Evaluation of a new chromogenic Salmonella plating medium

Oxoid Salmonella Chromogenic Medium (OSCM) was tested for its sensitivity and specificity as well as its use in isolation of Salmonella from stool specimens and from porcine faeces. Colonies of Salmonella enterica ssp. I, II, IV, and VI-strains grow onto the ivory-coloured turbid plates purple to mauve, size 1-2 mm in diameter. Contrarily, E. coli, Enterobacter spp., Klebsiella spp., S. sonnei and the most of C. freundii strains appear as turquoise to blue colonies. Proteus spp., Providencia spp. and Morganella morganii grow light with brownish precipitation. S. dysenteriae, S. jlexneri and S. boydii are widely inhibited. Pseudomonads, Aeromonas spp., grampositive bacteria and C. albicans are completely inhibited. Its recovery rate and sensitivity in isolation of salmonella from stool specimens is comparable to Hektoen Enteric agar. OSCM was superior in isolation of Salmonella from porcine faeces compared with XLD

IroN, a Novel Outer Membrane Siderophore Receptor Characteristic of Salmonella enterica

Speciation in enterobacteria involved horizontal gene transfer. Therefore, analysis of genes acquired by horizontal transfer that are present in one species but not its close relatives is expected to give insights into how new bacterial species were formed. In this study we characterize iroN, a gene located downstream of the iroBC operon in the iroA locus of Salmonella enterica serotype Typhi. Like iroBC, the iroN gene is present in all phylogenetic lineages of S. enterica but is absent from closely related species such as Salmonella bongori or Escherichia coli. Comparison of the deduced amino acid sequence of iroN with other proteins suggested that this gene encodes an outer membrane siderophore receptor protein. Mutational analysis in S. enterica and expression in E. coli identified a 78-kDa outer membrane protein as the iroN gene product. When introduced into an E. coli fepA cir fiu aroB mutant on a cosmid, iroN mediated utilization of structurally related catecholate siderophores, including N-(2,3-dihydroxybenzoyl)-l-serine, myxochelin A, benzaldehyde-2,3-dihydroxybenzhydrazone, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-l-lysine, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-l-lysine amide, and enterochelin. These results suggest that the iroA locus functions in iron acquisition in S. enterica

Isolierung und Charakterisierung von Shigatoxin-produzierendenE. coli-Stämmen aus Stuhlproben: Ergebnisse einer Sentinel-Studie

Zur Erfassung der Häufigkeit und des Typenspektrums von Shigatoxin-produzierendenE. coli-Stämmen (EHEC-Bakterien) sowie zur Evaluierung der Praktikabilität, Spezifität und Sensitivität eines Verfahrens zur Diagnostik von EHEC wurde eine Sentinel-Studie im Einzugsbereich (1,1 Mio. Einwohner) eines privat niedergelassenen Untersuchungslabors durchgeführt. Von 3835 untersuchten Durchfallstühlen konnten in ca. 3 % EHEC-Bakterien nachgewiesen werden, die zu einem ungewöhnlich breiten Spektrum von Serovaren und Klonen mit sehr verschiedenen Virulenzfaktoren gehörten. So ließen sich nur ca. 10 % der isolierten EHEC-Stämme als O157 identifizieren, aber ebenso häufig auch O103, O26, O8 oder Ont-Stämme. Ein kombiniertes Verfahren von bestimmten kulturellen und molekularen Methoden erwies sich als praktikabel für die Routinediagnostik unter den zeitlichen und ökonomischen Anforderungen und Bedingungen von privat niedergelassenen Laboratorien.In order to record the incidence and clonal types of shigatoxin-producing E. coli of human origin (EHEC) and to evaluate the feasibility, sensitivity and specificity of a protocol for screening and isolation of EHEC under conditions clinical stool diagnostics a pilot study (Sentinel-study) was carried out with private clinical laboratory (covering 1.1 Mio. inhabitants). 3 % EHEC bacteria were detected among 3835 stool samples investigated from patients suffering with watery and bloody diarrhoea. These isolates belong to a broad range of serovars and clones with a spectrum of various virulence factors. Thus, about 10 % of the isolates have been identified as E. coli O157:H7/-, only, but with the same frequency E. coli O103:H2, O26:H11/-, O8:H or Ont. The protocol of combined bacterial enrichment and molecular methods turned out to be valuable and feasible under conditions and economic requests of private diagnostic laboratories covering ca. 85 % of primary diagnostics

Mechanical damage to Gram-negative bacteria by surface plating with the Drigalski-spatula technique

Colony counting by spreading bacterial suspensions on plating media by various techniques is of general concern. Comparative studies between hand plating (Drigalski-spatula technique) for different time intervals and spiral plating resulted in significant differences in colony counts. Lower counts of Gram-negative bacteria were obtained by using hand plating for more than 10 s, compared with short time hand plating (5 s) or spiral plating. Colony counting of Gram-positive bacteria showed no differences between both techniques. Further characterisation of Escherichia coli cells spread with the Drigalski-spatula technique by electron microscopy revealed a large number of damaged cells compared to control samples. The data clearly shows that the mechanical forces during hand plating are sufficient to damage E. coli cells

Evaluation of a new chromogenic Salmonella plating medium

Oxoid Salmonella Chromogenic Medium (OSCM) was tested for its sensitivity and specificity as well as its use in isolation of Salmonella from stool specimens and from porcine faeces. Colonies of Salmonella enterica ssp. I, II, IV, and VI-strains grow onto the ivory-coloured turbid plates purple to mauve, size 1-2 mm in diameter. Contrarily, E. coli, Enterobacter spp., Klebsiella spp., S. sonnei and the most of C. freundii strains appear as turquoise to blue colonies. Proteus spp., Providencia spp. and Morganella morganii grow light with brownish precipitation. S. dysenteriae, S. jlexneri and S. boydii are widely inhibited. Pseudomonads, Aeromonas spp., grampositive bacteria and C. albicans are completely inhibited. Its recovery rate and sensitivity in isolation of salmonella from stool specimens is comparable to Hektoen Enteric agar. OSCM was superior in isolation of Salmonella from porcine faeces compared with XLD.</p

Salmonella typhimurium IroN and FepA Proteins Mediate Uptake of Enterobactin but Differ in Their Specificity for Other Siderophores

Salmonella typhimurium possesses two outer membrane receptor proteins, IroN and FepA, which have been implicated in the uptake of enterobactin. To determine whether both receptors have identical substrate specificities, fepA and iroN mutants and a double mutant were characterized. While both receptors transported enterobactin, the uptake of corynebactin and myxochelin C was selectively mediated by IroN and FepA, respectively