Microbiology Flashcards
What are the four processes that occur in septicaemia?
Capillary leak – albumin and other plasma proteins lead to hypovolaemia
Coagulopathy – leads to bleeding and thrombosis, endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected
Metabolic derangement – particularly acidosis
Myocardial failure – and multi-organ failure
What is a typical MRI feature of TB meningitis?
Leptomeningeal enhancement
Name two types of amoeba that cause encephalitis.
Naegleria fowleri
Acanthamoeba species and Balamuthia mandrillaris
What is toxoplasmosis and how is it spread?
Obligate intracellular parasite
Spread via oral, transplacental or organ transplant route
From raw/undercooked meats (particularly in France) and contact with cat faeces
List some organisms that can cause brain abscesses.
Staphylococci Streptococci Gram-negative organisms (mainly in neonates) TB Actinomyces and Nocardia species
Describe the Gram-stain and microscopic appearance of:
a. S. pneumoniae
b. N. meningitidis
c. L. monocytogenes
d. TB
e. Cryptococcus
a. S. pneumoniae
Gram-positive alpha-haemolytic diplococci
b. N. meningitidis
Gram-negative non-haemolytic diplococci
c. L. monocytogenes
Gram-positive rods
d. TB
Stains positively with Ziehl-Neelsen (red and blue)
e. Cryptococcus
Stains positively with India ink (appears like an orbit – yeast in the middle with a capsule around the outside)
What is another key clinical feature of Cryptococcal meningitis?
High opening pressure
What is the generic therapy used in meningitis?
Ceftriaxone 2 g IV BD
If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
NOTE: this is because ceftriaxone does NOT cover Listeria
What is the generic therapy used in meningo-encephalitis?
Aciclovir 10 mg/kg IV TDS
Ceftriaxone 2 g IV BD
If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
Name the specific therapy for meningitis caused by:
a. S. pneumoniae
b. N. meningitidis
c. H. influenzae
d. Group B Streptococcus
e. Listeria
f. Gram-negative bacilli
g. Pseudomonas
a. S. pneumoniae Pen G 18-24 mu/day b. N. meningitidis Ceftriaxone 4 g/day c. H. influenzae Cefotaxime 12 g/day d. Group B Streptococcus Pen G 18-24 mu/day e. Listeria Ampicillin 12 g/day f. Gram-negative bacilli Cefotaxime 12 g/day g. Pseudomonas Meropenem 6 g/day
What type of toxin is produced by Staphylococcus aureus?
Enterotoxin – this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2
What type of organism is Bacillus cereus?
Gram-positive rods that are spore-forming
Name three types of Clostridium infection and describe the diseases that they cause.
Clostridium botulinum – causes botulism
• From canned food
• Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses
- Causes descending paralysis
• Treated with antitoxin
Clostridium perfringens – food poisoning
• From reheated food
• Generates a superantigen that mainly affects the colon
• Causes watery diarrhoea and cramps that last 24 hours
Clostridium difficile – pseudomembranous colitis
• Hospital-acquired infection related to antibiotic use
Which antibiotics are most commonly implicated in C. difficile colitis?
Cephalosporins
Clindamycin
Ciprofloxacin
What type of organism is Listeria monocytogenes?
Gram-positive, rod-shaped, facultative anaerobe
Beta-haemolytic, aesculin-positive with tumbling motility
What type of organisms are Enterobacteriaceae?
Facultative anaerobes
Lactose fermenters
Oxidase-negative
What type of bacteria are Salmonella enteritidis?
Gram-negatives
Oxidase negative
Urease negative
Non-lactose fermenting
Produce hydrogen sulphide (form black colonies)
Grows on TSI agar, XLD agar and selenite F broth
Which antigens are found on Salmonellae?
Cell wall O (groups A-I)
Flagellar H
Capsular Vi (virulence, antiphagocytic)
NOTE: differences in these antigens help identify types of Salmonellae
Describe the presentation of Salmonella typhi.
Slow onset fever and constipation
May cause splenomegaly, rose spots, bradycardia, anaemia and leucopaenia
Blood cultures may be positive
Transmitted only by humans
Ingested by monocytes and multiplies in Peyer’s patches and spreads via the endoreticular system
How is Salmonella typhi treated?
Ceftriaxone
List some types of Shigella.
Shigella sonnei
Shigella dysenteriae
Shigella flexneri (MSM)
NOTE: avoid antibiotic treatment (use ciprofloxacin if necessary)
What are the microbiological features of Vibrio?
