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infectious diseases > Bacterial infection > Flashcards

Bacterial infection Flashcards

1
Q

BACTERIAL disease by PATHOGEN (5)

A
  • Gram positive
  • Gram negative
  • Mycobacteria
  • Intracellular bacteria
  • Spirochaetes
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2
Q

Bacterial infections: Overview

A

Human and bacteria = symbiotes (definition: an organism in partnership with another, such that each benefit from them being together)

Bacterial disease results from a breach of the measures that limit bacteria to their ‘normal’ roles.

When treating infections we should therefore consider what factors may have aided pathogenesis e.g. malnutrition, ‘barrier’ breech by cancer, plastic, immunosuppression.

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3
Q

Bacteria: Definition

A

Prokaryotic micro-organism without a membrane bound nucleus.

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4
Q

Classification of bacteria (3)

A
  • Gram stain (positive/negative)
  • Shape (cocci, bacilli, spirochaete)
  • Aerobes/anaerobes
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5
Q

Gram stain: Definition

A

Staining technique:

Gram POSITIVE: thick peptidoglycan wall = PURPLE
Gram NEGATIVE: thin peptidoglycan wall = PINK

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6
Q

Bacteria: Shape (Morphology)

A
  • Cocci: round
  • Bacilli: rod-shaped
  • Spirochaete: spiral
  • Coccobacillio: intermediate between rods and cocci
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7
Q

Bacteraemia: Defintion

A

Bacteria circulating in the blood stream

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8
Q

Bacteriocidal: Definition

A

Kills bacteria both in and out of the replication cycle.

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9
Q

Bacteriostatic: Definition

A

Stops replication without killing existing bacteria.

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10
Q

Capsulate bacteria: Definition

A

Bacteria with thick outer capsule.

These are destroyed in the spleen. Following splenectomy (or splenic infarction e.g. sickle cell anaemia) there is an increased risk of infection by capsulate bacteria and prophylactic vaccination should be offered.

Examples of capsulate bacteria: H. influenzae, Neisseria meningitis, strep pneumoniae

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11
Q

Commensal bacteria: Definition

A

An organism that lives in/on the host without causing harm.

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12
Q

Endotoxin: Definition

A
  • Lipopolysaccharide complex
  • Found on the outer membrane of Gram Negative bacteria
  • Can elicit an inflammatory response
  • Activates complement via the alternative pathway
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13
Q

Enterotoxin: Definition

A

Exotoxin that targets the gut.

Example: Clostridium difficile toxin

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14
Q

Exotoxin: Definition

A
  • Toxins secreted by bacteria.
  • They act at a site distant from bacterial growth.
  • Production of an exotoxin can determine virulence.
  • Example: botulinum, tetanus, diptheria, shiga toxins,
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15
Q

Flagella: Definition

A

Tail-like appendage that moves to propel the bacterium.

Example: Helicobacter pylori

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16
Q

Nosocomial: Definition

A

Acquired in a hospital/healthcare setting.

17
Q

Obligate intracellular: Definition

A

Bacteria that can only survive in host cells, therefore induce a cell-mediated immune response.

They will not grow on standard culture media.

18
Q

Ziehl-Neelson stain: Definition

A

It is a type of differential bacteriological stain used to identify acid-fast organisms, mainly Mycobacteria. Acid fast organisms are those which are capable of retaining the primary stain when treated with an acid (fast=holding capacity).

Mycolic acid in the cell wall of mycobacteria resist Gram staining but will appear red with acid fast techniques (= acid-fast stain)

19
Q

Aerobes vs. Anaerobes: Definition

A

An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. In contrast, an anaerobic organism (anaerobe) is any organism that does not require oxygen for growth.

  • Obligate aerobes: only grow in the presence of oxygen
  • Obligate anaerobes: only grow in the absence of oxygen
  • Faculative anaerobes: can survive in either environment
  • Microaerophilic bacteria: prefer low oxygen concentrations
20
Q

Bacteria: Gram positive (4)

A
  • Staphylococci
  • Streptococci
  • Enterococci
  • Clostridium species
21
Q

Bacteria: Gram negative (11)

A
  • Neisseria
  • Helicobacter pylori
  • E. coli
  • Shigella
  • Campylobacter jejuni
  • Klebsiella pneumoniae
  • Pseudomonas aeruginosa
  • H. influenzae
  • Bordetella pertusis (Whooping cough)
  • Vibrio cholerae (cholera)
  • Yersinia pestis (plague)
22
Q

Bacteria: Mycobacteria (2)

A
  • M. tubercolosis

- M. leprae

23
Q

Bacteria: Intracellular bacteria (3)

A
  • Chlamydia
  • Rickettsia (rickettsial disease)
  • Coxiella burnetti
24
Q

Bacteria: Spirochaetes (3)

A
  • Borrelia burgdoferi (Lyme disease)
  • Treponema (syphillis)
  • Leptospira (Weil’s disease)
25
Q

Tuberculosis: Definition

A

Tuberculosis (TB) is an infection caused by Mycobacterium tuberculosis that most commonly affects the lungs. Understanding the pathophysiology of TB can be difficult - the key is to differentiate between primary and secondary disease.

26
Q

Tuberculosis: Primary tuberculosis

A

A non-immune host who is exposed to M. tuberculosis may develop primary infection of the lungs. A small lung lesion known as a Ghon focus develops. The Ghon focus is composed of tubercle-laden macrophages. The combination of a Ghon focus and hilar lymph nodes is known as a Ghon complex

In immunocompotent people the intially lesion usually heals by fibrosis. Those who are immunocompromised may develop disseminated disease (miliary tuberculosis).

