Microbiology Flashcards
1
Q
Define colonisation
A
The microorganism can be cultured from the host but is not causing disease.
Other words - commensal or asymptomatic carriage
2
Q
Define infection
A
The microorganism can be cultured from the host and it is causing disease
3
Q
Define opportunistic pathogen/infection
A
Microorganism that only cause disease when the host defence is somehow compromised
4
Q
Define virulence/pathogenicity
A
The degree to which a given organism is pathogenic
5
Q
Describe the nomenclature of bacteria
A
Staphylococcus (genus) aureus (species)
Name commonly reflects the shape
6
Q
Describe the colonial morphology of staph aureus
A
Gold and round
7
Q
Describe the colonial morphology of staph epidermiditis and saprophyticus
A
White and round
8
Q
Describe the colonial morphology of strep pyogenes
A
White, round, beta haem
9
Q
Describe the colonial morphology of pseudomonas aeruginosa
A
Green, irregular, mucoid, smells like swimming pool
10
Q
Describe the colonial morphology of e.coli
A
Greyish, round, faecal smell
11
Q
Describe the colonial morphology of Neisseria
A
Greyish, round
Only grows on chocolate agar
12
Q
What is grown on blood agars
A
Streptococcus and other
13
Q
What is grown on chocolate agars
A
(cooked blood)
Fastidious Neisseria
14
Q
What is grown on MacConkey agars
A
Lactose status
15
Q
What is grown on CLED agars
A
Stops motile proteus swarming
Lactose status
16
Q
What is grown on xylose lysine deoxycholate agar (XLD) agar
A
Selective growth
Salmonella and shigella from clinical samples and food
Both go red - ferment lactose
Salmonella - turns back dots - due to hydrogen sulphide production
17
Q
What layer soaks up crystal violet
A
Peptidoglycan layer
Gram negative - washed away
Gram positive - cannot be
18
Q
What colour do gram positive bacteria stain
A
Purple
19
Q
What colour do gram negative bacteria stain
A
Pink
20
Q
Describe the steps of gram stain
A
Crystal violet
Iodine
Alcohol (gram negative will become colourless)
Safranin (gram negative becomes pink)
21
Q
What is the mnemonic for gram staining
A
Come in and stain
Crystal violet
Iodine
Alcohol
Safranin
22
Q
What gram stain is staphylococcus aureus
A
Gram positive cocci (bunch of grapes)
23
Q
What gram stain is e.coli
A
Gram negative rod, short and stubby
24
Q
What gram stain is Neisseria meningitidis
A
Gram negative diplococci
25
What gram stain is bacillus cereus
Gram negative rod, long rod, some occurring in chains
26
What is the role of the catalase test
What would show on the test
Differentiates between staphylococcus and streptococcus genus
Staph = +
strep = -
27
On a catalase test does staph show are
Positive (weak bubbling)
28
On a catalase test what does strep show as
Negative (no bubbling)
29
Describe the method of catalase test
Apply hydrogen peroxide 3% to a small sample of pure colony
Observe for any bubbling
Any weak bubbling = positive
30
What is the role of the coagulase test
Is it staph aureus?
Differentiates staph aureus (which produces enzyme coagulase) from s. epidermis and s. saprophyticus
31
A +ve coagulase test would be which bacteria
Staph aureus
32
Describe the method of the coagulase test
Apply rabbit plasma to a small sample of pure colony
Observe for fibrin clot clumps
33
Describe the role of optochin
Differentiating alpha-haemolytic streps
S. pneumonia = susceptible
All other alpha streps are resistant
34
What is the role of the Lancefield serotyping
Differentiates beta haemolytic streps
Relies on different, group-specific carbohydrates antigen presents on the cell wall
35
Describe an infection of c. difficle
Antibiotic therapy = disruption of colonic microflora
C. diff exposure and colonisation
C. diff toxin A and B cause mucosal injury and inflammation
= pseudomembranous colitis = toxic megacolon = perforation and death
36
What is the treatment of c. diff
10 days oral fidaxomicin or vancomycin
37
What is the treatment of meningitis
Cephalosporins - IV cefotaxime/IV ceftriaxone
Over 50/immunocompromised - IV amoxicillin to cover listeria
38
What treatment is given for contacts of meningitis
One oral dose of ciprofloxacin
39
What is the treatment of meningococcal septicaemia
Immediate IM benzylpenicillin (community)
IV cefotaxime (hospital)
40
What medication is given to UTIs during pregnancy
Cefalexin
41
What medication is given to UTIs
Oral nitrofurantoin or trimethoprim
Simple = 3 days
Complicated = 7 days
42
Describe the pathophysiology of helicobacter pylori infection
Colonise gastric mucosa
Urease enzyme = urea = NH3 + CO2