Comma-shaped
Late lactose-fermenters
Oxidase-positive
Gram-negative
Name and describe the key features of other types of Vibrio.
Vibrio parahaemolyticus – caused by ingestion of raw/undercooked seafood, causes self-limiting diarrhoea, grows on salty agar
Vibrio vulnificus – causes cellulitis in shellfish handlers, can cause fatal septicaemia with D&V in HIV patients, treated with doxycycline
What are the main microbiological features of Campylobacter?
Comma-shaped Microaerophilic Oxidase-positive Gram-negative Motile
What are the key microbiological features of Entamoeba histolytica?
Motile trophozoite in diarrhoeal illness
Non-motile cyst in non-diarrhoeal illness
Killed by boiling
Contains four nuclei
No animal reservoir
Describe the pathophysiology of diarrhoeal illness caused by Entamoeba histolytica?
Ingestion of cysts trophozoites move into the ileum colonise the colon causes flask-shaped ulcers
How is Entamoeba histolytica infection diagnosed and treated?
Diagnosis: stool microscopy, serology of invasive disease
Treatment: metronidazole + paromomycin
What are the key microbiological features of Giardia lamblia?
Pear-shaped trophozoites
Two nuclei
Four flagellae and a suction disc
Outline the pathophysiologiy of GI disease caused by Giardia.
Transmitted by ingestion of cyst from faecally contaminated water
Excystation in the duodenum leads to trophozoite attachment
Results in malabsorption of protein and fat
Presentation: foul-smelling non-bloody diarrhoea, cramps, flatulence, NO fever
What are the main features of Cryptosporidium parvum?
Causes severe diarrhoea in the immunocompromised
Oocysts can be seen in the stool using modified Kinyoun acid fast stain
Rx: paromomycin
Which stain is used to identify PCP?
Silver stain (Grocott-Gomori stain)
Which organisms do the following defects make you susceptible to?
a. T cell defect
b. B cell defect
c. Neutrophil defect
d. Complement defect
a. T cell defect Sepsis CMV, EBV, VZV Candida, PCP Usually aggressive opportunistic infections b. B cell defect Streptococcus, Staphylococcus, Haemophilus Giardia Usually recurrent sinopulmonary infections c. Neutrophil defect Staphylococcus, Pseudomonas Candida, nocardia, aspergillus d. Complement defect Neisseria
What is Actinomyces and what does it cause?
Gram-positive rod that causes lung abscesses in immunocompromised patients (particularly alcoholics)
NOTE: it’s closely associated with Nocardia
Describe the histological features of Actinomyces.
Basophilic sulfur granules
Gram-positive rods that branch as they grow
How is non-severe C. difficile disease treated?
Metronidazole 400 mg TDS for 10-14 days
If intolerant or not responding at 72 hours, change to vancomycin 125 mg QDS for 10-14 days
Describe the MRI appearance of sporadic CJD.
Increased signal in the basal ganglia
Increased intensity on DWI MRI of the cortex and basal ganglia
On which chromosome is the normal prion gene found?
20
On which codon are the three polymorphisms of prion proteins found? What are the three polymorphisms?
Codon 129 MM (predisposes to prion diseases) MV VV NOTE: M = methionine, V = valine
Which gene mutation is associated with prion diseases?
PRNP
Which investigation is most useful for vCJD?
Tonsillar biopsy – prions localise in lymphoid tissue
NOTE: this is not useful in CJD
Outline the clinical features of iatrogenic CJD.
Starts with progressive ataxia
Dementia and myoclonus occur at a later stage
Describe the clinical features of Gerstmann-Straussler-Sheinker syndrome.
Slowly progressive ataxia
Diminished reflexes
Dementia
NOTE: PRNP P102L mutation is most common
Describe the clinical features of fatal familial insomnia.
Untreatable insomnia Dysautonomia (blood pressure and heart rate dysregulation) Ataxia Thalamic degeneration NOTE: PRNP D178N mutation is most common
What number of white cells in the urine represents inflammation?
More than 10^4/mL
In which patient groups should screening of the urine for white cells before MC&S NOT be performed?
Immunocompromised patients, pregnant women and children
List some causes of sterile pyuria.
STIs (e.g. chlamydia) TB Prior antibiotic treatment (MOST COMMON) Calculi Catheterisation Bladder cancer
What type of agar is used for urine culture? What do the colours suggest?
Chromogenic agar
• Pink = E. coli
• Blue = other coliforms
• Light blue = Gram-positives
In which groups of patients is a short course of antibiotics not appropriate?
