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IASM > MICROBIOLOGY - viruses, testing methods, sterilization, antimicrobials (IAS50, 51, 60(antimicrobial type part) > Flashcards

MICROBIOLOGY - viruses, testing methods, sterilization, antimicrobials (IAS50, 51, 60(antimicrobial type part) Flashcards

1
Q

Virus genetic material? What is the genetic material covered by

How can the covering be destroyed

A

DNA or RNA, enclosed in capsid

capsid can be destroyed by heat or bleach (NaOCl)

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2
Q

Some viruses have lipid envelope - where is it derived from and how can it be destroyed

A

Cell membrane of host cell (essentially a phospholipid bilayer)

destroyed by soap, alcohol, detergent

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3
Q

Define defective viruses and give an example

A

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

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4
Q

Lytic cycle?

A

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)

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5
Q

Synthesis of viral nucleic acids, viral proteins for DNA and RNA virus?

A

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)

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6
Q

How do viruses with latent cycle cause recurring infections

A

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

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7
Q

How do oncogenic or retroviruses exert effect

A

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)

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8
Q

How to classify viruses:

A

1) DNA or RNA

2) No. of strands OR for RNA: +ve or -ve sense

3) Enveloped or unenveloped

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9
Q

DNA viruses - classify them and give examples

A

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

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10
Q

RNA viruses: classify them and give examples

A

+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

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11
Q

Define: incubation period, period of infectivity

A

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

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12
Q

Compare pathogenesis: localized infections and systemic infections

A

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

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13
Q

Viral culture/transport medium components?

A

Live cell culture/infected animal

transport medium need: pH buffer, pH indicator, antibacterials, proteins to maintain virus stability

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14
Q

Which form of PCR for RNA viruses

A

reverse transcriptase PCR

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15
Q

Groups of viruses causing skin rash?

A

Herpesvirus, enterovirus, vaccine-preventable virus

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16
Q

Herpesvirus classification?

Symptoms/morphology/transmission method for each?

A

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

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17
Q

Infectious mononucleosis viral causes?

A

CMV, HIV, other herpesviruses

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18
Q

Enterovirus - name some examples and what diseases they cause that give skin rash symptoms

A

Enterovirus A71: Hand foot mouth disease
Parvovirus B19: erythema infectiosum (slapped cheek syndrome)

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19
Q

Name some vaccine-preventable viruses causing skin rash

How is mpox most commonly transmitted?

A

measles, mumps, rubella, mpox

mpox: MSM

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20
Q

Name 5 big groups of respiratory viruses?

Name 4 other groups of viruses that can also cause respiratory diseases?

A

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)

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21
Q

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

A

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

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22
Q

Respiratory syncytial viruses (RSVs):

Name 1 disease it can cause

What does it form in cell culture

Seasonality and peak?

A

Acute bronchiolitis (blockage of bronchioles) in young children

syncytium, multinucleated giant cells

All year seasonality, peak in summer

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23
Q

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

A

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)
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24
Q

Diseases caused by influenza?

Medication to treat influenza?

A

self-limiting URTI, LRTI, chronic illness exacerbation, encephalitis, myocarditis

In children taking aspirin: Reyes’ syndrome

Oseltamivir (NA inhibitor) / Zanamivir

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25
Q

Evolution of influenza A strain?

A

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.

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26
Q

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?

A

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

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27
Q

Most significant disease adenovirus causes?

What other diseases can adenovirus cause?

A

Common cold

gastroenteritis, conjunctivitis, myocarditis

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28
Q

3 types of viruses that can cause viral pneumonia in young immunocompetent children?

A

RSV, influenza A/B, adenovirus

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29
Q

Name diseases caused by: rhinoviruses

which enterovirus is linked with acute LRTI

A

Common cold but sometimes asthma

Enterovirus D68

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30
Q

Which enterovirus causes infective myocarditis

What other viruses can cause myocarditis

A

Enterovirus B (Coxsackievirus B3), influenza, adenovirus

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31
Q

2 major types of viruses causing gastroenteritis?

2 more types of viruses that can cause gastroenteritis?

A

rotavirus, norovirus/sapovirus

astrovirus, enteric adenovirus

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32
Q

Rotavirus - most common in what type of people?

Structure?

Symptoms?

How can it be prevented

A

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

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33
Q

Norovirus infection age demographic? Any vaccines available?

A

ALL ages, no

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34
Q

How are noroviruses, sapoviruses, astrovirus and enteric adenoviruses transmitted

morphology of astrovirus and enteric adenovirus?

