An evaluation of commercial thiosulphate citrate bile salt sucrose agar (TCBS)

Deletion of vp0057, a Gene Encoding a Ser/Thr Protein Kinase, Impacts the Proteome and Promotes Iron Uptake and Competitive Advantage in Vibrio parahaemolyticus

The marine bacterial pathogen Vibrio parahaemolyticus is a major cause of food-borne gastroenteritis. Recent findings have demonstrated that protein phosphorylation is fundamental to the regulation of many physiological processes in pathogenic bacteria, including bacterial virulence. However, the underlying mechanisms remain to be completely clarified. Using bioinformatics analysis, we found that VP0057 may be a potential Ser/Thr protein kinase with phosphorylation activity. Thus, we constructed the vp0057-deletion mutant (Δvp0057) from the wild-type V. parahaemolyticus serotype O3:K6 and employed a mass spectrometry-based proteomic strategy to characterize proteome-wide changes in response to vp0057 deletion, owing to the potential roles of VP0057 in V. parahaemolyticus. One hundred ninety-seven differentially expressed proteins were identified in the Δvp0057 strain compared with the wild-type strain, among which 135 proteins were upregulated and 62 proteins were downregulated. Detailed annotation of these differentially expressed proteins was conducted. Notably, iron-related and T6SS1-related proteins were upregulated in the Δvp0057 strain, corroborating the results by quantitative PCR. Further experiments proved that vp0057 deletion promotes Fe²⁺ and Fe³⁺ uptake and provides a growth competition advantage, which is controlled by iron-related and T6SS1-related proteins, respectively. Although the regulatory roles and mechanisms of VP0057 remain to be revealed in V. parahaemolyticus, our systemic analysis of the protein profile of Δvp0057 provides a promising starting point for the intensive exploration of VP0057.

Differential specificity of selective culture media for enumeration of pathogenic vibrios: advantages and limitations of multi-plating methods

Plating environmental samples on vibrio-selective chromogenic media is a commonly used technique that allows one to quickly estimate concentrations of putative vibrio pathogens or to isolate them for further study. Although this approach is convenient, its usefulness depends directly on how well the procedure selects against false positives. We tested whether a chromogenic medium, CHROMagar Vibrio (CaV), used alone (single-plating) or in combination (double-plating) with a traditional medium thiosulfate-citrate-bile-salts (TCBS), could improve the discrimination among three pathogenic vibrio species (Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus) and thereby decrease the number of false-positive colonies that must be screened by molecular methods. Assays were conducted on water samples from two estuarine environments (one subtropical, one tropical) in a variety of seasonal conditions. The results of the double-plating method were confirmed by PCR and 16S rRNA sequencing. Our data indicate that there is no significant difference in the false-positive rate between CaV and TCBS when using a single-plating technique, but determining color changes on the two media sequentially (double-plating) reduced the rate of false positive identification in most cases. The improvement achieved was about two-fold on average, but varied greatly (from 0- to 5-fold) and depended on the sampling time and location. The double-plating method was most effective for V. vulnificus in warm months, when overall V. vulnificus abundance is high (false positive rates as low as 2%, n=178). Similar results were obtained for V. cholerae (minimum false positive rate of 16%, n=146). In contrast, the false positive rate for V. parahaemolyticus was always high (minimum of 59%, n=109). Sequence analysis of false-positive isolates indicated that the majority of confounding isolates are from the Vibrionaceae family, however, members of distantly related bacterial groups were also able to grow on vibrio-selective media, even when using the double-plating method. In conclusion, the double-plating assay is a simple means to increase the efficiency of identifying pathogenic vibrios in aquatic environments and to reduce the number of molecular assays required for identity confirmation. However, the high spatial and temporal variability in the performance of the media mean that molecular approaches are still essential to obtain the most accurate vibrio abundance estimates from environmental samples.

Activation of cholera toxin production by anaerobic respiration of trimethylamine N-oxide in Vibrio cholerae

