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94 Cards in this Set

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What are the names for different arrangements and numbers of flagella?

Monotrichous - single flagellum

Lophotrichous - multiple, at same spot

Amphitrichous- single flagellum on opposite ends

Peritrichous - project in all directions, E.Coli

What is VBNC?

Viable but non-culturable

Some die, releasing nutrients

What is specific growth rate?

meangrowth rate

the number ofgenerations per unit time

u = 1/g

What is the doubling time?

Mean generation time
Time for all cells to double
g = 1/u

What is a mesophile?

Optimum growth between 20-45oC

What are osmophiles?

Able to live in high osmotic pressures - high sugar

What are halophiles?

Thrive in high salt

What are psychrophiles?

Optimum 15-20. OK at 0

What are psychrotrophs?

Optimum room temp.

OK at 5

What are thermophiles?
Grow 50-80
Survive in higher temps.

How are ROS generated?

O2 + e− → O2·−
O2·− + e− + 2H+ → H2O2
H2O2 + e− + H+ → H2O + ·OH

How are ROS removed?

Superoxide Dismutase (SOD)2O2·− + 2H+→ H2O2+ O2

Catalase 2H2O2 → 2H2O + O2

How can species be separated based on oxygen-tolerance?

Presence of SOD and Catalase - anaerobes have neither

Where does it grow in anaerobic tube? At top, aerobic, etc.

What are microaerophiles?

Grow best in low 2-10% O2

Helicobacter pylori

What is convalescence?

Time spent recovering from an illness

What are microbes that cause disease in healthy hosts called?


What are microbes that cause disease in immuno-compromised hosts called?

Opportunistic pathogens

e.g. S. aureus

What is ID50?

Numberof cells administered that result in disease for 50 % of the population

Measure of pathogenicity

What is the name for bacteria circulating in blood?


What is the name for toxins circulating in blood?


What is septicemia?

Whenthe concentration of the bloodborneagent increases to a life-threatening level

What is type III secretion system?

Appendage found in several Gram-negative bacteria.

Used as a sensory probe to detect present of host and secrete proteins to help infect them.

What are M cells?

Gut epithelial cells

Transport antigens from gut lumen by trancytosis to basolateral side - APCs

Subverted by Salmonella.

What are invasins?


enzymesthat break down host tissues

Staphylokinase - activates plasminogen to form plasmin - digests fibrin clots. Cleaves IgG and C3b - inhibits phagocytosis

What are Siderophores

small, high-affinity iron chelating compounds

Main classes: hydroxamatesand catechols

How can lysozyme action be overcome?

S.aureus protein OatA - acetylates NAM

How does coagulase aid evasion?

Reacts with prothrombin in blood - causes clotting by fibrinogen to fibrin

What factors affect transmission?

Stability in environment
Environmental conditions
Host factors - normal flora

What is vertical transmission?

From parents to offspring
Through sperm, ovum, placenta, milk and blood

What is antigenic shift?

Exchange of homologous genes between different strains of a virus
Pathogen not recognised by host

What is antigenic drift?

natural mutation over time of known strains of influenza

Reduced response by immune system

What is epidemiology the study of?

patterns, causes, and effects of health and disease conditions in defined populations.

What is an endemic?

The habitual presence of a disease withina given geographic area

What is an epidermic?

•The occurrence in a community or regionof a group of illnesses of similar nature, clearly in excess of normalexpectancy, and derived from a common or from a propagated source

What is a pandemic?

•A worldwide epidemic

What is infectivity?

thepropensityfor transmission

What is pathogenicity?

• the propensityfor an agent to cause disease or clinical symptoms.

Canbe measured byID50

What is virulence?

•Thepropensity for an agent to cause severe disease.

Measured by the case fatality ratio,can also be examined in the lab as Lethal Dose 50 (LD50) –the number of cells administered that result in deathfor 50 % of the population

What is an incubation period?

