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Microbiology Flashcards

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1
Q

What are prion proteins?

A

Infectious proteins with no DNA or RNA
Rare, but cause incurable brain infection
Cannot easily removed by sterilisation or disinfection

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2
Q

What are viruses?

A

RNA or DNA
Protein coat +/- lipid envelope
Obligate intracellular parasite

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3
Q

What are the diagnostic methods for parasites?

A

Viral cell culture
Antigen or antibody detection in blood (serology)
PCR to detect DNA or RNA

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4
Q

What are bacteria?

A 
Contain DNA and RNA 
One double strand chromosome, sometimes with extra plasmids
Cell membrane and cell wall +/- capsule 
Flagellae for movement 
Pili/fimbriae for adhesion
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5
Q

What are the bacterial shapes?

A 
coccus = round 
bacillus = rod shaped 
spirochaetes = spirals
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6
Q

What colour does gram positive stain?

A

Purple

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7
Q

What colour does gram negative stain?

A

Pink

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8
Q

What does a gram positive cell wall look like?

A

Thick layer of peptidoglycan

This will hold the purple colour

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9
Q

What does a gram negative cell wall look like?

A

Thin layer of peptidoglycan

Cannot hold the purple colour, so shows pink

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10
Q

Why does mycobacterium tuberculosis not stain well with gram stain?

A

Has a thick waxy coat which does not take up the stain

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11
Q

What is a pathogen?

A

A harmful organism

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12
Q

What is a commensal?

A

An organism that is part of the normal flora

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13
Q

What is an opportunistic pathogen?

A

An organism that will probably only cause infection in n immunocompromised individual

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14
Q

What is a contaminant?

A

An organism that has got into the culture by a accident

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15
Q

What is pathogenicity?

A

The ability of a microorganism to produce disease

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16
Q

What is virulence?

A

The degree of pathogenicity of an organism (how easily the organism can cause disease)

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17
Q

By which method to bacteria replicate?

A

Binary fission

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18
Q

how quickly can bacteria double their numbers in ideal growth conditions?

A

Every 20 minutes

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19
Q

What are the four stages of the bacterial growth curve?

A

Lag phase = DNA replication
Log phase = Exponential growth
Stationary phase = Rate of growth equal to rate of death
Death phase = Limited nutrients, so bacteria compete and some die

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20
Q

What is an exotoxin?

A

Mostly produced by gram positive bacteria

Usually produced inside the cell then exported from it

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21
Q

What is an endotoxin?

A

Mostly produced by gram negative bacteria

Part of the gram negative bacterial cell wall, released when bacterial cell dies

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22
Q

What are the diagnostic methods for bacteria?

A 
Microscopy (gram stained film)
Culture 
Detection of antigen 
Detection of antibodies in blood (serology)
PCR
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23
Q

What types of fungi are there?

A 
Moulds = Produce spores and hyphae
Yeasts = Reproduce through budding
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24
Q

What is the most common cause of mould infection in humans?

