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Chapter 4 Dey/Engley (Difco) neutralization broth has also been recommended by the ASTM standard E2871-12 [125]. Sodium thiosulfate (chemical formula Na 2 S 2 O 3 ) is commonly used for neutralizing disinfectants containing iodine or chlorine derivatives [71, 117, 213]. Sodium thiosulfate acts as a neutralizing agent by reacting with the free chlorine in a solution and releasing the components as harmless molecules such as water (H 2 0) and sodium chloride (NaCl) [214]. Dey/Engley neutralization broth inhibits bacterial growth. Dey/Engley has previously been used to neutralize sodium hydroxide and benzalkonium chloride [134, 149]. Dey/Engley contains a mixture of neutralizing agents including sodium thioglycolate, sodium thiosulfate, sodium bisulfite, polysorbate 80, lecithin (soybean extract) that allows broad spectrum efficacy against disinfectant agents [215]. 4.1.7. Use of test controls The inclusion of test controls (coupons or test surfaces) is crucial in order to validate the efficacy of any antimicrobial or disinfectant under examination. The use of additional coupons (not in contact with disinfectants or neutralizing agent) confirms that any reduction in cells enumerated is independent of any other chemical agents present in the media or other factors such as decline in viable cells over extended time. Hamilton et al. also highlighted the importance of using controls in order to validate harvesting and disaggregation steps of biofilm cells for accurate enumeration of any cell reported antimicrobial or disinfectant effect [183]. This is supported by the data presented in earlier chapters of this thesis demonstrating that completeness of biofilm removal from surfaces is dependent on strain and the age of the biofilm. Page 127
Chapter 4 4.1.8. Duration of contact time According to the CEN standards a contact time between the bacterial suspension and the test disinfectant should not be more than 5 minutes. However the CEN standards only examine efficacy of disinfectant products against surface adherent bacteria. The time allowed for disinfectant agents in contact with biofilm may be a crucial component contributing to complete destruction of the biofilm cells. Møretrø used a contact time of 5 minutes for the biofilm and suspension assay [134]. Gehan et al. used contact times of 10, 30 and 60 minutes in order to assess the efficacy of disinfectants in a suspension test with a set of organisms (P. aeruginosa, E. coli, S. aureus, S. Typhimurium, A. fumigates, Fusarium spp.) against quaternary ammonium compound and sodium chloride [216]. Parks et al. found an increased contact time (50 minutes) was necessary to significantly reduce the number of viable cells of S. Typhimurium attached to stainless steel and polyvinyl plastic surfaces using aerosolized sodium hypochlorite [207]. Nguyen et al., used contact times of 0.5, 1, 2, 3, 5, and 7 minutes to evaluate the efficacy of quaternary ammonium compounds, sodium hypochlorite and a solution of peroxyacetic acid/organic acids S. Typhimurium biofilm [217]. Therefore, in order to gain a better insight into the time needed for effective disinfection of an established biofilm, contact times of 10, 45 and 90 minutes were evaluated in this work. 4.1.9. Survival of Salmonella cells after contact with disinfectant agents. Although the accepted criteria for disinfectant efficacy are defined in terms of quantitative log 10 reduction in cell counts in practical terms the persistence of even very low residual numbers of viable Salmonella is likely to result in regrowth over time given appropriate conditions. Therefore a very marked reduction in mean log 10 density or even reduction below the level of enumeration is not sufficient to ensure that the environment is Salmonella free. To assess if biofilm eradication was complete (if Page 128
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Salmonella enterica - biofilm forma
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Table of Contents Page Number 1.16.
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Table of Contents Page Number 4.1.2
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Table of Contents Page Number 6.8.4
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List of Abbreviations Table Page Nu
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List of Abbreviations List of Abbre
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Summary of Content Summary of Conte
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“To show your true ability is alw
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Acknowledgements ever met, Fiona th
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Acknowledgements This Ph.D. thesis
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Chapter 1 1.1. Salmonella Salmonell
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Chapter 1 may impose enormous costs
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Chapter 1 cracks or penetration of
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Chapter 1 detected by agglutination
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Chapter 1 become colonized with >10
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Chapter 1 antigens [z27],[z45] [1].
