Bacteria and Protozoa Flashcards
What causes amoebiasis and how is it transmitted?
- entamoeba histolytica protozoa
- faeco-oral
Symptoms of amoebiasis:
- mild diarrhoea or severe amoebic dysentery
- liver and colonic abscesses
- bloody diarrhoea
Investigations of amoebiasis:
- stool microscopy - trophozoites (15 min/hot stool)
- amobie liver abscess - anchovy sauce, single mass right lobe, positive serology
Most common organism in animal bites:
pasteurella multocida
Most common organisms in human bites:
- streptococci spp
- staph aureus
- eikenella
- fusobacterium
- prevotella
What type of organism causes anthrax and how is it transmitted?
- bacillus anthracis
- gram positive rod
- infected carcasses
What is anthrax also known as?
Woolsorter’s disease
Features of anthrax:
- painless black eschar
- non-tender
- marked oedema
- GI bleeding
How does aspergilloma come about and how does it present?
- mycetoma colonises existing lung cavity secondary to TB, cancer, CF
- usually asymptomatic
- cough, haemoptysis
- may have crescent sign on CXR
- high titres Aspergillus Precipitins
What causes botulism and what part causes the symptoms?
- gram positive anaerobe clostridium botulinum
- neurotoxin irreversibly blocks Ach release and affects bulbar muscles and ANS
Features of botulism:
- fully conscious, no sensory disturbance
- flaccid paralysis
- diplopia
- ataxia
- bulbar palsy
What causes campylobacter, transmission and incubation:
- most common bacterial cause infectious intestinal disease
- gram negative campylobacter jejuni
- faeco-oral
- incubation period: 1-6 days
Features of campylobacter:
- headache, malaise
- diarrhoea often bloody
- abdominal pain may mimic appendicits
Complications of campylobacter:
- Guillain-Barre syndrome
- Reiter’s syndrome
- septicaemia, endocarditis, arthritis
Which organism causes cat scratch disease?
gram negative rod: Bartonella Henselae
Which organisms most commonly cause cellulitis?
- streptococcus pyogenes
- staphylococcus aureus
Who should receive IV Abx for cellulitis?
- Eron III or IV
- severe or rapidly deteriorating
- <1yo or frail
- immunocompromised
- significant lymphoedema
- facial cellulitis or periorbital cellulitis
Class I Eron classification:
no systemic toxicity and no uncontrolled co-morbidities
Class II Eron classification:
-systemically unwell
or
-systemically well with co-morbidity
Class III Eron classification:
-significant systemic upset or -unstable co-morbidities or -life-threatening infection
Class IV Eron classification:
-sepsis syndrome
or
-severe life-threatening infection e.g. necrotising fasciitis
What organism causes cholera?
- vibro cholerae
- gram negative
What symptoms does cholera cause?
- profuse rice water diarrhoea
- dehydration
- hypoglycaemia
What causes cryptosporidiosis?
- commonest protozoal causes of diarrhoea
- cryptosporidium hominis and parvum
- more common in immunocompromised patients and young children
Features of cryptosporidiosis:
- watery diarrhoea
- abdominal cramps
- fever
- immunocompromised: entire GI tract e.g. sclerosing cholangitis and pancreatitis
Diagnosis of cryptosporidiosis:
- stool: modified Ziehl Neelsen stain
- red cysts
What causes diphtheria:
- gram positive Corynebacterium diphtheriae
- necrotic mucosal cells on tonsils create diphtheric membrane - systemic distribution may cause necrosis of myocardial, neural and renal tissue
Common presentation of diphtheria:
- Eastern Europe/Russia/Asia
- sore throat - diphtheric membrane - very pseudomembrane on posterior pharyngeal wall
- bulky cervical lymphadenopathy
- neuritis e.g. cranial nerves
- heart block
Investigation of diphtheria:
culture of throat swab: tellurite agar or Loeffler’e media
What causes enteric fever and how does it spread?
- Salmonella type and paratyphi
- faeco-oral route
Features of enteric fever:
- initially systemic upset
- abdominal pain and distension
- constipation more common in typhoid than diarrhoea
- rose spots on trunk (more in paratyphoid)
Complications of enteric fever:
- osteomyelitis (esp sickle cell)
- GI bleed/perforation
- meningitis
- cholecystitis
- chronic carriage
What causes e.coli?
