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Toxic plastic waste floating underwater in the ocean
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“Microplastic pollution in the ocean contributes to antibiotic resistance”

Maria Belen
Maria Belen Sathicq
Post-doctoral fellow at the Institute for Water Research of the Italian National Research Council (CNR)

It is now well known that the wide­spread use of antibi­otics – to treat patients, but espe­cial­ly to treat farm ani­mals – has accel­er­at­ed bac­te­r­i­al resis­tance to these treat­ments, ren­der­ing many inef­fec­tive. Also, no new antibi­otics have been dis­cov­ered in decades, putting us at risk of a future with­out them – leav­ing humans vul­ner­a­ble to micro­bial infec­tions. The grow­ing phe­nom­e­non of antibi­ot­ic resis­tance there­fore rep­re­sents one of the most seri­ous threats to human and ani­mal health today. And a bet­ter under­stand­ing of the dif­fer­ent dri­vers of this resis­tance is becom­ing urgent.

Recent­ly, researchers estab­lished a con­nec­tion between this prob­lem and anoth­er major issue of our time: microplas­tic pol­lu­tion in the sea. These plas­tic par­ti­cles, less than 5mm in size, come from the degra­da­tion of plas­tic waste, or direct­ly from cer­tain prod­ucts them­selves, such as cos­met­ics. Because of their small size, microplas­tics found in water (oceans, lakes, rivers) are often ingest­ed by aquat­ic ani­mals, but also by humans since they can be present in tap water and bot­tles. They are sus­pect­ed of hav­ing harm­ful effects on health, and stud­ies to bet­ter under­stand the risks involved are cur­rent­ly being conducted. 

Over the past decade, when micro­bial sam­ples from microplas­tics float­ing in the seas and oceans were stud­ied, path­o­gen­ic bac­te­ria capa­ble of infect­ing humans of the Vib­rio, Sal­mo­nel­la or Legionel­la fam­i­ly were found. Fur­ther­more, many of these bac­te­ria car­ry the genes for antibi­ot­ic resis­tance. Nor­mal­ly, these bac­te­ria are not present in marine waters because they can­not sur­vive in water pH and salin­i­ty, or due to oth­er envi­ron­men­tal fac­tors, but over time their pres­ence in coastal waters has increased. This is main­ly due to the dis­charge of domes­tic, indus­tri­al or agri­cul­tur­al waste­water in the sea… but also of microplas­tics. The asso­ci­a­tion between microplas­tics and path­o­gen­ic bac­te­ria seems to be respon­si­ble for the longevi­ty of these bac­te­ria in marine envi­ron­ments, their repro­duc­tion, and their trans­port to regions far from the place of dis­charge into the sea. Biol­o­gist Maria Belen Sathicq, post-doc­tor­al fel­low at IRSA (CNR), is study­ing this micro­bial ecol­o­gy through the AENEAS research project.

What are the main dan­gers of the microplastic/antibiotic resis­tant bac­te­ria bino­mi­al for human and envi­ron­men­tal health?

Plas­tic pol­lu­tion has a major impact on com­mer­cial fish­ing and aqua­cul­ture activ­i­ties. When microplas­tics accu­mu­late in the tis­sues of marine ani­mals, they also con­t­a­m­i­nate all lev­els of the food chain, right up to our plates. But plas­tic debris also pro­vides a float­ing sub­strate that acts as a car­ri­er for harm­ful algae, organ­ic pol­lu­tants and poten­tial­ly path­o­gen­ic microor­gan­isms. In addi­tion, microplas­tics can facil­i­tate the trans­fer of genes for antibi­ot­ic resis­tance to aquat­ic ani­mals that ingest or fil­ter them… and then to con­sumers of fish and seafood, espe­cial­ly when ingest­ed raw. 

A 2018 study found that the gut micro­bio­ta of peo­ple who spend a lot of time near pol­lut­ed coast­lines often car­ry antibi­ot­ic-resis­tant bacteria.

A 2018 study found that the gut micro­bio­ta of peo­ple who spend a lot of time near pol­lut­ed coast­lines often car­ry antibi­ot­ic-resis­tant bac­te­ria. As for the envi­ron­ment, microplas­tics also induce resis­tance in aquat­ic micro­bial ecosys­tems to oth­er pol­lu­tants, such as heavy met­als. How­ev­er, while these phe­nom­e­na are con­firmed by sev­er­al exper­i­men­tal stud­ies, the search for evi­dence of the impact of microplas­tics on micro­bial com­mu­ni­ties in the nat­ur­al envi­ron­ment is still in its infancy.

What is the “plas­ti­sphere” and how is this new eco­log­i­cal niche formed in which antibi­ot­ic-resis­tant bac­te­ria pro­lif­er­ate, among others?

