Plasmid profiling and antibiotic resistance of Vibrio strains isolated from cultured penaeid shrimp

Resistance to different antibiotics was found in 26 of the 30 strains analyzed, more than 70% of the strains analyzed were resistant to carbenicillin and ampicillin and a significant correlation was found between the resistance to both antibiotics. Plasmids were found in 80% of the strains analyzed, and 11 different plasmid profiles were observed. The most common profile obtained had only a 21.2-kbp plasmid, a significant correlation was found between the presence of this plasmid and resistance to carbenicillin, although some exceptions could be detected. Plasmids were cured from a cephalothin resistant strain and reintroduced into the plasmid-free cell and into Escherichia coli DH5alpha, both strains gained resistance to this antibiotic.

Antibiotic resistance of Aeromonas hydrophila isolated from marketed fish and prawn of South India

A total of 319 strains of Aeromonas hydrophila were isolated from 536 fish and 278 prawns for a 2-year period. All the strains were tested for resistance to 15 antibiotics and 100% of the strains was resistant to methicillin and rifampicin followed by bacitracin and novobiocin (99%). Only 3% of the strains exhibited resistance against chloramphenicol. The multiple antibiotic resistance (MAR) indexing of A. hydrophila strains showed that all of them originated from high-risk sources.

Screening and characterization of aldehyde dehydrogenase gene from Halomonas salina strain AS11

A population survey was made of moderately halophilic bacteria in prawn pond sediment in the Songkla region of Thailand. Twenty-two isolated halophilic bacteria capable of growing on modified ATCC culture medium 1270 for halobacterium were then assayed for aldehyde dehydrogenase (ALDH) activity which might be involved in the metabolism of xenobiotic compounds. One isolate, designated AS11, was selected based on its high amount of ALDH activity. This organism can grow at sodium chloride concentrations ranging from 2.5 to 25%, although optimum growth occurs at 5% NaCl. Phenotypic and phylogenetic studies indicated that AS11 was an isolate of Halomonas salina. The aldh gene coding for this enzyme was then cloned. The open reading frame of the aldh gene was 1521-bp long and coded for a protein of 506 amino acid residues with a calculated molecular mass of 55 kDa. The aldh gene product proved to be 76% identical to the NAD-dependent acetaldehyde dehydrogenase gene from Pseudomonase aeruginosa.

Genetic diversity of attached bacteria in the hindgut of the deposit-feeding shrimp Neotrypaea (formerly Callianassa) californiensis (decapoda: thalassinidae)

Microbial colonization of marine invertebrate guts is widespread, but in general the roles that these bacteria play in the nutrition of their hosts are unknown. To examine the diversity and potential nutritional roles of hindgut microbiota in a deposit feeder, PCR-amplified 16S rRNA genes were cloned from the bacterial community attached to the hindguts of the thalassinid shrimp Neotrypaea californiensis exposed to different feeding treatments. Partial 16S rDNA sequences were analyzed for 30 clones for three shrimp per treatment for a total of 270 clones. No effects of host starvation or high-protein diets were apparent on hindgut bacterial community composition. Diversity analyses indicated high variability between bacterial communities in individual shrimp hindguts, but partial 16S rDNA sequences revealed remarkable species-level similarity (>98%) within clusters of sequences from the different shrimp hindguts, and many sequences from different shrimp hindguts were identical. Sequences belonged to three main groups of bacteria: Cytophaga-Flavobacteria-Bacteroides (CFB), proteobacteria, and gram-positives. Of the 270 sequences, 40% belonged to the alpha-proteobacteria, > or = 5% each to the gamma- and epsilon -proteobacteria, and > or =20% each to the gram-positive and CFB groups. All except one sequence are novel with < or = 95% sequence similarity to known genes. Despite weak similarity to known taxa,about 75% of the sequences were most closely related to known symbiotic and sedimentary bacteria. The bacteria in shrimp hindguts represent new species that have not yet been en-countered in other environments, and gut environments may be a rich source of the difficult-to-culture and novel components of marine bacterial diversity.

