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medical microbiology > Microbiology of Cystic Fibrosis > Flashcards

Microbiology of Cystic Fibrosis Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

How are bacterial organisms kept to a minimum in the lung?

A

by non-inflammatory responses such as the mucociliary escalator, coughing, alveolar macrophages, defensins, and surfactant.

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2
Q

Which responses are required in infection of the lung?

A

full-scale immuno-defences, white cells and their products

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3
Q

Which particular inflammatory response is destructive to native cells as well as infecting bacteria

A

white cell oxidation products

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4
Q

What is the result of lung infection in CF patients?

A

patients-complex series of events leads to chronic colonisation of the lungs by bacteria capable of surviving the harsh conditions.

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5
Q

What is the primary reason for the seriousness of infection in lung for CF patients?

A

Mucociliary clearance is stopped, bacteria are not cleared and the immune defences are activated.

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6
Q

What does the thick mucus, DNA, white cells, bacteria and their exo-products form?

A

a complex sputum.

A vicious circle follows with lack of clearance of bacteria leading to inflammation, more white cells and thicker sputum.

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7
Q

What is the primary cause of morbidity and mortality?

A

Inflammation as a result of the body’s response to the presence of bacteria

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8
Q

In CF, what is the role of the bacteria?

A

the presence of bacteria is the trigger not the direct agent of disease.

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9
Q

what was the first pathogen identified as associated with lung disease in CF patients?

A

Staphylococcus aureus

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10
Q

What is the most important pathogen of CF lung disease infecting approximately 60% of the CF population?

A

Pseudomonas aeruginosa

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11
Q

Where does it live? Humans ingest the organism from which sources?

A

It lives in water and soil and can be found on vegetables and living plants as well as in water taps, drains and other wet surfaces.

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12
Q

Why is the binding ability for Pseudomonas aeruginosa increased in the CF respiratory epithelium?

A

partly attributable to dehydration of respiratory secretions resulting in impairment of the muco-ciliary system, which normally rids the lungs of inhaled particles and bacteria.

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13
Q

What is prototrophic?

A

Doesn’t need a specific growth requirement

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14
Q

patients eventually develop what kind of chronic infection?

A

chronic infection with an unusual phenotype of Pseudomonas aeruginosa referred to as mucoid

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15
Q

How does The pseudomonad attach in a mucoid infection?

A

approaches the cell very slowly ,slows down further and then attaches itself to the cell or another organism that is present.

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16
Q

After attachment, what does it produce?

A

an exopolysaccharide or alginate, which coats the organism making it “slimy” or mucoid.

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17
Q

The mucoid exopolysaccharide or alginate produced by these pseudomonads in chronic infection of the CF lung, may have give the microbe what advantage?

A

may shield the organism from the immune system.

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18
Q

Such mucoid strains secrete less of what, than non-mucoid strains?

A

the proteases (proteinases) and toxins

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19
Q

They grow more slowly in what?

A

biofilms ( slimy coat )in the airways of these patients, making a penetration barrier, thus accounting for the high resistivity.

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20
Q

What is seldom isolated in human infections and is rarely found as a pathogen in non-CF patients?

A

Burkholderia cepacia

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21
Q

Where does it live?

A

occurs in the environment(soil)
They are occasionally isolated from samples obtained from food stores, salad bars or greenhouses and are frequently auxotrophic when isolated from CF sputum.

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22
Q

What does it infect way more often than humans?

A

are pathogens for vegetables.

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23
Q

When did this species emerged as a pathogen?

A

about 20 years ago

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24
Q

Where and why has it become an issue?

A

endemic in some large CF centres due to cross-infection during social activities and in some cases, CF clinic appointments where they meet fellow CF sufferers they have known for a long period.

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25
Q

How many distinct clinical patterns of B.cepacia infection in CF have been observed

A

three

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26
Q

Which pattern is seen as most mild?