A

Aspergillus spp

usually in immunocompromised

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25
What is the most common cause of fungal infection in humans?
Candida spp Yeast Stain as lage gram positive oval structures
26
What are the gram positive aerobic cocci?
``` Streptococci = chains Staphylococci = clusters ```
27
How do you differentiate between streptococcus species?
Haemolysis seen on blood agar
28
What are the possible results of streptococcal haemolysis?
Alpha haemolysis = partial haemolysis, greenish discolouration around colony Beta haemolysis = complete haemolysis, clearing around colony, most virulent Gamma haemolysis = no haemolysis
29
What are the alpha haemolytic streptococci?
Streptococcus pneumoniae | Streptococcus "viridans"
30
What infections can be caused by Streptococcus pneumoniae?
Commonest cause of pneumonia | Also causes meningitis
31
Where would the Streptococcus "viridans" normally colonise and what infection can they cause if they reach a normally sterile site?
Common commensals of the URT, bowel and vagina Endocarditis
32
What are the beta haemolytic streptococci?
Group A strep (Strep. pyogenes) | Group B strep
33
What infections can be caused by Group A Streptococcus (Strep. pyogenes)?
Streptococcal sore throat (tonsillitis) (+ rash gives scarlet fever) Skin and soft tissue infections (e.g. necrotising fasciitis) Puerperal sepsis (life threatening infection in pregnant and recently post natal women)
34
What are the non-haemolytic streptococci?
Most important are the enterococci (part of normal bowel flora)
35
What infection can be caused by the Enterococci?
Commonest cause of UTI
36
Which test is used to distinguish between Staphylococcus species?
Coagulase test
37
What are the possible results if a Staphylococcus coagulase test?
Coagulase positive | Coagulase negative
38
What is the one coagulase positive Staphylococcus?
Staphylococcus aureus
39
Which infections can be caused by Staphylococcus aureus?
Commonest cause of skin, soft tissue and wound infection Commonest cause of bone and joint infection Enterotoxin producing strains cause food poisoning Staph. aureus bacteraemia
40
What are the coagulase negative Staphylococci?
Many species of skin commensals | Inc. Staph epidermidis
41
What infections can be caused by coagulase negative Staphylococci?
Prosthetic joint and heart valve infection | IV catheter infection
42
Which antibiotics can be used to treat Streptococcus pneumoniae?
Most UK strains still resistant to penicillin
43
Which antibiotics can be used to treat Group A Streptococci?
All strains still sensitive to penicillin and amoxicillin
44
Which antibiotics can be used to treat Enterococci?
Most trains still sensitive to amoxicillin (not penicillin)
45
What is the antibiotic of choice for Staphylococcus aureus?
Flucloxacillin
46
What are antibiotic resistant strains of Staphylococcus aureus resistant to?
MRSA | All penicillins, all cephalosporins, plus others
47
What is pyrexia?
Raised temperature (fever)
48
What is rigor?
Shivering attack as raised temperature drops | Sign of fever or pyrexia
49
Above which temperature is fever diagnosed?
>38 degrees C
50
What causes sepsis?
Small blood vessels become leaky in severe infection and fluid is lost into the tissues Lower blood volume leads to septic shock
51
What are the gram negative aerobic cocci?
Diplococci (appear in pairs) Neisseria meningitidis Neisseria gonorrhoeae
52
What infection can be caused by Neisseria meningitidis?
Commonest cause of bacterial meningitis
53
What infection can be caused by Neisseria gonorrhoeae?
Gonorrhoea
54
What are the gram negative aerobic large bacilli?
Coliforms | Look like E.coli on gram film and blood culture
55
How are the coliforms differentiated from each other?
Biochemical reactions | Antigenic structure of cell wall (serotyping)
56
What are the gut commensal coliforms?
``` Most E.coli spp. Klebsiella spp. Enterobacter spp. Proteus spp. Many more ```
57
What are the gut pathogen coliforms?
Salmonella spp. Shigella spp. Verotoxin producing E.coli (E.coli O157, E.coli O104)
58
What infections can be caused by the coliforms?
Any coliform in a normally sterile site, e.g. UTI Peritonitis Biliary tract infection
59
What is the first line antibiotic treatment for coliform infections?
Gentamicin
60
