Microbiology Flashcards
(266 cards)
1
Q
Define pathogen
A
Organism that causes/is capable of causing disease
2
Q
Define commensal
A
Organism which colonises the host but causes no disease in normal circumstances
3
Q
What is an opportunist pathogen?
A
Microbe that only causes disease if host defences are compromised
4
Q
What is virulence/pathogenicity?
A
Degree to which a given organism is pathogenic
5
Q
What is asymptomatic carriage?
A
When a pathogen is carried harmlessly at a tissue site where it causes no disease
6
Q
How are bacteria named?
A
By genus (staphylococcus), then species (aureus)
7
Q
What colour does gram positive stain?
A
Purple/blue
8
Q
What colour does gram negative stain?
A
Red/pink
9
Q
What shape is bacillus?
A
Rod-like
10
Q
What shape is described by ‘coccus’?
A
Circular
11
Q
What is a vibrio?
A
Curved rod
12
Q
What is a spirochaete?
A
Spiral rod
13
Q
Which bacteria is more complex, gram positive/negative?
A
Negative
14
Q
Describe the structure of a gram positive bacteria
A
-Cytoplasmic membrane
-Lipoteichoic acid
-Peptidoglycan
-Capsule
15
Q
Describe the structure of a gram negative bacteria
A
-Inner membrane
-Outer membrane
-Peptidoglycan
-Periplasmic space
-Lipoprotein
-Lipopolysaccharide (endotoxin)
-Capsule
16
Q
Name the stain that turns gram +ve bacteria purple
A
Crystal violet
17
Q
What is the temperature of the bacterial environment?
A
< -80 degrees - +80 degrees
18
Q
What is the ideal temp for spores?
A
120 degrees
19
Q
What is the pH of the bacterial environment?
A
<4-9
20
Q
What light is ideal in the bacterial environment?
A
UV
21
Q
How often do E.coli + S.aureus double?
A
20-30 min
22
Q
What is an endotoxin?
A
Component of the outer membrane of bacteria, eg lipopolysaccharide in Gram negative bacteria
23
Q
What is an exotoxin?
A
Secreted proteins of Gram positive and Gram negative bacteria
24
Q
What are the 2 methods by which genetic variation is created in bacteria
A
-Mutations
-Gene transfer
25
Name 3 types of mutation by which bacteria have genetic variation
-Base substitution
-Deletion
-Insertion
26
Name 3 methods of gene transfer by which bacteria have genetic variation
-Transformation e.g. via plasmid
-Transduction e.g. via phage
-Conjugation e.g. via sex pilus
27
What are bacteriophages?
Viruses that infect bacteria
28
Describe transduction
DNA transferred between bacteria by donor bacterium DNA being packaged into a virus + transferred during infection
29
Describe bacterial transformation
Free DNA is taken up from environment + incorporated into chromosome
30
Describe bacterial conjugation
Small tube forms between 2 bacterial cells + plasmid is transferred
31
Name a key obligate intracellular bacteria
Chlamydia
32
Name a key bacteria that can be cultured on artificial media + has no cell wall
Mycoplasma pneumoniae
33
What type of bacteria are N. meningitidis + N. gonorrhoeae
Neisseria-aerobic, gram -ve, cocci, growing as single cells
34
What type of bacteria are S. aureus + S. epidermidis
Aerobic, gram +ve, cocci
35
Name the 2 categories of aerobic gram positive cocci
Staphylococcus + streptococcus
36
Name the 3 types of streptococcus, aerobic, gram +ve, cocci
Alpha-haemolytic, Beta-haemolytic + Non haemolytic
37
Name the 3 types of bacteria that grow as single cells
Rods, cocci + spirochaetes
38
Name the 3 types of bacteria that are rods
-Gram +ve
-Gram -ve
-ZIEHL-NEELSEN
STAIN POSITIVE
39
How are staphylococci classified?
Coagulase positive
Coagulase negative
40
What is coagulase?
Enzyme produced by bacteria that clots blood plasma
41
What is the most important staphylococcus?
S. aureus - coag +ve
42
What is the normal habitat of staphylococci?
Nose + skin
43
How can you visually differentiate between staphylococcus + streptococcus?
Strep=chains
Staph=clusters
44
How does staphylococcus aureus spread?
