"Thermo-Chemical Disinfection Process is Tested Using Three Cultures of Vegetative Bacteria" is a great example of a paper on infections. The inactivation curve is done by plotting temperature against time (Holger 2002, p. 47). The area under the curve is then determined using the trapezoid rule. Afterward the D – the value of the thermal processes can be determined (Yoshihiro, Eugene and Ludwig 2002, 250). For all the graphs, X-axis is the plot for temperature whereas y-axis represents time in seconds An inactivation curve of Staphylococcus aureus bacteria An inactivation curve of Streptococcus faecalis An inactivation curve of Escherichia coli The explanation for the shapes of the inactivation curves. For all the curves, the temperature increases as the time for inoculation increase at the start.
This is a clear indication that the bacteria survived the low temperatures. However, the situation changes after the temperature reaches 1 degree as the temperature increase but the time decrease for the Streptococcus faecalis and E. Coli while that of Staphylococcus aureus changes at 2-degree temperature. This indicates that the bacteria became inactive and succumbed to the high temperatures. Thus, the inactivation was a success.
The resistance to heat temperature observed at first especially for Staphylococcus aureus could be related to the ground beef although it was eliminated by increased temperature as time went on. Appropriate data to determine the D values* for each organism and reasons for the choice. The D - value is the time taken to reduce initial microbial numbers at a specific temperature (Seymour 2005, p. 85). The area under the curve is calculated to obtain the D - value. The shape of the curves then is determined using the trapezoid rule (Rikimaru 2002, 297).
The data most appropriate is that at 35oc because that is where maximum inactivation was achieved for all three bacteria. D= Log 10 N1 – Log 10 N0 / T2 – T1 Staphylococcus aureus At 35oc=-log10 5.8*101 - log10 4.0*106/ 5-1=1.8-6.6/4=1.2 Streptococcus faecalis At 30oc D= log10 4.6*101-log 10 1.2*106 /5-1 =1.6-6.0/ 4=1.4 Escherichia coli At 30ocD = log 10 9.6*101- log 10 4.2*106/5-1 =1.9-6.6 / 4 =1.175 (iv) The D values and comment briefly Staphylococcus aureus At 5oc = log 10 9.0*102 - log 10 5.0*106/ 5-1 =2.95-6.70/4= 0.937 At 20oc =log 10 1.5*102- log10 3.5*106 / 5-1=2.2-6.5/4=1.075 At 35oc=-log10 5.8*101 - log10 4.0*106/ 5-1=1.8-6.6/4=1.2 Streptococcus faecalis At 5oc D =log 10 8.2*102-log 10 3.2*106 / 5-1=2.9-6.5/4= 0.9 At 20oc D= log 10 3.0*101-log 10 2.3*106 /5-1=1.4-6.4/4 =1.25 At 30oc D= log10 4.6*101-log 10 1.2*106 /5-1 =1.6-6.0/ 4=1.4 Escherichia coli At 5oc D = log 10 4.4*102-log 10 5.6*106 /5-1 = 2.6-6.7/ 4 =1.025 At 20oc D = log10 1.2*102-log 10 4.6*106 /5-1 = 2-6 /4 =1.0 At 30ocD = log 10 9.6*101- log 10 4.2*106/5-1 =1.9-6.6 / 4 =1.175 D= Log 10 N1 – Log 10 N0/ T2 – T1 = log10 1.2*102-log 10 4.6*106/5-1= 2-6/ 4 = 1.0 The D – value obtained ranges from a value of one to two at maximum.
The D - value is the decimal reduction time, this is the time required at a certain temperature to kill 90% of the organisms being studied. From the values above, the inactivation was achieved very fast because the D-value shows an average of one. The D - value is used to measure how susceptible a bacterial population is to change in temperature (Doors 2011, p. 111-119). The spore log reduction (SLR) is the value required to reduce the bacterial population to a value of zero or one (Hao, Barbosa & Weiss 2010, p.
665). The D - value is normally calculated using the limited Holcomb- Spearman- Karber method (Gazso & Ponta 2005, p. 169).
Doors, G 2011, Kinetics and mechanism of bacterial inactivation by ultra sound waves and sonoprotective effect of milk components, Journal of Food Science, 76 (2): 111-119
Gazso, L., & Ponta, C 2005, Radiation inactivation of bioterrorism agents, IOS Press.
Hao, F., Gustavo, B., & Jochen, W 2010, ultrasound technologies for rood and bioprocessing.
Holger, F., & Rabenar, P 2002, a challenge for science, medicine, and the public health system, Pennsylvania, PA: Karger publishers.
Marimargaret, R., & Jack, Y 2007, Sterilization technology for the health care facility, Pennsylvania, PA: Karger publishers.
Mullan, W 2007, Calculator for determining the F value of a thermal process, retrieved from
http://www.dairyscience.info/calculators-models/134-d-value-thermal-process.html Rikimaru, H 2002, trends in high pressure bioscience and biotechnology, New York, NY: Elsevier publication.
Seymour, S 2002, Disinfection, sterilization, and preservation, New York, NY: Wilkins publication.
Yoshihiro, T., Harry, E. S., Horst, L 2002, Biological systems under extreme conditions:
structure and function, Springer publications.
Juneja, V., Huang, L., & Marks, H 2001 Approaches for modeling thermal inactivation of
foodborne pathogens, American Chemical Society, 931: 235- 251.