What are the gram negative aerobic small bacilli?
``` Pseudomonas aeruginosa Legionella pneumophila (Legionnaires' disease) ```
61
What are the gram negative microaerophilic bacilli?
Spiral or curved Gram negative bacilli = Vibrio cholerae Campylobacter spp Helicobacter pylori
62
What infection is caused by Vibrio cholerae?
Cholera
63
What infection is caused by Campylobacter?
Commonest cause of bacterial diarrhoea in the UK
64
What infections can be caused by Helicobacter pylori?
Gastritis | Duodenal ulcers
65
What is the gram negative aerobic small (cocco)bacillus and what infection does it cause?
Haemophilus influenzae | Common cause of chest infection
66
What are the strict anaerobes?
Clostridium spp. | Bacteroides spp.
67
What is the classification of the Clostridium spp?
Gram postive anaerobic bacilli
68
What type of Clostridium spp. are there and what infections do they cause?
Clostridium difficile = Antibiotic associated diarrhoea Clostridium perfringens = "Gas" gangrene Clostridium tetani = Tetanus
69
What is the classification of the Bacteroides spp?
Gram negative anaerobic bacilli
70
What infections can be caused by the Bacteroides spp?
Usually non pathogenic | Only cause infection in sterile sites (e.g. peritoneum, biliary tract)
71
What is the first line treatment for infections caused by anaerobes?
Metronidazole
72
What are the Mycobacteria?
Have a thick waxy outer coat which does not take up Gram Stain Stained by acid fast bacilli or acid-alcohol fast bacilli
73
What infection can be caused by Mycobacterium tuberculosis?
TB
74
What are the Spirochaetes?
Spiral shaped spectre that do not stain on gram stain Treponema pallidum Borrelia burgdorferi
75
What infection is caused by Treponema pallidum ?
Syphilis
76
What infection is caused by Borrelia burgdorferi?
Lyme disease
77
How does genetic variation in bacteria occur?
Mutation | Gene transfer
78
How do mutations in bacterial DNA cause genetic variation?
Rapid bacterial grwoth increases chance of genetic mutation This leads to new variants of the organism Many fail to survive, but rare strains can be successful
79
What are the three methods of gene transfer?
Transformation Conjugation Transduction
80
How does transformation lead to genetic variation?
DNA released from dead bacteria can be taken up by living bacteria and incorporated into palms or bacterial chromosome
81
How does conjugation lead to genetic variation?
Bacterial "sex" | Sex pilus is produced by one bacteria through which plasmids DNA can be transferred
82
How does transduction lead to genetic variation?
Viruses that infect bacteria can transfer bits of DNA from one bacteria to another
83
What are the main mechanisms of antibiotic resistance?
Production of enzymes that destroy antibiotics Altered antibiotic binding sites Alteration of cel wall porins Up-regulation of efflux pumps
84
Which enzymes can be produced to destroy antibiotics?
Beta-lactamase = resistance to early penicillins like amoxicillin Extended spectrum beta-lactamse = resistance to all penicillins and cephalosporins Carbapenemase = resistance to all penicillins, all cephalosporins and carbapenems
85
How do altered antibiotic binding sites cause antibiotic resistance?
Genetic mutation alters antibiotic binding sites | Antibiotics that cannot bind have no effect on bacteria
86
Give an example of altered antibiotic sites leading to antibiotic resistance?
Alteration of penicillin binding protein on Staph aureus resulted in fluxloxacillin resistance (MRSA)
87
How do changes to cell wall porins cause antibiotic resistance?
Alterations to porins may result in bacterial cell wall becoming impermeable to the antibiotic
88
How does up regulation of efflux pumps cause antibiotic resistance?
Antibiotic is removed from the cell before it has time to act
89
Give an example of up regulation of efflux pumps leading to antibiotic resistance?
Common mechanism of resistance in fungi e.g. Candida spp.
90
Why must antibiotics be selectively toxic?
To kill bacteria without killing surrounding tissue
91
What is the difference between bactericidal and bacteriostatic?
``` Bactericidal = Kill bacteria Bacteriostatic = Inhibit bacteria growth ```
92
By which three mechanisms can antibiotics work?