Vibrio cholerae is a gram-negative bacterium that causes cholera. Although the pathogenesis caused by this deadly pathogen takes place in the intestine, commonly thought to be anaerobic, anaerobiosis-induced virulence regulations are not fully elucidated. Anerobic growth of the V. cholerae strain, N16961, was promoted when trimethylamine N-oxide (TMAO) was used as an alternative electron acceptor. Strikingly, cholera toxin (CT) production was markedly induced during anaerobic TMAO respiration. N16961 mutants unable to metabolize TMAO were incapable of producing CT, suggesting a mechanistic link between anaerobic TMAO respiration and CT production. TMAO reductase is transported to the periplasm via the twin arginine transport (TAT) system. A similar defect in both anaerobic TMAO respiration and CT production was also observed in a N16961 TAT mutant. In contrast, the abilities to grow on TMAO and to produce CT were not affected in a mutant of the general secretion pathway. This suggests that V. cholerae may utilize the TAT system to secrete CT during TMAO respiration. During anaerobic growth with TMAO, N16961 cells exhibit green fluorescence when stained with 2',7'-dichlorofluorescein diacetate, a specific dye for reactive oxygen species (ROS). Furthermore, CT production was decreased in the presence of an ROS scavenger suggesting a positive role of ROS in regulating CT production. When TMAO was co-administered to infant mice infected with N16961, the mice exhibited more severe pathogenic symptoms. Together, our results reveal a novel anaerobic growth condition that stimulates V. cholerae to produce its major virulence factor.

Vibrios of the spotted rose snapper Lutjanus guttatus Steindachner, 1869 from northwestern Mexico

AIM

To characterize and identify vibrios present in wild and cultured juvenile snappers (Lutjanus guttatus) in northwestern Mexico.

METHODS AND RESULTS

Spotted rose snapper juveniles were collected at four localities in northwestern Mexico. Bacteria were isolated from external lesions, kidney, liver, and spleen from cultured and wild caught organisms. In total, 280 isolates were obtained and fingerprinted with rep-PCR (GTG5). Nearly 93.2% of the strains belonged to the Vibrionaceae family. Species and genera identified were Photobacterium damselae subsp. damselae (76 strains), Photobacterium leiognathi (13), Vibrio sp. (24), Vibrio alginolyticus (12), Vibrio campbellii (19), Vibrio fortis (9), Vibrio harveyi (49), Vibrio ichthyoenteri (4), Vibrio mediterranei (4), Vibrio parahaemolyticus (1), Vibrio ponticus (2), Vibrio rotiferianus (22), and four potential new species.

CONCLUSIONS

A wide diversity of vibrios was found in the external lesions and internal organs of both wild and cultured spotted rose snapper juveniles. In total, 12 species of vibrios and four potential new species were identified.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study on the vibrios present in the spotted rose snapper and therefore might serve as a basis for future studies and diagnosis.

Evaluation of an alkaline phosphatase-labeled oligonucleotide probe for detection and enumeration of vibrio spp. from shrimp hatchery environment

An alkaline phosphatase (AP)-labeled genus-specific oligonucleotide probe was developed to detect and enumerate vibrios in shrimp larvae and their surrounding environment. The probe was evaluated using 35 laboratory isolates of Vibrio species and 29 isolates of non-vibrio species. The probe was specific for the Vibrio species and no cross reaction was found with the non-vibrios included in the study. The total Vibrio counts obtained by plating on thiosulfate-citrate-bile salts-sucrose agar (TCBS) and using oligonucleotide probe were compared. Total Vibrio counts obtained by probe were comparatively higher than the counts obtained by plating on TCBS agar. The difference between the counts obtained by the probe and by plating on TCBS agar ranged from 2 to 21 times. The study reveals that the use of a non-selective medium such as T1N3 agar followed by detection using a genus-specific probe would help to precisely enumerate the total Vibrio load in the aquaculture environments.

An investigation into the changed physiological state of Vibrio bacteria as a survival mechanism in response to cold temperatures and studies on their sensitivity to heating and freezing

AIMS

To induce pathogenic Vibrio bacteria into a changed physiological state, in response to cold temperatures in sea water, and assess their sensitivity to heating and freezing, as compared with normal cells.

METHODS AND RESULTS

Cells of exponential phase Vibrio vulnificus, V. cholerae and V. parahaemolyticus were washed and inoculated into flasks of sea water, which were stored at 20 and 4 degrees C. Cells stored at 20 degrees C could be recovered after 60 d on non-selective agar (heart infusion agar; HIA) and on the selective agar (thiosulphate citrate bile salts agar) which is used in most Vibrio detection methodology. At 4 degrees C cells became non-culturable on both agars over time. The non-culturable cells appeared to be metabolically active and maintained their membrane integrity, whilst undergoing a change in morphology from rod-shaped to coccoid cells. Resuscitation was possible, in some cases, by an upshift in temperature before plating and the addition of catalase to HIA plates was found to increase recovery. Studies were carried out to assess the sensitivity of the non-culturable cells to heating and freezing compared with the normal cells. Vibrio organisms, whether culturable or in the non-culturable form, were not inactivated by freezing to -20 degrees C. Heating studies showed that V. parahaemolyticus was very heat resistant at low temperatures. However, a pasteurization regime of 2 min at 70 degrees C was found to be effective against all three strains. Experiments showed that the non-culturable cells of all three strains were similar in their heat resistance or, in some cases, were more heat sensitive than cells in the normal form.

