Microbiology Flashcards
1
Q
Define pathogen
A
An organism that causes or is capable of causing disease
2
Q
Define commensal
A
An organism which colonises a host but causes no disease under normal conditions
3
Q
Define opportunistic pathogen
A
A microbe that only causes disease if the host’s defenses are compromised
4
Q
Define virulence/pathogenicity
A
The degree to which a given organism is pathogenic
5
Q
Define asymptomatic carriage
A
When a pathogen is harmlessly carried at a tissue site where it causes no disease
6
Q
What is a bacillus
A
rod shaped
7
Q
What is a cocci
A
round
8
Q
What does purple suggest
A
Gram positive
9
Q
What does pink suggest
A
Gram negative
10
Q
What is a diplococcus
A
Two cocci
11
Q
What is a vibrio
A
A curved rod
12
Q
What is a spirochaete
A
A spiral rod
13
Q
What are the sterile sites in the body
A
Lungs, gall bladder, bladder, kidneys
14
Q
In what form is bacterial DNA found
A
Double stranded circular DNA
15
Q
What stain is needed to identify TB and why
A
Zeill Neeson as the TB has a thick waxy surface
16
Q
What causes toxic shock
A
When the inate immune system acts against lypolysaccharide
17
Q
How long can spores last and what temperatures can they survive in
A
50years in water and 120 degrees heat
18
Q
What is dessication
A
A state of extreme drying
19
Q
What temperatures can bacteria tolerate
A
-80 to 80
20
Q
What pH can bacteria tolerate
A
4 to 9
21
Q
How do bacteria divide
A
binary fission
22
Q
What is an endotoxin
A
From gram negative LPS cell wall, weak non specific antigen. Heat stable and cant be converted to toxoid
23
Q
What is an exotoxin
A
A protein secreted by mainly gram positive, specific action with high antigenicity. Heat labile and can be converted tot toxoid
24
Q
What is a toxoid
A
A toxin which has been treated so that it loses it’s toxicity but retains it’s antigenicity
25
What is used for transformation
Plasmid
26
What is used for transduction
phage
27
What is used for conjugation
sex pillus (between recipient and donor)
28
What genes does a plasmid contain
Transfer promotion, plasmid maintenance and antibiotic or virulence determining genes
29
Which bacteria cant be cultured artificially
Obligate intracellular bacteria
30
Which shaped bacteria are tested with ZN stain
Rods
31
What is a bacteriaphage
Where one bacteria phages another and steals DNA by transduction
32
Examples of obligate intracellular bacteria
Rickettsia, chlamydia, coxiella
33
Bacteria with no cell wall (mollicutes)
Mycoplasma pneumoniae
34
Bacteria which grow as filaments
Actinomyces, streptomyces
35
Why is gonorrhoea more painful in men
As they have a longer urethra
36
What does large gram positive rods suggest
Clostridia
37
What stain is used at first in gram staining
Crystal violet
38
What is added in gram staining to fix the cell wall
Iodine
39
What is used to decolourise in gram staining
Ethanol or acetone
40
What is used to counterstain in gram staining
Safronin (pink)
41
What are gram positive clusters
Staphlococci
42
What are gram positive chains
Streptococci
43
Why do gram positive stain purple
1 cell wall. Decolouriser dehydrates cell, CV-1 gets stuck in peptidoglycan. The counterstain isnt taken so the cell stays purple
44
Why do gram negative stain pink
Decolouriser interacts with lipid and causes loss of CV-1 and outer LPS membrane. Cell appears pink with counter stain
45
Anaerobic gram negative cocci
Veillonella
46
Aerobic gram negative cocci
Neisseria
47
Anaerobic gram positive cocci
Peptostreptococcus
48
Aerobic gram positive cocci
Staphylococcus or streptococcus
49
Name a commensal of the skin
Staphylococcus epidermidis
50
Alpha haemolytic streptococcus
S. pneumoniae, S. oralis, S. milleri
51
Lancefield A beta haemolytic streptococcus
S. pyogenes
52
Lancefield B beta haemolytic streptococcus
S. algalactiae
53
What does S. algalactiae cause
UTI or meningitidis
54
Non haemolytic streptococcus
S. bovis
55
Enterococcus Streptococcus
E. faecalis (Lancefield D)
56
What is catalase testing
Distinguishs strep and staph. Catalase converts H2O2 from flavoproteins into water and oxygen
57
Positive catalase test result
Staph, gram negatives and funghi
58
Negative catalase test result
Strep
59
What is coagulase testing
Distinguishes staph. Coagulase activates prothrombin and therefore fibrin to fibrinogen
60
How is free coagulase detected
tube coagulase test
61
How is bound coagulase detected
Slide coagulase test
62
What is a positive coagulase test
Clot formation, Staph aureus
63
What is a negative coagulase test
Clear, staph epidermidis
64
