Microbiology Flashcards
(144 cards)
1
Q
why is chocolate agar useful
A
easier to grow organism not easily grown
2
Q
why is MacConkey agar useful
A
contains bile salts = inhibit gram positive growth
stains lactose = lactose fermenters pink, nonlactose fermenters white
3
Q
why is CLED agar useful
A
differentiate microorganisms in urine
classify lacotse/nonlactose fermenters in gram negative bacilli
4
Q
why is gonoccocus agar useful
A
promote growth of neisseria gonorrhoea and other neisserias
contains antibiotics/antifungals to inhibit growth of other organisms
5
Q
why is XLD agar useful
A
very selective isolates salmonella red at pH 7.4 shigella/salmonella = red other gut bacteria = yellow
6
Q
why is sabouraud agar useful
A
grows funghi inhibits bacteria
7
Q
what is a pathogen
A
organism capable of causing disease
8
Q
what is a commensal
A
organism which colonises the host but normally causes no disease
9
Q
what is an opportunistic pathogen
A
microbe that only causes disease if host defence are compromised
10
Q
what is pathogenicity/virulence
A
degree to which a given organism is pathogenic/damage causing
virulence factor = product or strategy which contributes to virulence
11
Q
what is an asymptomatic carriage
A
when a pathogen is carried harmlessly at a tissue site where it causes no disease
12
Q
what is a gram stain
A
method to determine bacteria type between gram positive and gram negative
13
Q
what is a capsule
A
peptigoglycan layer that surrounds some bacteria = allows it to hide from immune system and is antiphagocytic
14
Q
what are funghi
A
eurokaryotic cells with chitinous cell walls
heterotrophic and generate spores
15
Q
name 3 common fungal infection
A
nappy rash
vulvovaginal candidiasis
athletes foot
16
Q
what are the 3 common life threatening fungal infections
A
candida line infections
intra-abdominal infections
fungal asthma
17
Q
infectivity definition
A
ability to become established in the host (adherence and immune defence)
18
Q
invasiveness definition
A
ability to penetrate mucosal surfaces to reach sterile sites
19
Q
what is chronic carrier state
A
steady state between virus replication in host cells and virus death through host responses
20
Q
what is an endotoxin
A
component of outer membrane of bacterium from gram negative bacteria ONLY = LPS based
21
Q
what is an exotoxin
A
secreted proteins of gram negative and gram positive bacteria which causes harm to the host = protein based
22
Q
how does bacteria directly cause harm
A
destroy phagocytes/cells
endo/exooxins
23
Q
how does bacteria indirectly cause harm
A
inflammation
immune pathology
diorrhoea
24
Q
name a gram positive coagulase positive bacteria
A
staphylococcus aureus
25
name a gram positive catalase positive coagulase negative bacteria
staphylococcus epidermidis
| staphylococcus saproplyticus
26
what is the difference between staphylococcus and streptococcus
```
staphylococcus = catalase positive
streptococcus = catalase negative
```
27
describe alpha haemolytic streptococcus
greening on agar
| viridans group strep
28
how to determine if bacteria is strep pneumoniae
optochonin test
| if sensitive to optochonin disc = positive
29
describe beta haemolytic streptococcus
clearing on agar
| different groups A,B,C, G
30
what is lancefield grouping
bacteria have carb cell surface antigens e.g. A, B etc
antiserum for each group added to a suspension of bacteria
agglutination = recognition
31
give examples of each group of streptococcus
```
A = tonsilitis
B = sepsis, meningitis
C = UTI
```
32
what are the features of enterobacter
rods with flagella
| facultatively anaerobic
33
what does the outer layer of gram negative bacteria contain
lipid A = toxic
core antigens
somatic antigens
34
name 5 important enterobacter
```
escherichia coli
shigella
salmonella
proteus mirabilis
klebsiella pneumoniae
```
35
how do allylamines work
= fungicidal
inhibit biosynthesis pathway of ergosterol metabolism = affect membrane = kills fungus
high first pass metabolism
36
how do azoles work
= fungistatic
inhibit ergosterol synthesis
used for more invasive fungus
high doses = hepatitis
37
how do polyenes work
= fungicidal
affect activity of membrane bound proteins = disrupt insertion of molecules into membrane
cause nephrotoxicity
38
what are the 4 main features of antifungals
1. poor bioavailability
2. poor penetration to difficult areas
3. have few drug interactions
4. limited drug toxicity
39
name 2 gram negative bacillus that ferments lactose
E.coli
| klebsiella
40
name 2 gram negative bacillus that does not ferment lactose
Shigella
| salmonella
41
what are the sterile sites in the body
```
blood
CSF
lower respiratory tract
pleural fluid
peritoneal cavity
joints
urinary tract
```
42
which sites would you be able to culture normal flora
```
mouth
skin
vagina
urethra
large intestine
```
43
the HIV envelope contains
RNA
capsid
reverse transcriptase
44
describe antimicrobial resistance in MRSA
s.aureus is resistant to vancomycin
45
what are the clinical signs of sepsis
```
