Mesnage - Bacterial Growth Flashcards
name 5 requirements for bacterial growth
temp, pH, osmotic pressure, nutrients and oxygen
what happens in bacteria when the temperature is too high, too low and at the optimum?
high: denaturation and collaps of cytoplasmic mem, thermal lysis (breaking of Van der Waals)
low: membrane gelling therefore transport so slow = no growth
optimum: maximum growth rate
name 4 groups of organisms based on their optimum temperature
psychrophile
mesophile
thermophile
extreme thermophile
how have psychrophiles adapted to cold temperatures?
increased membrane fluidity by increasing (poly)unsat fat content & methyl branched f/a's and decreasing acyl chain length antifreeze proteins (bind to ice crystals) cryprotectants eg trehalose and exopolysaccharides cold-adapted enzymes; increased no of helices, decreasing weak bonds and interdomain reactions (=flexibility)
how have thermophiles adapted to hot temperatures?
- genome protection: DNA binding proteins (stability), supercoils by DNA gyrases, increase of G&C bases (3 H-bonds)
- modification of mem composition: ether linked phospholipids and single lipid layer of glycerol tetraethers)
- thermostable proteins: h.phobic interactions and more ionic bonds
- thermostable chaperones eg thermosome in Pyrodictium abyssi
how do microbes adapt their metabolism to extremes of pH?
in high pH use Na+ for metabolism/coupling/flagella movement
in low pH use H+ for metabolism/coupling/flagella movement
why are some gram (+) bacteria more resistant to high salt levels?
thick peptidoglycan cell wall
how do microbes respond to osmotic stress?
regulation of H2O by passive diffusion and aquaporins. production of compatible solutes by mechanosensitive channels
halophiles require salt to function, how are these salt ions used?
stabilisation of S-layer glycoprotein by Na+
accumulation of K+ as a compatible source
which enzyme combination converts H2O2 to H2O?
catalase and peroxidase
which enzyme combinations convert O2- to H2O2 to H2O?
superoxidase dismutase + catalase
superoxidase reductase + catalase
name 3 toxic forms of oxygen
superoxide (O2-) hydrogen peroxide (H2O2) hydroxyl radical (OH•)
name the 5 types of MO based on whether they use O2 for respiration or not. also say which enzymes they use for respiration
obligate anaerobes: catalase + SOD obligate aerobes facultative aerobes: catalase + SOD microaerophiles anaerobes aerotolerant: SOD
name 3 methods of directly measuring bacterial growth
flow cytometry
visable counting
microscopic counts
name 3 methods of indirectly measuring bacterial growth
OD
dry weight
metabolic activity
list the limitations of using OD for measuring bacterial growth
need high cell density (>10^7 cells/ml)
can’t tell the difference between dead/live cells
OD values differ on organism type
does work on moulds/filamentous bacteria
name and describe the 4 stages of bac growth
lag: metabolism starts but no division
log: exponential increase in population
stationary: microbial death = microbial production
death: population is declining
name the 3 physical methods of antimicrobial control
heat
irradiation
filtration
define thermal death point
minimum temp at which organisms are killed in 10 min in a particular solution
define thermal death time
min time required to kill all bacteria in a particular liquid at a given temp
name 3 ways in which temp acts as antimicrobial control
moist heat (boiling water/autoclave) - 15min at 121 (pressure for spores) dry heat (oven) - direct flaming, incineration (>150 degrees for 2hrs) pasteurisation: mild heat <100/HTST - 72/UHT - 140
name the 2 methods of irradiation for antimicrobial control and describe them and their uses
ionising radiations: (X/gamma rays or e-) used in food and med/lab equipment/DNA damage by reactive oxygen species
non-ionising radiations: UV light used for surface decontamination/DNA damage by breaks
describe the types of filtration used in antimicrobial control and their applications
sterilises gases/liquids that will be damaged by heat
nucleopore (solids)/membrane filter (liquids)/depth filters (gases)
define bacteriostatic
stops bacteria from reproducing but doesnt kill them otherwise
define bactericidal
substance that kills bacteria
define bacteriolytic
dissolution/destruction of bacteria
name the 3 types of chemical used in antimicrobial control
sterilants: completely eliminating/destroying all forms MO incl. spores eg ethylene oxide (used for objects)
disinfectants: kill MOs but not necessarily endospores eg alcohol (used for objects)
antiseptics and germicides: inhibit growth/kill MOs eg handwash (used for tissues)
name the 3 methods of measuring MO activity and describe them
1) disc diffusion method: innoculate plate with liquid culture of test MO/discs containing antimicrobial agents are placed on the surface/incubate 24-48hrs/test organism shows susceptibility to some agents indicated by inhibition of bacterial growth around discs.
