Microbiological determination of total coliforms, E. coli, and
AMPR or CAFR E. coli
Wastewater samples (100 mL) were filtered through 5-cmdiameter 0.45-mm nitrocellulose membranes (Sartorius Stedim
Biotech, Goettingen, Germany). The membranes were then laid on
plates containing chromogenic agar growth medium (EC X-GLUC
agar; Biolife Italiana, Milan, Italy) to count total coliforms in the
presence or absence of antibiotics, and to select the E. coli green
colonies, which are positive for the b-glucoronidase activity. When
the number of bacterial colonies was too high to be counted, the
wastewater samples were diluted in Ca2 þ-free and Mg2e-free
phosphate buffered saline by 102 to 104 to have a reliable colony
number. Since green colonies can be mostly ascribed to b-glucoronidase-positive Enterobacteria, and E. coli is by far the prevalentone compared to Salmonella and Shigella (Fekadu et al., 2015), the
latter-ones were not taken into consideration. Considering the
EUCAST breakpoint tables, that classify Enterobacteria as AMPR and
CAFR when the MIC is >8 mg/mL