is, short penetration times are insufficient for bacteria to move in depth into the defect and adhere to the surface. A certain time is required for the bacteria to penetrate into the surface irregularities, and this elapsed time increases for smaller defects. Larger defects, of about 8 mm depth and 40 mm side length, require just half a minute for aluminium and steel, while for defects with 3 to 4 mm depth, a longer time is necessary, of about 4 min. However, after a certain time period there is no beneficial effect in keeping bacteria suspension on the material surface, as this does not allow the detection of smaller size defects and there is even a risk of favouring irreversible attachment of the cells. Thus, there is a detection limit which is the minimum defect size for a certain time of exposure and this depends on the material.
It must be noticed that these values were achieved for the R. erythropolis cells under study in the absence of additional means to improve their mobility. That is, the cells were not submitted to electrical or magnetic fields to facilitate their movement and the bacteria under study have no flagella and, although they may produce biosurfactants that could decrease the surface tension of the suspension, the cells were washed and resuspended in fresh aqueous medium without surfactants. Therefore, the motility observed and the entrance in the defects should have been the result of hydrophobic interactions and low electrostatic forces (between the net surface charge of the cells and the surface of the
materials tested) [17] and capillarity phenomena as well.
Plotting the minimum defect depth and length as a function of the penetration time for the tested materials (Fig. 7), it can be seen that in aluminium, for a penetration time of 4 min a defect reference G of 4.3 mm depth can be detected and it does not vary for longer penetration periods. The same applies in steel where a detection limit exists for a dwell time of 4 min and the smallest defect size is of 2.9 mm (defect reference G).
In copper, it was seen that increasing the penetration time above 3 min, copper destroyed the bacterial cells due to its
bactericide effect. In fact, longer deposition times in copper led to a significant number of dead cells and a considerable decrease in the detection limit after 4 min of exposure, with no viable cells being visible after 5 min. The bactericidal effect of copper is well known and was used by the Romans in water piping systems, cutlery and cookware several centuries before the description of micro-organisms was first reported [18]. Therefore, a detection limit of 6.8 mm depth could be estimated in copper after the optimum penetration time of 3 min. This is an interesting result in terms of both time for detectability and minimum defect dimension identifiable compared to the other materials studied. It should be noticed from Fig. 6 that, for a penetration time of 5 min, there are no surviving bacteria indicating defects.
Another experiment was performed on steel and this aimed at studying the revelation stage (stage 6) as defined in Fig. 1. For this, bacterial growth inside the defects was promoted, to allow its visualization by the naked eye.
is, short penetration times are insufficient for bacteria to move in depth into the defect and adhere to the surface. A certain time is required for the bacteria to penetrate into the surface irregularities, and this elapsed time increases for smaller defects. Larger defects, of about 8 mm depth and 40 mm side length, require just half a minute for aluminium and steel, while for defects with 3 to 4 mm depth, a longer time is necessary, of about 4 min. However, after a certain time period there is no beneficial effect in keeping bacteria suspension on the material surface, as this does not allow the detection of smaller size defects and there is even a risk of favouring irreversible attachment of the cells. Thus, there is a detection limit which is the minimum defect size for a certain time of exposure and this depends on the material.
It must be noticed that these values were achieved for the R. erythropolis cells under study in the absence of additional means to improve their mobility. That is, the cells were not submitted to electrical or magnetic fields to facilitate their movement and the bacteria under study have no flagella and, although they may produce biosurfactants that could decrease the surface tension of the suspension, the cells were washed and resuspended in fresh aqueous medium without surfactants. Therefore, the motility observed and the entrance in the defects should have been the result of hydrophobic interactions and low electrostatic forces (between the net surface charge of the cells and the surface of the
materials tested) [17] and capillarity phenomena as well.
Plotting the minimum defect depth and length as a function of the penetration time for the tested materials (Fig. 7), it can be seen that in aluminium, for a penetration time of 4 min a defect reference G of 4.3 mm depth can be detected and it does not vary for longer penetration periods. The same applies in steel where a detection limit exists for a dwell time of 4 min and the smallest defect size is of 2.9 mm (defect reference G).
