Microbiology Flashcards
what is the most common route of entry of pathogens into CNS?
haematogenous
what are the causes of meningitis?
neisseria meningitides (3 serotypes)
streptococcus pneumoniae
haemophillus influenzae
what is the most common infection of CNS?
coxsackie B
echovirus
which is becoming the leading cause of encephalitis worldwide?
West Nile Virus
what is pyogenic vertebral oseteomyelitis?
common vertebral infection
e.g. staph/strep
which is the best imaging modality in detecting parenchymal abnormalities?
MRI
normal cell count (x106/l) in CSF
0-5 leucocytes
normal protein level in CSF in g/l
0.15-0.40
normal glucose levels in CSF mmol/l
2.2-3.3
60% blood glucose levels
purulent meningitis CSF findings (bacterial)
- turbid
- 1000-2000 polymorphs
- gram stain
- 0.5-3.0g/l protein (high)
- 0-2.2 mmol/l glucose (low)
aseptic meningitis CSF findings
- clear, slightly turbid
- 15-500 lymphocytes
- -ve gram stain
- 0.5-1.0g (protein)
- normal glucose
differentials for aseptic meningitis
- viral meningitis
- partially Abx treated bacterial meningitis
- brain abscess
- TB/fungal meningitis
TB meningitis findings CSF
- clear, slightly turbid
- 30-500 lymphocytes/some polymorphs
- -ve gram stain
- 1.0-6.0g/l protein
- 0-2.2. mmol/l glucose
gram stain colours
gram positive = more purple
gram negative = more pink
gram-negative diplocci meningitis
neisseria meningitis
Ziehl-Neelson stain coloir
red and blue
stain for cryptococcal
India Ink
how does Cryptococcal appear on India Ink?
orbit structure (yeast in middle, capsule around edge)
high opening pressure on LP
cryptococcal meningitis
what is early indication of HIV infection?
chronic swelling of parotids
what is lymphoid interstitial pneuominitis?
lung condition associated with HIV
lymphoproliferation due to immune activation
when is HIV most commonly transmitted in pregnancy?
end of pregnancy when placenta is tired
when placenta is unhealthy (e.g. malaria)
which drugs work to stop HIV entry?
- fusion inhibitors e.g. Enfurvirtide
- CCR5 coreceptor antagonists e.g. Maraviroc
what HIV drugs affect the pretranscriptional stage?
- NRTI e.g. Zidovudaine, Eruticutabine
- NtRTI e.g. tenofavir
- NNRTI e.g. Efavirenz
what HIV drugs target postranscriptional ?
integrase inhibitors e.g. Raltegravir
PI e.g. ritonavir
what did the ARROW trial show?
no difference in outcome when clinical monitoring is compared to labaratory monitoring in HIV
what is immune reconstitution inflammatory syndrome (IRIS)?
revamping the immune system can lead to severe inflammatory response
= deterioration in clinical state
features of PCP pneumonia clinically and X-ray
X-ray: widespread bilateral ground glass shadowing
reduced exercise tolerance, low sats
how to confirm PCP pneumonia?
bronchoalveolar lavage cytology
= cysts using silver stain (Grocott-Gomoti stain)
T cell defects result in..
- viral infections
- aggressive, opportunistic infections
B cell defects lead to..
- bacteria: staph, pseudomonas
- fungi: candida, aspergillus
what is actinomyces?
gram +ve rod that branches as grows
basophillic sulphur granules
= lung abscess in immunocompromised/alcoholics
slow growing and difficult to treat
C. difficle severity score
1+ of
- T > 38.5
- HR > 90
WCC > 15
- rising creatinine
- clinical signs of severe colitis/ colitis on radiology
- failure to respond to therapy at 72 hours
severe C. diff treatment
Vancomycin
what is C. diff ribotype 027?
associated with increased severity of disease
produces more toxin A + B
why do PPIs cause increase risk of C. diff?
raise pH of stomach
- more GI flora and C diff spores survive stomach and travel down to colon
what do the 2 toxins produced by C. diff do?
- damages epithelial cells (cytotoxin) = neutrophil infiltration
- disrupts tight junctions = lots of fluid loss
some lab findings in C. diff
High WCC
low CRP
what is 14-3-3 protein a marker of?
marker of rapid neurodegeneration
what Chr is normal prion gene found on? what is its role?
Ch20
prion protein role in copper metabolism
what are the 3 polymorphisms of codon 129?
