Antibiotic-resistant vibrios in farmed shrimp

Identification and characterization of a novel bacteriocin gene cluster in Lysinibacillus boronitolerans

Although the antibiotics inhibit or kill pathogens, the abuse leads to the resistance formation and even "Super Bacteria." Therefore, it is urgent to explore the natural and safe alternatives such as bacteriocin. In this study, an uncharacterized bacteriocin gene cluster for Lysinibacillus boronitolerans was first predicted by genome sequencing and bioinformatics analysis, of which including two biosynthetic genes, a regulatory gene, a transport-related gene, and six other genes. Subsequently, the 10.24-kb gene cluster was expressed in Escherichia coli BL21, and the lysate effectively inhibited the growths of pathogenic bacteria containing Bacillus pumilus, Bacillus velezensis, Pseudomonas syringae pv. tomato DC3000, and Xanthomonas axonopodis pv. manihotis. The antibacterial substance was purified by 70% ammonium sulfate precipitation and further identified by liquid chromatography-tandem mass spectrometry. The results showed that the antibacterial substance consisted of 44 amino acids and had 24.1% sequence identity with the cyanobacterin Piricyclamide 7005 E4 PirE4, a bacteriocin analogue. The minimal set of genes required for the biosynthesis of the antibacterial substance was determined by site-directed mutagenesis, suggesting both a transcriptional repressor and a phosphohydroxythreonine transaminase were essential. Subsequently, the evolution and conservation of the two proteins were analyzed among 22 Lysinibacillus species. Among them, the residues responsible for functions were identified. Collectively, our results set a solid foundation for investigation of the biosynthesis and application of bacteriocin.

In Silico and In Vitro Investigation of Phytochemicals Against Shrimp AHPND Syndrome Causing PirA/B Toxins of Vibrio parahaemolyticus

In Southeast Asia, the penaeid shrimp aquaculture production faces a new pandemic bacterial disease called acute hepatopancreatic necrosis disease (AHPND). The highly profitable pacific white shrimp, Litopenaeus vannamei, has become a challenging species due to severe lethal infections. Recent research has identified a critical pathogen, Vibrio parahaemolyticus, which caused significant loss in the shrimp industry. The disease pathway involves a virulence plasmid encoding binary protein toxins (PirA/B) that cause cell death. The protein toxins were inherited and conjugatively transferred to other Vibrio species through a post-segregational killing system. In this study, "in silico" (Glide, 2021) analysis identified four phytocompounds as myricetin (Myr), ( +)-taxifolin (TF), (-)-epigallocatechin gallate (EGCG), and strychnine (STN) which could be most effective against both the toxins concerning its docking score and affinity. The interactions of complexes and the critical amino acids involved in docking were analyzed using the Discovery Studio (version 2016). Molecular dynamic studies showed lower root mean square deviations (RMSD) and improved stabilization of ( +)-taxifolin (TF) and (-)-epigallocatechin-3-gallate (EGCG) against both the protein toxins. The antibacterial potential of all four selected compounds had tested against pathogenic strains of V. parahaemolyticus through minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The best MBC results were observed at concentrations of 1 mg/mL for EGCG and 1.25 mg/mL for TF. Moreover, the complete reduction of viable cell counts in the in vitro bactericidal activity had recorded after 24 h of incubation.

Insights into molecular aspects of pathogenesis and disease management in acute hepatopancreatic necrosis disease (AHPND): An updated review

Shrimp aquaculture is a rapidly growing sector that makes a significant economic contribution. However, the aquaculture industry is confronted with significant challenges, and infectious diseases, notably Acute Hepatopancreatic Necrosis Disease (AHPND), have emerged as severe threat. AHPND is caused by pathogens carrying the pVA-1 plasmid, which expresses the PirAB toxin, and it has wreaked havoc in shrimp aquaculture, imposing substantial economic burdens. To address this issue, it is crucial to delve into shrimp's immune responses. Therefore, this comprehensive review offers an in-depth examination of AHPND outbreaks, encompassing various facets such as environmental factors, host susceptibility, and the mechanisms employed by the pathogens. Traditional approaches to combat AHPND, primarily relying on chemicals and antibiotics, have raised concerns related to antibiotic resistance and have demonstrated limited success in disease control. Hence this review spotlights recent advancements in molecular diagnostics, therapeutic agents, and research related to shrimp immunity. Understanding these developments is crucial in the ongoing battle against AHPND. In conclusion, this review underscores the pressing need to comprehend the underlying mechanisms of AHPND pathogenesis and emphasizes the importance of developing comprehensive and effective solutions to combat this devastating disease, which continues to threaten the sustainability of shrimp farming.

