Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation
Shiga toxin producing Escherichia coli (STEC) strains vary in acid resistance; however, little is known about the underlying mechanisms that result in strain specific differences. Among 25 STEC O157:H7 strains tested, 7 strains flocculated when grown statically for 18 h in minimal salts medium at 37...
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Frontiers Media S.A.
2017-07-01
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| Series: | Frontiers in Microbiology |
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| Online Access: | http://journal.frontiersin.org/article/10.3389/fmicb.2017.01404/full |
| _version_ | 1819061330712199168 |
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| author | Kathryn L. Kay Kathryn L. Kay Frederick Breidt Frederick Breidt Pina M. Fratamico Gian M. Baranzoni Gwang-Hee Kim Gwang-Hee Kim Amy M. Grunden Deog-Hwan Oh |
| author_facet | Kathryn L. Kay Kathryn L. Kay Frederick Breidt Frederick Breidt Pina M. Fratamico Gian M. Baranzoni Gwang-Hee Kim Gwang-Hee Kim Amy M. Grunden Deog-Hwan Oh |
| author_sort | Kathryn L. Kay |
| collection | DOAJ |
| description | Shiga toxin producing Escherichia coli (STEC) strains vary in acid resistance; however, little is known about the underlying mechanisms that result in strain specific differences. Among 25 STEC O157:H7 strains tested, 7 strains flocculated when grown statically for 18 h in minimal salts medium at 37°C, while 18 strains did not. Interestingly, the flocculation phenotype (cells came out of suspension) was found to correlate with degree of acid sensitivity in an assay with 400 mM acetic acid solution at pH 3.3 targeting acidified foods. Strains exhibiting flocculation were more acid sensitive and were designated FAS, for flocculation acid sensitive, while the acid resistant strain designated PAR for planktonic acid resistant. Flocculation was not observed for any strains during growth in complex medium (Luria Bertani broth). STEC strains B201 and B241 were chosen as representative FAS (2.4 log reduction) and PAR (0.15 log reduction) strains, respectively, due to differences in acid resistance and flocculation phenotype. Results from electron microscopy showed evidence of fimbriae production in B201, whereas fimbriae were not observed in B241.Curli fimbriae production was identified through plating on Congo red differential medium, and all FAS strains showed curli fimbriae production. Surprisingly, 5 PAR strains also had evidence of curli production. Transcriptomic and targeted gene expression data for B201 and B241indicated that csg and hde (curli and acid induced chaperone genes, respectively) expression positively correlated with the phenotypic differences observed for these strains. These data suggest that FAS strains grown in minimal medium express curli, resulting in a flocculation phenotype. This may be regulated by GcvB, which positively regulates curli fimbriae production and represses acid chaperone proteins. RpoS and other regulatory mechanisms may impact curli fimbriae production, as well. These findings may help elucidate mechanisms underlying differences among STEC strains in relating acid resistance and biofilm formation. |
| first_indexed | 2024-12-21T14:41:11Z |
| format | Article |
| id | doaj.art-28da5edca9ef4cf5af07eae2e3c2fb14 |
| institution | Directory Open Access Journal |
| issn | 1664-302X |
| language | English |
| last_indexed | 2024-12-21T14:41:11Z |
| publishDate | 2017-07-01 |
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| series | Frontiers in Microbiology |