Women with a history of UTI caused by antibiotic resistant organisms
More than 7 days of symptoms
Men
Which part of the kidney is more susceptible to infection?
Renal medulla
NOTE: the kidney is a frequent site for abscesses in patients with S. aureus endocarditis
What is the main treatment option for pyelonephritis?
Co-amoxiclav with or without gentamicin
What is the incubation period for hepatitis A?
2-6 weeks
Describe the molecular organisation of hepatitis B virus.
DNA virus with four overlapping reading frames (core, X, polymerase and surface antigen)
NOTE: as they overlap, a mutation in one reading frame could affect others
What is a strong indicator of risk of cirrhosis in people with hepatitis B infection?
HBV DNA level (copies/mL)
What components constitute the viral RNA genome of hepatitis C?
Core
Envelope
Non-structural components
NOTE: most drugs used for hep C are protease inhibitors
What is the incubation period of HCV?
6-8 weeks
List some treatment options for chronic HBV.
Interferon alpha Lamivudine Tenofovir Entecavir Emtricitabine
How is HCV treated?
Early treatment with peginterferon alfa
How is the response to treatment with peginterferon-alfa assessed in HCV infection?
Sustained viral response (SVR12) – no HCV RNA 12 weeks after stopping treatment
NOTE: SVR 24 can also be done
What is the main difference in the treatment of genotype 1 and non-genotype 1 HCV?
Genotype 1 and 4 – less responsive to ribavirin and protease-based therapy, requires longer treatment
Genotype 2 and 3 - more responsive to protease-based therapy
NOTE: ribavirin can also be used to treat RSV
Outline the treatment of hepatitis E.
Supportive
Ribavirin
Name three major pathogens that cause surgical site infections.
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
What are the three levels of surgical site infections?
Superficial incisional – skin and subcutaneous tissues
Deep incisional – fascial and muscle layers
Organ/space infection – any part of the anatomy that is not the incision
List some bacterial factors that enable bacteria to cause septic arthritis.
Staphylococcus aureus has receptors such as fibronectin-binding protein
Kingella kingae have bacterial pili which adhere to the synovium
Some strains of S. aureus produce Panton-Valentine Leukocidin which is associated with fulminant infections
List some host factors that increase the risk of septic arthritis.
Leukocyte-derived proteases and cytokines
Raised intra-articular pressure
Deletion of macrophage-derived cytokines
Absence of IL-10
Outline the presentation of chronic osteomyelitis.
Pain
Brodie’s abscess
Sinus tract
Name two techniques for treating chronic osteomyelitis.
Laubenbach technique – debridement all the way to healthy bleeding bone and removal of all prosthetic material. Double lumen irrigation used to instil antibiotics into the central lumen
Papineau technique – complete excision of infected tissue and necrotic bone followed by open cancellous bone grafting and split skin grafting to the close the wound
Which organism most commonly causes prosthetic joint infection?
Coagulase-negative staphylococcus
Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
How is prosthetic joint infection diagnosed?
Radiology – shows loosening of the prosthesis
CRP > 13.5 for prosthetic knees
CRP > 5 for prosthetic hips
Joint aspiration (>1700/mL if knee; >4200/mL if hip)
How should specimens be taken intraoperatively?
Specimens should be taken from at least 5 sites around the implant and sent for histology
NOTE: if 3 or more specimens yield identical organisms, this is suggestive of prosthetic joint infection
List 5 HAIs in order of prevalence.
Pneumonia Surgical site infection UTI Blood stream infection Gastrointestinal infection
Define pyrexia of unknown origin.
A fever > 38.3 degrees lasting > 3 weeks with an uncertain diagnosis after 7 days in hospital
List some differentials for PUO.
Infection • Infectious endocarditis • HIV • TB Inflammation • Polymyalgia rheumatica • Still’s disease • Sarcoidosis • ANCA-associated vasculitis • Rheumatoid arthritis Malignancy • Malignant lymphoma • Castleman’s disease
List some infectious causes of PUO.
Bacteria • TB/NTM • Enteric fever (e.g. Salmonella typhi) • Zoonoses Viruses • EBV/CMV • HIV • Hepatitis Fungi • Cryptococcosis • Histoplasmosis Parasites • Malaria • Amoebic liver abscess • Schistosomiasis • Toxoplasmosis • Trypanosomiasis
What are the different components of EBV serology?
