A method based on the treatment of sludge with beef extract recovered, with similar efficiency, the three groups of bacteriophages studied from different kinds of sludges. The three groups of bacteriophages were found in high numbers in the different sludge types, the highest value being that of somatic coliphages in primary sludge of a biological treatment plant (1·1 × 105 pfu g−1) and the lowest being that of Bacteroides fragilis phages (110 pfu g−1) in de‐watered, anaerobically, mesophilically‐digested sludge. All phages studied accumulated in the sludges. In primary and activated sludges, all three types accumulated similarly but in lime‐treated sludge and de‐watered, anaerobically, mesophilically‐digested sludge, the relative proportion of F‐specific bacteriophages decreased significantly with respect to somatic coliphages and bacteriophages infecting B. fragilis. All phages survived successfully in stored sludge, depending on the temperature, and again, F‐specific bacteriophages survived less successfully than the others.

Levels of somatic and F-specific coliphages, and phages infecting Bacteroides fragilis were measured in 257 samples collected in different freshwater environments with different levels and characteristics of faecal pollution. In samples with recent pollution of domestic origin, the numbers of the three groups of phages were highly correlated, thus showing that their excretion is fairly constant. In this set of samples somatic coliphages, which were the most abundant, and F-specific coliphages outnumbered significantly Bact. fragilis phages. Normalized lines of the numbers of the three groups of phages in water samples and their sediments show that they settle similarly. The correlation between the values of the three groups of phages was not observed in waters with intermediate levels of pollution. An increase in the relative numbers of coliphages with respect to numbers of phages infecting Bact. fragilis was observed. In waters with persistent faecal pollution a dramatic change was recorded in the relative numbers of the different groups of phages. Phages infecting Bact. fragilis suffered the lowest reduction in numbers.

Concentrations of fecal bacteria, somatic and F-specific coliphages, and phages infecting Bacteroidesfragilis in naturally occurring black mussels (Mytilus edulis) were determined. Mussels were collected over a 7-month period at four sampling sites with different levels of fecal pollution. Concentrations of both fecal bacteria and bacteriophages in mussel meat paralleled the concentration of fecal bacteria in the overlying waters. Mussels bioaccumulated efficiently, although with different efficiencies, all of the microorganisms studied. Ratios comparing the levels of microorganisms in mussels were determined. These ratios changed in mussels collected at the different sites. They suggest that bacteriophages infecting B. fragilis and somatic coliphages have the

The effect of different treatments and methods of titration on the recovery of phages infecting Bacteroides fragilis as well as for both somatic and male specific coliphages in environmental samples were evaluated. Recovery of phages infecting B. fragilis is highly dependent on the treatment of the samples. The influence of the treatment in the recovery of coliphages was either null or low. Titration method had some influence on the recovery of phages, mainly those of B.fragilis, from sludge and sediment samples.

No abstract