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Pathology and Laboratory Science > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is antibiotic resistance driven by?

A

Use and misuse of antibiotics Transmission in community and healthcare setting Globalisation

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2
Q

Mechanisms of antibiotic resistance?

A

Intrinsic resistance Acquired resistance through horizontal gene transfer and chromosomal mutations

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3
Q

What percentage of S. aureus infections in NZ are caused by MRSA?

A

5-15%

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4
Q

What confers the resistance to beta-lactam antibiotics in MRSA?

A

Presence of mecA gene which produces an abnormal penicillin-binding protein

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5
Q

Treatment for MRSA?

A

Vancomycin

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6
Q

What is an ESBL?

A

Extended-spectrum beta-lactamases - hydrolyse penicillins, cephalosporins, monobactams - often resistant to gentamicin, ciprofloxacin and co-tramoxazole

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7
Q

How do you treat ESBLs?

A

Carbapenem such as meropenem

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8
Q

What populations are at high risk of developing an infection from vancomycin-resistant enterococci?

A

○ Dialysis patients ○ Transplants ○ Haematology patients ○ ICU patients

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9
Q

Are enterococci Gram +ve or Gram -ve?

A

Gram positive

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10
Q

Why are enterococci hard to eradicate and treat?

A

Relatively low virulence, but have many genes encoding adhesion proteins so can develop resistance quickly

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11
Q

What are the main organisms associated with healthcare associated infections? (9)

A

• Staphylococcus aureus • Escherichia coli (UTI) • CoNS (coagulase negative Staphylococcus infection) • Klebsiella pneumoniae • Enterococcus faecalis • Candida albicans • Viruses: ○ Influenza ○ Norovirus • Clostridium difficile

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12
Q

What is the commonest cause of nosocomial diarrhoea?

A

Clostridium difficile

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13
Q

Treatment for Clostridium difficile diarrhoea?

A

Metronidazole PO

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14
Q

What is impetigo?

A

High contagious skin infection restricted to the epidermis

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15
Q

Clinical presentation of impetigo?

A

Usually found on face, hands and neck and is generally mild and self-limiting disease that heals without scarring

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16
Q

Pathogens associated with impetigo?

A

Almost always caused by S. aureus. Occasionally associated with S. pyogenes

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17
Q

Treatment of impetigo?

A

No school 2-3 days Basic hygiene Topical antibiotics for localised rashes (fusidic acid 2% cream tds) Oral antibiotics for extensive lesions (flucloxaxillin or cephalexin)

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18
Q

What is an abscess?

A

Collection of pus within the dermis and deeper skin tissues that is tender and fluctuant

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19
Q

Pathogens associated with abscesses?

A

Most common is S.aureus. Rarely, can be polymicrobial

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20
Q

Difference between a furuncle and a carbuncle?

A

Furuncle involves one hair follicle, carbuncle involves several hair follicles

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21
Q

Treatment of abscess without systemic symptoms?

A

Incision and drainage + covering with dry dressing

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22
Q

Treatment of abscess )+/- MRSA) with systemic symptoms?

A

Incision and drainage + flucloxacillin PO (if MRSA treat with co-trimoxazole or clindamycin)

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23
Q

What is cellulitis?

A

Bacterial infection of the skin affecting the dermis and subcutaneous fat

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24
Q

Risk factors for cellulitis?