Prevalence and antimicrobial resistance profiles of Vibrio spp. and Enterococcus spp. in retail shrimp in Northern California

Shrimp is one of the most consumed seafood products globally. Antimicrobial drugs play an integral role in disease mitigation in aquaculture settings, but their prevalent use raises public health concerns on the emergence and spread of antimicrobial resistant microorganisms. Vibrio spp., as the most common causative agents of seafood-borne infections in humans, and Enterococcus spp., as an indicator organism, are focal bacteria of interest for the monitoring of antimicrobial resistance (AMR) in seafood. In this study, 400 samples of retail shrimp were collected from randomly selected grocery stores in the Greater Sacramento, California, area between September 2019 and June 2020. The prevalence of Vibrio spp. and Enterococcus spp. was 60.25% (241/400) and 89.75% (359/400), respectively. Subsamples of Vibrio (n = 110) and Enterococcus (n = 110) isolates were subjected to antimicrobial susceptibility testing (AST). Vibrio isolates had high phenotypic resistance to ampicillin (52/110, 47.27%) and cefoxitin (39/110, 35.45%). Enterococcus were most frequently resistant to lincomycin (106/110, 96.36%), quinupristin-dalfopristin (96/110, 87.27%), ciprofloxacin (93/110, 84.55%), linezolid (86/110, 78.18%), and erythromycin (58/110, 52.73%). For both Vibrio and Enterococcus, no significant associations were observed between multidrug resistance (MDR, resistance to ≥3 drug classes) in isolates from farm raised and wild caught shrimp (p > 0.05) and in isolates of domestic and imported origin (p > 0.05). Whole genome sequencing (WGS) of a subset of Vibrio isolates (n = 42) speciated isolates as primarily V. metschnikovii (24/42; 57.14%) and V. parahaemolyticus (12/42; 28.57%), and detected 27 unique antimicrobial resistance genes (ARGs) across these isolates, most commonly qnrVC6 (19.05%, 8/42), dfrA31 (11.90%, 5/42), dfrA6 (9.5%, 4/42), qnrVC1 (9.5%, 4/42). Additionally, WGS predicted phenotypic resistance in Vibrio isolates with an overall sensitivity of 11.54% and specificity of 96.05%. This study provides insights on the prevalence and distribution of AMR in Vibrio spp. and Enterococcus spp. from retail shrimp in California which are important for food safety and public health and exemplifies the value of surveillance in monitoring the spread of AMR and its genetic determinants.

Investigation of antibiotic-resistant vibrios associated with shrimp (Penaeus vannamei) farms

For the sustainable farming of disease-free and healthy shrimps, antimicrobial use is frequent nowadays in shrimp-cultured system. Considering the serious impact of global antimicrobial resistance (AMR), the present study was focused to investigate the prevalence of antimicrobial-resistant vibrios among infected shrimps (Penaeus vannamei) from two brackish water-cultured farms. Diverse species of vibrios viz. V. alginolyticus, V. parahaemolyticus, V. cholerae, V. mimicus, and V. fluvialis along with Aeromonas hydrophila, A. salmonicida and Shewanella algae were recovered from the shrimps on TCBS medium. Shannon-Wiener diversity index and H' (loge) were 1.506 and 1.69 for the isolates from farm 1 and farm 2, respectively. V. alginolyticus was found to be the most resistant isolate by showing multiple antibiotic resistance (MAR) index of 0.60 followed by V. mimicus (0.54) and V. parahaemolyticus (0.42). Among the 35 antibiotics of 15 different classes tested, tetracyclines, beta-lactams and cephalosporins were found as the most resistant antibiotic classes. All the isolates possessed a MAR index > 0.2 and the majority exhibited minimum inhibitory concentration (MIC) > 256 mcg/ml, thereby indicating the excess exposure of antibiotics in the systems. An enhanced altered resistance phenotype and a significant shift in the MAR index were noticed after plasmid curing. Public health is further concerning because plasmid-borne AMR is evident among the isolates and the studied shrimp samples are significant in the food industry. This baseline information will help the authorities to curb antimicrobial use and pave the way for establishing new alternative strategies by undertaking a multidimensional "One-Health" approach.