Disrupts mucous and release toxins = ulcers
43
What is the gram stain of helicobacter pylori
Gram negative
44
What is the treatment of h. pylori
Triple therapy
Abx + Abx + PPI
Amoxicillin + metronidazole + omeprazole
45
What antibiotics inhibit cell wall synthesis
Glycopeptides - vancomycin, teicoplanin
Beta lactams
- penicillin
- cephalosporins
- carbapenems
46
Give 3 examples of cephalosporins
Cephalexin
Cefotaxime
Ceftriaxone
47
Give 2 examples of carbapenems
Imipenem
Ertapenem
48
What is used to treat MRSA and c. diff infections
Glycopeptide vancomycin
49
What antibiotics inhibit protein synthesis
Chloramphenicol
Macrolides
Tetracyclines
Aminoglycosides
50
Name 2 examples of macrolides
Clarithromycin
Erythromycin
51
Name an example of tetracyclines
Doxycycline
52
Name 2 examples of aminoglycosides
Gentamicin
Streptomycin
53
What antibiotic is generally used for people with penicillin allergies
Macrolides
54
Name 4 ways in which antibiotics can inhibit nucleic acid synthesis
Inhibit folate synthesis
Inhibit DNA gyrase
Bind to RNA
DNA strand breaks
55
Which antibiotics inhibit folate synthesis
Trimethoprim
Sulphonamides - sulphamthoxazole
56
Which antibiotics inhibit DNA gyrase
Fluroquinolones - ciprofloxacin
57
Which antibiotics bind to RNA polymerase
Rifampicin
58
Which antibiotic causes DNA strand breaks
Metronidazole
59
How is antibiotic sensitivity testing performed
Lawn of test microorganism onto Mueller-Hinton agar
Place antibiotic discs onto lawn and incubate
Measure diameter
60
What are beta-lactamase producing bacteria resistant to
Penicillin-derived Ab
61
Describe how MRSA is resistant
Carries a gene called mecA - unique transpeptidase that is not inhibited by B-lactam antibiotics
Is able to continue peptidoglycan crosslinking (PBP2a) and resist
62
What is MRSA resistant to
B-lactams
63
What is a common resistance mechanism in bacteria
Efflux pumps
64
What is a side effect of isoniazid
Numb/tingly extremities
I can't feel my hands - Ison
65
What is a side effect of ethambutol
Eye
Ocular side effects
66
What is a side effect of rifampicin
Orange/red urine
Red and orange picin
67
What is a side effect of pyrazinamide
Arthralgia
68
Name the 4 treatments for mycobacteria (TB)
Isoniazid
Ethambutol
Rifampicin
Pyrazinamide
69
What bacteria do not stain using the traditional gram method
Mycobacterium, actinomycetes, parasite cryptosporidium
Have waxy, lipid cell walls
Ziehl-Neelson stain used
70
What is acid-fastness a property of
Mycobacteria
71
Describe Ziehl-Neelson stain
Heating the sample with a strong dye (carbol fuchsin)
Heat makes the bacteria resistant to decolourisation by acid = acid-fast
When slide flooded with acid - mycobacteria retains the pink dye
Everything else decolourised blue
72
Name 3 features of fungi
Eukaryotes
Cell wall is made of chitin and glucan
Clinically usually opportunistic
73
What are the two forms of fungi
Yeast - single cell that divide via budding
Moulds - form multicellular hyphae or spores
74
Describe the treatment of fungi
Antifungal drugs - target the cell wall/plasma membrane (do not work that well)
- azole
Generally difficult to treat once systemic
75
Describe candida albicans
Most pathogenic = candida spp.
Vaginal/oral infections, sepsis line/catheter infections
Can kill rapidly
76
Describe aspergillus fumigatus
Most pathogenic = Asp. spp
Lung infections in CF, allergic disease
Poor prognosis - kills slowly
77
Define a virus
Infectious, obligate intracellular parasite, compromising of genetic material (DNA or RNA) surrounded by a protein and/or membrane
78
Describe the generic Lifecyle of a virus
1. Attachment
2. Entry
3. Genome released
4. Transcription
5. Translation
6. Genome replication
7. Assembly
8. Exit
79
Name 5 ways in which virus cause disease with an example
Direct destruction of host cells - poliovirus
Modification of host cell - rotavirus
'Over-reactivity' of immune system - HBV infection
Damage through cell proliferation - human papillomavirus
Evasion of host defences - varicella zoster virus
80
Name the ways in which virus can be identified
PCR
Serology
Histopathology
81
What treatment is used in hepatitis C infection
Direct acting antivirals
82
What treatment is used in HIV infection
Highly acting anti-retroviral therapies
83
What is the treatment for herpes viral sepsis
Aciclovir
84
Describe protozoa
Microscopic unicellular eukaryotes
Can be free living or parasitic
Classification based on movements - amoeboid, ciliates, sporozoan, flagellates
85
Name 4 examples of protozoa
Malaria
Giardia lamblia
Toxoplasmosis spp.
