Iddya Karunasagar

Mass mortality of Penaeus monodon larvae due to antibiotic-resistant Vibrio harveyi infection

Abstract The cause of mass mortality in Penaeus monodon larvae in a hatchery was investigated. Antibiotic-resistant Vibrio harveyi could be isolated from all the infected larvae. These bacteria were absent in healthy eggs and nauplii. Although the intake seawater had V. harveyi , these strains were sensitive to antibiotics. The results suggest that antibiotic-resistant V. harveyi had been colonising larval tanks. The isolates from moribund larvae showed much lower LD 50 values than isolates from natural seawater, thus indicating their higher virulence.

Biofilm formation by Salmonella spp. on food contact surfaces and their sensitivity to sanitizers

Biofilm formation by two poultry isolates of Salmonella on three commonly used food contact surfaces viz plastic, cement and stainless steel were studied. Biofilm formation of both the isolates showed a similar trend with the highest density being on plastic followed by cement and steel. Salmonella weltevreden formed biofilm with a cell density of 3.4 x 10(7), 1.57 x 10(6) and 3 x 10(5) cfu/cm2 on plastic, cement and steel respectively while Salmonella FCM 40 biofilm on plastic, cement and steel were of the order of 1.2 x 10(7), 4.96 x 10(6) and 2.23 x 10(5) cfu/cm2 respectively. The sensitivity of the biofilm cells grown on these surfaces to different levels of two sanitizers namely hypochlorite and iodophor for varying exposure times was studied. Biofilm cells offered greater resistance when compared to their planktonic counterparts. Such biofilm cells in a food processing unit are not usually removed by the normal cleaning procedure and therefore could be a source of contamination of foods coming in contact with such surfaces.

Human Health Consequences of Use of Antimicrobial Agents in Aquaculture

Intensive use of antimicrobial agents in aquaculture provides a selective pressure creating reservoirs of drug-resistant bacteria and transferable resistance genes in fish pathogens and other bacteria in the aquatic environment. From these reservoirs, resistance genes may disseminate by horizontal gene transfer and reach human pathogens, or drug-resistant pathogens from the aquatic environment may reach humans directly. Horizontal gene transfer may occur in the aquaculture environment, in the food chain, or in the human intestinal tract. Among the antimicrobial agents commonly used in aquaculture, several are classified by the World Health Organisation as critically important for use in humans. Occurrence of resistance to these antimicrobial agents in human pathogens severely limits the therapeutic options in human infections. Considering the rapid growth and importance of aquaculture industry in many regions of the world and the widespread, intensive, and often unregulated use of antimicrobial agents in this area of animal production, efforts are needed to prevent development and spread of antimicrobial resistance in aquaculture to reduce the risk to human health.

Seasonal Variation in Abundance of Total and Pathogenic Vibrio parahaemolyticus Bacteria in Oysters along the Southwest Coast of India

ABSTRACT The seasonal abundance of Vibrio parahaemolyticus in oysters from two estuaries along the southwest coast of India was studied by colony hybridization using nonradioactive labeled oligonucleotide probes. The density of total V. parahaemolyticus bacteria was determined using a probe binding to the tlh (thermolabile hemolysin) gene, and the density of pathogenic V. parahaemolyticus bacteria was determined by using a probe binding to the tdh (thermostable direct hemolysin) gene. Furthermore, the prevalence of V. parahaemolyticus was studied by PCR amplification of the toxR, tdh, and trh genes. PCR was performed directly with oyster homogenates and also following enrichment in alkaline peptone water for 6 and 18 h. V. parahaemolyticus was detected in 93.87% of the samples, and the densities ranged from <10 to 104 organisms per g. Pathogenic V. parahaemolyticus could be detected in 5 of 49 samples (10.2%) by colony hybridization using the tdh probe and in 3 of 49 samples (6.1%) by PCR. Isolates from one of the samples belonged to the pandemic serotype O3:K6. Twenty-nine of the 49 samples analyzed (59.3%) were positive as determined by PCR for the presence of the trh gene in the enrichment broth media. trh-positive V. parahaemolyticus was frequently found in oysters from India.

Inhibition of shrimp pathogenic vibrios by a marine Pseudomonas I-2 strain

Abstract A marine bacterial strain, Pseudomonas I-2, produced inhibitory compounds against shrimp pathogenic vibrios including Vibrio harveyi, V. fluvialis, V. parahaemolyticus, V. damsela and V. vulnificus. The inhibitory substance was found to be a low molecular weight compound, heat stable, soluble in chloroform and resistant to proteolytic enzymes. The chloroform extract brought down V. harveyi levels in water by over a log unit when applied at 20 μg/ml while the extract did not affect shrimp larvae even at 50 μg/ml level. This marine Pseudomonas I-2 has potential applications for control of shrimp pathogenic vibrios in aquaculture systems.

