Pam Shelton Biology Undergraduate, Health Science Concentration Tennessee Technological University

1. 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

2. 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).”

3. Introduction (cont) • Streptococcus bovis (Group D) • Group B Streptococcusis “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).”

4. 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).”

5. 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

6. 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

7. 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

8. 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

9. Materials and Methods

10. 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.

11. Results and Discussion

12. 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”

13. Results and Discussion

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.

15. Results and Discussion

16. 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

17. 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

18. Questions?