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General Med 1 > Path Labs - Exam 3 > Flashcards

Path Labs - Exam 3 Flashcards

1
Q

What type of bacteria usually has an offensive smell?

A

Gram negative, i.e. E coli

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2
Q

How is a gram stain performed?

A
  1. place matchead-sized drop of tap water on centre of slide
  2. Using wire loop, mic colony and water - spread drop widely
  3. dry and heat fix

STAIN:

  1. flood - crystal violet. Leave 30s
  2. Rinse with tap water
  3. flood - iodine 30s
  4. Rinse with tap water
  5. Decolorize with alcohol - several seconds
  6. Rinse
  7. Flood - dilute carbol fuchsin 30 s
  8. Rinse and blot dry

MICROSCOPE
11. place drop of oil over spot of light on slide and swing to 100x

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3
Q

What magnification is required, using the light microscope, in order to recognise bacterial morphology on the Gram stain?

A

1000

i.e. 100x lens - already 10x microscope

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4
Q

Why are mycoplasmas not seen in specimens which have been Gram stained?

A

They lack peptidoglycan cell wall that which the gram stain binds to.

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5
Q

What is the purpose of the streaking technique used when inoculating a specimen onto an agar plate?

A

It effectively dilutes the specimen so that individual colony morphologies can be studied and recognised.

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6
Q

Give the genus and species name of one commensal bacterium that you would expect to find in the oropharynx

A

Strep, staph, moraxella ssp.

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7
Q

Give the genus and species name of one commensal bacterium that you would expect to find on the hands

A

Staph. epidermis

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8
Q

Give the genus and species name of one commensal bacterium that you would expect to find in the bowel

A

faecalibacterium, Escherichia coli

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9
Q

Give the genus and species name of one commensal bacterium that you would expect to find in the vagina

A

lactobacilli

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10
Q

How may the growth of commensal bacteria confuse the process of identifying pathogens in a specimen collected from an ill patient.

A

contamination - these can interfere with the laboratory detection of pathogenic bacteria as both will grow on agar plates. Therefore use streaking technique to purify.

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11
Q

How can you tell the difference between Staph aureus and other types of staph?

A

S aureus is coagulase positive.

Other staph = ‘coagulase negative staph’

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12
Q

How can you tell the difference between Strep and Staph?

A

Catalase test

Staph - catalase positive (oxygen bubbles)

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13
Q

What two broad groups will be differentiated by the oxidase test?

A

Enterobacteriaceae (negative) vs other gram negative rods

Often used to distinguish between E and Pseudomonas aeruginosa (-ve)

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14
Q

How is a coagulase test performed?

A

Slide coagulase test. This is the rapid but less reliable form of the test. A portion of a staphylococccal colony is emulsified in a drop of plasma on a glass slide using a wooden toothpick, producing a milky suspension. If coagulase is present, the bacteria and fibrin will clump together within minutes, giving the suspension a granular appearance. The suspension remains homogenous if coagulase is not present.

Vs Tube Coagulase Test

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15
Q

How does the oxidase test work?

A

The test detects the presence of CYTOCHROME OXIDASE, an enzyme in the electron transport chain of some bacteria but not others. In the test, a colourless compound takes the place of oxygen in the real chemical reaction, and when this is reduced it becomes blue.

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16
Q

Most bacteria have an outer layer of polysaccharide. What are the 3 different layer types of polysaccharide?

A

a) glycocalyx – very thin layer
b) capsule – thicker layer
c) slime - Amorphous polysccharide extending into the environment

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17
Q

How is capsular serotyping done?

A

In a given species of encapsulated bacteria, there are generally a number of different antigenic types, determined by the type and the arrangement of the polysaccharides.
Specific antibodies raised in animals (eg. mice, rabbits) can be used in the serotyping of encapsulated bacteria by observing their agglutination when mixed with different antibodies (antisera).

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18
Q

How many capsular serotypes are there for Neisseria meningitidis?

A

13

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19
Q

How many capsular serotypes are there for Streptococcus pneumoniae?

A

90

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20
Q

How many capsular serotypes are there for Haemophilus influenzae?

A

6 encapsulated serotypes. Other non encapsulated serotypes exist

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21
Q

Name the serotypes for Neisseria meningitidis

A

A,B,C,D,E,W,X,Y,Z,H,I,K,L

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22
Q

Name the serotypes for Haemophilus influenzae

A

A-F

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23
Q

Which serotypes of N. meningitidis cause most disease in Australia?

