Survival of orally administered E. coli K 12 in alimentary tract of man

Determining glycosyltransferase functional order via lethality due to accumulated O-antigen intermediates, exemplified with Shigella flexneri O-antigen biosynthesis

The O antigen (OAg) polysaccharide is one of the most diverse surface molecules of Gram-negative bacterial pathogens. The structural classification of OAg, based on serological typing and sequence analysis, is important in epidemiology and the surveillance of outbreaks of bacterial infections. Despite the diverse chemical structures of OAg repeating units (RUs), the genetic basis of RU assembly remains poorly understood and represents a major limitation in assigning gene functions in polysaccharide biosynthesis. Here, we describe a genetic approach to interrogate the functional order of glycosyltransferases (GTs). Using Shigella flexneri as a model, we established an initial glycosyltransferase (IT)-controlled system, which allows functional order allocation of the subsequent GT in a 2-fold manner as follows: (i) first, by reporting the growth defects caused by the sequestration of UndP through disruption of late GTs and (ii) second, by comparing the molecular sizes of stalled OAg intermediates when each putative GT is disrupted. Using this approach, we demonstrate that for RfbF and RfbG, the GT involved in the assembly of S. flexneri backbone OAg RU, RfbG, is responsible for both the committed step of OAg synthesis and the third transferase for the second L-Rha. We also show that RfbF functions as the last GT to complete the S. flexneri OAg RU backbone. We propose that this simple and effective genetic approach can be also extended to define the functional order of enzymatic synthesis of other diverse polysaccharides produced both by Gram-negative and Gram-positive bacteria.IMPORTANCEThe genetic basis of enzymatic assembly of structurally diverse O antigen (OAg) repeating units (RUs) in Gram-negative pathogens is poorly understood, representing a major limitation in our understanding of gene functions for the synthesis of bacterial polysaccharides. We present a simple genetic approach to confidently assign glycosyltransferase (GT) functions and the order in which they act during assembly of the OAg RU. We employed this approach to determine the functional order of GTs involved in Shigella flexneri OAg assembly. This approach can be generally applied in interrogating GT functions encoded by other bacterial polysaccharides to advance our understanding of diverse gene functions in the biosynthesis of polysaccharides, key knowledge in advancing biosynthetic polysaccharide production.

Safety and efficacy of a feed additive consisting of l-threonine (produced with Escherichia coliCGMCC 7.455) for all animal species (Kempex Holland B.V.)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of the feed additive consisting of l-threonine produced by fermentation with Escherichia coli CGMCC 7.455 when used as a nutritional additive in feed and water for drinking for all animal species and categories. The production strain is genetically modified. None of the introduced genetic modifications raised a safety concern. Viable cells of the production strain and its DNA were not detected in the final additive. Therefore, the final product does not give raise to any safety concern regarding the genetic modification of the production strain. The use of l-threonine (≥ 98.5%) produced with E. coli CGMCC 7.455 to supplement feed is safe for the target species. The Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) has concerns on the safety of the simultaneous oral administration of l-threonine via water for drinking and feed due to possible amino acid imbalances and hygienic reasons. The use of l-threonine produced with E. coli CGMCC 7.455 in animal nutrition raises no safety concerns to consumers of animal products and to the environment. In the absence of data, the FEEDAP Panel cannot conclude on the potential of the additive to be irritant to skin or eyes, or on its potential to be a dermal sensitiser. The endotoxin activity in the additive does not pose a risk for the user via inhalation. The additive l-threonine is regarded as an effective source of the amino acid l-threonine for all non-ruminant species. In order to be as efficacious in ruminants as in non-ruminants, it should be protected from ruminal degradation.

Safety and efficacy of a feed additive consisting of l-tryptophan (produced with Escherichia coliCGMCC 7.460) for all animal species (Kempex Holland B.V.)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of the feed additive consisting of l-tryptophan produced by fermentation with Escherichia coli CGMCC 7.460 when used as a nutritional additive in feed and water for drinking for all animal species and categories. The production strain is not genetically modified. Viable cells of the production strain were not detected in the final additive. The additive does not give rise to any safety concern regarding the production strain. The use of l-tryptophan (≥ 98%) produced with E. coli CGMCC 7.460 to supplement feed is safe for non-ruminant species. There may be a risk for an increased production of toxic metabolites when unprotected tryptophan is used in ruminants. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) has concerns on the safety of the simultaneous oral administration of l-tryptophan via water for drinking and feed due to possible amino acid imbalances and hygienic reasons. The use of l-tryptophan produced with E. coli CGMCC 7.460 in animal nutrition raises no safety concerns to consumers of animal products and to the environment. In the absence of data, the FEEDAP Panel cannot conclude on the potential of the additive to be irritant to skin or eyes, or on its potential to be a dermal sensitiser. The endotoxin activity of the additive in combination with the high dusting potential may represent a risk of exposure by inhalation to endotoxins for users. The additive l-tryptophan is regarded as an effective source of the amino acid l-tryptophan for all non-ruminant species. To be as efficacious in ruminants as in non-ruminants, it should be protected from ruminal degradation.

Genetic mutation in Escherichia coli genome during adaptation to the murine intestine is optimized for the host diet

Mammalian gut microbes colonize the intestinal tract of their host and adapt to establish a microbial ecosystem. The host diet changes the nutrient profile of the intestine and has a high impact on microbiota composition. Genetic mutations in Escherichia coli, a prevalent species in the human gut, allow for adaptation to the mammalian intestine, as reported in previous studies. However, the extent of colonization fitness in the intestine elevated by genetic mutation and the effects of diet change on these mutations in E. coli are still poorly known. Here, we show that notable mutations in sugar metabolism-related genes (gatC, araC, and malI) were detected in the E. coli K-12 genome just 2 weeks after colonization in the germ-free mouse intestine. In addition to elevated fitness by deletion of gatC, as previously reported, deletion of araC and malI also elevated E. coli fitness in the murine intestine in a host diet-dependent manner. In vitro cultures of medium containing nutrients abundant in the intestine (e.g., galactose, N-acetylglucosamine, and asparagine) also showed increased E. coli fitness after deletion of the genes-of-interest associated with their metabolism. Furthermore, the host diet was found to influence the developmental trajectory of gene mutations in E. coli. Taken together, we suggest that genetic mutations in E. coli are selected in response to the intestinal environment, which facilitates efficient utilization of nutrients abundant in the intestine under laboratory conditions. Our study offers some insight into the possible adaptation mechanisms of gut microbes.IMPORTANCEThe gut microbiota is closely associated with human health and is greatly impacted by the host diet. Bacteria such as Escherichia coli live in the gut all throughout the life of a human host and adapt to the intestinal environment. Adaptive mutations in E. coli are reported to enhance fitness in the mammalian intestine, but to what extent is still poorly known. It is also unknown whether the host diet affects what genes are mutated and to what extent fitness is affected. This study suggests that genetic mutations in the E. coli K-12 strain are selected in response to the intestinal environment and facilitate efficient utilization of abundant nutrients in the germ-free mouse intestine. Our study provides a better understanding of these intestinal adaptation mechanisms of gut microbes.

