Microbiology Flashcards
1
Q
What is the most common cause of UTI’s?
A
E.coli
2
Q
What is a commensal?
A
Organism that colonises host but causes no disease normally
3
Q
What is an opportunistic pathogen?
A
Microbe that only causes disease if the host defence is commpromised
4
Q
What is virulence?
A
The degree to which an organism is pathogenic
5
Q
What are the stages of gram staining?
A
- Fixation of material to microscope slide
- Application of primary stain
- Application of iodine
- Decolourisation step
- Application of counterstian
6
Q
What agent is used as a primary stain and what colour does it stain cells?
A
Crystal violet- turns all cells purple
7
Q
What is applied after crystal violet and what does it form?
A
Iodine- crystal violet iodine complex formed
8
Q
What is added in the decolourisatoin step?
A
Acetone or ethanol
9
Q
What differentiated in the decolourisation step (4)?
A
Gram +ve and Gram -ve bacteria
10
Q
What colour do gram positive bacteria stain?
A
Purple
11
Q
What colour to gram negative bacteria stain?
A
Pik
12
Q
What is added as a counterstain to make gram -ve’s pink?
A
Safranin
13
Q
Pneumonic to remember order of stains?
A
Come In And Stain Crystal violet Iodine Alcohol Safranin
14
Q
What is the differene between gram positive and gram negative bacteria?
A
Gram +ve: Thick cell wall (thick layer of peptigoglycan)
Gram -ve: Thin layer of peptidoglycan (thin cell wall), high lipid content
15
Q
What are the two types of gram positive cocci?
A
Staphylococcus
Streptococcus
16
Q
What are the types of gram positive rods?
A
Corneybacteria, mycobacteria, isteria, bacillus, nocardia
17
Q
What test can be done to differentiate staphylococcus?
A
Coagulase test
18
Q
What organism would a positive coagulase test indicate?
A
Staph, aureus
19
Q
What would a negative coagulase test indicate?
A
Coagulase negative staphylococcus (epidermis, saprophiticus)
20
Q
What happens in a coagulase test and what is it used for?
A
Used to differentiate staph. aureus from other types of staph.
Coagulase is an enzyme produced by S. aureus that converts soluble fibrinogen to insoluble fibrin, causing clumping.
21
Q
What test is done to differentiate gram positive cocci?
A
Catalase test
22
Q
What bacteria are present if it is catalase positive?
A
Staphylococcus
23
Q
What bacteria are present if it is catalase negative?
A
Streptococcus
24
Q
What is a catalase test?
A
Catalase is an enzyme that converts hydrogen peroxide to water and oxygen gas. Bacterial isolate is added to hydrogen peroxide and if positive, bubbles of oxygen are observed
25
How can streptococcus be differentiated?
Haemolysis on blood agar
26
What is blood agar and what does it test?
Agar plate that contains sheeps blood:
| Tests the ability of an organism to produce hemolysins, enzymes that break down red blood cells
27
What are the three outcomes of haemolysis on blood agar?
Alpha
Beta
Gamma
28
What does alpha haemolysis look like?
Partial lysis--> Green on red plate
29
What does beta haemolysis look like on a blood agar plate?
Complete lysis--> Clear
30
What does gamma haemolysis look like on a blood agar plate?
No lysis--> Remains red.
31
What organism is present is there is greening of the BAP?
Alpha haemolytic strep
32
How are alpha haemolytic streps differentiated?
Optochin test
33
What is the optochin test?
Optochin antibiotic disk is placed on plate, which will inhibit growth of susceptible bacteria
34
What bacteria are optochin resistant?
Viridans strep
35
What bacteria are optochin sensitive?
S. Pneumonia
36
What bacteria are present if there is complete lysis (clear) BAP?
S. pyogens
| Lancefield groups A, B, C, G
37
What bacteria are present if there is no lysis (red BAP)?
Lancefield D: S. bovis, enterococcus.
38
What kind of bacteria is S. aureus and what kind of infections does it usually cause?
