Microbiology Flashcards
(247 cards)
1
Q
Define pathogen
A
An organism that causes/can cause a disease
2
Q
Define commensal
A
Organism colonising the host but usually causes no disease
3
Q
Define opportunist pathogen
A
Microbe only causing disease if host diseases compromised
4
Q
Define virulence/pathogenicity
A
Degree to which an organism is pathogenic
5
Q
Define asymptomatic carriage
A
Pathogen carried harmlessly at a tissue site, causing no disease
6
Q
How is a gram stain done (4 steps)?
A
- Add crystal violet
- Add iodine
- Add acetate/alcohol to decolourise
- Add sapranin counter stain
7
Q
What colour will gram positive bacteria be after staining?
A
Retain crystal violet- PURPLE
8
Q
What colour will gram negative be after staining?
A
Safranin stains PINK
9
Q
What are 3 gram positive cocci?
A
Staphylococci
Streptococci
Enterococci
10
Q
What are 3 gram positive bacilli?
A
Bacillus
Clostridia
Corynebacteria
11
Q
Why are gram positive and gram negative different colours?
A
Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out on addition of ethanol. They are stained pink or red by the counterstain
12
Q
What are 2 gram negative cocci?
A
Neisseria
Moraxella
13
Q
What are 5 gram negative bacilli?
A
E. Coli
Campylobacter
Salmonella
Shingles
Proteus
14
Q
What are 7 types of agar cultures?
A
Blood agar
Chocolate agar
Cled agar
MacConkey agar
XLD agar
Sabourard agar
15
Q
How is chocolate agar made and why I it used?
A
Blood agar cooked at 80 degrees for 5 mins
-Nutrients are released
16
Q
What type of microorganism are grown on MacConkey agar?
A
Only gram negative bacilli
17
Q
Why is MacConkey agar used?
A
Differentiates lactose fermenting from non-lactose fermenting
18
Q
What temperature can bacteria survive at?
A
-800 to 80 degrees
1200c for spores
19
Q
What pH can bacteria survive at?
A
4-9
20
Q
How long can bacteria survive in water?
A
2 hours-3 months
spores can live >50 years
21
Q
Describe the structure of a bacterial cell?
A
Capsule- sugar polymer that can inhibit immune system
Cell wall- phospholipid membrane
Usually no nuclear membrane
1 circular chromosome
22
Q
Describe the cytoplasmic membranes of gram positive and gram negative bacteria
A
Positive: single membrane
Negative: 2 membranes
23
Q
Describe the peptidoglycan membranes of gram positive and negative bacteria
A
Gram positive: thick membrane
Gram negative: thin layer between the 2 cytoplasmic membranes
24
Q
Where are lipoteichoic and teichoic acids present?
A
Gram positive
25
When is endotoxin present?
Gram negative
26
What is endotoxin?
Outer membrane of gram negative bacteria
27
What locations in the body are sterile?
Blood
CSF
Joints
Bladder
Lower resp tract
Pleural fluid
Peritoneal cavity
28
What locations in the body are colonised with flora?
GI tract
Skin
Oral cavity
Vagina
Urethra
29
How is bacterial growth rate measured?
Shining light and measuring absorption
30
What is exotoxin?
Proteins secreted from gram negative and gram positive bacteria
-mainly gram positive
31
Describe the antigenicity (binding to immune system) of endotoxin and exotoxin
Endotoxin: weak
Exotoxin: strong
32
Describe the specificity of endotoxin and exotoxin
Endotoxin: unspecific
Exotoxin: specific
33
Describe the heat specificity of endotoxin and exotoxin
Endotoxin: heat stable
Exotoxin: unstable
34
What can be converted to toxoid (non-active toxin)?
Endotoxin
35
What effect does botulism have?
Inhibits nervous system
36
What effect does tetanus have?
