Antibiotics as pollution in freshwater environment

Several studies have shown that there are high levels of antibiotics in watercourses around the world. We also know that this occurrence can cause the development of antibiotic-resistant bacteria in nature and a spread of these bacteria. However, there may also be other risks with antibiotics in watercourses that are much less well known. We know that freshwater environments are habitats for many species, microorganisms as well as plants and animals, and in recent years these environments have lost a large part of their biological diversity. In our studies, we investigate whether low concentrations of the antibiotic sulfamethoxazole (SMX), which is commonly found in aquatic environments, affect freshwater crayfish. We have exposed crayfish to antibiotics and investigated whether the bacterial flora in their guts differ from crayfish not exposed to antibiotics. We found that there are very large individual differences in the species composition of the animals' intestinal microflora, which makes it difficult to interpret results after an antibiotic exposure. In order to develop the methodology and obtain more reliable results, we now analyze the bacterial content in the crayfish's faeces before and after exposure in each individual.

We also investigate whether crayfish exposed to low levels of antibiotics are more susceptible to various pathogens, such as viruses, bacteria or crayfish plague. We have found that the resistance to a common viral disease called white spot disease became slightly worse in the animals exposed to low levels of SMX. When, on the other hand, the crayfish's sensitivity to bacterial infections was tested, the antibiotic-exposed crayfish survived longer than the control crayfish group. This may indicate that the antibiotic accumulates in the crayfish's tissues, which may be a risk for resistance development.

When we compared the intestinal bacteria after antibiotic exposure with a control group, we found in some of the exposed animals an increased number of bacteria of the genus Vibrio. These bacteria are most common in seawater environments, but some species also occur in freshwater. One of the species we discovered was Vibrio areninigrae, which turned out to be pathogenic to the crayfish. The species also proved to be resistant to the antibiotic we exposed the crayfish to. It may therefore be important to pay attention to whether exposure over a longer period results in an increased risk of multiplication of these bacterial species in freshwater environments. Read more in our publications.