A

fecal-oral route

astrovirus: 30nm, non-enveloped, star-like shape with 5-6 points
enteric adenovirus: 100nm, non-enveloped DNA virus, icosahedral

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35
Q

Diseases that can cause hemorrhagic fever? How are these transmitted?

A

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

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36
Q

Dengue fever symptoms?

A

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

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37
Q

Hantavirus symptoms?

A

Renal infections

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38
Q

CNS infections?

A

Meningitis, encephalitis, meningoencephalitis

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39
Q

Viruses causing CNS infections?

A

Japanese encephalitis virus, herpesvirus, enterovirus, rabies

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40
Q

Japanese encephalitis virus symptoms Diagnosis?

A

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

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41
Q

Other viruses that can cause acute meningoencephalitis?

A

Herpesvirus, enterovirus, rabies, Zika virus

42
Q

Zika virus symptoms?

A

fetal microcephaly - leads to severe mental retardation when fetus infected during pregnancy

43
Q

Rabies: fatality and any medication available?

A

Fatal BUT vaccine and prophylaxis available

44
Q

Cancer-causing viruses?

A

HPV, EBV, HBV/HCV

45
Q

What diseases do each cancer-causing virus cause?

A

HPV: cervical cancer, oropharyngeal cancer

EBV: nasopharyngeal carcinoma

HBV/HCV: hepatocellular carcinoma

46
Q

Can Hepatitis D exist as an infection on its own

A

NO - needs co-infection with hep B

47
Q

Name 1 prion disease

A

Creutzfeld-Jakob disease (due to misfolding of PrP protein)

48
Q

Laboratory test for disease diagnosis: what can be tested?

A

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

49
Q

Basic principle of electron microscopy in diagnosis?

A

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

50
Q

What can gram stain differentiate

A

Gram +ve and -ve bacteria, Candida (appears gram positive)

51
Q

Which stain used to test for acid-fast bacteria

Name 1 fluorescent stain

A

Ziehl-Neelsen stain

immunofluorescent stain (apple-green fluorescence)

52
Q

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

A

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

53
Q

If clear result given for MacConkey agar which other agar can differentiate Salmonella - and what morphology on that agar?

A

XLD agar - black colonies

54
Q

Which agar to test for Vibrio cholerae?

A

TCBS agar - cholerae gives YELLOW colonies

other vibrios appear blue/green

55
Q

Color of E. coli on CHROMID agar?

A

Red

56
Q

SELDOM ASKED but just in case - what does CLED agar test for?

A

Differentiate between lactose fermenters and lactose non-fermenters (similar to MacConkey)

lactose fermenters: yellow
lactose non-fermenters: blue

57
Q

Name 4 stains/inks used to test for fungi

Name 2 specific agars that can grow fungi besides differential media

A

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

58
Q

The gold standard for viral diagnosis?

A

Viral culture in cell line

59
Q

Name 2 possible appearances of cytopathic effect (CPE) of cells

A

Cell shrinkage, detachment (form plaques)

60
Q

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

A

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

61
Q

3 assays to detect viral antigen?

A

1) immunofluorescence assay

2) Enzyme immunoassay

3) Immunochromatographic assay / lateral flow assay / RAT

62
Q

Mechanisms for:

1) immunofluorescence assay

2) Enzyme immunoassay (for which antigens)

3) Immunochromatographic assay / lateral flow assay / RAT

A

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.

63
Q

Some examples of RAT (give 3) and name advantages and disadvantages of RAT

A

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

64
Q

Uses for PCR?

A

can identify pathogens that are slow/hard to grow

replication of a DNA sequence much faster than growing pathogen

65
Q

Which form of PCR for DNA and RNA viruses? especially which system’s viruses?

A

DNA: PCR
RNA: RT-PCR (reverse transcription PCR)

respiratory viruses

66
Q

How many cycles for PCR tests to be sensitive?

A

50-60 cycles

67
Q

For the primers and immunofluorescent probe how many base pairs

And what sequence are they based on

A

20bp

based on a unique 100bp sequence only found in the viral genome

68
Q

Function of real time PCR and multiplex PCR?

1 major disadvantage of multiplex PCR?

A

Rt-PCR: relative quantification of viral nucleic acid in samples

multiplex PCR: simultaneous detection of multiple viruses

CANNOT quantify nucleic acid

69
Q

Advantages and disadvantages of PCR?

A

Advantages:
* Results available rapidly, high sensitivity and specificity.

  • Disadvantages:
  • special equipment and expertise, cannot differentiate between residual nucleic acid and viable viruses
70
Q

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?