O antigen biogenesis sensitises Escherichia coli K-12 to bile salts, providing a plausible explanation for its evolutionary loss

Escherichia coli K-12 is a model organism for bacteriology and has served as a workhorse for molecular biology and biochemistry for over a century since its first isolation in 1922. However, Escherichia coli K-12 strains are phenotypically devoid of an O antigen (OAg) since early reports in the scientific literature. Recent studies have reported the presence of independent mutations that abolish OAg repeating-unit (RU) biogenesis in E. coli K-12 strains from the same original source, suggesting unknown evolutionary forces have selected for inactivation of OAg biogenesis during the early propagation of K-12. Here, we show for the first time that restoration of OAg in E. coli K-12 strain MG1655 synergistically sensitises bacteria to vancomycin with bile salts (VBS). Suppressor mutants surviving lethal doses of VBS primarily contained disruptions in OAg biogenesis. We present data supporting a model where the transient presence and accumulation of lipid-linked OAg intermediates in the periplasmic leaflet of the inner membrane interfere with peptidoglycan sacculus biosynthesis, causing growth defects that are synergistically enhanced by bile salts. Lastly, we demonstrate that continuous bile salt exposure of OAg-producing MG1655 in the laboratory, can recreate a scenario where OAg disruption is selected for as an evolutionary fitness benefit. Our work thus provides a plausible explanation for the long-held mystery of the selective pressure that may have led to the loss of OAg biogenesis in E. coli K-12; this opens new avenues for exploring long-standing questions on the intricate network coordinating the synthesis of different cell envelope components in Gram-negative bacteria.

Oral Immunization with Escherichia coli Nissle 1917 Expressing SARS-CoV-2 Spike Protein Induces Mucosal and Systemic Antibody Responses in Mice

As of October 2022, the COVID-19 pandemic continues to pose a major public health conundrum, with increased rates of symptomatic infections in vaccinated individuals. An ideal vaccine candidate for the prevention of outbreaks should be rapidly scalable, easy to administer, and able to elicit a potent mucosal immunity. Towards this aim, we proposed an engineered Escherichia coli (E. coli) Nissle 1917 (EcN) strain with SARS-CoV-2 spike protein (SP)-coding plasmid, which was able to expose SP on its cellular surface by a hybridization with the adhesin involved in diffuse adherence 1 (AIDA1). In this study, we presented the effectiveness of a 16-week intragastrically administered, engineered EcN in producing specific systemic and mucosal immunoglobulins against SARS-CoV-2 SP in mice. We observed a time-dependent increase in anti-SARS-CoV-2 SP IgG antibodies in the sera at week 4, with a titre that more than doubled by week 12 and a stable circulating titre by week 16 (+309% and +325% vs. control; both p < 0.001). A parallel rise in mucosal IgA antibody titre in stools, measured via intestinal and bronchoalveolar lavage fluids of the treated mice, reached a plateau by week 12 and until the end of the immunization protocol (+300, +47, and +150%, at week 16; all p < 0.001 vs. controls). If confirmed in animal models of infection, our data indicated that the engineered EcN may be a potential candidate as an oral vaccine against COVID-19. It is safe, inexpensive, and, most importantly, able to stimulate the production of both systemic and mucosal anti-SARS-CoV-2 spike-protein antibodies.

Laboratory strains of Escherichia coli K-12: things are seldom what they seem

Escherichia coli K-12 was originally isolated 100 years ago and since then it has become an invaluable model organism and a cornerstone of molecular biology research. However, despite its pedigree, since its initial isolation E. coli K-12 has been repeatedly cultured, passaged and mutagenized, resulting in an organism that carries many genetic changes. To understand more about this important model organism, we have sequenced the genomes of two ancestral K-12 strains, WG1 and EMG2, considered to be the progenitors of many key laboratory strains. Our analysis confirms that these strains still carry genetic elements such as bacteriophage lambda (λ) and the F plasmid, but also indicates that they have undergone extensive laboratory-based evolution. Thus, scrutinizing the genomes of ancestral E. coli K-12 strains leads us to examine whether E. coli K-12 is a sufficiently robust model organism for 21st century microbiology.

Bps polysaccharide of Bordetella pertussis resists antimicrobial peptides by functioning as a dual surface shield and decoy and converts Escherichia coli into a respiratory pathogen

Infections and disease caused by the obligate human pathogen Bordetella pertussis (Bp) are increasing, despite widespread vaccinations. The current acellular pertussis vaccines remain ineffective against nasopharyngeal colonization, carriage, and transmission. In this work, we tested the hypothesis that Bordetella polysaccharide (Bps), a member of the poly-β-1,6-N-acetyl-D-glucosamine (PNAG/PGA) family of polysaccharides promotes respiratory tract colonization of Bp by resisting killing by antimicrobial peptides (AMPs). Genetic deletion of the bpsA-D locus, as well as treatment with the specific glycoside hydrolase Dispersin B, increased susceptibility to AMP-mediated killing. Bps was found to be both cell surface-associated and released during laboratory growth and mouse infections. Addition of bacterial supernatants containing Bps and purified Bps increased B. pertussis resistance to AMPs. By utilizing ELISA, immunoblot and flow cytometry assays, we show that Bps functions as a dual surface shield and decoy. Co-inoculation of C57BL/6J mice with a Bps-proficient strain enhanced respiratory tract survival of the Bps-deficient strain. In combination, the presented results highlight the critical role of Bps as a central driver of B. pertussis pathogenesis. Heterologous production of Bps in a non-pathogenic E. coli K12 strain increased AMP resistance in vitro, and augmented bacterial survival and pathology in the mouse respiratory tract. These studies can serve as a foundation for other PNAG/PGA polysaccharides and for the development of an effective Bp vaccine that includes Bps.

