Enterobacterial Autoinducer of Growth Enhances Shiga Toxin Production by Enterohemorrhagic Escherichia coli
http://www.100md.com
微生物临床杂志 2006年第6期
Robert Koch Institut, Wernigerode, Germany
Department of Genetics, University of Leicester, Leicester, United Kingdom
ABSTRACT
The addition of the enterobacterial autoinducer of growth to nutrient-poor minimal medium markedly accelerated the exponential growth rates of strains of enterohemorrhagic Escherichia coli but had little or no effect on maximal cell densities in stationary phase. Growth in the presence of the autoinducer resulted in an approximately twofold enhancement in Shiga toxin production.
TEXT
Mammalian signaling molecules such as the catecholamine neuroendocrine hormone L-norepinephrine (NE) can stimulate the growth of a number of pathogenic bacteria and, in some cases, the expression of virulence properties (1, 2, 6, 7, 9, 10, 12, 17). In addition, transient exposure of Escherichia coli to NE in a serum-containing minimal medium induced the production of a heat-stable autoinducer of growth (AI), which elicited responses similar to those with NE, including induction of more AI (11). Similar effects were later observed for a range of enterobacterial species (4). In the case of E. coli, the mechanism of growth stimulation by NE includes facilitation of iron acquisition from the mammalian iron-binding proteins transferrin and lactoferrin (5). However, the activity of AI is not confined to bacterial growth under the iron-limited conditions of a serum-containing medium. We recently demonstrated resuscitation by enterobacterial AI of highly stressed populations of pathogenic isolates of enterohemorrhagic E. coli (EHEC) and Salmonella enterica serovar Typhimurium in iron-containing nutrient-rich media (16). AI also enhanced the sensitivity and speed of enrichment of Bacillus cereus and Bacillus anthracis spores in both serum-supplemented medium and buffered peptone water (15). The present paper provides another example of iron-independent AI activity, with important practical implications for the detection of Shiga toxin-producing EHEC strains.
A new nutrient-poor minimal medium (NPMM) formulation that avoids the use of antibiotics and bile salts as selective supplements has been developed for enrichment of EHEC from clinical, food, and environmental samples (W. Voigt, A. Fruth, H.-H. Sonneborn, H. Tschpe, and R. Reissbrodt, Abstr. VTEC 2003 Meet., p. 149, 2003). This medium comprises 100 mM K2HPO4 (pH 7.2 ± 0.1) containing trace elements (40 mg/liter of MgSO4 · 7H2O, 4 mg/liter of ferric ammonium citrate, 6 mg/liter of MnSO4 · 4H2O), vitamins (0.2 mg/liter [each] of pyridoxal-HCl, thiamine, and nicotinic acid amide), and pancreatic casein peptone (0.2% [wt/vol]) as a source of amino acids (14). During developmental work, it was observed that aspartate, glutamate, and serine were significantly depleted during the growth of EHEC strains, as measured by capillary electrophoresis of samples taken before and after growth. Therefore, the medium was additionally supplemented with L-aspartic acid (0.08% [wt/vol]), L-glutamic acid (0.12% [wt/vol]), and L-serine at various concentrations, as described below. The medium was supplemented as required with 50 μM NE (Sigma Chemical Co.) or with 2% (vol/vol) AI prepared as previously described (4, 8, 16). Briefly, serum-SAPI medium (2.77 mM glucose, 6.25 mM NH4NO3, 1.84 mM KH2PO4, 3.35 mM KCl, 1.01 mM MgSO4, and 30% [vol/vol] adult bovine serum, pH 7.5) containing 50 μM NE was inoculated at approximately 100 to 1,000 CFU/ml with the producing strain and incubated overnight at 37°C in a humidified 5% CO2 atmosphere. Bacteria were pelleted by centrifugation (6,000 x g for 15 min), and the culture supernatants were filter sterilized and stored at –20°C until required. Sterile preparations were serially diluted in fresh sterile SAPI medium, and samples of each dilution were added at 2% (vol/vol) to serum-SAPI medium inoculated with 100 to 1,000 CFU/ml of an indicator strain. The dilution that promoted bacterial growth after overnight incubation at 37°C to an optical density at 620 nm (OD620) of 0.4, which represents 108 CFU/ml, was used as a supplement to NPMM, as described below. For the experiments reported here, we prepared AI from cultures of a strain that we had previously reported to be Yersinia ruckeri (16) but subsequently confirmed (on the basis of the Bactid-System [CDC, Atlanta, Ga.]) to be E. coli. It should be noted, however, that virtually any strain of E. coli or any other enterobacterial species that produces enterobactin can be used both for production of AI and as an indicator strain for AI activity.
