Speciation, serotyping, antimicrobial sensitivity and plasmid content of Proteeae from the environment of calf-rearing units in South West England

Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system

Providencia alcalifaciens is a Gram-negative bacterium found in various water and land environments and organisms, including insects and mammals. Some P. alcalifaciens strains encode gene homologs of virulence factors found in pathogenic Enterobacterales members, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are pathogenic determinants in P. alcalifaciens is not known. In this study, we investigated P. alcalifaciens-host interactions at the cellular level, focusing on the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS1b is widespread in Providencia spp. and encoded on the chromosome. A large plasmid that is present in a subset of P. alcalifaciens strains, primarily isolated from diarrheal patients, encodes for T3SS1a. We show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, lyses its internalization vacuole, and proliferates in the cytosol. This triggers caspase-4-dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS1a in entry, vacuole lysis, and cytosolic proliferation is host cell type-specific, playing a more prominent role in intestinal epithelial cells than in macrophages or insect cells. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa and induces mild epithelial damage with negligible fluid accumulation in a T3SS1a- and T3SS1b-independent manner. However, T3SS1b was required for the rapid killing of Drosophila melanogaster. We propose that the acquisition of two T3SS has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.

Significance and Roles of Proteus spp. Bacteria in Natural Environments

Proteus spp. bacteria were first described in 1885 by Gustav Hauser, who had revealed their feature of intensive swarming growth. Currently, the genus is divided into Proteus mirabilis, Proteus vulgaris, Proteus penneri, Proteus hauseri, and three unnamed genomospecies 4, 5, and 6 and consists of 80 O-antigenic serogroups. The bacteria are known to be human opportunistic pathogens, isolated from urine, wounds, and other clinical sources. It is postulated that intestines are a reservoir of these proteolytic organisms. Many wild and domestic animals may be hosts of Proteus spp. bacteria, which are commonly known to play a role of parasites or commensals. However, interesting examples of their symbiotic relationships with higher organisms have also been described. Proteus spp. bacteria present in soil or water habitats are often regarded as indicators of fecal pollution, posing a threat of poisoning when the contaminated water or seafood is consumed. The health risk may also be connected with drug-resistant strains sourcing from intestines. Positive aspects of the bacteria presence in water and soil are connected with exceptional features displayed by autochthonic Proteus spp. strains detected in these environments. These rods acquire various metabolic abilities allowing their adaptation to different environmental conditions, such as high concentrations of heavy metals or toxic substances, which may be exploited as sources of energy and nutrition by the bacteria. The Proteus spp. abilities to tolerate or utilize polluting compounds as well as promote plant growth provide a possibility of employing these microorganisms in bioremediation and environmental protection.

Clonality of Providencia stuartii isolates involved in outbreak that occurred in a burn unit

In order to investigate an outbreak of multidrug-resistant Providencia stuartii that occurred in a burn unit, we analyzed by pulsed-field gel electrophoresis (PFGE) all isolates of P. stuartii collected during 4 months of 2005 from patients and from a tracheal aspirator. Seventeen clinical isolates of P. stuartii, extended-spectrum beta-lactamase (ESBL) producing, were collected from 17 patients. All these isolates were nosocomially acquired. Three other isolates were collected from the aspirator probe, the aspirator reservoir and from the aspirator tube. Three different antibiotypes were identified without correlation with the genotype. Two PFGE types were obtained (types A and B) with predominance of one (type A) that was observed for 15 isolates. P. stuartii isolates collected from different components of the aspirator (probe, reservoir and tube) yielded PFGE type A. This study suggests the bi-clonality of the outbreak and that transmission of epidemic P. stuartii isolates was through a common source. The aspirator probe, contaminated from aspirator that functioned as a reservoir of bacteria, seems to be the route of transmission of P. stuartii. Furthermore, this study shows the utility of PFGE in typing for the purpose of understanding the epidemiological behaviour of P. stuartii and as a basis for the development of rational control strategies.

Molecular characterization of the genera Proteus, Morganella, and Providencia by ribotyping

The so-called Proteus-Providencia group is constituted at present by three genera and 10 species. Several of the recognized species are common opportunistic pathogens for humans and animals. Different methods based on the study of phenotypic characters have been used in the past with variable levels of efficiency for typing some species for epidemiological purposes. We have determined the rRNA gene restriction patterns (ribotypes) for the type strains of the 10 different species of the genera Proteus, Morganella, and Providencia. Visual inspection of EcoRV- and HincII-digested DNA from the type strains showed remarkably different patterns for both enzymes, but EcoRV provided better differentiation. Both endonucleases were retained to study a large number of wild and collection strains belonging to the different species. Clinical isolates of Proteus mirabilis, Proteus penneri, Morganella morganii, and Providencia heimbachae showed patterns identical or very similar to those of the respective type strains, so that groups of related patterns (ribogroups) were found to correspond to the diverse species. On the contrary, distinct ribogroups were detected within Providencia alcalifaciens (two ribogroups with both enzymes), Providencia rettgeri (four ribogroups with EcoRV and five with HincII), Providencia stuartii (two ribogroups with EcoRV), Providencia rustigianii (two ribogroups with HincII), and Proteus vulgaris (two ribogroups with both enzymes). The pattern shown by the ancient P. vulgaris type strain NCTC 4175 differed considerably from both P. vulgaris ribogroups as well as from the newly proposed type strain ATCC 29905 and from any other strain in this study, thus confirming its atypical nature. Minor differences were frequently observed among patterns of strains belonging to the same ribogroup. These differences were assumed to define ribotypes within each ribogroup. No correlation was observed between ribogroups or ribotypes and biogroups of P. vulgaris, P. alcalifaciens, P. stuartii, and P. rettgeri. Since, not only different species showed different rRNA gene restriction patterns, but also different ribogroups and ribotypes have been found in the majority of the species, ribotyping would be a sensitive method for molecular characterization of clinical isolates belonging to the genera Proteus, Morganella, and Providencia.