Aerosol + touch
45
Name 4 virulence factors of staphylococcus aureus
-Pore-forming toxins
-Proteases
-Toxic shock syndrome toxin
-Protein A
46
Name some examples of a s. aureus infection
-Scalded skin syndrome
-Toxic shock syndrome
-Food poisoning
-Abscesses
-Impetigo
-Pneumonia
-Endocarditis
47
Give 2 examples of coagulase-negative Staphylococci
S,epidermis + S.saprophyticus
48
Give an example of beta haemolysis
S.pyogenes
49
What are the most important Lancefield groups?
A + B
50
Which Lancefield group is S,pyogenes?
A
51
Which Lancefield group is S.galactiae?
B
52
Name 3 S.pyogenes enzyme virulence factors + what they do
-Hyaluronidase - spreading
-Streptokinase - breaks down clots
-C5a peptidase - reduces chemotaxis
53
Name 2 S.pyogenes toxin virulence factors + what they do
-Streptolysins O&S - binds cholesterol
-Erythrogenic toxin - SPeA – exaggerated response
54
Name 5 infections caused by S.pyogenes
-Wound infection e.g. cellulitis, puerperal fever
-Tonsillitis + pharyngitis-most common
-Otitis media
-Scarlet fever
-Impetigo
55
Name 4 conditions caused by S.pneumoniae
-Pneumonia
-Otitis media
-Sinusitis
-Meningitis
56
Name 3 predisposing factors for S.pneumoniae infection
-impaired mucus trapping (e.g. viral infection)
-Hypogammaglobulinaemia
-Asplenia
57
Name 3 S.pneumoniae virulence factors
Capsule-antiphagocytic
-Inflammatory wall constituents
-Cytotoxins
58
What group are Viridans streptococci in?
Alpha/non-haemolytic
59
What do Viridans group streptococci do?
-Cause dental caries abscesses
-Important with infective endocarditis
Cause deep organ abscesses
60
Name 4 gram +ve bacilli
-Listeria monocytogenes
-Bacillus anthracis
-Corynebacterium diphtheriae
-Clostridia
61
Name 3 signs/symptoms of Clostridia infection
-Neck stiffness
-Sore throat
-Difficulty opening mouth (due to masseter spasm)
62
What stain is used for gram -ve bacteria?
Fuchsin/safranin counterstain
63
What is the toxic part of LPS + what can it cause?
Lipid A-can cause sepsis when broken down + released into blood
64
What are virulence factors?
Any product/strategy that contributes to pathogenicity/virulence
65
Name 4 colonisation factors
-Adhesins
-Invasin
-Nutrient acquisition
-Defence against the host
66
What are coliforms?
Rod-shaped, motile, anaerobic bacteria that colonise the intestinal tract
67
What is another name for coliforms?
Enterobacteria
68
Name a process that helps differentiate between different enterobacteria
Lactose fermentation-produces acids
69
How does lactose fermentation bacterial differentiation work?
Fermentation product (acid) changes colour of different test substances
70
How does MacConkey agar work?
Acid produced by fermentation turns neutral dye red
71
What is XLD + how does it help differentiate bacteria?
-XLD=xylose lysine deoxycholate
-Lactose fermentation by some bacteria turns phenol red -> yellow
-Salmonella can't ferment lactose but reduces thiosulphate to make hydrogen sulphide (black)
72
What kind of bacteria are mycobacteria?
Gram positive, aerobic, slightly curved, beaded, bacilli-but don't take up Gram stain
73
What stain is used on myobacteria?
Ziehl-Neelsen/acid fast positive
74
What bacteria causes TB?
Mycobacterium tuberculosis
75
What does M. kansasil cause?
Chronic lung infection
76
What does M. leprae cause?
Leprosy
77
What property of mycobacteria make them resistant to Gram stain?
High lipid content with mycolic acids in cell wall
78
What are the components of Ziehl-Neelsen stain?
-Carbol fuchsin
-Acid alcohol
-Methylene blue
79
What are 2 key lipid components of myobacteria?
-Mycolic acids
-Lipoarabinomannan
80
Is M.tuberculosis fast/slow growing?
Slow growing
81
What are the ramifications of TB being slow growing?
