Molecular identification of Streptococcus sp. and antibiotic resistance genes present in Tilapia farms (Oreochromis niloticus) from the Northern Pacific region, Costa Rica

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.

A Review of Current Bacterial Resistance to Antibiotics in Food Animals

“…Notably, the plasmid metagenomic focusing on the mobile genetic elements (MGEs) may have great potential to identify ARGs in complex environments ( Liu et al, 2019 ). Meanwhile, Oviedo-Bolaños collected 450 individuals from tilapia ponds and organ pools in the Northern Pacific region, Costa Rica, and identified ARGs (including tet M, tet O, fex A, and erm B) by the PCR method ( Oviedo-Bolaños et al, 2021 ). The results showed that S. iniae was not detected, and 60% of the ponds and 46% of the organ pools were positive for Streptococcus agalactiae with tet O (29.1%), and tet M (12.7%) and erm B (1.8%), respectively.…”

“…It is favorable to improve the knowledge of the diseases infected with Streptococcus sp. and to efficiently prevent and control these pathogens in tilapia farming worldwide ( Oviedo-Bolaños et al, 2021 ).…”

Investigating the Effect of an Oxytetracycline Treatment on the Gut Microbiome and Antimicrobial Resistance Gene Dynamics in Nile Tilapia (Oreochromis niloticus)

“…Oxytetracycline is a natural broad-spectrum antibiotic extensively used in global aquaculture due to its limited side effects in the host and broad-spectrum activity against both Gram-negative and Gram-positive bacteria, through the inhibition of protein syn-thesis [11][12][13]. In tilapia, OTC has been shown to successfully treat a range of bacterial diseases including Francisellosis, motile Aeromonas septicemia, and Streptococcosis, which are significant disease challenges for this sector [14][15][16]. Across the global aquaculture industry, OTC is often administered orally in the diet during disease outbreaks, where doses range 50 to 250 mg/kg/day for typically between four and eight days, up to 21 days, depending on the fish species and farming country [17,18].…”

Multi‐antibiotics resistance phenotype of pathogenic Vibrio parahaemolyticus isolated from acute hepatopancreatic necrosis disease in Litopenaeus vannamei farmed in the Mekong Delta

“…The recommended antibiotics for the treatment of V. parahaemolyticus are tetracycline or ciprofloxacin, which can also be used in severe or prolonged disease of V. parahaemolyticus (see review by Elmahdi et al, 2016). However, the increasing diversity of ARGs in aquatic gut microorganisms has been reported in recent studies based on polymerase chain reaction (PCR) and metagenomic analysis (e.g., Liu et al, 2019; Oviedo‐Bolaños et al, 2021). In addition to Aeromonas , the ARGs in the intestinal bacteria of shrimp are also mainly derived from Vibrio (accounting for 2.8%–51%) plasmids (Liu et al, 2019).…”