A novel titanium wound chamber for the study of wound infections in pigs

In the face of emerging multidrug-resistant microbes, reliable animal models are needed to study potential new therapies in infected wounds. To this end, we implanted screw-top titanium chambers subdermally in full-thickness wounds on both flanks (n = 6 per flank) of 2 Goettinger minipigs. After 1 wk, chambers were inoculated with Staphylococcus aureus, Pseudomonas aeruginosa, or vehicle only. Throughout the study, wound fluid was harvested for quantitative bacterial cultures to monitor infection. Animals were followed for 4 wk, after which tissue biopsies were taken for histologic analysis and quantitative bacterial counts. The implanted titanium chambers were well tolerated by the pigs throughout the study. After inoculation of the chambers, wound infection was established and maintained for 14 d. Despite infection, no systemic effects were noted. Cross-contamination was negligible, compared with the vehicle-only control. After tissue ingrowth, each chamber creates a closed system that allows harvest of exudate or application of substances without loss of material from the chamber. Because 12 chambers are implanted in each pig, researchers have the opportunity to compare multiple treatment options (for example, antibiotics, antimicrobial peptides, gene therapy) in the same animal, with no interindividual variation. We conclude that the use of titanium chambers in pigs provides a reliable and reproducible in vivo model to investigate wound healing, wound infection, and treatment options.     

Lability of the pAA Virulence Plasmid in Escherichia coli O104:H4: Implications for Virulence in Humans

Background

Escherichia coli O104:H4 that caused the large German outbreak in 2011 is a highly virulent hybrid of enterohemorrhagic (EHEC) and enteroaggregative (EAEC) E. coli. The strain displays “stacked-brick” aggregative adherence to human intestinal epithelial cells mediated by aggregative adherence fimbriae I (AAF/I) encoded on the pAA plasmid. The AAF/I-mediated augmented intestinal adherence might facilitate systemic absorption of Shiga toxin, the major virulence factor of EHEC, presumably enhancing virulence of the outbreak strain. However, the stability of pAA in the outbreak strain is unknown. We therefore tested outbreak isolates for pAA, monitored pAA loss during infection, and determined the impact of pAA loss on adherence and clinical outcome of infection.

Methodology/Principal Findings

E. coli O104:H4 outbreak isolates from 170 patients (128 with hemolytic uremic syndrome [HUS] and 42 with diarrhea without HUS) were tested for pAA using polymerase chain reaction and plasmid profiling. pAA-harboring bacteria in stool samples were quantified using colony blot hybridization, and adherence to HCT-8 cells was determined. Isolates from 12 (7.1%) patients lacked pAA. Analyses of sequential stool samples demonstrated that the percentages of pAA-positive populations in the initial stools were significantly higher than those in the follow-up stools collected two to eight days later in disease (P≤0.01). This indicates a rapid loss of pAA during infections of humans. The pAA loss was associated with loss of the aggregative adherence phenotype and significantly reduced correlation with HUS (P  = 0.001).

Conclusions/Significance

The pAA plasmid can be lost by E. coli O104:H4 outbreak strain in the human gut in the course of disease. pAA loss might attenuate virulence and diminish the ability to cause HUS. The pAA instability has clinical, diagnostic, epidemiologic, and evolutionary implications.     

Cloning of an agr homologue of Staphylococcus saprophyticus

An agr homologue of Staphylococcus saprophyticus was identified, cloned and sequenced. The gene locus shows homologies to other staphylococcal agr systems, especially to those of S. epidermidis and S. lugdunensis. A putative RNAIII was identified and found to be differentially expressed during the growth phases. In contrast to the RNAIII molecules of S. epidermidis and S. aureus it does not contain an open reading frame that codes for a protein with homologies to the delta-toxin. Using PCR, the agr was found to be present in clinical isolates of S. saprophyticus.     

Evolutionary rates for tuf genes in endosymbionts of aphids

The gene encoding elongation factor Tu (tuf) in aphid endosymbionts (genus Buchnera) evolves at rates of 1.3 x 10(-10) to 2.5 x 10(-10) nonsynonymous substitutions and 3.9 x 10(-9) to 8.0 x 10(-9) synonymous substitutions per position per year. These rates, which are at present among the most reliable substitution rates for protein-coding genes of bacteria, have been obtained by calibrating the nodes in the phylogenetic tree produced from the Buchnera EF-Tu sequences using divergence times for the corresponding ancestral aphid hosts. We also present data suggesting that the rates of nonsynonymous substitutions are significantly higher in the endosymbiont lineages than in the closely related free-living bacteria Escherichia coli and Salmonella typhimurium. Synonymous substitution rates for Buchnera approximate estimated mutation rates for E. coli and S. typhimurium, as expected if synonymous changes act as neutral mutations in Buchnera. We relate the observed differences in substitution frequencies to the absence of selective codon preferences in Buchnera and to the influence of Muller's ratchet on small asexual populations.      

