Biofilms formation on the stainless steel AISI 321 surface in terms of surface roughness and Е.сoli initial number
The results of the research of stainless food steel surface roughness impact on biofilm Esсheriсhia coli formation have been given. The stainless plates AISI 321 of surface roughness Rа = 0.955 mkm, Rа = 0.63 mkm and Rа = 0.16 mkm were used in the research. It was found that at favorable temperatures bacterium coli is able to form biofilms of medium and high density on the stainless steel surface of roughness 0.955 mkm during 9–12 hours. Though, biofilms density at initial E. coli number up to 1000 per cm2 of area was on the average 1.8–2.2 times (Р ≤ 0.05) lower in comparison with the biofilm formed in cases with initial cell number 2000–10 000 and 20000–50000 on cm2 of stainless steel surface. Biofilm formation intensity on the steel of roughness 0.63 mkm surface was rather decelerated comparing to the surface of roughness 0.955 mkm. Nevertheless, as for density the biofilms in cases with initial E. coli number 2000–10 000 and 20000–50000 on cm2 of surface were of high density from 12 hours of incubation, i.e. the same as in case with the surface of roughness 0.955 mkm. Film forming process at such initial E. coli number on the surface of roughness 0,63 mkm was completed at the 24th hour while on the surface of roughness 0.955 mkm – at the 18th hour of incubation. For the steel of roughness 0,16 mkm the film forming process was greatly decelerated comparing to the surfaces of roughness 0.955 and 0.63 mkm. After 9 hours of E. coli incubation on the steel of roughness 0.16 mkm the biofilms were on the average 2,0 times (Р ≤ 0.05) lower density in comparison with roughness 0,955 mkm and 1.3–1.6 times (Р ≤ 0.05) lower comparing to roughness 0,63 mkm irrespective of the initial E. coli number. After 12 hours of E. coli incubation in case with initial number up to 1 000 per cm2 of area the biofilm was still weak, and in cases with initial number 2000–10 000 and 20000–50000 on cm2 of surface – of medium density – 0.805 and 0.916 units correspondingly. Only after 24 hours of E. coli incubation the biofilms in all cases were of high density.
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