•Theperiod between exposure to the agent and onset of infection (with symptoms orsigns of infection)

What is a A noncommunicable disease?

non-infectious and non-transmissible among people

iron uptake

siderophores are excreted intothe medium and then the iron-siderophorecomplexis takenupby specificreceptors

onceinside the cell they arecleaved torelease the iron molecule

iron acquisition - other methods

somebacteria can also import siderophores made by other bacteria

some bacteria produce toxins only when iron concentrations are low - killhuman cells,releasing stored iron for uptake

iron abstinence

replacedits small number of iron-sulphur clusterenzymes with those that use manganese instead

What are biofilms?

Name a gram-negative pathogen with a propensity to form biofilms

theyexist within an extracellular polysaccharide slime thathelps glue them together and bind them to different surfaces

Pseudomonas aeruginosa

Advantage of biofilms

biofilmsoffer protection from phagocytes, disinfectants and antibiotics

motile bacteria recognize asurface and aggregate together more readily than non-motilebacteria

Mechanism for switching surface proteins

1. genetic recombination - RecA-mediatedstrand exchange

2. DNA inversion - occurs between two inverted repeatsites which the recombinase binds

3. strand slippage

Natural transformation advantages

DNA for:

Genetic diversity, repair and as food

What is the source of DNA for transformation

free DNA is abundant in theenvironment as it is released by dead organisms

some bacteria secrete DNA or lysetheir cells

mechanismof DNA uptake

setof competence (com) genes are involved in transformationCompetenceis a specialised physiological state where bacteria become able to take up DNA

Which enzyme improves accuracy of DNA replication?

proof-reading (3’-5’exonuclease) activity

Polymerase involved

DNAPIII - alpha subunit with Pol, e - proofreading

DNAPI - both

What can defects in MMR encourage?

horizontal gene transfer

blocks interspecies recombinationbecause mismatches in heteroduplex DNA are recognised and the exchange aborted by MutHLS

Are RNA viruses stable?

No - RNA copying enzymes lack proof-reading capacity

Retroviruses replication

e.g. HIV. Convert RNA genome into DNA for integration.

Can + or - function as mRNA?

+strand (mRNA) functions as mRNA

–strand (complementary to mRNA) must be copied to make mRNA

HIV genetic information conversions

RNAgenome into dsDNA


DNA strand synthesised first and then RNA degraded by RNaseH before second DNA strandmade for transport to the nucleus

What is HIVreverse transcriptase extremely tolerant of?

non-standard base pairs

What is the source of individual variation in retroviruses?

env gene

Example of a HIV drug

AZT - nucleoside drug inhibitor

Resembles thymidine but blocks DNA synthesis

N3 rather than 3' OH

Resistance to AZT

block binding of the AZT nucleoside in the polymerase active site

Different oxygen enzymes in organisms

SOD Catalase

Obligate aerobe Yes Yes

Facultative anaerobe Yes Yes

Aerotolerant anaerobe Yes No

Strict anaerobe No No

Microaerophile Yes Maybe

Biofilm steps

Cell deposition

cell absorption


Cell-to-cell signalling and onset of exopolymer production

Convective and diffusive transport of O2 and nutrients

Replication and growth

Secretion of polysaccharide matrix

Detachment, erosion and sloughing

What do biofilms contain?


Oxygen-nutrient gradient

Cell-cell signals

positively charger antimicrobial binds to negatively charged slime

Three phases response to infection

Innate -

Early-induced innate - recruit of effector cells, recognition of PAMPs

Adaptive - Ag to lymphoid tissue, T/B cell recognition - clonal expansion and differentiation

innate immunity

. Lysozymes. Cleavesβ1-4 glycosidic

Lactoferrin - sequesters free Fe, binds LPS and produces peroxides - disrupts membrane permeability and causes lysis

Cathelicidins -•Destroysbacterial membranes in phagosomes,following fusion with lysosomes of macrophage.•Insertinto bacterial membrane

Defensins -•Inmucus, produced by epithelial cells and phagocytic cell.

•Amphipathicproteins that cause pores to form in bacterial membranes. Ion leaves and waterfollows down the osmotic gradient

Complement activation

•ClassicalPathway - Antigen:antibody complexes detected on pathogen surface

•MB-LectionPathway - Mannose-bindingprotein (a lectin) is upregulated in acute phase(inflammation). Binds bacterial cell walls, viral envelopes, antigen-antibodycomplexes

•AlternativePathway - Complement proteins(like C3b) bind directly to repetitive pathogen surface structures such as LPS

MAC, opsonisation, phagocyte recruitment

How is infection detected?