Gram +ve, Coagulase +, catalase + Staphylococcus (cluster)
| Skin infection
39
What kind of bacertia is MRSA?
Gram +ve, Coagulase +ve Staphylococcus
40
What kind of bacteria is S.pneumonia and where does it usually affect?
Gram +ve, Catalase -ve, alpha haem Streptococcus
| Affects ENT
41
What kind of bacteria is S. pygones and where does it usually affect?
Group A streptococcus
| Throat + skin
42
How are gram negative bacilli differentiated?
By their appearance on MacConkey agar
43
What is MacConkey agar and how does it differentiate gram negative bacteria?
Inhibits Gram-positive organisms and differentiates Gram-negative organisms by lactose fermentation.
44
What colour will lactose fermenting bacteria turn MacConkey agar?
Pink
45
What colour will non-lactose fermenting bacteria stain MacConkey agar?
White/ clear
46
What are the main lactose fermenting bacteria?
E.Coli
| Klebsiella
47
What are the main non lactose fermenting bacteria?
Shigella
Salmonella
Pseudomonas
Proteus
48
How are lactose fermenting bacteria further differentiated?
Biochemical identification (API strip) + Sensitivity tests
49
How are non lactose fermenting bacteria further differentiated?
Oxidase test
50
What bacteria tests positive in the oxidase test?
Pseudomonas
51
What non lactose fermenting bacteria tests negative in an oxidase test?
Shigella, Salmonella, Proteus
52
What type of bacteria is E.Coli and what are the main infections it causes?
Lactose fermenting Gram -ve bacteria:
UTI's
Travellers diarrhoea
53
What type of bacteria is Klebsiella and what are the main infections it causes?
Lactose fermenting gram -ve bacilli:
| Pneumonia, meningitis
54
What type of bacteria is pseudomonas and what infections does it commonly cause?
Non-lactose fermenting, Oxidasae +ve gram negative bacilli:
| Pneumonia
55
What type of bacteria is Shigella and what infections does it commonly cause?
Non-lactose fermenting, Oxidasae -ve gram negative bacilli:
| Shigellosis (diarrhoea/ fever)
56
What type of bacteria is Salmonella and what infections does it commonly cause?
Non-lactose fermenting, Oxidasae -ve gram negative bacilli:
| Salmonellosis (diarrhoea)
57
What type of bacteria is Neisseria and what infections does it commonly cause?
Gram negative cocci:
| Gonorrhoea, meningitis
58
What are the most common gram positive rods?
Corneybacteria, Mycobacteria, Listeria, Bacillus, Nocardia
59
What are the most common gram negative cocci?
Neisseria (gonorrhoea), Moraxella
60
What are the two most common causes of meningitis and what type of bacteria are they?
N. meningitidis (meningococcus)--> Gram negative cocci
S. pneumonia--> Gram positive cocci
(Diplococci)
61
Which Hepatis is the only DNA virus (instead of RNA)?
Hep B
62
Which forms of hepatitis are spread by faecal-oral transmission?
Hep A & E
63
Which forms of hepatitis are spread by blood-blood transmission?
B, C, D
64
How does acute non-inflammatory diarrhoea present?
Watery and non-bloody with no fever
65
How does acute inflammatory diarrhoea present?
Bloody, possibly with pus and fever
66
What is bloody diarrhoea also known as?
Dysentry
67
What are the two ways bacterial toxins can enter the body?
Secrete exotoxins directly into food
| Enter the body and secrete enterotoxins
68
What bacteria produce preformed exotoxins?
Staph. aureus
| Bacillus cereus
69
What are the main pathogens that cause noninflammatory acute diarrhoea?
```
E.coli (ETEC)
Vibrio cholerae
Staph. aureus
Bacillus cereus
Listeria
Norovirus
Giardia lamblia
```
70
What are the main pathogens that cause inflammatory diarrhoea?
```
Salmonella
Shigella
Campylobacter
C.Diff
STEC
```
71
What does a presentation of diarrhoea with vomiting suggest?