Prevalence, Antibiotics Resistance and Plasmid Profiling of Vibrio spp. Isolated from Cultured Shrimp in Peninsular Malaysia

Vibrio is the most common bacterium associated with diseases in crustaceans. Outbreaks of vibriosis pose a serious threat to shrimp production. Therefore, antibiotics are commonly used as preventative and therapeutic measures. Unfortunately, improper use of antibiotics leads to antibiotic resistance. Nevertheless, information on the occurrence of Vibrio spp. and antibiotic use in shrimp, particularly in Malaysia, is minimal. This study aimed to provide information on the occurrence of Vibrio spp., its status of antibiotic resistance and the plasmid profiles of Vibrio spp. isolated from cultured shrimp in Peninsular Malaysia. Shrimp were sampled from seven farms that were located in different geographical regions of Peninsular Malaysia. According to the observations, 85% of the shrimp were healthy, whereas 15% were unhealthy. Subsequently, 225 presumptive Vibrio isolates were subjected to biochemical tests and molecular detection using the pyrH gene. The isolates were also tested for antibiotic susceptibility against 16 antibiotics and were subjected to plasmid profiling. Eventually, 13 different Vibrio spp. were successfully isolated and characterized using the pyrH gene. They were the following: V. parahaemolyticus (55%), V. communis (9%), V. campbellii (8%), V. owensii (7%), V. rotiferianus (5%), Vibrio spp. (4%), V. alginolyticus (3%), V. brasiliensis (2%), V. natriegens (2%), V. xuii (1%), V. harveyi (1%), V. hepatarius (0.4%) and P. damselae (3%). Antibiotic susceptibility profiles revealed that all isolates were resistant to penicillin G (100%), but susceptible to norfloxacin (96%). Furthermore, 16% of the isolates revealed MAR of less than 0.2, while 84% were greater than 0.2. A total of 125 isolates harbored plasmids with molecular weights between 1.0 and above 10 kb, detected among the resistant isolates. The resistant isolates were mediated by both chromosomal and plasmid factors. These findings support the use of surveillance data on the emerging patterns of antimicrobial-resistance and plasmid profiles of Vibrio spp. in shrimp farms. The findings from this study can be used to develop a better disease management strategy for shrimp farming.

Vibriosis Outbreaks in Aquaculture: Addressing Environmental and Public Health Concerns and Preventive Therapies Using Gilthead Seabream Farming as a Model System

Bacterial and viral diseases in aquaculture result in severe production and economic losses. Among pathogenic bacteria, species belonging to the Vibrio genus are one of the most common and widespread disease-causing agents. Vibrio infections play a leading role in constraining the sustainable growth of the aquaculture sector worldwide and, consequently, are the target of manifold disease prevention strategies. During the early, larval stages of development, Vibrio species are a common cause of high mortality rates in reared fish and shellfish, circumstances under which the host organisms might be highly susceptible to disease preventive or treatment strategies such as vaccines and antibiotics use, respectively. Regardless of host developmental stage, Vibrio infections may occur suddenly and can lead to the loss of the entire population reared in a given aquaculture system. Furthermore, the frequency of Vibrio-associated diseases in humans is increasing globally and has been linked to anthropic activities, in particular human-driven climate change and intensive livestock production. In this context, here we cover the current knowledge of Vibrio infections in fish aquaculture, with a focus on the model species gilthead seabream (Sparus aurata), a highly valuable reared fish in the Mediterranean climatic zone. Molecular methods currently used for fast detection and identification of Vibrio pathogens and their antibiotic resistance profiles are addressed. Targeted therapeutic approaches are critically examined. They include vaccination, phage therapy and probiotics supplementation, which bear promise in supressing vibriosis in land-based fish rearing and in mitigating possible threats to human health and the environment. This literature review suggests that antibiotic resistance is increasing among Vibrio species, with the use of probiotics constituting a promising, sustainable approach to prevent Vibrio infections in aquaculture.

Salpianthus macrodontus Extracts, a Novel Source of Phenolic Compounds with Antibacterial Activity against Potentially Pathogenic Bacteria Isolated from White Shrimp

This study aimed to evaluate the antibacterial activity in vitro of Salpianthus macrodontus and Azadirachta indica extracts against potentially pathogenic bacteria for Pacific white shrimp. Furthermore, the extracts with higher inhibitory activity were analyzed to identify compounds responsible for bacterial inhibition and evaluate their effect on motility and biofilm formation. S. macrodontus and A. indica extracts were prepared using methanol, acetone, and hexane by ultrasound. The minimum inhibitory concentration (MIC) of the extracts was determined against Vibrio parahaemolyticus, V. harveyi, Photobacterium damselae and P. leiognathi. The polyphenol profile of those extracts showing the highest bacterial inhibition were determined. Besides, the bacterial swimming and swarming motility and biofilm formation were determined. The highest inhibitory activity against the four pathogens was found with the acetonic extract of S. macrodontus leaf (MIC of 50 mg/mL for Vibrio spp. and 25 mg/mL for Photobacterium spp.) and the methanol extract of S. macrodontus flower (MIC of 50 mg/mL for all pathogens tested). Both extracts affected the swarming and swimming motility and the biofilm formation of the tested bacteria. The main phenolic compounds related to Vibrio bacteria inhibition were naringin, vanillic acid, and rosmarinic acid, whilst hesperidin, kaempferol pentosyl-rutinoside, and rhamnetin were related to Photobacterium bacteria inhibition.