Viral capsid antigen (VCA) IgM – rises early in acute infection
VCA IgG – rises later in infection
EBNA-1 IgG – rises later in infection
EBNA DNA – rapidly cleared if immunocompetent so will be negative in most, may be positive if immunocompromised
NOTE: the heterophile antibody test is not recommended because of poor sensitivity and specificity
List two causes of very high ferritin.
Adult-onset Still’s disease
Macrophage activation syndrome
Outline the major and minor criteria for infective endocarditis.
Major • Persistent bacteraemia (> 2 positive blood cultures) • Vegetations on echocardiogram • Positive serology for Bartonella, Coxiella or Brucella Minor • Predisposition (murmur, IVDU) • Raised inflammatory markers • Immune complexes (RBC in urine) • Embolic phenomena (Janeway lesions) • Atypical echo • 1 positive blood culture 2 major + 1 minor OR 3 minor = infective endocarditis
IMPORTANT: 3 blood cultures should be taken in suspected infective endocarditis
Outline the key features of Adult-onset Still’s disease.
Salmon pink rash Arthralgia Sore throat Lymphadenopathy Fever
List some miscellaneous causes of PUO.
Subacute thyroiditis
Addison’s disease
PE
Dressler’s syndrome
Drugs – idiosyncratic or adverse drug reaction
NOTE: 25% of drug reactions will cause eosinophilia and a rash
Give examples of zoonoses in the UK that are transmitted by:
a. Farm/wild animals
b. Companion animals
a. Farm/wild animals Campylobacter Salmonella b. Companion animals Toxoplasmosis Bartonella Ringworm Psittacosis
For Campylobacter, describe the following:
a. Reservoir
b. Transmission
c. Clinical presentation
d. Investigations
e. Management
a. Reservoir Poultry Cattle b. Transmission Contaminated food c. Clinical presentation Bloating Diarrhoea Cramps d. Investigations Stool culture e. Management Supportive
For Salmonella, describe the following:
a. Reservoir
b. Transmission
c. Clinical presentation
d. Investigations
e. Management
a. Reservoir Poultry Reptiles/amphibians b. Transmission Contaminated food Poor hygiene c. Clinical presentation Diarrhoea Vomiting Fever d. Investigations Stool culture e. Management Supportive Ciprofloxacin Azithromycin
For Cat Scratch Disease, describe the following:
a. Presentation
b. Investigations
c. Management
a. Presentation Macule at site of inoculation Becomes pustular Regional adenopathy Systemic symptoms (FLAWS) b. Investigations Serology c. Management Erythromycin Doxycycline
For baciliary angiomatosis, describe the following:
a. Presentation
b. Investigations
c. Management
a. Presentation Skin papules Disseminated multi-organ and vasculature involvement Leads to bursting of blood vessels in various organs and tissues Can be FATAL b. Investigations Histopathology Serology c. Management Erythromycin Doxycycline Rifampicin
For Toxoplasmosis, describe the following:
a. Reservoir
b. Transmission
c. Clinical presentation
d. Investigations
e. Management
a. Reservoir Cats Sheep b. Transmission Infected meat Faecal contamination c. Clinical presentation Fever Adenopathy Stillbirth Infants with progressive visual, hearing, motor and cognitive issues Seizures Neuropathy d. Investigations Serology e. Management Spiramycin Pyrimethamine + sulfadizine
For Brucellosis, describe the following:
a. Reservoir
b. Transmission
c. Clinical presentation
d. Investigations
e. Management
a. Reservoir Cattle Goats b. Transmission Unpasteurised milk Undercooked meat Aerosolisation c. Clinical presentation Fever (and rest of FLAWS) Back pain/bone pain Orchitis Focal abscess (psoas or liver) Hepatosplenomegaly d. Investigations Blood/pus culture Serology NOTE: the lab should be warned that you are sending suspected Brucella (they are Gram-negative cocco-bacilli) e. Management Doxycycline + gentamicin or rifampicin
Which two infectious agents can cause rat bite fever?
Streptobacillus moniliformis
Spirilum minus
For rat bite fever, describe the following:
a. Reservoir
b. Transmission
c. Clinical presentation
d. Investigations
e. Management
a. Reservoir Rats b. Transmission Bites Contact with infected urine or droppings c. Clinical presentation Fevers Polyarthralgia Maculopapular progressing to purpuric rash Can progress to endocarditis d. Investigations Joint fluid MC&S Blood culture e. Management Penicillins
List the most prevalent pathogens causing CAP in the following age groups:
a. 0-1 months
b. 1-6 months
c. 6 months – 5 years
d. 16-30 years
a. 0-1 months Escherichia coli Group B Streptococcus Listeria monocytogenes b. 1-6 months Chlamydia trachomatis Staphylococcus aureus RSV c. 6 months – 5 years Mycoplasma pneumoniae Influenza d. 16-30 years Mycoplasma pneumoniae Streptococcus pneumoniae
What medium is Legionella grown on?