27
Q

Tuberculosis: Secondary (post-primary) tuberculosis

A

If the host becomes immunocompromised the initial infection may become reactivated. Reactivation generally occurs in the apex of the lungs and may spread locally or to more distant sites. Possible causes of immunocomprise include:

  • Immunosuppressive drugs including steroids
  • HIV
  • Malnutrition
28
Q

Tuberculosis:

A

The lungs remain the most common site for secondary tuberculosis.

Extra-pulmonary infection may occur in the following areas:
- Extra-thoracic lymph nodes
- Intra-thoracic lymph nodes
- Pleural 
- Gastrointestinal 
- Spine 
- Central nervous system 
(tuberculous meningitis - the most serious complication)
- Vertebral bodies (Pott's disease)
- Cervical lymph nodes (scrofuloderma)
- Renal
- Genitourinary 
- Miliary
29
Q

Tuberculosis: Drug therapy

standard therapy for active tuberculosis

A

The standard therapy for treating active tuberculosis is:

Initial phase - first 2 months (RIPE)

  • Rifampicin
  • Isoniazid
  • Pyrazinamide
  • Ethambutol (the 2006 NICE guidelines now recommend giving a ‘fourth drug’ such as ethambutol routinely - previously this was only added if drug-resistant tuberculosis was suspected)

Continuation phase - next 4 months

  • Rifampicin
  • Isoniazid

Patients with meningeal tuberculosis are treated for a prolonged period (at least 12 months) with the addition of steroids.

30
Q

Tuberculosis: Drug therapy

for latent tuberculosis

A

NICE now give two choices for treating latent tuberculosis:

  • 3 months of isoniazid (with pyridoxine) and rifampicin, or
  • 6 months of isoniazid (with pyridoxine)
31
Q

Tuberculosis: Drug therapy - DOT

A

Directly observed therapy with a three times a week dosing regimen may be indicated in certain groups, including:

  • homeless people with active tuberculosis
  • patients who are likely to have poor concordance
  • all prisoners with active or latent tuberculosis
32
Q

Tuberculosis: Screening

A

The Mantoux test is the main technique used to screen for latent tuberculosis. In recent years the interferon-gamma blood test has also been introduced. It is used in a number of specific situations such as:

  • the Mantoux test is positive or equivocal
  • people where a tuberculin test may be falsely negative (see below)

Mantoux test
0.1 ml of 1:1,000 purified protein derivative (PPD) injected intradermally
result read 2-3 days later

33
Q

Tuberculosis: Diagnostic tests

A

Latent TB:

  • Tuberculin skin test (TST)
  • Interferon-gamma release assays (IGRAs)

(Neither test can diagnosis/exclude active disease + immunosuppressed states reduce the sensitivity of both tests)

Active pulmonary TB:

  • CXR
  • Sputum smear
  • Sputum culture
  • Nucleic acid amplification test (NAAT)

Extra-pulmonary TB

  • Investigate for coexisting pulmonary disease
  • Aspiration or biopsy (obtain material)
  • NAAT can be carried out o
34
Q

Tuberculosis: Pathology

A
  • The macrophages often migrate to regional lymph nodes, the lung lesion plus affected lymph nodes is referred to as a Ghon complex.
  • This leads to the formation of a granuloma which is a collection of epithelioid histiocytes.
  • There is the presence of caseous necrosis in the centre.
  • The inflammatory response is mediated by a type 4 hypersensitivity reaction.
  • In healthy individuals the disease may be contained, in the immunocompromised disseminated (miliary TB) may occur.

Diagnosis: Waxy membrane of mycobacteria prevents binding with normal stains. Ziehl - Neelsen staining is typically used. Culture based methods take far longer.

35
Q

Tuberculosis: Rifampicin

  • Mechanism of action
  • Side effects
A
  • mechanism of action: inhibits bacterial DNA dependent RNA polymerase preventing transcription of DNA into mRNA
  • potent liver enzyme inducer
  • hepatitis, orange secretions
  • flu-like symptoms
36
Q

Tuberculosis: Isoniazid

  • Mechanism of action
  • Side effects
A
  • mechanism of action: inhibits mycolic acid synthesis
    peripheral neuropathy: prevent with pyridoxine (Vitamin B6)
  • hepatitis, agranulocytosis
  • liver enzyme inhibitor
37
Q

Tuberculosis: Pyrazinamide

  • Mechanism of action
  • Side effects
A
  • mechanism of action: converted by pyrazinamidase into pyrazinoic acid which in turn inhibits fatty acid synthase (FAS) I
  • hyperuricaemia causing gout
  • arthralgia, myalgia
  • hepatitis
38
Q

Tuberculosis: Ethambutol

  • Mechanism of action
  • Side effects
A
  • mechanism of action: inhibits the enzyme arabinosyl transferase which polymerizes arabinose into arabinan
  • optic neuritis: check visual acuity before and during treatment
  • dose needs adjusting in patients with renal impairment
39
Q

Drug-resistant TB

A

Drug resistance may be:

  • To any single agent
  • Multidrug resistant TB
  • Extensively drug resistant TB

NAAT should be requested for all patients with risk factors for drug resistance, this includes:

  • Contact with drug resistant disease
  • Birth/residence in country where >5% new cases are drug resistant

infectious diseases (8 decks)

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