Bacteria and the environment
All environmental compartments are connected. Humans and animals constantly exchange pathogenic or non-pathogenic bacteria, with or without resistance to antibiotics. These bacteria can easily spread into the environment though different routes.
The spread of antibiotic resistance
Humans, pets, livestock and fish farms rely on similar classes of antibiotics to fight infectious diseases. Both pathogenic and non-pathogenic bacteria evolve or exchange the ability to survive when exposed to these antibiotics. Then, they can spread into the environment through different routes, e.g. through water sanitation systems (1), as wastewater treatment facilities do not entirely remove antibiotic resistant bacteria before releasing water into waterways. Another common route is through the application of animal manure containing resistant bacteria to fields with cultivated crops (2), where such bacteria can flourish on the plants (3).
The uptake of these resistant bacteria can then happen through the food chain, when humans later consume these plants (4) or the contaminated flesh of animals and fish harbouring resistant bacteria (5). As bacteria can easily reach water reserves, water distribution infrastructure is also a potential route for the spread of these bacteria (6). Even wildlife, insects and other bugs are potential carriers of antibiotic resistant microbes (7). Tourism, migration and food imports (8) are nevertheless reported as the fastest way of spreading resistant strains of bacteria across borders.
At the healthcare facility level, resistant bacteria can spread by contact between patients or with healthcare staff, or through contaminated surfaces and medical devices (see HEALTHCARE-ASSOCIATED INFECTIONS).
Foodborne transmission of resistant bacteria is a common route for the spread of antibiotic resistance. Treating livestock with antibiotics can also be detrimental for the farmers' health, as they can acquire resistant bacteria from the animals and transmit them to others. Several studies have revealed high transmission rates of MRSA between animals and farm workers.(39)
Resistant bacteria from human sources have been detected in sewage treatment plants, in treated water released into the environment and in sludge applied to farmland. A 2013 report to the British Parliament stated that the highest concentrations of antibiotics and resistant bacteria were recorded “in effluent released from hospitals and drug manufacturing sites in developing countries”.(40)
More recently, a drug resistant “superbug” (E. coli) was found in drinking water samples from France, indicating that all potential reservoirs –human, animal and environmental, are now contaminated by ESBLs.(83)
Between 2015 and 2016, an atypically large outbreak of Elizabethkingia anophelis infections occurred in Wisconsin (USA), affecting 60 patients, among whom 1/3 of them died. Usually, this bacteria carried by mosquitos is not directly transmitted to human and is rarely responsible for infections, but rather contaminates the environment, in particular water. After an in-depth investigation from American and French research teams, the outbreak-causing strain was reported to be extremely mutant and resistant to a large number of antibiotics, thus increasing the pathogenic power of the bacteria and its transmission to human through the environmental reservoirs(96).