In the human pharmaceutical and veterinary industries, Monoglycerides are known for their ability to combat a wide range of bacteria and viruses. In practice, these molecules are used as sustainable anti-infective compounds, replacing the use of prophylactic antibiotics.
The spread of Early Mortality Syndrome / Acute Hepatopancreatic Necrosis Disease (EMS / AHPND) in shrimp caused by Vibrio bacteria has left significant consequences; therefore, 1-monoglycerides have been studied for development in the aquaculture industry.
Comprehensive Solution
Although many pathogens have been found to be associated with AHPND, the main causative agent is a strain of Vibrio parahaemolyticus. This bacterium shares close similarities with V. cholera and V. harveyi, prompting researchers to seek solutions to combat mortality rates.
Vibrio parahaemolyticus is transmitted through various means, such as phytoplankton, zooplankton, or unfavorable pond residues, etc.
Addressing AHPND requires a comprehensive approach. The adoption of a holistic approach, focusing on reducing infection concentrations in shrimp ponds, preventing colony formation in farmed animals, and combating toxins produced by Vibrio parahaemolyticus, has been proposed to restore balance and mitigate the impact of AHPND.
One of the proposed methods to prevent AHPND is to disrupt the adhesion of bacteria to the shrimp's stomach wall. Feeding 1-monoglycerides is believed to counteract the formation of V. parahaemolyticus colonies by preventing bacterial invasion and multiplication. Specific types of monoglycerides are also known for their emulsifying properties, which can increase the permeability of early-stage biofilms. This combination is considered the strength of 1-monoglycerides against the progression of AHPND.
Effects of 1-monoglycerides
1-monoglycerides are non-corrosive compounds, active independently of pH, and highly heat-stable. This makes them suitable for feed additive applications.
1-monoglycerides are known for their antibacterial and antiviral effects in human pharmaceuticals as well as in veterinary medicine. They are not classified as antibiotics because the molecules do not actually kill pathogens. Instead, they prevent bacteria from acquiring energy and water, causing the bacteria to gradually lose energy and water until they die.
Basic research conducted by the University of Lisbon shows that the homeostasis of bacterial cells is severely affected by 1-monoglycerides through changes in membrane stability and the blocking of a membrane absorber called aquaporin-3.
Treated bacteria cannot absorb enough glycerol – their main energy source – and therefore cannot multiply to establish a safe presence in a new host. Since colony formation is inhibited, the bacteria's quorum sensing, which leads to biofilm and toxin production, is effectively regulated.
1-monoglyceride Formulations
Two types of formulations have been tested in Thailand:
+ Containing only short-chain 1-monoglycerides
+ Containing both short- and medium-chain 1-monoglycerides
Both formulations were tested in dry powder form and added to shrimp feed. Five farms were selected, including: 2 farms with chronic AHPND issues, 2 farms with occasional outbreaks, and 1 farm with no history of AHPND.
Results showed that the formulation containing both short- and medium-chain 1-monoglycerides performed better. Mortality rates significantly decreased, and early harvesting was not required. Shrimp from the 2 farms with AHPND issues showed poor shell quality, indicating a compromised health status likely caused by the presence of a high pathogen load. Ponds with no history of AHPND showed better growth performance.
The synergy between short- and medium-chain 1-monoglycerides was confirmed by an additional trial conducted by an independent research laboratory and in vivo testing. Shrimp with Vibrio issues, fed with short- and medium-chain 1-monoglycerides in their diet, showed a 16% reduction in mortality compared to shrimp fed only short-chain monoglycerides.
Another trial showed a shift in bacterial colonies from blue to yellow in shrimp culture environments when fed 1-monoglycerides via artemia.
Another field trial showed better results when 1-monoglyceride molecules were incorporated into the feed mixture before pelleting. The experiment showed that shrimp treated with 1-monoglycerides in their diet yielded better results than control groups in terms of growth and survival rates.
1-monoglycerides in dry powder vs. liquid form
Mechanism: 1-monoglycerides are typically applied in dry form by attaching the molecules to a carrier. Within the digestive tract, 1-monoglycerides are released from the carrier and then exert their anti-infective activity. The liquid formulation performed best, reducing mortality by up to 80% compared to the positive control group. Shrimp received 0.8% of their diet consisting of liquid 1-monoglycerides once daily. In this treatment group, a small number of shrimp died, accounting for approximately 6.7%, but the cause of death was likely cannibalism rather than AHPND.
Histological analyses of sampled shrimp, conducted at the Aquaculture Pathology Laboratory at the University of Arizona, showed a significant reduction in infection rates in shrimp fed liquid 1-monoglycerides. Complete elimination of Vibrio parahaemolyticus is not possible, but the minimal presence of this bacterium in shrimp tissue did not necessarily lead to the development of AHPND in the trial.
Several field trials are currently underway to study the long-term effects of liquid 1-monoglycerides. Preliminary data shows promising results. Most ponds have not shown AHPND outbreaks to date. In ponds at heavily infected farms, AHPND development could not always be prevented, but it was delayed for several weeks.
Source: Global Aquaculture Advocate
