N. Mezrioui et B. Baleux, RESISTANCE PATTERNS OF ESCHERICHIA-COLI STRAINS ISOLATED FROM DOMESTIC SEWAGE BEFORE AND AFTER TREATMENT IN BOTH AEROBIC LAGOON AND ACTIVATED-SLUDGE, Water research, 28(11), 1994, pp. 2399-2406
This work compares antibiotic resistance of 870 E. coli strains isolat
ed from domestic raw sewage, in the effluent from aerobic lagoons and
activated sludge plants. Efficiency of both treatment systems in remov
ing faecal coliforms (FC) has also been evaluated. Reduction of FC was
greater in the aerobic lagoon (99.99% in summer) than in the activate
d sludge system (91.30% in summer). Although the aerobic lagoon is eff
icient in removing faecal coliforms in comparisons with the activated
sludge plant, it discharges these bacteria into receptor environments
in larger (30.10(3) CFU/100 ml) or smaller quantities (9.10(2) CFU/100
ml) according to season. Among these FC, E. coli which was relatively
high (on average 80%) constitutes a health problem when it is resista
nt to antibiotics. As for percentage of global antibiotic-resistance (
evaluated by Gallery ATBG-method), the E. coli strains isolated from t
he effluent of the aerobic lagoon showed significantly higher antibiot
ic-resistance (34.66%) than those isolated from domestic sewage (23%).
In the activated sludge, the percentage of antibiotic resistant strai
ns (resistance to at least one antibiotic) showed seasonal changes in
the inflow and outflow water samples. The increase of the percentage o
f antibiotic resistant strains of E. coli in the outflow of the lagoon
system is probably related to the selection of antibiotic resistant s
trains by this kind of treatment. Transfer of antibiotic-resistance be
tween E. coli strains can occur in the wastewaters treated by this sys
tem. Survival experiments on two strains of E. coli, E. coli resistant
to seven antibiotics and E. coli 0126:B16 sensitive to the 15 tested
antibiotics, isolated from the environment, show the ability of resist
ant bacteria to survive better than sensitive ones in waste water trea
ted in lagoons.