### Problem 3

### Antimicrobial Drug Action

The undermentioned experiment was performed to analyze the consequence of antibiotics on the growing and viability of Staphylococcus aureus.

Samples ( 10ml ) from a civilization of S. aureus turning exponentially in Mueller-Hinton stock were pipette into flasks incorporating synercid, or synercid and Achromycin, at the minimal concentration required to suppress growing and incubation was continued at 37°C. A farther sample served as an antibiotic-free control. Aliquots were taken at intervals for finding of civilization denseness by an optical method and for finding of feasible cell Numberss by thining the civilization with unfertile saline and plating extra 0.2ml samples onto the surface of Mueller-Hinton agar. After 24 h incubation at 37°C the figure of settlements on each home base was counted and the consequences obtained are recorded in the Table below.

During the 50 min incubation the optical denseness of the antibiotic-free control suspension of bacteriums increased by 75 % while the optical densenesss of the other civilizations remained changeless. Synercid is a mixture of two constituents, quinupristin and dalfopristin in the ratio of 30:70 ( w/w ) . The minimal growing repressive concentrations of quinupristin and dalfopristin are 30 and 20 µg/ml severally. When quinupristin, dalfopristin and Achromycin were added separately to civilizations of S. aureus at their minimal growing repressive concentrations, there was no alteration in feasible cell Numberss during 50 min incubation.

### Time ( min )

0

10

10

10

25

25

25

25

50

50

50

50

50

Dilution factor

105

104

105

106

103

104

105

106

102

103

104

105

106

Antibiotic

Conc. µg/ml

Colonies counteda

None

210

192

215

226

25

17

272

250

33

30

334

342

40

30

Synercid

1

136

147

10

15

415

426

40

45

90

100

10

9

Synercid + Achromycin

1

2

272

290

22

35

635

650

60

70

4

10

a Where no Numberss are given the check was non carried out.

### Questions

### 1. What decisions can be drawn from these informations on the effects of the antibiotics on S.aureus?

Synercid is known to be bactericidal to most Gram positive bacteriums including S. aureus, but the single compounds quinupristin and dalfopristin are bacteriostatic. This shows that the combination of the two antibiotics has a interactive consequence and is much more effectual used in combination. Tetracycline is besides bacteriostatic ; this is the ground why the figure of feasible cells during the 50 minute incubation did non alter when the three antibiotics were added individually. The information shows that utilizing antibiotic combination of synercid and Achromycin in this illustration is of greater benefit than utilizing synercid entirely. At 105 dilution factor, the figure of settlements observed with the antibiotic synercid lessenings by around 15 crease by the 50 minute grade. The usage of synercid and Achromycin in combination evidently has a more powerful consequence on the bacteriums than that of synercid entirely, demoing a unit of ammunition a 40 fold lessening in settlement Numberss, this shows that synercid and Achromycin have a interactive consequence.

### 2. What is the average coevals clip in proceedingss of the beings turning in the antibiotic free control civilization?

Work out the mean of the 2 vaules of the civilization incorporating no antibiotic.

### Time ( min )

0

10

10

10

25

25

25

25

50

50

50

50

50

Dilution factor

105

104

105

106

103

104

105

106

102

103

104

105

106

Antibiotic

Conc. µg/ml

Colonies counteda

None

201

220.5

21

261

31.5

338

35

Synercid

1

141.5

12.5

420.5

42.5

95

9.5

Synercid + Achromycin

1

2

281

28.5

642.5

65

7

Then work out the settlement organizing units utilizing:

Number of settlements x dilution of home base / volume of incoculum

201 ten 105/0.2 = 10.05 ten 107 cfu

220 ten 105/0.2 = 11 ten 107 cfu

21 ten 106/0.2 = 10.05 ten 107 cfu

261 ten 105/0.2 = 13.05 ten 107 cfu

31.5 ten 106/0.2 = 15.75 ten 107 cfu

338 ten 105/0.2 = 16.9 ten 107 cfu

35 ten 106/0.2 = 17.5 ten 107 cfu

### Then log these consequences.

Log 10.05 x 107 = 8.002

Log 11 x 107 = 8.04

Log 10.05 x 107 = 8.002

Log 13.05 x 107 = 8.116

Log 15.75 x 107 = 8.2

Log 16.9 x 107 = 8.228

Log 17.5 x 107 = 8.24

These consequences can now be plotted on a graph against clip.

To be able to work out the average coevals clip, the specific growing rate must be determined. This is achieved utilizing the undermentioned equation:

µ= ( loge Nt – loge No ) /t

Where Nt = figure at clip t=t, No= figure at clip t=0 and µ= specific growing rate.

So,

µ= 8.228-8.002/50= 0.00452 h-1

Average coevals clip is calculated by the undermentioned equation:

T= 0.693/µ

Where T = intend coevals clip and µ = specific growing rate

So,

T= 0.693/0.00452 = 153.3 mins

### Mentions

Strohl, WR ( 1997 ) . Biotechnology of Antibiotics. 2nd edition. Marcel Dekker. New York.

Scotton, PG, Rigoli, R & A ; Vaglia, A ( 2002 ) . Combination of Quinupristin/Dalfopristin and Glycopeptidein Severe Methicillin-Resistant Staphylococcal Infections Failing Previous Glycopeptide Regimens. Infection. 30 ( 3 ) : 161-163.

Hugo, WB & A ; Russell, AD, ( 1998 ) . Pharmaceutical microbiology. Blackwell scientific discipline, UK.