Week 2 Flashcards
What is not usually added to growing microbes and why?
Inorganic elements such as phosphates or sulphates because they are usually present in adequate amount as contaminants.
What are some growth factors and when are they added?
Blood, serum,vitamins may be added to sterile medium just before pouring but after heat sterilisation.
What are buffering agents?
Can use soluble phosphate to absorb change in pH produced by bacteria.
Name and describe the 2 possible chemical composition of a media.
- Complex media: most common (don’t know exactly all the chemicals in it)
- Defined media: for specific/sensitive purposes (know everything in it)
What are the 4 different types/functions a growth media can carry out?
- Basal media
- Enriched media
- Selective media
- Indicator/differential media
What is a basal media used for?
- General purpose base media for growing non-fastidious microbes
- typically complex
What is the purpose of enriched media?
- Allow growth of fastidious microbes
- Starts as basal media then add other things. ie. growth factors
What is a selective media used for?
- Selective agents encourage growth of specific microbes and suppress others
What is the purpose of an indicator media?
- Contain component causing an observable change when microbes grow
Name 4 types of agar.
- Nutrient agar
- Horse blood agar
- Chocolate agar
- MacConkey agar
What is NA made of and what type of bacteria is it suitable for?
- Made of basal media and is for non-fastidious bacteria
- Base medium for other media
What is HBA made of and what is its purpose?
- Made of enriched media and is for fastidious bacteria.
- Indicator for haemolysis which is achieved through using high temp to lyse the blood cells.
What is CHA made of and what is its purpose?
- Made of enriched media and is for very fastidious bacteria.
- Very high temp lyse blood cells so all contents inside are readily available for bacteria to use.
What is MAC made of and what is its purpose?
- Made of selective media that contains bile salts, lactose and neutral red.
- The purpose is isolation and enumeration (counting) of coliforms (bacteria in gut) and intestinal bacterial pathogens.
What is the purpose of bile salts in MAC?
- Selective agent for presence of coliform in bacteria.
What is the purpose of neutral red in MAC?
- Turn pink if bacteria are lactose fermenter (produce acidic products).
When is an enrichment media used and how does it achieve its purpose?
- If desired bacterium is only present in low numbers in a MIXED culture use this.
- Does so by chemically inhibiting other bacteria, nutritionally favouring desired bacteria, manipulating growth environment to suit desired bacterium.
What happens to water activity when external salt concentration is high?
- Water activity is low (chemically and structurally unavailable to bacteria).
What types of microbe cause problems to humans and why?
- Mesophiles because it grows at 37 degrees Celsius.
What are anaerobes?
- Microbes which cannot use oxygen.
- Obligate (strict) anaerobes are killed by oxygen.
What are obligate aerobes?
- Require oxygen
What are facultative anaerobes?
- Can grow without oxygen but grow better with it
What are microaerophiles?
- Need oxygen but at lower then atmospheric concentrations.
Why is it that some microbes cannot grow in oxygen?
- Oxygen can generate reactive oxygen species (ROS) which is toxic.
- ROS can oxidise sulphydryl group in proteins denaturing enzyme and can damage lipids+nucleic acids
- Only some bacteria possess enzymes (catalase, peroxidase) and pigments (carotenoids) which detoxify ROS.
Name the 3 types of microbes growing at different pH.
- acidophiles (0-5.8)
- neutrophiles (5.5-8)
- alkalophiles (8.5-11.5)
What are biofilms?
- Attached microbes in complex, slime encased communities.
- Mixed microbial community that may possess different characteristics which may benefit others in that community.
What is quorum sensing and how does it work?
- Communication using molecular signals in density-dependent manner.
- Depending on conc. of molecular signals, it will elicit or not elicit a response in neighbouring cells.
What are the tow types of method of selecting a single cell?
- Streak dilution
- Limiting dilution followed by spread or pour plate
Describe an algae. (4)
- Eukaryote
- Spherical or filamentous
- Photosynthesise using chlorophyll and other pigments
- Fresh water and marine environment.
What is a parasite? Give a few examples.
- Any organism which benefits at the cost of the host.
- Caused by bacteria, viruses, fungi and algae, protozoa, helminths, arthropods
What are some advantages of parasitism?