Misidentification of Vibrio cholerae O155 isolated from imported shrimp as O serogroup O139 due to cross-agglutination with commercial O139 antisera

Fish and shellfish products imported into Denmark are routinely analyzed for pathogenic Vibrio spp., particularly Vibrio cholerae, if products originate from subtropical or tropical areas. A V. cholerae strain that agglutinated commercial O139 antiserum but not the O1, Inaba, or Ogawa antisera was isolated from imported raw frozen shrimp. The toxigenicity of the strain was analyzed, and the results of a polymerase chain reaction showed that the V. cholerae strain did not contain the virulence genes ctx, tcpA, and zot, which are normally found in V. cholerae O1 and O139. The strain was resistant to colistin and spectinomycin. The high susceptibility of the strain to antimicrobial agents was confirmed by the lack of an SXT element, a self-transmissible, chromosomal genetic element that is normally present in 0139 strains and encodes resistance to sulfonamides, trimethoprim, and streptomycin. The strain contained two plasmids, in contrast to other O139 strains, which normally do not contain plasmids. The characteristics of the strain led to further agglutination testing with other antisera that are not commercially available, and the strain was found to agglutinate O155 antiserum in repeated testing. Manufacturers of 0139 antiserum should be aware of the closely related O antigens of the O139, O22, and O155 serogroups and should be aware that their commercial diagnostic O139 antiserum must be absorbed to remove cross-reacting agglutinins of O22 and O155 strains.

Adhesion and colonization of Vibrio cholerae O1 on shrimp and crab carapaces

The potential of Vibrio cholerae O1 to attach to and colonize the carapaces of shrimp and crabs was evaluated. One million cells of V. cholerae O1 were spread within a circle on the external surfaces of separated carapaces and stored at 22 +/- 0.2 degrees C in a moist environment to permit adherence. Attached vibrios were counted directly by an immunofluorescence technique and by the pour plate technique after detachment of the cells. To study the colonization process, rifampicin-resistant strains of V. cholerae O1 were used. V. cholerae O1 strains, including those resistant to rifampicin, were able to attach to shrimp and crab carapaces. Dorsal crab carapaces showed higher levels of attachment than ventral carapaces. Colonization of V. cholerae O1 on these carapaces was also demonstrated. Both attachment and colonization on the shrimp exoskeleton were optimal at a salinity of 1.0 to 1.5%, a pH of 6.0 to 7.0, and a temperature of 37 degrees C. Less than 2% attachment at 3 degrees C contrasted with >20% attachment at 37 degrees C. Even at 3% NaCl, some attachment was observed. Although attachment percentages may appear low (2 to 20%), they represent significant numbers, about 3.7 to 5.6 log10 CFU per carapace. A rugose V. cholerae O1 strain attached to and colonized the shrimp carapace in a fashion very similar to that of the smooth strain from which it was derived. The ability of V. cholerae O1 to attach to and colonize exoskeletons of edible crustaceans provides a potential means of survival in aquatic environments. Concentrations of vibrios that may be reached on a single crab or shrimp carapace are clearly of concern with regard to public health.

Carriage of Vibrio species by shrimps harvested from the coastal waters of South West Cameroon

OBJECTIVES

To determine the prevalence of Vibrio spp in unprocessed shrimps and their susceptibility to antibiotics.

DESIGN

A prospective study of Vibrio spp associated with shrimps harvested from the coastal waters of South West Cameroon.

SETTING

A laboratory based study at the Department of Life Sciences, University of Buea. Two hundred and thirty six shrimps harvested from the coastal towns of Limbe and Tiko, Cameroon, were examined for the prevalence of Vibrio spp using standard microbiologic procedures. The antibiotic sensitivity of isolates was determined using the Kirby-Bauer disc diffusion technique.

RESULTS

Of the 236 shrimps examined, 73 (30.9%) were contaminated with Vibrio spp. Further, a total of 125 Vibrio strains were isolated from the contaminated shrimps. Of this number, 33 (26.4%) were V. cholerae, 55 (44%) V. parahaemolyticus, 34 (27.2%) V. alginolyticus and three (2.4%) V. vulnificus. Antibiotic susceptibility generally ranged from 68.8% for polymyxin B to 99.2% for gentamycin. Multiple resistant strains were noted, especially with V. parahaemolyticus and V. alginolyticus

CONCLUSION

Shrimps maintain a reservoir of potential Vibrio spp in the coastal area of South West Cameroon. This finding is of epidemiologic and clinical significance.