Bac­te­ria, algae and fun­gi attach them­selves to the sur­face of var­i­ous hard sub­strates – nat­ur­al or arti­fi­cial. This then gives rise to a biofilm – an adhe­sive and pro­tec­tive matrix pro­duced by the microor­gan­isms them­selves – in which they live. In 2013, Zettler and col­leagues pro­posed the term “plas­ti­sphere” to refer to the micro­bial com­mu­ni­ties dis­cov­ered on microplas­tics col­lect­ed in the North Atlantic. Since then, sev­er­al research stud­ies have shown that plas­tic can allow spe­cif­ic micro­bial com­mu­ni­ties to sur­vive in water. Microplas­tics are thus a new eco­log­i­cal niche offer­ing bac­te­ria greater chances of sur­vival in the nat­ur­al envi­ron­ment, and in which genet­ic exchange between dif­fer­ent indi­vid­u­als or species is favoured by the prox­im­i­ty pro­vid­ed by the biofilm.

Your AENEAS project is com­ing to an end. What meth­ods were used and what results were obtained?

The project, born in 2019 thanks to the sup­port of the AXA Research Fund, aimed to study the impact of microplas­tics on micro­bial com­mu­ni­ties in coastal waters of the north­ern Mediter­ranean region, with a par­tic­u­lar focus on the poten­tial selec­tion of antibi­ot­ic resis­tance with­in com­mu­ni­ties exposed to microplas­tic pol­lu­tion. We first assessed plas­tic com­po­si­tion and micro­bial com­mu­ni­ty diver­si­ty on microplas­tics at six sites along the north­ern Tyrrhen­ian Sea coast. We found that the dom­i­nant poly­mer there was poly­eth­yl­ene, and that its great­est con­cen­tra­tion was not in sites with the great­est anthro­pogenic impact (such as ports), as might have been expect­ed, but in less fre­quent­ed areas, such as nature reserves. 

The bac­te­r­i­al colonies present on microplas­tics and in water are very diverse, but poten­tial­ly path­o­gen­ic Vib­rio bac­te­ria and antibi­ot­ic resis­tance genes (espe­cial­ly against tetra­cy­cline), are the most abun­dant on microplas­tics in water. In a sec­ond step, we analysed the role of dif­fer­ent poly­mers on bac­te­ria, in par­tic­u­lar on pathogens. We main­ly stud­ied tyre rub­ber, a type of plas­tic with a very com­plex chem­i­cal com­po­si­tion. Indeed, this mate­r­i­al exerts selec­tion, and poten­tial­ly path­o­gen­ic bac­te­ria (e.g. Pseudomonas, Aeromonas, Acine­to­bac­ter) are rel­a­tive­ly more abun­dant where it is found. Final­ly, we are plan­ning a sur­vey to under­stand the lev­el of risk per­cep­tion of cit­i­zens liv­ing around these issues who live near the coastal areas we are study­ing, it will involve high school students.

Going for­ward, what are the most press­ing areas to study to curb the spread of antibi­ot­ic resistance?

There is still much to be learned about the role of microplas­tics in the spread of antibi­ot­ic resis­tance, although research has already accu­mu­lat­ed a great deal of evi­dence via lab­o­ra­to­ry stud­ies. How­ev­er, results strong­ly sug­gest that microplas­tics act as a long-term reser­voir for antibi­ot­ic resis­tance due to their dura­bil­i­ty, but the role of each type of poly­mer and addi­tive needs to be stud­ied. It is also impor­tant to eval­u­ate the behav­iour of bio­plas­tics; a promis­ing sub­sti­tute for petro­le­um-based plas­tics, that may be sim­i­lar to oth­er con­ven­tion­al plas­tics in terms of micro­bial com­mu­ni­ty formation. 

The grow­ing threat of antibi­ot­ic resis­tance requires a mul­ti-sec­toral approach, which views human, ani­mal and envi­ron­men­tal health as con­nect­ed and depen­dent on each oth­er (One Health con­cept). There are still many issues to be resolved: human abuse of antibi­otics, exces­sive use of these drugs in ani­mal farm­ing, and the effec­tive­ness of waste­water treat­ment plants in remov­ing pol­lu­tants such as microplastics.

Interview by Annalisa Plaitano

Contributors

Maria Belen

Maria Belen Sathicq

Post-doctoral fellow at the Institute for Water Research of the Italian National Research Council (CNR)

An Argentinean biologist, living and working in Italy, Maria Belen has a BSc in Biology, from the Universidad Nacional de La Plata (Buenos Aires, Argentina), and a PhD from the same University specialising in water quality assessment. Before arriving at the Molecular Ecology Group (IRSA-CNR) she worked on the use of phytoplankton as a pollution indicator, with emphasis on cyanobacteria. Currently she has an AXA postdoctoral fellowship with her project ENEAS, which aims to understand the role of microplastics in the spread of antibiotic resistant bacteria in the Tyrrhenian Sea.