MM (predisposes to prion disease)
MV
VV
structure of normal prion protein vs abnormal?
normal = alpha-helical abnormal = beta pleated sheet
prion disease classification
- sporadic: Creutzfelt-Jakob Disease
- acquired: Kuru, vCJD (BSE), iatrogenic CJD
- genetic (PRNP mutation): Familial Fatal Insomnia, GSS syndrome
investigation results in sporadic CJD
EEG: triphasic complexes
MRI: increase signal in basal ganglia
increase 14-3-3 protein
tonsillar biopsy = not useful
vCJD investigation results
- MRI: pulvinar sign
- EEG: non specific slow waves
- 14-3-3 normal
- MM at codon 129
- tonsillar biopsy = 100% sensitivve
most common mutation in Gerstmann-Strausser-Sheinker Syndrome
PRNP P102L
features of Fatal Familial Insomnia
untreatable insomnia
BP/HR dyregulation. ataxia, thalamic degeneration
what is Kuru linked to?
cannabalism
symptomatic treatment of CJD
clonazepam for myoclonus
treatment of CJD - delaying prion conversion
quinacrine
pentosan
tetracycline
what is staphylococcus saprophyticus?
coag -ve
infections in younger women
virulence factor (P. fimbriae) = allows adhesion of epithelial
what are the neurogenic malfunction that can cause obstruction in renal tract?
- poliomyelitis
- tabes dorsalis
- diabetic neuropathy
- spinal cord injuries
what does white cell pyuria?
indicative of infection
what does squamous epithelial cells in urine culture signify?
contamination
how many CFU do you need to identify a UTI?
> 105 with urinary symptoms
organisms typical of UTI = >103 CFU/ml
what could cause a sterile pyuria (raised WCC but no growth)?
- prior treatment with Abx
- chlamydia
- TB
- calculi
- catheterisation
- bladder
- neoplasm
what culture is used for UTIs?
chromogenic agar
colours that the agar can turn and cause
- pink: E. coli
- blue: other coliforms
- light blue: gram +ve
what is the incubation period of Hep A?
2-6 weeks after get hepatitis
describe the Hep B virus
DNA virus
4 overlapping reading frames
what are the treatment options for Chronic Hep B?
interferon alpha
lamivudine
tenofavir
entevavir
what time of virus is Hep C
flavivirdiae virus
best way to check for Hep C
HCV RNA check for virus in blood
treatment for Hep C
early treatment with peginterferon alpha
response guided therapy
what to remember about treating genotype 1 Hep C?
high dose, longer lasting ribavirin needed
features of hep D infection
smallest virus
needs presence of Hep B to replication
Hep B + D = super infection
what type of virus of Hep E
hepeviridae family
genotypes of Hep E
1+2: human, epidemic
3+4: swine and other
sources of Hep E
shellfish
blood transfusion
sausages
what are the rare complication of Hep E?
CNS disease (Bell's Palsy, GB) Chronic infection
Treatment of Hep E
supportive
ribavirin
type of virus is Hep G
Pegivirus
3 levels of SSIs
superficial incisional (skin and subcutaneous) deep incisional (fascial, muscle layer) organ/space infection
features of MRSA and tx
gram +ve cocci
haemolytic
Tx: Linezolid
preventing SSRs pre-operatively
- age
- underlying issues (obesity, low albumin, smoking etc)
- pre-operative showering (shower with soap on day)
- hair removal (micro-abrasions = multiplication of bacteria)
- nasal decontamination (if found to carry S. aureus)
- Abx prophylaxis (at induction of prophylaxis)
preventing SSRs intra-operatively
\+ve pressure ventilation sterilisation instruments aseptic prep normothermia (dec temp = dec oxygen) oxygenation >95%
pathophysiology of septic arthritis
- bacterial proliferation in synovial fluid = host inflammatory response
- joint damage = host derived protein (e.g. fibronectin) exposed –> bacteria adhere
bacterial factors that influence in septic arthritis
- S. aureus: fibronectin-binding protein (recognises selected host proteins)
- Kingella Kinga: bactieral pili (help adhere to synovium)
- some S. aureus strains = cytotoxin PVL = fulminant infection
what joint is mostly affected in septic arthritis?
50% knee
rarer causes of septic arthritis
lyme disease
brucellosis
mycobacteria
fungi
chronic osteomyeltiis presentation
pain
brodies abscess
sinus tract
treatment for chronic ostemyelitis
- radical debridement
- remove sequestra (dead bony tissue)
- Lautenbach technique
- Papineau technique
Lautenbach technique
- debridement to healthy bleeding bone
- double lumen irrigation system inserted
- fluid and Abx irrigated for 3 weeks
Papineau technique
complete excision of infected tissue/necrotic bone
bone grafting of osseous defect
most common cause of prosthetic join infection
coagulase negative staphylocci
single stage revision of PJI
- remove dead bone/material
- replant new prosthesis with Abx impregnated cement
two stage revision of PJI
- remove, put in spacer
- Abx for 6 weeks
- re-debride
- implant with Abx impregnated cement
what is the most common HAI?
pneumonia
features of C. difficle
gram +ve
spore forming anaerobe
features of S. aureus
gram +ve cocci in clusters
differentials for PUO
- infection
- AI/ inflammatory, vasculitides
- malignancy
- medication
extra tests to remember to do in PUO
- HIV test
- EBV/CMV test
- extended serology tests (Q-fever, Bartonella, Brucella)
parasites that can cause PUO
- malaria
- amoebic liver abscess
- schistosomasis
- toxoplasmosis
- trypanosomiasis
fungi that can cause PUO
- cryptococcus
- histoplasmosis
EBV serology
- viral capsid antigen (appear quickly when symptomatic)
- EBNA-1 IgG appear late on in disease
how does a PET-CT scan work?