- nutrients, protection from environment
What are some disadvantages of parasitism?
- immune response (attacks by antibodies, phagocytic cells)
What is a definite host and an intermediate host?
- Definite host is the host in which sexual reproduction of the parasite occurs.
- Intermediate host is the host that serves as a temporary but essential environment for development of a parasite and completion of its life cycle.
What is a transmission vector?
- a living organism (usually arthropod or other animal) that transfers an infective agent between hosts.
Describe a protozoa.
- Unicellular eukaryote
- Usually motile
- Obtains food by ingesting other organisms.organic material (uses vacuoles)
- Mostly free living but some are human parasites.
What are some modes of transmissions in protozoa?
- Through insect (plasmodium spp.)
- Ingestion of infective stages (toxoplasma gondii)
- Sexual transmission (STIs)
What is are 4 diseases caused by protozoa.
- Malaria caused by plasmodium spp (single celled protozoan parasite.
- Giardiasis caused by giardia lamblia (a diarrhoeal disease)
- Helminths can also cause disease
- Hookworms can cal cause disease
What are some symptoms of malaria?
- Acute: fever and anaemia (due to lysis of RBCs), headache, diarrhoea, vomitting
- Chronic: anaemia, swelling of spleen and liver (working too much to remove abnormal RBCs)
- Celebral malaria: responsible for almost all deaths (caused only by P.falciparum). Infected RBCs adhere to vascular epithelial cell (so don;t go through spleen to be removed)
How is malaria diagnosed?
- Through patient history, symptoms, blood smears (peripheral blood, smears prepared and stained with Giesmsa stain then use light microscopy)
What are treatment and prevention options for malaria?
- Anti malarial drugs
- Prevention can include use of chemoprophylaxis (drug), insect repellent, bed nets
How does giardiasis spread?
- A water borne disease transmitted through faecal-oral route (ingestion of contaminated water)
How does malaria spread?
- Vary in severity: P.falciparum (most malignant infection) and P.knowlesi (rare human nfections)
- Spread by female mosquitoes genus Anopheles. Goes through two distinctive life cycles (liver and blood).
What are some symptoms of giardiasis and when do they show?
- Diarrhoea –> weight loss, dehydration
- greasy stool, stomach cramps, farting, nausea
- appears 1-2 weeks after infection
What is the life cycle of giardiasis? (4)
- Cyst and trophozoite
- It has 2 nuclei, 8 flagella and a ventral sucking disc (mechanical sucker) to attach to intestinal wall
- Lives in intestine and passed in faeces
- Cyst is dormant and trophozoite die in external environment so must become cyst again
What do treatments and prevention include for giardiasis?
- Drinking fluids (metronidazole)
- Good hygiene, avoid contaminated water sources (cyst resistant to chlorine), boil water or filter it
What are helminths and what are the 3 main groups?
- Multicellular parasitic worms
- Tapeworm (cestodes), flukes (trematodes & digenea), roundworms (nematodes- cylindrical bodies, lack specialised attachment organs)
- Tapeworm and flukes are platyhelminths (flat bodies, muscular suckers/hooks)
What is the life cycle of helminths?
- Larval stage and adult stage
How are helminths spread?
- Via intermediate host: accidental ingestion of larvae in tissue of another host
- Faecal-oral route: accidental ingestion of eggs or larvae from faeces of infected host
- Active skin penetration: larval stage invade skin
- Injection by blood-sucking insect
How are hookworms transmitted?
- Begins and ends in small intestine
- Eggs hatch in soil and larvae penetrate skin
- It is carried to the lunch and swallowed so it can reach the small intestine
- It grows and attaches to intestinal wall and suck blood
- It produces eggs which are passed in stools
What are some symptoms of hookworm disease?
- Rash, itch
- Light infection: mild diarrhoea and cramps
- Heavy infection: anaemia, abdominal pain, weight loss, diarrhoea
- Heavy, chronic infection: stunted growth and mental development
What are some treatment and prevention of hookworm disease?
- Treatment by mebendazole, pyrantel
- Prevent by avoiding contact with contaminated soil, improved hygiene and sanitation.