The EHEC strains analyzed in this study were from the culture collection of the Robert Koch Institute, Wernigerode, Germany. Bacteria from overnight nutrient agar cultures were inoculated into NPMM at approximately 2 x 102 CFU/ml and incubated at 37°C with horizontal shaking at 150 rpm. Culture growth (OD620) was monitored in a Bioscreen C apparatus (Thermolabsystems, Helsinki, Finland) (16), and Shiga toxin production was determined with a commercially available enzyme-linked immunosorbent assay (ELISA) kit (r-Biopharm, Darmstadt, Germany) and reported as the OD450. Two-tailed Student's t test was used to determine the differences in toxin production between culture conditions; differences were considered statistically significant when P values were <0.05.
Figure 1 illustrates a Bioscreen C analysis of the growth of E. coli strain 97-10085 in the presence or absence of AI. Supplementation with AI significantly accelerated exponential growth, such that between 7 and 10 h, the doubling time of the culture in the presence of AI was consistently approximately half that in the absence of AI. After prolonged incubation, however, OD620 levels in AI-free medium and AI-supplemented medium were similar. This is in contrast with the situation in serum-SAPI medium (11), in which growth in the absence of AI is limited to between 100- and 1,000-fold, primarily (but perhaps not exclusively) because iron availability is restricted by the presence of serum transferrin. Indeed, AI was so designated because of its ability to induce bacterial growth under the specific conditions of serum-SAPI medium (11). Under the relatively iron-rich conditions used in this study, however, the activity of AI is seen as an enhancement of the growth rate rather than the final cell density.
Table 1 shows the effects of supplementation of NPMM with NE or AI on toxin production by EHEC strains of various serogroups in NPMM containing 0.2% L-serine. There was considerable variation in toxin levels among the strains tested; OD450 levels ranging from <0.4 to >4 were observed consistently over at least three independent experiments with each strain. Supplementation with NE enhanced Shiga toxin levels significantly in 5 of the 10 strains, while supplementation with AI enhanced toxin levels significantly in all 10 strains. This was perhaps due to strain variability in the production of AI in response to NE. Maximal growth levels (OD620) of cultures with or without AI supplementation were not significantly different (data not shown).
To determine if the effect of AI was enhanced by incipient nutrient starvation, strain 97-10085 was inoculated into NPMM supplemented with lower concentrations of L-serine and assayed for growth and Shiga toxin production (Fig. 2). The OD620 levels reached after 24 h of incubation in medium supplemented with 0.05 or 0.1% (wt/vol) L-serine were significantly lower (P = 0.05) than those reached in medium supplemented with 0.2% (wt/vol) L-serine (Fig. 2a). The addition of AI resulted in a slight but not statistically significant reduction (P > 0.05) in the maximum OD620 level achieved after 24 h of incubation at each concentration of L-serine (Fig. 2a). Analysis of toxin production in the same cultures indicated that adding increasing concentrations of L-serine resulted in only small increases in Shiga toxin production but that supplementation with 2% (vol/vol) AI markedly enhanced Shiga toxin production at all L-serine concentrations tested (Fig. 2b). Similar data were obtained with the nine other strains listed in Table 1 (data not shown).