A

B and C. B accounts for most cases, and C accounts for about 1/3.

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24
Q

Which groups of people in the Australian population are most predisposed to serious infection with S. pneumoniae?

A
  • Adults over 65
  • children under 2
  • immunocompromised people
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25
Q

Which serogroup of H. influenzae is the most virulent, and why is it now an uncommon pathogen in Australia?

A
  • type B (Hib)

- Vaccinations

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26
Q

What categories of vaccines are there?

A
  1. Live (Attenuated) vaccines
  2. Inactivated vaccines – contain one or a few components of the organism, i.e. polysaccharide. It cannot replicate.
    a) conjugated
    b) non-conjugated
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27
Q

What vaccines are available in Australia for Neisseria meningitidis?

A
  • meningococcal B vaccine Bexsero® available on private market
  • meningococcal ACWY vaccine available on prescription for travellers
  • Meningococcal C vaccination is recommended as part of routine childhood immunization – given at 12m
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28
Q

What vaccines are available in Australia for Streptococcus pneumonia?

A

Pneumococcal vaccine is recommended as part of routine childhood immunisation, – given at 2m, 4m, 6m. Booster at 12m and 4 years.

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29
Q

What vaccines are available in Australia for Haemophilus influenzae?

A

Hib vaccination is recommended as part of routine childhood immunization – 2,4,6 months. Booster at 12 months.

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30
Q

What are some of the functions of bacterial capsules?

A
  • permeability barrier
  • adherence to surfaces
  • carbohydrate reserve for subsequent metabolism
  • resistance to phagocytosis by cells of the immune 
system
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31
Q

What are the two categories of phagocytosis attachment?

A

• unenhanced attachment - earlier, faster
- inefficient
Bacteria with PAMPS bind with pattern recognition receptor on phagocyte, which activates phagocyte causing phagocytosis.

• enhanced attachment - slightly delayed
- more efficient
Done through opsonisation. Bacteria are coated with opsonsins which makes phagocytosis.

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32
Q

In bacterial phagocytosis, antibodies or the C3b component of the complement system can act as opsonisers for enhanced attachment. What are the two different receptors for the IgG antibody and C3b?

A
  • IgG antibody – the Fc receptor

- C3b – CR1 receptor

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33
Q

Why do asplenic patients have problems with bacteria with capsules?

A

The early immune response to bacterial capsules is opsonisation with C3b. These can then be phagocytized in the spleen. C3b production is also enhanced by IgM from splenic marginal zone B-cells.
Antibodies directed against capsular antigens occur later in the immune response, however asplenic patients may not survive this long.

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34
Q

What do marginal zone B cells do?

A
  • encounter antigens in the marginal zone of the spleen
  • rapid production of IgM and IgG antibodies in a T cell-dependant manner
  • these exist only in the spleen
  • IgM binds to polysaccharide capsule
35
Q

What do follicular B cells do?

A
  • encounter antigens in germinal centres of follicles in lymphoid tissue
  • require T cell help to produce antibodies that are high affinity and isotype switched, as well as memory B cells.
36
Q

What causes of asplenia and hyposplenism?

A

Asplenia:

  • splenectomy
  • congenital

Hyposplenism:

  • sickle cell disease
  • inflammatory bowel disease
  • coeliac disease
  • lupus
  • allogeneic bone marrow transplantation
37
Q

Describe the vaccination schedule recommended for asplenic patients, or those facing elective splenectomy

A

Persons with an absent or dysfunctional spleen are at a life-long increased risk of fulminant bacterial infection, most notably invasive pneumococcal disease (IPD) - Pneumococcal, meningococcal, Hib and influenza vaccination are particularly recommended for all persons with asplenia

38
Q

What is OPSI?

A

An overwhelming post-splenectomy infection (OPSI) is a rare but rapidly fatal infection occurring in individuals following removal of the spleen. The infections are typically characterized by either meningitis or sepsis, and are caused by encapsulated organisms including Streptococcus pneumoniae.

39
Q

How do you test for PKU?

A

Blood test for:

  • Phenylalanine
  • Tyrosine
  • DHPR activities and pterin levels

PKU if very high phenylalanine

40
Q

In regard to PKU, what is the relevant reaction, including enzymes?

A

Substrate: Phenylalanine
Product: Tyrosine

Enzymes:
Phenylalanine hydroxylase (PAH)
Dihydropteridine reductase (DHPR)
41
Q

What does tyrosine go on to produce?

A

DOPA

Which produces:

a) melanins
b) dopamine

42
Q

What would you expect to see in a blood test of someone with PKU?