CONCLUSIONS

Cells in the changed physiological form would not be detected in fish or seafood products by the current Vibrio detection methods. Freezing had no effect in reducing cell numbers. Vibrio parahaemolyticus was very heat resistant in the low temperature pasteurization studies. The higher pasteurization regime of 70 degrees C for 2 min was effective against all three pathogens. Non-culturable cells had similar heat sensitivity or were more heat sensitive than cells in the normal state. SIGNIFICANCE OF IMPACT OF THE STUDY: The study has highlighted a need for the development of better Vibrio detection methods. The low temperature pasteurization of oysters, which has been recommended in the USA, would not be adequate against the strain of V. parahaemolyticus used in this study. Heating regimes which were found to control cells in the normal form will also be effective for the control of the cells with changed physiology.

Comparison of selective media for the detection of Vibrio vulnificus in environmental samples

AIMS

To compare two selective agars, cellobiose-colistin (CC) agar and a modification of the Vibrio vulnificus medium (VVMc agar), for the isolation of Vibrio vulnificus from environmental samples.

METHODS AND RESULTS

The efficiencies of recovery of V. vulnificus collection strains on CC, VVM, VVMc and on thiosulphate-citrate-bile salts-sucrose (TCBS) agar were compared and similar efficiencies were obtained. A slightly higher recovery was observed on VVMc agar. The detection of V. vulnificus in environmental samples (eels and water) was performed by combining culture-based methods (CC and VVMc agars) with DNA-based methods using species-specific probes based on the cytolysin-haemolysin and the 16S rDNA genes. A lower accompanying microbiota was found on CC agar than on VVMc agar.

CONCLUSION

The comparison between CC and VVMc agars confirms that both are useful for the detection of V. vulnificus in environmental samples. However, the use of any of these media should be combined with a species-specific probe.

SIGNIFICANCE AND IMPACT OF THE STUDY

The combined use of a selective medium and a specific probe provides a feasible method for the detection of V. vulnificus for epidemiological and ecological studies.

A selective medium and a specific probe for detection of Vibrio vulnificus

A selective medium (VVM) and a specific 16S rRNA gene (rDNA) probe (V3VV) for the detection of Vibrio vulnificus were developed. The medium contains D-(+)-cellobiose as the main carbon source and electrolytes (MgCl(2)-6H(2)O and KCl), which stimulate bacterial growth. Polymyxin B, colistin, and moderate alkalinity and salinity provide selectivity properties. V. vulnificus grows on VVM as flat, bright yellow colonies. Other Vibrio species tested either did not grow or showed green-bluish colonies, with the exception of V. campbelli, V. carchariae, and V. navarrensis. There is a higher colony count on VVM agar than on cellobiose-colistin agar or on modified cellobiose-polymyxin B-colistin agar. The specific probe was evaluated by colony hybridization and dot blot hybridization with PCR-amplified 16S rDNA using collection strains and environmental isolates. No strain studied other than V. vulnificus showed positive hybridization with this oligonucleotide. The combined use of VVM agar and the V3VV probe provided the recovery of V. vulnificus from mixed bacterial suspensions and spiked mussels.

Current perspectives on the epidemiology and pathogenesis of clinically significant Vibrio spp

Recent taxonomic advances have now implicated several different Vibrio species as human pathogens. While the most common clinical presentation of Vibrio infection continues to be gastroenteritis, an increasing number of extraintestinal infections are being reported, particularly in immunocompromised individuals. Detection of Vibrio infections requires a good clinical history and the use of appropriate isolation and identification procedures by the laboratory to confirm illnesses attributed to Vibrio species. Except for Vibrio cholerae O1 and Vibrio parahaemolyticus, there is little direct evidence linking the production of a myriad of cell-associated or extracellular factors produced by each species with human disease and pathogenesis. Many questions regarding pathogenic Vibrio species remain unanswered, including their frequency and distribution in environmental specimens (water, shellfish), infective doses, virulence potential of individual isolates, and markers associated with such strains.