PRR (e.g. TLR) recognise PAMPs

•TLR3 –binds dsRNA
•TLR4– binds LPS
TLR5 - flagellin

Role of phagocytic cells in innate immunity

Respiratory burst

Or oxygen independent; charged proteinsthat damage the membrane, lysozyme, lactoferrin, proteases and hydrolytic enzymes

Extracellular ; nitric oxideis released and kills nearby microbes

NK cells

•NKcells contains granules in the cytoplasm, which contain

–Perforin;makes pore in cells

–Proteases, aka granzyme

cells marked by MHCI

•Cancerousand virus-infected cells lose MHCI, and are killed by NK cells

•If acell is coated with antibodies, NK cells recognise this cell and kill it by antibody-dependentcell-mediatedcytoxicity (ADCC)

Induced innate response

TLR activation triggers cytokine and chemokine production

Explain the Inflammatory Response

bacteria trigger macrophages to release cytokines and chemokines

Vasodilation and increased vascular permeabiltiy

Inflammatory cell migrate into tissue - release inflammatory mediators

What does the innate immune system result in that activates adaptive immunity?

–Lymphcontaining antigen and antigen-presenting cells

–Complementfragments on microbial surfaces

–Releaseof cytokines and chemokines thatactivate T lymphocytes

Adaptive immunity - T cell-mediated

–Recognizeantigen on surface of dendritic cells–ActivatedT cells travel to the thymus to mature


Adaptive immunity - B cell antibody response

•Whenantigen is detected

–Bcell can act as an APC to activate T cells

–Ifa corresponding Th cell is available, B cell matures in BM anddifferentiates

•Plasmacells–Makeantibodies against antigens

•MemoryB cells–Readyto initiate rapid response

Consequences of antibody binding


complement fixation




Overview of adaptive

(>96 h)


Transport of antigen to lymphoidtissue

Recognition by B and T cells

Clonal expansion and differentiation

Removal of infectious agent

Example of microbes entering through skin q

S. aureus

Gram pos

C. tetani - gram-pos.

Which organism has type III secretion system?

Gram-negative bacteria.

sensory probe to detect the presence of eukaryotic organisms and secrete proteins that help the bacteria infect them.

Where aretype III secretion systems encoded?


Mucosa entry site - which cells are involved?

How is this function subverted?

–Gutepithelia contains microfold (M)cells

roleof M cells is to transport antigens from the gut lumen by transcytosis

–antigenfrom one side of the cell to the other, where it is provided toAPCs on the basolateral side

•Salmonellainduce ruffling in M cells

respiratorytract entry

- Adhesins

- Inhibitingciliaryactivity


–Activatesplasminogen to form the protease plasmin, which digests fibrin clots and allowsmovement of bacterial cells

–CleavesIgG andcomplement component C3b, inhibiting phagocytosis


–Hyaluronicacid is a non-sulfated glycosaminoglycan distributed widely throughoutconnective, epithelial and neural tissues


How is CathelicidinLL-37 cleaved?

metalloproteinase secreted from S.aureus


Coagulasereacts with prothrombin in the blood

cause sblood to clot by converting fibrinogen to fibrin

What does superantigen do?

–Bridge the MHC class II protein onantigen presenting cells with the T cell receptor on the surface of T cells

What is α-haemolysin?

cytolytic toxin



targetsmembranes rich in this lipid

How can O2 be removed in growing chamber

2H2 + O2 ---> 2H2O

Palladium pellets catalyse reaction

Indole test;


Kirby-Bauer Method

•Canbe used to determine whether the bacterium is “susceptible”, “intermediate”, or“resistant” to the tested antibacterial

Methods for MIC

Etest strips


Ccore is dehydrated - enables heat resistance, long-term dormancy

Small acid-soluble spore proteins - protect DNA from UV radiation + carbon source

Producing spores enables bacteria to endure extreme stress and spread easily

Is TB gram-positive or neg