Enantiomeric composition of the polycyclic musks HHCB and AHTN in different aquatic species

Synthetic polycyclic musk fragrances are mainly represented by the compounds HHCB (Galaxolide(TM)) and AHTN (Tonalide(TM)). Because of their volume of use and their bioaccumulation potential, there is concern with respect to their environmental safety. HHCB and AHTN are chiral compounds, and gas chromatography using modified cyclodextrins as chiral stationary phases coupled to high-resolution mass spectrometry enabled enantioselective analysis even under unfavorable matrix conditions. The gas chromatographic elution order of (4S,7RS)- and (4R,7RS)-HHCB was assigned using synthetic (4S, 7RS)-HHCB. Fish and mussels reared in a pond associated with a municipal waste water treatment plant and semipermeable membrane devices exposed in the pond were analyzed for HHCB and AHTN. The highest lipid concentrations of HHCB and AHTN were observed in mussels (Dreissena polymorpha), tench (Tinca tinca), and crucian carp (Carassius carassius). Pronounced deviations in enantiomeric composition from racemic HHCB were observed in crucian carp and from racemic AHTN in tench. Correlations between lipid levels, enrichment, and enantioselective biotransformation of HHCB or AHTN were not seen. Selective biotransformation depended on both the compound and the species involved. The present study gives the first account of the enantiomeric composition of HHCB and AHTN in aquatic species. The lactone, 1,3,4,6,7,8-hexahydro-4,6,6,7,8, 8-hexamethylcyclopenta[g]-2-benzopyran-1-one, an oxidation product of HHCB, has been identified for the first time in environmental samples. Copyright 1999 Wiley-Liss, Inc.     

Characterization of 13 newly isolated strains of anaerobic, cellulolytic, thermophilic bacteria

Characteristics of 13 newly isolated thermophilic, anaerobic, and cellulolytic strains were compared with previously described strains of Clostridium thermocellum: ATCC 27405 and JW20 (ATCC 31549). Colony morphology, antibiotic sensitivity, fermentation end-products, and cellulose degradation were documented. All 13 strains were sensitive to erythromycin (5 μg/ml) and chloramphenicol (25 μg/ml), and all strains but one were sensitive to kanamycin (20 μg/ml). Polymerase chain reaction (PCR) amplification using primers based on gene sequences from C. thermocellum ATCC 27405 was successful for all 13 strains in the case of the hydrogenase gene and 11 strains in the case of phosphotransacetylase/acetate kinase genes. Ten strains amplified a product of the expected size with primers developed to be specific for C. thermocellum 16SrRNA primers. Two of the 13 strains did not amplify any product with the PCR primers designed for the phosphotransacetylase/acetate kinase and 16SrRNA primers. A MboI-like GATC- recognizing restriction activity was present in all of the five strains examined. The results of this study have several positive implications with respect to future development of a transformation system for cellulolytic thermophiles. Journal of Industrial Microbiology & Biotechnology (2001) 27, 275–280. Received 12 September 2000/ Accepted in revised form 20 November 2000     

First description of Escherichia coli producing CTX-M-15- extended spectrum - lactamases (ESBL) in outpatients from south-eastern Nigeria

ABSTRACT: We studied the presence of extended spectrum beta lactamases (ESBLs) in 44 clinical isolates of Escherichia coli collected from two university teaching hospitals in South-Eastern Nigeria. Species identification was performed by standard microbiology methods and re-confirmed by MALDI-TOF technology. Phenotypic characterization of ESBL enzymes was done by double disc synergy test and presence of ESBL genes was determined by specific PCR followed by sequencing. Transfer of plasmid DNA was carried out by transformation using E. coli DH5 alpha as recipient strain. Phenotypic characterization identified all isolates to be ESBL positive. 77% of strains were from urine, 13.6% from vaginal swabs and 9.0% from wound swabs. 63.6% were from female patients, 68% were from outpatients and 95.5% from patients younger than 30 years. All ESBL producers were positive in a PCR for blaCTX-M-1 cluster, in exemplary strains blaCTX-M-15 was found by sequencing. In all strains ISEcp1 was found upstream and ORF477 downstream of blaCTX-M. PCR for blaTEM and blaOXA-1 was positive in 93.1% of strains, whereas blaSHV was not detected, aac(6')-Ib-cr was found in 97.7% of strains. RAPD analysis revealed seven different clonal groups named A through G with the majority of the strains (65.9%) belonging to clone A. Transfer of an ESBL plasmid with co-resistance to gentamicin, kanamycin, tobramycin, doxycycline and trimethropim-sulfamethoxazole was successful in 19 (43.2%) strains. This study showed a high rate of CTX-M-1 cluster - ESBLs in South-Eastern Nigeria and further confirms the worldwide spread of CTX-M ESBL in clinical isolates. KEYWORDS: Outpatients, ESBL, CTX-M, Escherichia coli.