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Characterization and persistence of potential human pathogenic vibrios in aquatic environments
Kristianstad University, School of Education and Environment. (Biomedicin, Avdelningen för Naturvetenskap)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Vibrio spp., natural inhabitants of aquatic environments, are one of the most common causes of bacterial gastroenteritis in the world, being spread to humans via the ingestion of seafood, contaminated drinking water or exposure to seawater. The majority of Vibrio spp. are avirulent, but certain strains may sporadically be human pathogenic. Vibrio cholerae may cause cholera and fatal wound infections, Vibrio parahaemolyticus may cause gastroenteritis and Vibrio vulnificus may cause wound infections and sepsis. To expand current knowledge of the occurrence, ecological niche and persistence of potential human pathogenic Vibrio spp. in aquatic environments, occurrence and laboratory studies were performed. The seasonal variation of Vibrio spp. in clams and mussels from Mozambique and Sweden were studied, with isolated strains characterized and compared with those isolated from water samples collected in India. Results showed that the numbers of Vibrio spp. in Mozambican clams peaked during the warmer rainy season and that the dominating species was V. parahaemolyticus. Biochemical fingerprinting and virulence screened by PCR revealed a high similarity among strains from the different aquatic environments. However, isolate functional hemolytic analyses and antibiotic resistance patterns differed between strains; Swedish and Indian strains were less sensitive to the tested antibiotics and had a lower hemolytic capacity than those from Mozambique. Molecular analysis of bacterial DNA from Swedish mussels showed the presence of the three Vibrio spp. most commonly linked with human illness, as well as their associated virulence genes. The strains isolated from marine and clinical environments were equally and highly harmful to the tested eukaryotic cells. The persistence of clinical V. cholerae in aquatic environments was investigated in vivo. Strains were exposed to mussels, with bacterial uptake and elimination then examined. The mussels were able to avoid the most potent strain by complete closure of shells. The less potent strain was accumulated in mussel tissue in low levels and one marine control strain to a higher degree. Mussels eliminated the pathogenic strain less efficiently than they did the marine strain. One clinical and one marine strain were then exposed to 4°C for 21 days, with the temperature then increased to 20°C. The clinical strain was more prone to lose culturability than the marine strain at 4°C, the former performed significantly better in regaining culturability after the temperature up-shift. Subsequently, the persistence of the clinical strain in natural bottom sediment, incubating as above, was studied and results showed a similar decrease in culturable numbers in the sediment as in the water. As the clinical V. cholerae strains did not carry any of the standard set of virulence genes, the ability to change from non-culturable to culturable may be of great importance to strain pathogenicity. The results also show that natural bottom sediment may be a potential reservoir of human pathogenic Vibrio spp.

Place, publisher, year, edition, pages
Kristianstad: Kristianstad University , 2012.
Keyword [en]
Vibrio cholerae, Vibrio parahaemolyticus, Mozambique, Sweden, molluscs, occurrence, persistence, sediment, TCBS, PCR, PhP, antibiotic resistance
National Category
Microbiology
Identifiers
URN: urn:nbn:se:hkr:diva-9789ISBN: 978-­‐91-­‐628-­‐8482-­‐6 (print)OAI: oai:DiVA.org:hkr-9789DiVA: diva2:561062
Available from: 2012-10-17 Created: 2012-10-17Bibliographically approved
List of papers
1. Characteristics of potentially pathogenic vibrios from subtropical Mozambique compared with isolates from tropical India and boreal Sweden
Open this publication in new window or tab >>Characteristics of potentially pathogenic vibrios from subtropical Mozambique compared with isolates from tropical India and boreal Sweden
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2013 (English)In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 83, no 2, 255-264 p.Article in journal (Refereed) Published
Abstract [en]

Reported outbreaks of Vibrio parahaemolyticus have increased worldwide, particularly in regions of high seafood consumption. In Mozambique, seafood constitutes an important food resource and diarrheal diseases are common among its inhabitants. Edible clams were collected in Maputo Bay during both the dry and rainy seasons, with the results showing the number of viable counts of vibrios in clams to peak during the latter. Vibrio parahaemolyticus was the predominant species identified among the isolated strains. Although only one of 109 total strains carried the tdh virulence gene, 69% of isolates showed evidence of hemolytic capacity when subjected to a functional test. Similar virulence patterns and biochemical properties were found in strains isolated from Indian and Swedish marine waters. Antibiotic resistance was, however, more pronounced in strains isolated from these latter two environments.

