**1. Introduction**

The environmental spread of antibiotic resistant bacteria has been recognized as a growing public health threat [1,2]. Hospitals are "hotspots" for antibiotic use and not only play an important role in antibiotic dissemination but also in the release of antibiotic resistant bacteria into the environment. Hospital wastewater treatment plants containing antibiotic residues can favour the development of antibiotic resistance due to the selective pressure placed on bacteria [3,4]. Moreover, antibiotic resistance genes (ARGs) carried by bacterial contaminants can be transferred to other bacterial populations including pathogenic bacteria found in hospital wastewater [1]. Hospital effluents can reach water bodies used in agriculture or for domestic purposes. From there, antibiotic resistant bacteria and/or ARGs can be transferred to humans.

In recent years, the presence of antibiotic resistant *Escherichia coli* (*E. coli*), particularly extended-spectrum beta-lactamase (ESBL)-producing isolates, in surface water has attracted attention [5]. A direct relationship between clinical *E. coli* isolates and the quantity of ESBL-producing *E. coli* strains found in hospital wastewater has been demonstrated [6]. Consequently, the existence of ESBL-producing *E. coli* carriers in hospitals may lead to their environmental spread [6].

Antibiotic resistance causes prolonged illness, excess mortality, and higher costs for patients and health systems [7–9]. Despite increased warnings and numerous efforts to contain it, antibiotic resistance has been increasing [10–13]. At the recent United Nations general assembly, it was highlighted that antibiotic resistance is among the greatest global health risks, requiring urgent attention [14].

The risks are potentially more serious in low- and middle-income countries where many hospitals either do not have wastewater treatment plants or they are ineffective. To make matters worse, in many places, but particularly rural areas, surface water is used for agriculture and domestic purposes or even consumed untreated. Most research on antibiotic resistant bacteria in hospital wastewater originates from high-income countries [15].

Therefore, this study sought to investigate the prevalence of resistant *E. coli* isolates to commonly used antibiotics, ESBL-producing isolates along with genes coding for cephalosporin resistance *blaCTX-M* and *blaTEM*, and a gene coding for ciprofloxacin resistance *qepA*, in hospital wastewater in a rural and an urban hospital in Vietnam.
