Production by Aeromonas of common enterobacterial antigen and its possible taxonomic significance

Draft Genome Sequence of a Tetracycline-Resistant Plesiomonas shigelloides Strain Isolated from Aquaculture-Reared Tilapia

We hereby present the 3.7-Mb draft genome sequence of Plesiomonas shigelloides strain FM82, isolated from a tilapia (Oreochromis niloticus) reared in a fish farm in Rio de Janeiro, Brazil. P. shigelloides strain FM82 carries antimicrobial resistance, biofilm, and CRISPR-related genes.

Plesiomonas shigelloides Revisited

After many years in the family Vibrionaceae, the genus Plesiomonas, represented by a single species, P. shigelloides, currently resides in the family Enterobacteriaceae, although its most appropriate phylogenetic position may yet to be determined. Common environmental reservoirs for plesiomonads include freshwater ecosystems and estuaries and inhabitants of these aquatic environs. Long suspected as being an etiologic agent of bacterial gastroenteritis, convincing evidence supporting this conclusion has accumulated over the past 2 decades in the form of a series of foodborne outbreaks solely or partially attributable to P. shigelloides. The prevalence of P. shigelloides enteritis varies considerably, with higher rates reported from Southeast Asia and Africa and lower numbers from North America and Europe. Reasons for these differences may include hygiene conditions, dietary habits, regional occupations, or other unknown factors. Other human illnesses caused by P. shigelloides include septicemia and central nervous system disease, eye infections, and a variety of miscellaneous ailments. For years, recognizable virulence factors potentially associated with P. shigelloides pathogenicity were lacking; however, several good candidates now have been reported, including a cytotoxic hemolysin, iron acquisition systems, and lipopolysaccharide. While P. shigelloides is easy to identify biochemically, it is often overlooked in stool samples due to its smaller colony size or relatively low prevalence in gastrointestinal samples. However, one FDA-approved PCR-based culture-independent diagnostic test system to detect multiple enteropathogens (FilmArray) includes P. shigelloides on its panel. Plesiomonads produce β-lactamases but are typically susceptible to many first-line antimicrobial agents, including quinolones and carbapenems.

Rapid determination of members of the family Enterobacteriaceae in drinking water by an immunological assay using a monoclonal antibody against enterobacterial common antigen

An immunological method for the detection of members of the family Enterobacteriaceae in drinking water was developed. The method was based on a sandwich enzyme-linked immunosorbent assay (ELISA) with monoclonal antibody immunoglobulin G2a 898 against enterobacterial common antigen. The enterobacterial common antigen sandwich ELISA combined with selective preenrichment culture could be performed in only 24 h. Six hundred sixty-eight water samples from a variety of German public water supplies were screened to verify the effectiveness of the new method. Ninety-eight percent of the results obtained by the immunological method could be confirmed by conventional microbiological methods. The immunological method proved to be considerably faster and more specific and sensitive than the standard method specified by the German drinking water regulations.

Qualitative and quantitative determination of enterobacterial common antigen (ECA) with monoclonal antibodies: expression of ECA by two Actinobacillus species

The presence and quantity of the enterobacterial common antigen (ECA) in several species belonging to the family Enterobacteriaceae as well as to other gram-negative families were determined by a solid-phase enzyme-linked immunosorbent assay system and Western blotting by using mouse monoclonal antibodies specific for ECA. Except for Erwinia chrysanthemi, previously known to be an exception, all species known or presumed to belong to Enterobacteriaceae produced ECA (89 of 90 species). Most species not belonging to Enterobacteriaceae did not produce ECA (25 of 28 species), with one already known (Plesiomonas shigelloides) and two hitherto unknown (Actinobacillus equuli and Actinobacillus suis) exceptions. Interestingly, all strains of P. shigelloides produced ECA, regardless of the presence of the Shigella sonnei cross-reacting O antigen. Quantitation of the amount of ECA in members of the family Enterobacteriaceae revealed a remarkable heterogeneity among genera and species as well as within one species. We conclude that the rapid, sensitive, and reliable determination of ECA is a useful aid in taxonomic classification and may help to characterize the relatedness of the family Enterobacteriaceae to other families. However, a quantitative analysis of ECA appears to be without value for these purposes.