Keyword
Vibrio spp, Vibrio parahaemolyticus, qPCR, probe hybridization, TCBS-agar, persistence in clams, PhenePlate system, antibiotic resistance, hemolysis
National Category
Microbiology
Identifiers
urn:nbn:se:hkr:diva-9610 (URN)10.1111/j.1574-6941.2012.01471.x (DOI)000313252600001 ()
Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2014-06-24Bibliographically approved
2. Occurrence and potential pathogenesis of Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus on the South Coast of Sweden
Open this publication in new window or tab >>Occurrence and potential pathogenesis of Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus on the South Coast of Sweden
2011 (English)In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 78, no 2, 306-313 p.Article in journal (Refereed) Published
Abstract [en]

During the summer of 2006, several wound infections - of which three were fatal caused by Vibrio cholerae were reported from patients who had been exposed to water from the Baltic Sea. Before these reports, we initiated a sampling project investigating the occurrence of potential human pathogenic V. cholerae, Vibrio vulnificus and Vibrio parahaemolyticus in The Sound between Sweden and Denmark. The Blue mussel (Mytilus edulis) was used as an indicator to follow the occurrence of vibrios over time. Molecular analyses showed high frequencies of the most potent human pathogenic Vibrio spp.; 53% of mussel samples were positive for V. cholerae (although none were positive for the cholera toxin gene), 63% for V. vulnificus and 79% for V. parahaemolyticus (of which 47% were tdh(+) and/or trh(+)). Viable vibrios were also isolated from the mussel meat and screened for virulence by PCR. The mortality of eukaryotic cells when exposed to bacteria was tested in vivo, with results showing that the Vibrio strains, independent of species and origin, were harmful to the cells. Despite severe infections and several deaths, no report on potential human pathogenic vibrios in this area had been published before this study.

Keyword
Vibrio cholerae, Vibrio vulnificus, Vibrio parahaemolyticus, ecology, microbiology, wound infections, thermostable direct hemolysin, iii secretion system, wound-infection, mytilus-edulis, multiplex pcr, non-o1, temperature, bacteria, salinity, epidemiology
National Category
Microbiology
Identifiers
urn:nbn:se:hkr:diva-8790 (URN)10.1111/j.1574-6941.2011.01157.x (DOI)000296849000012 ()21692819 (PubMedID)
Available from: 2011-12-07 Created: 2011-12-06 Last updated: 2014-06-24Bibliographically approved
3. The origin of Vibrio cholerae influences uptake and persistence in the blue mussel Mytilus edulis
Open this publication in new window or tab >>The origin of Vibrio cholerae influences uptake and persistence in the blue mussel Mytilus edulis
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2012 (English)In: Journal of Shellfish Research, ISSN 0730-8000, Vol. 31, no 1, 87-92 p.Article in journal (Refereed) Published
Abstract [en]

Vibrio cholerae may cause diarrheal diseases and wound infections, both of which have the potential to be fatal. Transmission to humans is often linked to consumption of contaminated shellfish/drinking water or dermal exposure to water (e.g. when swimming). In this study, we investigated whether different isolates of Vibrio cholerae differ in terms of accumulation, persistence, and viability when encountering blue mussels (Mytilus edulis). Mussel uptake and elimination of three different V. cholerae strains were compared: one fatal clinical non-O1/O139 isolate, one highly potent El Tor biotype, and one marine strain isolated from blue mussels. The results showed that the uptake of the marine strain was significantly higher than the clinical strain, but the elimination process of the marine strain was also more efficient. The El Tor strain was not at all ingested by the mussels. In addition, the survival of bacteria when incubated together with M. edulis hemocytes was tested in vitro. The viability of clinical strains was unaffected by the presence of hemocytes, and the marine strains were even more resistant and able to multiply. We conclude that the highly virulent El Tor biotype was not taken up by the mussels and could thereby escape the mussels' elimination process. The potentially fatal non-O1/O139 V. cholerae strain may accumulate in low numbers, but could be very persistent in mussels.

Keyword
mussel, Mytilus edulis, Vibrio cholerae, pathogenic, depuration, hemocytes
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-9251 (URN)10.2983/035.031.0111 (DOI)000302846800011 ()
Available from: 2012-05-02 Created: 2012-05-02 Last updated: 2014-06-24Bibliographically approved
4. The importance of marine sediments as a reservoir for human pathogenic Vibrio cholerae in cold water conditions
Open this publication in new window or tab >>The importance of marine sediments as a reservoir for human pathogenic Vibrio cholerae in cold water conditions
(English)Article in journal (Refereed) Submitted
National Category
Biological Sciences
Identifiers
urn:nbn:se:hkr:diva-9788 (URN)
Available from: 2012-10-17 Created: 2012-10-17 Last updated: 2014-06-24Bibliographically approved

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