Safety and efficacy of a feed additive consisting of l-lysine sulfate produced by Escherichia coli CGMCC 7.398 for all animal species (Kempex Holland B.V.)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of l-lysine sulfate produced by the genetically modified strain Escherichia coli CGMCC 7.398 as a nutritional feed additive for all animal species. Neither the production strain nor its recombinant DNA were detected in the final product. The additive does not pose any safety concerns associated with the production strain. The additive under assessment is considered safe for the target species. When using l-lysine sulfate, the background sulfur/sulfate content in the compound feed should be taken into account. l-lysine sulfate produced by E. coli CGMCC 7.398 is safe for the consumers and for the environment. In the absence of data, the FEEDAP Panel cannot conclude on the potential of the additive under assessment to be irritant to skin or eyes, or on its potential to be a dermal sensitiser. The endotoxin activity of the additive represents a risk by inhalation for users handling the additive. The additive l-lysine sulfate is considered as an efficacious source of the essential amino acid l-lysine for non-ruminant animal species. For the supplemental l-lysine to be as efficacious in ruminants as it is in non-ruminant species, this would require protection against degradation in the rumen.

Safety and efficacy of a feed additive consisting of l-methionine produced by the combined activities of Corynebacterium glutamicum KCCM 80245 and Escherichia coli KCCM 80246 for all animal species (CJ Europe GmbH)

Following a request from the European Commission, the FEEDAP Panel was asked to deliver a scientific opinion on the safety and efficacy of l-methionine ≥ 98.5% or ≥ 90% produced by the combined activities of Corynebacterium glutamicum KCCM 80245 and Escherichia coli KCCM 80246) as nutritional additive for all animal species. The two production strains are genetically modified. l-Methionine is intended to be used in feed or water for drinking for all animal species. Neither viable cells nor recombinant DNA of the production strains were detected in the final products. The additive does not pose any safety concern associated with the genetic modification of the production strains. The use of both products of l-methionine produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 in supplementing feed to compensate for l-methionine deficiency in feedingstuffs is safe for the target species. The FEEDAP Panel has concerns about the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed. The use of both products of l-methionine produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 in animal nutrition is considered safe for the consumers and for the environment. The additive, in either product, is not an irritant to skin/eyes and not a dermal sensitiser and shows no toxicity by inhalation. Considering the respiratory exposure to endotoxins, l-methionine ≥ 90% is a risk for the user. Both products of the additive produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 are considered as an efficacious source of the essential amino acid l-methionine for non-ruminant animal species. For the supplemental l-methionine to be as efficacious in ruminants as in non-ruminant species, it would require protection against degradation in the rumen.

Safety and efficacy of a feed additive consisting of l-valine produced by Escherichia coli CCTCC M2020321 for all animal species (Kempex Holland BV)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of l-valine as a nutritional additive for all animal species. The production strain and its DNA were not detected in the final additive. Therefore, the final product does not give raise to any safety concern with regard to the genetic modification of the production strain. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concludes that l-valine produced using Escherichia coli CCTCC M2020321 is safe when supplemented in appropriate amounts to the diet according to the nutritional needs of the target species. The FEEDAP Panel has concerns on the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed. The use of l-valine produced using E. coli CCTCC M2020321 in animal nutrition is considered safe for the consumers and for the environment. The FEEDAP Panel cannot conclude on the potential of l-valine produced using E. coli CCTCC M2020321 to be toxic by inhalation, irritant to the skin or eyes, or a dermal sensitiser due to the lack of data. The endotoxin activity of the additive does not represent a hazard for users handling the additive when exposed by inhalation. The additive l-valine produced by fermentation using E. coli CCTCC M2020321 is regarded as an efficacious source of the essential amino acid l-valine for non-ruminant nutrition. For the supplemental l-valine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen.

Safety and efficacy of a feed additive consisting of disodium 5'-guanylate produced with Corynebacterium stationisKCCM 10530 and Escherichia coli K-12 KFCC 11067 for all animal species (CJ Europe GmbH)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of disodium 5'-guanylate produced by fermentation with Corynebacterium stationis KCCM 10530 and Escherichia coli K-12 KFCC 11067 when used as a sensory additive (flavouring compound) in feed and water for drinking for all animal species. The additive does not raise safety concerns under the proposed conditions of use for the target species, consumers the users and the environment. The Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) expressed reservations on the use of the additive in water for drinking due to concerns on its impact on hygienic conditions of the water. The Panel concluded that the additive is efficacious to contribute to the flavour of feed.

Safety and efficacy of the feed additive consisting of l-tryptophan produced by Escherichia coli KCCM 80210 for all animal species (Daesang Europe BV)

Following a request from the European Commission, the Panel on Additives and Products or substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of the feed additive consisting of l-tryptophan produced by fermentation with Escherichia coli KCCM 80210 when used as a nutritional additive in feed for all animal species and categories. The production strain E. coli KCCM 80210 is safe for the production of l-tryptophan and it was not detected in the final product. The Panel notes that two out of five batches of the additive do not comply with the minimum specification of 98% l-tryptophan on a dry matter basis proposed by the applicant. The use of l-tryptophan (≥ 98%) produced by E. coli KCCM 80210 in supplementing feed to compensate for l-tryptophan deficiency in feedingstuffs is safe for non-ruminant target species. There may be a risk for an increased production of toxic metabolites when unprotected l-tryptophan is used in ruminants. The use of l-tryptophan produced by E. coli KCCM 80210 in animal nutrition raises no safety concerns to consumers of animal products and to the environment. The additive under assessment is considered a mild eye irritant. The endotoxin activity of the additive and its dusting potential indicate a risk by inhalation for the users. The additive is not a skin irritant and is not a skin sensitiser. The additive l-tryptophan is regarded as an effective source of the amino acid l-tryptophan for all non-ruminant species. In order to be as efficacious in ruminants as in non-ruminants, it should be protected from ruminal degradation.

Microbiota control of maternal behavior regulates early postnatal growth of offspring

Maternal behavior is necessary for optimal development and growth of offspring. The intestinal microbiota has emerged as a critical regulator of growth and development in the early postnatal period life. Here, we describe the identification of an intestinal Escherichia coli strain that is pathogenic to the maternal-offspring system during the early postnatal stage of life and results in growth stunting of the offspring. However, rather than having a direct pathogenic effect on the infant, we found that this particular E. coli strain was pathogenic to the dams by interfering with the maturation of maternal behavior. This resulted in malnourishment of the pups and impaired insulin-like growth factor 1 (IGF-1) signaling, leading to the consequential stunted growth. Our work provides a new understanding of how the microbiota regulates postnatal growth and an additional variable that must be considered when studying the regulation of maternal behavior.

