Micro Flashcards
How long does it take to make culture microorganisms?
Days. Mycobacteria and other fastidious organisms can be weeks
How long does an antibody detection test take?
The test can be rapid (<24hrs) but it takes a minimum of two weeks for exposure to develop antibodies
What are the two results of a gram stain and what do they mean?
Purple is positive and pink is negative.
What types of things can you culture?
Pus, swab, fluids like urine, CSF and joint aspirate, faeces.
What are 3 examples of gram positive cocci?
Staphylococci, streptococci and enterococci
What are 3 examples of gram negative cocci?
Neisseria and moraxella
What are 5 examples of gram positive bacilli?
B anthrancis, C diptheriae, listeria monocytogenes, clostridia and propionobacteria.
What is the resolving power of the naked eye?
100 micrometers
What is the resolving power of a light microscope?
0.2 micrometers
What is the definition of a pathogen?
An organism that causes or is capable of causing disease
What is a commensal?
An organism which colonises the host but causes no disease in normal circumstances
What is an opportunist pathogen?
a microbe that only causes no diseases in normal circumstances
What is the definition of virulence or pathogenicity?
the degree to which a given organism is pathogenic
What is the definition of asymptomatic carriage?
When a pathogen is carried harmlessly at a tissue site which causes no disease
What are the 3 formations of groups of cocci?
Diplococcus, chain, cluster
What are the 3 formations of groups of bacilli?
Chain, vibrio (curved) and spirochaete (spiral)
What is the role of a bacterium’s capsule?
Allows bacteria to bind to things and evade phagocytosis
Which part of the bacteria allows the classification between gram positive and gram negative?
The cell wall
What is the role of the frimbrae?
Binds to the surface of other cells
What is the role of the pilli?
Help attachment to mucosal cells. Involved in bacterial conjugation.
What is the Ziehl-Neelsen stain?
An acid fast stain which is used to identify acid fast organisms, mainly mycobacteria.
How do you conduct the Ziehl Neelsen stain?
- Apply carbolfuchsin
- Apply heat
- Apply acid alcohol
- Apply methylene blue as a counter stain
What do the different results of the Ziehl Neelsen stain mean?
Pink= acid fast Blue= non-acid fast
How do you conduct a gram stain?
- add crystal violet
- add iodine
- add ethanol to decolourise
- add the counterstain- safranin
What is the main difference between gram positive and gram negative cells walls?
Gram positive has a thick layer of peptidoglycan and gram negative has a thin layer.
What are the components of a gram positive cell wall?
Capsule, thick layer of peptidoglycan and an inner membrane
What are the components of a gram negative cell wall?
Capsule, lipopolysaccharide (endotoxin), outer membrane, lipoprotein, periplasmic space, thin wall of peptidoglycan and an inner membrane.
How is growth rate of identified in bacteria?
Increase in cell number rather than an increase in cell size
How do bacteria reproduce?
By binary fission
What is the definition of generation time?
The interval required for a cell to divide
How do you calculate generation time?
Time taken to divide/ number of generations
What are the 4 phases of bacterial growth and what do they look like on a graph?
Lag is a slow increase in the number Log is a steep increase Stationary is a plateau Death is a steep decrease (axis are y=log number of bacteria, x= time)
What is happening during lag phase?
Cells are adjusting to new media
What is happening during log phase?
Reproduction, cells in optimum growth phase
What is happening during stationary phase?
Exhaustion of resources or accumulation of waste product.
What are the two types of bacterial toxin?
Endo and exotoxins
What is an endotoxin?
component of the outer membrane of bacteria. It is a non-specific lipopolysaccharide which is produced by gram negative bacteria
What is an exotoxin?
Secreted proteins by gram positive and gram negative bacteria. They are specific and can be converted to toxoid.
What is a toxoid?
A toxoid is a toxin which can be treated so that it loses its toxicity but retains its antigenicity
Is bacterial DNA double or single stranded?
Double
What are the causes of genetic variation in bacteria?
Mutation
Gene transfer- transformation via plasmid, transduction via phage or conjugation via sex pillus.
What does a negative result for a coagulase test indicate?
Staphylococci
What does a positive result for a coagulase test indicate?
Streptococci
What does a positive result for a coagulase test indicate?
S.aureus
What does a negative result for a coagulase test indicate?
Staphylococci
What colour is alpha haemolysis?
Green
What colour is beta haemolysis?
Surrounding becomes transparent
What colour is gamma haemolysis?
Nothing happens so red.
What does beta haemolysis indicate?
S. pyogenes
How is staph. aureus transmitted?
Aerosol and touch
What does MRSA stand for?
methicillin resistant staphlococcus aureus
What is MRSA resistant to?
B lactams, gentamicin, erythromycin, and tetracyclin.
What are the virulence factors of staphlococcus aureus?