It has been proposed that AI preparations contain enterobactin and its breakdown products, the so-called enterobactin complex formed by enterobactin-producing strains under conditions of iron limitation (3, 13, 15). In the iron-restricted environment of serum-SAPI medium, the presence of siderophores would clearly explain enhanced growth and concomitant toxin expression, as reported by Lyte and coworkers (8, 11). It is unlikely, however, that the iron supply alone is responsible for the properties of AI reported here, first because the medium used is sufficiently iron-rich that an additional iron source is not required for growth, and second because the toxin Stx2, which is produced by many of the EHEC strains tested here, is not iron regulated (18). High-performance liquid chromatography analysis of the AI preparations used in this study indicated that they do indeed contain components of the enterobactin complex (data not shown), but additional compounds are also present, and further detailed analysis is ongoing to determine their nature and activity.
In terms of the application of our work, Table 1 illustrates the effectiveness of NPMM supplemented with AI compared with a commercially available culture medium for EHEC diagnosis. Partially purified AI is very simple and cheap to prepare. We therefore propose that AI-supplemented NPMM be used routinely to enhance the sensitivity of Shiga toxin detection in food and environmental samples. This is especially relevant when speed of detection is an important consideration. Any enhancement in toxin production will shorten the time required for unequivocal detection, which may be particularly valuable if a diagnostic result can be obtained in a single working day rather than after an overnight enrichment step.
ACKNOWLEDGMENTS
We appreciate the skillful assistance of Christel Rackwitz, Ilse Riencker, and Annette Weller. We are very grateful to Mark Lyte for useful comments on an early version of the manuscript.
REFERENCES
Alverdy, J., C. Holbrook, F. Rocha, L. Seiden, R. L. Wu, M. Musch, E. Chang, D. Ohman, and S. Suh. 2000. Gut-derived sepsis occurs when the right pathogen with the right virulence genes meets the right host: evidence for in vivo virulence expression in Pseudomonas aeruginosa. Ann. Surg. 232:480-489.
Belay, T., and G. Sonnenfeld. 2002. Differential effects of catecholamines on in vitro growth of pathogenic bacteria. Life Sci. 71:447-456.
Burton, C. L., S. R. Chhabra, S. Swift, T. J. Baldwin, H. Withers, S. J. Hill, and P. Williams. 2002. The growth response of Escherichia coli to neurotransmitters and related catecholamine drugs requires a functional enterobactin biosynthesis and uptake system. Infect. Immun. 70:5913-5923.
Freestone, P. P. E., R. D. Haigh, P. H. Williams, and M. Lyte. 1999. Stimulation of bacterial growth by heat-stable norepinephrine-induced autoinducers. FEMS Microbiol. Lett. 172:53-60.
Freestone, P. P. E., M. Lyte, C. P. Neal, A. F. Maggs, R. D. Haigh, and P. H. Williams. 2000. The mammalian neuroendocrine hormone norepinephrine supplies iron for bacterial growth in the presence of transferrin or lactoferrin. J. Bacteriol. 182:6091-6098.
Freestone, P. P. E., P. H. Williams, R. D. Haigh, A. F. Maggs, C. P. Neal, and M. Lyte. 2002. Growth stimulation of intestinal commensal Escherichia coli by catecholamines: a possible contributory factor in trauma-induced sepsis. Shock 18:465-470.
Kinney, K. S., C. E. Austin, D. S. Morton, and G. Sonnenfeld. 2000. Norepinephrine as a growth stimulating factor in bacteria—mechanistic studies. Life Sci. 67:3075-3085.
Lyte, M., B. P. Arulanandam, and C. D. Frank. 1996. Production of Shiga-like toxins by Escherichia coli O157:H7 can be influenced by the neuroendocrine hormone norepinephrine. J. Lab. Clin. Med. 128:392-398.
Lyte, M., A. K. Erickson, B. P. Arulanandam, C. D. Frank, M. A. Crawford, and D. H. Francis. 1997. Norepinephrine-induced expression of the K99 pilus adhesin of enterotoxigenic Escherichia coli. Biochem. Biophys. Res. Commun. 232:682-686.
Lyte, M., and S. Ernst. 1992. Catecholamine induced growth of gram negative bacteria. Life Sci. 50:203-212.
Lyte, M., C. D. Frank, and B. T. Green. 1996. Production of an autoinducer of growth by norepinephrine cultured Escherichia coli O157:H7. FEMS Microbiol. Lett. 139:155-159.