New selective plating medium for isolation of Vibrio vulnificus biogroup 1

A new plating medium (VV agar) has been developed as an alternative to thiosulfate-citrate-bile salts-sucrose (TCBS) agar for the isolation of Vibrio vulnificus. Salicin (2% wt/vol) is employed as the source of carbohydrate, with potassium tellurite (0.0005% wt/vol), crystal violet (0.00015% wt/vol), oxgall (0.8% wt/vol), and a pH of 8.6 to inhibit growth of gram-positive and gram-negative organisms other than V. vulnificus. Because strains of V. vulnificus do not strongly ferment salicin in VV agar, a pH indicator has not been included in the medium. Growth of V. vulnificus appears on VV agar as large grey colonies with black centers. Other non-Vibrio strains which grow on the medium produce smaller colonies and fail to take up tellurite. VV agar has proved to be more effective than TCBS agar in inhibiting members of the Enterobacteriaceae as well as gram-positive cocci. Only Vibrio strains capable of utilizing salicin grow well on VV agar. Recovery and growth of V. vulnificus are superior on VV agar, compared with TCBS agar.

Statistical evaluation of a quality control method for isolation of pathogenic Vibrio species on selected thiosulfate-citrate-bile salts-sucrose agars

The recovery of Vibrio cholerae, Vibrio fluvialis, Vibrio parahaemolyticus, and Vibrio vulnificus, employing eight strains of each species, was studied by using four brands of thiosulfate-citrate-bile salts-sucrose (TCBS) agar prepared according to manufacturers' instructions and following a standardized procedure. A standardized broth inoculum of each strain was placed on duplicate plates of each brand of TCBS agar and also on tryptic soy agar (Difco Laboratories) containing 1% (wt/vol) NaCl, the latter serving as the control. Plates were inoculated in a sequence designed to compensate for bias associated with multiplication of the bacteria during the inoculation procedure. Colony counts and quality of growth were recorded after incubation for 18 h at 35 degrees C. The comparison procedure was repeated four times at weekly intervals. Data were analyzed by using an analysis of variance model. The recovery and quality of growth of each species varied significantly on the different brands of TCBS agar. Significant variability was also identified for some components of the inoculation procedure. Modifications of the inoculation procedure are suggested to minimize sources of variance. A simplified statistical procedure, based on the t test, is described for media quality control for laboratories routinely isolating pathogenic Vibrio spp.

Vibrio parahaemolyticus and related halophilic Vibrios

Approximately 30 years have elapsed since Dr. Fujino's original discovery that Vibrio parahaemolyticus (then termed Pasteurella parahemolytica) was the cause of "summer diarrhea" in Japan. Since that finding, V. parahaemolyticus has been established as a cause of gastroenteritis in numbers and places approaching global proportions. It has been isolated in marine and estuarine areas almost worldwide and despite its halophilic nature, V. parahaemolyticus has been isolated from saline-free waters. The relationship of this organism to the environment reveals a close association with other marine organisms especially copepods on which the Vibrios depend for survival in winter months and growth in summer months. There is a uniquely provocative disparity between human strains of V. parahaemolyticus which are Kanagawa phenomenon (KP) positive and the environmental strains which to a large extent are KP negative, the significance being that pathogenicity is measured according to the Kanagawa phenomenon (hemolytic activity) reaction. The hemolysin of the pathogenic strains is a thermostable, cardiotoxic protein, which thus far has not been implicated in the mechanism(s) which causes human gastroenteritis. The interest in this organism has been widened in recent years by the finding that similar organisms, V. alginolyticus, lactose positive vibrios and group F vibrios also cause serious disease in humans.

A non-pathogenic vibrio for the routine quality control of TCBS cholera medium

A non-pathogenic "indicator" organism to relapse Vibrio cholerae in the routine quality control of TCBS medium was sought among a large collection of freeze-dried vibrios isolated mostly from environmental sources. One strain, which was consistently more sensitive to inhibition of growth on TCBS medium that strains of V. cholerae and V. parahaemolyticus, is recommended for this purpose. It has been deposited with, and is available from, the National Collection of Type Cultures as NCTC 11218.

A simple laboratory method for the diagnosis of V. cholerae

In many developing countries where cholera occurs, bacteriological facilities at the local level are lacking and either cholera may be unreported or other diarrhoeal diseases may be mistakenly reported as cholera. A simple and practical method, suitable for use in small hospitals and health centres and by field teams of health workers is described. Swab samples are streaked on to various media (TTGA and TCBS were found to be the most satisfactory), incubated overnight at 35 degrees C and read. The characteristics which distinguish Vibrio cholerae colonies from others developing are described. In tests on 309 cholera patients, culture on TTGA gave 100% and on TCBS 96.7% positives.