extras Flashcards
How does C. diphtheriae cause damage, which organs are most badly affected?
It releases an AB exotoxin that prevents protein synthesis within cells. Intoxication of the heart and kidneys is fatal.
Describe the structure of the influenza virus
It is a RNA virus consisting of 8 weakly linked RNA segments, surrounded by a capsule with spike proteins (haemagglutinin and neuraminidase)
How does bordetella pertussis cause disease
Releases tracheal cytotoxin which incapacitates ciliated cells, resulting in buildup of mucus and bacteria in the lower RT
Why does the convalescence period in pertussis take months following treatment?
Erythromycin eliminates the bacteria, but ciliated cells must also be replenished
What are the differences between pneumococcal pneumonia and H. pneumoniae pneumonia? (3)
S. pneumoniae is gram positive whereas H. pneumoniae is gram negative.
Strep occurs due to lowered immunity in a healthy carrier, while H occurs in those who are immunocompromised (alcoholic, diabetic, cancer, poor nutrition)
Strep can be treated with penicillin/optichin while H is resistant to penicillin so penicillinase resistant 2nd gen cephalosporins are used
What are two similarities of Q fever and chlamydial pneumonia/ ornithosis
Both are obligate intracellular and cause atypical pneumonia
What is a major complication of Q fever
Endocarditis
Where does blastomycosis begin and where does it spread?
Begins with infection of the lungs and spreads to skin to cause cutaneous ulcers
How is leptospirosis transmitted
Dogs and cats shed the bacteria in their urine, which contaminates water. It can then enter the body through damaged skin or the digestive tract.
What are two complications of leptospirosis
Severe liver and kidney disease
How much more likely are females to develop gonorrhoea after a single exposure than males
Thrice (60-90% compared to 20-35%)
Gonorrhoea symptoms
Pus and painful urination
What part of the female body is infected and why- gonorrhoea
Cervix (columnar epithelium) and not vagina (stratified squamous)
How is the causative agent of syphilis cultured
Treponema pallidum can be grown in cell cultures only
Are antibodies effective against treponema pallidum? Why/ why not?
No, CMI only due to lipid outer layer of the bacteria ‘teflon coated’
Which 3 factors may contribute to increased risk of vaginitis and why
Pregnancy, oral contraceptives and use of broad spectrum antibiotics. Suppress the growth of lactobacilli (normal flora) which obtain energy from sexual hormones, leading to opportunistic infection
What treatments can be used to restore acidity of the vagina
Acetic acid gels and replacement lactobacilli
What symptoms are the same vs different for males v females with genital herpes
Vesicles appear on external genitals (female) vs base of penis (male)
Both have dysuria (painful urination) and trouble walking
How is genital herpes cured
It is not curable, antivirals like acyclovir could possibly be used
Why is topical podofilax/ podophyllum used to treat genital warts
Caused by human papillomavirus
Podofilax contains zinc which inhibits viral replication
What major condition is genital warts associated with
Cervical cancer
How is lymphogranuloma venereum diagnosed
Iodine staining of pus from lymph nodes
Common feature between 3 common causes of bacterial meningitis. How does this relate to type of vaccine used?