Neal, C. P., P. P. Freestone, A. F. Maggs, R. D. Haigh, P. H. Williams, and M. Lyte. 2001. Catecholamine inotropes as growth factors for Staphylococcus epidermidis and other coagulase-negative staphylococci. FEMS Microbiol. Lett. 194:163-169.
O'Brien, I. G., and F. Gibson. 1970. The structure of enterochelin and related 2,3-dihydroxy-N-benzoylserine conjugates from Escherichia coli. Biochim. Biophys. Acta 215:393-402.
Reissbrodt, R., W. Beer, R. Müller, and H. Claus. 1995. Characterization of casein peptones by HPLC. Profiles and microbiological parameters. Acta Biotechnol. 15:223-232.
Reissbrodt, R., A. Rassbach, B. Burghardt, I. Riencker, H. Mietke, J. Schleif, H. Tschpe, M. Lyte, and P. H. Williams. 2004. Assessment of a new selective chromogenic Bacillus cereus group plating medium, and use of enterobacterial autoinducer of growth for cultural identification of Bacillus species. J. Clin. Microbiol. 42:3795-3798.
Reissbrodt, R., I. Riencker, J. M. Romanova, P. P. E. Freestone, R. D. Haigh, M. Lyte, H. Tschpe, and P. H. Williams. 2002. Resuscitation of Salmonella enterica serovar Typhimurium and enterohemorrhagic E. coli from the viable but nonculturable state by heat-stable enterobacterial autoinducer. Appl. Environ. Microbiol. 68:4788-4794.
Roberts, A., J. B. Matthews, S. S. Socransky, P. P. E. Freestone, P. H. Williams, and I. L. C. Chapple. 2002. Stress and the periodontal diseases: effects of catecholamines on the growth of periodontal bacteria in vitro. Oral Microbiol. Immunol. 17:296-303.
Sung, L. M., M. P. Jackson, A. D. O'Brien, and R. K. Holmes. 1990. Transcription of the Shiga-like toxin type II and Shiga-like toxin type II variant operons of Escherichia coli. J. Bacteriol. 172:6386-6395.(W. Voigt, A. Fruth, H. Ts)
Department of Genetics, University of Leicester, Leicester, United Kingdom
ABSTRACT
The addition of the enterobacterial autoinducer of growth to nutrient-poor minimal medium markedly accelerated the exponential growth rates of strains of enterohemorrhagic Escherichia coli but had little or no effect on maximal cell densities in stationary phase. Growth in the presence of the autoinducer resulted in an approximately twofold enhancement in Shiga toxin production.
TEXT
Mammalian signaling molecules such as the catecholamine neuroendocrine hormone L-norepinephrine (NE) can stimulate the growth of a number of pathogenic bacteria and, in some cases, the expression of virulence properties (1, 2, 6, 7, 9, 10, 12, 17). In addition, transient exposure of Escherichia coli to NE in a serum-containing minimal medium induced the production of a heat-stable autoinducer of growth (AI), which elicited responses similar to those with NE, including induction of more AI (11). Similar effects were later observed for a range of enterobacterial species (4). In the case of E. coli, the mechanism of growth stimulation by NE includes facilitation of iron acquisition from the mammalian iron-binding proteins transferrin and lactoferrin (5). However, the activity of AI is not confined to bacterial growth under the iron-limited conditions of a serum-containing medium. We recently demonstrated resuscitation by enterobacterial AI of highly stressed populations of pathogenic isolates of enterohemorrhagic E. coli (EHEC) and Salmonella enterica serovar Typhimurium in iron-containing nutrient-rich media (16). AI also enhanced the sensitivity and speed of enrichment of Bacillus cereus and Bacillus anthracis spores in both serum-supplemented medium and buffered peptone water (15). The present paper provides another example of iron-independent AI activity, with important practical implications for the detection of Shiga toxin-producing EHEC strains.