-Gradual disease onset
-Much longer to diagnose
-Longer to treat
82
What is primary TB?
-Initial contact made by alveolar macrophages
-Bacilli taken in lymphatics to hilar lymph nodes
83
What is latent TB?
-Cell mediated immune response from T-cells
-No clinical disease, but detectable response on tuberculin skin test
84
What is pulmonary TB?
-Can happen straight after primary infection or months later after reactivation
-Granulomas form around bacilli that have settled in apex
-TB can spread in lung-more lesions
85
How does TB spread?
Aerosol transmission
86
How does the body's immune system react to TB?
-Macrophages phagocytose mycobacteria
-BUT, mycobacteria adapted to intracellular environment + can withstand
87
How is intracellular killing of mycobacteria activated?
-CD-4 T cells generate interferon gamma-activates killing
88
What happens if granulomas fail to contain myobacteria?
Cavity full of live mycobacteria forms-causes TB
89
What does the body form to contain mycobacteria?
Granulomas-cause metabolic shutdown in mycobacteria
90
What is a granuloma made of?
-Macrophages
-Type 1 helper T cells
-These make IFN-y + other cytokines
91
What can cause granumlomas to become unstable?
-CD4 delpetion
-TNF-alpha depletion
92
How does nucleic acid detection work?
-Purifies + concentrates M.TB
-Sonicates to release genomic material
-Perform PCR
93
What is a positive about nucleic acid detection?
-Rapid diagnosis
94
How does the Tuberculin skin test work?
-Intradermal injection of purified protein derivative
-Stimulates T cell response-measured
-Diagnostic test
95
Name 4 drugs that are standard therapy for TB
-Isoniazid
-Rifampicin
-Pyrazinamide
-Ethambutol
96
What are second-line Tx for TB?
-Injectable agents e.g. streptomycin, cycloserine
97
Do TB Tx's have side effects?
Many wide-ranging + severe side effects-include liver damage
98
What are some challenges with TB Tx?
-Long Tx
-Expensive
-Lots of antibiotic resistance
99
What is a virus?
-Infectious, obligate intracellular parasite comprising genetic material surrounded by a protein coat and/or a membrane
100
What does obligate mean?
Totally dependent on living cells for replication + existence
101
What are the main differences between viruses + bacteria?
-Bacteria have cell walls, organelles, DNA + RNA, and are alive
-Viruses have none of these and aren't alive
102
Name 3 viral shapes
-Helical
-Icosahedral
-Complex
103
What are virions?
Viruses outside of an infected cell-can survive for some time but can't replicate
104
What is a viral envelope?
Lipid coat derived from plasma membrane of host cell
105
How do viruses replicate?
-Using machinery of host cell
106
What are the 5 steps of viral replication?
-Virus attachment to specific receptor on host cell
-Central viral core carrying nucleic acid + proteins enters cell
-Virus uses host materials to replicate-transcription to mRNA
-Assembly of virion
-Release of new virus particles
107
What are the 2 ways in which new viral particles are released + examples?
-Bursting out of cell-causes cell death e.g. rhinovirus
-Budding/exocytosis e.g. HIV, influenza
108
Name 5 ways in which viruses cause disease
-Direct destruction of host cells
-Modification of host cell
-Over-reactivity of immune system
-Damage through proliferation
-Evasion of host defences
109
Give an example of how viruses can cause disease by modifying host cells
Rota virus atrophies villi + flattens epithelial cells-decreases small intestine s.a.-nutrients not absorbed, hyperosmotic state, profuse diarrhoea
110
Give an example of how viruses can cause disease by causing over-reactivity of the immune system
Hepatitis B
111
Give an example of how viruses can cause disease by causing cell proliferation
HPV->cervical cancer
-partial viral replication + expression of some HPV proteins
-continuous expression of oncoproteins, causing cellular DNA mutations
-dysplasia + neoplasia
112
Give 5 examples of how viruses can cause disease by evading host defences
-Latency-virus not detectable but viral DNA lies latent + can reactivate, especially when immune system weakened e.g. herpes viridae, chickenpox->shingles
-Cell-cell spread e.g. with measles + HIV
-Antigenic variability-can change antigens e.g. influenza, HIV
-Prevention of host cell apoptosis e.g. herpesviridae
-Downregulation of interferon + other host defence proteins
113
What are the main infections caused by E.coli?