A

Chronic asymptomatic carriage of B.cepacia either alone or in combination with Pseudomonas aeruginosa.

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27
Q

What clinical presentation does the progressive pattern have?

A

Progressive deterioration over many months with recurrent fever, progressive weight loss and repeated hospitalisation.

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28
Q

Which pattern is usually fatal?

A

Rapid deterioration in previously mildly affected patients.

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29
Q

What is the true reason for the rapid decline?

A

it is true infection and not inflammation
Uniquely there is dissemination from the focus of the infection into the bloodstream

30
Q

Is B.cepacia or Pseudomonas aeruginosa more resistant to antibiotics?

A

B.cepacia is more resistant to antibiotics than Pseudomonas aeruginosa and resistance develops very easily.

31
Q

What is the role of Respiratory viruses in CF lung disease?

A

responsible for some of the increase of severity of the pulmonary disease in CF, due to the damage caused during a viral episode, leaving patients more susceptible to secondary colonization and infection with bacteria.

32
Q

How is Pulmonary function affected?

A

may be decreased by up to 30% for as long as one month during respiratory viral infections.

33
Q

Which bacteria are members of the normal flora in the upper respiratory tract(pharynx/mouth) and have a secondary role in CF lung disease?

A

Haemophilus influenza

34
Q

On isolation from CF patients, what is found?

A

most are non-capsulated and belong to different types, several different strains may co-exist in the respiratory tract.

35
Q

What is there role in disease?

A

No immune deficiency to these bacteria has been described in these patients but due to the frequent use of Ampicillin and other beta lactam antibiotics, beta laclamase producing strains (produce an enzyme to break down the antibiotic) are often isolated.

36
Q

What is Aspergillus fumigatus and where can be found?

A

The aspergilli are ubiquitous fungi and can be isolated from dead plant and animal substrates or from soil or air.

37
Q

where is Pathogenic Aspergillus fumigatus more often found?

A

is more often present in mouldy hay, grain and composting plant debris as well as warm, damp houses and badly stored foodstuffs.

38
Q

It is commonly isolated from the sputum of patients, but what % develop disease?

A

5-10% of them developing acute bronchopulmonary aspergillosis.

39
Q

what is this condition is treated with?

A

corticosteroids as in other patients and sometimes also antifungal agents.

40
Q

what other microbes have secondary roles?

A

such as Mycobacterium sp.( NOT myco.TB),Stenotrophomonas maltophilia, Alcaligenes

41
Q

which is a non-selective general purpose medium employed for the growth of pathogenic and non pathogenic bacteria?

A

Blood Agar base.
With added blood (usually at 7%) the medium is not only enriched, but becomes suitable for the determination of the typical haemolytic reactions important in helping to identify Streptococci and Staphylococci.

42
Q

which medium is able to support the growth of pathogenic gram positive cocci as well as coliforms and Pseudomonads?

A

MacConkey Agar

43
Q

what other diagnostic indicators does it provide?

A

bile tolerance, colony morphology and chromogenesis(colour)
usually used in parallel with other media such as Blood Agar.

44
Q

what is the Cepacia media used at Glan Clwyd for?

A

The medium selectively supports growth of B.cep from clinical samples whilst inhibiting many(but not all) of the organisms frequently found in the respiratory secretions of patient with CF

45
Q

how does it selectively isolate B.cepacie?

A

selectively isolates B.cepacie by using Polymixin B together with Ticarcillin as selective agents.

46
Q

why are antibiotics used in media?

A

antibiotics can be used in media for isolation purposes as well as treatment for patients with infection.

47
Q

which antibiotics can be used to help selectively isolate B.cepacie?

A

Nearly all strains appear resistant to Ticarcillin, Carbenicillin and Aminoglycosides.(Many isolates also show resistance to Chloramphenicol, Trimethoprim and Ceftazidine).

48
Q

what medium is used for the cultivation of Fungi and Yeasts?

A

Sabouraud Dextrose Agar .

