Microbiology Flashcards
1
Q
What is virulence?
A
The capacity of a microbe to cause damage to the host
2
Q
What factors are responsible for the variation in virulence between different species?
A
Adhesin Invasin Impedin Aggressin Modulin
3
Q
How do Adhesins contribute to virulence?
A
Allows the organism to bind to host tissue
4
Q
How do Invasins contribute to virulence?
A
Allows the organism to invade a host cell/tissue
5
Q
How do Impedins contribute to virulence?
A
Lets the organism to avoid host defense mechanisms
6
Q
How do aggressins contribute to virulence?
A
Cause damage to the host directly
7
Q
What organisms make up the skin microbiota?
A
- Staphylococci spp. (Coag -ve)
- Staphylococcus aureus
- Diptheroids (P.acnes)
- Streptococci spp.
- Bacillus spp
- Candida spp.
- Malassezia furfur
Mycobacterium (occasionally)
8
Q
What superficial lesions can a staph aureus infection cause?
A
Boil Carbuncle Abscess Folliculitis Impetigo
9
Q
What Toxinoses can be caused by a staph aureus infection?
A
Toxic Shock
Scalded Skin Syndrome
10
Q
How does Fibrinogen binding protein contribute to virulence?
A
It is an Adhesin
=> allows Staph Aureus to bind to host cells and infect
11
Q
How does Leukocidin (PVL) contribute to Virulence?
A
Kills leukocytes
12
Q
What is Toxic Shock Syndrome Toxin (TSST-1) and how does it contribute to virulence?
A
superantigen secreted by Staph. aureus
CAUSES:
- rash
- shock.
- desquamation
13
Q
Give examples of adhesins found on Staph. Aureus
A
- Fibrinogen-Binding (ClfA ClfB)
* Collagen-Binding (CNA)
14
Q
What is the Toxic Shock diagnostic criteria?
A
- Fever – 39˚C
- Diffuse Macular rash & desquamation (“sunburn”)
- Hypotension – ≤ 90 mm Hg (adults)
- ≥ 3 Organ systems involved – liver, blood, renal, mucous membranes, GI, muscular, CNS.
15
Q
Panton-Valentine Leukocidin (PVL) gives rise to what severe skin diseases?
A
- recurrent furunculosis
- sepsis/necrotising fasciitis
16
Q
PVL & alpha-toxin associated with MRSA causes what?
A
- necrotizing pnuemonia
- contagious severe skin infections
17
Q
What skin conditions does Strep. Pyogenes cause?
A
- Impetigo
- Cellulitis (Erysipelas)
- Necrotising Fasciitis
18
Q
How do modulins contribute to virulence?
A
Causes damage to the host indirectly
19
Q
How are Strep. Pyogenes classified?
A
Lancefield (Serotyping of Cell Wall Carbohydrate)
20
Q
What are the Major classifications of Strep. Pyogenes?
A
Major serotypes A-H and K-V (20)
21
Q
How is Group A Strep. Pyogenes further classified?
A
further subdivided according to M protein antigens
- M1 and M3 major serotype
- M3 and M18 severe invasive disease
22
Q
Is intact skin more or less likely to become infected?
A
Less likely
infection is more common if skin is broken
23
Q
How does dry skin protect from infection?
A
completely dries out the microorganisms
24
Q
How does sebum contribute to protecting against infection?
A
The fatty acids found in sebum inhibit bacterial growth
25
Give an example of transient bacteria flora
MRSA
intermittent => doesn't always show up in screening
26
What is the difference between pathogens and commensals?
Pathogens have the potential to cause disease
Commensals don't necessarily cause any illness
27
Give examples of competitive bacterial flora
* Staphylococcus epidermidis
* Corynebacterium sp. (diphtheroids)
* Propionibacterium sp.
28
Give examples of alpha-haemolytic Streptococci
Strep. pneumonia
| Strep. viridans (commensal/endocarditis)
29
Give examples of Beta-haemolytic streptococci
```
Group A (throat, SKIN)
Group B (neonatal meningitis)
Groups C,G
```
30
GIve examples of non-haemolytic streptococci
Enterococcus (gut commensal, UTI)
31
Give an example of a coagulase positive and coagulase negative strain of Staphylococcus
Coag. Positive = Staph Aureus
Coag. Negative = Staph. epidermidis
32
Is staphylococcus an aerobe or an anaerobe?
Aerobic and facultatively anaerobic
| => grows best aerobically but can grow anaerobically
33
Name toxins that can be produced by some variations of staphylococcus
* Enterotoxin –food poisoning
* SSSST –staphylococcal scalded skin syndrome toxin
* PVL –Panton Valentine Leucocidin
34
What antibiotic is used to treat staph. aureus infection?
FLUCLOXACILLIN
35
What can be used to treat MRSA?
Doxycycline
Co-trimoxazole
Clindamycin
**if bloodstream involved = Vancomycin**
36
If a patients blood cultures are consistently showing positive staph epidermidis, what must you consider?
Infection from an artificial material in the body
| e.g. new heart valve, catheter, IV line
37
What skin problems can staph. aureus infection cause?
