Background
Macrobrachium rosenbergii is a freshwater prawn species of which there is a considerable production range when compared to
Macrobrachium nipponense (information sourced from
http://www.fao.org/fishery/culturedspecies/Macrobrachium_rosenbergii/en). Seafood is affected by several bacteria, and the major factors affecting bacterial survival in sea water are: absence of required nutrients, presence of toxic substances in sea water, presence of bacteriophages, adsorption of bacteria and their sedimentation, the harmful action of the sunlight, utilization of bacteria as food by not only protozoa, but other predators and competitive, antagonistic effects of the microorganism [
1].
There are a wide range of bacteria such as
Vibrio cholerae,
Escherichia coli 0157:H7, Shigella,
Campylobacter jejuni, Leptospirosis, Salmonella,
Helicobacter pylori, Legionella and the
Mycobacterium avium complex reported from contaminated water (information sourced from
http://www.cdc.gov/healthyswimming) [
2,
3]. However, mostly
Vibrio species are pathogenic to marine organisms. Previously, pathogenicity of
Vibrio anguillarum,
Vibrio anginolyticus,
Vibrio panaeicida,
V. vulnificus,
Vibrio harveyi, and
Vibrio salmonicida was observed in the population of fish and other marine organisms such as eel [
4,
5]. Those associated with coral reef bleaching were
Vibrio campbellii,
Vibrio shiloi,
V. harveyi and
Vibrio fortis. These
Vibrios are a real cause of concern especially in the aquaculture industry [
6].
In terms of aquatic food borne diseases, various virulence factors highlight
Vibrio vulnificus,
Vibrio parahaemolyticus, and
V. cholerae considerably important. The factors primarily include the capsular polysaccharide, lipopolysaccharide, cytotoxins and flagellum [
7,
8]. While
V. parahaemolyticus and
V. cholerae are mostly related to oysters, causing gastroenteritis [
9].
Vibrio vulnificus was observed to cause primary septicemia not only in marine populations [
10], but also in humans. Most cases of infection were reported due to the consumption of seafood [
11], especially shellfish [
12‐
22].
Vibrio vulnificus was reported to have caused high fatality rates due to its invasiveness associated with soft-tissue infection and severe sepsis [
8]. This species was reported in an encapsulated form, which most commonly occurs in clinical isolates rather than environmental isolates [
17].
Other species such as
Vibrio fluvialis,
Vibrio mimicus,
Vibrio alginolyticus,
Photobacterium damsel (
Vibrio damsela),
Vibrio metschnikovii,
Vibrio cincimnatiensis,
Vibrio fuenisii and
Vibrio hollisae are also known to be pathogenic [
23,
24]. These can cause severe infections to environmental specimens as well as human.
Vibrio parahaemolyticus in particular was identified as a cause of food-borne illnesses [
25], and is associated with the consumption of crab [
26]. It was also associated with seafood contamination ranging from crustacean, molluscan shellfish to the giant water prawn.
Vibrio parahaemolyticus was previously studied of its infection in
M. rosenbergii, with the latter’s expressed immune genes [
27]. Studies even reported
N-acetylglucosamine binding protein in other species of
Vibrio. It was shown to have the ability to bind chitinaceous structures such as the outer covering of crustaceans [
28‐
30]. Several studies on GbpA in relation to
Vibrio show GbpA as an attachment factor to the host chitin (the exoskeleton of crustaceans is called a carapace and consists of chitin) [
28,
30,
31]. There are no studies yet on the aspect of GbpA in
V. parahaemolyticus in particular, and its attachment to chitin of
M. rosenbergii. The yet unmapped factors of
V. parahaemolyticus are involved in triggering bacteria to possibly enter the prawns (
M. rosenbergii) which are our concern in the present review article.
The farming of
M. rosenbergii in modern times started in the early 1960′s (
http://www.fao.org/docrep/005/y4100e/y4100e04.htm#P193_35649). It was during this time,
M. rosenbergii require brackish water conditions for its survival, though being found as a freshwater prawn [
32]. However,
V. parahaemolyticus was observed in both brackish and fresh water [
33]. From the above, the water conditions required by the prawn and bacteria appear quite similar. Hence, the term “conditions for growth” which precisely defines the effect of environmental factors cannot be ruled out in such studies. Therefore, the implication of dealing with host and the pathogen in connection with the environment is conferred by considering
M. rosenbergii,
V. parahaemolyticus, and magnesium. Based on this, a preliminary designed experiment was conducted by us in our lab at University of Malaya and the work is currently under communication as a research article. Our current review hypothesis the possible rhythmic roles that
V. parahaemolyticus GbpA and
M. rosenbergii chitin play in the presence of a magnesium environment which could indeed be very useful in not only farming of prawn, but also in future aquaculture research.