- facultative, anaerobic, lactose fermenting gram negative rod
- diarrhoea, UTIs, neonatal meningitis
O157:H7
- severe, haemorrhage, watery diarrhoea
- high mortality
- complicated by HUS - increased urea
- contaminated ground beef
Which organism most commonly causes travellers’ diarrhoea?
e. coli
Which organisms are the most common causes of acute food poisoning?
- staph aureus
- bacillus cereus
- clostridium perfringens
Which gastroenteritis organism causes non-bloody stools?
- e. coli
- giardiasis
- cholera
Which gastroenteritis organisms causes bloody stools?
- shigella
- campylobacter may cause blood diarrhoea
- amoebiasis
Gastroenteritis incubation period 1-6 hours:
- staph aureus
- bacillus cereus
Gastroenteritis incubation period 12-48 hours:
- salmonella
- e.coli
Gastroenteritis incubation period 48-72 hours:
- shigella
- campylobacter
Gastroenteritis incubation period > 7 days:
- giardiasis
- amoebiasis
Which organism causes giardiasis?
- flagellate protozoan Giardia Lamblia
- faeco-oral
Features of giardiasis?
- often asymptomatic
- lethargy, bloating, abdominal pain
- flatulence
- non-bloody diarrhoea
- chronic diarrhoea, malabsorption, lactose intolerance
Investigations for giardiasis?
- trophozite stool microscopy and cysts classically negative
- duodenal fluid aspirates or string tests
Risk factors for invasive aspergillosis:
- HIV
- leukaemia
- following broad spectrum Abx
Diagnosis of legionella:
urinary antigen
What causes leishmaniasis generally?
intracellular protozoa Leishmania spread by sand flies
What causes cutaneous Leishmaniasis and what are the features?
- Leishmania tropica/mexicana
- crusted lesion at site of bite
- South/Central America - risk of mucocutaneous so treat
- Africa/India conservative treatment
What causes mucocutaneous Leishmaniasis and features:
- Leishmania braziliensis
- skin lesions may spread to involve mucosal of nose, pharynx etc.
What causes visceral leishmaniasis and features:
- Leishmania donovani
- Mediterranean, Asia, South America, Africa
- fever, sweats, rigors
- massive splenomegaly, hepatomegaly
- poor appetite, weight loss
- grey skin
- pancytopenia secondary to hypersplenism
- gold standard for diagnosis is bone marrow or splenic aspirate
What is Lemierre’s syndrome and which bacteria most commonly causes it?
- infectious thrombophlebitis of internal jugular vein
- secondary to bacterial sore throat by fusobacterium necrophorum - peritonsillar abscess
- may have septic pulmonary emboli
What is leprosy caused by?
mycobacterium leprae
Features of leprosy:
- patches of hypopigmented skin, typically buttocks, face and extensor surfaces
- sensory loss
- low degree cell mediated immunity - lepromatous (multibacillary) - extensive skin, symmetrical nerve
- high degree cell mediated immunity - tuberculoid (paucibacillary) - limited skin, asymmetric nerve involvement, hair loss
What is leptospirosis cause by and how is it spread?
- spirochaete leptospirosis interrogans
- contact with infected rat urine
- consider Weil’s disease in high risk patients with hepatorenal failure
Features of leptospirosis:
early phase - bacteraemia -mild/subclinical -fever, flu like -subconjunctival suffusion/haemorrhage + bilateral conjunctivitis second immune phase - may lead to weil's -AKI -hepatitis -aseptic meningitis
What is Lyme Disease caused by?
spirochaete Borrelia Burgdorferi spread by ticks
Later features of lyme disease:
- > 30 days
- CVS: heart block, pericarditis, myocarditis
- neuro: facial nerve palsy, radicular pain, meningitis
- polyarthritis
Investigations for Lyme disease:
- erythema migrans - start abx
- ELISA ab to Borrelia first line
- nothing if asymptomatic
What causes malaria:
- plasmodium protozoa - female anopheles mosquito
- plasmodium falciparum most common
- vivax, ovale and malariae - benign
What is protective against malaria:
- G6PD deficiency
- HLA B53
- absence Duffy antigens
What symptom is characteristic of malaria?
fever on alternating days
- vivale/ovale: every 48 hours
- malariae: every 72 hours associated with nephrotic syndrome
Features of plasmodium falciparum malaria:
- shizonts on blood film
- parasitaemia
- hypoglycaemia
- acidosis
- fever
- severe anaemia
- complications: cerebral malaria, acute renal failure, ARDS, hypoglycaemia, DIC
How do you treat severe falciparum malaria?
