Microbiology Flashcards
Define ‘virulence’
Quality of being extremely poisonous, infectious or damaging OR the extent to which a disease or toxin possess this quality
Briefly describe gram negative bacteria
On staining appear red/pink; have an outer layer followed by thin peptidoglycan layer in the cell wall
Briefly describe gram positive bacteria
On staining appear violet/purple and have thick peptidoglycan cell wall
What are cocci bacteria?
Spherical appearance
What are bacilli bacteria?
Cylindrical rod appearance
What are spirochaetes bacteria?
Curved/spiral appearance
How can you distinguish between staphylococci and streptococci?
Staphylococci are catalase positive and streptococci are catalase negative
What is a virus?
Single cell with no organelles, has either a DNA or RNA strand (not both) and a protein capsid which surrounds and protects the genome
What are fungi?
Organism with mainly chitin cell wall, which have similar ultrastructure to eukaryotes but with 80S ribosomes
What are protozoa?
Unicellular eukaryotes (parasites) with 80s ribosomes
What are helminths?
Multicellular eukaryotes without a backbone or exoskeleton
What is a parasite?
Any living form which is dependent on other living things for survival and causing some damage to the host
Describe the structure of bacteria
Single circular chromosome is free in the cytoplasm (and sometimes plasmids), have 70s ribosomes, no mitochondria though or any membrane-based organelles
What is peptidoglycan?
A cross-linked complex of polysaccharides and peptides
What are pili?
Hair-like proteins which allow transfer of DNA between bacteria
What are fimbriae?
Hair-like proteins which interacts with cell surface receptors to allow binding
Describe the mechanisms by which bacteria adhere to the body
1) Stick to mucosa via Van der Waals at portal of entry
2) Proteins on microbe surface recognise host carbohydrates and bind OR pili/fimbriae attach
3) Surface molecules of microbe bind to complementary surface receptors on certain cells of the host tissue
What is a biofilm?
Accumulation of bacteria on a cell surface due to van der waals forces (begins as slime and proliferation forms biofilm)
What is viral antigenic shift?
Change in antigens on the surface of viruses to evade established immune responses
How do viruses harm the host?
Induce histological cell changes in certain areas (cause giant cells), cause cells to enter apoptosis, incorporate nucleic acid into genome which can cause cancers
What does catalase do?
Breaks down hydrogen peroxide to water and oxygen
What are exotoxins?
Toxins produced by gram negative and positive bacteria to help bacterial spread, lyse cells and block protein synthesis and cell function
What are endotoxins?
Toxins produced only by gram negative bacteria and cause an over-reaction of the immune response leading to host cell damage
How do bacteria persist in the human body despite immunological defences?
Bind the host antibody the wrong way –> antibody neutralisation, disrupt complement binding and produce antiphagocytic enzymes, detoxifies harmful substances such as free radicals and hydrogen peroxide and produces heat shock proteins to prevent denaturation at increased temperatures
Outline the course of viral infection
primary replication –> systemic spread –> secondary replication in susceptible organs following spread
Describe the different modes of virus transmission
Direct (horizontal) - host to host contact
Indirect (horizontal) - through food, water etc.
Transplacental (vertical)
Perinatal (vertical)
Breast milk (vertical)
Define incidence
Occurrence, rate or frequency of a disease
Define prevalence
The proportion of a population with the condition
What is meant by ‘reproduction number (RO)’?
The number of transmissions per source of virus
What is an antibiotic?
A natural antimicrobial substance produced by a microorganism
What is an antimicrobial?
A type of antibiotic that is synthesised chemically, or modified from natural resources
What are some bacterial targets for drugs?
Cell wall synthesis, bacterial protein synthesis, nucleic acid metabolism and bacterial cell membrane
Describe and name two antimicrobials that affect the bacterial cell wall
Beta lactams - inhibit cell wall synthesis by binding to transpeptidases which cross-like in the cell wall,, leading to an unsupported cell –> cell ruptures –> bacterial death
Glycopeptides - inhibit cell wall synthesis in gram positive bacteria by binding to cell wall precursors
Describe and name three antimicrobials that inhibit protein synthesis
Aminoglycerides - bind to 30s subunit of ribosome –> disrupts structure –> prevents translation initiation
Tetracyclines - bind 30s subunit (bacterial ribosome) –> prevents AA amino acid incorporation –> incomplete, non-functional proteins
Macrolides - bind to 50s subunit –> prevent translocation of protein along the ribosome
Describe and name two antimicrobials that inhibit nucleic synthesis
Quinolones - inhibit DNA synthesis
Rifampicin - inhibits RNA polymerase
Outline the infectious cycle of a virus
attachment and particle entry –> decoding and uncoating of genome –> translation of viral mRNA by host ribosomes –> genome replication –> assembly and release of particles containing genome
What is a viral capsid?
Protein shell of a virus
What are capsomeres?
One of the individual protein units which make up the capsil (outer coat)
Define ‘genome’
Complete set of genes present in a cell or organism
What is a nucleocapsid?
Capsid of a virus with the enclosed nucleic acid
Describe the function of viron proteins
Assemble protective shell, bind to specific external receptors on host cells, transmit signals to induce genome uncoating, induces fusion with host cell membrane, transports genome to appropriate site within host cell
What are RNA viruses?
Viruses containing RNA, if it has a positive polarity it can be transcribed immediately, if it has a negative polarity it has to be converted to positive before it can be translated
What are antivirals?
Drugs which target viral proteins, predominantly viral enzymes
Describe the influenza virus
Orthomyxocirus has an envelope, single stranded RNA, 8 segmented genes and surface spikes of haemagluttinin protein and neuraminidase
What does antigenic shift and drift of the influenza A virus involve, and what can this cause?
Antigenic shift involves the shift in haemagluttinin and can lead to a pandemic
Antigenic drift involves changes to the virus due to host to host transmission (evolution) and this leads to epidemics and involves haemagluttinin and neuraminidase proteins
Describe how amanitidine and rimantidine work to treat flu
Inhibits the viral M2 protein which decreases viral H+ influx and this inhibits viral uncoating and inhibits the coating process as a new viron aims to leave (by binding to haemagluttinin)
Describe how neuraminidase inhibitors work to treat flu
Stops neuraminidase from cleaving sialic acid from glycoconjugate and therefore stops viron release, aggregation of virons and also increases virus inactivation conducted by respiratory mucus
Describe the HIV virus
Single stranded RNA present, reverse transcriptase, integrasem protease
Describe the treatment of HIV
HAART (highly active anti-retroviral therapy) where drugs include inhibitors of reverse transcriptase, integrase, protease and fusion and entry modalities
Describe the hepatitis C virus
An enveloped virus with a single-strand of RNA
What is an emergent virus?
When a virus has adapted and emerged as a new disease/strain
What is a resurgent virus?
When a virus increases in prevalence one more after a period of little activity or occurrence
Define ‘serotype’
The type of organism, determined by its constituent antigens
