Abstract
Antibiotics used for humans and livestock are emerging as pollutants in aquatic environments. However, little is known about their effect on aquatic organisms, especially in crustaceans. In the present study, the freshwater crayfish Pacifastacus leniusculus was exposed during 21 days to environmental concentrations of sulfamethoxazole (SMX) (100 ng/L and 1 μg/L). Subsequently, the crayfish susceptibility to infection was evaluated by using White Spot Syndrome Virus (WSSV) challenge, a well-known crustacean pathogen. The median survival time of the infected crayfish exposed to 100 ng/L SMX was one day, whereas the control and the group exposed to 1 μg/L SMX survived for two and three days, respectively. In order to elucidate the effect of SMX upon the crayfish immune response, new sets of crayfish were exposed to the same SMX treatments to evaluate mRNA levels of immune-related genes which are expressed and present in hemocytes and intestine, and to perform total and differential hemocyte counts. These results show a significant down-regulation of the antimicrobial peptide (AMP) Crustin 3 in hemocytes from the 100 ng/L SMX group, as well as a significant up-regulation of the AMP Crustin 1 in intestines from the 1 μg/L SMX group. Semigranular and total hemocyte cell number were observed to be significantly lower after exposure to 100 ng/L SMX in comparison with the control group. The present study demonstrates that environmentally relevant SMX concentrations in the water at 100 ng/L led to an increased WSSV susceptibility, that may have been caused by a reduction of circulating hemocytes. Nevertheless, SMX concentrations of 1 μg/L could marginally and for a few days have an immunostimulatory effect.
Highlights
Antibiotics represent around 40% of the most frequently encountered pharmaceuticals contaminating the freshwater systems all over the world [1]
In order to investigate whether exposure to environmental-relevant concentrations of the antibiotic SMX had an effect on the crayfish survival to viral infection, crayfish were first exposed to SMX dissolved in water in aquaria for 21 days followed by an injection of White Spot Syndrome Virus (WSSV)
The results showed that crayfish exposed to 100 ng/L of SMX had a significantly lower number of semigranular cells (SGCs) and total hemocyte (THC) compared with the control group (P < 0.05), as well as a significantly lower number of granular cells (GCs) (P < 0.01), SGCs (P < 0.05) and THC (P < 0.01) in comparison with the group exposed to 1 μg/L of SMX (Fig. 5)
Summary
Antibiotics represent around 40% of the most frequently encountered pharmaceuticals contaminating the freshwater systems all over the world [1]. Sulfamethoxazole (SMX) is one of the most prominent, with concentrations ranging from ng/L to mg/L in different aquatic environments, including rivers and effluents of wastewater treatment plants [1,2,3,4,5,6,7]. Sulfamethoxazole is important due to its widespread use in human and veterinary medicine. It is usually administrated in combination with trimethoprim to treat diseases, and little information is available about pharmacodynamics, dosage, withdrawal period and turnover rate of SMX alone. Sulfamethoxazole is considered a persistent pollutant in the aquatic environments since it is not completely eliminated after wastewater treatment [5,8]. PH, salinity and dissolved organic matter in the water determine the photodegradation rate of SMX, and this rate is slower in environmental compartments, including estuarine and river water [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