Characterization of a novel shrimp pathogen, Vibrio brasiliensis, isolated from Pacific white shrimp, Penaeus vannamei

A novel pathogenic strain Vibrio 20190611023 was isolated from the hepatopancreas of moribund cultured Penaeus vannamei suffering from black gill disease. This strain was identified as V. brasiliensis based on the phylogenetic analyses of 16S rDNA gene and five other housekeeping genes (i.e., gapA, ftsZ, mreB, topA and gyrB). Some biochemical features of this strain were determined with an API 20NE system, and its haemolytic activity was determined using a sheep blood agar plate. The pathogenicity of this isolate 20190611023 was confirmed by the experimental challenge tests and histopathological examinations. P. vannamei were challenged via reverse gavage with different doses of bacterial suspensions. The calculated median lethal dose (LD₅₀ ) was (3.16 ± 1.78) × 10⁵  CFU/g (body weight). Moreover, antibiotic susceptibility tests were performed, the results of which showed that the strain 20190611023 was sensitive to chloramphenicol, compound sulphamethoxazole, ciprofloxacin, doxycycline and oxacillin, but resistant to erythromycin, kanamycin, gentamicin, cefoperazone, ceftriaxone, cefamezin and piperacillin. To our knowledge, this is the first report for demonstrating V. brasiliensis as a shrimp pathogen, which expands the host range of V. brasiliensis infection. The present study highlights that more attention should be paid to this novel pathogen in intensive shrimp aquaculture.

Occurrence and antibiogram signatures of some Vibrio species recovered from selected rivers in South West Nigeria

Vibrio species, widely distributed in water environments, has emerged as a prominent cause of water and food-related disease outbreaks posing significant risk to human and animal health worldwide. About 40% of presumptive isolates recovered from four selected rivers in Southwest Nigeria and, established as Vibrio species genus through polymerase chain reaction techniques., were subjected to antibiotic susceptibility testing against a panel of 18 commonly used antibiotics. The relative prevalence of key Vibrio species (V. parahaemolyticus, V. vulnificus, V. mimicus, V. harveyi, and V. cholerae) was in the order 17%, 13.3%, 4.4%, 2.2%, and 2.2% respectively. Antibiotic resistance by all Vibrio species was mostly observed against doxycycline (71-89%), erythromycin (86-100%), tetracycline (71-89%), rifampicin (86-100%), and sulfamethoxazole (87-100%), though susceptibility to meropenem (86-100%), cephalothin (60-100%), norfloxacin (93-100%), ciprofloxacin (88-100%), amikacin (64-100%), gentamicin (57-74%), and trimethoprim/sulfamethoxazole (57-81%) was equally observed in all species. Vibrio mimicus expressed highest resistance against streptomycin and chloramphenicol (64%), while V. vulnificus (52%) and V. cholerae (57%) had the highest resistance against cephalothin. High resistance against ampicillin (57%) and amoxicillin (50%) was exhibited by V. cholerae and V. mimicus respectively. Indexes of multiple antibiotic resistances (MARI) among Vibrio species ranged between 0.11 and 0.72 with the highest MAR index of 0.72 observed in one isolate of V. vulnificus. This study reveals high prevalence of Vibrio species in the selected rivers as well as elevated resistance against some first-line antibiotics, which suggests possible inappropriate antimicrobial usage around study communities. We conclude that the freshwater resources investigated are unfit for domestic, industrial, and recreational uses without treatment prior to use and are potential reservoirs of antibiotic-resistant Vibrio species in this environment.

Antimicrobial Power of Organic Acids and Nature-Identical Compounds against Two Vibrio spp.: An In Vitro Study

Vibrosis is one of the major threats in aquaculture farming, and due to the increasing antimicrobial resistance of different Vibrio species, there is an urgent need to replace conventional treatments with more sustainable solutions. Antimicrobial molecules such as organic acids (OA) and nature-identical compounds (NIC) are currently finding a central role in the infection management of terrestrial livestock, but little is known about their usage in aquaculture. The aim of this study was to perform a preliminary screening of the in vitro antimicrobial activity of a wide panel of OA and NIC against 2 Vibrio species characteristic of the Mediterranean area, Vibrio harveyi and Vibrio anguillarum, through minimal inhibitory/bactericidal concentration tests. The active principles that showed the best effective pathogen control were medium-chain fatty acids, sorbic and benzoic acid among OA and phenolic monoterpenoids (thymol, carvacrol and eugenol) and aromatic monoterpene aldehydes (vanillin and cinnamaldehyde) among NIC. These results showed how the usage of OA and NIC can open promising perspectives in terms of Vibrio spp. load control in aquaculture. Natural or nature-identical feed additives can make aquaculture production not only more efficient by reducing the need for medicated treatments, but also more sustainable.

