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Pathology and microbiology > 7- Infectious diseases > Flashcards

7- Infectious diseases Flashcards

1
Q

Basic characteristics of infectious disease

A
  • Genus/species – Bacteroides fragilis
  • Light microscope -1um diam./ 3-10um length
  • They are Procaryotic so have no nucleus/ membrane bound organelles only free-floating DNA strands – divides by binary fission (Asexual reproduction = identical daughter cells)
  • Doubling time – 20 min for E.coli
  • Differentiating Cell wall– Blue/purple (Gram positive), red (Gram negative)
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2
Q

What are pathogens

A

Organism that causes or is capable of causing disease

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3
Q

What are commensals

A

Organism which colonises the host but causes no disease in normal circumstances, unless they are in a place they shouldn’t be

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4
Q

What is an opportunistic pathogen

A

Microbe that only causes disease if host defenses are compromised (Opportunist infections)

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5
Q

What is Virulence/Pathogenicity

A

The degree to which a given organism is pathogenic

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6
Q

What is asymptomatic carriage

A

When a pathogen is carried harmlessly at a tissue site where it causes no disease

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7
Q

What is the morphology of bacteria

A
  • Shape, size and aggregation e.g. cocci, rods, clumps, chains, pairs
  • Cell wall structure – Gram positive (Thick peptidoglycan layer – absorbs the dye) / Gram negative (Thin peptidoglycan layer + outer membrane with lipopolysaccharides – contribute to antibiotic resistance)
  • Other structures – capsule, spore, flagella, pili
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8
Q

The species name can sometimes tell us…

A

the disease that it causes

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9
Q

Features of bacterial growth

A
  • Agar medium (media), broth
  • Aerobic (growth in oxygen), anaerobic (growth without oxygen), facultative (either)
  • Shape of colony – diameter, edge, domes or flat
  • Effect on medium – haemolysis (Breakdown of RBC) – indicated by zone clearing around colonies (Streptococcus), pigment production (Pseudomonas – Green pigment), acid from sugar – detected using a pH indicator e.g. lactose (Escherichia coli) (Catalase test – ability to produce catalase, used to separate staph a from other cocci)
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10
Q

Examples of microbes

most viruses

A

-Most viruses
-E.coli, S.aureus etc
-Mycobacterium
tuberculosis
-Fungi (Candida albicans)
-Mycobacterium
leprae

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11
Q

What is the situation and doubling time of most viruses

A

They are cells with a doubling time <1hr

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12
Q

What is the situation and doubling time of E coli, S aureus etc

A

They are broth or solid media and the doubling time is 20- 30 mins

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13
Q

What is the situation and doubling time of Mycobacterium
tuberculosis

A

They are broth or media and the doubling time is 24 hours

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14
Q

What is the situation and doubling time of fungi (Candida albicans)

A

They are broth or media and the doubling time is 30mins

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15
Q

What is the situation and doubling time of Mycobacterium
leprae

A

They are broth or media and the doubling time is 2 weeks

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16
Q

What do some antibiotics do

A

Many groups, split on chemical structure and mode of action such as penicillins (Gram +ve) and tetracyclines (Gram +ve and -ve)

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17
Q

When antibiotic groups split what can they be
B or B

A

either bactericidal (Kill bacteria) or bacteriostatic (Inhibiting bacterial synthesis)

18
Q

What is the activity of antibiotics determined by

A

Activity determined by Minimum Inhibitory Concentration (MIC) – the lower the MIC the more active the drug
-lowest concentration of an antibiotic that can inhibit the visible growth of a particular microorganism

19
Q

When does antibiotic resistance develop

A

soon after antibiotics used in treatment

20
Q

What is the most common mechanism of resistance
Via E

A

Most common mechanism is via enzyme – beta-lactamase (ESBL produced by gram -ve)

21
Q

More on resistance

A
  • Widespread and often indiscriminate use has led to multiresistant organisms (selection)
  • Several bacteria now very resistant (MRSA) and difficult to treat
22
Q

To combat resistance there is now

A

greater reliance now on infection control and/or vaccines

23
Q

Bacterial genetic variation can be

A

mutation or gene transfer

24
Q

What happens during mutation

BDI

A
  • Base substitution
  • Deletion
  • Insertion
25
Q

What happens during gene transfer

A
  • Transformation via plasmid (Where bacteria take up free DNA from environment and incorporate it)
  • Transduction via bacteriophage (a virus) where DNA is transferred between bacterias
  • Conjugation via sex pilus transfer of DNA via direct contact
26
Q

