Meeran Micriobio Flashcards
What is pneumocystis jirovecii?
It is a yeast-like fungus that primary affects immunocompromised patients - especially those with HIV and CD4 <200.
Presentation = dry cough, fever, weight loss and night sweats
CXR shows diffuse bilateral pulmonary infilttates and Gomori’s methenamine silver stain shows “flying-saucer” shaped cysts on microsopy.
What is streptococcus pneumoniae?
Alpha-haemolytic gram+ve diplococci (arranged in pairs).
You use the Quelling reation to stain this capsulated bacteria - mix anti-serum and methylene blue which causes capsule to swell to become visible under microscopy
Optochin-sensitivity also differentiates pneumococcus from Streptococcus viridans (also α-haemolytic), which is optochin-insensitve.
What is staphylococcus aureus?
Beta-haemolytic gram+ve cocci arranged in clusters (grape-like)
*All staphylococci are also catalase positive, whereas streptococci are catalase negative
In the GIT, S. aureus produces extotoxin TSST-1 which acts as a superantigen and causes non-specific activation of T cells with release of IL-1, IL-2 and TNF-alpha. This causes a massive immune response leadign to shock and multiple organ failure (with vomiting and diarrhoea approx 12-24hrs post-consumption)
What electrolyte imbalances can be revealed in Legionella pneumophilia?
It is a gram-ve rod which causes an atypical pneumonia
Blood chemistry can show hyponatraemia, hypophosphataemia and deranged LFTs
How do you diagnose legionella pneumophilia?
Culture of respiratory secretions on buffered charcoal yeast extract agar
or
rapid urinary antigen test
What is moraxella catarrhalis?
Aerobic Gram-negative diploccoci which is problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD).
Other targets of infection include ears, eyes and central nervous system.
What is haemophilus influenzae?
Gram-ve bacillus which can cause annual influenza outbreaks
Chocoalte agar is used to culture it. Further oxidase and catalase tests are positive
What is mycoplasma pneumoniae?
Obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis.
A cold-agglutinin test can be used for the diagnosis.
In rare cases, infection may lead to Stevenson–Johnson syndrome.
What is listeria monocytogenes?
Beta-haemolytic gram+ve rod that can cause non-invasive gastroenteritis.
It is found in refrigerated food and unpasteurised dairy products
Listeria demonstrates “tumbling motility” due to its flagellar-driven movements.
Neonates and immunocompromised patients are particularly susceptible. Invasive infection can cause more serious problems in these groups including septicaemia, meningitis and encephalitis.
What is virbio cholerae?
It is a comma-shaped oxidase positive bacteria which causes profuse watery diarrhoez with no inflammatory cells
Transmission = faecal-oral route
It secretes an enterotoxin which causes active secretion of sodium and chloride ions –> water loss due to osmotic pull of NaCl
What is giardia lamblia?
Pear-shaped trophozite containing two nuclei, four flagellae and a suction disc
Transmission is via the ingestion of a cyst from faecally contaminated food/water
Trophozites attach to the duodenum but do not invade –> inhibit protein absorption –> draw water into the GI lumen
Symptoms = foul-smelling non-bloody steatorrhoea with stool containing cysts on microscopy
What does salmonella typhi cause?
Enteric fever
It multiples in the Peyer’s patches of the small intestine.
Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
What is shigellae?
Non-motile, non-hydrogen sulphide producers
This bacteria causes dysentry via invasion of mucosal cells of the distal ileum and colon
What is campylobacter jejuni?
Oxidase positive, non-motile bacteria
Transmission via faecal-oral route, generally due to contami- nation by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
What is entamoeba histolytica?
It is a motile trophozite transmitted by the ingestion of cysts leading to colonisation of the caecum and colon –> “flask-shaped” ulcer
Clinical features involve dysentery, chronic weight loss and liver abscess formation
How would CSF results of mycobacterium tuberculosis present?
CSF appearance: clear/fibrin web
Protein: high
Glucose: low
WBC: high
What is leptospira interrogans?
Causes Leptospirosis (Weil’s syndrome)
Transmitted via animal contacts
1st stage: non-specific symptoms such as fever, headache, malaise and photophobia
2nd stage: formation of IgM antibodies with meningitis, liver damage (jaundice) and renal failure
Gold standard test = microscopic agglutination test
What is cryptococcus neoformans?
Polysaccharide encapsulated yeast which can cause subacute or chronic meningoencephalitis ususally in immunocompromised
Transmitted via inhalation (pigeon droppings)
Diagnosis: examination of CSF with india ink which reveals yeast cells with a surrounding halo. A cryptococcal antigen test can also be used (higher sensitivity)
How does a viral CSF appear?
Appearance: colourless
Protein: moderately raised
Glucose: normal
WCC: raised
What are the subtype serovars of chlamydia trachomatis and what do they cause?
It is a gram-ve obligate intracellular bacterium
Serovars D-K cause genital chlamydiosis resulting in dyspareunia, dysuria and vaginal/penile discharge
Serovars L1. L2 and L3 cause lymphogranuloma venereum which is a painless papule/ulcer on the genitals which heals spontaneously
What is syphilis caused by?
Treponema pallidum
What are the 3 clinical stages of syphilis?
Primary - firm painless chancre that appears approximately 1 month after sexual contact and resolves within a few weeks
Secondary - bacteriaemic stage with a widespread rash and lymphadenopathy
Tertiary (decades after primary infection and multi-organ involvement) - gummatous lesionson the skin and bone, aortic arch aneurysm, peripheral neuropathy, tabes dorsalis, Argyll-Robertson pupils
What is Haemophilus ducreyi?
Gram-ve coccobacillus that causes tropical ulcer diseaese (chancroid) and is sexually-transmitted. It can be cultured on chocolate agar.
Chancroid is characterized by a painful genital ulcer that leads to unilateral painful swollen inguinal lymph nodes. Infected lymph nodes may rupture releasing pus
Ddx to consider: syphilis, HSV1 and 2, lymphogranuloma venereum
What is a (rare) side effect of flucloxacillin?
Cholestatic jaundice which develops weeks after treatment cessation
Why is trimethoprim contra-indicated in pregnancy?
It is a folate metabolism inhibitor which interferes with DNA synthesis.