Occurrence of Clostridium botulinum in fresh and cured fish in retail trade in Cochin (India)

The occurrence of Clostridium botulinum in fresh (67) and cured fish (278) samples in retail trade in Cochin was studied. An overall prevalence of 19% (13/67) was found in fresh retail fish and types A to D were detected in the positive samples. In pelagic fish, incidence of C. botulinum was 18% (7/39) whereas in demersal fish, 21% (5/24) of the samples harboured C. botulinum. Incidence of C. botulinum in shrimp was 25% (1/4) and type D was found in the positive sample. Of 257 cured fish in retail trade tested for the presence of C. botulinum, the overall contamination level was 10% (25/257). Among the C. botulinum types A to D prevalent in fresh fish, types C and D were the predominant types found in cured products. In salt-dried shrimp, of the 21 samples analysed, 10 samples (48%) harboured C. botulinum.

Vibrio vulnificus as a health hazard for shrimp consumers

Over the last 30 years, a number of Vibrio species found in the aquatic environment have been indicated as cause of disease in human beings. Vibrio vulnificus is an emergent pathogen, an invasive and lethal marine bacterium related to wound infection and held accountable for gastroenteritis and primary septicemia. It occurs quite frequently in marine organisms, mainly in mollusks. This study aimed at isolating and identifying strains of V. vulnificus based upon the analysis of twenty samples of seabob shrimp, Xiphopenaeus kroyeri (Heller), purchased at the Mucuripe fish market (Fortaleza, Brazil). TCBS agar was used to isolate suspect strains. Seven of twenty-nine strains isolated from six different samples were confirmed as such by means of biochemical evidence and thus submitted to biological assays to determine their virulence. The susceptibility of the V. vulnificus strains to a number of antibiotics was tested. None of the V. vulnificus strains showed signs of virulence during a 24-hour observation period, possibly due to the shedding of the capsules by the cells. As to the results of the antimicrobial susceptibility tests, the seven above-mentioned V. vulnificus strains were found to be sensitive to nitrofurantoin (NT), ciprofloxacin (CIP), gentamicin (GN) and chloramphenicol (CO) and resistant to clindamycin (CI), penicillin (PN) and ampicillin (AP).

Unusual adaptive, cross protection responses and growth phase resistance against peroxide killing in a bacterial shrimp pathogen, Vibrio harveyi

Oxidant induced protection against peroxide killing was investigated in a prawn bacterial pathogen, Vibrio harveyi. Exposure to 250 microM H(2)O(2) induced adaptive protection against subsequent exposure to killing concentrations of H(2)O(2). In addition, 200 microM t-butyl hydroperoxide (tBOOH) induced cross protection to H(2)O(2) killing. On the other hand, peroxide pretreatment did not induce protection against tBOOH killing. Peroxide induced adaptive and cross protection responses required new protein synthesis and were abolished by addition of a protein synthesis inhibitor. Pretreatments of V. harveyi with 250 microM H(2)O(2) and 200 microM tBOOH induced an increase in peroxide scavenging enzymes, catalase and alkyl hydroperoxide reductase subunit C. In addition, stationary phase cells of V. harveyi were more resistant to H(2)O(2) and iodoacetamide killing but highly susceptible to tBOOH killing compared to exponential phase cells. Many aspects of the oxidative stress response of V. harveyi are different from those of other bacteria and these factors may be important for bacterial survival in the environment and during interactions with host shrimp.

Lactococcus garvieae infection in the giant freshwater prawn Macrobranchium rosenbergii confirmed by polymerase chain reaction and 16S rDNA sequencing

An epizootic bacterial infection in the giant freshwater prawn Macrobranchium rosenbergii occurred in Taiwan from May to June 1999. The cumulative mortality was approximately 30 to 75%. The diseased prawns showed opaque and whitish muscles and were approximately 2 mo old with total lengths from 5 to 6 cm. Histopathologically, they showed marked edema and necrotic lesions with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Three isolates from diseased prawns at different farms were tested using the API 20 Strepsystem and conventional tests and identified as Lactococcus garvieae. Experimental infections with these isolates gave gross signs and histopathological changes similar to those seen in the naturally infected prawns. The LD50 value of isolate MR1 was 6.6 x 10(5) colony forming units/prawn. Identification of MR1 was confirmed by a PCR assay for L. garvieae that gave the expected amplicon of 1100 bp. In addition, its 16S rDNA sequence (GenBank accession number AF283499) gave 99% sequence identity to Enterococcus seriolicida (synonym L. garvieae; GenBank accession number AF061005). This is the first report of confirmed L. garvieae infection in prawn aquaculture.