Pore forming toxins, proteases (exfolatin), toxic shock syndrome toxin (TSST), protein A which binds to the surface and binds Igs in the wrong direction.
When does s. epidermidis cause infections?
It is opportunistic so occurs in the debilitated, protheses, catheters
Whats the main virulence factor used by s. epidermidis?
The ability to form persistent biofilms
What do patients with s. saprophyticus present with?
Acute cystitis
How is streptococcus pyogenes?
Causes B haemolysis. It is also group A in lancefield typing
What are 5 common infections caused by s. pyogenes?
- Cellulitis
- Tonsilitis
- Pharyngitis
- Otitis media
- Impetigo
- Scarlet fever
What are the 4 virulence factors of s. pyogenes?
Enzymes
Toxins
Hyaluronic acid in the capsule
M protein which is a surface protein which encourages complement degradation.
What 4 infections are commonly caused by s. pneumoniae?
- pneumonia
- otitis media
- sinusitis
- meningitis
What are the 3 virulence factors of s.pneumoniae?
- capsule is antiphagocytic due to polysaccharides
- Inflammatory wall constituents
- Cytotoxin called pneumolysis- pore forming in the cells of the immune system
What type of haemolysis is viridans streptococci identified by?
Alpha or non-haemolytic
What does viridans streptococci cause?
Dental cavities and abscesses. Also endocarditis and deep organ abscesses
What does corynebacterium diptheriae cause?
Lymphadenopathy and a thick pseudo-membrane on tonsils
How do you treat corynebacterium diptheriae?
Anti-toxin and erythromycin
What is the H antigen?
The slender, threadlike portion of the flagella
What is a facultative anaerobe?
A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
What is the most abundant commensal?
E. coli
What does E.coli stand for?
Escherichia coli
What does E.coli cause?
Wound infections UTIs Gastroenteritis Traveller's diarrhoea Bacteraemia Meningitis
What is the main virulence factor of E.coli?
They have pilli which adhere to the tissue of the small intenstine. This affects G proteins and causes more Cl- to move into the tract which brings with it water.
What are the main causes of Shigella?
Damage to the intestinal mucosa which leads to acute infection of the large intestine and painful diarrhoea with blood and mucus in the stool
How does shigella cause the acute inflammation of the gut?
By releasing free radicals
What are the two most common infetions caused by salmonella?
Gastroenteritis
Typhoid (enteric fever)
How does salmonella spread?
Ingestion of contaminated food/ water
What are the signs and symptoms of typhoid?
Fever, headache, dry cough, hepatomegaly and splenomegaly
What does infective dose mean?
The number of bacteria required to cause an infection
What does vibrocholerae cause?
Cholera
How is vibrocholerae transmitted?
Faecal oral
What is the main symptom of cholera
RICE WATER STOOLS!!! WOOOOO
What is the pathogenicity of cholera?
The cholera toxin causes loss of Cl- and Na+ into the lumen, bringing water with it. Water moves into the intestine.
What does Bordetella pertussis cause?
Pertussis- whooping cough
How does N.meningitis spread?
Aerosol transmission
Where does N.Meningitis colonise?
The subarachnoid space
What are the virulence determinants of N.Meningitis?
- Capsule which is antiphagocytic
2. pilli promote cell invasion and colonisation
What is the major virulence determinant of Helicobacter pylori?
Secretes urease which hydrolyses urea to make NH3 and this neutralises hydrochloric acid in the stomach
What are the 2 stages in the chlamydia growth cycle?
- Elementary bodies- infectious, enter the cell through endocytosis. Prevent phagosome fusion
- Reticulate bodies- metabolically active
What are the three groups of worms?
Nematodes (round worms)
Trematodes (flat worms)
Cestodes (tape worms)
What is the prepatent period?
The period between infection and the appearance of eggs in the stool
How are intestinal nematodes transmitted?
Transmitted human to human by eggs or larvae
What is Loeffler’s syndrome caused by?
Larval migration through the lungs of ascan’s lumbricoides.
What are the signs and symptoms of loeffler’s syndrome?
Cough, fever, CXR inflitrate, wheeze, eosinophillia
How can you diagnose a worm infection?
Either doo microscopy of the stool for eggs or see the worm
What are the 2 main species of hookworm?
Anyclostoma duodenale and nector americanus
What are the signs and symptoms of a hookworm infection?
Papules at the site of entry, pulmonary symptoms and iron-deficiency anaemia
How long does a pin worm live for?
56 days
What are the clinical features of a pinworm infection?
Pruritis ani (itchy bum hole), appendicitis, vaginal penetration leading to endometriosis, salpingitis, infertility and paranasal sinusitis.
What is the treatment for pinworm?
Mebendazole, piperazine or pyrantel. Treat the whole family.
Where does the adult whip worm reside?
partly buried in the mucosa of the bowel
What are the symptoms of a whipworm infection?