Buffered charcoal yeast extract
How is PCP investigated?
Bronchoalveolar lavage
How is invasive aspergillosis treated?
Amphotericin B
Which organisms cause pneumonia in the following subgroups of patients:
a. HIV
b. Neutropaenia
c. Bone marrow transplant
d. Splenectomy
a. HIV PCP TB Atypical mycobacteria b. Neutropaenia Fungal (e.g. Aspergillus) c. Bone marrow transplant CMV d. Splenectomy Encapsulated organisms (e.g. Streptococcus pneumoniae, Haemophilus influenzae)
Which respiratory organism is investigated using immunofluorescence?
PCP
NOTE: PCP can also be detected using silver stain
What are the 1st and 2nd line treatment options for HAP?
1st = ciprofloxacin +/- vancomycin 2nd = tazocin AND vancomycin
Which antibiotics are used to treat HAP caused by:
a. MRSA
b. Pseudomonas
a. MRSA
Vancomycin
b. Pseudomonas
Tazocin OR ciprofloxacin +/- gentamicin
What is the difference between yeasts and moulds?
Yeast = unicellular Moulds = multicellular and has filaments (hyphae)
List three types of mycobacterial complex.
Mycobacterium tuberculosis complex • Mycobacterium tuberculosis • Mycobacterium bovis Mycobacterium avium complex • Mycobacterium avium • Mycobacterium intracellulare Mycobacterium abscessus complex • Mycobacterium abscessus • Mycobacterium massiliense • Mycobacterium bolletii
Describe the morphology of mycobacteria.
Non-motile rod-shaped bacteria
Relatively slow-growing
Cell wall composed of mycolic acids, complex waxes and glycoproteins
Acid-alcohol fast
List three examples of slow-growing non-tuberculous mycobacteria and the diseases that they cause.
Mycobacterium avium intracellulare
• May invade bronchial tree or pre-existing bronchiectasis/cavities
• Disseminated infection in immunocompromised patients
Mycobacterium marinum
• Swimming pool granuloma
Mycobacterium ulcerans
• Skin lesions (e.g. Bairnsdale ulcer, Buruli ulcer)
• Chronic progressive painless ulcer
List three examples of rapid-growing non-tuberculous mycobacteria.
Mycobacterium abscessus
Mycobacterium chelonae
Mycobacterium fortuitum
What are the two types of Mycobacterium leprae infection?
Paucibacillary tuberculoid – few skin lesions, robust T cell response
Multibacillary lepromatous – multiple skin lesions, poor T cell response
NOTE: tends to present with paraesthesia and hairless skin plaques
List some types of extra-pulmonary TB.
Lymphadenitis (scrofula) – cervical lymph nodes most commonly
Gastrointestinal – due to swallowing of tubercle
Peritoneal – ascitic or adhesive
Genitourinary
Bone and joint – due to haematogenous spread (e.g. Pott’s disease)
Miliary TB
Tuberculous meningitis
What is NAAT and why is it useful for TB?
Nucleic acid amplification test
Allows speciation and the detection of drug resistance mutations
Rapid
List some side-effects of:
a. Rifampicin
b. Isoniazid
c. Pyrazinamide
d. Ethambutol
a. Rifampicin Raised transaminases CYP450 induction Orange secretions b. Isoniazid Peripheral neuropathy (give with pyridoxine) Hepatotoxicity c. Pyrazinamide Hepatotoxicity Hyperuricaemia d. Ethambutol Visual disturbance
What is multi-drug resistant TB?
Resistant to rifampicin and isoniazid
What is extremely drug resistant TB?
Resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable (e.g. amikacin, capreomycin)
Which valvular defect is most common in rheumatic fever?
Mitral stenosis
What is the most common cause of hospital-acquired pneumonia?
Pseudomonas aeruginosa
Which congenital infection is associated with periventricular calcification?
CMV
Why does influenza cause respiratory disease in humans?
The virus has a haemagglutinin (HA) protein which must be cleaved for the virus to be able to fuse with the endosome membrane and release its genome into the host
Human airway tryptase found in the lining of the lung is capable of cleaving HA
NOTE: there are some mutated forms of influenza that do not require cleavage of HA to be able to enter host cells (these are particularly virulent)
Describe the influenza life cycle.