In vitro susceptibility to 15 antibiotics of vibrios isolated from penaeid shrimps in Northwestern Mexico

The sensitivity of 144 isolates of Vibrio spp isolated from shrimp was compared using common antibiotics and those used in the shrimp industry. The in vitro susceptibility of the isolates was studied using amikacin, ampicillin, carbenicillin, cephalothin, cefotaxime, ceftriaxone, chloramphenicol, gentamicin, netilmicin, nitrofurantoin, pefloxacin, trimethoprim-sulphamethoxazole, enrofloxacin, oxytetracycline and florfenicol. The relationship between the minimum inhibitory concentration and the disk inhibition zone was also studied for some antibiotics.

Microbicidal effect of medicinal plant extracts (Psidium guajava Linn. and Carica papaya Linn.) upon bacteria isolated from fish muscle and known to induce diarrhea in children

Out of the twenty-four samples of shrimp and fish muscle used for this study, twelve were collected near a large marine sewer for waste disposal, 3 km off the coast of Fortaleza (Brazil) and used for the isolation of E. coli. Other twelve were collected at the Mucuripe fresh fish market (Fortaleza, Brazil) and used for the isolation of Staphylococcus aureus. Ethanol, water and acetone-diluted extracts of guava and papaya leaf sprouts were tested on the bacteria in order to verify their microbicidal potential. The E. coli strains used in the trials were rated LT positive. The papaya leaf extracts (Carica papaya Linn) showed no microbicidal activity while the guava sprout extracts (Psidium guajava Linn) displayed halos exceeding 13 mm for both species, an effect considered to be inhibitory by the method employed. Guava sprout extracts by 50% diluted ethanol most effectively inhibited E. coli (EPEC), while those in 50% acetone were less effective. It may be concluded that guava sprout extracts constitute a feasible treatment option for diarrhea caused by E. coli or by S. aureus-produced toxins, due to their quick curative action, easy availability in tropical countries and low cost to the consumer.

Antibiotic- and metal-resistant strains of Vibrio parahaemolyticus isolated from shrimps

Enteropathogenic strains of Vibrio parahaemolyticus were isolated from shrimps, Penaeus monodon collected from the region of the Deltaic Sundarbans (West Bengal, India). About 63% of the isolated strains were resistant to ampicillin, cephalexin, and kanamycin. However, all these strains were sensitive to nitrofurantoin, nalidixic acid, tetracycline, and norfloxacin. The isolated strains were resistant to Ni2+] (75%), Cu2+ (87%), and Co2+ (37%), but all the strains were resistant against Cd2+, Zn2+, and Pb2+ at 10 mM concentration.

Molecular epidemiological survey of Listeria monocytogenes in seafoods and seafood-processing plants

To evaluate the role of seafoods in the epidemiology of human listeriosis and the role of the processing environment as a source of Listeria monocytogenes in seafood products, 305 L. monocytogenes isolates were characterized by multilocus enzyme electrophoresis using 21 genetic loci and restriction enzyme analysis of total DNA. Forty-four isolates were recovered from patients in Norway; 93 were isolated from seafoods, seafood-processing environments, and seawater from 55 different producers; and the remaining 168 isolates originated from six seafood-processing plants and one transport terminal examined in detail for L. monocytogenes. The patient isolates fell into 11 electrophoretic types, with four of them being responsible for 77% of the listeriosis cases in 1992 to 1996. Isolates from Norwegian seafoods and processing environments showed great genetic diversity, indicating that seafoods and seafood-processing environments do not offer a niche for specific L. monocytogenes strains. On the other hand, isolates from individual processing plants were genetically more homogenous, showing that plants are likely to be colonized with specific subclones of L. monocytogenes. The isolation of identical subclones of L. monocytogenes from both human patients and seafoods, including ready-to-eat products, suggests that such products may have been possible sources for listeriosis cases in Norway.

[Isolation of Listeria spp., Aeromonas spp., and Vibrio spp. from seafood products]

Forty-one strains of Listeria, Aeromonas and Vibrio have been isolated in 71 samples of seafood, both raw and ready to eat and frozen. L. monocytogenes, detected by PCR also, is found in the smoked salmon only. Aeromonas spp. and Vibrio spp. are isolated in the raw products (shrimps and shellfish). No relationship is found between the presence of such microrganisms and the common indicator bacteria. Finally, the health hazard related to strong contamination and the need to diversify the food safety assurance programmes, for the various products, are underlined.