A new nutrient-poor minimal medium (NPMM) formulation that avoids the use of antibiotics and bile salts as selective supplements has been developed for enrichment of EHEC from clinical, food, and environmental samples (W. Voigt, A. Fruth, H.-H. Sonneborn, H. Tschpe, and R. Reissbrodt, Abstr. VTEC 2003 Meet., p. 149, 2003). This medium comprises 100 mM K2HPO4 (pH 7.2 ± 0.1) containing trace elements (40 mg/liter of MgSO4 · 7H2O, 4 mg/liter of ferric ammonium citrate, 6 mg/liter of MnSO4 · 4H2O), vitamins (0.2 mg/liter [each] of pyridoxal-HCl, thiamine, and nicotinic acid amide), and pancreatic casein peptone (0.2% [wt/vol]) as a source of amino acids (14). During developmental work, it was observed that aspartate, glutamate, and serine were significantly depleted during the growth of EHEC strains, as measured by capillary electrophoresis of samples taken before and after growth. Therefore, the medium was additionally supplemented with L-aspartic acid (0.08% [wt/vol]), L-glutamic acid (0.12% [wt/vol]), and L-serine at various concentrations, as described below. The medium was supplemented as required with 50 μM NE (Sigma Chemical Co.) or with 2% (vol/vol) AI prepared as previously described (4, 8, 16). Briefly, serum-SAPI medium (2.77 mM glucose, 6.25 mM NH4NO3, 1.84 mM KH2PO4, 3.35 mM KCl, 1.01 mM MgSO4, and 30% [vol/vol] adult bovine serum, pH 7.5) containing 50 μM NE was inoculated at approximately 100 to 1,000 CFU/ml with the producing strain and incubated overnight at 37°C in a humidified 5% CO2 atmosphere. Bacteria were pelleted by centrifugation (6,000 x g for 15 min), and the culture supernatants were filter sterilized and stored at –20°C until required. Sterile preparations were serially diluted in fresh sterile SAPI medium, and samples of each dilution were added at 2% (vol/vol) to serum-SAPI medium inoculated with 100 to 1,000 CFU/ml of an indicator strain. The dilution that promoted bacterial growth after overnight incubation at 37°C to an optical density at 620 nm (OD620) of 0.4, which represents 108 CFU/ml, was used as a supplement to NPMM, as described below. For the experiments reported here, we prepared AI from cultures of a strain that we had previously reported to be Yersinia ruckeri (16) but subsequently confirmed (on the basis of the Bactid-System [CDC, Atlanta, Ga.]) to be E. coli. It should be noted, however, that virtually any strain of E. coli or any other enterobacterial species that produces enterobactin can be used both for production of AI and as an indicator strain for AI activity.
The EHEC strains analyzed in this study were from the culture collection of the Robert Koch Institute, Wernigerode, Germany. Bacteria from overnight nutrient agar cultures were inoculated into NPMM at approximately 2 x 102 CFU/ml and incubated at 37°C with horizontal shaking at 150 rpm. Culture growth (OD620) was monitored in a Bioscreen C apparatus (Thermolabsystems, Helsinki, Finland) (16), and Shiga toxin production was determined with a commercially available enzyme-linked immunosorbent assay (ELISA) kit (r-Biopharm, Darmstadt, Germany) and reported as the OD450. Two-tailed Student's t test was used to determine the differences in toxin production between culture conditions; differences were considered statistically significant when P values were <0.05.
Figure 1 illustrates a Bioscreen C analysis of the growth of E. coli strain 97-10085 in the presence or absence of AI. Supplementation with AI significantly accelerated exponential growth, such that between 7 and 10 h, the doubling time of the culture in the presence of AI was consistently approximately half that in the absence of AI. After prolonged incubation, however, OD620 levels in AI-free medium and AI-supplemented medium were similar. This is in contrast with the situation in serum-SAPI medium (11), in which growth in the absence of AI is limited to between 100- and 1,000-fold, primarily (but perhaps not exclusively) because iron availability is restricted by the presence of serum transferrin. Indeed, AI was so designated because of its ability to induce bacterial growth under the specific conditions of serum-SAPI medium (11). Under the relatively iron-rich conditions used in this study, however, the activity of AI is seen as an enhancement of the growth rate rather than the final cell density.