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Chapter 1 S. Agona has also been im
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Chapter 1 isolated from undercooked
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Chapter 1 The S. Typhimurium strain
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Chapter 1 ecosystem with the use of
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Chapter 1 [82]. Previous research h
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Chapter 1 to genes involved in flag
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Chapter 1 observation has also been
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Chapter 1 [119] and flow cell react
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Chapter 1 based disinfectant) the s
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Chapter 1 formation of two strains
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Chapter 1 shield the S. Agona cells
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Chapter 1 Key Objectives of this st
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Chapter 2 2. Abstract Food-borne pa
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Chapter 2 indicated that there may
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Chapter 2 taken from industrial set
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Chapter 2 2.1.4. CDC Biofilm Reacto
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Chapter 2 can be performed without
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Chapter 2 To summarise, previous au
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Chapter 2 2.3. Methods for examinin
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Chapter 2 and the biofilm formed th
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Chapter 2 2.4. Statistical Analysis
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Chapter 2 Table 2.1: Strain charact
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Chapter 2 XII. The gas port and med
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Chapter 2 II. Primary fixative cons
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Chapter 2 IX. Once the conditions w
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Chapter 2 Figure 2.1: Image of CBR
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Chapter 2 2.6. Results 2.6.1. Asses
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Chapter 2 2.6.3. SEM Analysis of su
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Chapter 2 Figure 2.6: Complete remo
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Chapter 2 2.6.5. Mean log 10 densit
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Chapter 2 2.6.6. Mean log 10 densit
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Chapter 2 Table 2.5: Mean log 10 de
Page 98 and 99: Chapter 2 The results displayed in
Page 100 and 101: Chapter 2 Table 2.7: Difference bet
Page 102 and 103: Chapter 2 Table 2.8: The mean log 1
Page 104 and 105: Chapter 2 Figure 2.7: Graph of the
Page 106 and 107: Chapter 2 also used “high” soni
Page 108 and 109: Chapter 2 2.8. Summary All 13 strai
Page 110 and 111: Chapter 3 3. Abstract It has been e
Page 112 and 113: Chapter 3 classified as persistent
Page 114 and 115: Chapter 3 was plated onto TSA for e
Page 116 and 117: Chapter 3 Figure 3.1: The mean log
Page 118 and 119: Chapter 3 Figure 3.3: SEM image of
Page 120 and 121: Chapter 3 Table 3.2: Difference bet
Page 122 and 123: Chapter 3 3.4.3. Intra-serovar vari
Page 124 and 125: Chapter 3 3.4.4. Strain variation i
Page 126 and 127: Chapter 3 3.4.5. The density of bio
Page 128 and 129: Chapter 3 3.5. Discussion As illust
Page 130 and 131: Chapter 3 As discussed in section 3
Page 132 and 133: Chapter 3 increased biofilm appeare
Page 134 and 135: Chapter 4 Examining the efficacy of
Page 136 and 137: Chapter 4 through laboratory based
Page 138 and 139: Chapter 4 acid and quaternary ammon
Page 140 and 141: Chapter 4 the surface the temperatu
Page 142 and 143: Chapter 4 availability of multiple
Page 144 and 145: Chapter 4 peracetic acid (100, 200,
Page 146 and 147: Chapter 4 As discussed previously,
Page 150 and 151: Chapter 4 sterilisation was achieve
Page 152 and 153: Chapter 4 IX. Aliquots of 100µl of
Page 154 and 155: Chapter 4 XV. XVI. XVII. XVIII. XIX
Page 156 and 157: Chapter 4 4.3. Results 4.3.1. Suspe
Page 158 and 159: Chapter 4 Table 4.3: Mean log 10 de
Page 160 and 161: Chapter 4 Benzalkonium chloride was
Page 162 and 163: Chapter 4 4.4. Discussion Suspensio
Page 164 and 165: Chapter 4 effective at eliminating
Page 166 and 167: Chapter 4 Surprisingly, Nguyen et a
Page 168 and 169: Chapter 4 though a contact time of
Page 170 and 171: Chapter 4 provide a more standardis
Page 172 and 173: Chapter 4 hours instead of the stan
Page 174 and 175: Chapter 5 5. Abstract Examining bio
Page 176 and 177: Chapter 5 dry and rough (bdar) morp
Page 178 and 179: Chapter 5 absence of curli and cell
Page 180 and 181: Chapter 5 studies such as the micro
Page 182 and 183: Chapter 5 discussed in chapter 4. T
Page 184 and 185: Chapter 5 5.2. Methods 5.2.1. Colon
Page 186 and 187: Chapter 5 XIII. XIV. XV. XVI. XVII.
Page 188 and 189: Chapter 5 XVI. XVII. XVIII. XIX. XX
Page 190 and 191: Chapter 5 5.3.2. Repeatability of m
Page 192 and 193: Chapter 5 Figure 5.2: Stained biofi
Page 194 and 195: Chapter 5 was formed at room temper
Page 196 and 197: Chapter 5 Table 5.3: The density of
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Chapter 5 5.3.4. The density of bio
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Chapter 5 Table 5.6: The difference
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Chapter 5 Table 5.7: The difference
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Chapter 5 Table 5.8: Summary of ass
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Chapter 5 interpretation therefore
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Chapter 5 measures of S. enterica b
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Chapter 5 cells peaks [165, 191]. D
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Chapter 5 5.5. Limitations of the s
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Chapter 6 Discussion of S. enterica
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Chapter 6 However, a number of auth
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Chapter 6 It is of interest to exam
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Chapter 6 were similar at 48 hours.
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Chapter 6 attributable to a small n
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Chapter 6 chosen as an appropriate
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Chapter 6 undetermined. However, th
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Chapter 6 reason for this may be du
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Chapter 6 Moreover, based on the re
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Chapter 6 responsible for increased
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Chapter 6 not fully capture the ran
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Chapter 6 However, the extent of bi
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Chapter 6 6.10. Conclusions and rec
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Chapter 6 studies may solve some of
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Bibliography Bibliography Page 221
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Bibliography 12. T. Takata, J.L., H
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Bibliography 29. Barker, J., M. Nae
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Bibliography 47. Threlfall, E.J., H
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Bibliography 65. CDC. Investigation
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Bibliography 83. Ledeboer, N., Frye
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Bibliography 100. Chia, T., Goulter
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Bibliography 117. Buckingham-Meyer,
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Bibliography 133. European Committe
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Bibliography Supernatant of a Hafni
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Bibliography 165. Díez-García, M.
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Bibliography cultivation of Staphyl
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Bibliography Compounds. 2012. Appli
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Bibliography 215. Buck, et al., A q
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Bibliography Canadian Journal of Ps
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Appendix 1 Appendix 1— List of Re
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Appendix 1 Appendix 1 - List of Equ
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Appendix 2 Colour index High outlie
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Appendix 3 Appendix 3-Figure 2: PFG
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Appendix 4 Poster Presentation Envi
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