Essay 1 Bio 205

1. Why isn't the Gram stain used on acid-fast bacteria? Explain your answer

A gram stain is a group of water based dyes which will readily stain the features of certain types of organisms with a typical peptidoglycan cell wall. The problem with acid fast bacteria is that they possess a very thick waxy lipid engrained into their cell wall that won't absorb any of the gram stain colors. Because the is little to no absorption of dye it would be very hard to see under the microscope.

2. Assume that after washing your hands, you leave ten bacteria cells on a new bar of soap. You then decide to do a plate count of the soap after it was left in the soap dish for 24 hours. You dilute 1g of the soap 1:106 and plate it on standard plate count agar. After 24 hours of incubation, there are 168 colonies. How many bacteria were on the soap? How did they get there?

The short answer to the question is that there were 168 million bacterial cells on the soap. I derived this data from the plate count calculation: number of colonies on the plate X the reciprocal of the dilution sample = number of bacteria per gram. In this example there were 168 colonies X 1,000,000 = 168 million bacteria per gram of soap. To figure out how many bacteria were on the soap after the initial 24 hours I made some assumptions. I assumed that the soap was not antibacterial soap thereby even being able to survive on the bar I also assumed that the bacterial growth would occur every two hours since the majority of bacteria go through binary fission every 1-3 hours. I made a table as listed below and filled it out as such.

Hour of Incubation number of bacteria hours of incubation number of bacteria

0

10

26

81920

2

20

28

163840

4

40

30

327680

6

80

32

655360

8

160

34

1310720

10

320

36

2621440

12

640

38

5242880

14

1280

40

10485760

16

2560

42

20971520

18

5120

44

41943040

20

10240

46...