* Boils and Carbuncles
* Minor skin sepsis (infected cuts etc.)
* Cellulitis
* Infected eczema
* Impetigo
* Wound infection
* Staphylococcal scalded skin syndrome
38
Is streptococcus aerobic or anaerobic?
Aerobic (and facultatively anaerobic)
| => grows best in air, but can grow without
39
What skin conditions can be caused by group A streptococcus?
* Infected eczema
* Impetigo
* Cellulitis
* Erysipelas
* Necrotising fasciitis
40
What is necrotising fasciitis?
Bacterial infection spreading along fascial planes below skin surface →rapid tissue destruction
41
How do we differentiate between the two types of necrotising fasciitis?
Type 1 –mixed anaerobes and coliforms, usually postabdominal surgery
Type II –Group A Strep infection
42
How is necrotising fasciitis usually managed?
Surgical removal and antibiotics
| Based on organisms isolated from tissue taken at operation
43
What is 'Tinea' the latin word for? And therefore what does 'Tinea Pedis' mean?
Tinea = ringworm (aka a FUNGAL infection)
Tinea pedis (athlete’s foot)
44
Describe the pathogenesis of a Dermatophyte (fungal infection)
- Fungus enters soggy skin
- Hyphae spread in keratin layer
- Infects keratinised tissues only (skin, hair, nails)
- Increased epidermal turnover => scaling
- Inflammatory response
- Hair follicles and shafts invaded
- Lesion grows outwards/ heals in centre
=> “ring” appearance
45
Who is more commonly affected by ringworm infections and where?
Males more commonly affected (Foot and groin)
Scalp ringworm mainly affects children
46
What sources of fungal infection are there?
Other infected humans (anthropophilic)
Animals (cats, dogs, cattle) (zoophilic fungi)
Soil (geophilic fungi)
47
What organisms are most likely to cause a ringworm?
Trichophyton rubrum
| Trichophyton mentagraphytes
48
What investigations can be done to test for fungal infections?
Woods light (fluorescence)
Skin scrapings, nail clippings, hair
=> Send to lab for microscopy and culture (2 weeks)
49
How should fungal infections be treated?
Small areas of infected skin, nails – Clotrimazole
Topical nail paint - amorolfine
Extensive skin/nail/scalp infections:
- Terbinafine orally
- Itraconazole orally
50
Where does candida usually cause infection?
Candida causes infection in skin folds where area is warm and moist
Seen under the breasts in females, groin areas, abdominal skin folds etc, nappy area in babies
51
What investigation can diagnose candida?
Skin swab for culture
52
What is used to treat a candida skin infection?
clotrimazole cream
oral fluconazole
53
What is the scabies incubation period?
Incubation period up to 6 weeks
54
How does scabies usually present?
Intensely itchy rash affecting finger webs, wrists, genital area
55
What treatments are used in scabies?
malathion lotion, applied overnight to whole body and washed off next day
benzyl benzoate (avoid in children)
56
What is a pediculosis and therefore what is Pediculus capitis?
Pediculosis = louse
=>Pediculus capitis = head louse
57
What is used to treat lice?
Malathion lotion (due to extreme itch)
58
If a patient with exfoliative skin conditions sheds huge numbers of scales and bacteria into the environment, why is this issue?
Infection control
Gm positive bacteria in the shedding can survive in the environment due to its cell wall structure
=> can infect other patients
59
What conditions does Varicella Zoster Virus cause?
Chickenpox (varicella) singles (zoster/ Herpes Zoster)
60
Describe the morphology of the lesions in chickenpox and how they change over time
Macules -> papules -> vesicles -> scabs -> recovery
61
Where are chickenpox lesions usually found on the body?
centripetal (more dense in the centre of body i.e. trunk)
62
What other symptoms can occur with a chickenpox rash?
inflamed skin
Fever
Itch
63
What are the secondary complications of chickenpox infection?
- secondary bacterial infection
- pneumonitis
- haemorrhagic rash
- scarring
- encephalitis
64
What can predispose to a more severe chickenpox infection?
- extremes of age
| - immunosuppression
65
What is the cause of neonatal chickenpox?
secondary to chickenpox in pregnant mother developed roughly 5 days before delivery
**if mother hasn't had it before delivery, an injection to prevent it can be given**
66
Describe the difference in distribution between chickenpox and shingles
Chickenpox = widespread
Shingles = in a specific dermatome
67
Who is most likely to reactivate the varicella zoster virus in order to develop shingles?
Elderly and immunocompromised
68
Describe the morphology of the lesions in shingles
Tingling/pain -> erythema -> vesicles -> crusts
69
If neuralgic pain due to shingles lasts more than 4 weeks, what is this called?
Post Herpetic Neuralgia
70
Who does post hepatic neuralgia most commonly affect?
- elderly patients
| - patients who get shingles in the trigeminal dermatome
71
Is scarring of the skin common in shingles?
No
72
How is ophthalmic zoster usually managed?
Ophthalmic division of trigeminal nerve = affected => affects eye and surrounding area
Tx = Urgent ophthalmic referral indicated
73
What other trigeminal distributions can shingles present in?