Chemical characterization of enterobacterial common antigen isolated from Plesiomonas shigelloides ATCC 14029

Serologically characterized samples of enterobacterial common antigen (ECA) from Plesiomonas shigelloides, Salmonella montevideo and Shigella sonnei were investigated by chemical methods including methylation and NMR techniques. All showed the same sugar composition and contained a lipid moiety with palmitic acid as main fatty acid and with a phosphodiester group. Additional enzymatic studies, reported in the preceding paper, provided evidence that the lipid moiety is an L-glycerophosphatidyl residue attached via a phosphodiester linkage to C-1 of GlcNAc as the reducing end of the ECA sugar chain. ECA of P. shigelloides showed the best-resolved 13C-NMR spectra, especially after the removal of non-stoichiometric O-acetyl groups at C-6 of GlcNAc of the ECA repeating unit and of the lipid moiety by mild acid hydrolysis (0.01 M HCl, 100 degrees C, 10 min). Subsequent 13C-NMR studies were therefore carried out with the mild-acid-treated ECA of P. shigelloides which allowed a tentative assignment of all resonances of the ECA repeating unit. 13C-NMR spectra of Salmonella and Shigella ECA were essentially the same as those obtained with Plesiomonas ECA. The same trisaccharide repeating unit was encountered as demonstrated previously in the cyclic form of ECA isolated from S. sonnei by Dell et al. [Carbohydr. Res. 133, 95-104 (1984)]. Methylation analysis, however, afforded small amounts of terminal GlcNAc thus proving, in combination with the demonstration of the attached lipid moiety, an acyclic nature of ECA from P. shigelloides and from the two enterobacterial species. The question of whether the cyclic form co-exists in S. sonnei phase I and possibly in other enterobacterial species or, whether it had been formed during extraction as an artifact, has not yet been answered. The way in which ECA was isolated in our studies would preclude the presence of a non-amphiphilic (cyclic) polysaccharide. The finding that the sugar chain of ECA is attached to an L-glycerophosphatidyl residue is in full corroboration with serological, enzymatic and gel electrophoretic studies shown in the preceding paper and with the character of ECA as a surface antigen being anchored by hydrophobic interactions in the outer membrane of Enterobacteriaceae and P. shigelloides.

Comparison of enterobacterial common antigen from different species by serological techniques

Enterobacterial common antigen (ECA) was isolated from a number of selected species (including Salmonella montevideo, Shigella sonnei and Plesiomonas shigelloides) using the extraction method described by Männel and Mayer [Eur. J. Biochem. 86, 361-370 (1978)]. ECA of all these species behaved identically in enzyme-linked immunosorption assay (ELISA) and in its inhibition using monoclonal anti-ECA antibodies. Immunoblotting showed a ladder-like pattern of at least 20 bands for all preparations tested. ECA modified at its lipid moiety (e.g. by phospholipases A2 and D or by mild acid hydrolysis) lost its coating capacity leaving, however, the serological reactivity as detected by inhibition assays intact. In contrast, reduction of the carboxylic groups of 2-acetamido-2-deoxy-D-mannopyranosyluronic acid destroyed the serological reactivity. Deacylated ECA was also not detectable in immunoblotting. Chemical reacylation restored the reactivity of deacylated ECA in ELISA and in immunoblot and thus proved the essential function of fatty acids for the physicochemical properties of the molecule. 2-Acetamido-2-deoxy-D-glucopyranose was identified as the reducing end of the ECA sugar chain after splitting off the lipid moiety by phospholipase D.

Demonstration of enterobacterial common antigen by bacterial agglutination

Potent antisera against the enterobacterial common antigen (ECA) agglutinate R bacteria of the Enterobacteriaceae family that possess unimpaired R-core structures of the Escherichia coli R1 or E. coli R4 core type. In these strains, known to be ECA immunogenic, ECA is most probably linked to the lipopolysaccharide R core. R mutants of other core types (e.g., Salmonella Ra, E. coli R2 or R3) or R mutants with incomplete core structures of the E. coli R1 type, as well as an rfaL mutant deficient in the O-translocase system, agglutinate to a much lesser extent or not at all. All the later mutants are nonimmunogenic; they possess the ECA in a free form, not linked to the R core. None of the S forms tested from many different enterobacterial genera was found to be agglutinable with the ECA antiserum. The dynamics of the ECA agglutinin formation in rabbits parallels the ECA hemagglutinin formation, indicating that the same antibody class might be involved in bacterial agglutination and hemagglutination.

