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Chapter 4 Surprisingly, Nguyen et al. found that 50 ppm sodium chlorite (equivalent to 50mg/L or 0.005%) was an effective disinfectant which achieved an >8 log 10 reduction in the number of viable cells removed from stainless steel and acrylic surfaces against a 24 hour S. Typhimurium. A ≥4 log 10 reduction in cells was achieved against a 48- and 96- hours biofilm on an acrylic surface using a petri-dish with a bacterial suspension in order to achieve biofilm development. As a result, the extensive differences in biofilm model may provide reason for the vast difference in results achieved [217] . Ramesh and colleagues also found that 250ppm (250mg/L) sodium hypochlorite was an effective disinfectant which resulted in a mean log 10 reduction of 6.26 after 1 minute contact time with a Salmonella biofilm formed on galvanised stainless steel over 4 days (96 hours) [150]. Ramesh et al. reported that after 2 minutes exposure 2 of the 13 disinfectants tested resulted no cells detected recovered from the surface. The two successful disinfectants were a 0.05% concentration of sodium hypochlorite (500mg/L or 500ppm) and a 1% concentration of alkaline peroxide [150].This is in complete contrast the results of this chapter that found even after a contact time of 90 minutes the same concentration was not effective at reducing the number of biofilm cells from the 48 hour or 168 hour biofilm. The large difference in log 10 reduction may be due to dissimilar biofilm conditions, substratum or biofilm removal methods. Ramesh et al. used a static biofilm model (microtiter plate) with stainless steel coupons and surface swabbing for bacterial removal. However, the use of swabbing or scraping may not be an accurate representation of a meaningful log 10 reduction unless it is confirmed that all viable cells are removed from the surface. SEM analysis was performed to visualise the intact biofilm, however the author gave no indication that SEM was used to confirm complete removal of the treated biofilm. Moreover, some disinfectants may contain other compounds such as gluteraldehyde which Page 145
Chapter 4 may prevent removal of the bacteria from the surfaces via swabbing, despite the cells remaining viable [221]. Therefore, it is possible that the use of disinfectant products with more than one active agent may result in an under estimation of viable cells remaining [221]. In addition, the high log 10 reduction of cells may also be a reflection of the biofilm substratum. As demonstrated in chapter one and two of this thesis, concrete is associated with a more dense biofilm compared with other surfaces such as stainless steel. The propensity to support dense biofilm formation may be due to increased surface roughness which may also increase resistance to disinfectant agents. Joseph et al. assessed the log 10 reduction in viable Salmonella cells in biofilm (48 hour development) after treatment with sodium hypochlorite (10, 20, 50 and 100 ppm) and iodophor for 5 intervals of 5-35 minutes [71]. The results from the research suggested that inactivation of S. Weltevreden biofilm with hypochlorite (no cells detected) was faster on cement and steel than on plastic (15 min vs. 20 minutes). Joseph et al. also reported that exposure for 20 minutes to 100ppm to hypochlorite (100mg/L or 0.01% solution) resulted in no viable cells detected [71]. This does not correlate with the findings reported in this chapter. However, the use of cotton swabs to remove the biofilm was used in this research without providing details of confirmation of complete removal via microscopy or other methods may cast some doubt on the confidence that can be placed in their conclusions. 4.4.3. The log 10 reduction achieved by benzalkonium chloride The results presented in this chapter indicated that benzalkonium chloride was the least effective disinfectant against a 48 hour and 7 day Salmonella biofilm. The most substantial reduction (1 log 10 reduction) was achieved Page 146
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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
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 148 and 149: Chapter 4 Dey/Engley (Difco) neutra
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 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
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
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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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