Skip to Main Content

The types of samples included natural undiluted and diluted samples and waters spiked with waste water. The sample selection varied between the laboratories. More samples were taken from inland fresh waters than from coastal brackish waters (Table 1(a)). The differences between the mean relative recovery values between Colilert-18 and MMPN when using natural and spiked inland and coastal samples were not statistically significant (P= 0.487–0.691; Table 1(a)). The mean relative difference of original and confirmed counts between Colilert-18 and MMPN methods was close to zero when analysing inland samples spiked with waste waters (Table 1(a)). When analysing natural inland and coastal samples, Colilert-18 seemed to result in lower original and confirmed MPN values than the MMPN method.

Table 1

A quantitative comparison between the relative differences of the original, confirmed and corrected E. coli results obtained using the Colilert-18 method and miniaturised MPN-48 and -72 method (a) when analysing natural and spiked inland and coastal samples and (b) in each laboratory

  Original 18-48
Original 18-72
Confirmed 18-72
Corrected 18-72
 
NMSDMSDMSDMSDDifference
(a) Sample category 
1. Inland – natural 107 −10.42 68.34 −12.10 68.47 −14.15 69.06 6.78 76.42 20.93 
2. Inland –spiked 114 −1.17 68.05 −2.99 67.50 −1.44 68.73 13.18 68.83 14.62 
3. Coastal –natural 38 −13.22 66.90 −14.31 66.56 −14.34 64.49 1.29 66.93 15.63 
4. Coastal – spiked 4 −19.76 13.69 −19.76 13.69 −23.47 6.86 −23.47 6.86 0.00 
Total 263 −6.96 67.44 −8.58 67.19 −8.81 67.81 8.30 71.23 17.11 
Difference of the mean values, F value 0.53 0.49 0.82 0.58   
Probability 0.663 0.691 0.487 0.628   
(b) Laboratory 
1 48 (48,0,0,0) −17.30 54.46 −20.41 54.30 −23.67 55.77 5.89 57.11 29.56 
2 47 (7,26,10,4) −1.25 65.23 −2.95 65.26 −1.52 65.43 13.92 77.77 15.44 
3 48 (2,46,0,0) −7.45 70.38 −11.16 68.50 −11.30 71.62 3.63 79.31 14.93 
4 43 (15,0,28,0) −23.56 68.04 −24.04 68.11 −23.48 66.51 −3.94 70.73 19.54 
5 36 (28,8,0,0) 12.61 80.52 12.61 80.52 12.12 80.27 18.09 86.71 5.97 
6 41 (7,34,0,0) −0.58 64.90 −0.58 64.90 0.14 64.69 14.40 53.51 14.26 
Total 263 (107,114,38,4) −6.96 67.44 −8.58 67.19 −8.81 67.81 8.30 71.23 17.11 
Difference of the mean values, F value 1.51 1.69 1.84 0.56   
Probability 0.188 0.138 0.105 0.734   
  Original 18-48
Original 18-72
Confirmed 18-72
Corrected 18-72
 
NMSDMSDMSDMSDDifference
(a) Sample category 
1. Inland – natural 107 −10.42 68.34 −12.10 68.47 −14.15 69.06 6.78 76.42 20.93 
2. Inland –spiked 114 −1.17 68.05 −2.99 67.50 −1.44 68.73 13.18 68.83 14.62 
3. Coastal –natural 38 −13.22 66.90 −14.31 66.56 −14.34 64.49 1.29 66.93 15.63 
4. Coastal – spiked 4 −19.76 13.69 −19.76 13.69 −23.47 6.86 −23.47 6.86 0.00 
Total 263 −6.96 67.44 −8.58 67.19 −8.81 67.81 8.30 71.23 17.11 
Difference of the mean values, F value 0.53 0.49 0.82 0.58   
Probability 0.663 0.691 0.487 0.628   
(b) Laboratory 
1 48 (48,0,0,0) −17.30 54.46 −20.41 54.30 −23.67 55.77 5.89 57.11 29.56 
2 47 (7,26,10,4) −1.25 65.23 −2.95 65.26 −1.52 65.43 13.92 77.77 15.44 
3 48 (2,46,0,0) −7.45 70.38 −11.16 68.50 −11.30 71.62 3.63 79.31 14.93 
4 43 (15,0,28,0) −23.56 68.04 −24.04 68.11 −23.48 66.51 −3.94 70.73 19.54 
5 36 (28,8,0,0) 12.61 80.52 12.61 80.52 12.12 80.27 18.09 86.71 5.97 
6 41 (7,34,0,0) −0.58 64.90 −0.58 64.90 0.14 64.69 14.40 53.51 14.26 
Total 263 (107,114,38,4) −6.96 67.44 −8.58 67.19 −8.81 67.81 8.30 71.23 17.11 
Difference of the mean values, F value 1.51 1.69 1.84 0.56   
Probability 0.188 0.138 0.105 0.734   

N, number of samples; D, distribution of samples in sample categories (1, 2, 3, 4); M, mean relative difference; SD, standard deviation; Difference, change of the mean value when confirmed results were corrected for the false negatives. Natural samples include both diluted and undiluted samples.

View Large

Close Modal
This Feature Is Available To Subscribers Only

or Create an Account

Close Modal
Close Modal
This site uses cookies. By continuing to use our website, you are agreeing to our privacy policy.
Accept