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Pathology > Bacteria > Flashcards

Bacteria Flashcards

1
Q

Which one of the following structures is NOT found in Gram-positive cell walls?

A

Lipopolysaccharide

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2
Q

MacConkey’s Agar plates are

A

A selective media for the growth of lactose fermenting gram negative bacteria

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3
Q

A positive result in which of the following bacteria diagnostic tests would generate oxygen?

A

Catalase

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4
Q

Which Lancefield Group does the bacterium Streptococcus pyogenes belong to?

A

Group A

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5
Q

What colour does Streptococcus pyogenes stain in a Gram stain?

A

Purple

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6
Q

What result will Streptococcus pyogenes give in a catalase test?

A

Negative

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7
Q

Streptococcus pyogenes growth on blood agar plates reveals…

A

Beta (clear) haemolysis

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8
Q

TSST-1 is a bacterial toxin that can cause systemic effects on the host leading to toxic shock syndrome. It is secreted by..

A

Staphylococcus aureus

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9
Q

Which of the following bacterial pathogens can evade the host immune response by secreting Protein A, which binds to the Fc portion of IgG molecules?

A

Staphylococcus aureus

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10
Q

A bacterial cell has a typical diameter of…

A

1 micrometre

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11
Q

The bacterial adhesins of Neisseria gonorrhoeae and Escherichia coli are in the form of..

A

Pili

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12
Q

A sputum sample is cultured, and a Gram-positive encapsulated bacterium is cultured from the sample that is catalase negative and Optichin sensitive. What is the most likely identity of this bacterium?

A

Streptococcus pneumoniae

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13
Q

Streptococcus pneumoniae bacterium’s polysaccharide capsule is important in the pathogenesis of this disease presentation because..

A

It prevents phagocytosis by macrophages and neutrophils

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14
Q

A 15-day old female infant (birth weight 2.6kg) presents with fever and respiratory failure. A cloudy cerebrospinal fluid sample from the patient showed 1042 cells/mm (normal range = 0-5 cells/mm ), with a predominance of neutrophils (83%), CSF protein of 435 mg/dL (normal range = 15-60 mg/dL), and glucose < 10 mg/dL (normal range = 50-80 mg/dL).

The infant’s blood and cerebrospinal fluid (CSF) cultures were positive for Gram-negative cocci that were oxidase positive. The neonate was hospitalized, needing mechanical ventilation and vasoactive drugs, and received 21 days treatment with penicillin.

A

Neisseria meningitidis

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15
Q

Bile salts used on

A

Gram negative bacilli

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16
Q

Catalase test identifies

A

Catalase enzyme present? Staphylococcus (+) or Streptococcus (-)

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17
Q

Catalase test method

A

Drop of H2O2 on sample, O2 release (fizzing and bubbling) is a positive result

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18
Q

Coagulase test identifies

A

S.aureus (+), coagulase negative staphylococcus

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19
Q

Coagulase test process

A

The two saline drops are emulsified with the test organism. A drop of plasma is placed on the inoculated saline drop corresponding to test, and mixed well, then the slide is rocked gently for about 10 seconds.

Clumping gives positive result

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20
Q

H2S method identifies

A

Salmonella (+), Shigella (-)

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21
Q

H2S method

A

Shows if bacteria can convert sodium thiosulphate to H2S.

Black centres (positive)

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22
Q

Haemolysis test

A

The types of haemolysis produced by different bacteria are described as alpha, beta or ‘gamma’, if bacteria lyses erythrocytes

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23
Q

If the bacteria cannot grow on bile salts, what type is it?

A

Haemophilus

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24
Q

Haemolysis test shows

A

If alpha do optochin test, if beta do Lancefield typing

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25
Q

Optochin test identifies

A

Used on alpha haemolysing streptococcus

Sensitive - S.pneumoniae
Resistant - viridans, S.mutans

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26
Q

Lancefield typing identifies

A

A- S.pyrogens
B - S.Agalactiae
D - Enterococcus, S.bovis

27
Q

Lancefield typing shows

A

Classifies catalase-negative, beta haemolysing, Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls.