temp = above 38.3 or below 36
heart rate above 90
WBC above 12
hypoxia
low BP
```
46
definition of antibiotic
molecule that binds to bacteria target site and affects reactions critical to bacterial survival
47
what are beta lactams and how do they work
penicillins, cephalosporins, carbapenems
| bind to peptidoglycan PBP on gram positive bacteria = inhibit cell wall synthesis = bactericidal
48
how does metronizadole and rifampicin work on bacteria
interfere with nucleic acid synthesis and function
49
how do flouroquinolones work on bacteria
inhibit DNA gyrase
50
how do sulphonamides and trimethoprim work on bacteria
inhibit folate synthesis and carbon metabolism
51
how do macrolides and tetracyclines work
inhibit 30S ribosome = inhibit protein metabolism
52
what does is mean if an antibiotic is bacteriostatic
inhibits bacterial growth by inhibiting protein synth, DNA replication + metabolism = reduce endotoxin production
= will eventually kill 90%
minimum inhibitory concentration required MIC
53
what does bactericidal mean
inhibit cell wall synthesis = kills bacteria = good for hard to treat infections
minimum bactericidal conc required MBC
54
what should the ratio of MIC to MBC be
MIC:MBC > 4
55
why is the concentration of antibiotic important
drug must occupy adequate number of binding sites
56
why is the time of action of an antibiotic important?
drug must stay at binding site for long enough time to interfere with bacteria
57
what is conc dependent killing
depends on height of conc above MIC = aminoglycosides have high conc dependent killing
58
what is time dependent killing
depends on time that conc stays above MIC = beta lactams, macrolides have high time dependent killing
59
what are cephalosporins used for
= beta lactams
used in penicillin allergies
resistant bugs
hard to reach places e.g. meningitis
60
what antibiotics are used for gram positive bacteria
beta lactams
61
what is vancomycin used for
gram positive bacteria
MRSA
penicillin allergy
62
what are macrolides used for
e.g. clarithromycin, erythromycin
gram +ve bacteria
atypical pneumonias
63
what are lincosamides used for
e.g. clindamycin
gram +ve
anaerobic cellulitis
64
what are tetracyclines used for
e.g. doxycycline
cellulitis
chest infection
penicillin allergy
65
what is ciprofloxacin used for
gram -ve specific
UTI
gallbladder/abdominal infections
66
what is trimethoprim used for
gram -ve UTI
67
what is nitrofurantoin used for
gram -ve UTI
68
what is the significance of beta lactamases
= enzymes produced by bacteria that provide resistance to beta lactam antibiotics
69
what are beta lactamase inhibitors
class of medicine that block the activity of beta lactamases = prevent degradation of beta lactams
70
what antibiotics are protected against beta lactamases
co-amoxiclav
cephalexin
cefuroxime
71
where can nematodes be found in the body
= roundworms
intestinal
under skin
tissue
72
where can trematodes be found in the body
= flatworms
intestinal
blood
liver
73
what is the pre-patent period (PPP)
interval between infection and presence of eggs in stool
74
what is the largest and most common worm
ascaris lumbricoides
75
what are the symptoms of loaffler's syndrome
```
= larvae in lungs
cough
wheeze
fever
eosinophilia
positive chest XR
```
76
what conditions can E.coli be responsible for
```
wound infections
UTI
gastroenteritis
traveller's diarrhoea
bactereamia
```
77
describe entero-toxigenic ecoli ETEC
virulence factors = toxin and pili/fimbriae
| act in small intestine = watery diarrhoea in tourists
78
describe entero-pathogenic ecoli EPEC
virulence factor = pedestal formation (lumps on epithelium)
| acts in small intestine = watery diarrhoea less than 1 year
79
describe entero-haemorrhagic ecoli EHEC
virulence factor = pedestal formation and shiga like toxin
| acts in large intestine = bloody diarrhoea and HUS = food borne
80
describe entero-invasive ecoli EIEC
virulence factors = invasins leading to inflammation/ulceration
acts in large intestine = bloody diarrhoea/dysentry (in children)
81
describe entero-aggregative ecoli EAEC
virulence factors = pili and cytotoxin = shorter villi + mucus production
acts in large intestine = chronic diarrhoea in children
82
describe uro-pathogenic ecoli UPEC
virulence factors = haemolysin = inflammation
| acts in urinary tract = UTI in women
83
describe the pathogenicity of entero-toxigenic ecoli
1. toxins cause G protein modification = locking in ON state
| 2. increased cAMP production = loss of Cl and H2O§
84
describe the pathogenicity of pedestal formation and which forms of ecoli does this occur with
1. pathogen adheres to microvilli with pathogenic pilli
2. T3SS acts like syringe = disrupts tight junctions and ion activity (diarrhoea)
3. microvilli reform into pedestal holding pathogen
= in entero-pathogenic and entero-haemorrhagic
85
which bacteria are obligate intracellular
rickettsia
chlamydia
coxellia
86
which bacteria have no cell wall
mycoplasma pneumoniae
87
which bacteria has filament growth
actinomyces
nocardia
streptomyces
88