| spelling | doaj.art-28da5edca9ef4cf5af07eae2e3c2fb142022-12-21T19:00:11ZengFrontiers Media S.A.Frontiers in Microbiology1664-302X2017-07-01810.3389/fmicb.2017.01404242069Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient LimitationKathryn L. Kay0Kathryn L. Kay1Frederick Breidt2Frederick Breidt3Pina M. Fratamico4Gian M. Baranzoni5Gwang-Hee Kim6Gwang-Hee Kim7Amy M. Grunden8Deog-Hwan Oh9Department of Plant and Microbial Biology, North Carolina State UniversityRaleigh, NC, United StatesFood Science Research Unit, United States Department of Agriculture-Agriculture Research ServiceRaleigh, NC, United StatesDepartment of Plant and Microbial Biology, North Carolina State UniversityRaleigh, NC, United StatesFood Science Research Unit, United States Department of Agriculture-Agriculture Research ServiceRaleigh, NC, United StatesUnited States Department of Agriculture, Agricultural Research Service, Eastern Regional Research CenterWyndmoor, PA, United StatesUnited States Department of Agriculture, Agricultural Research Service, Eastern Regional Research CenterWyndmoor, PA, United StatesUnited States Department of Agriculture, Agricultural Research Service, Eastern Regional Research CenterWyndmoor, PA, United StatesDepartment of Food Science and Biotechnology, College of Bioscience and Biotechnology, Kangwon National UniversityChuncheon, South KoreaDepartment of Plant and Microbial Biology, North Carolina State UniversityRaleigh, NC, United StatesDepartment of Food Science and Biotechnology, College of Bioscience and Biotechnology, Kangwon National UniversityChuncheon, South KoreaShiga toxin producing Escherichia coli (STEC) strains vary in acid resistance; however, little is known about the underlying mechanisms that result in strain specific differences. Among 25 STEC O157:H7 strains tested, 7 strains flocculated when grown statically for 18 h in minimal salts medium at 37°C, while 18 strains did not. Interestingly, the flocculation phenotype (cells came out of suspension) was found to correlate with degree of acid sensitivity in an assay with 400 mM acetic acid solution at pH 3.3 targeting acidified foods. Strains exhibiting flocculation were more acid sensitive and were designated FAS, for flocculation acid sensitive, while the acid resistant strain designated PAR for planktonic acid resistant. Flocculation was not observed for any strains during growth in complex medium (Luria Bertani broth). STEC strains B201 and B241 were chosen as representative FAS (2.4 log reduction) and PAR (0.15 log reduction) strains, respectively, due to differences in acid resistance and flocculation phenotype. Results from electron microscopy showed evidence of fimbriae production in B201, whereas fimbriae were not observed in B241.Curli fimbriae production was identified through plating on Congo red differential medium, and all FAS strains showed curli fimbriae production. Surprisingly, 5 PAR strains also had evidence of curli production. Transcriptomic and targeted gene expression data for B201 and B241indicated that csg and hde (curli and acid induced chaperone genes, respectively) expression positively correlated with the phenotypic differences observed for these strains. These data suggest that FAS strains grown in minimal medium express curli, resulting in a flocculation phenotype. This may be regulated by GcvB, which positively regulates curli fimbriae production and represses acid chaperone proteins. RpoS and other regulatory mechanisms may impact curli fimbriae production, as well. These findings may help elucidate mechanisms underlying differences among STEC strains in relating acid resistance and biofilm formation.http://journal.frontiersin.org/article/10.3389/fmicb.2017.01404/fullSTECacid resistancenutrient limitationcurliGcvB |
| spellingShingle | Kathryn L. Kay Kathryn L. Kay Frederick Breidt Frederick Breidt Pina M. Fratamico Gian M. Baranzoni Gwang-Hee Kim Gwang-Hee Kim Amy M. Grunden Deog-Hwan Oh Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation Frontiers in Microbiology STEC acid resistance nutrient limitation curli GcvB |
| title | Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation |
| title_full | Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation |
| title_fullStr | Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation |
| title_full_unstemmed | Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation |
| title_short | Escherichia coli O157:H7 Acid Sensitivity Correlates with Flocculation Phenotype during Nutrient Limitation |
| title_sort | escherichia coli o157 h7 acid sensitivity correlates with flocculation phenotype during nutrient limitation |
| topic | STEC acid resistance nutrient limitation curli GcvB |
| url | http://journal.frontiersin.org/article/10.3389/fmicb.2017.01404/full |
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