Organised into groups
A,B,C,D…

28
Q

Oxidase test identifies what cocci

A

Cocci - Neisseria (+), Non pathogenic (-)

29
Q

Oxidase test identifies what bacilli

A

Bacilli - (+) Pseudomonas

30
Q

Oxidase test shows

A

Determine if a bacterium produces certain cytochrome c oxidases.

The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced.

Oxidase-positive bacteria possess cytochrome oxidase (this oxidases the test strip)

31
Q

How is lactose fermentation tested?

A

MacConkey agar

If the bacterium can ferment lactose
(+) red
(-) yellow/clear

32
Q

Lactose fermentation shows

A

Tested on gram negative bacilli

If positive do indole test, if negative do oxidase test

33
Q

Indole test identifies

A

(+) Escherichia coli

(-)Klebsiella

34
Q

Indole test

A

Determine the ability of the organism to convert tryptophan into indole

A positive result is shown by the presence of a red or red-violet color in the surface alcohol layer of the broth. A negative result appears yellow

35
Q

Urease test identifies

A

(+) Proteus, negative shigella or salmonella (do H2S)

36
Q

Urease test

A

Detects secretion of the urease enzyme, which catalyzes the conversion of urea to ammonia and carbon dioxide.

Yellow (-) to red (+).

37
Q

Bordetella Pertussis

A

Gram negative
Whooping cough

Pertussis toxin

B unit binds membrane receptors on upper respiratory tract cells and pancreas, allowing A subunit to catalyse ADP ribosylation of Gi subunit –> Gi subunit remains in GDP bound inactive state –> unable to inhibit adenylate cyclase so increase cAMP - death of upper respiratory tract cells (less ATP available, altered cellular signalling - reduce function of tissue resident macrophages - reduced bacterial clearance)

38
Q

Clostridium difficile

A

Gram positive rod
Causes antibiotic associated colitus (diarrhea cause)
Yellow, plaque like lesions in the colon caused by exotoxin

39
Q

Escherichia coli

A

Gram negative rod (O-antigen possessing)

Commensal in gut despite containing LPS, (as separated from immune cells by epithelia of gut)

40
Q

H.pylori gram

A

Gram negative

41
Q

H.pylori evasion

A

LPS O antigen is Lewis antigen, resembling human blood group antigen –> false recognition as self so evade eliciting immune response.

Modifications to Lipid A of LPS cause change in microbe surface charge - prevents binding of cationic antimicrobial peptides and recognition by TLR complexes - lack of macrophage recognition.

Also modification to flagella prevent TLR5 recognition by macrophages - reduce immune cell recruitment.

42
Q

MRSA

A

Methilicillin resistant staphylococcus aureus
Gram positive coccus

Some methicillin resistant S aureus strains release Panton valentine leucocidin (production of this toxin makes strains more virulent. i.e caMRSA - community associated)

Pore forming cytotoxin which has 2 subunits (when joined form a pore that leaks cellular contents) –> cell lysis and activates then induces apoptosis of PMNs.

43
Q

Neisseria Meningitidis

A

Gram negative diplococcus –> meningitis and septicemia.

Transmission via respiratory droplets, blebbing sheds LPS (bacterial endotoxin) into blood stream

Immunoglobin A protease: Helps bacteria attach to the upper respiratory tract by cleaving IgA

44
Q

Neisseria meningitidis evasion

A

Capsule offers resistance to MAC attack by complement (lysis). When capsule KO, serum bacteria falls rapidly.

Factor H binding protein binds human factor H: an inhibitor of the complement factor C3b, thus presence of factor H on the bacteria, reduces opsonizing activity of factor C3b thus reducing the amount of MAC complex that can attack the gram negative bacteria

N.meningitides has a protective bacterial capsule Allows the bacteria to resists phagocytosis by PMNs as the serogroup B capsule mimics the NCAM-1 (neural cell adhesion protein)

45
Q

Pseudomonas aeruginosa

A

Gram negative rod, opportunistic, has LasI/LasR and RhII/RhIR (synthase enzymes) which catalyse auto inducer peptide

When threshold (bacterial) concentration reached then LasR binds autoinducer –> go from lag –> log/exponential phase: complex promotes expression of virulence factors to facilitate: cell aggregation, motility and biofilm formation.

46
Q

Salmonella

A

Gram negative rod.