How is reduced sensitivity to penicillin detected
Oxacillin disc
65
What does a positive latex test suggest
Staph aureus
66
What is haemolysis
Ability of bacteria to break down red blood cells on blood agar. Used for differentiating streptococci
67
Alpha haemolysis
Green due to hydrogen peroxide production
68
Which bacteria cause alpha haemolysis
S. pneumoniae, S. oralis, S. milleri
69
Beta haemolysis
Clear/white due to blood cell lysis by haemolysin
70
Which bacteria cause beta haemolysis
S pyogenes and S algalactiae
71
Gamma haemolysis
No haemolysis
72
Which bacteria cause gamma haemolysis
E. faecalis and S. epidermidis
73
Which bacteria is sensitive to optochin disc
Strep pneumoniae
74
What does tetanus cause
Muscle locks due to over stimulation of nerves
75
What does botulin cause
Muscle relaxes, blocks nerves
76
What type of infection is caused by pseudomonas
Oppurtunistic
77
ZN positive mycobacteria
M tuberculosis, M leprae, M avium intracellulare
78
Gram positive anaerobic rods
Clostridium and proprioribacterium (p.acnes)
79
How to remember propriobacterium acnes as a anaerobic rod
No air to spots. Spots stop you procreating with your rod, and getting a positive pregnancy test.
80
Gram positive aerobic rods
Corynebacterium (C. diptheriae), listeria, bacillus, erysipelothrix
81
Gram negative anaerobic
Bacteriodes
82
Gram negative aerobic
Coliforms (Shigella, salmonella), pseudomonas, parvobacteria (H. influenzae), vibrio (V. cholera)
83
Selective indicator media for gram negative bacilli
MacConkey agar and CLED (cysteine, lactose, electrolyte deficient)
84
How is motility used to differentiate between bacteria
Flagella staining patterns
85
Positive lactose fermentors (g-ve anaerobes)
E coli, klebsiella, enterobacter, citrobacter
86
Negative lactose fermentors (g-ve anaerobes)
Salmonella and shigella
87
Positive oxidative test
Vibrio, helicobacter, pseudomonas
88
Negative oxidase test
Colioforms, parvobacteria
89
Why do gram positive bacteria take up the gram stain
They have a thick peptidoglycan wall
90
Antibiotic for staph auresu
Flucoaxacillin
91
Where are staphlococcus normally found
Nose and skin
92
What is coagulase
An enzyme produced by bacteria which helps fibrin clots form around bacteria, protecting them from phagocytosis
93
In which type of infections do staphaloccus coagulase negative species cause
Oppurtunistic infections
94
Which organism causes 90% of osteomyelitis
Staph aureus
95
which antibiotics is MRSA resistant to
Beta lactams, gentamicin, erythromycin and tetracycline
96
Staph aureus virulence factors
Pore forming toxins (alpha haemolysin, PVL), proteases (exfoliatin), toxic shock syndrome (stimulates cytokine release), protein A (binds to and immobilises IgG)
97
Pyogenic staph aureus associated conditions
Wound infections, abscesses, impetigo, septicaemia, osteomyelitis, pneumonia and endocarditis
98
Toxin staph aureus associated conditions
Scalded skin syndrome, toxic shock syndrome, food poisoning
99
Coagulase negative Staph conditions
Infected implants, endocarditis, septicaemia
100
Staph epidermidis associated infections
Oppurtunistic
101
Staph epidermidis virulence factors
Ability to form persistent biofilms
102
Who gets oppurtunistic infections
Debilitated, prostheses and catheters
103
Staph saprophyticus infection
Acute cystitis
104
Staph saprophyticus virulence factors
Haemogglutinin for adhesion, urease which causes kidney stones
105
How do (staph epidermidis) bio films work
Antibiotics struggle to get through and a layer of metabolically inactive cells at the base protect the remaining cells
106
Features of streptococcus pyogenes
Beta haemolytic, group A lancefield. Faculative anaerobe, penicillin sensitive
107
What happens in alpha haemolysis
H2O2 reacts with Hb, causes partial greening
108
What happens in beta haemolysis
Haemolysins O and S, complete lysis
109
What happens in gamma haemolysis
No lysis
110
What are the three ways in which streptococci can be classified
Haemolysis, lancefield typing, biochemical properties
111
What is lancefield typing
Categorises catalase negative, beta haemolytic strep according to baceterial carbohydrate cell surface antigens. Clumpy indicates recognition
112
Name a Lancefield group A
Strep pyogenes
113
Name a lancefield group B and the infections it causes
S. agalactiae, neonatal infections
114
Examples of strep pyogenes infections
Wound infections, tonsilitis, pharyngitis, otitis media, impetigo, scarlet fever
115
Complications of strep pyogenes infections
Rheumatic fever, glomerulonephritis (antiSLO test used to assesss severity
