclease activity) is successful, the polymerase cleaves the reporter from probe, which gives a fluorescent signal
Define Ct value
and its relationship with viral load?
How can Ct value then quantify viral load
Ct value = the number of cycles at which the sample fluorescence is first flagged as exceeding the background threshold
The higher the viral load the lower the Ct value (less cycles needed to exceed the threshold to give detectable and sufficient fluorescent signal)
viral load can be converted from Ct value to copies/mL
Implications of viral load? (basically what can the viral load be used for in terms of planning/measuring)
Implications of viral load:
1) Windows of opportunity for anti-viral Rx to stop progression
2) Success of isolation and quarantine
3) Immunopathological damage; for immunomodulation
Steps for high-throughput NGS?
Analysis metrics:
Q30 meaning?
RPM-r (RPM ratio) meaning?
1) extract cell-free DNA (cfDNA) from dead bacti in peripheral venous blood
2) Isolate mcfDNA
3) library construction
4) sequencing and comparison of sequence with reference database
5) Analysis + clinical report
Q30: quality score of each base (where probi of wrong base call is 1: 1000)
RPM-r:
equals to RPM of sample/RPM (no template control, NTC)
Accounts to low-level microbial contamination by normalizing detection reads with respect to NTC (most other reads are from human DNA)
The higher the RPM-r the less likely the finding is due to background microbes
How to diagnose infection by host factors - more specifically what components can be tested
Test for patient antibody response towards microbial components
or cellular responses/biopsies
What to do if we want to MANUFACTURE antigens for testing/vaccines/produce antibodies?
Clone specific microbial antigens - recombinant plasmids
1) Cleave the foreign DNA we are interested in by EcoRI, run this section by PCR
2) cleave a plasmid also by EcoRI (to produce complimentary sticky ends)
3) recombine the cleaved foreign DNA and plasmid together by DNA ligase
4) insert the recombinant plasmid into bacteria and let the bacteria reproduce
5) bacteria lysed, the proteins of interest extracted and purified
Most basic principle of antibody detection?
For enzyme immunoassay (EIC) what to do next to confirm antigen presence
use of corresponding antigen (attach Ag onto microtiter plate)
if antibody is present, it would bind to the antigen
Anti-Ig enzymes are added to wash away Ab for other microbes.
4. Specific anti-human Ab with enzymes are added; they stick to the human Ab.
substrate added, which would be broken down by the enzyme to form a product of different color
gel electrophoresis (same as conventional PCR)
What do IgG+ and IgM+ mean
IgG+: previous infection (not recent)
IgM+: recent infection in last 1-3 months
What can indirect ELISA test for? What factor does its mechanism of testing depend on
Detects either IgM or IgG antibodies (it is basically an enzyme immunoassay)
depends on specificity of enzyme-conjugated antibody to test either for IgM or IgG
If we use IgG to test for infection, what increase in what duration suggests recent infection
How to find nAb titre
> /= 4-fold increase of IgG concentration within 10-14 days
Prepare agar plates each containing 100 PFU of viruses.
Add serum of different concentrations to each agar plate.
The serum nAb titre is the serum dilution which halves the number of PFU
Name some cellular responses that can be seen to diagnose infections
Name 1 biopsy that can be used to test for infections
Mantoux test, lymphocyte proliferation (eg staining for CD4+ and CD8+, checking for cytokine activation eg IFN-γ, TNF-α), checking for cytotoxic lymphocyte response against specific antigens
Checking for Negri bodies - indicates rabies virus infection
Name 1 bacteria and 1 class of virus that can be transmitted by droplets
Name 1 bacteria and classes of virus that can be airborne
N. meningitidis, respiratory viruses
Mycobacterium tuberculosis, VSV, respiratory viruses, measles virus
Name 2 bloodborne viruses
Japanese encephalitis, ebola
Name some vector borne viruses:
1) local arboviruses
2) arboviruses in returning travellers
One more: how is Hep E transmitted?