Stimulates nervous system
37
Describe the process of bacterial infection
1. Th cell activation
2. Th cells secrete INF + TNF and IL-2
3. Macrophage recruitment
38
How does genetic variation occur on a chromosome?
Base substitution
Deletion
Insertion
39
What is a plasmid?
Small circular DNA
Antibiotic resistant genes
40
How are genes transferred by transformation?
Uptake of exogenous substance (ie plasmid) leads to genetic alteration of cell
41
How does gene transfer occur by transduction?
Foreign DNA introduced via vector/ virus
42
How does gene transfer occur via conjugation?
Direct cell to cell contact that transfers genetic material
43
Is staphylococcus aerobic or anaerobic?
Aerobic
44
What is the normal habitat of staphylococcus?
Skin and nose
45
What is coagulate?
Enzyme that forms fibrin clot around bacteria and protects from phagocytosis
46
How is staphylococcus aureus spread?
Aerosol and touch
47
Is staphylococcus aureus coagulase positive or negative?
Positive
48
How does staphylococcus aureus show on blood agar?
Creamy/yellow
49
What are the 4 virulence factors of staphylococcus aureus?
Pore forming toxins
Proteases
Toxic shock syndrome
Protein A
50
What does MRSA stand for?
Methicillin resistant staphylococcus aureus
51
What are some conditions associated with staphylococcus aureus?
TSS
Wound infections
Food poisoning
Scalded skin syndrome
52
What are 2 coagulate negative staphylococci?
Staphylococcus epidermis
Staphylococcus saprophyticus
53
What shape are staphylococcus aureus cells?
Spherical clusters
54
Is streptococcus catalase positive or negative?
Negative
55
Are staphylococcus and streptococcus gram positive or negative?
Positive
56
What are the 3 groups of streptococcus?
Alpha haemolytic
Beta haemolytic
Non haemolytic/ gamma haemolytic
57
What type of agar is streptococcus haemolysis done on?
Blood agar
58
How alpha haemolytic streptococci appear?
Partial lysis- green/browning
59
What is an example of an alpha haemolytic strep?
S. Oralis
S. Sanguis
S. Pneomonie
60
How does beta haemolytic strep present?
Complete lysis- colourless
61
What is an example of a beta haemolytic strep?
S. Pyogenes
S. Agalactiae
62
How does gamma haemolytic strep appear?
No lysis
63
What is an example of gamma/nom haemolytic strep?
S. Bovis
S. Mutans
64
Are enterococcus catalase positive or negative?
Negative
65
What is an example of enterococcus?
E. Faecalis
66
What is optochin sensitivity tested on?
Alpha haemolytic strep
67
What is an example of a optchin resistant strep?
Viridans strep
68
What is an example of an optochin sensitive strep?
S. Pneumoniae
-all other alpha strep are resistant
69
What is antigenic zero-grouping carried out on?
Beta haemolytic strep
70
What is zeihl-neelsen stain test used for?
Mycobacteria do not take up gram stain so this is used to identify acid-fast bacilli and non acid-fast bacilli
71
What colour will acid fast bacilli be?
Red
72
What colour will non-acid fast bacilli be?
Blue
73
What is catalase test used for?
Differentiating streptococci and staphylococci
74
What is catalase positive?
Staphylococci
75
What is catalase negative?
Streptococci
76
Why is a coagulase test used?
Coagulase produced by staph. Aureus
-distinguishes it from other staph
77
What indicates positive coagulase result?
Clumping
78
What generates a coagulase positive response?
Staphylococcus aureus
79
How are beta haemolytic bacteria differentiated?
Lancefield grouping
80
What is lancefield grouping A, C and G?
Tonsillitis and skin infection
81
What is lancefield grouping B?
Neonatal sepsis and meningitis
82
What is lancefield grouping D?
UTI- enterococci
83
What indicates optochin sensitivity?
Clear zone of no growth around disc
84
Are oxidase positive bacteria anaerobic or aerobic?