The virus attaches to cells via the sialic acid receptor
They enter through endosomes
The acidity of the endosome triggers a fusion event by which the virus releases its genome into the host cell
The genome travels to the nucleus and takes over host factors to drive transcription and translation
New viral products are produced, which assemble at the surface of the cell and bud off producing hundreds of copies of the virus
Which specific mutation is associated with enabling influenza to cross into humans from birds?
PB2 627K (polymerase protein)
What is the mechanism of action of amantadine?
Targets the M2 ion channel
A single amino acid mutation (S31N) renders the virus resistant
List three examples of neuraminidase inhibitors.
Oseltamivir (Tamiflu) – oral
Zanamivir (Relenza) – inhaled or IV
Peramivir – IV
NOTE: effective if given < 48 hours after infection
List two examples of polymerase inhibitors used to treat influenza.
Favipiravir
Baloxavir
Outline the mechanism of action of aciclovir.
Guanosine (nucleoside) analogue that is incorporated into growing viral DNA and blocks further elongation
Requires activation by viral thymidine kinase (which is only present in host cells that are infected by the virus)
Aciclovir has a higher affinity for viral DNA polymerase than host DNA polymerase
What are two 2nd line treatment options for aciclovir-resistant VZV infection?
Foscarnet
Cidofovir
NOTE: they inhibit viral DNA synthesis
HSV encephalitis is a medical emergency. How should it be treated?
IMMEDIATE treatment with IV aciclovir 10 mg/kg TDS without waiting for test results
If confirmed, treat for 21 days
What is HSV meningitis and how should it be treated?
Usually self-limiting
Immunocompromised patients and those who are unwell enough to require hospital admission require treatment
IV aciclovir for 2-3 days followed by oral aciclovir for 10 days
List some indications for treatment of VZV.
Chickenpox in adults (high risk of pneumonitis)
Shingles in adults > 50 years (risk of post-herpetic neuralgia)
Infection in immunocompromised patients
Neonatal chickenpox
If increased risk of complications (e.g. underlying lung disease)
In which cells does CMV lie dormant?
Monocytes and dendritic cells
What is a characteristic histological feature of CMV infection?
Owl’s eye inclusions
What is the 1st line treatment option for CMV infection?
Ganciclovir (IV)
How is ganciclovir activated?
Requires activation by viral UL97 kinase enzyme
NOTE: ganciclovir is used in conjunction with IVIG in patients with CMV pneumonitis
What is a major side-effect of ganciclovir?
Bone marrow toxicity
NOTE: therefore, its use is limited in bone marrow transplant patients
What is the mechanism of action of foscarnet?
Non-competitive inhibitors of viral DNA polymerase
NOTE: foscarnet does NOT require activation
Tends to be used in CMV infections if ganciclovir is contraindicated
What is the mechanism of action of cidofovir?
Competitive inhibitors of viral DNA synthesis (nucleotide analogue)
NOTE: does not require activation
What is a major side-effect of foscarnet and cidofovir?
Nephrotoxicity
Cidofovir requires hydration and probenecid
What is the mechanism of action of maribavir?
Inhibits viral kinase
Effective in vitro, currently undergoing clinical trials
What is the mechanism of action of letermovir?
CMV DNA terminase inhibitor
Approved in the USA for CMV prophylaxis in bone marrow transplant patients
What are the roles of haemagglutinin and neuraminidase in the influenza virus?
Haemagglutinin – mediates viral binding and entry into target cell
Neuraminidase – allows release of progeny virus particles from the host cell
What are the 3 indications for use of neuraminidase inhibitors in the community according to NICE?
National surveillance indicates that influenza is circulating
Patient is in a risk group
Within 48 hours of onset of symptoms
What disease states does BK virus cause?
Bone marrow transplant haemorrhagic cystitis
Renal transplants BK nephritis and ureteric stenosis
Outline the treatment of BK haemorrhagic cystitis.
Bladder washouts
Reduce immunosuppression
Cidofovir IV (may consider intravesical)
Outline the treatment of BK nephropathy.
Reduce immunosuppression
IVIG
NOTE: cidofovir cannot be used because it is nephrotoxic
Outline the treatment of adenovirus infection in transplant patients.
Cidofovir IV IVIG Brincidofovir (prodrug of cidofovir currently undergoing clinical trials)
What are most cases of HSV drug resistance caused by?