Bloody diarrhoea, rectal prolapse, anaemia, eosinophillia
How do you treat a whipworm infection?
Mebenazole, albenazole
How do you identify mycobacteria?
The Ziehl Neelsen test
What are the main features of a mycobacteria?
Aerobic, non-spore forming, non-motile bacillus and a cell wall with high molecular weight lipids.
What are symptoms of leprosy?
Appearance of skin lesions, patches of skin with decreased sensation, numbness, eye problems, facial deformity
How do you do a Ziehl-Neelsen stain?
Add carbol fuchsin, add acid alcohol, add methylene blue
How does a granuloma form?
Mycobacteria are engulfed by macrophages but survive within them
Mycobacteria spread in macrophages in the blood to oxygen rich sites
Mycobacteria specific CD4+ helper cells are activated a few weeks later after MHCII presents the antigen
Helper T cells secrete INF-gamma which activates macrophages to become epitheliod macrophages which aggregate and wall off the mycobacteria in an anoxic and acidic environment.
How is hepatitis A spread?
Faecal-oral route
How is hepatitis B spread?
DNA virus, blood born, vertical and sexual transmission
What are the 5 basic properties of a virus?
- Grow only inside living cells
- Possess only one type of nucleic acid (RNA or DNA)
- No cell wall- either an outer lipid coat or a lipid envelope
- Essentially inert outside of a cell
- Protein receptors on the virus allow attachment to susceptible host cells.
What are the 6 stages of viral replication?
- Attachment
- Cell entry (only the core carrying nucleic acid and proteins associated with replication
- Interaction with host cell- uses the host’s enzymes for replication
- Replication
- Assembly
- Release by lysis or leaking
What are the 3 main features of fungi?
- Eukaryotic
- Chitinous cell wall
- Exist in yeast or mould forms
What is the difference between yeast and mould?
Yeast are single celled organisms that divide by budding and mould form multicellular hyphae and spores. Some fungi exist as both yeast and mould switching between the two when conditions suit- these are called dimorphic fungi.
What are the 5 methods of diagnosing fungal disease?
- microscopy
- histology
- culture
- molecular methods
- serology
What’s the fancy medicine name for a fungal nail infection?
Onychomyosis
How do you diagnose a nail infection?
Culture nail clippings/ scrapings
How do you treat a fungal nail infection?
terbinafine
How do you treat thrush?
Flucoazole or topical cream
What is (1,3)-beta-D- glucan?
Cell wall component of many fungi, released into serum during invasive infection and can be measured
What is the treatment for pneumocystis pneumonia?
Co-trimethazole
Why would terbinafine be used to treat a fungal nail infection?
It distributes extensively to poorly perfused areas such as nail beds
What are azoles?
Dose dependent inhibitors of 14 alpha-sterol demethylase
What are some examples of azoles?
Fluconazole
Itaconazole
Voriconazole
Posaconazole
What are the 5 different ways in which a virus can cause disease?
- Damage by direct destruction of host cells
- Damage by modification of host cell function or structure
- Damage by the over-reaction of the host in response to the infection
- Damage through cell proliferation and immortilisation
- Evasion of host defences
What is the gold standard diagnostic test for a pneumocytis pneumonia infection?
PCR
why is it more difficult to treat a fungal infection than a bacterial infection?
Fungal cells are eukaryotic and so are human cells so there is a greater risk of host cell toxicity.
How do polyenes work in the treatment of fungal diseases?
Pore formation in ergosterol containing membranes
How do echinocandins work in the treatment of fungal infections?
Inhibitors of 1,3 beta glucan synthase
What is the definition of a pathogen?
Micro-organism which is capable of causing disease
What is the definition of virulence factors?
Microbial factors that cause disease
What is the definition of infectivity?
The ability to become established in a host, can involve adherence and immune escape
What is the definition of virulence?
The ability to cause disease once established
What is the definition of invasiveness?
The capacity to penetrate mucosal surfaces to reach normally sterile sites
When do opportunistic infections arise?
When the immune status is altered
What is the process of oponisation?
Identifying an invading particle to phagocytes
In which three ways to bacteria compete with colonising flora?
- Sequestering nutrients
- Using novel metabolic pathways
- Out-competing other micro-organisms
What is the role of adhesins?
They help bacteria bind to mucosal surfaces
What are biofilms?
Bacteria which stick together on a surface by secreting an extracellular polymeric substance
When do protozoa trigger humoral immunity?
When they are in the blood
When do protozoa trigger cell-mediated immunity?
When they are in tissue
How is falciprum malaria transmitted?
By anopheles mosquito bite during a blood meal
What are the 4 plasmodia protozoa which cause malaria?
P. falciparum, p.vivax, p.ovale, p.malarie
What is the pathogenesis of malaria?