A

**High phenylalanine

Possibly low tyrosine

May see low DHPR activity and pterin levels if this is the cause of PKU (usually not)

43
Q

What is the most likely cause of too much phenylalanine (PKU)?

A

phenylalanine hydroxylase deficiency

44
Q

Why can’t PAH activity be measured directly in material from a blood sample?

A

It’s present in liver (and kidney) cells so isn’t free floating around in the blood

45
Q

Why do people with PKU have very fair skin and hair, and blue eyes?

A

PKU – low tyrosine – low DOPA – low melanins

46
Q

Is PKU management best coordinated by a family’s GP?

A

NO

Specialist team

47
Q

T or F

A key aspect of the PKU diet is to limit intake of foods with phenylalanine.

A

True

48
Q

Is it unsafe for people to stop following the diet as they get older?

A

Yes

49
Q

What sorts of foods do people with PKU need to avoid?

A

various high protein foods including milk and cheese, eggs, nuts, soybeans, beans, meat, fish, peas and beer.

Aspartame

50
Q

How do PKU patients get enough protein?

A

Because protein intake is low in the diet for PKU, a protein supplement is needed to make up what is missing from not eating foods high in protein

51
Q

Why is it unsafe to totally eliminate phenylalanine from the diet?

A

Phe is an essential amino acid which means some is needed for growth and to make the body’s protein, but only in small measured amounts

52
Q

What are the potential consequences of poorly controlled maternal hyperphenylalanaemia for the unborn foetus?

A
  • commonly born smaller
  • microcephaly,
  • mental retardation,
  • behavior problems,
  • characteristic facial features similar to those of the fetal alcohol syndrome, and
  • higher risks of heart defects
53
Q

In terms of genetics, what type of disorder is PKU?

A

autosomal recessive

mostly due to loss of function mutation in PAH gene

54
Q

Why does a PKU foetus develop normally in utero?

A

The mother clears excess phenylalanine through the placenta.

55
Q

What happens to a mother with PKU while she is pregnant?

A

Because the high level of phenylalanine in the maternal circulaAon crosses the placenta, the normal foetus of a phenylketonuric mother will suffer severe consequences unless the mother goes on a low phenylalanine diet throughout her pregnancy.

56
Q

What are some of the symptoms of PKU?

A
  • Intellectual disability
  • Delayed development
  • Behavioral, emotional and social problems
  • Psychiatric disorders
  • Neurological problems that may include seizures
  • Hyperactivity
  • Poor bone strength
  • Skin rashes (eczema)
  • A musty odor in the child’s breath, skin or urine, caused by too much phenylalanine in the body
  • Fair skin and blue eyes
  • microcephaly
57
Q

What cell type lines the ectocervical mucosa of the cervix?

A

Single layer of columnar mucous cells (columnar epithelium that secreted mucus)

58
Q

What is the cervical transformation zone?

A

The cervix contains two kinds of cells: rectangular columnar cells and flat, scale-like squamous cells. Columnar cells are constantly changing into squamous cells in an area of the cervix called the transformation (transitional) zone.
The transformation zone is an area of changing cells, and it is the most common place on the cervix for abnormal cells to develop. These abnormal cells can be detected on a Pap smear.

59
Q

1 What is a pap smear?

A

Screening test for cervical cancer and precursor lesions.

60
Q

How is a pap smear performed?

A
  1. Cells from the transformation zone of the cervix are obtained via spatula or brush
  2. Smeared onto slide, fixed and stained using papanicolaou method
  3. +/- Liquid based technique
  4. screened by scientist for cellular abnormality
61
Q

Why should women have regular pap smears?

A
  • screening is not 100% accurate

- abnormal changes might not be present yet

62
Q

What is the routine screening interval for pap smears in Australia?

A

2 years

63
Q

Describe the salient features of a normal pap smear.

A

Normal Pap smear:

  • superficial and intermediate squamous cells
  • abundant cytoplasm
  • small, regular nuclei
64
Q

What role does HPV play in cervical cancer?

A

It causes almost all of it by interfering with the cell cycle, proliferation and death.