IV artesunate
Where is plasmodium vivax most common?
central America, Indian subcontinent
Where is plasmodium ovale most common?
Africa
Antimalarials in pregnancy:
- chloroquine
- proguanil: folate supplementation
- doxycycline contraindicated
Children prophylaxis malaria:
- DEET for over 2 mo
- doxycyline for children >12yo
Which malarial drugs are contraindicated in epilepsy?
chloroquine and mefloquine
Doxycycline ADR:
photosensitivity, oesophagitis
Organisms causing meningitis in 0-3mo:
- group B strep
- e. coli
- listeria monocytogenes
Organisms causing meningitis in 3mo-6yo:
- neisseria meningitidis
- strep pneumoniae
- haemophilus influenzae
Organisms causing meningitis in 6yo-60yo:
- neisseria meningitidis
- strep pneumoniae
Organisms causing meningitis in >60yo:
- strep pneumoniae
- neisseria meningitidis
- listeria monocytogenes
Organisms causing meningitis in immunocompromised:
-listeria monocytogenes
CSF appearance in bacterial meningitis:
- cloudy
- low glucose <1/2
- high protein >1g/L
- 10-5000 WC polymorphs/mm3
CSF appearance in viral meningitis:
- clear/cloudy
- 60-80% of plasma glucose
- normal/raised protein
- 15-1000 WC lymphocytes/mm3
CSF appearance in tuberculous meningitis:
- slightly cloudy, fibrin web
- low glucose <1/2
- high protein >1g/L
- 30-300 lymphocytes/mm3
CSF appearance in fungal meningitis:
- cloudy
- low glucose
- high proteins
- > 20-200 lymphocytes/mm3
Differences with viral meningitis:
- more benign and common
- self limiting 7-14 days
- opening pressure 10-20cm3 (normal)
- most common non-polio enteroviruses: Coxsackie
Who gets screened for MRSA?
- all awaiting elective admissions
- all emergency admissions
- nasal swab (inside rim 5 sec) and skin lesions or wounds
Management of MRSA:
- nose: mupicorin tds 5 days
- skin: chlorhexidine glauconite od 5 days (axilla, groin, perineum)
- Abx: vancomycin, teicoplanin, linezolid
What may mycoplasma pneumonia not respond to?
- penicillins or cephalosporins
- lack of pepitdoglycan cell wall
Complications of mycoplasma pneumonia:
- cold agglutinins: haemolytic anaemia, thrombocytopenia
- erythema multiform, erythema nodosum
- meningoencephalitis, Guillain Barre
- bullous myringitis: painful vesicles on tympanic membrane
- pericarditis, myocarditis
- hepatitis, pancreatitis
- acute GN
Investigations for mycoplasma pneumonia:
- mycoplamsa serology
- positive cold agglutination test
Type I necrotising fasciitis:
- mixed aerobes and anaerobes
- often post surgery in diabetics
- most common
Type II necrotising fasciitis:
streptococcus pyogenes
Management of necrotising fasciitis:
- urgent surgical referral for debridement
- IV Abx
What type of organism is pseudomonas aeruginosa and what does it cause:
- aerobic gram negative, non lactose fermenting, oxidase positive
- chest infections (especially CF)
- skin: burns, wound infections, hot tube folliculitis
- otitis externa (especially in diabetes)
- UTI
What causes schistosomiasis?
bilharzia, parasitic flatworm infecting (3 species)
Shistosoma haematobium:
- egg clusters (pseudopapillomas) in bladder
- calcification on x-ray
- obstructive uropathy and kidney damage
- swimmer’s itch
- risk factor for squamous cell bladder cancer
- management: single oral dose praziquantel
Shistosoma mansoni and japonicum:
- mature in liver and go through portal system to distal colon
- progressive hepatomegaly and splenomegaly
- cirrhosis, variceal disease, cor pulmonale
Shistosoma intercalatum and mekongi:
- less prevalent
- intestinal schistosomiasis
How does a spinal epidural abscess come about and what is the most common organism:
- bacteria enters epidural space by contiguous spread (e.g. discitis), or haematogenous spread
- mostly staph aureus
How does staphylococcal toxic shock syndrome come about and what are the common features:
- TSST1 superantigen
- related to infected tampons
- fever, hypotension
- diffuse erythematous rash
- desquamation of rash esp of palms and soles
- CNS involvement, hepatitis, thrombocytopenia, renal failure, mucous membrane erythema
What is strongyloides stercoralis caused by and what are the features:
- human parasitic nematode worm
- larvae in soil and penetrate skin
- diarrhoea, abdominal pain and bloating, papulovesicular lesions where skin penetrate, larva currens, travels to lungs to cause pneumonitis like Loeffler’s
Features of tetanus infection:
- prodrome fever, lethargy, headache
- trismus (lockjaw)
- risus sardonicus
- opisthotonus
- spasms
What causes toxoplasmosis?
