Bacteria

Year 1 - Semester 1

types of infectious pathogen

prions, viruses, bacteria, fungi, parasites

virus

a fragment of genetic code within a protective shell of proteins or membrane which uses host cell transcription and translation machinery for replication

mycoplasma

a type of bacteria that doesn’t have a cell wall (pleomorphic) making it the smallest replicating organism, lives off live or dead organisms (parasitic/saprophytic) as they require external supply of cholesterol, amino acids and fatty acids

typical structures found in prokaryotic cells

cell wall, cell membrane, cytoplasm, nuclear region

functions of bacterial plasma membrane

transport of nutrients, energy generation, secretion, synthesis of peptidoglycan, contains regulatory proteins

peptidoglycan

a surface protein in bacterial plasma membranes that penicillin will bind to

main groups of bacteria based on cell wall structure

gram-positive and gram-negative

gram-positive bacteria

a group of bacteria characterized by a thick cell wall made of peptidoglycan that retains a violet color after being stained with crystal violet in the Gram stain test

gram-negative bacteria

bacteria with a distinctive cell envelope with a thin peptidoglycan layer situated between an inner cytoplasmic membrane and an outer membrane (so peptidoglycan isn’t outer layer) that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation

peptidoglycan

a polysaccharide backbone made of a polymer of two sugar derivatives which are linked by peptide bridges

acid-fast organisms

microbes that have a waxy cell wall that protects them from acids, alkalis and digestion in phagocytes and impedes the entry of molecules (bacteria contain mycolic acid)

pyrogenic

causes an inflammatory response resulting in a fever

endotoxins

lipopolysaccharides found in the outer membrane of gram-negative bacteria that can trigger a severe immune response, they are released when bacteria die

structures found on the surface of bacterial cells

flagella, fimbriae, pili, capsules

bacterial chemotaxis

bacteria sense a stimulus and switch flagella on and move towards the stimulus so that they can make use of it

what are flagella made of?

protein subunits called flagellin

fimbriae and pili

hair-like structures on the surface of bacterial cells which allow attachment to surfaces, bacterial conjugation and twitching motility

true bacterial capsule

a discrete detectable layer of polysaccharides deposited outside the cell wall

bacterial slime layer

a less discrete structure or matrix which embeds bacterial cells

how is bacterial genotypic classification determined?

entire genome, ribosomal rRNA sequences, DNA hybridisation, multilocus sequence typing

how is phenotypic bacterial classification determined?

cell morphology, physical characteristics, biochemical reactions, culture properties, oxygen requirements

function of porin proteins in bacterial cells

they form pores on the surface of the outer cell membrane which allows nutrinets to diffuse into the periplasmic space from outside

phases of bacterial growth

lag, exponential growth, stationary, decline

lag phase of bacterial growth

after inoculation metabolism is required to acquire essential constituents in order to divide

exponential phase of bacterial growth

binary fission causes exponential increase

stationary phase of bacterial growth

essential nutrients are depleted and toxic metabolic products accumulate in the media, competition causes some bacteria to die off

decline phase of bacterial growth

old cells die rapidly followed by young

ways to count bacteria

microscopic counting, colony counting, opacity, turbidity

bacterial enumeration via microscopic counting

an arbitrary number of fields are counted from a direct fixed smear within a counting chamber

bacterial enumeration via colony counting

serial dilution are made and a fixed volume is spread on each plate and incubated, the number of colonies is counted

heterotroph

an organism that uses pre-formed organic compounds for energy

autotroph

an organism that uses carbon dioxide for energy

requirements for bacterial nutrition

large quantities of carbon and nitrogen, peptones in culture media usually provide essential nutrients and C/N, phosphates are essential for nucleic acid production, sulphur is needed in amino acid production, Ca2+, Fe3+, Mg2+ and K+ are important enzyme co-factors

microbial responses to nutritional deficiency

extracellular molecules collect nutrients, cells enter semi-starvation state, sporulation and resting cells

defined culture medium

a medium that has known amounts of known chemicals

complex culture medium

a medium whose exact chemical composition is unknown

selective culture medium

a medium that limits the growth of unwanted microbes or alows the growth of desired ones

differential culture medium

a medium that enables differentiation between different microbes

factors that affect bacterial growth

temperature, pH, moisture, atmospheric composition, osmotic pressure

mesophilic

an organism that grows at moderate temperature between 20-45 degrees

microaerophiles

organisms that require oxygen but only in small amounts

aerobes

organisms that use oxygen in metabolism

anaerobes

organisms that can growth without oxygen

types of anaerobes

obligate, aerotolerant, facultative

obligate anaerobes

organisms that are killed or inhibited by oxygen

aerotolerant anaerobes

organisms that don’t use oxygen but are not killed by it

facultative anaerobes

organisms that can grow with or without oxygen

why are microorganisms preserved in labs?