116
S pyogenes virulence factors, on surface
Capsule, M protein encourages complement degradation
117
S pyogenes virulence factors, enzymes
Hyaluranidase (for spreading), Streptokinase (breaks down clots), C5a peptidase (reduces chemotaxis)
118
S pyogenes virulence factors, toxins
Streptolysins O and S (bind cholesterol) reason for Beta haemolysis. Erythrogenic toxin SB(beta)eA
119
S. pneumoniae features
Rust coloured sputum, chest consolidation, draughtman colonies
120
What is sputum
Fluid from the lower respiratory tract
121
What can make s.pneumonia change from a normal commensal of the oropharynx to pathogenic
Hypogammaglobulinaemia and asplenia
122
Which infections are caused by s.pneumoniae
Pneumonia, otitis media, sinusitis and meningitis
123
S pneumoniae virulence factors, capsule
Polysaccharide (antiphagolyic), polyvalent vaccine (children under 2 have different surface proteins so are at a higher risk)
124
S pneumoniae virulence factors, inflammatory wall consitituents
Teichoric acid (chlorine), peptidoglycan
125
S pneumoniae virulence factors, cytotoxin
Pneumolysin
126
What is viridans strep
General name for oral strep. alpha or non haemolytic. They cause abscesses or infective endocarditis. Milleri group are the post virulent
127
Which alpha haemolytic strep is optochin sensitive
S. pneumoniae
128
What are irregular gram positive rods
Cornyebacterium diptheriae
129
What is the treatment for cornyebacterium diptheriae
Erythromycin and antitoxin
130
How is diptheria spread
Droplets
131
What does diptheria require for growth
Potassium telluite
132
What does diptheria toxin do
Inhibits protein synthesis
133
What does diptheria vaccine consist of
Toxoid
134
What is a feature of gram positive bacteria
More peptidoglycan
135
What is a feature of gram negative bacteria
Both inner and outer membranes
136
What are the three components of LPS endotoxin
Outer lipid A component, Core R oligosaccharide antigen and Somatic O antigen of repeating carbohydrate units
137
Which part of LPS is responsible for toxicity
Outer lipid A component
138
Why dont mycobacteria gram stain
Outer mycolic acid lipid layer
139
Why dont mycoplasms gram stain
No peptidoglycans
140
Why group are mycobacteria and mycoplasms in
Gram negative
141
Gram negative virulence factors
Colonisation factors (adhesins, invasins, nutrient acquisition and defense) and toxins (usually secreted proteins which cause damage and subversion)
142
What are gamma proteobacteria
Enterobacteria (colioforms)
143
Describe enterobacteria
Rods which are covered in flagella. some are intestinal parasite. Faculative anaerobes as the gut is largely anaerobic. Mac conkey is used to culture
144
Lac positive phenotype of macconkey (latose fermenters, macconkey pink)
Commensal EColi
145
Lac negative phenotype on macconkey (non-lactose fermenters, macconkey pale)
Salmonella, shigella, proteus
146
How to differentiate between salmonella and shigella
Serology, shigella has no H antigen as it has no flagella
147
What is an example of a serotype
H antigen on flagella
148
What is an example of a serogroup
O antigen on LPS
149
Where is K angtigen found
EPS (capsule)
150
Whats the difference between bacteraemia and sepsis
Sepsis is bacteraemia when theres symptoms
151
Diseases caused by E coli
Wound infections, UTIs, Gastroenteritis, travellers diarrhoea, bacteraemia and a meningitis
152
Which Ecoli target the small intestine and what is the result of this
ETEC and EPEC and cause watery diarrhoea
153
Which Ecoli target the large intestine and what is the result of this
EHEC and EIEC and cause bloody diarrhoea
154
Which Ecoli causes chronic diarrhoea and where does it target
EAEC (aggregatitive) and it targets the large intestine
155
Which Ecoli targets the urinary tract and can cause cystitis
UPEC
156
Which toxins are produced by ETEC
Heat labile and heat stable toxin
157
What is the action of Heat labile toxin
Modifies Gs protein and locks it into the active GTP state, it permanently activates adenyl cyclate= more cAMP= more phosphorylation of CFTR ion transporter= more Cl- excretion= water cotransported= diarrhoea
158
What is the action of Heat stabile toxin
Mimics guanylin peptide hormone, activates GC-2C receptor causing more cGMP and CTFR activity etc. But has a smaller effect than heat labile
159
How do EHEC and EPEC work
Induce pedestal formation, adhere turn on TTSS. Microvilli rearrange into pedestal allowing the entry of the bacteria
160
Dysentry is a version of which bacteria
Shigella
161
Shigella has pathology like which Ecoli
