title: Widespread occurrence of phage-encoded exotoxin genes in terrestrial and aquatic environments in Southern California.
abstract: Many human diseases are caused by pathogens that produce exotoxins. The genes that encode these exotoxins are frequently encoded by mobile DNA elements such as plasmids or phage. Mobile DNA elements can move exotoxin genes among microbial hosts, converting avirulent bacteria into pathogens. Phage and bacteria from water, soil, and sediment environments represent a potential reservoir of phage- and plasmid-encoded exotoxin genes. The genes encoding exotoxins that are the causes of cholera, diphtheria, enterohemorrhagic diarrhea, and Staphylococcus aureus food poisoning were found in soil, sediment, and water samples by standard PCR assays from locations where the human diseases are uncommon or nonexistent. On average, at least one of the target exotoxin genes was detected in approximately 15% of the more than 300 environmental samples tested. The results of standard PCR assays were confirmed by quantitative PCR (QPCR) and Southern dot blot analyses. Agreement between the results of the standard PCR and QPCR ranged from 63% to 84%; and the agreement between standard PCR and Southern dot blots ranged from 50% to 66%. Both the cholera and shiga exotoxin genes were also found in the free phage DNA fraction. The results indicate that phage-encoded exotoxin genes are widespread and mobile in terrestrial and aquatic environments.
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182-4614, USA. vcasas@rohan.sdsu.edu
authors.forename: Veronica
authors.initials: V
authors.lastname: Casas
authors.forename: Jon
authors.initials: J
authors.lastname: Miyake
authors.forename: Heather
authors.initials: H
authors.lastname: Balsley
authors.forename: Julie
authors.initials: J
authors.lastname: Roark
authors.forename: Serena
authors.initials: S
authors.lastname: Telles
authors.forename: Steven
authors.initials: S
authors.lastname: Leeds
authors.forename: Ivan
authors.initials: I
authors.lastname: Zurita
authors.forename: Mya
authors.initials: M
authors.lastname: Breitbart
authors.forename: Doug
authors.initials: D
authors.lastname: Bartlett
authors.forename: Farooq
authors.initials: F
authors.lastname: Azam
authors.forename: Forest
authors.initials: F
authors.lastname: Rohwer
mesh_terms: D001424:Bacterial Infections / Q000453:epidemiology; D001435:Bacteriophages / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D015139:Blotting, Southern; D002140:California; D002772:Cholera Toxin / Q000235:genetics; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D004167:Diphtheria Toxin / Q000235:genetics; D004768:Enterotoxins / Q000235:genetics; D004784:Environmental Monitoring; D062665:Epidemiological Monitoring; D005098:Exotoxins / Q000235:genetics*; D005798:Genes, Bacterial; D016133:Polymerase Chain Reaction / Q000379:methods; D022621:Shiga Toxin / Q000235:genetics; D012988:Soil Microbiology; D013210:Staphylococcus / Q000235:genetics; D014871:Water Microbiology
chemical_list: D004269:DNA, Bacterial; D004167:Diphtheria Toxin; D004768:Enterotoxins; D005098:Exotoxins; D022621:Shiga Toxin; D002772:Cholera Toxin