Seasonality of the antibiotic resistance gene blaCTX-M in temperate Lake Maggiore

Abstract

The beta lactamase gene blaCTX-M, responsible of the resistance to cephalosporins, has been detected in microbes from hospitals to open waters. We studied the seasonality and stability of blaCTX-M in Lake Maggiore over 3 years and the role of potential inputs of allochthonous bacteria and/or antibiotic pollution in promoting its occurrence. blaCTX-M was mainly present from January to July in the pelagic microbial community and the gene occurrence was significantly related to low water temperature. To evaluate its temporal stability in the bacterial community over a short period, we measured blaCTX-M daily over the course of 6 days. The gene was below the limit of quantification except for one sampling when its abundance peaked, suggesting a point contamination. The bacterial community of the lake in which blaCTX-M was detected suggests that at least two distinct bacterial populations contained the gene. The occurrence of known blaCTX-M containing genera and the occurrence of the gene, however, did not overlap. Furthermore, the experimental addition of cefotaxime to lake water incubations did not promote abundance of the gene. These data imply that blaCTX-M was present in the environmental microbial community. Increases of gene abundances were likely caused by environmental parameters other than antibiotic contamination.

Antibiotic Resistance Genes and Potentially Pathogenic Bacteria in the Central Adriatic Sea: Are They Connected to Urban Wastewater Inputs?

“…Contrary to what was expected, the bla CTX-M gene was found in low concentrations in the Katalinića WWTP effluent and in <LOQ or null concentrations in the other WWTPs. It has been hypothesized that urban WWTPs are the principal source of bla CTX-M for aquatic environments [23,51] because bla CTX-M harboring strains isolated in rivers and wastewater were found to be related to nosocomial strains of the same geographical area [79,80].…”

“…Recent studies have shown that people's probability of contracting gastrointestinal and non-gastrointestinal illnesses increases in correlation with aquatic recreational activities because of antibiotic-resistant bacteria and other community-acquired microorganisms [19,20]. Furthermore, frequent bathing in coastal waters has been shown to be associated with gut colonization by E. coli harboring ARGs, including, for example, bla CTX-M genes, which provide resistance to clinically relevant antibiotics (cefotaxime) and which are easily mobilized via horizontal gene transfer (HGT), thus increasingly found in natural environments as well as in WWTPs [21][22][23].…”

Where do the antibiotic resistance genes come from? A modulated analysis of sources and loads of resistances in Lake Maggiore

“…The dynamics of the ARGs measured in Lake Maggiore are available from 2013 (detected monthly) and are characterized by large differences among genes (Di Cesare et al 2015 , Eckert et al 2019a , CIPAIS 2021 ): bacteria carrying sul 2 and tet A are constantly present and abundant in the waters of the lake in the last 10 years, bla CTX-M in 2015–6 was only sporadically quantifiable, missing the seasonality characterizing other years (present in winter/spring, absent for the rest of the year; Eckert et al 2019 ). The sul 2 gene, widely distributed and abundant in the microbiome of the lake, was also discharged in large numbers from the rivers (mainly from Toce, Tresa and Bardello), but without any correlation between loads and abundances in the lake.…”

“…This area hosts about 640000 inhabitants (CIPAIS 2003 ) and a large number of seasonal tourists, mainly in spring and summer (the number of tourists hosted in the watershed of the Lake in 2015–6 was between 4 and 5 million; USTAT Canton Ticino 2017 , ISTAT 2017a ). From 2013, the horizontal and vertical distribution of ARGs in Lake Maggiore has been assessed monthly by monitoring programs funded by the International Commission for the Protection of Italian-Swiss Waters (Di Cesare et al 2015 , CIPAIS 2018 , Eckert et al 2019a , Di Cesare et al 2020 , CIPAIS 2021 ). However, the relative contribution of the ARGs released from its watershed through the tributary rivers or from the WWTP effluents directly discharged into the lake to the resistome of the lake has never been investigated.…”

“…The selection of ARGs was guided by the results obtained by the CIPAIS long-term monitoring of Lake Maggiore, focusing on genes associated with resistance to the most commonly used antibiotics in the Lake Maggiore area (CIPAIS 2018 ). Two genes, sul 2 and tet A (encoding for the resistance to sulphonamides and tetracyclines, respectively) were almost always present in the lake (Di Cesare et al 2015 ); bla CTX-M (encoding for resistance to β-lactams) followed a seasonal dynamic within the lake bacterial community (Eckert et al 2019a ); erm B and qnr S (encoding for the resistance to macrolide-lincosamide-streptogramin and quinolones, respectively) were sporadically detected in the lake, and are classified as high-risk ARGs for human health (Zhang et al 2021 ). We also measured biotic and abiotic factors that may influence the bacterial community and their associated ARGs: bacterial cell number and size distribution, water flow, nitrogen and phosphorus compounds and total organic carbon.…”