In copper, it was seen that increasing the penetration time above 3 min, copper destroyed the bacterial cells due to its
bactericide effect. In fact, longer deposition times in copper led to a significant number of dead cells and a considerable decrease in the detection limit after 4 min of exposure, with no viable cells being visible after 5 min. The bactericidal effect of copper is well known and was used by the Romans in water piping systems, cutlery and cookware several centuries before the description of micro-organisms was first reported [18]. Therefore, a detection limit of 6.8 mm depth could be estimated in copper after the optimum penetration time of 3 min. This is an interesting result in terms of both time for detectability and minimum defect dimension identifiable compared to the other materials studied. It should be noticed from Fig. 6 that, for a penetration time of 5 min, there are no surviving bacteria indicating defects.
Another experiment was performed on steel and this aimed at studying the revelation stage (stage 6) as defined in Fig. 1. For this, bacterial growth inside the defects was promoted, to allow its visualization by the naked eye.
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is, short penetration times are insufficient for bacteria to move in depth into the defect and adhere to the surface. A certain time is required for the bacteria to penetrate into the surface irregularities, and this elapsed time increases for smaller defects. Larger defects, of about 8 mm depth and 40 mm side length, require just half a minute for aluminium and steel, while for defects with 3 to 4 mm depth, a longer time is necessary, of about 4 min. However, after a certain time period there is no beneficial effect in keeping bacteria suspension on the material surface, as this does not allow the detection of smaller size defects and there is even a risk of favouring irreversible attachment of the cells. Thus, there is a detection limit which is the minimum defect size for a certain time of exposure and this depends on the material.
It must be noticed that these values were achieved for the R. erythropolis cells under study in the absence of additional means to improve their mobility. That is, the cells were not submitted to electrical or magnetic fields to facilitate their movement and the bacteria under study have no flagella and, although they may produce biosurfactants that could decrease the surface tension of the suspension, the cells were washed and resuspended in fresh aqueous medium without surfactants. Therefore, the motility observed and the entrance in the defects should have been the result of hydrophobic interactions and low electrostatic forces (between the net surface charge of the cells and the surface of the
materials tested) [17] and capillarity phenomena as well.
Plotting the minimum defect depth and length as a function of the penetration time for the tested materials (Fig. 7),จะเห็นได้ว่าในอลูมิเนียมสำหรับการเจาะเวลา 4 นาทีจากการอ้างอิงกรัม ความลึก 4.3 มม. สามารถตรวจพบและไม่แตกต่างกันสำหรับระยะเวลาการเจาะอีกต่อไป เดียวกันใช้ในเหล็กที่เป็นขีดจำกัดที่มีอยู่สำหรับประทับเวลา 4 นาทีและข้อบกพร่องน้อยที่สุดคือ ขนาด 2.9 mm ( ข้อบกพร่องอ้างอิง g )
ทองแดง จะเห็นได้ว่าการเพิ่มการเจาะเวลาข้างต้น 3 นาที copper destroyed the bacterial cells due to its
bactericide effect. In fact, longer deposition times in copper led to a significant number of dead cells and a considerable decrease in the detection limit after 4 min of exposure, with no viable cells being visible after 5 min. The bactericidal effect of copper is well known and was used by the Romans in water piping systems, cutlery and cookware several centuries before the description of micro-organisms was first reported [18]. Therefore, a detection limit of 6.8 mm depth could be estimated in copper after the optimum penetration time of 3 min. This is an interesting result in terms of both time for detectability and minimum defect dimension identifiable compared to the other materials studied.มันควรจะสังเกตจากรูปที่ 6 นั้น สำหรับการเจาะเวลา 5 นาที ไม่มีอดตายแบคทีเรียบ่งชี้ข้อบกพร่อง .
การทดลองอื่นคือใช้เหล็ก และ นี้ มุ่งศึกษาการเปิดเผยขั้นตอน ( ระยะที่ 6 ) เป็น de จึงเน็ดในรูปที่ 1 นี้ การเติบโตของแบคทีเรียในข้อบกพร่องที่ได้รับการส่งเสริม เพื่อให้มองเห็นได้ด้วยตาเปล่า
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