Safety and efficacy of l-threonine produced using Escherichia coliCGMCC 13325 as a feed additive for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-threonine produced by fermentation when used as a nutritional additive in feed and water for drinking for all animal species and categories. The product under assessment is l-threonine produced using a genetically modified strain of E. coli CGMCC 13325. The Panel notes that three out of five batches of the additive do not comply with the minimum specification of 98.5% l-threonine on a dry matter basis proposed by the applicant. The production strain and its DNA were not detected in the final additive. Therefore, the final product does not give raise to any safety concern regarding the genetic modification of the production strain. The use of l-threonine produced using E. coli CGMCC 13325 in supplementing feed to compensate for threonine deficiency in feedingstuffs is safe for the target species. The FEEDAP Panel identified risks of nutritional imbalances and hygienic concerns for amino acids when administered simultaneously in feed and in water for drinking. The use of l-threonine produced by fermentation using E. coli CGMCC 13325 in animal nutrition is considered safe for the consumers and for the environment. There is a risk from the inhalation exposure to endotoxins for persons handling the additive. In the absence of data, the FEEDAP Panel cannot conclude on the potential of l-threonine produced using E. coli CGMCC 13325 to be a skin or eye irritant or a skin sensitiser. The additive under assessment is regarded as an effective source of the amino acid l-threonine for all non-ruminant species. For the supplemental l-threonine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen.

Safety and Efficacy of l-histidine monohydrochloride monohydrate produced by fermentation using Escherichia coli KCCM 80212 as a feed additive for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-histidine monohydrochloride (HCl) monohydrate produced by fermentation using Escherichia coli KCCM 80212 when used as a nutritional additive in feed for all animal species. The production strain is genetically modified. The production strain and its recombinant DNA were not detected in the final product. l-Histidine HCl monohydrate manufactured by fermentation using E. coli KCCM 80212 does not give rise to any safety concern regarding the genetic modification. The use of l-histidine HCl monohydrate produced by fermentation using E. coli KCCM 80212 is safe for the target species when used as a nutritional additive to supplement the diet in appropriate amounts to cover the requirements, depending on the species, the physiological state of the animal, the performance level, the environmental conditions, the background amino acid composition of the unsupplemented diet and the status of some essential trace elements such as copper and zinc. l-Histidine HCl monohydrate produced using E. coli KCCM 80212 supplemented at levels appropriate for the requirements of the target species is considered safe for the consumer. l-Histidine HCl monohydrate produced by E. coli KCCM 80212 is a skin sensitiser. There is a risk for persons handling the additive from the exposure to endotoxins by inhalation. The additive under assessment is not irritant to skin or eyes. The use of l-histidine HCl monohydrate produced using E. coli KCCM 80212 in animal nutrition is not expected to represent a risk to the environment. l-Histidine HCl monohydrate is considered an efficacious source of the essential amino acid l-histidine for non-ruminant animal species. For the supplemental l-histidine to be as efficacious in ruminants as in non-ruminant species, it would require protection against degradation in the rumen.

Safety of l-threonine produced by fermentation with Escherichia coli CGMCC 11473 as a feed additive for all animal species

The l‐threonine under assessment is produced by fermentation with a genetically modified strain of Escherichia coli and it is intended to be used as a nutritional additive for all animal species. In 2017 the Panel on Additives and products or Substances used in Animal Feed (FEEDAP) of EFSA issued an opinion on the safety and efficacy of the product. In that assessment, the Panel could not conclude on the safety of the additive for the target species, consumers and the environment due to the lack of data regarding the characterisation of the production strain and the resulting product. The applicant provided additional data on the identity of the production strain, the genetic modification, the susceptibility to antibiotics and the absence of cells and recombinant DNA of the production strain in the final product. The recipient strain is safe and the genetic modification does not raise concerns. Moreover, viable cells or DNA of the production strain were not detected in the final product. With this new information the FEEDAP Panel concluded that l‐threonine produced by E. coli CGMCC 11473 is safe for the all animal species, the consumers and the environment. The FEEDAP Panel could not conclude on the potential of the additive to be irritant to skin and eyes or on the skin sensitisation potential. It was concluded that there is a risk of exposure to endotoxins by inhalation for persons handling the additive.

Safety and efficacy of l-tryptophan produced by fermentation using Escherichia coli CGMCC 7.267 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-tryptophan produced by fermentation with a genetically modified strain of Escherichia coli CGMCC 7.267 when used as a nutritional additive in feed and water for drinking for all animal species and categories. The production strain E. coli CGMCC 7.267 is safe for the production of l-tryptophan. No viable cells or DNA of the production strain were detected in the additive under assessment. The use of l-tryptophan produced using E. coli CGMCC 7.267 in supplementing feed to compensate for tryptophan deficiency in feedingstuffs is safe for non-ruminant target species. However, excess doses would create amino acid imbalances with negative consequences on animal performance. The use of unprotected l-tryptophan in feed poses safety concerns for ruminants. The use of l-tryptophan produced by fermentation with E. coli CGMCC 7.267 in animal nutrition is considered safe for the consumers and for the environment. The endotoxin activity in the product and its dusting potential indicate an inhalation risk for the user. In the absence of data, the FEEDAP Panel cannot conclude on the potential of the additive to be irritant to skin and eyes or to be a skin sensitiser. The additive l-tryptophan produced using E. coli CGMCC 7.267 is regarded as an effective source of the amino acid l-tryptophan. In order to be as efficacious in ruminants as in non-ruminants, it should be protected from ruminal degradation.

Safety and efficacy of l-tryptophan produced by fermentation with Escherichia coli KCCM 80135 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l‐tryptophan produced by fermentation using Escherichia coli KCCM 80135 when used as a nutritional additive in feed and water for drinking for all animal species. The production strain and its recombinant DNA were not detected in the additive. l‐Tryptophan produced by fermentation with E. coli KCCM 80135 does not raise any safety concern with regard to the genetic modification of the production strain. The use of l‐tryptophan produced using E. coli KCCM 80135 in supplementing feed to compensate for tryptophan deficiency in feedingstuffs is safe for non‐ruminant target species. Using unprotected forms of tryptophan in ruminants can be a risk. The use of l‐tryptophan produced by fermentation using E. coli KCCM 80135 in animal nutrition presents no safety concerns to consumers of animal products. l‐Tryptophan produced by E. coli KCCM 80135 is not toxic by inhalation. The additive is not an irritant to skin and eyes, and it is not a skin sensitiser. The additive under assessment is considered safe for the environment. It is regarded as an effective source of the amino acid l‐tryptophan for all non‐ruminant species. If the additive l‐tryptophan is intended for use in ruminants, it should be protected from ruminal degradation.