Describe a fungi. (6)
- Eukaryote
- Cell wall of chitin
- Heterotrophic
- Saprophytic (breakdown organic material via secreted enzymes and then uptake by absorption-osomotrophic)
- 7 major fungal group (ending in ..mycota)
- Divided into moulds (filamentous) and yeasts (unicellular)
What are 4 distinct structures in fungi?
- Thallus: body or vegetative structure devoid of root, stem or leaf (single cell in yeasts, multicellular masses in moulds- made of hyphae in moulds)
- Spores: non-motile, useful for fungal identification
- Hyphae: vegetative organs that grow when fungal spores germinate (long filaments)
- Mycelium: tangled mass of hyphae
Describe yeast.
- Unicellular fungi that reproduce asexually by budding/fission or sexually by spores
Describe mould.
- Usually multi-cellular fungi that reproduce sexually by fusion of hyphae or asexually by despersion of spores.
What are some roles good fungi play?
- decomposers, fermenters, producers, research tools
What are some roles evil fungi play?
- disease, bio-deterioration, mycotoxins
What does Asperigillus Flavus do?
- Fungi that produce mycotoxins.
- Contaminates food (heat stable aflatoxins are produced and ingested with food which can cause liver disease and cancer)
What does Claviceps Purpura do?
- Fungi that produce mycotoxins.
- Parasitizes rye and other grasses (toxin ingested with grass/grain which can cause Ergot disease, psychotic delusion, abortion)
What are 3 ways to identify fungi?
- Macroscopically: colony characteristics, media, colour, texture
- Microscopically: presence and arrangement of fruiting or sporing bodies (wet mounts, slide culture technique)
- Biochemically: fermentation products
What types of media can be used to grow fungi?
- Sabouraud’s agar (SAB): glucose, peptone, agar, water, ~pH5, +/- antibiotics
- Malt extract agar (MEA): malt extract, agar, water, ~pH5, +/- antibiotics
- All in slightly acidic, low moisture conditions
What are the 3 types of mycoses?
- Superficial (can be cutaneous: involves epidermis or subcutaneous: involves dermis, muscle and fascia)
- Systematic: involves major body systems
- Opportunistic: targets immunocompromised patients (cryptococcosis)
What is a fungal infection associated with cutaneous mycoses and how is it diagnosed?
- Tinea and ringworm
- Diagnosed by microscopic examination, cultured on SAB
Describe Candidiasis fungal disease. (3)
- Caused by Candida albicans and aerobic fungus
- Part of normal microbiota of GIT, RT, vaginal area and mouth
- Can grow as yeast or mould depending on temp
How is Candidiasis transmitted and what are some symptoms?
- Spread through STI or can be nosocomial infection (acquired in hospital)
- Symptoms present in immunocompromised people by disrupting normal microbiota.
How is Candidiasis diagnosed and what are the treatment options?
- Diagnosed through symptoms, patient history and culture
- Treatment can be topical, systematic or in general
Describe Aspergillosis. (2)
- Caused by Aspergillus sp. an aerobic filamentous fungus.
- Present in soil, dust, some foods and water
How is Aspergillosis transmitted and what are some symptoms?
- Spread by inhaling fungal spores, ingestion of contaminated food or water
- Symptoms include allergic response, ingestion of contaminated food –> alfatoxins, pulmonary infection (A.fumigatus), A.flavus cause superficial and invasive disease (dissemination to brain, kidney, liver)
How is Aspergillosis diagnosed and what are some symptoms?
- diagnosed by direct examination of specimen (hyphae or sporing bodies), culture, detection of antigen
- Treatment includes use of voriconazole or itraconazole
Describe Histoplasmosis. (2)
- Cause by Histoplasma capsulatum an intracellular funcgus.
- Found in soil rich in bird/bat droppings (only bats and humans become diseased.
How is Histoplasmosis and what are some symptoms?
- Transmitted by inhalation of spores (dimorphic growth)
- Symptoms include 10 days of incubation, fever, cough, muscle aches (infects lung macrophages)
What are some treatment and prevention options for Histoplasmosis?
- Treatment include anti-fungal drugs but can resolve on its own.
- Prevention include wearing protective clothing/mask, soil decontamination.
