Pathogenic potential of enterococcus isolated from healthy people and wastewater

Introduction. Efficiency of wastewater treatment plants is a key for protection of common health. At the same time, all criteria for its evaluation are concerned about the overall biomass reduction rather than on pathogens that, in low amount, can still be present in the efflux.

Purpose of the study. Therefore it seems important to evaluate the effect of purification procedures on the pathogenic potential of bacteria. In the current study, it is performed using Enterococcus isolates, since pathogenic strains present considerable threat for human health, causing endocarditis, infections of urogenic tract, nosocomial infections, etc.

Materials and methods. PCR was used to evaluate the presence of potentially pathogenic genes in the extracted DNA. Seven genes were tested: genes of adhesion proteins (Esp, Asa1), proteins with lytic activity (cytolysine CylA, hyaluronidase hyl and gelatinase gelE), and antibiotic resistance factors (vanA, vanB). Three hundred sixty six isolates from wastewater plants of Moscow agglomeration and 168 from feces of healthy people were screened.

Results. Percentage of pathogenic isolates varied in different wastewater treatment plants (from 36 to 55%), with no relation with the volumes of treated sewage and the purification scheme of the plant. Similar species were recovered from wastewater plants and feces, with E. faecium (36% and 53%, correspondingly) and E. faecalis (28% and 38%) as most abundant. E. hirae was presented in different numbers (24% and 1.2%) as well as E. casseliflavus (3% and 0,6%). E. durans, E. thailandicus, E. avium, E. mundtii were found from 2.5 to 1%, in similar amounts from both sources. Minor species E. raffinosus, E. moraviensis, E. malodatus presented with single isolates in wastewater plants, and E. canintestini — in feces. The E. faecalis was the leader in percentage of pathogenic potential (75–80%). The most abundant pathogenic gene was gelE (30–33% from both sources) and asa1 (18–19%). CylA was found at similar levels (4,4–4,8%). Esp was found in 9% of wastewater plants isolates and in 14% from feces. Hyl was specific to isolates from wastewater plants (2,5%), and was present in all non-monor species (E. faecium, E. faecalis, E. hirae, E. durans, E. thailandicus) and at different stages of water treatment. Vancomycin resistance genes were not detected.

Limitations. When studying the pathogenic potential of enterococcal isolates from wastewater treatment plants in the city of Moscow and the Moscow region and the feces of practically healthy people, two samples were compared, consisting of 366 and 168 isolates, respectively, which represents a sufficient reference sample. The sample was limited by geography, so the conclusions can be applied to wastewater treatment plants in the city of Moscow and the Moscow region, where similar treatment schemes were used.

Conclusions. The data from this study suggests the pathogenic potential of bacteria from wastewater treatment plants to be a little bit more than that of isolates from feces of healthy people. The activated sludge can be a reservoir for pathogens and can bring contamination to the environment.

Compliance with ethical standards. The study of biological material from humans was approved by the Local Independent Ethics Committee (Minutes No. 98A of the meeting of the Local Independent Ethics Committee of the Federal State Budgetary Institution “GNCC named after A.N. Ryzhykh of the Ministry of Health of Russia dated 16.07.2018).

Contribution:
Pay G.V. — concept and design of the study, collection and processing of material, performing the experiments, statistical processing, writing, editing;
Rakitina D.V. — writing;
Pankova M.A. — samples collection, bacteria cultivation;
Fedets Z.E. — samples collection, bacteria cultivation;
Maniya T.R. — collection and processing of material, editing;
Zagaynova A.V. — concept and design of the study, editing, approval of the final version of the article.
All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.

Conflict of interest. The authors declare no conflict of interest.

Acknowledgment. The research was carried out within the framework of the research work “Development of unified methods, including sampling, for the determination of microbiological and parasitological contamination of wastewater” (code “Wastewater”). State contract 12.11.2021 No. 2123388100152000000000000/145.001.216.

Received: July 31, 2023 / Accepted: November 15, 2023 / Published: December 28, 2023