Safety and efficacy of l-tryptophan produced by fermentation with Escherichia coli CGMCC 7.248 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-tryptophan produced by fermentation with a genetically modified strain of Escherichia coli CGMCC 7.248 when used as a nutritional additive in feed and water for drinking for all animal species and categories. The production strain E. coli CGMCC 7.248 and its recombinant DNA were not detected in the final product. The product l-tryptophan, manufactured by fermentation with E. coli CGMCC 7.248, does not give rise to any safety concern with regard to the genetic modification of the production strain. l-Tryptophan produced by E. coli CGMCC 7.248 is safe for non-ruminant target species. The use of unprotected l-tryptophan in ruminant feed should be avoided. l-Tryptophan produced by fermentation by E. coli CGMCC 7.248 is safe for the consumer. The level of endotoxins present in the product and its dusting potential indicate an inhalation risk for the user. l-Tryptophan produced by E. coli CGMCC 7.248 is not a skin or eye irritant but it is a dermal sensitiser. The use of l-tryptophan produced by E. coli CGMCC 7.248 in animal nutrition does not pose a risk to the environment. The product under assessment is regarded as an effective source of the amino acid l-tryptophan for all non-ruminant species. For the supplemental l-tryptophan to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen.

Safety and efficacy of l-threonine produced by fermentation using Escherichia coli CGMCC 7.232 for all animal species

The product subject of this assessment is l‐threonine produced by fermentation with a genetically modified strain of Escherichia coli (CGMCC 7.232). It is intended to be used in feed and water for drinking for all animal species and categories. The production strain and its recombinant DNA were not detected in the additive. The product l‐threonine, manufactured by fermentation with E. coli CGMCC 7.232, does not raise any safety concern with regard to the genetic modification of the production strain. l‐Threonine produced using E. coli CGMCC 7.232 is considered safe for the target species. The FEEDAP Panel has concerns regarding the safety of the simultaneous administration of l‐threonine via water for drinking and feed. l‐Threonine produced using E. coli CGMCC 7.232 is safe for the consumer. In absence of data, the FEEDAP Panel cannot conclude on the potential of the additive to be irritant to skin and eyes or to be a skin sensitiser. There is a risk from the inhalation exposure to endotoxins for persons handling the additive. l‐Threonine produced using E. coli CGMCC 7.232 is safe for the environment. The product under assessment is considered an efficacious source of the amino acid l‐threonine for all animal species. For l‐threonine to be as efficacious in ruminants as in non‐ruminant species, it requires protection against degradation in the rumen.

Effects of Growth Surface Topography on Bacterial Signaling in Coculture Biofilms

Bacteria form interface-associated communities called biofilms, often comprising multiple species. Biofilms can be detrimental or beneficial in medical, industrial, and technological settings, and their stability and function are determined by interspecies communication via specific chemical signaling or metabolite exchange. The deterministic control of biofilm development, behavior, and properties remains an unmet challenge, limiting our ability to inhibit the formation of detrimental biofilms in biomedical settings and promote the growth of beneficial biofilms in biotechnology applications. Here, we describe the development of growth surfaces that promote the growth of commensal Escherichia coli instead of the opportunistic pathogen Pseudomonas aeruginosa. Periodically patterned growth surfaces induced robust morphological changes in surface-associated E. coli biofilms and influenced the antibiotic susceptibilities of E. coli and P. aeruginosa biofilms. Changes in the biofilm architecture resulted in the accumulation of a metabolite, indole, which controls the competition dynamics between the two species. Our results show that the surface on which a biofilm grows has important implications for species colonization, growth, and persistence when exposed to antibiotics.

Colonization resistance against genetically modified Escherichia coli K12 (W3110) strains is abrogated following broad-spectrum antibiotic treatment and acute ileitis

Escherichia coli K12 (EcK12) is commonly used for gene technology purposes and regarded as a security strain due to its inability to adhere to epithelial cells. The conventional intestinal microbiota composition is critical for physiological colonization resistance against most bacterial species including pathogens. We were therefore interested whether intestinal colonization by a genetically modified EcK12 (W3110) strain carrying a chloramphenicol resistance cassette was facilitated following broad-spectrum antibiotic treatment eradicating the intestinal microbiota or induction of small intestinal inflammation accompanied by distinct microbiota shifts. Whereas conventional C57BL/6 and BALB/c mice had virtually expelled the EcK12 (W3110) strain within the first 3 days upon peroral infection, EcK12 (W3110) could establish within the small and large intestines of gnotobiotic mice generated by quintuple antibiotic treatment. Gnotobiotic mice perorally infected with EcK12 (W3110) plus fecal transplant from conventional donors harbored lower intestinal EcK12 (W3110) loads compared to animals challenged with EcK12 (W3110) alone. Furthermore, EcK12 (W3110) infection of conventional mice after but not before induction of ileitis resulted in stable colonization of ileum and colon by EcK12 (W3110). Taken together, broad-spectrum antibiotic treatment and intestinal inflammation compromise colonization resistance and thus facilitate colonization of the intestinal tract with genetically modified EcK12 security strains.

Impact of metal ion homeostasis of genetically modified Escherichia coli Nissle 1917 and K12 (W3110) strains on colonization properties in the murine intestinal tract

Metal ions are integral parts of pro- as well as eukaryotic cell homeostasis. Escherichia coli proved a valuable in vitro model organism to elucidate essential mechanisms involved in uptake, storage, and export of metal ions. Given that E. coli Nissle 1917 is able to overcome murine colonization resistance, we generated several E. coli Nissle 1917 mutants with defects in zinc, iron, copper, nickel, manganese homeostasis and performed a comprehensive survey of the impact of metal ion transport and homeostasis for E. coli colonization capacities within the murine intestinal tract. Seven days following peroral infection of conventional mice with E. coli Nissle 1917 strains exhibiting defined defects in zinc or iron uptake, the respective mutant and parental strains could be cultured at comparable, but low levels from the colonic lumen. We next reassociated gnotobiotic mice in which the microbiota responsible for colonization resistance was abrogated by broad-spectrum antibiotics with six different E. coli K12 (W3110) mutants. Seven days following peroral challenge, each mutant and parental strain stably colonized duodenum, ileum, and colon at comparable levels. Taken together, defects in zinc, iron, copper, nickel, and manganese homeostasis do not compromise colonization capacities of E. coli in the murine intestinal tract.

Pro-inflammatory potential of Escherichia coli strains K12 and Nissle 1917 in a murine model of acute ileitis

Non-pathogenic Escherichia coli (Ec) strains K12 (EcK12) and Nissle 1917 (EcN) are used for gene technology and probiotic treatment of intestinal inflammation, respectively. We investigated intestinal colonization and potential pro-inflammatory properties of EcK12, EcN, and commensal E. coli (EcCo) strains in Toxoplasma (T.) gondii-induced acute ileitis. Whereas gnotobiotic animals generated by quintuple antibiotic treatment were protected from ileitis, mice replenished with conventional microbiota suffered from small intestinal necrosis 7 days post-T. gondii infection (p.i.). Irrespective of the Ec strain, recolonized mice revealed mild to moderate histopathological changes in their ileal mucosa. Upon stable recolonization with EcK12, EcN, or EcCo, development of inflammation was accompanied by pro-inflammatory responses at day 7 p.i., including increased ileal T lymphocyte and apoptotic cell numbers compared to T. gondii-infected gnotobiotic controls. Strikingly, either Ec strain was capable to translocate to extra-intestinal locations, such as MLN, spleen, and liver. Taken together, Ec strains used in gene technology and probiotic treatment are able to exert inflammatory responses in a murine model of small intestinal inflammation. In conclusion, the therapeutic use of Ec strains in patients with broad-spectrum antibiotic treatment and/or intestinal inflammation should be considered with caution.