What is the incidence and cost of healthcare associated infections

A
  • 300,000 HAIs per year in UK
  • Costs NHS £1 billion
27
Q

What is the affect of healthcare associated infections

A
  • Increasing problem in community settings such as nursing and residential homes
  • Major impact on mortality and morbidity increasing length of stay and cost
28
Q

What hygiene measures can be employed to reduce MRSA spreading

A
  • Clean hands before and after touching patients
  • Hands cleaned with soap and water, or alcohol gel or hand rub
  • Wear gloves and aprons when caring for a patient with MRSA
  • A patient with MRSA may be moved to a room on their own or into a separate area for people who have MRSA or other infections
29
Q

Infections and spread of MRSA (Staph A that’s resistant to antibiotics)

A

Infections- wounds/ bacteraemia (bacteria in blood)
Spread- hands/ formatted (surfaces)

30
Q

Figures and treatment of MRSA (Staph A that’s resistant to antibiotics)

A

Figures- 6000 cases of
bacteraemia/ yr
Treatment- Vancomycin
plus topicals if necessary

31
Q

Infections and spread of C.Diffile

A

Infections- Hospital-acquired
diarrhoea
(80% in >65 yr age group)
Spread- Hands and/or
environmental surfaces

31
Q

Figures and treatment of C diffile

A

Figures- 50,000
cases/yr
Treatment- Broad-spectrum antibiotics are cause – metronidazole or vancomycin plus fluids

32
Q

How to avoid contracting C diff

A
  • Wash hands thoroughly with soap and water before preparing/eating food, after handling raw food, after going to the toilet, after visiting hospitals and care homes
  • Take antibiotics only when necessary
  • Wash all dirty clothes, bedding, towels of infected patients in washing machine on hottest cycle. Clean toilet seats, flush handles, taps, after use with detergent and hot water
33
Q

What is chlamidiya trachomatis

A
  • Related to Chlamydophila pneumoniae and C.psittaci – Cause pneumonia
  • Obligate intracellular bacterium – Requires a host cell to replicate. BUT ARE NOT VIRUSES (Has cell wall and susceptible to antibiotics that target cell wall synthesis)
  • Produces Elementary (Infectious form) and Reticulate bodies (Replicative form) (EBs/RBs) can be seen by light microscope
  • Unique developmental cycle – EB taken up by host, transforms to RB to replicate  differentiate back to EB
33
Q

Chlamidiya trachomatis growth

A

Grown in tissue culture – as host cell needed. Divided into 3 groups:
* Serovars A-C = Trachoma
* Serovars D-K = NGU/ Conjunctivitis
* Serovars L1-L3 = Lymphogranuloma venereum

34
Q

What is chalmidiya trachomatis treated with

T A

A

Tetracycline, azithromycin

35
Q

What are the basic characteristic of viruses

A
  • DNA (Herpes) or RNA (HIV)
  • Require electron microscope to be seen (25 – 150nm)
  • Several morphological forms
  • No metabolic systems – requires tissue culture
36
Q

How do viruses grow

A
  • Many different types of cells used for culture – growth determined by cytopathic effect (Damage or changes occur in host cells) (CPE)
  • Growth recognised by unique appearance e.g. adenonvirus –grape-like clusters
  • Also by antibody neutralisation and erythrocyte agglutination
37
Q

What is the structure of viruses

A
  • Virion: the intact virus particle
  • Capsid: the protein coat
  • Capsomeres: the protein structural units which make up the capsid
  • Nucleic acid genome: either DNA or RNA
38
Q

What is protozoa

A
  • Eukaryote (3-2000um)
  • Contains nucleus, no cell wall
  • Unicellular, often in soil and water
  • Life cycle, trophozoite and cyst stages
38
Q

What lab tests are needed to diagnose a virus

A
  • CPE
  • Electron microscopy - morphology
  • Serology – antibody tests e.g. ELISA looking for >4 fold rise in titre
  • Molecular tests such as PCR and commercial DNA/RNA detection systems
39
Q

Bacteria and viruses

both detected using NAATs

A

Although both detected by NAATs (Nucleic acid amplification tests), otherwise different diagnostic approaches for bacteria and viruses

Pathology and microbiology (9 decks)

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