Mutations in viral thymidine kinase
What are most cases of CMV drug resistance caused by?
Mutations in protein kinase gene UL97
What are the main treatment options for drug resistant HSV and CMV infection?
Foscarnet and cidofovir
What is the herd immunity threshold?
Threshold = 1 – 1/R0
Describe the following types of vaccines:
a. Inactivated
b. Live attenuated
c. Toxoid
d. Subunit
e. Conjugate
f. Heterotypic
a. Inactivated
Whole microorganism is destroyed (using heat, radiation or antibiotics)
NO risk of causing infection in the host
Immune response may not be particularly strong or long-lasting
b. Live attenuated
Live organisms are modified to be less virulent
Risk of acquiring virulence
Should be avoided in pregnant women and immunocompromised patients
c. Toxoid
Inactivated toxin components
d. Subunit
Protein components of the microorganism or synthetic virus-like particles
Lack genetic material and are unable to replicate
e. Conjugate
Poorly immunogenic antigens are paired with a protein that is highly immunogenic (adjuvant)
f. Heterotypic
Using pathogens that infect other animals but do NOT cause disease in humans
List examples of the following types of vaccine:
a. Inactivated
b. Live attenuated
c. Toxoid
d. Subunit
e. Conjugate
f. Heterotypic
a. Inactivated Influenza Polio Cholera b. Live attenuated MMR Yellow fever c. Toxoid Diphtheria Tetanus d. Subunit Hepatitis B HPV e. Conjugate Haemophilus influenzae type B f. Heterotypic BCG
List some contraindications for vaccines.
Previous anaphylactic reactions
Anaphylactic reaction to egg is contraindicated with the influenza vaccine
Immunocompromised and pregnant women should not receive live attenuated vaccines
If acutely unwell on the day of vaccination
DTP is contraindicated if evidence of neurological abnormality
List some examples of serious reactions associated with the following vaccines:
a. DTP
b. Poliovirus
c. Measles
d. Rubella
e. T/DT/Td
f. Hepatitis B
a. DTP Encephalopathy Shock Anaphylaxis b. Poliovirus Guillain-Barre syndrome Polio c. Measles Anaphylaxis Thrombocytopaenia d. Rubella Acute arthritis e. T/DT/Td Guillain-Barre syndrome Brachial neuritis Anaphylaxis f. Hepatitis B Anaphylaxis
Which type of genome do all herpes viruses have?
DNA
What is the most common cause of UTI in young, sexually active women?
Staphylococcus saprophyticus
List some antibiotics that have anti-Pseudomonas activity.
Gentamicin
Ciprofloxacin
Tazocin
What is the most common viral cause of rapidly progressive glomerulonephritis?
Hepatitis B
Which organisms most commonly cause non-bloody diarrhoea and vomiting soon after eating contaminated food?
Bacillus cereus
Staphylococcus aureus
What are the two types of paralysis caused by clostridia?
Botulinum –> flaccid paralysis
Tetani –> spastic paralysis
What are the possible outcomes for neonates with congenital toxoplasmosis?
Asymptomatic (60%) at birth but go on to develop long-term sequelae such as deafness, low IQ and microcephaly Symptomatic (40%) at birth • Choroidoretinitis • Microcephaly/hydrocephalus • Intracranial calcifications • Seizures • Hepatosplenomegaly/jaundice
What is the triad of features in congenital rubella syndrome?
Cataracts
Congenital heart disease (PDA is most common)
Deafness
Other features: microphthalmia, glaucoma, retinopathy, ASD/VSD, microcephaly, meningoencephalopathy, developmental delay
How if Chlamydia trachomatis transmitted to the neonate and what disease does it cause in the neonate?
During delivery
Causes neonatal conjunctivitis (ophthalmia neonatorum) or pneumonia
NOTE: it is treated with erythromycin
Which mycoplasma species can cause neonatal infection?
Mycoplasma hominis
Ureaplasma urealyticum
What are the three main organisms that cause early-onset infection?
Group B Streptococcus
E. coli
Listeria monocytogenes
What type of bacterium is Group B Streptococcus?
Gram-positive coccus
Catalase negative
Beta haemolytic
What type of organism is Listeria monocytogenes and what disease can it cause?
Gram-positive rods
Causes sepsis in the mother and the newborn
Which antibiotics are commonly used to treat early-onset sepsis?
Benzylpenicillin + gentamicin
What are the main causes of late-onset sepsis?