Aerobic
85
Are oxidase negative bacteria anaerobic or aerobic?
Either
86
What are some oxidative positive bacteria?
Campylobacter
Helicobacter
V. Cholerae
87
What indicates oxidase positivity?
Blue colour change
88
What does a pink/red colour on MacConkey agar indicate?
Lactose fermenting bacteria
89
What does a whit/transparent result show on MacConkey agar?
Non-lactose fermenting bacteria
90
Why is XLD agar used?
Differentiates salmonella and shingella
91
How does salmonella show on XLD agar?
Red/pink with black spots
92
How does shingella show on XLD agar?
Red/pink colonies
93
How are streptococci differentiated using lancefield typing?
Groups coagulase negative and positive bacteria
- group A and B
94
What is in strep group A?
Strep pyogenes
95
What is in strep group B?
Strep agalactiae
96
What are the common clinical presentations of staph aureus?
Pain in shoulder
High temperature
Osteomyelitis in C6 and 7
97
How much osteomyelitis is staph aureus responsible for?
90%
98
How is staph aureus treated?
Flucoxacillin for 3 months
99
Where does staph epidermis occur?
Prosthetic limbs and catheters
100
What infections do strep pyogenes cause?
Wound infections
USUALLY tonsillitis and pharyngitis
Otitis media
Scarlet fever
101
What are the complications of strep pyogenes?
Rheumatic fever
Glomerulnephritis
Scarlett fever
102
What is the common presentation of strep pneumoniae?
Heavy smoker
Cough and severe chest pain for 2 days
Rust coloured sputum
Consolidation- lungs filled with fluid
103
What infections does strep pneumonie cause?
Pneumonia
Otitis media
Sinusitis
Meningitis
104
What are some predisposing factors for strep pneumoniae?
Impaired mucus trapping
Hypogammaglobulinemia
Asplenia
Diabetes
Renal disease
Sickle cell
Young age
105
What is the collective name for oral streptococci?
Viridans streptococci
106
What conditions are associated with Viridans strep?
Dental cavities and abscesses
Infective endocarditis
Deep organ abscesses
107
What is the common presentation of corynebacterium diptheriae?
Child with sore throat
2 days fever and malaise
Lymphadenopathy in neck
Rapid breathing
Grey membrane on tonsils
108
What will the swab show for corynebacterium diphtheriae?
Gram positive bacilli (rods)
109
How is corynebacterium diptheriae treated?
Antitoxin
Erythromycin
110
Why do gram negative find secreting a toxin more difficult than gram positive bacteria?
Toxin has to cross 2 membranes instead of just one
111
What infections are caused by E.coli?
Wound infections
UTI
Gastroenteritis
Travellers diarrhoea
Meningitis in infants
112
What is the MC species of shingella?
S. Sonnei
113
What does shingella damage to intestinal mucosa lead to?
Acute infection of large intestine
Painful diarrhoea with blood and mucus
114
How is shingella spread?
Contaminated water or food
115
What is the infective dose for shingella?
100 bacteria- very easy to be infected
116
What are the common properties of enterobacteria ?
Rod shaped
Mostly motile
Anaerobic
117
What are the common properties of shingella?
Non lactose
Non motile
118
What are the 2 types of salmonella?
S. Enterica
S. Bongori
119
What causes s. Bongori?
Rare- reptile contact
120
What is S. enterica responsible for?
Salmonellosis- infection caused by salmonella
121
What are infections caused by salmonella?
Gastroenteritis
Typhoid
Bacteraemia
122
What is the usual cause of food poisoning from milk and poultry?
Gastroenteritis
123
Is gastroenteritis localised or systemic?
Localised
124
Is typhoid systemic or localised?
Systemic
125
What causes typhoid?
Salmonella typhi and paratyphi
126
How is typhoid spread?
Faeco-orally
127
How does shingella cause infection?
