E Faecalis Lab Report

In the experiment involving varying pH levels, E. faecalis, S. epidermidis, L. lactis, and L. casei were subjected to different pH levels and then were allowed to incubate in order to determine the minimum, maximum, and optimum pH levels for growth of specific bacterial species. It was found that lower pH levels between 2 and 4 inhibited or promoted little to no growth for E. faecalis, S. epidermidis, and L. casei. It is evident that these bacteria were resistant to alkaline environments, however, it should be noted that certain mechanisms must have been acquired or involved in maintaining equilibrium within the bacterial cell. High alkalinity generally leads to physiological problems within microbes including the disruption of plasma membrane
epidermidis and E. coli were subjected to varying NaCl concentrations in order to test for the minimum and optimum salinities of individual bacterial species. Looking at the growth of E. coli under NaCl concentrations of 2, 5, 10, and 15%, the data collected showed optimal growth at lower concentrations, more specifically at 2%. Growth gradually decreased until no growth was present which occurred at NaCl concentrations of 15%. The data collected is representative of data observed from previous experiments conducted in literature. For example, an experiment performed by Jasna Hrenovic and Tomislav Ivankovic, found similar results such that the limiting concentrations of NaCl for multiplication and bacterial growth of E. coli was at 5%, with maximum growth established around 2% NaCl (Hrenovic and Ivankovic 2009). Growth of E. coli was reported to have tolerance levels up to 8% NaCl concentrations (Hrenovic and Ivankovic 2009). The data collected in table 2 shows limited growth at NaCl concentrations of 10% which could be caused by errors in mixing of each culture or improper transferring of the bacteria to its designated broth tube. In contrast, S. epidermidis seemed to grow optimally around 5% NaCl concentration, and then shows moderate growth at 10% NaCl with very little growth after this point. The data collected is similar to data found in literature however, it was found that S. epidermidis grows optimally around a concentration of 6
coli, B. subtilis, B. stearothermophilus, and M. cryophilis was analyzed and the cardinal temperatures for each individual species was determined. Analyzing the growth of E. coli, it was found that the optimal growth temperature was at 39°C with moderate growth between the range of 20 to 30°C and no growth at 60°C. According to this data the results suggest the bacteria to categorized as a mesophile (bacteria adapted to temperatures between 15 to 40°C). On the other hand, B. stearothermophilus grew only at higher temperatures, 60°C in particular, with no growth below this point, classifying this bacteria as a thermophile (around 40 to 80°C). In contrast, M. cryophilis only grew at lower temperatures, between 10 to 20°C, which makes this bacteria a psychrophile (adapted to temperatures below 20°C). B. subtilis showed temperature characteristics of a psychrotroph, growing specifically between temperature ranges of 10 to 30°C with no growth at higher temperatures. When bacterial cells are subjected to higher temperatures, different components of the bacterial cell including phospholipids, nucleic acids, and proteins become denatured resulting in the disruption of tertiary structures (Nadwell 1999). In comparison, when temperatures decrease below the optimal temperature, the affinity for substrates of bacterial cells also decreases, due to the hardening of lipids within the membrane (Nadwell 1999). This further causes a