Isolation of a pandemic O3:K6 clone of a Vibrio parahaemolyticus strain from environmental and clinical sources in Thailand

Application of an immunomagnetic enrichment method selective for Vibrio parahaemolyticus serovar K6 allowed isolation of a strain belonging to the pandemic O3:K6 clone of V. parahaemolyticus from fresh shellfish not implicated in a clinical case in southern Thailand. Arbitrarily primed PCR profiles of this strain, clinical O3:K6 strains isolated from sporadic diarrhea cases in the same area, and a standard pandemic O3:K6 strain were indistinguishable.

Distribution and content of class 1 integrons in different Vibrio cholerae O-serotype strains isolated in Thailand

In this study, 176 clinical and environmental Vibrio cholerae strains of different O serotypes isolated in Thailand from 1982 to 1995 were selected and studied for the presence of class 1 integrons, a new group of genetic elements which carry antibiotic resistance genes. Using PCR and DNA sequencing, we found that 44 isolates contained class 1 integrons harboring the aadB, aadA2, blaP1, dfrA1, and dfrA15 gene cassettes, which encode resistance to gentamicin, kanamycin, and tobramycin; streptomycin and spectinomycin; beta-lactams; and trimethoprim, respectively. Each cassette array contained only a single antibiotic resistance gene. Although resistance genes in class 1 integrons were found in strains from the same epidemic, as well as in unrelated non-O1, non-O139 strains isolated from children with diarrhea, they were found to encode only some of the antibiotic resistance expressed by the strains. Serotype O139 strains did not contain class 1 integrons. However, the appearance and disappearance of the O139 serotype in the coastal city Samutsakorn in 1992 and 1993 were associated with the emergence of a distinct V. cholerae O1 strain which contained the aadA2 resistance gene cassette. A 150-kb self-transmissible plasmid found in three O1 strains isolated in 1982 contained the aadB gene cassette. Surprisingly, several strains harbored two integrons containing different cassettes. Thus, class 1 integrons containing various resistance gene cassettes are distributed among different V. cholerae O serotypes of mainly clinical origin in Thailand.

Rapid and sensitive PCR detection of Vibrio penaeicida, the putative etiological agent of syndrome 93 in New Caledonia

Experimental infections of Penaeus (Litopenaeus) stylirostris were performed with a Vibrio penaeicida strain (AM101) isolated in New Caledonia from Syndrome 93 diseased shrimp. Cumulative mortalities resulting from intramuscular injection or immersion of shrimp in bacterial suspensions demonstrated high virulence for this bacterial strain and suggested that V. penaeicida could be the etiological agent of Syndrome 93. The median lethal dose (LD50) for AM101 was 1.3 x 10(4) CFU (colony forming units) ml-1 by immersion and less than 5 CFU shrimp-1 by intramuscular challenge, with mortality outbreaks at 48 and 22 h after challenge, respectively. A polymerase chain reaction (PCR) detection assay using a primer set designed from the 16S ribosomal RNA gene of V. penaeicida was developed. It gave an expected amplicon of approximately 310 bp in ethidium bromide-stained agarose gels. The specificity of these primers was assessed with different Vibrio species. Furthermore, DNA extracted by the Chelex method could be used to detect fewer than 20 cultured Vibrio cells in sea-water or shrimp hemolymph by this assay. It appears to be a reliable screening method for detecting V. penaeicida in shrimp and from the aquatic environment.

Toxic factors of Vibrio strains pathogenic to shrimp

Vibriosis is a major disease problem in shrimp aquaculture. 'Syndrome 93' is a seasonal juvenile vibriosis caused by Vibrio penaeicida which affects Litopenaeus stylirostris in grow-out ponds in New Caledonia. This study assessed the toxic activities of extracellular products (ECPs) from V. penaeicida, V. alginolyticus and V. nigripulchritudo using in vivo injections in healthy juvenile L. stylirostris (= Penaeus stylirostris) and in vitro assays on shrimp primary cell cultures and the fish cell line epithelioma papulosum cyprini (EPC). Toxic effects of ECPs were demonstrated for all pathogenic Vibrio strains tested both in vivo and in vitro, but for shrimp only; no effect was observed on the fish cell line. ECP toxicity for New Caledonian V. penaeicida was found only after cultivation at low temperature (20 degrees C) and not at higher temperature (30 degrees C). This points to the fact that 'Syndrome 93' episodes are triggered by temperature drops. The assays used here demonstrate the usefulness of primary shrimp cell cultures to study virulence mechanisms of shrimp pathogenic bacteria.