The prevalence of gentamicin 2'-N-acetyltransferase in the Proteeae and its role in the O-acetylation of peptidoglycan

The prevalence of aac(2')-Ia, a gene coding for gentamicin 2'-N-acetyltransferase in Providencia stuartii, among species of the Proteeae was investigated to determine if it is a common resistance factor and whether the correlation observed in P. stuartii between its expression and the levels of peptidoglycan O-acetylation represents a general feature of bacteria producing this form of modified peptidoglycan. An evaluation of the MICs of gentamicin for each of the species of the Proteeae did not reveal any apparent relationship between resistance and the degree of O-acetylation of peptidoglycan. The entire aac(2')-Ia gene was used as a probe in Southern hybridization experiments against genomic DNA from each species of the Proteeae. A sequence with strong homology to aac(2')-Ia was present only in Proteus penneri while weak hybridization was also observed to the restriction digested DNA from Providencia rettgeri. Other bacteria that O-acetylate peptidoglycan were also screened with this probe and a homologous DNA sequence was only found in Neisseria subflava. These data suggest that AAC(2')-Ia may contribute to the O-acetylation of peptidoglycan in P. stuartii, but a more specific enzyme must also be produced for this function.

Analysis of antibiotic resistance determinants in Proteus penneri

The plasmid profiles of 65 strains of Proteus penneri were analyzed to determine whether resistance was determined chromosomally or by plasmids. Only seven strains harboured one to three plasmids, although these strains exhibited resistance to a wide range of antibiotics. Markers for ampicillin and tetracycline resistance could be transferred to Escherichia coli by transformation. Plasmids carried resistance to chloramphenicol in two strains and resistance to sulfonamides in one strain. The result showed that resistance is determined chromosomally rather than by plasmids, however the possibility that these bacteria may acquire resistance plasmids which change their antibiotic susceptibility pattern cannot be excluded.

Production and characterization of a compound inhibitory to Vibrio parahaemolyticus from Proteus vulgaris

The production and characteristics of a compound in Proteus vulgaris G cultures which was capable of inhibiting Vibrio parahaemolyticus and other food-borne pathogens was investigated. Production was influenced by medium composition, pH and temperature but not by the extent of aeration. The compound was most inhibitory at the optimum temperature for growth of V. parahaemolyticus. The inhibitor was most stable at pH 7.0 and inhibition occurred even after heating at 70 degrees C for 30 min and after autoclaving. Ultrafiltration showed that the inhibitor had a molecular weight less than 1000. Thin layer chromatography of filtrates and subsequent peptidase digestion indicated that it was at least in part a peptide. The inhibitor purified by Sephadex G-15 gel filtration had a calculated molecular weight of 731 and contained only six amino acids.

Detection of genomic variation in Providencia stuartii clinical isolates by analysis of DNA restriction fragment length polymorphisms containing rRNA cistrons

Chromosomal DNA from 26 strains of Providencia stuartii isolated mainly in hospitals in the United Kingdom and reference strains of P. stuartii, P. rustigianii, and Proteus vulgaris were digested with the restriction endonucleases EcoRI and HindIII. After electrophoresis in agarose gels, the fragments were subjected to Southern blot hybridization analysis with a biotin-labeled cDNA probe transcribed from a mixture of 16S and 23S rRNA from P. stuartii NCTC 11800T. The pattern of bands (the rDNA fingerprint), which depended on restriction fragment length polymorphisms containing rRNA genes, was used as a measure of minor genomic variation within and between species. The P. stuartii clinical isolates had similar total digest patterns, but the rDNA fingerprints revealed some heterogeneity between strains, with EcoRI digests providing better strain discrimination than HindIII. Such rDNA fingerprints comprised between five and seven bands with sizes in the range of 5 to 28 kilobases. The 11 different EcoRI patterns were compared by numerical analysis, and several groups or subgroups of strains were identified. Over half (15 of 26) of the urease-negative isolates (subgroups Aa and Ab) had patterns that differed only by the presence or absence of a 25-kilobase band. Urease-negative strains from other clinical material were more heterogeneous in their patterns. No correlation was apparent between strain pattern group and urease production or geographic location of isolate. The P. stuartii rDNA fingerprints were quite distinct from those of allied Providencia and Proteus species and provided a more sensitive measure of minor genomic differences than total DNA digests did.