High throughput sequencing reveals the abundance and diversity of antibiotic-resistant bacteria in aquaculture wastewaters, Shandong, China

An innovative investigation was undertaken into the abundance and diversity of high antibiotic-resistant bacteria in aquaculture waters in Shandong Province, China, through cumulation incubation, PCR amplification of 16S rDNA, and high-throughput sequencing. The results showed that Vibrio, Bacillus, Vagococcus, Acinetobacter, Shewanella, Psychrobacter, Lactococcus, Enterococcus, Marinimonus and Myroids were abundant in the aquaculture waters, whereas other phylum including Actinobacteria, Deinococcus-Thermus, Omnitrophica and Nitrospirae had relatively lower abundance. Our studies revealed the presence of different bacteria in different locations in the aquaculture waters, most of which were resistant to multiple antibiotics. That is, the same microbial species from the same aquaculture wastewater can resist different antibiotics. Altogether, a considerable portion of the microbial community were found to be multi-drug resistant. It is essential that the spread of the antibiotic-resistant bacteria is controlled so that the distribution of antibiotic resistance genes to other environments is avoided.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02656-4.

Evaluation of Microalgae as Immunostimulants and Recombinant Vaccines for Diseases Prevention and Control in Aquaculture

Microalgae are often used as nutritional supplements for aquatic animals and are widely used in the aquaculture industry, providing direct or indirect nutrients for many aquatic animals. Microalgae are abundant in nature, of high nutritional value, and some of them are non-toxic and rich in antioxidants so that they can be explored as a medicinal carrier for human or animals. Natural wild-type microalgae can be adopted as an immunostimulant to enhance non-specific immune response and improve growth performance, among which Haematococcus pluvialis, Arthrospira (Spirulina) platensis, and Chlorella spp. are commonly used. At present, there have been some successful cases of using microalgae to develop oral vaccines in the aquaculture industry. Researchers usually develop recombinant vaccines based on Chlamydomonas reinhardtii, Dunaliella salina, and cyanobacteria. Among them, in the genetic modification of eukaryotic microalgae, many examples are expressing antigen genes in chloroplasts. They are all used for the prevention and control of single infectious diseases and most of them are resistant to shrimp virus infection. However, there is still no effective strategy targeting polymicrobial infections and few commercial vaccines are available. Although several species of microalgae are widely developed in the aquaculture industry, many of them have not yet established an effective and mature genetic manipulation system. This article systematically analyzes and discusses the above problems to provide ideas for the future development of highly effective microalgae recombinant oral vaccines.

Use of Bacteriophages to Control Vibrio Contamination of Microalgae Used as a Food Source for Oyster Larvae During Hatchery Culture

Cultured microalgae are the primary food source for oyster larvae during hatchery culture and are a potential vector for Vibrio spp. infection of larval cultures. Bacteriophages have shown potential for controlling contamination of Vibrio spp. in aquaculture systems and their application could be an effective biological control method to eliminate such bacterial contamination of microalgae. This study investigated whether Vibrio-free microalgae sources could be ensured via the application of Vibrio specific phages. As a first step, four different Vibrio bacteriophages (belonging to the Myoviridae viral family) were isolated from marine waters in Queensland, Australia and used in challenge tests against a Vibrio host species, previously isolated from New South Wales oyster hatchery and found to be closely related to V. alginolyticus (ATCC 17749). The genome sequence of one of the four isolated bacteriophages, Vibrio Φ-2, that displayed strongest virulence against the host was determined. The 242446 bp genome of this bacteriophage was predicted to encode 217 proteins with an average GC content of 43.91%, containing putative thymidine kinases and a lysin enzyme. Application of these bacteriophages to pathogenic Vibrio spp. contaminating microalgae suspensions resulted in significant decreases in their numbers within 2 h. Findings indicated that direct application of bacteriophages to microalgae suspensions could be an effective method of reducing the occurrence of vibriosis in oyster hatcheries.

