The objective of this study was to determine if acoustic emissions (AE) generated by three strains of Escherichia Coli (5024-parent strain, 8279-mutant strain and 8279-random/unrelated strain) could be used to differentiate each strain during their growth cycle. An acoustic sensor with an operating range of 35 kHz-100 kHz was inserted into the growth vessel and attached to a selected channel to capture AE data. The growth vessel was loaded with 60 ml of tryptic soy broth (TSB) (0.25% fructose) media with alginate (1.1%) or without alginate and inoculated with 1% (108 CFU/ml) of an E. coli strain. The growth vessel was placed in a monitoring chamber and incubated at 32°C for 8-9 h. The AE’s generated by each strain were collected throughout the growth cycle. All strains grown in media with and without alginate generated AE’s within 5 min post inoculation. Strains grown in media without alginate generated stronger (P < 0.0001) absolute energy (ABSE) and higher peak frequencies (PFRQ’s), than in media with alginate. The AE’s generated by strains 5024 and 8237 were stronger and easily distinguished from those generated by strain 8279. Strain 8237 generated 12% stronger ABSE from the 3rd to 8th h and 51% stronger PFRQ intensities than strain 5024 during 0-8 h. However, strain 5024 generated 15% stronger ABSE and 31% higher PFRQ’s during the final hour of growth. Strain 5024 generated the highest PFRQ’s from 5-50 kHz, while strain 8237 generated higher frequencies from 100-500 kHz. Fourteen distinguishable differences (P< 0.05) in generated PFRQ’s, between strains 5024 and 8237, were also observed in every 5 kHz increments from 100-500 kHz. Of these differences, strain 8237 generated higher frequencies within eight of the kHz ranges, while strain 5024 generated higher frequencies within six other kHz ranges. These data suggests that all bacteria may generate different AE’s, thus producing a unique “fingerprint” of sound that will allow for its identification.

The effect of sub-lethal chlorine stress on various strains/serotypes of Salmonella on biofilm formation and thermal resistance was studied. The effect of oxidative stress (induced by 150 ppm of chlorine in TSB) on Salmonella biofilm formation on polystyrene and stainless steel surfaces at three temperatures (4°C, 30°C, and room temperature) in nutrient rich (full strength TSB) and nutrient limited conditions (1/10th TSB) was evaluated. On polystyrene surface, chlorine stressed S. Heidelberg (strain ID 72), S. Newport (strain ID 107) and S. Typhimurium (ATCC 14028) formed stronger (P < 0.05) biofilms at 30°C. On stainless steel, the chlorine stressed S. Heidelberg (ATCC 8326) and S. Enteritidis (ATCC 4931) at room temperature formed stronger (P < 0.05) biofilms as compared to the non-stressed control cells. The thermal resistance of short-term (1h) and long-term (27d) chlorine stressed Salmonella Heidelberg and S. Typhimurium were compared with the non-stressed controls at three different temperatures (55°C, 58°C and 61°C) and two growth phases (logarithmic and stationary). The short-term stressed log phase cells (both serotypes) were found to be more sensitive (P< 0.05) to thermal inactivation in TSB. Upon long-term sub-lethal chlorine exposure, Salmonella developed a rugose morphotype on tryptic soy agar at 37°C. The rugose morphotype provided significant thermal protection (P< 0.05) against heat stress as compared to smooth morphotype. In chicken broth, at 55°C, short-term chlorine stressed stationary phase S. Typhimurium displayed a higher D55 value compared to non-stressed cells. The findings from this research reveal that some Salmonella strains have the potential to form stronger biofilms and exhibit higher thermal tolerance upon exposure to sub-lethal chlorine concentration.