Table 1 shows the effects of supplementation of NPMM with NE or AI on toxin production by EHEC strains of various serogroups in NPMM containing 0.2% L-serine. There was considerable variation in toxin levels among the strains tested; OD450 levels ranging from <0.4 to >4 were observed consistently over at least three independent experiments with each strain. Supplementation with NE enhanced Shiga toxin levels significantly in 5 of the 10 strains, while supplementation with AI enhanced toxin levels significantly in all 10 strains. This was perhaps due to strain variability in the production of AI in response to NE. Maximal growth levels (OD620) of cultures with or without AI supplementation were not significantly different (data not shown).
To determine if the effect of AI was enhanced by incipient nutrient starvation, strain 97-10085 was inoculated into NPMM supplemented with lower concentrations of L-serine and assayed for growth and Shiga toxin production (Fig. 2). The OD620 levels reached after 24 h of incubation in medium supplemented with 0.05 or 0.1% (wt/vol) L-serine were significantly lower (P = 0.05) than those reached in medium supplemented with 0.2% (wt/vol) L-serine (Fig. 2a). The addition of AI resulted in a slight but not statistically significant reduction (P > 0.05) in the maximum OD620 level achieved after 24 h of incubation at each concentration of L-serine (Fig. 2a). Analysis of toxin production in the same cultures indicated that adding increasing concentrations of L-serine resulted in only small increases in Shiga toxin production but that supplementation with 2% (vol/vol) AI markedly enhanced Shiga toxin production at all L-serine concentrations tested (Fig. 2b). Similar data were obtained with the nine other strains listed in Table 1 (data not shown).
It has been proposed that AI preparations contain enterobactin and its breakdown products, the so-called enterobactin complex formed by enterobactin-producing strains under conditions of iron limitation (3, 13, 15). In the iron-restricted environment of serum-SAPI medium, the presence of siderophores would clearly explain enhanced growth and concomitant toxin expression, as reported by Lyte and coworkers (8, 11). It is unlikely, however, that the iron supply alone is responsible for the properties of AI reported here, first because the medium used is sufficiently iron-rich that an additional iron source is not required for growth, and second because the toxin Stx2, which is produced by many of the EHEC strains tested here, is not iron regulated (18). High-performance liquid chromatography analysis of the AI preparations used in this study indicated that they do indeed contain components of the enterobactin complex (data not shown), but additional compounds are also present, and further detailed analysis is ongoing to determine their nature and activity.
In terms of the application of our work, Table 1 illustrates the effectiveness of NPMM supplemented with AI compared with a commercially available culture medium for EHEC diagnosis. Partially purified AI is very simple and cheap to prepare. We therefore propose that AI-supplemented NPMM be used routinely to enhance the sensitivity of Shiga toxin detection in food and environmental samples. This is especially relevant when speed of detection is an important consideration. Any enhancement in toxin production will shorten the time required for unequivocal detection, which may be particularly valuable if a diagnostic result can be obtained in a single working day rather than after an overnight enrichment step.
ACKNOWLEDGMENTS
We appreciate the skillful assistance of Christel Rackwitz, Ilse Riencker, and Annette Weller. We are very grateful to Mark Lyte for useful comments on an early version of the manuscript.
REFERENCES
Alverdy, J., C. Holbrook, F. Rocha, L. Seiden, R. L. Wu, M. Musch, E. Chang, D. Ohman, and S. Suh. 2000. Gut-derived sepsis occurs when the right pathogen with the right virulence genes meets the right host: evidence for in vivo virulence expression in Pseudomonas aeruginosa. Ann. Surg. 232:480-489.
Belay, T., and G. Sonnenfeld. 2002. Differential effects of catecholamines on in vitro growth of pathogenic bacteria. Life Sci. 71:447-456.
Burton, C. L., S. R. Chhabra, S. Swift, T. J. Baldwin, H. Withers, S. J. Hill, and P. Williams. 2002. The growth response of Escherichia coli to neurotransmitters and related catecholamine drugs requires a functional enterobactin biosynthesis and uptake system. Infect. Immun. 70:5913-5923.
