20 7 Bacteria are becoming increasingly resistant to antibiotics. Controlling the spread of antibiotic resistance is necessary. (a) Many types of bacteria are resistant to penicillin and tetracycline. (i) Which row of the table shows the part of a bacterial cell affected by these antibiotics? (1) Penicillin Tetracycline A cell wall cell wall B cell wall ribosome C ribosome cell wall D ribosome ribosome (ii) Which row of the table describes the action of penicillin and tetracycline? (1) Penicillin Tetracycline A bactericidal bactericidal B bactericidal bacteriostatic C bacteriostatic bactericidal D bacteriostatic bacteriostatic Turn over 21 (b) One method of controlling the spread of antibiotic resistance is to avoid unnecessary prescriptions of antibiotics. The table shows some illnesses and whether a prescription for antibiotics is recommended. Illness Antibiotic prescription Bronchitis may be recommended Ear infection may be recommended Influenza not recommended Fluid in the ear not recommended Strep throat recommended Urinary tract infection recommended Explain why these recommendations could reduce the spread of antibiotic resistance. (2) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... 22 (c) In an investigation, E.coli bacteria were isolated from animals reared for food and from some wild animals. The mean percentage of the E. coli isolated from each type of animal that were resistant to different types of antibiotics was determined. The table shows the results of this investigation, where n is the number of each type of animal. Antibiotic Mean percentage of resistant E.coli isolated from animals reared for food (%) Mean percentage of resistant E.coli isolated from wild animals (%) Broiler chicken n = 45 Village chicken n = 45 Cattle n = 12 Bat n = 13 Rodent n = 35 Ampicillin 50.00 8.89 8.33 0.00 8.57 Cephalothin 14.29 8.89 8.33 20.00 14.58 Chloramphenicol 46.43 0.00 0.00 0.00 0.00 Neomycin 50.00 2.22 25.00 0.00 5.71 Tetracycline 95.86 55.56 25.00 0.00 2.86 (i) Calculate the ratio of tetracycline-resistant E.coli in all the chickens to tetracycline-resistant E.coli in cattle. (2) Answer ................................................................ (ii) There was a total of 2 × 108 E.coli isolated from cattle and 6 × 109 E.coli isolated from rodents. Calculate how many more E.coli are resistant to cephalothin in rodents than in cattle. (2) Answer ................................................................ Turn over 23 (iii) Antibiotics can be added to animal feed. It is thought this use of antibiotics has contributed to the spread of antibiotic resistance. Evaluate the extent to which the results of this investigation support this idea. 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(Total for Question 7 = 12 marks)