1. Uptake to basolateral side of M cell
2. Macrophage phagocytoses
3. Induced apoptosis
4. Shigella moves laterally through cells destroying gut
5. Dying macrophage releases pro-inflammatory signals (cytokines)
6. Attracts leukocytes causing inflammation
128
What is bacteraemia?
Presence of bacteria in the blood
129
How does enteric fever occur?
1. Dissemination via macrophages -> lymph nodes
2. Enters bloodstream ->LIVER, SPLEEN, MARROW
3. Proliferate and released from macrophage-> bacteraemia
4. Organs affected = symptomatic
5. Colonises gallbladder -> small intestine
6. Produces typhoid toxin
130
What signs of enteric fever can be seen in s.intestine?
Inflammation and ulceration of payers patches
131
How can proteus mirabilis cause kidney and bladder stones?
Urease production -> ph increase -> calcium phosphate precipitation -> stones
132
What is the most common cause of proteus miribalis contraction?
Catheter UTI
133
Describe the structure of vibrio cholerae
Curved rods with single polar flagellum
134
How is vibrio cholerae transmitted?
Faeco-orally
135
Why is a high infective dose required for vibrio cholerae?
Sensitive to acid- hard to get past stomach
136
What are the effects of vibrio cholerae?
Watery diarrhoea- Up to 20L lost/day
-dehydration
-50-60% mortality if untreated
137
How is vibrio cholerae treated?
Oral rehydration
138
Describe the structure of pseudomonas aeruginosa
Rod shaped motile with single flagella
139
What infections can be caused by pseudomonas aerugionsa?
Localised: wounds, UTI, keratitis
Systemic: neutropenic patients (chemo, HIV,ect)
ICU: pneumonia
140
Does haemophilius influenzae cause flu?
No
141
What infections can be caused by haemophilius influenzae?
MENINGITIS
Bronchopneumonia
Bacteraemia
Epiglottitis ect
142
What are 2 types of beta-proteobacteria?
Neisseria
Bordetella pertussis
143
Who are Haemophilus influenzae infections usually seen in?
Young children
Adult smokers
144
What does legionella pneumophilia cause?
Legionnaires disease
-Pneumonia
145
Where does legionella pneumophilia grow?
Man-made aquatic environment
-parasite in amoeba
146
Where in the body does legionella pneumophilia grow?
Lives and replicates in alveolar macrophages
147
What does bordetella pertussis cause?
Pertussis= whooping cough
148
How is whooping cough spread?
Aerosol
- very infectious = low infective dose
149
What can whooping cough cause?
Sub-conjunctival haemorrhage
150
What are the symptoms of whooping cough?
Non-specific flu-like symptoms
Paroxysmal coughing (cough followed by inhalation resulting in whooping sound)
151
What is the structure of Neisseria?
Diplodocci- travel in pairs
152
What are the 2 species of Neisseria?
N. Meningitidis
N. Gonorrhoea
153
How is N.meningitidis spread?
Person-to-person aerosol
-Common in barracks and student halls
154
What diseases can be caused by N. Meningitidis?
Can cross nasopharyngeal epithelium -> blood stream
-Asymptomatic bacteraemia
-Meningitis
-Septicaemia VERY HIGH MORTALITY
155
What are the virulence determinants of N. Meningitidis?
Capsule anti-phagocytosis
Pilli promote invasion
156
How is N. Gonorrhoea spread?
Perso to person sexual contact
157
What conditions can N. Gonorrhoea cause?
Urethritis
Infection of Fallopian tubes
Can be asymptomatic in 30-50%
158
What is the most common cause of food poisoning in the UK and USA?
Campylobacter
159
What are the causes of campylobacter?
Undercooked poultry
Unpasteurised milk
160
What are the effects of campylobacter?
Mild-severe diarrhoea with blood
Usually self limiting within a week
161
How common is helicobacter pylori?
Present in 50% of global population
162
How does helicobacter pylori protect itself?