Effects of Carbon/Nitrogen Ratio on Growth, Intestinal Microbiota and Metabolome of Shrimp (Litopenaeus vannamei)

Increasing the C/N ratio of input feed has been reported as a practical approach for improving water quality and enhancing shrimp growth through changing the bacterial community of rearing water. However, little is known about the effects of different C/N ratios of feed input on the intestinal microbiota and metabolome of shrimp. In the present study, the effects of three different C/N ratio levels (CN6, CN10, and CN15) maintained by adding sucrose on the growth, intestinal microbiota and metabolome of Litopenaeus vannamei, and bioflocs formation were investigated after 17 days of feeding. The results indicated that higher C/N ratio (10 and 15), especially CN15, of feed input significantly enhance the length and weight of shrimp individuals accompanied by a significant accumulation of bioflocs, compared to that of CN6. The increase of C/N ratio input decreased the α-diversity of the intestinal microbiota and changed the microbial community structure through increasing the relative abundance of Actinobacteria, Rhodobacteraceae (mainly consist of Roseobacter and Paracoccus groups), Alteromonadaceae, and inhibiting the growth of Cyanobacteria, certain Rhodobacteraceae, Mycoplasmataceae and Vibrio. The change of microbial community caused by increasing C/N ratio input was closely associated with various bioactive metabolites of flavonoids, benzenoids, prenol lipids, and indole derivatives, which are benefit for shrimp growth either as an antimicrobial agent or as a nutrient component. Overall, this study demonstrated that manipulating high C/N ratio of feed input helps to the growth of shrimp through increasing the relative abundance of potential beneficial bacteria and the accumulation of various bioactive metabolites to suppress the growth of detrimental bacteria.

Bacillus subtilis, an ideal probiotic bacterium to shrimp and fish aquaculture that increase feed digestibility, prevent microbial diseases, and avoid water pollution

Beneficial microorganisms maintain the ecosystems, plants, animals and humans working in healthy conditions. In nature, around 95% of all microorganisms produce beneficial effects by increasing nutrients digestion and assimilation, preventing pathogens development and by improving environmental parameters. However, increase in human population and indiscriminate uses of antibiotics have been exerting a great pressure on agriculture, livestock, aquaculture, and also to the environment. This pressure has induced the decomposition of environmental parameters and the development of pathogenic strains resistant to most antibiotics. Therefore, all antibiotics have been restricted by corresponding authorities; hence, new and healthy alternatives to prevent or eliminate these pathogens need to be identified. Thus, probiotic bacteria utilization in aquaculture systems has emerged as a solution to prevent pathogens development, to enhance nutrients assimilation and to improve environmental parameters. In this sense, B. subtilis is an ideal multifunctional probiotic bacterium, with the capacity to solve these problems and also to increase aquaculture profitability.

Prevalence, antimicrobial susceptibility and plasmid profiling of Vibrio spp. isolated from cultured groupers in Peninsular Malaysia

BACKGROUND

Numerous prevalence studies of Vibrio spp. infection in fish have been extensively reported worldwide, including Malaysia. Unfortunately, information on the prevalence of Vibrio spp. in groupers (Epinephelus spp.) is limited. In this study, groupers obtained from nine farms located at different geographical regions in Malaysia were sampled for the presence of pathogenic Vibrio spp. and their susceptibility profiles against seven antibiotics.

RESULTS

Out of 270 grouper samples, 195 (72%) were detected with the presence of Vibrio spp. Vibrio communis showed highest prevalence in grouper (28%), followed by V. parahaemolyticus (25%), V. alginolyticus (19%), V. vulnificus (14%), V. rotiferianus (3%), Vibrio sp. (3%), V. campbellii (2%), V. mytili (2%), V. furnissii (2%), V. harveyi (1%), V. tubiashii (1%), V. fluvialis (0.3%) and V. diabolicus (0.3%). Assessment on the antibiotic susceptibility profiles of the Vibrio spp. revealed that majority of the isolates were susceptible to tetracycline, streptomycin, erythromycin and bacitracin, but resistance to ampicillin, penicillin G and vancomycin. The mean MAR index of the Vibrio isolates was 0.51, with 85% of the isolates showed MAR index value of higher than 0.2. Results indicate that the Vibrio spp. were continuously exposed to antibiotics. Furthermore, the plasmid profiles of Vibrio spp. showed that 38.7% of the isolates harbored plasmid with molecular weight of more than 10 kb, while 61.3% were without plasmid. During curing process, Vibrio spp. lost their plasmid, but remained resistant to ampicillin, penicillin G, bacitracin and vancomycin while a few isolates remained resistant to erythromycin, streptomycin and tetracycline. The results suggested that the resistance to antibiotics in isolated Vibrio spp. might be due to chromosomal and plasmid borne.