A

Obesity Diabetes Disrupted skin

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25
Treatment of mild cellulitis (no systemic symptoms)?
Oral flucloxacillin Oral Co-trimoxazole or clindamycin if MRSA
26
Treatment of severe cellulitis?
IV fluclox or cephalexin IV vanc if MRSA
27
What is necrotising fasciitis?
Aggressive subcutaneous infection which tracks along the superficial fascia very quickly
28
How does NF evolve? When is NF suspected?
Almost always presents as an initial cellulitis that deterioates very quickly - suspect it in all patients that do not improve after first 24 hours
29
What is the mortality of NF?
\>20%
30
Causative organisms for monomicrobial NF?
S. pyogenes S. aureus Vibrio vulnificus Aeromans
31
Risk factors for monomicrobial NF?
Obesity Venous insufficiency IVDU
32
Risk factors for polymicrobial NF?
GU-related (perianal abscess, penetrating abdo wound, surgery) IVDU with contaminated needles
33
Treatment of NF?
Surgical debridement Empiric antibiotics: - Tazabactam + piperacillin - ceftriaxone + metronidazole
34
What do yeasts look like on microscopy?
Round or oval shaped
35
How do yeasts reproduce?
Budding
36
What are some common examples of infectious yeasts? (2)
Candida albicans Cryptococcus neoformans
37
What do moulds look like on microscopy?
Tubular hyphae
38
How do moulds reproduce?
Spores
39
What are 3 examples of infectious moulds?
Dermatophytes Aspergillus species (e.g. fumigatus) Zygomycetes
40
What is the main difference between human and fungal cells?
The cell membrane of fungi contains ergosterol rather than cholesterol (can target this for an antifungal)
41
Systemic antifungals?
Amphotericin B Oral azoles (e.g. fluconazole) Echinocandins
42
Systemic/mucocutaneous antifungal?
Terbinafine
43
Topical antifungals?
Nystatin Topical azoles Amphotericin B pastilles
44
What is the most common fungal infection?
Candida albicans
45
Where is candida albicans commensal?
Mouth, gut, vagina (approx. 80% of population)
46
3 main clinical syndromes of candida infection?
1. local overgrowth on mucous membranes 2. invasive focal infection 3. widespread visceral dissemination in the neutropenic host/severely ill patient
47
What is this?
Candida albicans - dark budding yeasts with psuedohyphae on gram stain
48
What isthe main species of candida?
Candida albicans
49
Treatment for skin/mucosal candidiasis (no systemic involvement)?
Topical treatment: - Nystatin suspension or pastilles - Amphotericin B pastilles - Azole pessaries or cream
50
Treatment of serious/systemic candidiasis?
Oral or IV antifungal (e.g. azole)
51
What are the two variants of Cryptococcus?
- C. neoformans - C. gatti
52
What is the most common type of infection by Cryptococcus?
Aymptomatic pulmonary infection followed by haematogenous spread to CSF resulting in meningitis in the immunocompromised host
53
What are some features of cryptococcal meningitis?
Slowly progressive, chronic lymphocytic meningitis 10-100 WBCs in CSF with lymphocyte predominance High protein, low glucose in CSF Positive cryptococcal antigen in CSF and serum
54
What is this?
Cryptococcus species on India ink stain - encapsulated yeasts
55
Treatment of cryptoccocal meningitis?
LP to reduce pressure in CSF IV amphotericin B and IV or oral fluconazole for at least 6 weeks
56
What are 'tinea' infections caused by?
Dermatophyte infection
57
What are the most common dermatophyte species?
Trichophyton rubrum (70%) Trichophyton mentagrophytes Microsporum canis Epidermophytons
58
Are dermatophyte infections self-limiting?
No
59
Treatment for dermatophyte infections?
Skin: - Topical azole (e.g. clotrimazole, miconazole) Nails: - Oral terbinafine OR itraconazole
60
What is pityriasis versiocolour caused by?
Malassezia furfur yeast
61
Treatment of pityriasis versicolour?
Oral or topical azole for 2 weeks
62
What is a greasy rash on face/dandruff called?
Seborrhoeic dermatitis (caused by pityrosporum species)
63
Treatment of seborrhoeic dermatitis?
Topical azole
64
What is a spore-bearing, branching mould that is common in rotting vegetation?
*Aspergillus fumigatus*
65
What diseases does *Aspergillus fumigatus* cause?
- Cavitating pneumonia with multiple lesions (in immunocompromised hosts) - Allergic bronchopulmonary aspergillosis (ABPA)
66
What is this?
*Aspergillus* *species* - silver stain
67
Treatment of *Aspergillus* pneumonia?
Amphotericin B IV for weeks ?liposomal amphotericin B (less nephrotoxic) Voriconazole or other azoles Surgery
68
2 examples of endoparasites?
Tapeworms, roundworms
69
Two examples of ectoparasites?
Lice, scabies
70
Definition of a parasite
Life forms, larger than bacteria or viruses, that benefit at the expense of another life form (the host)
71
What are protozoa?
Unicellular eukaryotes that may be motile due to the presence of flagellae or cilia
72
4 important protozoal diseases?
* Plasmodium falciparum* - malaria * Toxoplasma gondii -* toxoplasmosis * Giardia lamblia -* giardiasis * Trichomonas vaginalis -* trichomoniasis
73