-Wound infections
-UTIs
-Gastroenteritis
-Traveller's diarrhoea
-Meningitis
-Bacteraemia
114
What is shigellosis + what causes it?
-Caused by shigella bacteria
-Severe bloody diarrhoea
115
What other bacteria shigella similar to? But how is it different?
-Similar to E.coli but has extra virulence plasmid
116
What are the two types of salmonella?
-S. enterica-salmonellosis
-S. bongori (rare)
117
What are the 3 forms of salmonellosis caused by S.enterica?
-Gastroenteritis-frequent cause of food poisoning
-Enteric/typhoid fever-bad drinking water/sanitation
-Bacteraemia-uncommon
118
How is shigella transmitted?
Person-to-person/contaminated water + food
119
How is salmonellosis transmitted?
Ingestion contaminated food/water
120
Describe the pathogenesis of salmonellosis
-Invasion of gut epithelium
-Transcytosed to basolateral membrane
-Enters submucosal macrophages
-Intracellular survival/replication
121
What is the most problematic bacterial infection for CF patients?
Pseudomonas aeruginosa
122
How does Vibrio cholerae spread?
-Shellfish ingestion
-Contaminated drinking water
-Faecal-oral route
123
Describe the structure of campylobacter
Spiral rod, uni/bipolar flagella
124
Describe the shape of helicobacter pylori
Spiral shaped + tuft of polar flagella
125
What conditions does H.pylori play a major role in?
-Gastritis
-Peptic ulcer disease
126
Name the 4 categories of aerobic gram negative rods + key examples
-Coliforms-escheria, salmonella, shigella
-Pseudomonads
-Vibrio-cholerae, campylobacter, helicobacter
-Parvobacteria-influenza
127
What are bacteroides?
Non-motile anaerobic rods
128
What are neisseria?
Gram negative aerobic cocci
129
Name the 2 clinically important species of neisseria
-N.meningitidis
-N.gonarrhoeae
130
What are spirochates?
Bacteria with a cell wall growing as single cells-not rods or cocci
131
Describe the structure of spirochates
Long, slender, helical, highly flexible, modified outer membrane, endoflagella
132
What bacterial infection causes Lyme disease + how?
-Borrelia burgdorferi infects small mammals
-Tick larvae feeds on infected animal
-Tick bites human - characteristic bull's eye rash
133
What bacteria causes symphilis?
Treponema pallidum
134
What are the 3 groups of obligate intracellular bacteria?
-Rickettsia
-Chlamydia
-Coxiella
135
What is unique about the growth cycle of chlamydia?
-2 developmental stages:
-Elementary bodies-infectious
-Reticulate bodies-replicative
136
What is a biovar?
A variant prokaryotic strain that differs physiologically or biochemically from other strains in a particular species
137
Name the 3 medically important members of Chlamydia
-C.trachomatis-3 biovars
-C.pneumoniae
C.psittaci
138
What are the 3 serovars of C.trachomatis + what do they cause?
-Trachoma biovar->blindness
-Genital tract biovar->most common STD, can cause infertility
-LGV biovar->causes LGV STD, mostly in tropics
139
What are fungi?
-Eukaryotic cells with chitin cell walls
-Heterotrophic (get food from other plants + animals)
-Move by growth or generation of spores
140
What is the difference between yeast + mould?
-Yeast = small single cell that divides by budding
-Mould = multicellular spores
141
What does dimorphic mean for fungi?
They can switch between being yeast + being mould when conditions suit-dangerous, can cause severe infection in healthy hosts
142
What is the main challenge with developing anti-fungals?
Fungi are eukaryotic-limited options for selective toxicity
143
What are the risk factors for mucosal candidiasis?
-Suppressed immune system (normally exists in humans with no harm to health)
-Diabetes
-Antibacterial therapy
-Mucosal disruption
144
How is mucosal candidiasis treated?
With topical or oral azoles (anti-fungals)
145
What is the worry with recurrent infections of mucosal candidiasis?
Recurrent infections can cause acquired resistance-sig. morbidity
146
What are dermatophytes?
Fungal organisms that require keratin for growth
147
What causes dermatophyte infections?
