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Flashcards in Microbiology Deck (260)
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What is involved in a gram stain?

apply crystal violet stain to fix bacteria, add iodide to bind to crystal violet and help fix it to cell wall, decolourize with ethanol and counter stain with safranin (pink)

in gram negative, the decolourizze interacts with lipids and cells lose their lipopolysaccharide membrane and the crystal violet complex so appears pink

in positive, the decolourize dehydrate the cell wall and crustal violet is trapped in the multilayed peptidoglycan


Methods for infection control?

decontaminate medical equipment, single used items, manage peripheral and central IV lines, manage short term catheters, outbreak control plan, specific antimicrobial prescribing policies, personal protective equipment worn by all staff, dispose sharps into sharps bin, never res heath or bend needles or overfill sharps bin, hand hygeiene


What is an endogenous infection?

infection of a patient by their own flora, especially in hospitalised patients with invasive devices and surgical aptients


Prevention of endogenous infection?

good nutrition and hydration, antispepsis/skin prep where indicated, control underlying disease, remove linses and catheters as soon as clinically possible, reduce antibitotic pressue as much as clinically possible


What are protozoa?

eukaryotic organisms that consume bacteria, algae and microfungi


What are the 5 main protozoa?

flagellates - allows movement, reproduce by binary fision

amoebae - flow through cytoplasma, produced by pseudopodia

sporozoans - no locomotory extensions, most intracellular parasites and reproduce by multiple fission

ciliates - cilia beat rhythmically with macro and micro nuclei

microsporida - makes resistant spores, unique polar filament, coiled inside spore


What has malaria incidence increased?

parasite resistance, climate changes, increased travel to area


How do viruses cause disease?

virus causes invagination of the cell membrane and attaches to cell receptors and released into cell cytoplasm, carry nuclei acids and replicate using cells proteins and forms a defense mechanism

virus moves in vacuole and acidification causes a change in surface proteins of virus to release products, this replicates until the cell lysis or exocytosis so it can spread to other cells, budding causes parts of the virus to be pinched off


How does a virus cause damage?

direct destruction of host cells e.g. polio, modification of host cell structure or function e.g. rotavirus and HIV, damage through overreactivity of host in response to infection e.g. hepatitis B and C, damage through cell proliferation and immortalisation e.g. HPV, virus evasion of the host defences


What makes up a cell wall of fungi?

polysaccharides and chitin, most don't have a capsule, and the cell wall is the sterol rich cytoplasmic membrane


What are the different forms of fungi?

moulds, yeasts, dimorphic


Who are most at risk of getting a fungal infection?

immunocompromised, especially neutrophil deficient (those who are healthy only get superficial infections e.g. athletes foot)


What does the fungal cell wall stain with?

Gomorra methernamine silver of periodic acid schiff reagent as it is too weak for gram stain, KOH


How do yeasts and moulds repoduce?

yeasts - asexual budding
moulds - spore formation


Shape of yeasts and moulds?

yeasts - round/oval
moulds - tubular


How do yeasts and moulds grow?

yeasts - grow in tissue and bud as tubular forms as a pseudohyphae
moulds - grow by longitudinal extension and branch to form interwoven mycelium


What are the 3 types of fungal infection?

superficial mycoses - in skin, hair, nails, mucus membranes with yeast and ringworm
subcutaneous mycoses - pigmented fungi with septate dark brown cells singly or in clusters e.g. madura foot
systemic mycoses - primary or opportunist pathogens


Treatment of fungal infections?

drugs to target sterols in cell membrane, topical or systemic
antifungal therapy binds to serols in cell walls, destabalising it and inhibits RNA and DNA synthesis and inhibits ergosterol biosynthesis and mircotubule assembly


Examples of fungal infections?

candidasis - on mucous membranes of mouth and vagina, a commensal yeast that causes disease when microflora disturbed

ringworm - direct or indirect transfer of infection keratin e.g. athelets foot

aspergillois - spores in soils and ducts can be invasive, allergic or asperfillomia

cryptococcosis - capsulate yeast in immunosuppressed


Is microbacteria gram positive or negative?

weak gram positive with a high lipid ontent


How can mycobacteria cause infection

survive a long time in macrophages and are slow growing, so immunodeficient are susceptible


How does leprosy cause damage?

has granulomas formed as a response to try and contain mycobacteria, these can cause damage to nerves which means risk of tumour and burns and the nose can collapse


How do mycobacteria appear in a Ziehl Neelson stain?

turns red then destained to be blue


How long does it take to culture TB?

solid = 3-8weeks
liquid = 1-3 weeks - then can used mycobacteria growth indicator tube using flurometric detection


What does PCR do in TB culturing?

amplifies nucleic acids, purifies and concetratesTB, sonicates to release henomic material and performs PCR, rapid result and detects rifampicin resistance using fluorensence


What test is used to detect re-activity of T cells for TB

tuberculin skin test looks for cell mediated immune defense


Difference between lepromatous and tuberculoid leprosy?

LL - lesions full of bacilli, poorly formed granulomatus, extensive skin lesions, Th2 response

TL - tissue hypersensitivity and granulomatas, causing tissue damage, immune reaction, Th1 response and CD4+ T cell response, producing IFN-Y and TNF-a


4 drugs for TB treatment?

rifampicin, isoniazid, pyrazinamid, ethambutol for 2 months followed by INH and RIF for 4 months


Examples of gram positive cocci?

staphylococci, streptococci, enterococci


Examples of gram negative cocci?

neisseria and moraxella