Macrobrachium rosenbergii lifecycle
Macrobrachium rosenbergii resides in the tropical environments of the freshwater (
http://www.fao.org/docrep/005/y4100e/y4100e04.htm#P193_35649), but is influenced by the areas of brackish water. The female prawn bears a gelatinous mass underneath and between the fourth pair of its walking legs. It is here that the male prawn deposits the sperm. After a few hours of mating, eggs are laid and are fertilized by the sperm. “Berried Females” is the terminology used for females carrying the eggs [
34]. During the course of embryo development, the eggs remain constantly adhered to the female. It is during this time that the females migrate towards estuaries as the larvae cannot survive in fresh water for more than 2 days. The eggs hatch in brackish water where the salinity ranges from approximately nine parts per thousand (ppt) to 19 ppt [
34], and they exist as free-swimming larvae at this stage.
Vibrio genomes and distribution
Vibrios are widely distributed in marine environments and are easily adaptable to changes. Hence, these bacteria are considered significant for elucidating correlation between genome evolution and adaptation [
35]. 16S rRNA sequence is the basis on which the
Vibrio species are largely classified within the Vibrionaceae family. To establish the DNA patterns of epidemiological interest, which are associated with the pathogenicity of the strain and to record correlation of diseases among bacteria with specific strains, serotyping was identified as one of the useful markers [
36]. Further, the distribution and emergence of pathogenic bacterial strains, the prediction of events [
37,
38] through construction of models, and the identification of evolutionary relationships were also done by multi-locus sequence typing/analysis, serogroup association and comparative genomics [
39]. For example, with the potential pathogenicity of
V. cholerae, V. parahaemolyticus, and the association of their serogroups, the specificity of the serogroups was correlated [
36,
40,
41]. Studies on comparative genomics of
Vibrio dealt with the phylogeny of 86 species of
Vibrio and nine house-keeping genes primarily targeting biodiversity and genome evolution [
42]. However, comparative genomic analysis among both the pandemic and non-pandemic Vibrios distributed worldwide has to glean into the bacterial adaptation, evolution as well as antibiotic resistance. Such studies have dealt with the role of integrons in
Vibrio species for which genes comprise of approximately 1–3 % of the genome [
43], genome plasticity shaped by HGT and comparative analysis of pandemic and non-pandemic species [
44,
45]. Considering the above studies, the distribution of
Vibrio in different environmental conditions could be a significant factor responsible for its evolution, resistance, virulence and adaptation.
Conclusion
With regard to food-borne illnesses,
V. parahaemolyticus contributes significantly to morbidity worldwide [
54].
Apart from controlling the severity of bacterial vigour caused by
V. parahaemolyticus, strategies to control disease spreading through seafood consumption caused by bacteria adapting to aquatic environments are indeed required and needs more attention. This is because, most human populations worldwide are relying on seafood consumption on a daily basis. There are many aquatic organisms which need to be considered for the control of bacterial infections from spreading. The basis of selecting
V. parahaemolyticus and
M. rosenbergii in the current review is because of the widely spreading early mortality syndrome (EMS), which is capable of producing a toxin similar to the cholera which can cause life-threatening diarrhoea [
84‐
86].
We think that the utilization of magnesium ion to check any possible interactions between GbpA and carapace (chitin) of the bacteria and prawn, respectively could probably assist us to understand the significance of a magnesium environment. In the present context, as V. parahaemolyticus is dealt in relation with M. rosenbergii, a giant freshwater prawn of commercial importance, further research based on the aspect of magnesium ion usage by both the prokaryotic or eukaryotic counterparts could help us understand the contamination strategies better. One such strategy could be tweaking the magnesium levels in order to avoid bacteria from entering aquatic organisms. Our review provides the understanding that maintaining magnesium could be important in order to avoid bacteria from multiplying rapidly to infectious levels. Hence, this could help minimize the risk of contamination in the aquaculture systems which might help control food-borne diseases in the long run.