Trichomonas vaginalis
86
Describe the cycle of malaria
Sporozoites (cell type that infects new hosts) develop in the salivary glands of Anopheles mosquitos
Leave the mosquito during a blood meal and enter the hosts liver and multiply
Cell infected with sporozoites eventually burst - releasing merozoites into the bloodstream
These infect red blood cells and rapidly multiply and reproduce, destroying the red blood cell hosts and releasing many new merozoites.
87
Describe the clinical picture of malaria
Non-specific symptoms
History of recent travel, possible insect bite or non-compliance with prophylaxis
88
What is the treatment of malaria
Oral chloroquine for uncomplicated
IV artesunate for complicated
89
Name the 5 malarial species
Most common = p. falciparum
P. malariae
P. vivax
P. ovale
P. knowlesi
90
Where is p. falciparum and p. malariae found
Widespread in sub. Saharan Africa, southeast asia, oceania and south america
P. malariae found in lower prevalance
91
Where is p. vivax found
Asia, America, Eastern europe, north africa
80% cases occur ethiopia, india and pakistan
92
Where is p. ovale found
Africa and west pacific
93
Where is p. knowlesi found
Forested areas of southeast asia
94
Name the 2 malaria species which can go dormant in the liver causing relapse
P. vivax
P. ovale
95
A bite which causes malaria is from what mosquito
Anopheles mosquito
96
Describe the diagnostic test of choice for malaria
Giemsa-stained thin and thick blood film smear
97
Describe 3 key features of gram positive bacteria
Prefer dry and dusty environments
Skin colonisers
Can spread by breathing in shed skin scales
98
Describe 2 key features of gram negative bacteria
Prefer wet and damp environments
Majority prefer to colonise mucous membranes
99
Describe h. pylori
Gram negative, spiral bacterium
100
What is the transmission of h. pylori
Oral-oral
Faecal-oral
101
Describe campylobacter
Traveller's diarrhoea
Spread by raw or improperly cooked poultry, untreated water, unpasteurised milk
Treatment = clarithromycin
Most common cause of gastroenteritis worldwide
102
What bacteria produced shiga toxins and what do they do
E.coli
Abdominal cramps
Bloody diarrhoea
Vomiting
Haemolytic uraemia syndrome
103
What virus causes gastroenteritis would be seen in a healthcare setting
Norovirus
104
Name the cause of meningitis
Usually bacterial - meningococcus, pneumococcus
Viruses
Less common infections
Non-infectious (rare)
medications
cancers
Autoimmune diseases - SLE
105
What is the structure of Neisseria meningitidis
Gram-negative diplococci
106
Describe the general infection of Neisseria meningitidis
Carried by 10-24% of the population
Humans only known reservoir
Transmission by respiratory droplets/naso-pharyngeal secretions
Incubation period 2-10 days - usually 3-4
107
What are the two manifestations of Neisseria meningitidis
Meningitis - a localised infection of the meninges, with local symptoms
Septicaemia - a systemic infection with widespread signs, and generalised organ damage
108
How many serogroups of Neisseria meningitidis are there
12 - based on the capsular polysaccharide
6 cause majority of cases of meningococcal disease
109
Describe the epidemiology of Neisseria meningitidis
Highest conc. sub-saharan countries
4-15% mortality
Most prevalent during winter
Frequent or prolonged close contact
Extremes of age (<2 months and > 60 years)
110
Describe the Brudzinski's neck sign
For meningitis
Flex neck when lying flap on back. Results in flexion of the hips and knees
111
What is petechiae
Rash seen in meningitis
Rash does not fade when glass is pressed firmly against
112
Name a complication of sepsis
Disseminated intravascular coagulation
113
Describe disseminated intravascular coagulation
Activation of coagulation pathways that results in formation of intravascular thrombi (clots) and depletion of platelets and coagulation facts.
Clots can cause arterial occlusions leading to gangrene of extremities and auto-amputations
114
How is a diagnosis of meningitis made
Before initiating antibiotics
- Blood sample
- CSF
- Throat swab for culture
115
What does group A streptococcus bacteria cause
Scarlet Fever
Sandpaper rash
Strawberry tongue
116
What does salmonella typhi bacteria cause
Typhoid fever
Risk factors - travel
Risk groups - food handlers, health and care staff, young children, doubtful hygiene
117
What does legionella pneumophilia bacteria cause
Legionnaires disease
Think - travel and water-related exposure
118
Name 6 opportunistic infections
Kaposi’s sarcoma.
Pneumocystis jirovecii pneumonia (PCP).
Cytomegalovirus infection.
Candidiasis (oesophageal or bronchial).
Lymphomas
Tuberculosis.
119
Septic arthiritis - what is the most common cause
Staph aureus
120
Septic arthiritis - what is the most common cause in prosthetic joints
Staph epidermidis
121
Septic arthiritis - what is the most common cause in immunosuppressed, elderly, IVDU
Pseudomonas epidermidis
122
Septic arthiritis - what is the most common cause in children
Haemophilus influenza
123
Septic arthiritis - what is the most common cause in sexually active young adults
N. gonococcus
124