- sporozoites infect hepatocytes and proliferate into merozoites
- Merozoites infect and multiply in RBCs which causes haemolytic anaemia
- Sequestion of red cells heavily parasitized by P. falciparum causes acute renal failure and cerebral malaria.
What is the presentation of malaria?
Non-specific flu like illness with malaise, headache and myalgia
Fever and chills
Cerebral malaria presents with confusion, seizures and coma
How do you diagnose malaria?
Parasitized red cells can be seen on blood films
How do worms evade the immune system?
Their glycoprotein coats are not recognised as foreign
What are the 5 groups of eukaryotes?
- Flagellates
- Amoebe
- Microsporidia
- Sporozoa
- Cilliates
What is african trypanosomiasis transmitted by?
Tsete fly bite
What are the symptoms of african trypanosomiasis?
Chancre Flu-like symptoms CNS involvement Coma Death
What is the pathogen which cause african trypanosomiasis?
Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense.
What is the common name for american trypansomiasis?
Chaga’s disease
How is Chaga’s disease spread?
By the triatomine bug
What are the symptoms of acute chaga’s disease?
Flu like symptoms
what are the symptoms of chronic chaga’s disease?
Cariomyopathy, meagoesophagus
What is the definition of antibiotics?
Agents produced by micro-organisms that kill or inhibit growth of other organisms in high dilution.
Which parasite causes giardiasis?
Giardia lamblia
How is giardiasis spread?
Faeco-oral
What are the signs and symptoms of giardiasis?
Diarrhoea, cramps, bloating, flactulence
How can giardiasis be diagnosed?
Stool microscopy which finds trophozites and/ or cysts in stool.
What is the treatment for giardiasis?
Metronidazole
What is amoebiasis?
It is also known as amoebic dysentry and is caused by any of the entamoeba group (entamoeba histolytica is the one for the exam)
How is amoebiasis spread?
Faeco-oral spread
What are the signs and symptoms for amoebiasis?
Dysentary, colitis, liver and lung abscesses
How is amoebiasis diagnosed?
Stool microscopy which shows trophozoites/ cysts in stool
How is amoebiasis treated?
Metronidazole
What are the signs of malaria?
Anaemia, jaundice, hepatomegaly and black water fever
What are 4 examples of beta lactams?
Penecillin, cephalosporins, carbapenems, glycopeptides
What are beta lactams’ mechanism of action?
Inhibits cell wall synthesis by binding to penicillin binding proteins on cell walls
What are the mechanisms of action of metroniazole and rifampicin?
They interfere with nucleic acid synthesis or function
What are the mechanisms of action of fluroquinolones?
Interfer with DNA gyrase
What is the mechanism of action of aminoglycosides, tetrocyclines, linosamides, macrolides and chloramphenicol?
Inhibition of ribosomal activity and protein synthesis
What is the mechanism of action of sulphonamides and trimethoprim?
Inhibition of folate synthesis and carbon unit metabolism
What is the definition of the minimum inhibitory concentration?
Lowest concentration of a chemical which prevents visible growth of bacteria
What is a bacteriostatic drug?
A drug that prevents growth of bacteria
What is a bacteriocidal drug?
An agent that kills bacteria
When would a bacteriocidal drug be more useful than a bacteriostatic drug?
In areas with poor perfusion, difficult to treat infections and if you need to eradicate the infection quickly (eg meningitis)
What are the two major determinants of anti-bacterial effects?
Concentration and the time that the antibiotic remains on the binding site
What are the 3 main ways in which bacteria can become resistant?
- Bacteria change the molecular configuration of antibiotic binding sites or masks them
- Antibiotic is destroyed or inactivated
- Prevent the antibiotic access by modifying porin channel sites
What does MRSA stand for?
Methicillin resistant staphlococcus aureus
What are the group of antimicrobials of last resort?
Carbopenems
What is a retrovirus?
A virus which uses reverse transcriptase to replicate
Where does HIV replicate?
Within CD4 cells
What happens to the HIV viral load over time?
It increases
What are symptoms of acute HIV syndrome?
Fever, sore throat, headache, mouth ulcers, mild lymphadenopathy, diffuse rash. They are similar to glandular fever/ flu and are usually within 4-6 weeks
What is the only possible symptom seen during clinical latency?
Enlarged lymph nodes
When is the diagnosis of AIDS made?
When CD4 <200 or an AIDS defining illness is present
What are the 10 main AIDs defining illnesses?
Pneumonia TB CMV infection Oral candidiasis Toxoplasma encephalitis lymphoma meningitis salmonella cyroptosporidium diarrhoea Kaposi sarcoma lesions on the skin
Which cancers does HIV increase the incidence of?
Any cancer associated with a virus
How is HIV managed?
HAART= highly active anti-retroviral therapy
3+ anti-retroviral drugs