Dengue, Japanese encephalitis
bunyavirus, zika, chikungunya, yellow fever, west nile
Organ transplant
Name some:
contact precautions
droplet precautions
airborne precautions
PPE, generally attempt to isolate patient, cleaning/sterilization
PPE (with face shield), attempt to isolate patient (patient should wear mask), cleaning/sterilization
PPE (with face shield AND N95 respirator), MUST isolate patient in negative pressure room (patient should wear mask), cleaning/sterilization, staff should be vaccinated if possible (eg VZV, measles)
Briefly define:
1) sterilization
2) disinfection
3) antisepsis
4) cleaning
Spaulding classification: (and which level of disinfection needed)
Critical device
semi-critical device
non-critical device
When do you need to do intermediate level disinfection
what does high level disinfection clear
General resistance list? (for reference only)
1) destroy ALL microbial life except prions
2) destroy most pathogens on inanimate objects
3) inhibit/destroy microbes on skin/living tissue
4) remove visible contaminants manually/mechanically
Critical: come into contact with sterile areas/bloodstream - sterilization
semi-critical: come into contact with mucous membrane - high level disinfection
non-critical: contact intact skin (low level disinfection)
For contact with mycobacteria
All microbes except spores
general resistance
prions > spores > mycobacteria > parasitic cysts > non-enveloped viruses > G-ve bacteria > fungi > G+ve bacteria > enveloped viruses
Name some pathways for sterilization (just briefly go thru this)
Heat (eg autoclave) - KNOW THAT BOILERS/THERMAL WASHER DISINFECTORS CANNOT STERILIZE
radiation (eg ionizing/UV)
Filtration (eg membrane filters)
Some chemicals and their disinfecting abilities: (read this)
Glutaraldehyde: high-level disinfectant (sterilization then 3 hours), non-corrosive but irritating
Formaldehyde
◦ Sterilization: 37% (formalin)
◦ Disinfection: 3–8%
OPA: high level disinfectant, may be better at inactivating myco than glutaraldehyde
chlorine-releasing agents (release Cl in water, inactivated by proteins) (hypochlorite solutions/powders)
iodine/iodophors: mainly for skin disinfection
WHEN USED SURFACE HAS TO BE CLEAN
chlorhexidine: works for Gram +ve, less effective against gram -ve, also is fungicidal
NOT EFFECTIVE against myco, spores, enveloped viruses
for skin disinfection/antiseptic, HAS RESIDUAL EFFECT
alcohol: need at least 70% ethanol or 60% isopropanol
NOT sporicidal
poor penetrative powers so used mainly for RAPID DISINFECTION
Where do beta-lactams act on? Give 3 examples of beta lactam subgroups (and 3-4 examples for each subgroup)
Bacterial cell wall
Penicillins (ampicillin, amoxillin, benzylpenicillin, methicillin)
cephalosporins (cefazolin, ceforoxime, ceftriaxone, cefepime)
carbapenems (imipenem, meropenem)
Name 1 more group of drugs that act on bacterial cell walls and give 1 example of that group
Name 1 more drug (not a glycopeptide nor beta-lactam) that also acts on cell wall
GLYCOPEPTIDES - VANCOMYCIN
bacitracin
Name 2 drug groups acting on bacterial nucleic synthesis (classify them based on the nucleic acid they target) and give at least 1 example per group
DNA synthesis: FLUOROQUINOLONE eg CIPROFLOXACIN, levofloxacin (~floxacin)
RNA synthesis: rifamycin, eg rifampin
Name at least 1 drug group targeting the 50s ribosome subunit (and 2-3 examples of the group)
MACROLIDES - ERYTHROMYCIN, clarithromycin, azithromycin (AT LEAST REMEMBER THIS!!!)
other groups: lincosamides (clindamycin), amphenicols (chloramphenicol), oxazolinidones (linezolid)
Name 2 drug groups targeting the 30s ribosome subunit (with examples for the group)
TETRACYCLINES (eg DOXYCYCLINE, minocycline)
AMINOGLYCOCIDES (eg GENTAMICIN, tobramycin, amikacin)
Name 2 drug groups inhibiting folic acid synthesis and examples
The drug that inhibits mycolic acid synthesis?
SULPHONAMIDES (sulfamethoxazole), aminopyrimidine (TRIMETHOPRIM)
isoniazid
How do penicillins/beta lactams act on bacteria
binds to penicillin-binding protein (PBP) which has transpeptidase
domain (specifically class A PBP has both transpeptidase and transglycosylase domain, class B only has TPase domain)
cell wall is no longer resistant to osmotic pressure, hence cell lysis
Bactericidal vs bacteriostatic? Give examples of medication for both categories
Bactericidal: kills bacti (99.9% decrease in original inoculum no)
beta-lactams, vancomycin, aminoglycosides, fluoroquinolones
bacteriostatic: inhibits bacti growth nut bacti no. is constant
macrolides, tetracyclines, sulphonamides, trimethoprim
Meaning of MIC and MBC?
minimal inhibitory concentration (MIC)
lowest concentration of antibiotic that inhibits visible growth overnight
antibiotic susceptibility testing (AST) should be done - by serial dilution of antibiotic and incubation of bacterial culture, or by gradient/disc diffusion tests
minimum bactericidal concentration (MBC)
lowest concentration of antibiotic that kills 99.9% of a microorganism
Name 1 antiviral and its function
oseltamavir - neuraminidase inhibitor (esp for influenza)
Name 3 major types of antifungals, examples and their functions
Those that act on cell membrane:
Azoles (eg fluconazole) - inhibit ergosterol synthesis
Polyenes (eg amphotericin B, nystatin)
Those that act on nucleic acid synthesis:
Nucleoside analogues eg 5-flucytosine
Those that inhibit cell wall synthesis (act on glucan):
Echinocandins eg micafungin