EIEC
162
Symptoms of shigella
Severe bloody diarrhoea, frequent passage of stools, small volume. blood and pus, cramps and pain
163
Shigella infectiivty
Acid tolerance good so only a small infective dose is needed. Person to person spread of via contaminated food/water. It overlies lymphoid follicles in peyers patches
164
How does shigella cause disease (exciting)
Induces apoptosis and reinfects adjacent cells from the basolateral membrane, host actin monomers are polymerised into actin rockets to propel through the cytoplasm. Apoptotic macrophages release cytokines and cause inflammation
165
Which Ecoli also produces shigella toxin
EHEC
166
What are the virulence features of shigella
Catalytic (glycoside which cleaves N-adenosine band in RNA) and receptor binding region
167
Which is the main type of salmonella
Salmonella enteritica
168
Which infections are caused by salmonella
Gasteroenteritis, enteric fever (typhoid, systemic disease) and bacteraemia rarely
169
How is salmonella caught
Ingested contaminated food/water
170
Describe the mechanism of salmonella infection
Invasion of small intestine epithelium, infalmmatory response, transcytosed to the basolateral membrane, enters submucosa, intracellular replication, membrane ruffling, systemic infections due to dissemination with m φs
171
Where are peyers patches
ileum
172
Describe the mechanism of gastroenteritis
Bacteria mediated endocytosis, induction of chemokine release, neutrophil recruitment and migration, neutrophil induced tissue injury. Inflammatory necrosis of mucosa. Fluid+electrolyte loss=diarrhoea
173
Enteric fever mechanism
Bacterial mediated endocytosis, transcytosis to basolateral membrane, survival in M φ, systemic spread. Initially little damage to the gut mucosa
174
What is a key feature of typhoid fever
Inflammation and ulceration of peyers patches
175
What is klebsiella
An environmental, oppurtnistic hospital acquired infective agenet which colonises the GI tract and oropharynx
176
Describe the stools in cholera
Rice water stools
177
How is cholera acquired
Faeco-oral route, high dose required (optimum ph 8)
178
Describe the appearance of cholera
Curved road with a single polar flagellum
179
Virulence factors of cholera
TCP pilli needed for colonisation, cholera toxin causes uncontrolled cAMP production causes Cl-, Na+ and therefore water loss
180
3 examples of localised acute infections
Burns/wounds, UTIs, keratitis
181
Systemic acute infections
Bacteraemia
182
Acute infection in ICU patients
Nosocomial penumonia
183
What does nosocomial mean
Originating in hospital
184
Who gets chronic infections
Cystic fibrosis patients
185
How is H. influenzae spread
nasopharyngeal carriage
186
Which H influenzae strains cause infections
Capsulate strains
187
Who gets H influenzae infetions
Children or smokers
188
How do you culture H influenzae
Chocolate agar as requires haem and NAD
189
H influenzae virulence factors
Pilli, capsule (can penetrate nasopharynx), type B main cause of meningitis- Hib vaccine. LPS causes inflammation
190
What is pseudomonas aeruginosa
Oppurtunistic pathogen found in many locations, notoriously difficult to treat
191
Legionella pneumophillia where is it found
Aquatic environments
192
Describe the pathogenicity of legionella pneumophilia
Bacteria take over macorphages, covers in ribosomes using the ER, using this as camouflage and evading phagocytosis
193
What causes symptoms in legionella pneumophilia
Upregulated inflammatory immune response caused by taken over macrophage. Causing more proinflammatory genes and excessive influx of neutrophils into the lungs
194
Causes of low neutrophil count
Leukaemia, chemotherapy and AIDS
195
Describe bordatella pertussis
Coccobacilli, fastiduous, low infective dose
196
Where does bordatella pertussis effect
upper respiratory tract, it adheres to the cilliated epithelium
197
Bordatella pertussis virulence factors
Pertussis toxin- locks Gi in off state which stops inhibition of adenylate cyclase= more cAMP. CγA toxin also increases cAMP
198
Which is the only gram negative cocci
Neisseria
199
Describe neisseria
Non flaggelated diplococci
200
Where can Neisseria be found during infection
CSF or urethral discharge
201
Name two neisseria
N. meningitidis (meningococcus) and N. gonorrhoeae
202
Describe meningococcus
Found in nasopharynx, aerosol transmission, crosses nasopharyngeal epithelium causes bacteraemia and if it crosses the BBB it causes meningitis
203
Which rash is distinctive of N. meningitidis
non blanching, petechial or purpuric rash