What is the most common mode of transmission of giardia? How does it survive?
Water contamination - can form a cyst that protects the cell from chlorine disinfection etc. so it can survive for a long time outside the body
74
What is this?
Cysts and trophozoites of *Giardia lamblia* (in faeces)
75
Treatment for giardiasis?
Metronidazole 500mg PO tds for 7 days
76
What are the 3 main routes of transmission of *Toxoplasma gondii*?
1. Food-borne 2. Zoonotic (esp. cats) 3. Congenital (mother to child infection)
77
What does infection with *T. gondii* cause?
- Normally a self-limiting mild illness that is acquired in childhood - Childhood illness results in persistent asymptomatic infection that may reactivate if immunocompromised resulting in serious disease (e.g. brain abscess) - Primary maternal infection during pregnancy may result in serious ocular and neurological infection in the foetus
78
What are the two most common organisms that cause malaria?
* Plasmodium falciparum* - severe disease * Plasmodium vivax* - benign disease
79
What is the vector for malaria?
*Anopheles* mosquito (females)
80
Where does the malaria parasite reside inside the host?
RBCs and liver
81
Classic symptoms of malaria include?
Attacks of cyclical fevers (cold stage, hot stage, sweating stage) that last for 6-10 hours and occur every 2 days (or every 3 days with more rare strains)
82
What is this?
Blood smear showing RBCs infected with *Plasmodium falciparum* in ring form (delicate rings with 1 or 2 chromatin dots)
83
How does *P. falciparum* cause disease?
Infects any RBC leading to a high parasite load, and inserts an abnormal protein into RBC membrane causing them to adhere to the endothelium in capillaries, resulting in sequestration, particularly in the brain and kidneys.
84
Why is *P. vivax* more benign than *P. falciparum?*
Low parasite load as it only infects young RBCs, and does not cause sequestration in capillaries so there is no risk of severe disease
85
Treatment of *P. falciparum*?
Quinine and doxycycline to kill merozoites in erythrocytes
86
Treatment of *P. vivax?*
Chloroquine (to kill merozoites in RBCs) and primaquine (to kill hypnozoites in liver that can reactivate later on in life)
87
Malaria prevention includes?
- Avoid malaria regions - Mosquito control - prophylactic treatment with doxycycline or mefloquine
88
Most common cause of pharyngitis?
Viruses - adenovirus, coronavirus, enterovirus, rhinovirus
89
Most common bacterial cause of pharyngitis?
*Streptococcus pyogenes* (GAS)
90
When would you want to take a swab for pharyngitis?
In Maori and Pacific Island populations, to treat GAS and prevent rheumatic fever
91
What is rheumatic fever?
Inflammatory disease involving heart joints, skin and brain that typically develops about 2-4 weeks after a throat infection
92
What are the criteria used for diagnosis of ARF? What are the major criteria?
Jones criteria Major criteria: - Polyarthritis - Carditis - Subcutaneous nodules - Erythema marginatum - Sydenham's chorea
93
When is the heart involved in ARF?
In about half of cases - permanent damage usually requires several bouts of ARF, but can occur after just one episode
94
What is the pathogenesis of ARF?
Due to molecular mimicry of anti-strep antibodies resulting in autoimmune assault on own tissues (autoantibodies against myosin, collagen and other native tissue components)
95
Age range of ARF?
4-19 years
96
Management of ARF?
Treat GAS infection with: - Penicillin V PO 2-3xdaily for 10/7 (\<20kg = 250mg, \>20kg = 500mg) - OR amoxicillin PO 50mg/kg/day od for 10/7 (max 1000mg) - OR single dose IM benzathine penicillin Prevent subsequent infection with secondary prophylaxis: - Benzathine penicillin IM monthly
97
What is PSGN?
Post-streptococcal glomerulonephritis. An uncommon type III hypersensitivity reaction that occurs 10-21 days post-GAS infection.
98
Symptoms and signs of PSGN?
Symptoms: - Pale skin - Lethargy - Loss of appetite - Headache - Dull back pain Clinical findings: - Dark coloured urine - Oedema - High blood pressure
99
Management of PSGN?
Supportive care
100
How do you decide severity of CAP?
CURB65 score C - confusion U - urea \>7mmol/L R - respiratory rate \>30/min B - blood pressure SBP \<90, DBP \<60 Age \>65 Low severity = 0-1 Moderate severity = 2 Severe = 3-5
101
What investigations are required for low severity CAP?
None (other than CXR)
102
What investigations are required for moderate severity CAP?
Blood cultures Sputum Pneumococcal +/- legionella urinary antigen PCR for selected pathogen
103
What investigations are required for severe CAP?
Blood cultures Sputum culture Pneumococcal + legionella urinary antigen PCR for pathogens including viral and atypical pathogens
104
Treatment of non-severe CAP?
Amoxicillin 500mg-1g PO tds for 7 days
105
Treatment for suspected atypical CAP (or patients that do not get better after 24-48 hours of treatment)?
Erythromycin/roxithromycin
106

Pathology and Laboratory Science (4 decks)

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