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Chapter 4 4.4. Discussion Suspension tests were performed in order to determine the minimum inhibitory concentration (MIC) of the disinfectant agents. The MIC is used to determine the concentration of disinfectants that inhibits visible bacterial growth. The purpose of this was to establish the efficacy of the disinfectants chosen against the strains studied in planktonic form. The results of the suspensions tests described Table 4.2 indicate that concentrations of 250mg/L (sodium hypochlorite), 0.5M (sodium hydroxide) and 0.01% (benzalkonium chloride) were sufficient to inhibit visible bacterial growth. If disinfectant products are examined solely using a suspension test method such as the ASTM standard 1040 [131] it is possible that while bacterial cells may be inhibited using low concentration of disinfectant agents the agents may not be effective if the bacterial cells have formed a biofilm. Notwithstanding the susceptibility of the strain in planktonic form, sodium hypochlorite and benzalkonium chloride (at a concentration twofold higher than the MIC) were not effective at eliminating all biofilm developed after 48 hours period and none of the 3 agents effective in eliminating the 168 hour biofilm (SL1344 and SL483) after contact times of 10, 45 and 90 minutes. Møretrø et al. also reported that the MIC of disinfectant agents such as 0.01-0.005% benzalkonium chloride was effective at eliminating bacterial growth in a suspension test however the same concentration was not effective at eliminating all bacterial cells from an established biofilm [134]. 4.4.1. The log 10 reduction achieved by sodium hydroxide Sodium hydroxide was the most effective disinfectant of all 3 examined. When used to treat a 48 hour biofilm no viable cells were detected after 10 Page 141
Chapter 4 minutes of contact. In addition no cells were recovered when the intact biofilm was incubated in broth for 24 hours confirming that the coupon had been sterilised. However the same concentration of sodium hydroxide was not effective at eliminating cells when a biofilm was established over an extended period of time. The results presented in this chapter indicate that despite an extensive contact time of 90 minutes only achieved a 2 log 10 reduction in the number of cells recovered from the surface. There are limited studies performed on sodium hydroxide as a disinfectant against an established Salmonella biofilm although its use has been documented in industry [218]. Chorianopoulos et al. used a 1mM solution of sodium hydroxide as part of an evaluation of the efficacy of eight disinfectants against Salmonella Enteritidis [147]. After treatment of a 5 day biofilm for 60 and 180 minutes Chorianopoulos et al. found that the log 10 reduction of S. Enteritidis cells recovered from the biofilm post treatment was with sodium hydroxide was 0.12 and 1.50 after 60 and 180 minutes respectively. This trend (slight reduction over the extended period of time) corresponds with what was reported in this chapter although the log 10 reduction reported by Chorianopoulos et al. was lower [147]. This difference in log 10 reduction may reflect variation in biofilm development methods and concentration of the disinfectant agent used. The work described by Chorianopoulos et al. examined the efficacy of sodium hydroxide at concentrations of 1mM, whereas the work in this chapter used a 1M solution based on the results of the MIC test. As discussed previously, there are very limited studies examining the efficacy of sodium hydroxide against an established biofilm. However Parkar et al. also found that a 2% concentration of sodium hydroxide (0.5M) with nitric acid (HNO 3 ) was the most effective disinfectant at reducing the number of thermophilic Bacillus flavothermus cells attached to steel after 18 hours biofilm formation [219]. The authors indicated that 30 minutes contact with the sodium hydroxide mixture at 75°C was Page 142
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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
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 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 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
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
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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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