CONCLUSIONS

This study demonstrates the prevalence of Vibrio spp. in groupers and the distribution of multidrug resistance strains that could be of concern to the farmers in Malaysia. In addition, data from this study can be further used in fish disease management plan.

Influence of food matrix type on extracellular products of Vibrio parahaemolyticus

BACKGROUND

Two strains of Vibrio parahaemolyticus (ATCC 17802 and 33847) in shrimp, oyster, freshwater fish, pork, chicken and egg fried rice were evaluated for production of hemolysin and exoenzymes of potential importance to the pathogenicity of this bacterium.

RESULTS

The two strains of V. parahaemolyticus produced hemolysin, gelatinase, caseinase, phospholipase, urease, DNase and amylase in selected food matrices. Significantly higher (p < 0.05) hemolytic activity was produced by V. parahaemolyticus in egg fried rice > shrimp > freshwater fish > chicken > oyster > pork. But the exoenzyme activities were not consistent with the hemolytic activity profile, being significantly higher (p < 0.05) in shrimp > freshwater fish > chicken > oyster > pork > egg fried rice. Filtrates of V. parahaemolyticus from shrimp, freshwater fish and chicken given intraperitoneally to adult mice induced marked liver and kidney damage and were highly lethal compared with the filtrates of V. parahaemolyticus from oyster > egg fried rice > pork.

CONCLUSION

From in vitro and in vivo tests, it appears that the food matrix type has a significant impact on the activity of extracellular products and the pathogenicity of V. parahaemolyticus. From a food safety aspect, it is important to determine which food matrices can stimulate V. parahaemolyticus to produce additional extracellular factors. This is the first report of non-seafood including freshwater fish and chicken contaminated with V. parahaemolyticus to have been shown to be toxic to mice in vivo.

Drug resistance, AmpC-β-lactamase and extended-spectrum β-lactamase-producing Enterobacteriaceae isolated from fish and shrimp

The present study aims to detect the production of extended-spectrum beta-lactamases (ESBL) by enterobacteria isolated from samples of fresh shrimp and fish obtained from the retail trade of the city of Sobral, Ceará State, Brazil. All bacterial isolates were submitted to identification and antimicrobial susceptibility testing using aminopenicillin, beta-lactamase inhibitors, carbapenem, 1st, 2nd, 3rd and 4th generation cephalosporins, and monobactam. Three types of beta-lactamases - ESBL, AmpC and KPC - were investigated. 103 strains were identified, and the most frequent species in shrimp and fish samples was Enterobacter cloacae (n = 54). All the strains were resistant to penicillin and more than 50% of the isolates were resistant to ampicillin and cephalothin. Resistance to three 3rd generation cephalosporins (cefotaxime, ceftriaxone and ceftazidime) and one fourth generation cephalosporin (cefepime) was detected in two isolates of E. cloacae from shrimp samples. Phenotypic detection of AmpC was confirmed in seven strains. The ESBL was detected in two strains of E. cloacae from shrimp samples. No strain showed KPC production. These data can be considered alarming, since food (shrimp and fish) may be carriers of enterobacteria resistant to drugs of clinical interest.

Antimicrobial Compounds from Eukaryotic Microalgae against Human Pathogens and Diseases in Aquaculture

The search for novel compounds of marine origin has increased in the last decades for their application in various areas such as pharmaceutical, human or animal nutrition, cosmetics or bioenergy. In this context of blue technology development, microalgae are of particular interest due to their immense biodiversity and their relatively simple growth needs. In this review, we discuss about the promising use of microalgae and microalgal compounds as sources of natural antibiotics against human pathogens but also about their potential to limit microbial infections in aquaculture. An alternative to conventional antibiotics is needed as the microbial resistance to these drugs is increasing in humans and animals. Furthermore, using natural antibiotics for livestock could meet the consumer demand to avoid chemicals in food, would support a sustainable aquaculture and present the advantage of being environmentally friendly. Using natural and renewable microalgal compounds is still in its early days, but considering the important research development and rapid improvement in culture, extraction and purification processes, the valorization of microalgae will surely extend in the future.