Coagulase negative staphylococci (e.g. S. epidermidis)
GBS
E. coli
Listeria monocytogenes
S. aureus
Enterococcus sp.
Gram-negatives (e.g. Klebsiella, Enterobacter, Pseudomonas)
Outline the treatment of late-onset sepsis.
Treat early with antibiotics
Guidelines differ
Example antibiotic regimen: 1st line = cefotaxime + vancomycin; 2nd line = meropenem
What is the main bacterial cause of meningitis at the moment?
Meningitis B
What type of organism is Streptococcus pneumoniae?
Gram-positive diplococcus
Alpha haemolytic
What type of organism is Haemophilus influenzae?
Gram-negative cocco-bacilli
What is the most common cause of death in:
a. Postnatal children (1-59 months)
b. Neonates
a. Postnatal children (1-59 months) Pneumonia Followed by congenital anomalies b. Neonates Prematurity Followed by intra-partum complications
Which children are mainly affected by Mycoplasma pneumoniae?
Older children (> 4 years)
List some extra-pulmonary manifestations of Mycoplasma pneumoniae.
Haemolysis – IgM antibodies to I antigen on erythrocytes, cold agglutinins
Neurological – encephalitis, aseptic meningitis, peripheral neuropathy, transverse myelitis
Polyarthralgia
Otitis media
Bullous myringitis (vesicles on the tympanic membrane – pathognomonic of Mycoplasma)
Erythema multiforme
List three examples of:
a. Yeast
b. Moulds
a. Yeast Candida Cryptococcus Histoplasma (dimorphic) b. Moulds Aspergillus Dermatophytes Agents of mucormycosis
List some patient groups that are at risk of invasive Candida infection.
VLBW infants
Immunocompromised
Patients on ITU (especially if they have lines in)
Patients receiving TPN
Immunocompetent patients who have had antibiotic treatment
List some agents that can cause candidiasis.
Candida albicans (MOST COMMON)
Candida glabrata
Candida krusei
Candida tropicalis
Describe a screening test for candidiasis.
Candida albicans forms a germ tube
Can be identified by microscopy
What does generalised candidiasis in babies usually occur secondary to?
Seborrhoeic dermatitis
What type of agar is needed for culturing Candida?
Sabouraud agar – impregnated with antibiotics to prevent bacteria from outcompeting the fungi
Outline the management of candidiasis.
At least 2 weeks of antifungals after the last negative culture
Echo and fundoscopy to look for endocarditis/endophthalmitis
Echinocandins – empirical for non-albicans infections
Fluconazole – empirical for Candida albicans
What is the treatment of choice for Cryptococcus infection?
Ambisome (amphotericin B)
NOTE: it is inherently resistant to echinocandins
Describe the appearance of Cryptococcus under the microscope.
Distinct capsule around the yeast
India ink can be used to stain
NOTE: the capsule is not always present
Why might a lumbar puncture be negative in cryptococcal meningitis?
Cryptococcal meningitis can cause hydrocephalus which prevents the circulation of CSF meaning that the sample taken at LP may not have been exposed to CSF within other parts of the ventricular system
Outline the treatment options for Cryptococcus infection.
3 weeks amphotericin B (ambisome) +/- flucytosine
Repeat LP for pressure measurement
Secondary suppression – fluconazole
List the aetiological agents that can cause Aspergillus infection.
Aspergillus fumigatus Aspergillus flavus Aspergillus niger Aspergillus niduland Aspergillus terreus
List some investigations used in the diagnosis of Aspergillus infection.
Blood test Serology (check IgE for allergic response (e.g. ABPA)) • Antigen detection (galactomannan) • Also detected in BAL PCR Histology Culture
What is the mainstay of treatment for aspergillosis?
Amphotericin for at least 6 weeks
Other options: voriconazole, caspofungin, itraconazole
What is tinea pedis caused by?
Tricophyton rubrum (MOST COMMON) Tricophyton interdigitale Epidermophyton floccosum (can also cause tinea cruris)
What is pityriasis versicolor caused by?
Malassezia furfur
NOTE: it has a spaghetti and meatballs appearance on microscopy
Which groups of patients are affected by mucormycosis?
Immunocompromised patients
Patients with poorly controlled diabetes
What is the characteristic clinical manifestation of mucormycosis?
Cellulitis of the orbit and face which progresses with discharge and black pus from the palate and nose
NOTE: black eschars may be seen as the fungus destroys tissues
What is the term used to describe invasion of the brain by mucormycosis?
Rhinocerebral mucormycosis