2) minimum inhibitory concentration (MIC): lowest conc of drug inhibiting the visible growth of a test organism after 24-48hr incubation (can use E-test which uses a strip of paper with a gradient of antimicrobial - look at lowest conc of antimicrobial that allows no growth)
3) Minimum bacterial conc (MBC): lowest conc of a drug killing >99.9% test organism after overnight incubation
name 5 chemical compounds that are used in antimicrobial control and describe how they work
1) phenolic compounds: local anaesthetic @ low conc/antibacterial @ high conc - disrupts cytoplasmic membranes/denatures proteins
2) alcohols: denatures proteins/lipid solvent = disrupted cytoplasmic membrane/active conc between 60-85%
3) aldehydes: alkylating agents; modify proteins & DNA, causes death/formalin/formaldehyde/glutaraldehyde
4) quaternary ammonium compounds (QUAT): interact with phospholipids @ cytoplasmic membrane (cationic detergents) eg didecyldimethylammonium chloride & benzalkonium chloride
5) halogen releasing agents
i) Cl-releasing agents: sodium hyperchlorite (bleach)
ii) iodine releasing agents: (iodine/iodophores) v powerful but stain target DNA & proteins -
what was Louis Pasteur’s contribution to antimicrobials?
Formally demonstrated the theory of germs
what was the purpose of Koch’s postulates?
name the 4 postulates
to determine the relationship between of microbe and disease
1) MO must be found in all those suffering the disease, not in healthy people
2) MO must be isolated from diseased organism and grown in pure culture
3) cultured MO should cause disease in a healthy organism
4) The MO must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent
which antibiotic did Rudolph Emmerich & Oscar Loew discover? how effective was it?
Pyocyanase (P. aeruginosa) shown to have antibacterial activity large-scale production and application to patients
effective: unstable, sporadic effectiveness and toxic
which antibiotic did Paul Ehrlich discover? how effective was it?
Salvarsan, a dye linked to arsenic (“magic bullet”)
Successful treatment of syphilis, replacing mercury compounds
effective: important toxicity, painful and debilitating side effects
which antibiotic did Alexander Fleming discover? how effective was it?
Penicillin
produced by a fungus
effective: yes
which antibiotic did Gerhard Domagk discover?
Prontosil red, dye tested in vitro/in vivo (systematic screen) eg sulfonamide
name 4 major classes of antibiotics
cell wall synthesis inhibitors
DNA-directed RNA polymerase inhibitors
Protein synthesis inhibitors
Lipid biosynthesis inhibitors
define nosocomial disease
a health care associated disease
give 2 reasons why antibiotic resistance leads to financial losses in health care systems
1) extra treatments are required (drugs are expensive)
2) people have to stay longer in hospital due to infections that are harder to treat
name the 5 causes of antibiotic resistance
1) antibiotic misuse in human therapeutics (eg treating viral infections by mistake/over the counter antibiotics in countries)
2) farming (treatment of animals with subtherapeutic doses)
3) agriculture (treating plant diseases)
4) aquaculture (fish given them - leach into water sources eg sea)
5) pets
define pharmacokinetics
what the body does to the antibiotics – study of the time course of drug absorption, distribution, metabolism and excretion
define pharmocodynamics
what the antibiotics do to the body – relationship between drug conc at the site of action and the resulting effect, including the time course and intensity of the therapeutic and adverse effects (want to find drug that works at efficient but safe concentration for a while)
what are the 3 properties of an ideal antibiotic?
1) TARGET - selective toxicity/inhibition of essential bacterial process
2) STABILITY & EFFECTIVENESS - pharmacokinetics and pharmacodynamics
3) LOW COST
describe the structure of peptidoglycan
Repeating units of GlcNAc (N-acetylglucosamine) and MurNAc (N-acetylmuramic acid). MurNAc has peptide chains that come off of it made up of D&L a/a’s. The 4th a/a on one peptide is linked to the 3rd a/a on the neighbouring peptide (this is achieved by D,D-transpeptidase).
describe the mechanism of action of the beta-lactam antibiotics
beta-lactams (eg penicillin) are structural homologues of D-ala-D-ala (repeat unit found in a MurNAc peptide). D-D-transpeptidase is a penicillin binding protein which are essential for bacterial cell wall synthesis.
PBPs (ie D,D-transpeptidases) bind D-ala-D-ala BUT in the presence of penicillin (a beta-lactam) the PBP can’t bind D-ala-D-ala meaning there is no crosslinking and bacterial cell wall synthesis is inhibited.
name the 4 methods of resistance to beta-lactams
Inactivation by beta-lactamases
Mutations of the target enzyme
Secretion of the antibiotic (gram -ve bacteria)
Modification of the synthetic pathway targeted by beta-lactams
describe the inactivation of beta-lactams by beta-lactamases
Beta-lactam ring in beta-lactam antibiotics undergoes nucleophilic attack by the serine residue on beta-lactamase
describe how mutations in D,D-transpeptidase leads to resistance to beta-lactams
Reduction of PBP affinity for beta-lactams – ‘’low affinity PBP’’
Overexpression of the PBP targeted by beta-lactams
describe how gram negative bacteria can be resistant to beta-lactams
the drug has to cross the outer membrane of the bacterium. some gram negative bacteria have transporters which actively pump the drug out of the bacterium
how do modifications in the synthetic pathway targeted by beta-lactams result in beta-lactam resistance?
instead of using D,D-transpeptidases (the structural homologue of beta-lactams) L,D-transpeptidases are used. This means that this enzyme doesn’t recognise penicillin
