Efect o antibiotics on bacteria afect o penicillin on micrococcus mi crococcus luteus which is Gram +ve, and varied the strength o the penicillin disks. I had to do several repeats at each strength,
Aim: My aim is to investigate the efect o diferent concentrations o antiiotics on the growth o acteria. !he aim o this investigation is to "nd out what efect out o two antiiotics, penicillin and streptomycin has on the growth and multiplication o two diferent species o acteria. !he two diferent types o acteria we will e using are #$coli #$coli and micrococcus luteus. %ypothesis: I predict that as the concentration o the antiiotics increases the acteria growth decreases &ull %ypothesis: !here is no link etween the concentration concentration o antiiotics and the efects it has on the growth growth o the acteria !heory: !heory: Antiiotics work in ' ways, which are listed elow: (. )ell Memrane *isruption $ !his involves making the cell ully permeale which results in sustances moving into it causing it to urst and so kills the acteria . Inhiiting &ucleic Acid ynthesis $ !his method doesn-t kill the acteria of ut keeps the growth level static. !he acteria isn-t ale to replicate its *&A and so no inary "ssion occurs, causing the growth level to ecome static . Inhiiting )ell /all ynthesis $ !his is where an antiiotic inhiits the en0yme re1uired to orm cross links within the cell wall and as a result the acteria looses its structure and is unale to unction properly . '. Inhiiting m2&A !ranslation !ranslation $ !his is where the !ranslation !ranslation part o protein synthesis is inhiited y inding across the acterial riosome meaning m eaning proteins and en0ymes the acteria it re1uires isn-t made and so dies. !hereore, it is logical logical to presume that the higher higher the concentration o antiiotics the more more efective it will e in wiping out, and killing the acteria. 3ecause the more antiiotic molecules there is in the solution means there is a higher chance that these antiiotic molecules will come upon a acterial cell and disrupt the cell and kill it . o in conclusion it is logical to state that the higher the concentration o antiiotic the more m ore efective the antiiotic will e at killing o the acteria. *ependant 4ariale: The zone of inhibition (of killed bacteria) in mm (+/- 0.5mm). Measured with a ruler. !here
are a numer o diferent ways o measuring the efectiveness o the antiiotics ut I will e using the techni1ue o measuring the 0one o inhiition. !his method provides data which can easily e measured. Independent 4ariale 5or me to ully determine the efectiveness o the antiiotic there will have to e an independent variale, which is the concentration o the antiiotic. o I have decided that I am going to use a wide degree o concentrations o antiiotic and the gap etween the concentrations needs to e kept to a minimum cause the optimum concentration may e let out i the gaps are too ig. Also ecause the results will e analy0ed y the spearman-s rank correlation I will use 6 data values. Apparatus: 7 5our sterilised Agar plates, 7 Glass spreader, 7 Masking tape, 7 /a8 /a8 pencil, 7 9a roll, 7 A eaker with 6; alcohol, 7 #$ coli <)ulture= 7 Micrococcus luteus
enicillin >enicillin
2esults: !he ollowing is a tale to show how large the 0one o inhiition or each antiiotic is in mm. !he >etri dishes were let or ' hours at a temperature o ?). <+@$.?)=. *iferent antiiotics Bone o inhiition@ mm <+@$ .mm=
2isk Assessment Glassware: *angerous i glass is roken. 9ow risk and perectly sae i used properly. *o not try to pick up pieces o roken glass with your hands, especially rom a wet sink. 2eport all reakages immediately so that staf can deal with it. Inorm all students o any roken glass so they move away rom it and avoid inCury. Inorm staf so they can deal with it. eek medical attention. Trip Hazards: 3ags, coats, chairs. 9ow risk i ags, coats and chairs are put or stored in a sae area. >ut aggage etc well under enches, away rom the working area or store at the ront o la. Inorm staf and seek medical attention. %elp the person i possile. Bunsen Burner: )ould urn the skin and can set clothing on "re. 9ow risk i used correctly and saely. >ull lever down when 3unsen urner is not in use, this reduces the intensity o the Dame so contact o Dame with oCects is less likely, wear saety glasses and la coat. 3reak "re alarm, seek medical attention, and wash with cold water. Escherichia coli: )an cause ood poisoning, diarrhoea and inections can e atal. 9ow risk ecause low concentration is used. 9ow risk i ollowed the method careully. /ear saety goggles, gloves and la coat. !ell staf and seek medical help immediately. Bacillus subtilis: )an cause severe eye inections 9ow risk ecause low concentration is used. 9ow risk i ollowed the method careully. /ear saety goggles, gloves and la coat. !ell staf and seek medical help immediately. Controlling variables: •
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!o e sure that only the antiiotic is responsile or the clear 0one that will e present in the >etri dish all other variales must e kept constant. I will do this y: 4olume $ !he total volume o the acteria, ufer and water solution will e Ecm .!his will eliminate the volume ecoming a variale which may give erroneous results. urace area o Agar $ I will keep this constant y using >etri dishes all the same si0es. !his will prevent surace area ecoming a variale cause having a higher surace area may afect the rate at which the acteria are killed. Also the same to keep the si0e o clear 0one to e measured the same urace area o /ells $ I will keep this at mm, to prevent this ecoming a variale. !emperature $ all dishes are in the same incuator. Amount o nutrient availale or acterial growth $ use the same amount o agar or each. #.coli was used or oth dishes to keep the strain o acteria same. terilised syringes, orceps and loop are used or oth dishes, so unwanted contamination is avoided.
