Download Effects of pH on the Growth of Staphylococcus aureus

Effects of pH on the Growth of
Staphylococcus aureus, Streptococcus
bovis, and Escherichia coli species
Pam Shelton
Biology Undergraduate, Health Science Concentration
Tennessee Technological University
Introduction/Background
 Staphylococcus aureus
• “responsible for a wide range of human
disease, including septicemia; endocarditis
and pneumonia; and wound, bone and joint
infection (Feil et al 2003).”
• “associated with nosocomial infections
(Caiazza and O’Toole 2003).”
Introduction (cont)
 Streptococcus bovis (Group D)
• Group B Streptococcus is “the most common
cause of bacterial infection in the newborn
(Curtis et al 2003).”
• Streptococcus bovis (Group D Streptococcus)
is important to understand because it is
“capable of causing fulminant neonatal sepsis
or meningitis that is indistinguishable clinically
from that caused by group B streptococcus
(Gavin et al 2003).”
Introduction (cont)
 Escherichia coli
• Associated with food products
• “presence of feces on meat products is a
primary source of foodborne pathogens, such
as Escherichia coli 0157:H7 (Ashby 2003).”
Introduction (cont)
 All cause disease if present in large
amounts or immune system is
compromised
 Learning about growth allows for
development of ways to limit growth
Objective/Hypothesis
 Hypothesis: Various bacteria require
different pH levels in order to grow properly.


each organism will have an optimal pH
specific for that particular organism.
most organism will have similar ranges in
which they prefer to grow.
 Objective: To determine the pH range and
optimal pH for the growth of Staphylococcus
aureus, Streptococcus bovis, and Escherichia
coli
Materials and Methods
 Set of tubes containing 3 mL Tryptic Soy
Broth (TSB) were treated with varying
amounts of HCl or NaOH to adjust pH from 1
to 14
•
•
pH measured with pH paper
Similar to method used by Kelly et al (2003)
 Tubes were inoculated with one of the
organisms and incubated at 36 °C for 48 hrs
 Amount of growth was measured and
recorded
Materials and Methods
 Another set of tubes were prepared with the
same method except with a more narrow pH
range
 Tubes were inoculated and incubated with the
previous method
 Three trials of the procedure were done for
each organism
•
Temperature of incubation, incubation time, and
broth composition (except pH) were constant in
each trial
Materials and Methods
Results and Discussion
 S. aureus preferred a pH range of 4.0 – 9.25 in trials 1and 2 and
4.5 – 9.25 in trial 3
 Optimal pH of S. aureus was around pH 7
 This agrees, for the most part, with the work previously done
Feeherry et al (2003).
•
“S. aureus growth occurs in the pH range 4.5 to 9.3 (7.2 optimum).”
 There is slight disagreement with the lowest (4.0) and highest
(9.25) values of the pH range found in this experiment. This is
probably due to experimental error.
•
•
The pH paper used is not as accurate as a pH meter
It can be assumed that in trial 1 and 2, the range is within the
expected 4.5 – 9.3.
Results and Discussion
Staphylococcus growth
2.5
amount of growth
2
1.5
1
0.5
0
1
2
3
4
4.25
4.5
4.75
5
6
7
8
pH
9
9.25
9.5
9.75
10
11
12
13
14
Results and Discussion
 S. bovis only grew very close to pH 7
 This agrees Chamkha et al (2003)
 “strain B7…grew optimally at pH 7”
Results and Discussion
Streptococcus growth
2.5
amount of growth
2
1.5
1
0.5
0
1
2
3
4
5
6
6.25
6.5
6.75
7
7.25
pH
7.5
7.75
8
9
10
11
12
13
14
Results and Discussion
 E. coli grew equally well in the range of pH 7 to pH 9.
 These results disagree with the previous work
 E. coli is capable of growing in a “pH range of 2.5 – 9.3
(Vinneras et al 2003).”
 even with experimental error taken into consideration, these
results are too extreme to go unnoticed
 Explanation:
 To survive in extremely acidic conditions, E. coli has evolved
three adaptive acid resistance strategies to maintain internal
pH (Gong et al 2003).”
 “all strains succumbed to pH 2.5 in the absence of arginine
(Gong et al 2003).”
 This growth broth did not contain arginine. So, it was
incapable of acid tolerance.
Results and Discussion
Escherichia coli growth
2.5
amount of growth
2
1.5
1
0.5
0
1
2
3
4
5
6
6.25
6.5
6.75
7
8
ph
9
9.25
9.5
9.75
10
11
12
13
14
Results and Discussion
 As expected in my hypothesis, the growth of
microorganisms is effected by the pH of their surrounding
environment.
 I also expected:


most organism would have similar ranges in which they
prefer to grow.
each organism would have an optimal pH specific for that
particular organism.
 This was disproved through the results of this experiment.
 ranges varied greatly depending on the particular organism
 the optimal pH was closely centered around 7 for most
organisms
Summary and Conclusions
 pH effects growth of microorganisms
 Organisms have a wide variety of
preferred pH ranges
 Most organisms optimal pH is centered
closely around 7
 Information about growth of
microorganisms can help prevent the
spread of disease
Questions?