Molecular identification of Streptococcus sp. and antibiotic resistance genes present in Tilapia farms (Oreochromis niloticus) from the Northern Pacific region, Costa Rica
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Date
2021
Authors
Karen Oviedo-Bolaños
Jorengeth Abad Rodríguez-Rodríguez
Carolina Sancho-Blanco
Juan Esteban Barquero-Chanto
Nelson Peña-Navarro
Cesar Marcial Escobedo-Bonilla
Rodolfo Umaña-Castro
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Abstract
Streptococcosis is a bacterial disease in tilapia that produces economic losses, caused
mainly by Streptococcus agalactiae and S. iniae. It is treated using oxytetracycline and
florfenicol, which when inappropriately used promotes the selection of antibiotic resistance
genes (ARGs). The disease has been mainly associated with stress events such as
variations in temperature. The aims of the present study were (1) to detect by molecular
methods two species of Streptococcus sp. in a tilapia farm, (2) to relate their presence to
physicochemical parameters in the culture system, and (3) to detect the presence of ARGs
in tilapia tissues and/or ponds. Tilapia grow-out ponds (n = 30) were sampled, collecting
15 individuals per pond. The physicochemical parameters of water were measured in
each pond. Per pond, organs such as the liver, spleen, brain, and eyes were collected from
each individual. Then, each organ type was pooled with the respective organ of the other
individuals, processed for DNA extraction, and used for PCR analyses to determine the
presence of S. agalactiae and S. iniae and for the detection of ARGs (tetM, tetO, fexA,
and ermB). The correlations between the presence of S. agalactiae and water physicochemical
parameters were determined. Sixty percent of the ponds and 46% of the organ
pools were positive for S. agalactiae, whereas S. iniae was not detected. The positive
samples showed the following resistance genes: tet(O) (29.1%), tet(M) (12.7%), and
erm(B) (1.8%). A moderate but significant positive correlation was found between
temperature and the presence of S. agalactiae. This work reported the molecular detection
of two species of Streptococcus and ARGs, providing information that allows fast and
effective control of these pathogens in tilapia farming. In addition, a future complementary
study on Streptococcus sp. serotype distribution and antibiotic resistance genes from
tilapia cultured in Costa Rica could also contribute to increase the knowledge of
S. agalactiae infections in tilapia farming worldwide.
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Keywords
Aquaculture, Tilapia, Streptococcosis, Antibiotic resistance genes (ARGs), Endpoint PCR, Water quality
Citation
https://doi.org/10.1007/s10499-021-00751-0