Uses urea -> ammonia -> neutralises stomach acid
163
What are infections commonly caused by helicobacter pylori?
Gastritis
Peptic ulcer disease
- gastric cancer
164
What is the most common STI?
Chlamydia trachomatis
165
What are the 2 phases of chlamydia growth?
1. Elementary bodies- dormant
-infects cell and prevents phagocytosis
2. Reticulate bodies- metabolically active
-replicative and non-infectious
166
What diseases can chlamydia cause?
Usually asymptomatic
Uterus and ovaries - pelvic inflammatory disease
Can cause conjunctivitis
Can cause trachoma - blindness
167
How do staphylococci appear under the microscope?
Clusters
168
How does streptococcus appear under the microscope?
Chains
169
Define acute diarrhoea
Lasts <2 weeks
170
Define chronic diarrhoea
>4 weeks
171
What are the 2 categories of acute diarrhoea?
Non-inflammatory (watery)
Inflammatory/ dysentery (bloody)
172
What are the 2 ways that pathogens can cause diarrhoea?
Secrete endotoxins directly into food
Enter the body and distrust intestinal homeostasis via enterotoxins
173
What are 2 pathogens that can cause non inflammatory diarrhoea?
ETEC
Vibrio cholerae
174
What are 2 pathogens that can cause inflammatory diarrhoea?
Salmonella
Shingella
Campylobacter
C. Difficile
175
What are the risk factors of diarrhoea?
PPI use
Recent travel to developing countries
Abx treatment
Immunosupression
176
What pathogen is associated with reheating rice?
Bacillus cereus
177
What is the MC cause of travellers diarrhoea?
ETEC
178
How is ETEC diarrhoea treated?
Ciprofloxacin
179
What pathogen is associated with cruise ships and care homes?
Norovirus
180
What is a cause of long lasting diarrhoea?
Giardia lamblia
181
How is giardia lamblia treated?
Metronidazole
182
How are shingella and salmonella treated?
Ciprofloxacin
183
How is C. Difficile treated?
Vancomycin
184
What is c. Difficile associated with?
Antibiotic use
185
What layers does cellulitis involve?
Deeper dermis and subcutaneous fat
186
When does cellulitis occur?
Following a break in normal skin integrity
187
What are the MC sites of cellulitis?
Legs
Face
Arms
188
What are 2 causes of cellulitis?
Beta haemolytic strep
- s. Pyrogenes and s. Agalactiae
Staph aureus
189
What are the risk factors of cellulitis?
Skin wounds
Diabetes
Bites
Elderly
Swollen legs
190
What are the symptoms of cellulitis?
“Tracking” erythema
Pain, warmth and swelling
Associated wound
191
How is cellulitis treated?
Elevate and mobilise limb
Flucoxacillin or clindamycin
192
Define necrotising fasciitis
Necrotising infection of deep structures of the skin and underlying fascia
193
What causes necrotising fasciitis?
Break in the skin causes infection of fascia -> thrombosis of adjacent tissue -> necrosis and anaesthesia of more superficial layers
194
What causes type 1 necrotising fasciitis?
Aerobic and anaerobic organisms
195
What is the MC cause of type 2 necrotising fasciitis?
Strep pyogenes
196
What are the symptoms of necrotising fasciitis?
Erythema, warmth and tenderness
Quickly spreading blue grey colouring and loss of sensation
Crepitus (joint crunching)
197
Define debridement
removal of dead, damaged, or infected tissue
198
How is necrotising fasciitis treated?
Surgical exploration and debridement
Piperacillin + clindamycin
199
How is strep pyogenes treated?
amoxicillin
200
What is the MC cause of osteomyelitis?
Staph aureus
201
What is the MC cause of osteomyelitis in IVD users?
Pseudomonas
E. Coli
202
What is the MC cause of osteomyelitis in hip/knee replacement patients?
Staph epidermidis
203
How is osteomyelitis treated?