Laboratory adapted Escherichia coli K-12 becomes a pathogen of Caenorhabditis elegans upon restoration of O antigen biosynthesis

Escherichia coli has been the leading model organism for many decades. It is a fundamental player in modern biology, facilitating the molecular biology revolution of the last century. The acceptance of E. coli as model organism is predicated primarily on the study of one E. coli lineage; E. coli K-12. However, the antecedents of today's laboratory strains have undergone extensive mutagenesis to create genetically tractable offspring but which resulted in loss of several genetic traits such as O antigen expression. Here we have repaired the wbbL locus, restoring the ability of E. coli K-12 strain MG1655 to express the O antigen. We demonstrate that O antigen production results in drastic alterations of many phenotypes and the density of the O antigen is critical for the observed phenotypes. Importantly, O antigen production enables laboratory strains of E. coli to enter the gut of the Caenorhabditis elegans worm and to kill C. elegans at rates similar to pathogenic bacterial species. We demonstrate C. elegans killing is a feature of other commensal E. coli. We show killing is associated with bacterial resistance to mechanical shear and persistence in the C. elegans gut. These results suggest C. elegans is not an effective model of human-pathogenic E. coli infectious disease.

Complete genome sequence and comparative analysis of the wild-type commensal Escherichia coli strain SE11 isolated from a healthy adult

We sequenced and analyzed the genome of a commensal Escherichia coli (E. coli) strain SE11 (O152:H28) recently isolated from feces of a healthy adult and classified into E. coli phylogenetic group B1. SE11 harbored a 4.8 Mb chromosome encoding 4679 protein-coding genes and six plasmids encoding 323 protein-coding genes. None of the SE11 genes had sequence similarity to known genes encoding phage- and plasmid-borne virulence factors found in pathogenic E. coli strains. The comparative genome analysis with the laboratory strain K-12 MG1655 identified 62 poorly conserved genes between these two non-pathogenic strains and 1186 genes absent in MG1655. These genes in SE11 were mostly encoded in large insertion regions on the chromosome or in the plasmids, and were notably abundant in genes of fimbriae and autotransporters, which are cell surface appendages that largely contribute to the adherence ability of bacteria to host cells and bacterial conjugation. These data suggest that SE11 may have evolved to acquire and accumulate the functions advantageous for stable colonization of intestinal cells, and that the adhesion-associated functions are important for the commensality of E. coli in human gut habitat.

Laboratory strains of Escherichia coli: model citizens or deceitful delinquents growing old disgracefully?

Escherichia coli stands unchallenged as biology's premier model organism. However, we propose, equipped with insights from the post-genomic era, a contrary view: that microbiology's chief idol has feet of clay. E. coli laboratory strains, particularly E. coli K-12, are far from model citizens, but instead degenerate and deceitful delinquents growing old disgracefully in our scientific institutions. E. coli K-12 is neither archetype nor ancestor. In addition, it has a far from optimal provenance for a model organism, with strong grounds for believing that current versions of the strain are quite distinct from any original wild-type free-living ancestor. In addition, it is usually studied under conditions far removed from its natural habitats and in ignorance of the selective pressures that have shaped its evolution. Fortunately, a flood of information from high-throughput genome sequencing, together with a new 'eco-evo' view of this model organism, promises to help put K-12 better into context.

Barriers to coliphage infection of commensal intestinal flora of laboratory mice

BACKGROUND

Growth characteristics of coliphage viruses indicate that they are adapted to live with their Eschericia coli hosts in the intestinal tract. However, coliphage experimentally introduced by ingestion persist only transiently if at all in the gut of humans and other animals. This study attempted to identify the barriers to long term establishment of exogenous coliphage in the gastrointestinal (GI) tracts of laboratory mice. Intestinal contents were screened for the presence of coliphage and host bacteria, and strains of E. coli bacteria from different segments of the GI tract were tested for susceptibility to six common laboratory coliphages.

RESULTS

Contrary to expectations, coliphage were not evident in the GI tracts of laboratory mice, although they were occasionally detected in feces. Commensal flora showed extreme variability within groups of mice despite identical handling and diet. Less than 20% of 48 mice tested carried E. coli in their gut, and of 22 commensal E. coli strains isolated and tested, 59% were completely resistant to infection by lambda, M13, P1, T4, T7, and PhiX174 coliphage. Lysogeny could not be demonstrated in the commensal strains as mitomycin C failed to induce detectable phage. Pre-existing immunity to phages was not evident as sera and fecal washes did not contain significant antibody titers to six laboratory phage types.

CONCLUSION

Lack of sufficient susceptible host bacteria seems to be the most likely barrier to establishment of new coliphage infections in the mouse gut.

Biodegradation of aromatic compounds by Escherichia coli

Although Escherichia coli has long been recognized as the best-understood living organism, little was known about its abilities to use aromatic compounds as sole carbon and energy sources. This review gives an extensive overview of the current knowledge of the catabolism of aromatic compounds by E. coli. After giving a general overview of the aromatic compounds that E. coli strains encounter and mineralize in the different habitats that they colonize, we provide an up-to-date status report on the genes and proteins involved in the catabolism of such compounds, namely, several aromatic acids (phenylacetic acid, 3- and 4-hydroxyphenylacetic acid, phenylpropionic acid, 3-hydroxyphenylpropionic acid, and 3-hydroxycinnamic acid) and amines (phenylethylamine, tyramine, and dopamine). Other enzymatic activities acting on aromatic compounds in E. coli are also reviewed and evaluated. The review also reflects the present impact of genomic research and how the analysis of the whole E. coli genome reveals novel aromatic catabolic functions. Moreover, evolutionary considerations derived from sequence comparisons between the aromatic catabolic clusters of E. coli and homologous clusters from an increasing number of bacteria are also discussed. The recent progress in the understanding of the fundamentals that govern the degradation of aromatic compounds in E. coli makes this bacterium a very useful model system to decipher biochemical, genetic, evolutionary, and ecological aspects of the catabolism of such compounds. In the last part of the review, we discuss strategies and concepts to metabolically engineer E. coli to suit specific needs for biodegradation and biotransformation of aromatics and we provide several examples based on selected studies. Finally, conclusions derived from this review may serve as a lead for future research and applications.

