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Specific pathogens (bacteria and fungi) Flashcards

1
Q

Shigella and salmonella are

A

Intracellular pathogens

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2
Q

What is an important element of salmonella and shigella?

A

T3SS

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3
Q

Shigella

A

Gram negative rod

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4
Q

Salmonella

A

Gram negative rod

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5
Q

Neisseria meningitidis

A

Gram negative bacterium

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6
Q

Neisseria meningitidis virulence?

A

Lipopolysaccharide in the outer membrane> endotoxin responsible for septic shock and haemorrhage due to the destruction of red blood cell.

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7
Q

How does neisseria meningitidis avoid phagocytosis?

A

Polysaccharide capsule

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8
Q

How does neisseria meningitidis attach to nasopharynx?

A

Fibriae to mediate attachment to the epithelial cells of the nasopharynx.

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9
Q

How does neisseria meningitidis evade adaptive immune system?

A

Produce IgA protease to cleave IgA antibodies.

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10
Q

How does neisseria meningitidis inhibit complement?

A

Has a factor H binding protein - inhibit the alternative complement pathway.

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11
Q

Streptococcus pneumoniae

A

Gram positive cocci

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12
Q

How is strep pneumoniae haemolysis different in aerobic vs anaerobic conditions?

A

Alpha haemolytic under aerobic or beta haemolytic under anaerobic bacteria.

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13
Q

How does strep pneumoniae avoid phagocytosis?

A

Capsule inhibits phagocytosis by immune cells.

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14
Q

Streptococcus pyogenes

A

Gram positive coccus

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15
Q

Is streptococcus pyogenes part of the normal flora?

A

Yes

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16
Q

What does it haemolyse/ Lancefield group

A

Beta haemolytic.

Predominant species harbouring the Lancefield group A antigen

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17
Q

What does strep pyogenes cause?

A

Pharyngitis, cellulitis (strawberry rash), rheumatic fever and glomerulonephritis.

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18
Q

Strep pyogenes toxin?

A

Streptococcal pyrogenic exotoxin A (SpeA) superantigen

Responsible for the rash of scarlet fever and responsible for many of the symptoms of streptococcal toxic shock syndrome.

-

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19
Q

How does strep pyogenes evade DNA?

A

Secretes DNases to digest NET’s web of DNA

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20
Q

How does strep pyogenes evade complement?

A

C5a peptidases cleaves C5a, a potent neutrophil chemotaxin.

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21
Q

What does streptokinase do?

A

Enzymatically activates plasminogen’s plasmin to digest fibrin and other proteins.

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22
Q

What releases streptokinase?

A

Strep pyogenes

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23
Q

Streptococcus pharyngitidis is

A

Strep throat causing group A streptococcus (i.e pyogenes)

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24
Q

Where is staph aureus found?

A

Flora of the upper respiratory tract and on the skin

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25
Q

Is staph aureus found in the microbiota?

A

Not part of the normal microbiota: when it is prevalent here, it is a colonisation.

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26
Q

What is a commensal?

A

Colonises in around 30% of the human population

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27
Q

What does staph aureus cause?

A

Abscesses, surgical wound and burn infections, food poisoning

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28
Q

How can staph aureus evade phagocytosis?

A

Produces coagulase to clot plasma and coat bacterial cell

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29
Q

What toxins does staph aureus release? What do they cause?

A

TSST1 - toxic shock syndrome
Enterotoxin -gastroenteritis
(Superantigens)

Exfoliation toxin - acts as a protease that cleaves desmoglein in desmosomes - scalded skin syndrome

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30
Q

How does staph aureus evade the adaptive immune system?

A

IgG binding protein, binds to the Fc region of an antibody.

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31
Q

Clostridium difficile is .

A

Gram positive rod spore forming, anaerobic motile bacteria.

Prevalent in soil

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32
Q

Clostridium tetani

A

Common soil bacteria causes tetanus. Forms spores.

