BY270 Human Biochemistry and Metabolism - University of Brighton

Analysis of class data comparing antimicrobial sensitivity testing methods

Examine the class data provided for antibiotic sensitivity tests against Staphylococcus aureus and Escherichia coli. Perform the necessary calculations and then fill in this work sheet. Clear and concise answers to the questions on this sheet are all that is required. Please do not write up the answers in any other format.

Part A.

1. Calculate the mean diameter zone length and standard deviation for the Kirby-Bauer test zones, the Stokes' test zones and the Stoke's control zones for the two organisms. Present the results in two separate tables - one for each organism.

2. Compare the zone sizes obtained for the test organism in the two methods ( not the controls) using the t -test . Provide the results ONLY for any comparisons which show a statistically significant difference .

3. Which of the two methods appears to give the most reliable and reproducible results? Ignore the controls and clearly state your reasons on the basis of your calculations only.

Part B.

1. For the data from the Stokes' method, compare the average test and control zone sizes obtained during the class. Assuming that the control organism is resistant to the antibiotic in each case, clearly state whether each of the two organisms is sensitive or resistant to each of the antibiotics.

2. For the data from the Kirby-Bauer method, information obtained from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) is provided. These reading are the cut off points at which an organism is considered to the resistant to the antibiotic. Where possible, compare the average test zone size with the EUCAST information provided and clearly state whether each of the two organisms is sensitive or resistant to each of the antibiotics.

Part C.

1. Pseudomonas aeruginosa is on the World Health Organisation's Priority Pathogens list for the development of new antibiotics . Give one reason for this .

2. Drug resistance patterns for Staphylococcus aureus and Pseudomonas aeruginosa are monitored across 30 European countries through the European Antimicrobial Resistance Surveillance Network (EARS-Net). What is the most commonly reported drug resistant bacterial species identified through this scheme?