Analisis Keberadaan Gen Resistensi Antibiotik blaCTX-M Pada Bakteri Escherichia coli di Hilir Sungai Bekasi Menggunakan Metode Polymerase Chain Reaction = Analysis of the Existence of the blaCTX-M Antibiotic Resistance Gene in Escherichia coli Bacteria in the Downstream Bekasi River Using the Polymerase Chain Reaction Method