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33
Q

What toxins do C.diff produce? What effect?

A

Enterotoxin A and cytotoxin B, which disrupts the cytoskeletal signal transductions in the host by targeting and inactivating Rho family of GTPases.
Produce inflammation and diarrhea (bloody).

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34
Q

What is the tetanus toxin, what effect does it have?

A

Tetanospasmin (i.e tetanus toxins) responsible for symptoms of tetanus by blocking the release of inhibitor neurotransmitters glycine and gamma-aminobutyric acid at motor nerve endings - widespread activation of motor neurons and muscle spasms throughout the body.

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35
Q

What is the only natural reservoir of shigella?

A

Humans

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36
Q

Escherichia coli..

A

Gram negative anaerobic rod

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37
Q

Most e.coli are..

A

Harmless but some serotypes (EPEC, ETEC) etc can cause serious food poisoning

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38
Q

E.coli transmission

A

Fecal-oral transmission.

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39
Q

E.coli what colour on MacConkey agar?

A

Appears pink on MacConkey’s agar.

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40
Q

Shigella causes?

A

Dysentery and diarrhoea

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41
Q

Shigella toxin?

A

Shiga toxin, which is haemolytic similar to the verotoxin produce by enterohemorrhagic E. coli.

Shiga toxin can cause potentially fatal haemolytic-uremic symptoms. Secretes toxin via T3SS.

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42
Q

What causes typhoid fever?

A

Salmonella invading the bloodstream (typhoidal form) or spreads through body, invades organs, and secretes endotoxins (septic form - septic shock).

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43
Q

What do non-typhoidal salmonella cause?

A

Non-typhoidal serotypes cause a self-limiting GI disease by entering via M cells in the gastric mucosa.

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44
Q

What is EHEC? What does it cause?

A

Enterohemorrhagic E coli.

Responsible for outbreaks of bloody diarrhoea and haemolytic ureic syndrome (HUS: loss red blood cells, acute kidney failure, low platelets.)

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45
Q

What is ETEC? What does it cause?

A

Most common cause of traveller’s diarrhoea (enterotoxigenic E coli).

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46
Q

What is EPEC? What does it cause?

A

Enteropathogenic E coli.

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47
Q

What is EPEC? What does it cause?

A

Enteropathogenic E coli.

Causes diarrhoea.

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48
Q

EPEC infection results in

A

Infection results in a decrease of Cl-/HCO3- exchange and NHE3 via EPECs T3SS.

Increased permeability and water follows Cl- into the intestinal lumen.

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49
Q

What toxins to ETEC produce?

A

Heat labile enterotoxin (LT) and heat-stable enterotoxin (ST)-LT

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50
Q

How does heat labile enterotoxin act?

A

Acts (after entry and acidification in endosome) by raising cAMP levels through ADP ribosylation of the alpha subunit of the Gs protein, leading to constitutive activation of AC.

Stimulate activation of the CFTR channel - stimulating secretion of chloride ions into gut lumen - water follows.

Loss of electrolytes and water

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51
Q

What is enteric O antigen?

A

Represents the polysaccharide component of the gram negative LPS. (Enteric= natural habitat is the intestinal tract of humans and animals).

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52
Q

N gonorrhoeae

A

Gram negative coccus

Causes sexually transmitted genitourinary infection gonorrhoea, as well as septic arthritis, disseminated gonococcemia, gonococcal ophthalmia neonatorum.

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53
Q

How is N gonorrhoeae transmitted?

A

N gonorrhoeae may be transmitted through vaginal, oral or anal sex.

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54
Q

How does gonorrhoeae present differently in men and women?

A

Men are more often asymptomatic carriers of gonorrhoea.

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55
Q

After infection with N gonorrhoeae what happens?

A

After infection, the bacterium adheres to epithelial cells via type IV pili, at the mucosal site that is infected.

After adherence, the bacterium replicates into microcolonies - Stimulates release of cytokines and chemokine from host immune cells - recruitment of macrophages and neutrophils.