S.aureus food poisoning or viral gastroenteritis
72
What should be suspected if symptoms come on within 6 hours of ingesting food?
S. aureus of B. cereus (preformed exotoxin) infection
73
What is the main cause of travellers diarrhoea?
Enterotoxigenic E. coli (ETEC)
74
What is the most common cause of Osteomyelitis?
Staph. aureus
75
What is the most common cause of septic arthritis?
S. aureus
| Young sexually active adults: Neisseria gonorrhoea
76
What is the most common bacterial STI?
Chlamydia
77
What are the main symptoms of chlamydia?
70% asymptomatic
Men: Urethritis, Testicular pain
Women: Vaginal discharge, lower abdominal/ pelvic pain
78
What is the first line investigation for STI?
NAAT (Nucleic acid amplification test)
79
How is chlamydia treated?
Doxycycline/ Azithromycin antibiotics
80
What is the second most common STI in the UK?
Gonorrhea (Niesseria gonorrhoea)
81
How does gonorrhea present?
Usually asymptomatic
Men: Urethritis with purulent discharge and dysuria
Women: Pelvic pain with vaginal discharge, itch and dysuria
82
What is the most common cause of viral meningitis?
Enteroviruses
| Herpes simplex
83
What pathogen causes TB?
Mycobacterium tuberculosis
84
What kind of antibiotic is usually used to treat gram positive bacteria and why?
Those that inhibit cell wall synthesis as gram positive bacteria have thick cell walls
85
What are the different types of antibiotic that inhibit cell wall synthesis?
Penicillins
Glyopeptides
Cephalosporins
Carbapenems
86
What are the main types of glyopeptides/
Vancomycin
| Teicoplanin
87
What are the main types of penicillins?
Benzylpenicillin
Amoxicillin
Flucloxacillin
88
What are the main types of cephalosporins?
Cephalexin
Cefotaxime
Ceftriaxone
89
What are the main types of carbapenems?
Imipenem
| Estapenem
90
When are Carbapenems usually used?
For the treatment of severe infections or infection caused by multiple resistant bacteria
91
What types of antibiotic inhibit protein synthesis?
Cholaramphenicol
Macrolides
Tetracyclines
Aminoglycosides
92
What would be used instead of penicillin in those with a penicillin allergy?
Macrolides (e.g. Clarithromycin, Erythromycin)
93
What are the different ways antibiotics can inhibit nucleic acid synthesis?
Inhibit folate synthesis
Inhibit DNA Gyrase
Bind to DNA polymerase
Break DNA strands
94
What are the main types of antibiotic that inhibit nucleic acid synthesis?
```
Rifamipcin
Fluroquinolones
Ciprofloxacin
Trimethoprim
Sulphonamids
Sulphamethoxazole
Metronidazole
```
95
Why should you never give the antibiotic Trimethroprim to pregnant women?
It inhibit folate synthesis and folate is very important during pregnancy to prevent spina bifida
96
What antibiotic is the first line in staph infections?
Penicillins e.g. Flucloxacillin
97
What is the main antibiotic used for UTI's?
Nitrofurantoin or Trimethoprim
98
What antibiotic is used to treat MRSA?
Vancomycin
99
What are mycobacteria?
Aerobic, non-spore forming bacilli
100
What are the two main types of mycobacteria?
TB + Leprosy
101
How are Mycobacteria investigated?
Zeihl-Neelsen stain instead of gram staining
102
What are the two outcomes of Zeihl-Neelsen staining?
Acid-fast bacteria stain red
| Non acid-fast bacteria stain blue
103
How can viruses be identified>
PCR
Nucleic acid amplification tests (NAAT)
Serology: look for antibodies in response
104
What can be given to treat severe viral infections?
Antivirals: End in 'vir' e.g. Acyclovir
105
What are protozoa?
Microscopic unicellular eukaryotes
106
How are protozoa classified?
Based on movement: ameoiboids, ciliates, sporozoan, flagellates
107
What are the most common types of protozoa?
Malaria
Giardia Lamblia
Toxoplasmiosis
Trichomonas vaginalis