Acting on bacterial cell wall = Human cells do not have a cell wall Affecting the bacterial ribosome = Structurally different from human ribosomes Acting in bacterial DNA = Structurally different from human DNA
93
Which groups of antibiotics work on the bacterial cell wall?
Penicillins Cephalosporins Glyopeptides
94
What are the advantages of the penicillins?
Safe, very few side effects Narrow to broad spectrum Excreted rapidly via kidneys Safe in pregnancy
95
What are the disadvantages of the penicillins?
Some patients are allergic - allergy to one means allergy to all of the family, and sometimes also cephalosporins Frequent dosing needed due to rapid excretion
96
What are the three forms of penicillin available?
``` Benzylpenicillin (IV) Phenoxymethyl penicillin (Oral) Benzathine penicillin (IM) ```
97
Which penicillin can only be used for gram positive organisms and why might it be prescribed?
Flucloxacillin (IV, Oral) Only used for Staphylococci and Streptococci Skin and soft tissue infection Wound infection Cellulitis
98
Which penicillins can be used for gram positive and negative organisms?
Amoxicillin (IV, Oral) Co-Amoxiclav (IV, Ora) Tazocin (IV)
99
Why is Co-Amoxiclav more effective than Amoxicillin?
Clavunic acid is a beta-lactamase inhibitor, and so prevents the destruction of amoxicillin
100
Which penicillin can only be used for gram negative organisms and why might it be prescribed?
Temocillin (IV) Only active against coliforms Brought back due to increasing bacterial resistance Still active against EBSL producing organisms
101
What are the advantages of the cephalosporins?
Excreted via kidneys and urine Few side effects Safe in pregnancy
102
What are the disadvantages of the cephalosporins?
Broad spectrum antibiotics, significantly affect the normal bowel flora Increased risk of C.diff
103
Give examples of the glycopeptides?
Vancomycin (IV) Teicoplanin (IV) Excreted via kidneys and urine
104
What kinds of bacteria are the glycopeptides active against?
ONLY active against organisms with a gram positive cell wall
105
Are penicillins bactericidal or bacteriostatic?
Bactericidal
106
Are cephalosporins bactericidal or bacteriostatic?
Bactericidal
107
Are glycolpeptides bactericidal or bacteriostatic?
Bactericidal
108
Which groups of antibiotics inhibit protein synthesis?
The macrolides The tetracyclines The aminoglycosides Others (clindamycin, chloramphenicol)
109
Are macrolides bactericidal or bacteriostatic?
Bacteriostatic
110
Are tetracyclines bactericidal or bacteriostatic?
Bacteriostatic
111
Are aminoglycosides bactericidal or bacteriostatic?
Bactericidal
112
Give examples form the macrolide family?
Erythromycin Clarythromycin Azithromycin
113
How are the macrolides excreted?
Via the liver, biliary tract and into the gut
114
Which macrolide is safe in pregnancy?
Erythromycin
115
Which kinds of infections are macrolides useful in treating?
Infections in which bacteria hide from hot cell immunity by getting into the host cells Macrolides are lipophilic
116
Give an example of an aminoglycoside?
Gemtamicin (IV)
117
Which organisms is gentamicin effective against?
Gram negative aerobes such as coliform and pseudomonas aeruginosa
118
How is gentamicin excreted?
Via urine
119
In what way is gentamicin toxic?
Damages kidneys and CN VIII, causing dizziness and deafness | Must monitor bloods carefully
120
Which groups of antibiotics act on bacterial DNA?
Metronidazole Trimethoprim (+/- sulphonamide) Fluroquinolones
121
Which infections are metronidazole used to treat?
True anaerobic infections | Some protozoal infections
122
How can trimethoprim be administered?
On its own, orally | In combination with sulphamethoxazole, orally or IV, as co-trimoxazole (synergistic effect)
123
Which bacteria is trimethoprim effective against?
Some Gram negative and some Gram positive bacteria
124
How is trimethoprim excreted?
Via urine
125
Give examples of Fluroquinolones?
Ciprofloxaxin (IV, Oral) | Levofloxacin (IV)
126
Are fluroquinolones bactericidal or bacteriostatic?
Bactericidal
127
How are fluroquinolones excreted?
Via urine
128
Which antibiotic should you really not drink alcohol when taking?
Metronidazole
129
What are the 4 C antibiotics?
Cephalosporins Co-Amoxiclav Ciprofloxacin Clindamycin
130
Why do we avoid use of the 4 C antibiotics?
Broad spectrum | Associated with increased risk of C.diff

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