- toxoplasma gondii - obligate intracellular protozoa that infects via GI, lung or broken skin
- oocytes release trophozoites which migrate around body
- usually cats or rats
What does toxoplasmosis cause in immunocompetent:
- asymptomatic
- self-limiting
- resembles infectious mononucleosis
- less commonly meningoencephalitis and myocarditis
- no treatment unless severe or immunocompromised
What are the features of congenital toxoplasmosis?
- transplacental spread from mother
- neurological damage: cerebral calcification, hydrocephalus, chorioretinitis
- opthalmic damage: retinopathy, cataracts
Trypanosoma Rhodesiense:
- African trypanosomiasis - sleeping sickness (East Africa)
- tsetse fly
- chancre - painless subcutaneous nodule at site of infection
- intermitten fever
- posterior cervical lymphadenopathy
- later: CNS involvement (IV melarsoprol)
American Trypanosomiasis:
- protozoan Trypanosoma cruzi
- 95% asymptomatic in acute phase - chagoma
- chronic Chagas’ disease affects heart (myocarditis - cardiomyopathy and arrhythmias) and GI (megaoesophagus and megacolon)
MOA of mycobacterium tuberculosis:
- macrophages migrate to regional lymph nodes and lung lesion - Ghon complex
- granuloma - epithelioid histiocytes
- caseous necrosis in centre
- type IV hypersensitivity reaction
Screening of tuberculosis:
- waxy membrane prevents binding of normal stains
- Ziehl Neelsen stain
- screening: Mantoux test, interferon gamma blood test if mantoux test positive
How is a Mantoux test carried out and results interpreted:
-0.1ml of 1:1000 PPD injected intradermally
-results 2-3 days later
<6mm - negative (give BCG if unvaccinated)
6-15mm - positive (no BCG, previous TB infection or BCG)
>15mm - strongly positive (suggests TB infection)
What might cause a false negative Mantoux test?
- miliary TB
- sarcoidosis
- HIV
- lymphoma
- very young age
- steroids
- fever
- hypoalbuminaemia
- anaemia
Diagnosis of TB:
- CXR: upper lobe cavitation, bilateral hilar lymphadenopathy
- sputum smears (Ziehl Neelsen)
- Sputum culture (more sensitive but slower)
- NAAT (rapid diagnosis, more sensitive than smear but less than culture)
How to treat latent TB:
-3m isoniazid (with pyridoxine) and rifampicin
-6m isoniazid (with pyridoxine)
consider interaction with rifampicin
Primary TB:
- non-immune hoest develops primary infection of lungs
- lesion - Ghon complex
- immunocompetent - initial lesion heals by firosis
- disseminated disease - miliary tuberculosis travels through pulmonary venous system
Secondary TB:
- if host becomes immunocompromised, initial infection reactivated
- in apex of lungs and may spread
- extra pulmonary: CNS, vertebral bodies (Pott’s), cervical lymph nodes (scrofuloderma), renal, GI tract
Management of active TB in first 2 months (acute phase):
- rifampicin
- isoniazid
- pyrazinamide
- ethambutol
Management of TB in continuation phase (next 4 month):
- rifampicin
- isoniazid
How do you treat meningeal tuberculosis?
12 months min with steroids
Rifampicin ADR:
- potent liver enzyme inducer
- hepatitis
- orange secretions
- flu-like
Isoniazid ADR:
- peripheral neuropathy (prevent with pyridoxine vit B6)
- hepatitis
- agranulocytosis
- liver enzyme enzyme inhibitor
Pyrazinamide ADR:
- hyperuricaemia causing gout
- arthralgia
- myalgia
- hepatitis
Ethambutol ADR:
optic neuritis
Most common surgical site infection:
staph aureus
Most common organisms causing post splenectomy sepsis:
- haemophilus influenza
- strep pneumoniae
- meningococci