56
Q

How does N gonorrhoeae evade the immune response?

A

Opa proteins to bind receptors on immune cells and prevent immune response. These proteins undergo phase variation: frameshift result in different Opa genes being translated every time.

Via antigenic variation (rearrangement of the pilli gene)

57
Q

How is N meningitidis spread?

A

Through saliva and respiratory secretions during coughing, sneezing, kissing chewing on toys etc.

58
Q

How does sialyation produce evasion?

A

Sialylation of the lipopolysaccharide causes resistance to serum bactericidal activity.

Not seen as foreign

59
Q

How do super antigens work?

A

Superantigens/ enterotoxins are capable of indiscriminately activating T cells of the immune system causing system wide inflammation and other serious- potentially fatal- symptoms.

60
Q

How are spores formed? Why is it beneficial

A

Triggered by lack of nutrients, usually occurring in gram positive bacteria. It is a non-reproductive structure, enabling bacterium to survive long periods of environmental stress.

61
Q

What do salmonella and shigella turn MacConkey’s agar?

A

Doesn’t ferment lactose, yellow

62
Q

Gram negative rod grows on MacConkey;s agar, can ferment lactose but is unable to ferment indole from tryptophan…

A

Klebsiella

63
Q

What bacteria is more sensitive to beta lactam antibiotics?

A

Gram positive

64
Q

Acid fast stain bacteria stain pink with

A

Carbolfuschin (counter stain is blue).

65
Q

Most common bacteria to cause septic shock are…

A

Streptococcus pneumoniae, neisseria meningitidis and staphylococcus aureus.

66
Q

Gram positive rod grows aerobically and can form spores

A

Bacillus

67
Q

Does salmonella have an animal reservoir?

A

No animal reservoir

68
Q

What state does salmonella reach in humans?

A

Chronic carrier state in humans.

69
Q

Pseudomonas aeruginosa

A

Encapsulated, gram negative, rod shaped.

70
Q

What does pseudomonas cause?

A

Causes pneumonia, septic shock, UTI, necrotising enterocolitis, and haemorrhage and necrosis (e.g people with burns.)

71
Q

What is the most frequent coloniser of medical decides e.g catheters?

A

Pseudomonas aeruginosa

72
Q

This commensal microorganism has a rigid cell wall, and is capable of causing opportunistic infections of the mouth, gut and vagina. Infections are more common in people with HIV infection.

A

Candidas albicans

73
Q

Infection with this human pathogen, for which an effective vaccine is not available, is treated with chloroquine, artemesinin derivatives and doxycycline.

A

Malaria

74
Q

Which human pathogen is best described by the following statement?

Promastigotes of this protozooal parasite are transmitted to humans by the bite of the sandfly. The promastigotes enter macrophages where the parasite replicates. The most common clinical manifestation is non-healing raised skin lesions.

A

Leishmeniasis (infantum or chagasi or donovani)

75
Q

Which human pathogen is best described by the following statement?
This single celled pathogen causes a form of pneumonia in immune compromised individuals that is refractory to treatment with anti-bacterial antibiotics and used to be the leading cause of death in HIV/AIDS patients.

A

Pneumocystis jirovecii

76
Q

This filamentous fungus produces spores that can trigger a type III immune pathology in the lung of sensitized individuals due to the build up of antigen/antibody complexes that trigger complement activation.

A

Aspergillus clavatus

77
Q

In the small intestine, cholera toxin acts by

A

ADP-ribosylation of Gs which makes it constitutively active which results in phosphorylation and activation of Cl- channels

78
Q

A protein filament that facilitates the attachment between bacterial cells during conjugation.

A

Sex Pilus

79
Q

A polymer of glycerol phosphate or ribitol phosphate that is present in the cell wall of Gram positive bacteria.

A

Teichoic acid

80
Q

A non-reproductive structure formed by some Gram positive bacteria, that enables the bacterium to withstand long periods of environmental stress.