Freestone, P. P. E., R. D. Haigh, P. H. Williams, and M. Lyte. 1999. Stimulation of bacterial growth by heat-stable norepinephrine-induced autoinducers. FEMS Microbiol. Lett. 172:53-60.
Freestone, P. P. E., M. Lyte, C. P. Neal, A. F. Maggs, R. D. Haigh, and P. H. Williams. 2000. The mammalian neuroendocrine hormone norepinephrine supplies iron for bacterial growth in the presence of transferrin or lactoferrin. J. Bacteriol. 182:6091-6098.
Freestone, P. P. E., P. H. Williams, R. D. Haigh, A. F. Maggs, C. P. Neal, and M. Lyte. 2002. Growth stimulation of intestinal commensal Escherichia coli by catecholamines: a possible contributory factor in trauma-induced sepsis. Shock 18:465-470.
Kinney, K. S., C. E. Austin, D. S. Morton, and G. Sonnenfeld. 2000. Norepinephrine as a growth stimulating factor in bacteria—mechanistic studies. Life Sci. 67:3075-3085.
Lyte, M., B. P. Arulanandam, and C. D. Frank. 1996. Production of Shiga-like toxins by Escherichia coli O157:H7 can be influenced by the neuroendocrine hormone norepinephrine. J. Lab. Clin. Med. 128:392-398.
Lyte, M., A. K. Erickson, B. P. Arulanandam, C. D. Frank, M. A. Crawford, and D. H. Francis. 1997. Norepinephrine-induced expression of the K99 pilus adhesin of enterotoxigenic Escherichia coli. Biochem. Biophys. Res. Commun. 232:682-686.
Lyte, M., and S. Ernst. 1992. Catecholamine induced growth of gram negative bacteria. Life Sci. 50:203-212.
Lyte, M., C. D. Frank, and B. T. Green. 1996. Production of an autoinducer of growth by norepinephrine cultured Escherichia coli O157:H7. FEMS Microbiol. Lett. 139:155-159.
Neal, C. P., P. P. Freestone, A. F. Maggs, R. D. Haigh, P. H. Williams, and M. Lyte. 2001. Catecholamine inotropes as growth factors for Staphylococcus epidermidis and other coagulase-negative staphylococci. FEMS Microbiol. Lett. 194:163-169.
O'Brien, I. G., and F. Gibson. 1970. The structure of enterochelin and related 2,3-dihydroxy-N-benzoylserine conjugates from Escherichia coli. Biochim. Biophys. Acta 215:393-402.
Reissbrodt, R., W. Beer, R. Müller, and H. Claus. 1995. Characterization of casein peptones by HPLC. Profiles and microbiological parameters. Acta Biotechnol. 15:223-232.
Reissbrodt, R., A. Rassbach, B. Burghardt, I. Riencker, H. Mietke, J. Schleif, H. Tschpe, M. Lyte, and P. H. Williams. 2004. Assessment of a new selective chromogenic Bacillus cereus group plating medium, and use of enterobacterial autoinducer of growth for cultural identification of Bacillus species. J. Clin. Microbiol. 42:3795-3798.
Reissbrodt, R., I. Riencker, J. M. Romanova, P. P. E. Freestone, R. D. Haigh, M. Lyte, H. Tschpe, and P. H. Williams. 2002. Resuscitation of Salmonella enterica serovar Typhimurium and enterohemorrhagic E. coli from the viable but nonculturable state by heat-stable enterobacterial autoinducer. Appl. Environ. Microbiol. 68:4788-4794.
Roberts, A., J. B. Matthews, S. S. Socransky, P. P. E. Freestone, P. H. Williams, and I. L. C. Chapple. 2002. Stress and the periodontal diseases: effects of catecholamines on the growth of periodontal bacteria in vitro. Oral Microbiol. Immunol. 17:296-303.
Sung, L. M., M. P. Jackson, A. D. O'Brien, and R. K. Holmes. 1990. Transcription of the Shiga-like toxin type II and Shiga-like toxin type II variant operons of Escherichia coli. J. Bacteriol. 172:6386-6395.(W. Voigt, A. Fruth, H. Ts)