- fluoro-D glucose accumulates in cells with increased rate of glycolysis
- kidney light up as where FDG is excreted
what is a very high ferritin associated with?
- adult onset Still’s disease (salmon pink rash)
- macrophage activation syndrome
what is the test for latent TB?
IGRA
Duke’s criteria for IE
2 major
or
1 major + 3 minor
major criteria for IE
persistent bacteraemia (>2 BCs)
echo - vegetations
+ver serology for Bartonella, Coxiella or Brucella
minor criteria for IE
- predisposition (murmur, IVDU)
- inflammatory markers (fever, CRP high)
- immune complexes (splinters, haematuria)
- embolic phenomena (janeway lesion, CVA)
- atypical ECHO
- 1 +ve BC`
reservoir, source and symptoms of Campylobacter
reservoir: poultry, cattle
contaminated food
Presentation: diarrhoea, bloating, cramps
salmonella reservoir, symptoms and management
reservoir: poultry
symptoms: diarrhoea, vomiting, fever
Mx: supportive, ciprofloxacin, azithromycin
Bartonella henselae:
reservoir, source, causes what
- reservoir: kittens > cats
- scratches, bites
- causes cat scratch disease or bacilliary angiomatosis
- diagnosed via serology
cat scratch disease and management
- macule at site, becomes pustular
- regional adenopathy
- systemic Sx
- Mx: erythromycin, doxycycline
bacilliary angiomatosis and Mx
- immunocompromised
- skin papules
- disseminated multi-organ and vasculature involvement
- Mx: erythromycin + doxycycline + RIFAMPICIN
TOXOPLASMOSIS reservoir symptoms investigation management
cats/sheep
fever, adenopathy, still birth, seizures
serology
Mx: spiramycin, pyrimethamine + sulfadiazine
BRUCELLOSIS reservoir symptoms investigation management
cattle/goats unpasturised milk, undercooked meat Px: fever, back pain, orchitis, focal absecess Blood culture Mx: doxycycline + gentamicin
COXIELLA BURNETII - Q FEVER reservoir symptoms investigation management
goats/sheep/cattle aerosolisation, unpasturised milk Px: flu like, pneumonia, hepatitis, endocarditis, focal absecess Serology Mx: doxycycline
RABIES (LYSSA VIRUS) reservoir symptoms investigation management
dogs/cats/bats
seizures, excessive salivation, agitation, confusion
serology
Mx: Ig, vaccine
RAT BLUE FEVER
organisms
symptoms
management
- streptobacillus moniliformis
- fevers, polyarthralgia, rash
- can progress to endocarditis
- Mx; penicillin
causes of viral haemorrhagic fever
- ebola (bats)
- lass (rats)
- crimean congo haemorrhagic fever (ticks)
sail sign
double heart border
LLL collapse
features of strep pneumoniae
gram +ve cocci
alpha-haemolytic
optochin-sensitive
main organisms causing CAP
S. pneumoniae H. influenzae Moraxella catarrhalis Staph aureus Klebsiella pneumoniae
atypical causes of CAP
legionella
mycoplasma
Coxiella burnetti (Q fever)
chlamydia psittaci
urea and RR cut offs in CURB
urea >7
RR > 30
bronchitis causing organisms
viruses
S. pneumoniae
H. influenzae
Moraxella catarrhalis
causes of cavitation on CXR
staph aureus
Klebsiella pneumoniae
TB
features of H. influenzae
gram -ve cocco bacilli
chocolate agar plate
what investigations in legionella pneumophilia?
grown on buffered charcoal yeast extract
urinary antigen
stains in TB and coloir
auramine stain + Ziehl Neelson stain
red rods = acid fast bacilli
causes of HAP
Enterobacteriae (e.g. E coli, K. pneumoniae)
Staph aureus
Pseudomonas sp
PCP type of organism and Ix
protozoan
walk test = de sat on exercise
CXR: bat wing shadowing
3 lung diseases caused by aspergillus fumigatus
- allergic bronchopulmonary aspergillosis (chronic wheeze, eosinophilia, bronchiectasis)
- aspergilloma
- invasive aspergillosis (immunocompromised)