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Chapter 6 chosen as an appropriate method for investigating the efficacy of disinfectants against a pre-established biofilm on concrete surfaces. The results detailed in chapter 4 indicated that using the CBR, sodium hydroxide was effective at eradicating a 48 hour Salmonella biofilm for the two strains examined (S. Typhimurium SL1344 and S. Agona SL483). However, the same concentration of sodium hydroxide was not effective at eradicating all viable cells from a 168 hour biofilm of the same strains. Previous research has suggested that Salmonella biofilm density does not increase substantially over time and that the duration of development time does not affect treatment with disinfectant agents [56, 149]. Therefore, an important finding of this research was to demonstrate that age of biofilm may be important in studies investigating the efficacy of disinfectants against an established biofilm. When biofilm was formed using the CBR, there was a reduction in the number if viable cells directly after disinfection treatment with sodium hypochlorite and benzalkonium chloride. However, neither of the disinfectants was effective at eliminating all viable cells from the 48 hour or 168 hour biofilm. This highlights the need for careful consideration of content and concentration of disinfectants used for cleaning food processing environments that may be subject to contamination or presence of biofilm. As described in chapter 5, when all 13 strains were assessed using a microtitre plate method, the results indicated that none of the 3 disinfectants were effective at eliminating the biofilm from the surface of the plate post 48- or 168 hour biofilm formation. This result was unexpected considering that sodium hydroxide was effective against the same bacterial strains when examined in the CBR system after 48 hours incubation. Although there were differences in the test procedures, Page 203
Chapter 6 considering the same concentration of disinfectants and contact times were used in both it would be reasonable to expect a similar result. The variation in methods may have contributed to differences in the apparent efficacy of the disinfectants against the biofilm formed. After the biofilm was treated with sodium hydroxide the biofilm was removed from the surface through sonication and cells were enumerated by viable counts using the plate count method. Therefore one hypothesis is that cells were viable on coupons after sodium hydroxide exposure but were more vulnerable to the effects of sonication used to detach biofilm from the coupon. However this would not explain why no viable cells were recovered from a 2 nd set of coupons treated with sodium hydroxide that were re-incubated in broth post treatment (no sonication). The difference in efficacy of sodium hydroxide may also be biofilm substratum related. The biofilm was formed on concrete using the CBR whereas the microtitre plate consists on polystyrene plastic wells. Polystyrene as a substratum was not studied in the CBR although polycarbonate plastic was involved in the CBR studies. The results presented in chapters 2 and 3 of this thesis indicated that the biofilm substratum can influence the density of biofilm formed. Previous authors have also suggested that difference in surface structure such as surface roughness may allow for resistance to disinfectants [102]. Korber et al. found the presence of crevices in glass resulted in increased bacterial survival compared with a smooth glass surface. It is also possible that the conditions for media flow and shear stress on biofilm formed in the CBR impacted in some way to enhance the porosity of biofilm allowing more rapid penetration of sodium hydroxide solution to all parts of the biofilm and therefore more efficient killing. The reason why sodium hydroxide was effective against biofilm formed in the CBR but not against biofilm formed in microtitre plate remains Page 204
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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
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Chapter 2 The results displayed in
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Chapter 2 Table 2.7: Difference bet
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Chapter 2 Table 2.8: The mean log 1
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Chapter 2 Figure 2.7: Graph of the
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Chapter 2 also used “high” soni
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Chapter 2 2.8. Summary All 13 strai
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Chapter 3 3. Abstract It has been e
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Chapter 3 classified as persistent
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Chapter 3 was plated onto TSA for e
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Chapter 3 Figure 3.1: The mean log
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Chapter 3 Figure 3.3: SEM image of
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Chapter 3 Table 3.2: Difference bet
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Chapter 3 3.4.3. Intra-serovar vari
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Chapter 3 3.4.4. Strain variation i
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Chapter 3 3.4.5. The density of bio
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Chapter 3 3.5. Discussion As illust
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Chapter 3 As discussed in section 3
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Chapter 3 increased biofilm appeare
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Chapter 4 Examining the efficacy of
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Chapter 4 through laboratory based
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Chapter 4 acid and quaternary ammon
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Chapter 4 the surface the temperatu
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Chapter 4 availability of multiple
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Chapter 4 peracetic acid (100, 200,
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Chapter 4 As discussed previously,
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Chapter 4 Dey/Engley (Difco) neutra
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Chapter 4 sterilisation was achieve
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Chapter 4 IX. Aliquots of 100µl of
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Chapter 4 XV. XVI. XVII. XVIII. XIX
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Chapter 4 4.3. Results 4.3.1. Suspe
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Chapter 4 Table 4.3: Mean log 10 de
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Chapter 4 Benzalkonium chloride was
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Chapter 4 4.4. Discussion Suspensio
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Chapter 4 effective at eliminating
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Chapter 4 Surprisingly, Nguyen et a
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Chapter 4 though a contact time of
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Chapter 4 provide a more standardis
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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
Page 198 and 199: Chapter 5 5.3.4. The density of bio
Page 200 and 201: Chapter 5 Table 5.6: The difference
Page 202 and 203: Chapter 5 Table 5.7: The difference
Page 204 and 205: Chapter 5 Table 5.8: Summary of ass
Page 206 and 207: Chapter 5 interpretation therefore
Page 208 and 209: Chapter 5 measures of S. enterica b
Page 210 and 211: Chapter 5 cells peaks [165, 191]. D
Page 212 and 213: Chapter 5 5.5. Limitations of the s
Page 214 and 215: Chapter 6 Discussion of S. enterica
Page 216 and 217: Chapter 6 However, a number of auth
Page 218 and 219: Chapter 6 It is of interest to exam
Page 220 and 221: Chapter 6 were similar at 48 hours.
Page 222 and 223: Chapter 6 attributable to a small n
Page 226 and 227: Chapter 6 undetermined. However, th
Page 228 and 229: Chapter 6 reason for this may be du
Page 230 and 231: Chapter 6 Moreover, based on the re
Page 232 and 233: Chapter 6 responsible for increased
Page 234 and 235: Chapter 6 not fully capture the ran
Page 236 and 237: Chapter 6 However, the extent of bi
Page 238 and 239: Chapter 6 6.10. Conclusions and rec
Page 240 and 241: Chapter 6 studies may solve some of
Page 242 and 243: Bibliography Bibliography Page 221
Page 244 and 245: Bibliography 12. T. Takata, J.L., H
Page 246 and 247: Bibliography 29. Barker, J., M. Nae
Page 248 and 249: Bibliography 47. Threlfall, E.J., H
Page 250 and 251: Bibliography 65. CDC. Investigation
Page 252 and 253: Bibliography 83. Ledeboer, N., Frye
Page 254 and 255: Bibliography 100. Chia, T., Goulter
Page 256 and 257: Bibliography 117. Buckingham-Meyer,
Page 258 and 259: Bibliography 133. European Committe
Page 260 and 261: Bibliography Supernatant of a Hafni
Page 262 and 263: Bibliography 165. Díez-García, M.
Page 264 and 265: Bibliography cultivation of Staphyl
Page 266 and 267: Bibliography Compounds. 2012. Appli
Page 268 and 269: Bibliography 215. Buck, et al., A q
Page 270 and 271: Bibliography Canadian Journal of Ps
Page 272 and 273: Appendix 1 Appendix 1— List of Re
Page 274 and 275:
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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