Strategic measures for the control of surging antimicrobial resistance in Hong Kong and mainland of China

Cheng, Vincent CC; Wong, Sally CY; Ho, Pak-Leung; Yuen, Kwok-Yung

The nondiscretionary use of antibiotics in agriculture and human medicine has led to the discharge of many residual antimicrobial compounds and their derivatives into the sewage system, which is considered an emerging environmental niche for the dissemination of antimicrobial resistance genes. The coastal water of Bohai Bay in northern China was investigated for the presence of 21 antibiotics from six different classes. Antibiotic levels in the north Bohai Bay were generally higher than those in the South, highlighting the remarkable effects of high-density aquaculture activities on the exposure of the environment to antimicrobials. The antibiotic levels found in the six rivers flowing into the Bohai Bay were generally higher than those in Bohai Bay, reflecting the importance of river discharge as the source of these antibiotics. 54 In eastern China, the occurrence and dissipation of 14 selected antibiotics, including tetracyclines, sulfonamides, macrolides, fluoroquinolones and chloramphenicol, were investigated in two swine wastewater treatment systems. As anticipated, highest contamination by tetracycline, oxytetracycline, chlortetracycline, doxycycline and sulfadiazine was noted in the sample tested, with maximum concentrations reaching 41.6, 23.8, 13.7, 685.6 and 98.8 mg/L, respectively. 55 In southern China, fluoroquinolones (ciprofloxacin, norfloxacin and ofloxacin), macrolides (dehydroerythromycin, roxithromycin and clarithromycin), sulfonamides (sulfamethoxazole and sulfamethazine) and trimethoprim were ubiquitous in wastewater. Fluoroquinolones (norfloxacin) were the most abundantly detected antibiotic in raw sewage, with a maximum concentration of up to 6.415 mg/L. A median percentage of 67% of sulfonamides and 86% of macrolides remained in the final effluent after treatment in sewage treatment plants. 56 In the urban regions of southern China, sulfamethoxazole was the most frequently detected antibiotic residue in the Guangzhou section of the major Pearl River. The maximum concentration of sulfamethoxazole reached 5.597 mg/L in the raw wastewater from a large-scale sewage treatment plant in Guangzhou. 57 In Hong Kong, a study revealed that cephalexin, amoxicillin, ofloxacin and erythromycin were ubiquitous in seawater throughout Victoria Harbor, indicating their continuous discharge into the environment. 58 In the sewage treatment plants in Hong Kong, cephalexin, ofloxacin and erythromycin were found in concentrations of 1.020-5.640, 0.142-7.900, 0.243-4.740 mg/L in influent, respectively. 59 This degree of contamination was comparable to levels reported in urban regions in mainland China. As expected, these residual antibiotics in wastewater will select for and enrich resistance genes in the environmental bacteria; these, in turn, could eventually enter the food chain via food animals and agricultural produce, which are in close contact with the soil and water that are inevitably contaminated by animal and human sewage. In China, the occurrence and diversity of many different transmissible genes conferring fluoroquinolone resistance (qnrA, qnrD, oqxA and aac(69)-Ib-cr) and ESBLs (CTX-M-27 and CTX-M-14) co-existed in different isolates and serovars of non-typhoidal Salmonella from foodproducing animals. The presence of MDROs in food-producing animals may carry a risk for the global dissemination of antibiotic resistance. 60 In Hong Kong, longitudinal studies have confirmed the endemic presence of ESBL-producing E. coli isola