Detection of new hosts for white spot syndrome virus of shrimp using nested polymerase chain reaction

The presence of white spot syndrome virus (WSSV) of shrimp in various marine crustaceans was studied by using polymerase chain reaction (PCR). The incidence of the virus in non-cultured crustaceans from shrimp farms was also studied. The results indicate that wild-caught asymptomatic marine shrimp such as Metapenaeus dobsoni, Parapenaeopsis stylifera, Solenocera indica and Squilla mantis carry WSSV. This virus could be detected in apparently healthy marine crabs Charybdis annulata, C. cruciata, Macrophthalmus sulcatus, Gelasimus marionis nitidus and Metopograpsus messor. The virus could also be detected in asymptomatic Macrobrachium rosenbergii cultured inland far away from coast. Detection of carrier animals required two-step nested PCR.

Application of polymerase chain reaction for detection of Vibrio parahaemolyticus associated with tropical seafoods and coastal environment.

Aims: To study the incidence of Vibrio parahaemolyticus in seafoods, water and sediment by molecular techniques vs conventional microbiological methods.

Biofilm formation by Vibrio harveyi on surfaces

Abstract The role of biofilm in the survival and persistence of the bacterial shrimp pathogen Vibrio harveyi and its possible role in perpetuating infection in shrimp hatcheries was studied. Vibrio harveyi formed biofilms on all three substrates tested: cement slab, high density polyethylene (HDPE) plastic and steel coupons. Cell density was highest on the plastic surface followed by the cement slab and the steel surface. Biofilm on the three surfaces also exhibited differential sensitivity to the sanitiser chlorine, maximum resistance being found on the concrete slab followed by plastic and steel coupons. Planktonic cells were sensitive to short exposure to low levels of chlorine. Biofilm formation occurred even in the presence of the antibiotics chloramphenicol and tetracycline, both added to the medium at 50 ppm.

Histopathological and bacteriological study of white spot syndrome of Penaeus monodon along the west coast of India

Abstract White spot syndrome (WSS) is a serious viral disease of shrimp causing severe mortalities in several parts of Asia. This paper describes the histopathology of the syndrome which occurred on the west coast of India. The affected shrimp showed white spots on the carapace and post abdominal segments and histopathologically, hypertrophied nuclei with eosinophilic to basophilic intranuclear inclusion bodies were detected in the epithelial cells of the stomach. Moderate to heavy septicaemia was noticed in moribund shrimp.

Polymerase Chain Reaction in Detection of Gymnodinium mikimotoi and Alexandrium minutum in Field Samples from Southwest India

Abstract: Polymerase chain reaction (PCR) primers were constructed for the detection of two toxic dinoflagellate species, Gymnodinium mikimotoi and Alexandrium minutum. The primers amplified a product of expected size from cultured cells of G. mikimotoi and A. minutum. The species-specific primers targeting G. mikimotoi did not yield any product with a wide range of other cultured algae used as negative controls. Primers designed for A. minutum were species-group-specific since it PCR yielded a product from the closely related species A. ostenfeldii and A. andersonii, but not from other species of this genus tested. The confirmation of PCR products was performed by digestion of the products with restriction enzymes. Sensitivity analyses of the primers on DNA template from cultured cells was positive by PCR at a DNA template concentration of 1.5 × 10−4 ng/μl (0.3 cells/L) for A. minutum, and at a DNA concentration of 2.5 × 10−2 ng/μl (697 cells/L) for G. mikimotoi. The PCR method for detection of G. mikimotoi and A. minutum was applied on field samples collected with a plankton net. Gymnodinium mikimotoi could be detected in 11 field samples by microscopy, and all these field samples were positive by PCR. The cell counts of G. mikimotoi in simultaneously collected water samples ranged from 306 to 2077/L. Alexandrium minutum could be detected by microscopy in 3 different field samples. The cell counts in water samples collected at the same time as the net samples ranged from 115 to 1115 cells/L. Alexandrium minutum was detected by PCR in these field samples, with the exception of the sample displaying the lowest cell count (115 cells/L). Plankton samples that were negative by microscopy for any of the two target species were also negative by PCR. All the PCR products from field samples were confirmed by restriction enzyme digestion. The application of PCR-based detection of harmful algal bloom species for aquaculture and monitoring purposes in natural field samples is discussed.