  1. 1 What role does HPV play in cervical cancer?
    - integration of HPV into host cell DNA allows for over expression of E6 and E7 viral genes which encode protein
    - E6 and E7 enhance degradation of p53 – interrupts cell death pathways
    - E7 prevents function of p21 which is a cell cycle inhibitor
    - E7 inactivates Rb gene, blocking its proliferation-inhibitory function
65
Q

Describe the life cycle of HPV infection

A
  • HPV infects squamous epithelial cells in the cervix, glans of the penis, penile shaft, scrotum, anal verge
  • Virus enters cell
  • Virus uncoats and delivers genome to host cell nucleus
  • Viral DNA replicated and then segregated into progeny cells
  • One stays in basal layer to act as reservoir
  • Other migrates, and HPV inhibits its normal exit from cell cycle
  • Host immune system usually clears virus within 6m, or 12-24m in high risk types.
66
Q

What are the risk factors for HPV infection?

A
  • sexual contact – greater number of lifetime sexual partners and early first sexual intercourse
  • tobacco use
  • immune suppression (i.e. HIV)
67
Q

Describe the cytological changes HPV infection

A
  • nuclear enlargement and membrane irregularity
  • hyperchromasia
  • binucleation
  • cytoplasmic clearing
68
Q

What is the natural history of HPV infection?

A
  • acute infection resulting in viral replication leading to development of either a subclinical or a clinically evident infection
  • subclinical usually resolve without symptoms
  • clinically evident may produce either:
    a) low-grade disease
    b) high grade disease – consequence of persistent infection
  • The majority of low-grade lesions regress without treatment
  • A significant proportion of high-grade lesions progress to invasive cancer if left untreated
  • Time from high grade to cancer is about 7-10 years
69
Q

What is HSIL/CIN3?

A

Severely abnormal cells are found on the surface of the cervix.

Cervical intraepithelial neoplasia with diffuse atypia (structural abnormality), loss of maturation and expansion of dysplastic cells (proliferation of abnormal type – enlargement of tissue) to the epithelial surfaces

70
Q

Describe the cytological changes of HSIL/CIN3

A
  • squamous cells with increased nuclear to cytoplasmic ratio

- large, irregular, dark-staining nuclei

71
Q

What is the natural history of HSIL/CIN3?

A
  • Small percentage of CIN I progress to higher grade, remainder regress or persist. Can progress to CIN3
72
Q

What is Colposcopy?

A

a medical diagnostic procedure to examine an illuminated, magnified view of the cervix and the tissues of the vagina and vulva.
Colposcope gives enlarged view of areas. Abnormal lesions can be detected, and biopsies can be taken as necessary.

73
Q

What is the significance of an aceto-white area?

A

Areas of acetowhiteness correlate with higher nuclear density which may indicate precancerous or cancerous lesions. They will be considered for biopsy

74
Q

What is a LLETZ procedure?

A

LLETZ Procedure (Large Loop Excision of the Transformation Zone of the cervix) This procedure is done when your pap smear, colposcopy or biopsy has shown abnormal cells on the surface of your cervix. Abnormal cells are removed

75
Q

What is SCC?

A
  • Squamous cell carcinoma

- most common subtype of cervical cancer - ~80%

76
Q

Describe the histological changes of SCC.

A

Characterised by nests and infiltrative tongues of malignant squamous cells with large, irregular and hyperchromatic nuclei invading beyond the epithelium into cervical stroma

77
Q

What are the clinical features of cervical SCC?

A

SCC of the skin begins as a small nodule and as it enlarges the center becomes necrotic and sloughs and the nodule turns into an ulcer.

  • unusual bleeding, i.e. between periods, after menopause or after intercourse
  • pain during intercourse
  • unusual vaginal discharge
78
Q

What factors affect prognosis in SCC?

A

If it has spread anywhere else, how big it is, is it invasive etc

SCC tends to have good prognosis

79
Q

For whom is the HPV vaccination currently recommended in Australia?

A

National HPV Vaccination program:
- males and females aged 12-13

People outside this age can get it, but they will need to pay for it. It is recommended before a person is sexually active

80
Q

Do vaccinations provide protection from all HPV types?

A

No, only types 6, 11, 16 and 18

6 and 11 cause condylomas

81
Q

How effective is the vaccination at preventing cervical precancerous lesions?

A
  • it won’t affect existing HPV
  • as the HPVs it protects against only cause 70% of cervical cancers, it is estimated that it will prevent up to 70%.
  • It is not currently known hot long protection lasts
82
Q

Do women who have been vaccinated need to have regular pap smears (based on current recommendations)?

A

YES – it doesn’t prevent against all HPV types or existing infections

83
Q

The HPV vaccine is poised to dramatically alter the future of the Australian cervical cancer screening program. List a few of the proposed changes.

A
  • commence at age 25

- 5 yearly screening interval

General Med 1 (24 decks)

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