-Human-human or animal-human transmission
-Caused by Trichophyton spp., Microsporum spp. Or Epidermophyton floccosum
148
How are dermatophyte infections treated?
Topical/oral azoles or terbinafine
149
Give 3 examples of dermatophyte infections
-Tinea capitis-infection of scalp hair
-Tinea corporis-aka ringworm (not a worm)
-Tinea cruris-affects genitals + inner thigh
150
At what temperatures are dimorphic fungi mould + yeasts?
-Mould at 25-30 degrees
-Convert to yeast at 37 degrees
151
Give 3 examples of dimorphic fungi
-Histoplasma capsulatum
-Blastomyces dermatitidis
-Sporothrix schenkii
152
What condition does coccidioides cause, where is it found?
Coccidioidomycosis aka Valley fever, found in warmer, arid regions of America
153
What are the symptoms of coccidioidomycosis?
-2/3 cases asymptomatic
-Most of rest=pneumonia 1-3wks post-exposure
-Can get fine papular rash, myalgia, headache, chest pain
-Severe disease can lead to resp failure or septic shock
154
Name 5 late manifestations of coccidioides
-Cavitatory lung disease
-Vertebral osteomyelitis/chronic arthritis
-Ulcers + abscesses
-Cervical lymphadenopathy
-Chronic meningitis
155
What are the main causes of invasive candidiasis?
-Infection of prosthetics
-Intra-abdominal disease
156
157
Name 6 infective differential diagnoses of meningitis
-TB
-Cryptococcus
-Dimorphic fungi
-Lyme
-Brucella
-Syphilis
158
Name 5 non-infective differential diagnoses of acute/chronic meningitis
-Sarcoidosis
-Behcet's
-SLE
-Malignant meningitis
-Drug induced meningitis
159
Name the 2 species of Cryptococcus that cause most disease in humans
-C.neoformans
-C.gatti
160
What is Cryptococcus infection associated with + why?
Rotting wood + bird guano - Cryptococci grow at 40 degrees-birds have higher body temp
161
How would you treat a Cryptococcal infection?
-Liposomal amphotericin B
-Flucytosine
-Maintenance fluconazole
162
What fungi cause Mucormycosis? is it a serious infection?
Mucoraceous moulds aka zygomyctes cause rare but severe + rapidly progressing disease
163
Name 5 key anti-fungals
-Amphotericin B
-Echinocandins
-The azoles e.g. fluconazole, Isavuconazole
164
What are protozoa?
Single-celled animals
165
What are the 5 major groups of protozoa?
-Flagellates
-Amoebae
-Microsporidia
-Sporozoa
-Cilliates
166
Give 3 examples of flagellates + how they spread
-Trypanosoma-insect bites, African + American species
-Leishmania-sandfly bite
-Trichomonas vaginalis-sexually transmitted
-Giardia lamblia-faeco-oral spread
167
Give an example of a amoebae + how it spreads
Entaemoeba histolytica, spread by faeco-oral route
168
Give 3 examples of sporozoa + how they spread
-Toxoplasma gondii-ingestion of contamintaed food + water/feline faeces
-Cryptosporoidium-waterborne
-Plasmodium
169
How is malaria transmitted?
Female anopheles mosquito
170
How many species of malaria are there? Name them
5:
-Plasmodium falciparum
-Plasmodium ovale
-Plasmodium vivax
-Plasmodium malariae
-Plasmodium knowlesi
171
How is malaria diagnosed?
Blood film-light microscopy
172
What are the symptoms of malaria?
FEVER
Chills
Headache
Myalgia
Fatigue
Diarrhoea
Vomiting
Abdo pain
173
What are the signs of malaria?
-Anaemia
-Jaundice
-'Black water fever'
-Hepatosplenomegaly
174
How is black water ever caused in malaria patients?
Haemoglobin passes into urine from haemolysis
175
What is the lifecycle of a mosquito?
