Lanthanum-based concentration and microrespirometric detection of microbes in water

Rapid concentration and detection of microorganisms, particularly pathogens, are important but remain a challenge. In this research, lanthanum chloride (LaCl3) was used to concentrate E. coli in water and the results were compared with those obtained using traditional flocculants, such as ferric sulfate and aluminum sulfate. A turbidimetric assay and a microrespirometric assay were employed to enumerate the bacteria in water samples by monitoring the absorbance of bacteria and the oxygen-based fluorescence intensity, respectively. The microrespirometric method requires less time than the turbidimetric assay. Both assays could linearly enumerate the bacteria at the concentration range from 101 to 109 cells/mL. Based on the turbidimetric assay, the relative concentration efficiencies of the three flocculants were 75% (LaCl3), 40% (FeCl3) and 33% (Al2(SO4)3), while for the microrespirometric assay, the concentration efficiencies were 85% (LaCl3), 34% (FeCl3) and 32% (Al2(SO4)3). The microbial recovery rates, defined as the ratio of cell number in the sediment after coagulation/flocculation to that of the controls, were 94% (LaCl3), 69% (FeCl3) and 51% (Al2(SO4)3) from the turbidimetric assay. The results demonstrate that compared with traditional flocculants, LaCl3 has higher relative concentration and recovery efficiencies and thus possesses the potential for microbial concentration in water samples.