A

Gel electrophoresis

Cannot quantify amount of viral nucleic acid - real time PCR (qPCR/ Rt-PCR)

71
Q

Minimum limit for detection for real time PCR?

A

200 bacterial gene fragment copies/ 200 live bacteria per mL of blood

72
Q

Steps for real time PCR?

A

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

73
Q

Define Ct value

and its relationship with viral load?

How can Ct value then quantify viral load

A

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

74
Q

Implications of viral load? (basically what can the viral load be used for in terms of planning/measuring)

A

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

75
Q

Steps for high-throughput NGS?

Analysis metrics:
Q30 meaning?
RPM-r (RPM ratio) meaning?

A

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

76
Q

How to diagnose infection by host factors - more specifically what components can be tested

A

Test for patient antibody response towards microbial components

or cellular responses/biopsies

77
Q

What to do if we want to MANUFACTURE antigens for testing/vaccines/produce antibodies?

A

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

78
Q

Most basic principle of antibody detection?

For enzyme immunoassay (EIC) what to do next to confirm antigen presence

A

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)

79
Q

What do IgG+ and IgM+ mean

A

IgG+: previous infection (not recent)

IgM+: recent infection in last 1-3 months

80
Q

What can indirect ELISA test for? What factor does its mechanism of testing depend on

A

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

81
Q

If we use IgG to test for infection, what increase in what duration suggests recent infection

How to find nAb titre

A

> /= 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

82
Q

Name some cellular responses that can be seen to diagnose infections

Name 1 biopsy that can be used to test for infections

A

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

83
Q

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

A

N. meningitidis, respiratory viruses

Mycobacterium tuberculosis, VSV, respiratory viruses, measles virus

84
Q

Name 2 bloodborne viruses

A

Japanese encephalitis, ebola

85
Q

Name some vector borne viruses:

1) local arboviruses

2) arboviruses in returning travellers

One more: how is Hep E transmitted?

A

Dengue, Japanese encephalitis

bunyavirus, zika, chikungunya, yellow fever, west nile

Organ transplant

86
Q

Name some:
contact precautions
droplet precautions
airborne precautions

A

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)

87
Q

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)

A

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

88
Q

Name some pathways for sterilization (just briefly go thru this)

A

Heat (eg autoclave) - KNOW THAT BOILERS/THERMAL WASHER DISINFECTORS CANNOT STERILIZE

radiation (eg ionizing/UV)

Filtration (eg membrane filters)

89
Q

Some chemicals and their disinfecting abilities: (read this)

A

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

90
Q

Where do beta-lactams act on? Give 3 examples of beta lactam subgroups (and 3-4 examples for each subgroup)

A

Bacterial cell wall

Penicillins (ampicillin, amoxillin, benzylpenicillin, methicillin)

cephalosporins (cefazolin, ceforoxime, ceftriaxone, cefepime)

carbapenems (imipenem, meropenem)

91
Q

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

A

GLYCOPEPTIDES - VANCOMYCIN

bacitracin

92
Q

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

A

DNA synthesis: FLUOROQUINOLONE eg CIPROFLOXACIN, levofloxacin (~floxacin)

RNA synthesis: rifamycin, eg rifampin

93
Q

Name at least 1 drug group targeting the 50s ribosome subunit (and 2-3 examples of the group)

A

MACROLIDES - ERYTHROMYCIN, clarithromycin, azithromycin (AT LEAST REMEMBER THIS!!!)

other groups: lincosamides (clindamycin), amphenicols (chloramphenicol), oxazolinidones (linezolid)

94
Q

Name 2 drug groups targeting the 30s ribosome subunit (with examples for the group)

A

TETRACYCLINES (eg DOXYCYCLINE, minocycline)

AMINOGLYCOCIDES (eg GENTAMICIN, tobramycin, amikacin)

95
Q

Name 2 drug groups inhibiting folic acid synthesis and examples

The drug that inhibits mycolic acid synthesis?

A

SULPHONAMIDES (sulfamethoxazole), aminopyrimidine (TRIMETHOPRIM)

isoniazid

96
Q

How do penicillins/beta lactams act on bacteria

A

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

97
Q

Bactericidal vs bacteriostatic? Give examples of medication for both categories

A

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

98
Q

Meaning of MIC and MBC?

A

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

99
Q

Name 1 antiviral and its function

A

oseltamavir - neuraminidase inhibitor (esp for influenza)

100
Q

Name 3 major types of antifungals, examples and their functions

A

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

IASM (16 decks)

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