4 WEEKS
176
Describe the steps before initial human infection for malaria
-Mosquito bites infected human
-It ingests plasmodium gametocytes
-Mosquito now infected for life
-Gametocytes develop in mosquito, end up as sporozoites in salivary glands
177
Describe how malaria is transmitted to humans from mosquitos
-Mosquito takes next blood meal + injects sporozoites into human
178
Describe what happens in humans after initial malaria infection
-Sporozoites infect hepatocytes in liver
-This develops into a schizont, which bursts + infects erythrocytes
179
Describe the blood stage of malaria infection
-Trophozoite matures
-Develops into a schizont
-Schizont ruptures + re-infects another RBC
180
How long does the blood stage of malaria last + what symptoms does it cause?
48hrs
-Causes cyclical fever when RBC's rupture, haemolysis, anaemia + jaundice from bilirubinaemia
181
What are the 3 stages of the malaria cycle?
-Mosquito stages
-Human liver stages
-Human blood stages
181
What are the 3 cycles in malaria?
-Sporogonic cycle (in mosquito)
-Exo-erythrocytic cycle (in human liver)
-Erythrocytic cycle (in human blood)
182
Which species of malaria can be more serious + why?
P.falciparum causes infected RBC's to have knobs on surface that adhere to endothelial cells-causes more severe malaria as small vessels become blocked by clumps of RBC's
183
What are the cerebral symptoms of malaria?
-Drowsiness
-Increased ICP
-Seizures
-Coma
184
What are the respiratory symptoms of malaria?
-Anaemia + lactic acidosis increase resp rate
-Increased vascular permeability causes fluid to leak into lungs = pulmonary oedema
-ARDS (acute resp disease syndrome)
185
What are the symptoms of malaria related to the kidneys?
-Vascular occlusion->dehydration->hypotension
-Haemolysis->haemoglobinuria
-Fatigue
-Haematuria
-Renal failure
186
How does malaria cause DIC?
DIC = disseminated intravascular coagulation caused as lots of micro clots in blood but lack of clotting factors causes bleeding
187
How do you treat complicated malaria?
IV quinine + doxycycline
188
How do you treat uncomplicated malaria?
-ACTs e.g. riamet
-Quinine
-Doxycycline
-PO Chloroquine
189
What is primiquine used to treat?
Relapses of malaria-from dormant hypnozoites
190
Define antibiotic
An agent produced by micro-organisms that kill/inhibit the growth of other micro-organisms in high dilution
191
How do antibiotics work?
They bind to a crucial binding point on the bacteria-binding point varies by antibiotic class
192
What 4 areas do antibiotics target?
-Cell wall synthesis
-Nucleic acid synthesis
-Protein synthesis
-Folate synthesis
193
What kind of antibiotics target cell wall synthesis? Give an example
Beta lactams e.g. penicillins
194
Name the 4 classes of beta lactams
-Penicillins
-Cephalosporins
-Carbapenems
-Monobactams
195
How do beta lactams target the cell wall?
They attack the peptidoglycan by binding to penicillin binding protein sites covalently + irreversibly
196
Which kind of bacteria are beta lactams best at targeting + why?
Gram positive (peptidoglycan protected in gram -ve by lipopolysaccharide layer)
197
What types of antibiotic target nucleic acid synthesis + what do they target?
-Quinolones-DNA gyrase
-Rifampin-RNA polymerase
198
What types of antibiotic target protein synthesis?
-Aminoglycosides e.g. Gentamicin
-Tetracyclines e.g. Doxycycline
-Lincosamides
Macrolides
199
What kinds of antibiotic target folate synthesis?
-Sulfonamides
-Trimethoprim
200
What do bactericidal antibiotics do?
Kill the bacteria by inhibiting cell wall synthesis
201
What are bactericidal antibiotics used for + why?
Used for hard to treat infections/need to eradicate it quickly (meningitis), or if poor penetration (endocarditis)(kill >99% 8-24hrs)
202
What do bacteriostatic antibiotics do?
Prevent bacterial growth by inhibiting protein synthesis/DNA replication/metabolism (still kill >90% bacteria in 18-24hrs)
203
What is MIC?
Minimum inhibitory concentration
204
What is MBC?
Minimum bactericidal concentration
205
What are the 2 major determinants of anti bacterial effects?
-Antibiotic concentration (occupies enough binding sites)
-Antibiotic time (remains on binding sites long enough to inhibit metabolic processes of bacteria)
206
What 4 ways can bacteria resist antibiotics?