Surgical debridement
Flucloxacillin and fusidic acid
204
What is the MC cause of septic arthritis?
Staph aureus
205
How is N.gonorrhoea treated?
Ceftriaxone
206
How is c. Trachomatis (chlamydia) treated?
Doxycycline or azithromycin
207
What is protective against malaria?
Sickle cell trait (HbS)
208
What is the MC cause of malaria?
F. Falciparum
209
Define antimicrobial agent
Substance with inhibitory properties against microorganisms but minimal effects on mammalian cell
210
Define antibiotic
Substance produced by microorganisms that inhibit or kill the growth of other bacteria
211
Define empirical therapy
Antimicrobial regimen used when there is a delay in initiating therapy but there is a clinical diagnosis of infection
212
Define directed therapy
Directed antimicrobial regimens are prescribed to target a specific pathogen
213
Define antibiotic resistance
Ability of a microorganism to avoid the harmful evens of an antimicrobial by destroying it, removing it or blocking its effects
214
Define antibiotic susceptiblity
Level of vulnerability of a microorganism to an antimicrobial
215
What are 2 types of antibiotics that inhibit cell wall synthesis?
Beta-lactams
Glycopeptides
216
What are 3 types of beta lactams?
Penicillins
Cephalosporins
Carbapenems
217
What are 3 types of penicillins?
Benzylpenicillin
Flucoxacillin
Ampicillin/amoxicillin
218
What is benxylpenicillin used to treat?
Strep
Pneumonia
Meningitis
219
What is Flucoxacillin used to treat?
Staph aureus
220
What is amoxicillin used to treat?
UTI
listeria
Enterococci
221
What is a 1st gen cephalosporin?
Cephalexin
222
What is a 2nd generation cephalosporin?
Cefuroxime
223
What is a 3rd generation cephalosporin?
Ceftazidime
224
What are cephalosporins used to treat?
Strep
Nisseriere
225
What are 2 carbapenems?
Imipenem
Ertapenem
226
What are carbapenems used to treat?
Enterobacteria
227
When are carbapenems contraindicated?
Breastfeeding
228
What are 4 ways antibiotics can inhibit nucleic acid synthesis?
Inhibiting folate synthesis
Inhibits DNA gyrase
Binding to RNA polymerase
Breaking DNA strands
229
What are 3 antibiotics that inhibit folate synthesis?
Trimethoprim
Sulfamethozazole
Co-trimoxazole (both)
230
What is trimethoprim used to treat?
UTI
231
When is trimethoprim contraindicated?
pregnancy
- interferes with folate = spina bifida
232
What is co-trimoxazole used to treat?
PCP (pneumonia)
233
How do fluoroquinolones (eg. Ciprofloxacin) work?
Inhibit DNA gyrase
234
How does Rifampicin work?
binds to RNA polymerase
235
How does metronidazole work?
Breaks DNA strands
236
What is metrinidazole used to treat?
Parasites eg giardia lamblia
237
What are 4 types of antibiotics that inhibit protein synthesis?
Chlormaphenicol
Macrolides
Tetracyclines
Aminoglycosides
238
When is chloramphenicol contraindicated?
Pregnancy
Breast feeding
- Grey baby syndrome
239
What type of antibiotics are clarithromycin and erythromycin?
Macrolides
240
What are 2 tetracyclines?
Tetracycline
Doxycycline
241
What type of drug are gentamycin and streptomycin?
Aminoglycosides
242
What is used to treat severe sepsis?
Gentamycin
243
When are tetracyclines contraindicated?
Children <12
244
What are 2 lactose fermenting bacteria?
CEEK
Citrobacter
Enterobacter
E.Coli
Klebsiella
245
What is an example of a non motile non lactose fermenting bacteria?
Shingella
246
What are 2 motile non lactose fermenting bacteria?
Proteus
Salmonella
247
How is strep viridians treated?
Benzylpenicillin + gentamycin