The Escherichia coli K-12 gntP gene allows E. coli F-18 to occupy a distinct nutritional niche in the streptomycin-treated mouse large intestine

Escherichia coli F-18 is a human fecal isolate that makes type 1 fimbriae, encoded by the fim gene cluster, and is an excellent colonizer of the streptomycin-treated mouse intestine. E. coli F-18 fimA::tet, lacking type 1 fimbriae, was constructed by bacteriophage P1 transduction of the fim region of the E. coli K-12 strain ORN151, containing the tetracycline resistance gene from Tn10 inserted in the fimA gene, into E. coli F-18. E. coli F-18 fimA::tet was found to occupy a distinct niche in the streptomycin-treated mouse intestine when fed in small numbers (10(4) CFU) to mice, along with large numbers (10(10) CFU) of E. coli F-18, as defined by the ability of the E. coli F-18 fimA::tet strain to grow and colonize only 1 order of magnitude below E. coli F-18. The same effect was observed when mice already colonized with E. coli F-18 were fed small numbers of E. coli F-18 fimA::tet. Experiments which show that the E. coli K-12 gene responsible for this effect is not fim::tet but gntP, which maps immediately downstream of the fim gene cluster, are presented. gntP encodes a high-affinity gluconate permease, suggesting that the distinct niche in the mouse large intestine is defined by the presence of gluconate. The data presented here support the idea that small numbers of an ingested microorganism can colonize the intestine as long as it can utilize an available nutrient better than any of the other resident species can.

Rapid and accurate identification of Escherichia coli K-12 strains

A specific PCR for the identification of K-12 strains, based on the genetic structure of the O-antigen gene cluster (rfb) of Escherichia coli K-12, is described. The assay clearly differentiates E. coli K-12-derived strains from other E. coli strains used in the laboratory or isolated from human and animal clinical specimens, from food, or from environmental samples. Moreover, lineages of K-12 strains can be distinguished with a second PCR based on the same gene cluster. The method presents a useful tool in identifying K-12 for monitoring strains which are used as biologically safe vehicles in biotechnological research, development, and production processes.

Enteral feeding of premature infants with Lactobacillus GG

The objectives of this study were to determine whether or not the probiotic Lactobacillus GG can colonise the immature bowel of premature infants and if so, does colonisation result in a reduction of the size of the bowel reservoir of nosocomial pathogens such as enterobacteriaceae, enterococci, yeasts or staphylococci, and does colonisation with Lactobacillus GG have any effect on the clinical progress and outcome. Twenty preterm infants with a gestational age of 33 weeks or less who were resident on a neonatal unit were studied from the initiation of milk feeds until discharge. The infants were randomised to receive either milk feeds or milk feeds supplemented with Lactobacillus GG 10(8) colony forming units twice a day for two weeks. The clinical features of the two groups of infants were similar. Orally administered Lactobacillus GG was well tolerated and did colonise the bowel of premature infants. However, colonisation with Lactobacillus GG did not reduce the faecal reservoir of potential pathogens and there was no evidence that colonisation had any positive clinical benefit for this particular group of infants.

Escherichia coli K12 does not colonize the gastrointestinal tract of Fischer-344 rats

The colonizing potential of Escherichia coli K12 containing a vector coding for somidobove (bovine somatotropin) was determined. Treated male and female Fischer-344 rats were given a single oral gavage inoculum of sucrose with/without tetracycline (15 micrograms/ml). Untreated control animals received similar drinking water regimes. All animals survived until termination. There were no clinical signs of toxicity observed and no treatment-related effect upon body weight, food consumption, or efficiency of food utilization. Fresh fecal samples were collected from each rat every 24 h following inoculation and the population of the marked strain was quantitated until no bacterial colonies were observed for two consecutive days. While all inoculated rats were positive at 24 h, by 72 and 96 h all had become negative for the test (marked) strain, as were the corresponding control group throughout the test. The frozen stock of the marked strain used as the positive control demonstrated that the agar plates were selective for the test strain. Fourteen days following inoculation, all groups of rats were killed and the gastrointestinal tracts removed and treated to recover the marked strain. There was no evidence of the marked strain in the gastrointestinal tract of any from any group. Thus, the E. coli K12 host/vector system used in this experiment does not colonize the gastrointestinal tract of Fischer-344 rats.

Fate in sewage of a recombinant Escherichia coli K-12 strain used in the commercial production of bovine somatotropin

The fate of a derivative of Escherichia coli strain W3110G [pBGH1], a strain used for production of bovine somatotropin, was examined in semi-continuous activated sludge (SCAS) units. A nalidixic acid-resistant derivative of W3110G [pBGH1], strain LBB270 [pBGH1], was used to facilitate tracking. SCAS units (300 ml) containing municipal mixed liquor were operated on a daily cycle of 23 h aeration and 1 h setting followed by decanting of clear supernatant (175 ml) and refilling with fresh primary effluent. SCAS units were inoculated with two concentrations of E. coli LBB270 [pBGH1] and operated for 200 h. Viable levels of E. coli LBB270 [pBGH1] were measured daily in aerated mixed liquor and decanted supernatant. Viable counts in the mixed liquor decreased from 10,000- to 100,000-fold in less than 200 h. Losses of E. coli LBB270 [pBGH1] in decanted supernatants accounted for less than 2-fold of the total losses observed in the SCAS units. The E. coli LBB270 [pBGH1] was not evenly distributed in the mixed liquor, but became preferentially associated with the settleable floc. These results show that E. coli LBB270 [pBGH1] was unable to survive in municipal sludge even when inoculated at concentrations greater than, or comparable to, levels of indigenous microorganisms.

Absence of persistence and transfer of genetic material by recombinant Escherichia coli in conventional, antibiotic-treated mice

Strain BST-1 is a derivative of Escherichia coli K-12 that carries a plasmid designated pURA-4 and is the expression system used by The Upjohn Company in the production of recombinant bovine somatotropin (rbSt). This plasmid also encodes an ampicillin resistance gene. The plasmidless carrier strain, BST-1C, contains a gene for tetracycline resistance which is provided by the chromosomal insertion of the transposon Tn10. Therefore, BST-1 is resistant to ampicillin and tetracycline, while BST-1C is resistant only to tetracycline. The Food and Drug Administration requested that we conduct an environmental assessment study to monitor the 'persistence of the recombinant live K-12 E. coli organism compared to the host E. coli organism'. In addition, we were requested to monitor 'the potential transfer of genetic material from (our) recombinant organism to the indigenous microflora' of the mouse gastrointestinal (GI) tract. The differences in persistence were determined by monitoring shedding of BST-1 and BST-1C in the feces of conventionally reared, outbred mice inoculated with either of the two strains. Even with antibiotic selective pressure applied (tetracycline in the water), BST-1 did not persist as well as the non-plasmid carrying parental stain, BST-1C. In the gene transfer experiments, transfer of pURA-4 was monitored by the appearance of the ampicillin resistance marker and/or by hybridization assays for the rbSt gene in indigenous, mouse-colonizing E. coli strains which had been made streptomycin resistant. At the limit of detection, no transfer of pURA-4 was detected either in vitro or in vivo. These data support an interpretation that BST-1 does not present an environmental hazard as measured by colonization/persistence in the gut of conventionally reared mammals.