to allow vaccine production, for research and teaching

how are microorganisms preserved in a lab?

freezing in liquid nitrogen or with a cryoprotectant or desiccation (freeze drying and storing as ampoules in the dark)

aseptic technique

a technique that prevents microbial contamination of cultures or wounds

sepsis

microbial contamination

asepsis

absence of significant contamination

antimicrobial chemicals

substances expected to destroy pathogens by not to achieve sterilisation

disinfectant

an antimicrobial used on inanimate objects

antiseptic

an antimicrobial used on living tissue

disinfection

the destruction of microorganisms by direct exposure to chemical or physical agents

sterilisation

destroying all microbial life on lab and surgical procedures

antisepsis

when chemicals are applied to body surfaces to destroy/inhibit pathogens

bacteriostatic

something that inhibits bacterial reproduction

bactericidal

something that kills bacteria

factors that affect the efficacy of microbial inactivation

type of microbe, life cycle phase, presence of organic matter, number of microbes present, exposure time, working concentration

physical methods for microbial inactivation

refrigeration, freezing, boiling, vacuum packing, pasteurisation, filtration, radiation

flash pasteurisation

heating a substance to 72 degrees for 15 seconds (high temp short time)

ultra high temp pasteurisation

heating a substance to 140 degrees for 1 second, sterilises product but can affect taste

thermal death point

lowest temperature at which all microbes in a liquid suspension will be killed in 10 mins

thermal death time

minimum length of time in which all bacterial will be killed at a given temperature

decimal reduction time

time taken for 90% of bacteria at a given temperature to be killed

what is the most resistant type of microbe?

prions

what is the least resistant type of microbe?

viruses with lipid envelopes

autoclave

steaming under pressure to improve sterilisation as steam can directly contact material

features of moist heat sterilisation

denatures proteins, steam can reach higher temperature so more effective, steam must directly contact material to sterilise it

dry heat sterilisation methods

direct flaming, incineration, hot-air sterilisation

is filtration effective at removing viruses?

no, because they are too small

types of radiation used for sterilisation

gamma radiation and ultraviolet light

chemical methods for microbial inactivation

disinfectants, detergents, acidification, sulfur dioxide, increasing osmotic pressure

how does increasing osmotic pressure prevent food spoilage?

water is drawn out of cells which causes them to become dehydrates or die

how does sulphur dioxide prevent food spoilage?

acts as a reductant and antibacterial

acidic-anionic detergents

detergents where the anion reacts with the plasma membrane of cells

cationic detergents

detergents made of quaternary ammonium compounds which are strongly bactericidal

types of disinfectants

surfactants, phenols/phenolics, halogens, alcohols, heavy metals

features of phenol disinfectants

skin irritant, strong odour, acts as local anaesthetic

features of phenolic disinfectants

effective against gram-positive bacteria, they destroy plasma membranes and denature proteins

features of chlorine disinfectants

oxidising agents, widely used, form bleach with water, fair sporicidal activity, used in pools and drinking water

features of iodine disinfectants

more reactive and germicidal, alters protein synthesis and membranes, wound antiseptic when mixed with alcohol, form detergent complexes with organic molecules

features of alcohol disinfectants

killd bacteria and fungi but not endospores or naked viruses, denature proteins and disrupt plasma membranes, evaporate so don’t leave a residue, used to mechanically wip microbes off skin, not good for open wounds as they coagulate proteins

features of heavy metal disinfectants

toxic as metal ions combine why sulfhydryl groups to denature proteins

when are silver disinfectants used?

to protect infants against eye infections

when are copper disinfectants used?

to kill algae in pools and fish tanks and in dairy cow footbaths

pathogen

a microbe that causes harm to the host

commensal

a microbe that does not cause harm and is considered part of the normal flora

saprophyte

a microorganism that feeds on and decomposes dead organic material

infection

the colonisation of a host by microorganisms that have the potential to cause disease

pathogenesis of a disease

the biological mechanisms that lead to the diseased state

virulence

the relative ability of a pathogen to cause disease in the host

opportunistic pathogen

a microorganism that can be part of the normal flora but may be harmful if it moves from one part of the body to another

strict pathogen

a microorganism always associated with disease

2 main parts of bacterial pathogenesis

bacterial virulence factors that damage/alter host cells and tissues, host response

steps of bacterial pathogenesis

1. exposure to pathogen

2. pathogen adheres to skin or mucosa

3. pathogen invades through epithelium

4. pathogen colonises, grows and produces virulence factors

5. further growth of pathogen at original and distal sites

6. further interaction of virulence factor with host molecules causes damage

features of a pathogen that determines pathogenesis

virulence, environmental stability, route of entry, infective dose, tissue tropism, susceptibility to host defence, interaction with other pathogens

features of host that determine pathogenesis

species, breed, age, sex, genetic factors, physiological factors, immune competence