A

Endospore

81
Q

What is a cause of blood-stained sputum?

A

Streptoccocus pneumoniae, hameophilus influenzae, staphylococcus pneumoniae

82
Q

Which one of the following bacteria grows on MacConkeys agar plates and ferments lactose?

A

E. Coli or Klebsiella

83
Q

“A Gram negative coccus that resides in the nasopharyngeal tract of humans. After colonising the nasopharynx, bacteria can cross the nasopharyngeal epithelium to enter the blood stream where the bacteria proliferate and, if unchecked, can lead to a fatal septicaemia”

A

Neisseria meningitidis

84
Q

Staphylococcus epidermidis is best described as a:

A

Opportunist pathogen, is part of the flora on the skin but can become pathogenic infecting artificial heart valves and prosthetic limbs, catalase positive, coagulase negative, Gram-positive

85
Q

Which bacteria grows as a Gram positive obligate anaerobe that forms spores?

A

Clostridium

86
Q

Which cells does LPS primarily act on?

A

Macrophages

87
Q

How is LPS released by bacteria?

A

Not released, integral part of cell wall

88
Q

How is tetanus treated?

A

Treated with tetanus antitoxin + benzodiazepines (prevent spasm)

89
Q

How is pneumonia transmitted (strep pneumoniae)?

A

Pneumococcal infections are not considered communicable (no animal resevoir), usually part of normal flora and cause disease when predisposing factors occur

90
Q

Which Gram positive bacterium secretes an exotoxin that binds irreversibly to receptors in the spinal cord and brain stem and blocks neurotransmission by cleaving membrane proteins involved in neuroexocytosis?

A

Clostridium tetani or botulinum

91
Q

What is fungi?

A

Eukaryotic organisms in the kingdom of fungi, separate from other eukaryotic life. This is because of the rigid chitin cell walls. Fungi either grow unicellularly or as hyphae.

92
Q

What is athlete’s foot?

A

Caused by a number of different fungi.

Form of fungal infection of the skin - fungi inhabit dead layers of skin and digest keratin.

Transmitted through direct and indirect contact, particularly in warm wet environment

93
Q

What causes thrush/ candidiasis ?

A

Candida albicans

94
Q

Where is candida albicans found?

A

Yeast that is a normal part of the mouth, gut and vaginal microbiome. Very common in untreated HIV, often appearing before any other opportunistic pathogens.

95
Q

When may candida infections become problematic?

A

If the normal micro biome is disrupted e.g following antibiotic treatment, candida infections can be a problem.

96
Q

How can candidiasis progress?

A

Can develop into an invasive disease unexplained fever that is unresponsive to antibiotics, multiple non-painful cutaneous lesions, yeast in urine samples, iv catheter grows yeast.

97
Q

What is ringworm/ dermotrophytosis?

A

Fungal infection of the skin. Can be caused by many forms of fungi.

98
Q

How are fungal infections implicated in AIDS?

A

Fungal infections are much more common and have more potential to become problematic in individuals who are immunodeficient either from treatment, infection by HIV or genetic causes.

99
Q

What are yeasts?

A

Fungi that grow as single cells

100
Q

What is pneumocystis?

A

Pneumonia caused by pneumocystis defined AIDS as a syndrome at first.

Can be found in the lungs of healthy people, but is a classic opportunistic pathogen that causes pneumonia only in the immunocompromised.

Non-productive cough, weight loss, night sweats, chest X ray shows widespread infiltrates

101
Q

What is cryptococcus? What does it cause?

A

Cryptococcus: free living encapsulated yeast.

Infection of immunocompetent patients is very rare. Usually in AIDS patients. Causes self-limiting pneumonia, large fungal mass, skin infections, meningitis. Treatment to eradicate is essential in case of CNS involvement

102
Q

How does cryptococcus present in vitro?

A

Gives white mucoid colonies on sabour and dextrose plates.

103
Q

What is aspergillus?