Exopolysaccharide-producing lactic acid bacteria strains from traditional Thai fermented foods: isolation, identification and exopolysaccharide characterization

Lactic Acid Bacteria (LAB) isolated from various traditional Thai fermented foods were screened for exopolysaccharides (EPS) production. From 104 isolates, two rod-shaped and five coccal-shaped LAB were able to produce EPS from sucrose on solid media. However, only the cocci were capable of producing EPS in liquid media and these were identified as Pediococcus pentosaceus. Pediococcus pentosaceus strains AP-1 and AP-3 produced EPS in high yield. In liquid media containing sucrose as carbon source, the amount of EPS produced by AP-1 and AP-3 strains was 6.0 and 2.5 g/L, respectively. The isolated and purified EPSs were chemically characterized. On the basis of sugar composition, methylation analysis and nuclear magnetic resonance spectroscopy, both the EPSs were shown to belong to the same dextran class. In particular, both EPSs differed from linear dextran by branching through 3,6-di-Osubstituted alpha-D-glucopyranosyl residues. The EPS from P. pentosaceus AP-3 was characterized by a relatively higher degree of branching and by a higher molecular weight than that from P. pentosaceus AP-1.

Evaluation of TaqMan PCR assay for detecting Salmonella in raw meat and shrimp

We evaluated the TaqMan Salmonella amplification/detection kit from PE Applied Biosystems, which uses a polymerase chain reaction (PCR) assay for rapid detection of Salmonella in food samples. This system uses the 5' nuclease activity of Taq DNA polymerase, which digests an internal fluorogenic probe to monitor the amplification of the target gene. The system's sensitivity and specificity were evaluated using 42 serotypes of 68 Salmonella strains isolated from fecal samples from patients in Tokyo, Japan, and 39 non-Salmonella strains in 22 genera. There were no false-negative or false-positive results. This PCR assay can detect 3 CFU per PCR tube of Salmonella in pure culture (120 CFU/ml of TSB culture). PCR signals were attenuated with artificially contaminated shrimp, but a similar detection limit was obtained. TaqMan's performance was tested with 100 meat and chicken samples purchased from stores in Tokyo. Overall, two of the DNA extraction protocols (the Chelex and EnviroAmp methods) worked equally well, with some exceptions. Of the 100 samples analyzed, 10 were positive for Salmonella with both conventional culture methods and the kit and 89 were negative with both. One sample was negative by the culture method but positive by the kit assay. These results indicate that TaqMan is a reliable and rapid method for Salmonella analysis in the food industry. With this system, food samples can be analyzed for Salmonella in less than 20 h.

Arbitrarily primed PCR to type Vibrio spp. pathogenic for shrimp

A molecular typing study on Vibrio strains implicated in shrimp disease outbreaks in New Caledonia and Japan was conducted by using AP-PCR (arbitrarily primed PCR). It allowed rapid identification of isolates at the genospecies level and studies of infraspecific population structures of epidemiological interest. Clusters identified within the species Vibrio penaeicida were related to their area of origin, allowing discrimination between Japanese and New Caledonian isolates, as well as between those from two different bays in New Caledonia separated by only 50 km. Other subclusters of New Caledonian V. penaeicida isolates could be identified, but it was not possible to link those differences to accurate epidemiological features. This contribution of AP-PCR to the study of vibriosis in penaeid shrimps demonstrates its high discriminating power and the relevance of the epidemiological information provided. This approach would contribute to better knowledge of the ecology of Vibrio spp. and their implication in shrimp disease in aquaculture.

Extension of shelf life of whole and peeled shrimp with organic acid salts and bifidobacteria

Microbiological and sensory characteristics of treated whole and peeled shrimp from the east coast of Saudi Arabia were evaluated. Shrimp samples were treated with organic acid salts with or without Bifidobacterium breve culture and stored in ice. Peeling alone extended the microbiological shelf life by 4 days. Treatment of whole shrimp with sodium acetate alone or potassium sorbate with bifidobacteria prolonged the microbiological shelf life by 3 days and increased the microbial generation time from 12.8 h (control) to 30.1 h or 31.4 h, respectively. The microbiological and sensory shelf life of peeled shrimp treated with sodium acetate was more than 17 days. Sodium acetate extended the microbial lag phase and lengthened the generation time (38.7 h compared to 15.8 h for the control). Micrococci and coryneforms were the predominant microorganisms in whole shrimp during storage. Treatment with sodium acetate maintained better sensory characteristics for peeled shrimp than potassium sorbate combined with bifidobacteria.