-Change antibiotic target
-Destroy antibiotic
-Prevent antibiotic access
-Remove antibiotic from bacteria
207
Give 3 examples of bacteria changing the shape of antibiotic binding sites
-MRSA (methicilin resistant S.aureus)
-VRE-vancomycin binding to enterococci reduced
-MDR-TB-Rifampicin activity reduced by changes to RNA polymerase in MTB
208
Give an example where antibiotic is destroyed/inactivated by bacteria
-Penicillins + cephalosporins hydrolysed-can't bind to PBP
209
Give an example of intrinsic antibiotic resistance
-Vancomycin can't penetrate outer membrane of gram -ve bacteria
210
Define acquired resistance
A bacterium which was previously susceptible obtains the ability to resist the activity of a particular antibiotic
211
How can bacteria acquire resistance?
-Spontaneous gene mutation
-Horizontal gene transfer
212
Name 2 important gram +ve resistant bacteria
-MRSA-Methicillin resistant Staphylococcus aureus
-VRE-vancomycin-resistant enterococci
213
Name an important gram -ve resistant bacteria
Extended spectrum beta lactamase (ESBL)
214
Name a key, relatively new bacteria resistant to gram negative bacteria
Carbapenem resistant enterobacteriae
215
What is the biggest challenge with MRSA
It confers resistance to all beta-lactam antibiotics, not just methicillin
216
What antibiotics can be used to treat MRSA?
Glycopeptides e.g.
-Vancomycin-but can't cross BBB
-Teicoplanin
also can be used for those with penicillin allergies
217
What antibiotics are used to treat severe pneumonia
Macrolides e.g.
-Clarithromycin
-Erythromycin
218
What can Clindamycin be used to treat?
-Cellulitis
-Necrosing fasciitis
219
What is Doxycyline used to treat?
Broad spec, but mainly gram +ve, can be used to treat cellulitis if penicillin allergy, pneumonia
220
What type of antibiotic is Gentamicin + what is it used to treat?
Aminoglycoside, used to treat gram -ve + streps e.g. UTIs + infective endocarditis
221
Give an example of a folate antagonist antibiotic
Trimethoprim
222
Name an antibiotic that is only used for the sickest patients, the immunocompromised, resistant gram -ves, whose use at STH is restricted
Meropenem-broad activity, works against ESBLs + AmpCs
223
What are ESBLs?
Extended Spectrum Beta-Lactamase-resistant bacteria
224
What are AmpCs?
Ampicillin Class C beta-lactamases-resistant to beta-lactams
225
What antibiotic is used to treat S.aureus?
Flucloxacillin
226
What are the UN AIDS 90/90/90 goals?
-90% of people living with HIV being diagnosed
-90% diagnosed on ART (antiretroviral therapy)
-90% viral suppression for those on ART by 2020
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How can HIV transmission be prevented?
-STI Tx
-Male + female condoms
-HIV counselling + testing
-Behavioural change
-Tx as prevention
-Pre + post exposure prophylaxis
-Male circumcision
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What is the U=U statement on HIV?
Undetectable = untransmittable
Those who receive effective antiretroviral therpay + have maintained an undetectable viral load cannot transmit the virus to a sexual partner
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How can HIV be transmitted?
-Sexual
-Vertical (mother to baby)
-Blood
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What is PreP?
Pre-exposure prophylaxis, can have a tablet/injection for HIV
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How effective is post-exposure prophylaxis? When can it be taken?
Not as effective as PreP, should be taken within 72hrs after sex
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What are the benefits of knowing HIV status?
-Access to appropriate treatment and care
-Reduction in morbidity and mortality
-Reduction of vertical transmission
-Reduction of sexual transmission
-Public health / partner notification
-Cost-effective
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When would you test for HIV?
-Clinician suspected-clinical indicators
-Routine in screening in high prevalence locations
-Antenatal routine screening
-Screening is high risk groups
-Patient initiated requests
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What are some symptoms of HIV?
-Flu-like-illness, rash
-Blood dyscrasias
-Multi-dermatomal shingles
-Lymphadenopathy
-Weight loss/diarrhoea/night sweats
-Oral/oesophageal candidiasis/hairy leukoplakia
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How do you screen for HIV?