A

Filamentous fungi can cause many symptoms

104
Q

What does aspergillus cause?

A

Bronchopulmonary aspergillosis in allergic individuals
Aspergilloma in lung cavities
Invasive aspergillosis in neutropenics and severely immunocompromised patients. This has a high mortality rate.

105
Q

What do antifungals include?

A

Fluconazole, Nystatin, Amphotericin B

106
Q

How does cryptococcus evade phagocytosis?

A

Capsule

107
Q

How is cryptococcus stained?

A

India ink exclusion

108
Q

How can candida grow?

A

Yeast, pseudohyphae and hyphae

109
Q

What bacterium is TB?

A

Mycobacterium

110
Q

Does mycobacterium gram stain? How is it stained?

A

No, carbol fuchsin (pink) with methylene blue counterstain

111
Q

How does mycobacterium present under the microscope and why?

A

Unicellular with branched rods cells are seen in a cording pattern, due to the presence of fatty acids in the cell wall that stick together.

112
Q

What are unique features of the Mtb cell wall?

A

Lipoarabinomannan (LAM)

Mycolic acids (MA)

113
Q

What is LAM in Mtb cell wall?

A

Lipoarabinomannan (LAM): consists of 2 sugars, lipid portion which associates with cell membrane.

114
Q

What is MA in Mtb cell wall?

A

Mycolic acids (MA): negative charge to outer membrane, associates with glycolipids, acid found in the middle, long acyl chain at one end associates with lipid (fatty acid)

115
Q

What happens to 5% that cannot contain primary Tb infection?

A

Primary disease

116
Q

What is a primary complex (TB)?

A

Ghon focus in combination with hilar or paratracheal lymphadenopathy

117
Q

What is post primary/secondary disease (TB)?

A

Occurs in 5% of primary infection patients, arises from reactivation of dormant TB in organs - often decades after initial infection when host immune defence weakened

118
Q

What cytokines are important in a TB infection?

A 
IL-12 (activating Th1)
IFN gamma (generated intracellular pathogen response)
TNF alpha (recruits CD4+ for granuloma)
119
Q

What cytokine drives macrophage fusion (TB granuloma)?

A

IFN gamma

120
Q

What is the vaccine for TB?

A

BCG

121
Q

What is the test for TB?

A

Mantoux (tuberculin) test as example: Inject tuberculin or PPD into skin

A person who has been exposed to the bacteria is expected to mount an immune response in the skin containing the bacterial proteins. The response is a classical example of delayed-type hypersensitivity reaction (DTH), a type IV of hypersensitivities

122
Q

What type of vaccine is BCG?

A

Live attenuated mycobacterium bovis

123
Q

What is the most likely cause for the formation of the granuloma?

A

Delayed type hypersensitivity immune response to MTb

124
Q

What is the nature of the giant cells?

A

Macrophage fusion

125
Q

A positive Mantoux (tuberculin) test alone is not proof of recent MTb infection

A

True

126
Q

Up to a third of the world’s population has had a sub-clinical MTb infection

A

True

127
Q

There are sparse or no detectable acid-fast bacilli in the granuloma

A

True

128
Q

The lesions are rich in acid-fast bacilli

A

False

129
Q

It can be very difficult to isolate MTb in sputum from such an infected individual

A

True

130
Q

Do granulomas give rise to lung cancer?

A

No

131
Q

Epithelioid cells are due to metaplasia of epithelium

A

False

132
Q

Is BCG is effective as a vaccine against adult pulmonary tuberculosis

A

No

133
Q

Is BCG vaccination dangerous in immunodeficient patients?

A

Yes

134
Q

Is BCG effective against systemic spread of MTb in infants

A

Yes

135
Q

Non-virulent mycobacteria are common in the environment

A

True

136
Q

Maximal inflammation at a Mantoux test site?

A

72 hours

137
Q

What bacteria has round colonies and distinctive colour?

A

S.Aureus

Pathology (21 decks)

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