T3SS1 –> inject effectors into host cytosol and for entry into small intestine epithelial cells and formation of salmonella containing vacuole.

Acidification of SCV –> T3SS2 expression, required for survival in host cytosol and intracellular replication.

47
Q

Shigella

A

Gram negative

Shigella needs TSS3: commensal –> pathogenic –> bacillary dysentery

48
Q

Salmonella effector proteins

A

AvrA effector protein –> deubuitinase: ubiquinated I kappa B alpha mixed with AvrA –> caused it to decrease –> Covalent modifications deregulate MAPK and NF kappa B signalling

49
Q

Shigella effector proteins

A

Effector proteins
IpaB mediates membrane fusion, IcsA recruits N-WASP for actin polymerisation, Vira cleaves tubulin at head of actin tail

Ospf = T3SS effector, inhibits MAPK and thus proinflammatory pathways

50
Q

Shigella toxin

A

Toxins
Translation inhibitors: Shiga toxin in shigella has enterotoxic and cytotoxic properties removes adenine form 28 S rRNA of human ribosomes -enterocyte cell death

51
Q

Staphylococcus aureus

A

Gram positive coccus, colonizes skin/mucosa

Superantigen include:
- Enterotoxin –> gastroenteritis (cytokines activates vomit center via ENS)

  • Toxic shock syndrome toxin –> toxic shock syndrome (progresses to multiple organ failure and shock)
  • Exfoliation toxin –> scalded skin syndrome in children (toxin cleaves desmoglein 1 of desmosomes)
52
Q

Streptococcus pneumoniae

A

Gram positive spherical bacterium

Polysaccharide capsule (virulent) inhibits phagocytosis –> allows growth of bacteria until anti-capsular Igs made, and masks cell surface molecules, resists lysis by MAC and mimics host molecules –> virulent

Evidence for gene transfer of virulence factors

53
Q

Streptococcus pyrogenes

A

Gram positive coccus

Spe A and SpeC = superantigens, induce inflammation by non-specifically activated T cells and stimulating inflammatory cytokines, responsible for the rash and the toxic shock like syndrome.

Induce human mononuclear cells to synthesize TNFα, IL-1β and IL-6 suggesting –> mediate the fever, shock and organ failure observed in patients with StrepTSS

Spe B = cysteine protease –> degrades Ig, C3b and ECM

M-antigen = contributes to invasiveness through its ability to impede phagocytosis of streptococci by human polymorphonuclear leukocytes (PMNL)

Type specific antibody against the M-protein enhances phagocytosis

Toxic shock like syndrome –> (toxic shock)

54
Q

UPEC

A

Gram negative rod

Type 1 fimbriae –> Entails FimH adhesion, tip binds mannosylated uroplakins on luminal bladder surface –> apoptosis of bladder epithelial cells. Lower UTI –> painful urination, pelvic pressure and bladder infection (cystitis).

P fimbrae –> PapG on tip –> binds D galactose D galactose moieties on P blood group antigen of RBCs and urothelial cells after adhered produces a and b haemolysins –> lysis of urinary tract cells –> upper UTI (pyelonephritis)

55
Q

Vibrio cholerae

A

Gram negative vibrio

56
Q

Which bacteria would give acid fast staining?

A

Mycobacterium tuberculosis

57
Q

Koch’s four postulates

A
  1. The organism must always be present, in every case of the disease.
  2. The organism must be isolated from a host containing the disease and grown in pure culture.
  3. Samples of the organism taken from pure culture must cause the same disease when inoculated into a healthy, susceptible animal in the laboratory.
  4. The organism must be isolated from the inoculated animal and must be identified as the same original organism first isolated from the originally diseased host.
58
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

59
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

60
Q

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

Pneumocystitis

61
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

62
Q

Which type of bacterial toxin is being described in the following sentence? “These toxins indiscriminately activate T cells of the immune system causing system-wide inflammation and other serious, potentially fatal, symptoms.”

A

Superantigen / Endotoxin

63
Q

A lipid found in high concentration in the cell wall of acid-fast bacteria.

A

Mycolic acid (peptidoglycan-arabinogalactan-mycolic acid wall structure)

64
Q

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

A

Sex Pilus

Pathology (21 decks)

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