Pathogenic microorganisms isolated in secondary water supply for 152 high-rise buildings in Chongqing city

  Objective   To detect pathogenic microorganisms in secondary water supply for high-rise buildings in Chongqing city and to examine the spectrum, dominant strains, virulence genes and drug resistance of the isolated pathogenic bacteria.

  Methods   A total of 152 tap water samples were collected from secondary water supply for 152 high-rise buildings (18 stories and higher and built not later than 5 years for each of the buildings) at 6 districts of Chongqing city during 2020 and 2021. Bacteria isolation and identification, drug sensitivity test, whole genome sequencing and virus nucleic acid detection were carried out for the samples.

  Results   Totally 128 bacterial strains were isolated from 96 samples, with single strain from 67 samples, two strains from 23 samples and three strains from 5 samples; no bacterial strain was isolated from another 56 samples. The top three bacteria frequently isolated were Bacillus (25.0% of all isolations), Pseudomonas (18.0%) and Acinetobacter (7.8%). The isolated pathogenic/conditional pathogenic strains included 10 Bacillus cereus, 6 Bacillus turingiensis, 6 Acinetobacter johnsonii, 6 Pseudomonas alcaligenes, 4 Staphylococcus haemolyticus, 3 Micrococcus luteus, 3 Mycobacterium fortuitum, 3 Pseudomonas aeruginosa; Sphingomonas oligokine and Stenotrophomonas maltophilia were also detected. The isolated strains of Pseudomonas aeruginosa were resistant to 8 kinds of antibiotics, and those of Bacillus cereus/Bacillus thuringiensis were resistant to β-lactam antibiotics. All water samples were negative for nucleic acid of norovirus, rotavirus and novel coronavirus. The phylogenetic tree analysis with whole gene sequencing showed that the phylogenetic relationship of the two isolated Bacillus thuringiensis strains is closer to the pathogenic strain 97 – 27.

  Conclusion   There was pathogenic bacterial contamination caused by Bacillus, Pseudomonas, Acinetobacter and other pathogenic strains in secondary water supply of high-rise buildings in Chongqing city and human health effect of the contamination needs to be concerned.