Antibiotic and heavy-metal resistance of Vibrio parahaemolyticus isolated from fresh shrimps in Shanghai fish markets, China

Vibrio parahaemolyticus is a causative agent of human serious seafood-borne gastroenteritis disease and even death. Shrimps, often eaten raw or undercooked, are an important reservoir of the bacterium. In this study, we isolated and characterized a total of 400 V. parahaemolyticus strains from commonly consumed fresh shrimps (Litopenaeus vannamei, Macrobrachium rosenbergii, Penaeus monodon, and Exopalaemon carinicauda) in Shanghai fish markets, China in 2013-2014. The results revealed an extremely low occurrence of pathogenic V. parahaemolyticus carrying two major toxic genes (tdh and trh, 0.0 and 0.5 %). However, high incidences of antibiotic resistance were observed among the strains against ampicillin (99 %), streptomycin (45.25 %), rifampicin (38.25 %), and spectinomycin (25.50 %). Approximately 24 % of the strains derived from the P. monodon sample displayed multidrug resistant (MDR) phenotypes, followed by 19, 12, and 6 % from the E. carinicauda, L. vannamei, and M. rosenbergii samples, respectively. Moreover, tolerance to heavy metals of Cr(3+) and Zn(2+) was observed in 90 antibiotic resistant strains, the majority of which also displayed resistance to Cu(2+) (93.3 %), Pb(2+) (87.8 %), and Cd(2+)(73.3 %). The pulsed-field gel electrophoresis (PFGE)-based genotyping of these strains revealed a total of 71 distinct pulsotypes, demonstrating a large degree of genomic variation among the isolates. The wide distribution of MDR and heavy-metal resistance isolates in the PFGE clusters suggested the co-existence of a number of resistant determinants in V. parahaemolyticus population in the detected samples. This study provided data in support of aquatic animal health management and food safety risk assessment in aquaculture industry.

Occurrence and Antibiotic Resistance of Vibrio parahaemolyticus from Shellfish in Selangor, Malaysia

High consumer demand for shellfish has led to the need for large-scale, reliable shellfish supply through aquaculture or shellfish farming. However, bacterial infections which can spread rapidly among shellfish poses a major threat to this industry. Shellfish farmers therefore often resort to extensive use of antibiotics, both prophylactically and therapeutically, in order to protect their stocks. The extensive use of antibiotics in aquaculture has been postulated to represent a major contributing factor in the rising incidence of antimicrobial resistant pathogenic bacteria in shellfish. This study aimed to investigate the incidence of pathogenic Vibrio parahaemolyticus and determine the antibiotic resistance profile as well as to perform plasmid curing in order to determine the antibiotic resistance mediation. Based on colony morphology, all 450 samples tested were positive for Vibrio sp; however, tox-R assay showed that only 44.4% (200/450) of these were V. parahaemolyticus. Out of these 200 samples, 6.5% (13/200) were trh-positive while none were tdh-positive. Antibiotic resistance was determined for all V. parahaemolyticus identified against 14 commonly used antibiotics and the multiple antibiotic resistance index (MAR) was calculated. The isolates demonstrated high resistance to several antibiotics tested- including second and third-line antibiotics- with 88% resistant to ampicillin, 81% to amikacin,70.5% to kanamycin, 73% to cefotaxime, and 51.5% to ceftazidime. The MAR index ranged from 0.00 to 0.79 with the majority of samples having an index of 0.36 (resistant to five antibiotics). Among the 13 trh-positive strains, almost 70% (9/13) demonstrated resistance to 4 or more antibiotics. Plasmid profiling for all V. parahaemolyticus isolates revealed that 86.5% (173/200) contained plasmids - ranging from 1 to 7 plasmids with DNA band sizes ranging from 1.2 kb to greater than 10 kb. 6/13 of the pathogenic V. pathogenic strains contained plasmid. After plasmid curing, the plasmid containing pathogenic strains isolated in our study have chromosomally mediated ampicillin resistance while the remaining resistance phenotypes are plasmid mediated. Overall, our results indicate that while the incidence of pathogenic V. parahaemolyticus in shellfish in Selangor still appears to be at relatively reassuring levels, antibiotic resistance is a real concern and warrants ongoing surveillance.

An insight of traditional plasmid curing in Vibrio species

As the causative agent of foodborne related illness, Vibrio species causes a huge impact on the public health and management. Vibrio species is often associated with seafood as the latter plays a role as a vehicle to transmit bacterial infections. Hence, antibiotics are used not to promote growth but rather to prevent and treat bacterial infections. The extensive use of antibiotics in the aquaculture industry and environment has led to the emerging of antibiotic resistant strains. This phenomenon has triggered an alarming public health concern due to the increase number of pathogenic Vibrio strains that are resistant to clinically used antibiotics and is found in the environment. Antibiotic resistance and the genes location in the strains can be detected through plasmid curing assay. The results derived from plasmid curing assay is fast, cost effective, sufficient in providing insights, and influence the antibiotic management policies in the aquaculture industry. This presentation aims in discussing and providing insights on various curing agents in Vibrio species. To our best of knowledge, this is a first review written discussing on plasmid curing in Vibrio species.