which bacteria are spirochaetes
leptospira
treponema
borrelia
89
describe the growth cycle of chlamydia
```
elementary bodies
= infectious stage
enters cell
inhibits phagosome function
become reticulate bodies
```
```
reticulate bodies
= not infectious stage
intracellular replication
convert back to EB
cell lysis and EB release
```
90
name the 3 most important types of chlamydia
```
C.trachomatis = most common STD, conjunctivitis
C.pneumoniae = atypical CAP pathogen
C.psittaci = severe pneumonia
```
91
name 6 typical bacteria that commonly cause CAP
```
strep. pneumoniae
hameophilus influenzae
staph. aureus
group A strep
moraxella catarrhalis
aerobic gram negative bacteria e/g/ klebsiella/e.coli
```
92
name 3 atypical bacteria that commonly cause CAP
legionella
mycoplasma pneumoniae
chlamydia pneumoniae
93
name 4 viruses that commonly cause CAP
influenza A and B
parainfluenza virus
rhinovirus
adenovirus
94
describe a spirochete bacterium
has endoflagellum between outer membrane and peptodoglycan = allows corkscrew movement
95
describe borrelia burgdorferi
= lyme disease
tick-borne
cause rash/flu-like symptoms
spreads through extracellular matrix to bloodstream and other organs
96
descrive leptospira interrogans
spread from animal urine to human through mucous membrane
| cause flu-like symptoms - Weil's disease in severe cases
97
describe treponema pallidum
= syphilis
primary stage = localised infection v. infectious
secondary stage = systemic infection lymph nodes, skin, joints, vessels
tertiary stage = granuloma in soft tissue = cardio/neurosyphilis
treat with flucloxacillin
98
name 3 important mycobacteria
M. tuberculosis = TB
M. leprae = leorosy
M. avium complex (MAC) = infection in AIDS and chronic lung disease
99
what are the 4 types of protozoa and give an example for each
```
flagellates - trypanosoma (sleeping sickness),
trichromonas vaginalis (STI), GIARDIA LAMBLIA
```
sporozoans - plasmodium, toxoplasma gondii (toxoplasmosis)
amoebae - entamoeba histolytica (amoebic dysentery)
ciliates - balatidium coli (colonic ulceration)
100
what is significant to remember about trichomonas vaginalis
dont confuse it with chlamydia
101
name the 4 disease causing plasmodium
p. falciparum
p. ovale
p. vivax
p. malariae
102
what is the vector for malaria
female anopheles mosquito around stagnant water = 3-4 week infected lifecycle
103
what is the hypnozoite stage in the malaria life cycle
after schizonts rupture in hepatocyte releasing merozoites into the bloodstream = p.ovale and p.vivax can lie dormant in the liver and reactivate
104
what are most protozoa treated with
metronizadole
105
what is giardia lamblia
parasitic microorganism that infects the small intestine
causes giardiasis = diarrhoea/bloating/cramps
foecal oral spread
travel associated
stool microscopy diagnosis
metronizadole treatment
106
describe the process of a gram stain
1. fixation
2. crystal violet
3. iodine
4. decolorisation using ethanol
5. application of safranin as counter stain
6. gram positive bacteria not decolourised by ethanol = purple
gram negative is decolourised so retain pink of safranin counterstain
107
describe zeihl-neelson staining for mycobacteria
1. cells stained using carbol fuchsin = red
2. washing with acid alcohol = removes carbol fuschin from background cells = mycobacterium remain red because it is acid-fast (holds fast to the dye)
3. slide stained with methylene blue
4. mycobacterium stained purple = identified
need 10,000 acid fast bacilli per ml
108
name 3 methods of culturing mycobacteria
1. soft culture
2. liquid culture
3. nucleic acid detection
109
what are cytopathic effects
viruses have to be grown in cells so cannot be cultured
| CPE = effects observed when viruses are cultured inside living cells
110
what is serology
study/detection of antibodies in serum
mainly IgM/IgG
IgM appears within a week of infection and remains in blood up to 12 weeks
IgG appears later but remains within blood for years for immunity
111
what swabs are used for bacterial and viral infection
```
green = viral
black/charcoal = bacterial
```
112
how do mycobacteria cause disease in the body
1. mycobacteria engulfed by macrophage = phagolysosome = APC
2. CD4 T cells recognise APC = interferons and interleukins stimulate macrophage activity
granuloma formation
113
describe granuloma formation as part of mycobacterial disease
1. highly stimulated macrophages = become epithelioid cells = fuse to become Langhans giant cells = fibroblasts laid down around granuloma
2. central tissue necrosis = caseating necrosis = cavity in tissues e.g. in the lungs in TB
114
describe the immunology of tuberculoid leprosy
Th1 response (IFN+TNF) = tissue hypersensitivity and granulomas = tissue damage
115
describe the immunology of lepromatous leprosy
Th2 response (IL 4,5,10) = lesions full of bacilli and NO granuloma = skin lesions
116
what 4 drugs are used to treat TB
```
RIPE
rifampicin
isoniazid
pyrazinamide
ethambutol
```
117
name 3 viruses that cause direct host cell destruction
hip!