All capsulated. All vaccines are based on the capsular antigens
Haemophilus influenza vaccine is based on
Hib capsular antigen
Meningococcal vaccine is based on
Capsular antigens of A or C serotypes
Meningococcal A is most prevalent in
Africa and middle east
Meningococcal C is most prevalent in
North America
How is N. meningitidis cultured
Chocolate agar = heated blood agar kills RBCs, releasing haem
N. meningitidis treatments
Doxycycline, ofloxacin, erythromycin
How does C. tetani cause disease
It is an anaerobic bacteria. When it is in an aerobic environment such as the blood, the bacteria dies, releasing tetanospasmin a potent neurotoxin. The toxin inhibits the relaxation pathway in the CNS, resulting in rigid paralysis and pain
Which serological type of C. botulinum has an exotoxin that is the most resistant to heat
Type A
Under what conditions is C. botulinum exotoxin released, how does this differ to that of C. tetani
Anaerobic whereas tetanospasmin is released upon death in aerobic conditions
What kind of contact is required to contract leprosy
Prolonged intimate contact
How is polio virus dangerous
Kills motor nerve cells leading to paralysis and can enter CNS
Why is post-exposure prophylaxis effective for rabies
The virus has a long incubation period so there is time for a vaccine to be administered and stimulate the immune system
How do arboviruses survive between transmission periods
Hibernation and transovarian transmission
How do arboviruses cause harm
The virus multiplies in the reticuloendothelial system and becomes localised in target organs, causing necrosis, inflammation and fever. It then enters nervous pathways and then the CNS
How is yellow fever linked to dengue haemorrhagic fever
The arbovirus localises in the liver, killing liver cells and impairing clotting factor production. Reduced clotting factor results in haemorrhage
What causes symptoms in BSE
The prion causes mass accumulation of misfolded proteins (beta sheets instead of alpha) in the CNS leading to neurological symptoms
How is S. mutans cariogenic
Salivary amylase converts sucrose to glucose and fructose. The bacteria converts glucose to dextran, a gummy polysaccharide which forms plaque, and breaks fructose to lactic acid which breaks down tooth enamel.
How does staphylococcal intoxication occur, which species is involved
S. aureus. Cooked food (bacteria destroyed) is contaminated by unclean hands. Staph is transferred. When the food is reheated, the bacteria are killed but the enterotoxins remain
How can shigella be identified in the lab?
Does not produce colour on MacConkey agar.
Describe the antigens on salmonella
O antigen = LPS
H antigen = flagella
Virulent (Vi) = surrounds O
What differentiates S. typhi from other salmonella
It multiplies in macrophages rather than epithelial cells
How does v. cholerae cause rice water diarrhoea
LT toxin causes cells to secrete potassium ions and water, leading to rice water diarrhoea
Which serotype of V. cholerae is responsible for pandemic cholera
O139
What toxin is produced by yersinia enterocolitica
Similar to stable toxin (ST) of enterotoxigenic E coli
What enzyme is produced by yersinia, how does this inform antibiotic choice
Produces beta lactamase so cannot be treated with penicillin or cephalosporins
Which exotoxins are produced by C. difficile and which is an enterotoxin
A (enterotoxin) and B
True or false: Bacillus cereus produces spores and toxins
True
What coinfection is common with rotavirus and why
Rota exposes receptors for ETEC, leading to more severe diarrhoea
Who is rotavirus most common in and when
Infants and children in winter
What type of vaccine is the mumps vaccine
MMR is live attenuated
How does cytomegalovirus cause owl eye appearance
Incorporates into nucleus of epithelial cells. Viral inclusion body causes enlarged nucleus and cytomegaly.
Symptoms of ergotism
Hallucinogenic symptoms, nausea and vomiting
What are two severe complications of aflatoxin poisoning
Cirrhosis of liver and cancer (carcinogen)
What toxin of S. pyogenes causes puerperal fever
Superantigen (exotoxin)
How does s. pyogenes cause rheumatic fever and endocardial damage
Misdirected immune response to cardiac myosin which resembles M protein on streptococci (antigenic mimicry)
Major symptom of tularaemia
Ulceroglandular tularaemia = swollen lymph nodes
What two toxins are produced by bacillus anthracis
Oedema factor (causes oedema) and lethal toxin (kills macrophages)
How does C. perfringens cause ischaemia in gas gangrene
Alpha toxin destroys RBCs (it is a membrane disrupting toxin), reducing oxygen carrying capacity of blood -> ischaemia and necrosis
How does plague caused by Y. pestis progress
Bubonic plague (lymph nodes) -> septicaemic plague -> pneumonic plague (haemorrhage from lungs- necrotising haemorrhagic pneumonia)
Why do relapses occur in relapsing fever
Due to infection by antigenically different serotypes of the borrelia species
Visceral leishmaniasis is caused by
Leishmania donovani
Cutaneous leishmaniasis is caused by
Leishmania tropicalis and braziliensis
Urinary schistosomiasis is caused by
Schistosoma haematobium
Intestinal inflammation in schistosomiasis is caused by
Schistosoma mansoni and schistosoma japonicum