49
Q

what properties help fungi and yeast grow instead of bacteria?

A

It has an acid PH(yeast and fungi are not as sensitive as bacteria and can tolerate pH levels less than 6),and contains Chloramphenicol (another antibiotic) which inhibits the quicker growing bacteria and allows the slower growing yeasts and fungi to flourish.

50
Q

how to identify Staphylococci?

A

Colonial appearance on solid media
Gram Film
Coagulase
DNAse

51
Q

how to identify Pseudomonas?

A

Colonial appearance on solid media
Gram film
Oxidase

52
Q

what colour do they appear?

A

greenish-blue colour (due to the production of pyocyanin and the yellow green fluorescent pigment fluorescin)

53
Q

how long are Burkholderia cepacia incubated for?

A

Incubation should be up to 2 days at 37o followed by a further 6 days at 30o.

54
Q

what colour do they appear?

A

are purplish-pink on the media used by Glan Clwyd.

55
Q

how else do you identify them on media?

A

They are gram negative, motile, and the great bulk are oxidase positive, but be careful as some strains are oxidase negative.

56
Q

how to distinguish cultures that cannot be distinguished by morphology and cultural characters?

A

may exhibit distinct differences in their biochemical reactions

57
Q

Any organism suspected of being B.cepacia may be identified further with biochemical reactions by the use of what?

A

an API or Analytical Profile Index. This system is used as an identification system. There are a selection of “API Strips” depending on the type of organism you wish to identify.

58
Q

what is API 20E?

A

is the standardised identification system for Enterobacteriacae and other non-fastidious, Gram negative rods such as cepacia. It uses 21 miniaturised biochemical tests and a database.

59
Q

what do the microtubes contain?

A

dehydrated substrates which are inoculated with a bacterial suspension that reconstitutes the media .

60
Q

During incubation, what changes can be seen?

A

metabolism produces colour changes that are either spontaneous or revealed by the addition of reagents.

61
Q

how are results obtained?

A

The reactions are read according to the Reading Table and the identification is obtained by referring to the API identification software.

62
Q

how to identify Haemophilus influenzae?

A

Colonial appearance on solid media
Resistant to Bacitracin
X and V Factors

63
Q

how to identify yeasts?

A

Colonial appearance on solid media, production of a germ tube, possible further I.D. using sugar fermentation tests (API)

64
Q

how to identify fungi?

A

Colonial appearance on solid media and microscopy for further I.D.

65
Q

Organisms which are identified as pathogenic undergo a series of tests to provide what?

A

a sensitivity pattern for use when treating the patient.

66
Q

how each organism prepared for sensitivity tests?

A

Each organism is suspended in 4ml. nutrient broth using a 1ul loopful of colony, 10 ul of which is inoculated onto the test agar,
in this case an iso-sensitest agar,

67
Q

what is an iso-sensitest agar

A

one which is carefully constructed to give a reproducible, semi-defined medium in which undefined components are kept to a minimal level, allowing the growth of the great majority of micro-organisms without further supplementation

68
Q

what is then do with this inoculum?

A

This inoculum is then spread all over the plate using a cotton-tipped swab and the required range of antibiotics placed onto the agar surface. These plates are then incubated overnight

69
Q

how are results recorded?

A

the results recorded by comparing to a known strain of the relevant organism.

70
Q

Gram positive organisms such as Staphylococci are tested against which antibiotics?

A

Penicillin, Erythromycin, Gentamycin, Ciprofloxacin, Tetracycline,
Fusidic Acid and Methicilin.

71
Q

Pseudomonas organisms are tested against which antibiotics?

A

Gentamycin, Tazobactam, Ciprofloxacin and Ceftazidine.

72
Q

Haemophilus sp. are tested against which antibiotics?

A

Amoxicillin, Tetracycline, Erythromycin, Trimethoprim, Augmentin and Ciprofloxacin.

medical microbiology (29 decks)

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