Ophthalmic division
Maxillary division
Mandibular division
74
When is it possible for ophthalmic zoster to occur in children?
- if chickenpox is caught in utero
| - if child becomes immunocompromised
75
What is Ramsay-Hunt syndrome?
- Vesicles and pain in ear canal and throat
- Facial palsy (7th nerve palsy)
- Irritation of the 8th cranial nerve
=> Deafness
=> Vertigo
=> Tinnitus (ringing/buzzing)
76
What type of vaccine is available for chickenpox?
Live attenuated vaccine
77
Who is the chickenpox vaccine used for?
Children in some countries (NOT UK)
Used in susceptible health care workers
Used in high titre to reduce impact of shingles in elderly
UK: routinely in 70 year olds
78
Describe the appearance of herpes simplex virus
Blistering rash at vermillion border
Can be spread:
- herpetic whitlow (finger)
- eczema herpeticum (this can be life threatening)
79
What Type of Herpes Virus causes oral and genital lesions?
Type 1
80
What Type of Herpes Virus causes only genital herpes?
Type 2
81
What antiviral can be used to treat herpes?
Aciclovir
incorporated into viral DNA inhibiting replication
**Does not eliminate latent virus**
82
When are antibody tests used as opposed to swabbing the site of viral infection?
where virus infected site is inaccessible
83
What infections can cause erythema multiforme?
Herpes simplex virus
| Mycoplasma pneumoniae bacterium
84
Describe the morphology of the lesions seen in Molluscum contagiosum
Fleshy, firm, umbilicated, pearlescent nodules
| 1 to 2 mm diameter
85
How long does it usually take for Molluscum Contagiosum to disappear?
Self limiting but take months to disappear
86
Is Molluscum Contagiosum more common in adults or children?
Children
87
How is Molluscum Contagiosum sometimes transmitted?
Sexual transmission
88
What can be used to treat Molluscum Contagiosum?
local application of liquid nitrogen
89
What skin manifestations are caused by Human papilloma virus (HPV)?
Warts and verrucas
90
What is used to treat warts and verrucas?
Topical salicylic acid
91
What other illnesses can be caused by HPV?
Genital warts
Cervical cancer
Head and neck cancer
92
What types of HPV usually cause genital warts?
HPV Types 6 and 11
93
What types of HPV usually cause cervical cancer?
HPV types 16 and 18
94
What is herpangina?
Blistering rash at back of mouth
Caused by enterovirus not herpes virus
- coxsackie virus
- echovirus
95
How is herpangina diagnosed?
Swab of lesion
| sample of stool for enterovirus PCR
96
What viruses usually cause family outbreaks of hand, foot and mouth disease?
Enteroviruses (especially coxsackie viruses)
97
What virus causes "slapped cheek" syndrome?
erythrovirus (parvovirus B19)
98
What type of rash develops after "slapped cheek" disappears?
lacy macular rash on the body appears
In adults:
rash may be absent
acute polyarthritis of the small joints eg hands
99
What other complications does Parvovirus B19 cause?
- spontaneous abortion
- Aplastic crises
- sudden drop in haemoglobin (important in patients
with RBC disorders eg. Leukaemia)
- Chronic anaemia
(in immunosuppressed patients)
100
How is parvovirus B19 diagnosed?
parvovirus B19 IgM test
Not skin swab!
101
What is Orf and how is it diagnosed?
Virus of sheep “scabby mouth”
Firm, fleshy nodule on hands of farmers
Clinical diagnosis, lab confirmation not used
102
Describe the appearance of a primary syphilis infection
Painless ulcers at site of entry
103
Describe what occurs in a secondary syphilis infection
- Red rash over body
- especially soles of feet and palms of hands
- Mucous membrane “snail track” ulcers
104
What body systems become involved in a tertiary syphilis infection?
CNS, cardiovascular, gummatous
105
What bacteria is sexually transmitted in order to cause syphilis?
Treponema pallidum
106
How is syphilis diagnosed?
Diagnosis by blood test or swab of ulcer for PCR
107
What is used to treat syphilis?
injections of penicillin
108
Is syphilis a bacterial, fungal or viral infection?
Bacterial
109
What is known to cause Lyme's disease?
Ticks
| Bacteria = Borrelia burgdorferi
110
How does Lyme's disease present?
Early: erythema migrans
Late: heart block, nerve palsies, arthritis
111
What antibiotics are used to treat lyme's disease?
doxycycline or amoxicillin
112
Out of everyone who becomes infected by the Zika virus, how many actually become ill?
1 in 5 people
113
When do symptoms of Zika infection usually start and subside?
Symptom onset: 3–12 days after exposure
| Symptoms resolution: 2–7 days after onset
114
What are the symptoms of Zika virus?
```
Mild fever
Rash (mostly maculopapular)
Headaches
Arthralgia
Myalgia
Non-purulent conjunctivitis
```
115
What helps to spread Zika virus?
Mosquito
| Sexual transmission also seen person to person
116
Name 2 severe complications of Zika virus
Microcephaly
| Guillain Barré syndrome