HIV
influenza
polio
118
name 2 viruses that cause modification of host cell function/structure
HIV
| rotavirus
119
name 3 viruses that cause an over-reactive host response
Hep B
Hep C
HIV
120
name a virus that causes cell proliferation and immortalisation
HPV
121
describe 3 ways viruses evade host cell defence
persistence (measles)
variability (flu)
host defence modulation (all viruses)
122
describe a rotavirus infection
1. acid resistant rotavirus invades jejunal epithelial cells = cause villi and microvilli to atrophy
2. reduced SA and enzyme conc = no sugar absorption = hyperosmosis = diarrhoea
123
describe a Hepatitis B infection
1. HBV infection causes antibody and cytotoxic T lymphocyte response = hepatocyte destruction = liver damage
2. steady state reached between hepatocyte destruction and viral replication = no spread
124
describe cervical carcinoma development
1. HPV infects superbasal layer of genital tract = replicates as mucosal cells move up
2. HPV and host cell genome integration = p53 suppression = carcinogenesis
125
what is wuncheria bancroftii
human parasitic worm = filariworm
| causes lymphatic filariasis = lymphoedema
126
what disease do schistosome flatworms cause
schistosomiasis which can cause bladder cancer
127
what disease is associated with the hookworm
iron deficient anaemia
128
describe the humoural response to viruses
IgA and IgM block viral binding and aid agglutination
| complement and GB antibody = opsonisation and cell lysis
129
describe the cell mediated response to viruses
interferon prevents infection of non-infected cells
| cytotoxic T lymphocytes directly kill infected cells and activate antibody dependent cell destruction
130
which viruses virulence factors include direct cell cytotoxicity
```
flu = respiratory epithelium
shingles = skin cells
HIV = T cells
```
131
which viruses show antigenic variation
rhinovirus
influenza
HIV
132
which viruses cause immune suppression
MMR
EBV
HIV
CMV
133
name 3 ways protozoa evade host defence
surface antigen variability
intracellular phase
shed outer coat
134
describe a delayed type hypersensitivity reaction (type 4) for example in TB
1. intracellular infection (TB) = Tdth cells stimulated = influx of inflammatory cells
2. second contact = Tcth secretes IFN TNF IL = macrophage recruitment
3. prolongued DTH = granuloma formation = lytic enzymes cause tissue damage
135
name 3 ways bacteria can resist phagocytosis
polysaccharide capsule
M protein
phagolysosome escape
136
what is an API strip
card with self contained series of biochemical reaction tubes which identify bacteria based on metabolic and enzymatic properties
137
what is B.fragilis
anareobic gram negative bacteria lives naturally in the colon
is usually commensal but can cause infection after surgery/trauma or if displaced into bloodstream
138
what is a Mz disc
contains metronidazole
| confirms presence of anaerobic bacteria if prevents bacteria growth
139
what number of bacteria cultured indicate significant bacteriuria
10^5 bacteria/ml
140
what number of bacteria cultured suggests doubtful significance of bacteriuria
between 10^4-10^5 bacteria/ml
141
(simply) how does HIV cause immune dysfunction
1. CD4 cell death =
- direct cytotoxicity
- impaired homeostasis
- premature apoptosis
- reduce T cell production
2. CD8 CTL increased activation but decreased cytotoxic function
3. B cells increased activation but antibodies non specific
4. decreased function of
- natural killer cells
- macrophages
- neutrophils
142
describe the progression of an HIV infection
1. acute primary infection = low then high CD4 count
2. asymptomatic phase = progressive loss of CD4
3. early symptomatic phase = manifestation of clinical features
(roughly 5-10 years later)
4. AIDS = CD4 < 200
143
what are the HIV infection markers
CD4 count
| HIV viral load = RNA concentration
144
how is malaria treated
```
non p.falciparum:
chloroquine
primaquine to prevent relapse
p.falciparum:
complicated = quinine + IV artesunate
non-complicated = oral quinine + riamet
```