Fate in water of a recombinantEscherichia coli K-12 strain used in the commercial production of bovine somatotropin

The fate in water of Escherichia coli K-12 strain LBB269, both plasmid-free and carrying the recombinant plasmid pBGH1, was studied. E. coli K-12 strain LBB269 (pBGH1) is a nalidixic acid resistant derivative of W3110G (pBGH1), the microorganism used by Monsanto Company for the commercial production of bovine somatotropin. Water samples were obtained from the Missouri River and from the Monsanto Life Sciences Research Center aqueous waste basin. Strains LBB269 and LBB269 (pBGH1) were grown in fermentation vessel under bovine somatotropin (BST) production conditions, and inoculated into the water samples. The inoculated water samples were incubated at 26 degrees C, and the number of viable E. coli cells was determined as a function of time. In sterile water from both sources, the two strains remained at a constant level for at least 28 days; LBB269 (pBGH1) remained at a constant level in sterile water for at least 300 days. In non-sterile water from both sources, the two strains declined from an initial concentration of about 3.0 x 10(6) cells per ml to less than 10 cells per ml in 147 h. The study conditions did not adversely affect the populations of indigenous microorganisms. The selective loss of strains LBB269 and LBB269 (pBGH1) demonstrates that these E. coli strains do not survive in environmental sources of water. In addition, it was observed that the presence of pBGH1 had essentially no effect on the disappearance of strain LBB269 from either source of water.

Survival of Lactobacillus species (strain GG) in human gastrointestinal tract

A newly isolated strain of a species of Lactobacillus of human origin, designated GG (Lactobacillus GG), has been studied to determine its ability to survive in the human gastrointestinal tract. When fed to 76 volunteers as a frozen concentrate or as a fermented preparation in milk or whey, Lactobacillus GG was recovered in the feces of all subjects receiving the fermented milk or whey and in 86% receiving the frozen concentrate when a single fecal specimen was cultured. The organism was also present in the feces of subjects concurrently receiving ampicillin. After terminating feeding of the organism, Lactobacillus GG persisted in the feces of 87% of volunteers four days later and in 33% of subjects seven days later. Lactobacillus GG lowered fecal bacterial beta-glucuronidase activity by approximately 80% in volunteers given the organism for four weeks. These studies demonstrate that Lactobacillus GG can survive and temporarily colonize the human gastrointestinal tract and can affect the metabolic activity of the resident microflora.

Effect of broad-spectrum parenteral antibiotics on "colonization resistance" of intestinal microflora of humans

Studies with animals have shown that the normal intestinal microflora protects against colonization by new strains ("colonization resistance") and that this protective effect may be related to the anaerobic component of the microflora. However, colonization resistance has not been shown in humans. We administered cefoxitin, piperacillin, cefoperazone, and aztreonam intravenously to healthy subjects for 9 days and monitored the acquisition of new isolates in the fecal flora. Seven of sixteen antibiotic-treated subjects but none of four untreated controls became colonized by gram-negative bacilli. However, there was no correlation between colonization and the particular drug given or the extent of suppression of anaerobes or of any other component of the fecal microflora. Cefoxitin and piperacillin were associated with the greatest increases in the numbers of drug-resistant bacteria and in fecal beta-lactamase content. The results of this study support the concept that colonization resistance occurs in humans and is diminished by antibiotic administration but fail to support the hypothesis that resistance is related to the anaerobic microflora.

Relative colonizing abilities of human fecal and K 12 strains of Escherichia coli in the large intestines of streptomycin-treated mice

Male CD-1 mice, fed streptomycin in their drinking water, were used to study colonization of the mouse intestine by both fecal Escherichia coli strains isolated from healthy humans and Escherichia coli K12 strains which are routinely used as hosts for recombinant DNA. Prior to use in mice, all the strains were made resistant to streptomycin. Several facts emerged from these studies: (a) Strains isolated from different healthy humans colonized the mouse intestine with equal ability (approximately 10(8) cells/g feces), but may have colonized biochemically distinct sites. (b) K12 strains tested had, at most, one hundredth the colonizing ability of human fecal strains. (c) Rifampicin-resistant mutants of strains which contain one or no plasmids were poor colonizers relative to their parents. (d) Rifampicin-resistant mutants of strains which contain six or more plasmids retained the colonizing abilities of their parents. (e) Introduction of the F-amp or pJBK5 plasmid into HS-4, a human fecal strain which does not normally carry these plasmids, reduced its colonizing ability 1000-fold. (f) Strains used in this study colonized the mouse caecum and colon exclusively. The system presented here offers a simple, rapid test to determine whether a specific genetic alteration in a bacterium (e.g. antibiotic resistance) results in enhanced, reduced, or unchanged colonizing ability. Such a test might prove to be of value as a part of the clinical testing of antibiotics.

Relative colonizing abilities of human fecal and K 12 strains of Escherichia coli in the large intestines of streptomycin-treated mice

Male CD-1 mice, fed streptomycin in their drinking water, were used to study colonization of the mouse intestine by both fecal Escherichia coli strains isolated from healthy humans and Escherichia coli K12 strains which are routinely used as hosts for recombinant DNA. Prior to use in mice, all the strains were made resistant to streptomycin. Several facts emerged from these studies: (a) Strains isolated from different healthy humans colonized the mouse intestine with equal ability (approximately 10(8) cells/g feces), but may have colonized biochemically distinct sites. (b) K12 strains tested had, at most, one hundredth the colonizing ability of human fecal strains. (c) Rifampicin-resistant mutants of strains which contain one or no plasmids were poor colonizers relative to their parents. (d) Rifampicin-resistant mutants of strains which contain six or more plasmids retained the colonizing abilities of their parents. (e) Introduction of the F-amp or pJBK5 plasmid into HS-4, a human fecal strain which does not normally carry these plasmids, reduced its colonizing ability 1000-fold. (f) Strains used in this study colonized the mouse caecum and colon exclusively. The system presented here offers a simple, rapid test to determine whether a specific genetic alteration in a bacterium (e.g. antibiotic resistance) results in enhanced, reduced, or unchanged colonizing ability. Such a test might prove to be of value as a part of the clinical testing of antibiotics.