Flashcards in Microbiology Deck (260)
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