-Venous blood sample is best-can detect most infections at 4 wks (can repeat at 7wks if suspicion). Test has high sensitivity + specificity
-HIV point of care test-immediate result, lower sensitivity + specificity
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What kind of virus is HIV?
Retrovirus-uses reverse transcriptase to make DNA copy that is integrated into DNA of infected cell
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Describe the HIV genome structure
Small RNA virus-expresses just 10 genes
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What characterises HIV as a lentivirus?
Long incubation period
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How does HIV replicate?
-HIV glycoproteins dock + fuse to CD4 + CCR5 receptors
-Viral capsid enters cell + releases enzymes + n.a.
-Reverse transcriptase is used to convert RNA into DNA-viral DNA then integrated into host cells
-Viral DNA read + viral proteins made
-Buds out of cell, matures more + working virus created
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What is the primary receptor for HIV?
CD4
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Describe genetic resistance to HIV
1% Caucasians homozygous for depletion in CCR5 gene so can't get HIV, ppl with 1 copy can catch disease but progression is much slower
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Why can HIV mutate so rapidly?
-Error-prone replication
-Rapid replication
-Large population sizes of new virus being produced
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Why is early initiation of ART for HIV benficial?
-Reduced transmission risk
-Smaller reservoir, delayed progression
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What are the signs + symptoms of acute HIV infection?
-V high viral load in blood
-Symptoms of acute retroviral syndrome:
-Glandular fever-like symptoms
-Fever
-Sore throat, oral ulcers
-Upper trunk skin rash
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Why is HIV relatively inaccessible to antibodies in the blood?
-HIV can pass directly from cell to cell
-HIV also has many genes that help virus evade immune system responses e.g. envelope spike is highly glycosylated-hard for antibodies to bind
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Why is life-expectancy of HIV patients on ART still reduced?
-Adherence, side effects, drug resistance issues
-Increase in NADIs (non-AIDS-defining illnesses), related to persistent immune activation + viral reservoir persisting
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What are the key populations for HIV?
-Sex workers + clients
-Gay men + men who have sex with men
-People who inject drugs
-Transgender ppl
-Prisoners
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What are the socio-economic impacts of HIV/AIDS in Africa?
-Reduced life expectancy
-Loss of economically-productive adults
-Increased spending on healthcare
-Change in social structure-orphans cared for by elderly grandparents
-Stigma persists
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Why does the transmission of HIV vary by sex?
-M->F transmission 2-3x more likely
-Young women + teenagers more vulnerable to infection
-Risk increases during pregnancy
-STIs cause inflammation/ulceration of female genital tract
-Sexual violence against women
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What are the 3 methods of paediatric transmission of HIV?
-In utero-particularly 3rd trimester-transplacental
-Intra partum-exposure to maternal blood + secretions during delivery
-Breast milk-ingestion of contaminated milk
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What 2 markers are used to monitor HIV infection?
-CD4 cell count
-HIV viral load
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What would CD4 levels be like in an AIDS patient?
<200
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What is the most common opportunistic infection in AIDS
PCP-pneumocystis pneumonia, symptoms = fevers, SOB, dry cough, pleuritic chest pain, exertional drop in O2 sats
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What is the Tx for HIV?
HAART (highly active anti-retroviral therapy)
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Name the 3 organisms most commonly found in blood cultures in infective endocarditis (from most common)
-Coagulase -ve staph (50%)
-Coliforms
-Staph. aureus
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What is the most common source of coagulase -ve staph in I.E.?
IV line contamination
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What is the most common source of coliforms in I.E.?
UTI bowel sepsis
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What is the most common source of staph. aureus in I.E.?
Skin, soft tissue, IV sites, pneumonia
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What is the most common source of pseudomonas spp. in I.E.?
UTI IV catheters
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What is the most common source of strep pneumoniae in I.E.?
Pneumonia
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What is the most common source of alpha-haemolytic streptococci in I.E.?
Oral cavity
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What criteria is used to diagnose infective endocarditis?
Modified Duke criteria
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What criteria must be met to diagnose 'definite' infective endocarditis?
-2 major OR
-1 major + 3 minor OR
-5 minor
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What are the major criteria for infective endocarditis?
-Positive blood culture with typical IE microorganism
-New partial dehiscence of prosthetic valve/ new valvular regurgitation
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