Enterobacterial common antigen

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Strain-related differences in immunosuppressive effects of Enterobacteriaceae and their lipopolysaccharides on production in rabbits of antibody to enterobacterial common antigen

Certain polysaccharides have been shown to inhibit the antibody response of rabbits to the common enterobacterial antigen (CA). The present investigation revealed that striking differences exist in the immunosuppressive effects of enteric bacteria and their lipolysaccharides (lps), depending upon CA production by the strains. Mixtures of immunogenic strains (Escherichia coli F2378 [R4], E. coli F470 [R1], or Shigella boydii F3140 [R]) and non-immunogenic CA-producing strains, such as E. coli O1, E. coli O113, Salmonella montevideo, and S. minnesota, as well as the R mutants E. coli F614 (R1), E. coli F757 (R1), and S. typhimurium his 642 (Ra), failed to elicit CA antibodies. In contrast, mixtures of the immunogen and CA-negative strains S. typhimurium his 386 (Ra) and S. minnesota P595 (Re) or R555 (Ra) yielded antibodies in titers similar to those elicited by the immunogen alone. Further, LPS of CA-positive but not of CA-negative strains exerted this immunosuppressive effect. Quantitative studies revealed that LPS of S. minnesota in amounts of 100 mug/ml was strongly immunosuppressive, in amounts of 20 mug/ml slightly effective, and in amounts of 4 mug/ml ineffective. It is postulated that hitherto unknown differences exist, either in composition or in configuration, between LPS obtained from different microorganisms to account for the strain-related differences in immunosuppressive effects and, further, that the immunosuppressive LPS interacts with immunogenic CA.

Isolation and characterization of the antigen of Neisseria gonorrhoeae

The beta antigen of Neisseria gonorrhoeae has been isolated from the alkaline-extracted gonococcal endotoxin by ion exchange, molecular sieve, and powder block electrophoretic chromatography. Hemagglutination inhibition studies indicate that the preparation is essentially free of common enterobacterial and gonococcal alpha antigen. Analysis of the isolated antigen by immunodiffusion and acrylamide gel electrophoresis reveal only one detectable component. Chemical studies indicate that the antigen is an acidic glycoprotein composed primarily of four major amino acids: alanine, glutamic acid, glycine, and proline. The antigen has an s(20,w) of 8.55, and spectral analysis in the ultraviolet and visible range reveals a single absorption peak at 217 nm.

Immunogenicity of the common enterobacterial antigen produced by smooth and rough strains

Enterobacteriaceae share a common antigen (CA). This antigen exists as a powerful immunogen, when produced by Escherichia coli O14, and as a minimally effective immunogen, when present in cultures of most other smooth strains. The present study was directed toward the assessment of immunogenicity of this antigen produced by various rough mutants and their parent strains as well as that of viable and nonviable bacterial suspensions. Rabbits were immunized intravenously, and the passive hemagglutination test was used for the quantitation of CA antibodies. The following results were obtained. (i) Immunization of rabbits with viable or heat-killed (1 hr, 100 C) suspensions of smooth parent strains resulted in only slight or insignificant antibody production. Of seven additional smooth strains of Enterobacteriaceae tested, none induced CA antibodies upon immunization with killed (1 hr, 100 C) suspensions, and only two engendered antibodies in moderate titers when viable suspensions were used, possibly due to the presence of undetected R mutant cells. (ii) In contrast, administration of viable suspensions of the corresponding mutant strains, regardless of core types, including E. coli R1, R2, R3, and Salmonella Ra types, caused a significant antibody response. (iii) The immunogenicity of R mutants differed strikingly, inasmuch as mutants with the R1 core [E. coli O8(-):K27(-)(R) and Shigella boydii type 3(-)(R)] engendered CA antibodies when heated suspensions were administered, in contrast to heated suspensions of mutants with the R2, R3, and Ra cores. (iv) Viability per se is not an abolute requirement for immunogenicity of R2 mutants, since CA antibodies were engendered by suspensions killed at 60 C or by merthiolate or formaldehyde. (v) Ethanol fractionation revealed that immunogenic CA of the R1 mutant is ethanol-insoluble and that of the parental smooth strain is ethanol-soluble; thus, CA of R1 mutants resembles that of E. coli O14 in both immunogenicity and ethanol insolubility.