Field enhancement in a doubly resonant optical parametric oscillator.

Single-resonant and (signal/idler) double-resonant optical parametric oscillators differ fundamentally on the conversion efficiency back to the pump wave. The nonpresent idler in the single-resonant case allows for signal intracavity enhancement well beyond the pump power level. This paper answers the question, how the phase-matched back conversion in a doubly-resonant system can be overcome to reveal substantial power enhancement, and what parameters it depends on. In a degenerate double-resonant OPO (DROPO) pumped by a thin-disk oscillator, an enhancement up to a factor of four is shown experimentally. Support of a semianalytical theory is presented with exceptionally simple relations between enhancement and intracavity losses. Interestingly, our theory predicts no fundamental limit to the maximal field enhancement or conversion efficiency.

Serotypes, virulence markers and cell invasion ability of Shiga toxin-producing Escherichia coli strains isolated from healthy dairy cattle.

AIM: The occurrence of virulence markers, serotypes and invasive ability were investigated in Shiga toxin-producing Escherichia coli (STEC) isolated from faecal samples of healthy dairy cattle at Rio de Janeiro State, Brazil. METHODS AND RESULTS: From 1562 stx-positive faecal samples, 105 STEC strains were isolated by immuno-magnetic separation (IMS) or plating onto MacConkey agar (MC) followed by colony hybridisation. Fifty (47·6%) strains belonged to nine serotypes (O8:H19, O22:H8, O22:H16, O74:H42, O113:H21, O141:H21, O157:H7, O171:H2 and ONT:H21). The prevalent serotypes were O157:H7 (12·4%), O113:H21 (6·7%) and O8:H19 (5·7%). Virulence genes were identified by polymerase chain reaction (PCR). E-hlyA (77·1%) was the more prevalent virulence marker, followed by espP (64·8%), saa (39%), eae (24·8%) and astA (21·9%). All O157:H7 strains carried the γ (gamma) variant of the locus of enterocyte effacement (LEE) genes and the stx2c gene, while the stx1/stx2 genotype prevailed among the eae-negative strains. None of the eae-positive STEC produced the localized adherence (LA) phenotype in HEp-2 or Caco-2 cells. However, intimate attachment (judged by the fluorescent actin staining test) was detected in some eae-positive strains, both in HEp-2 (23·1%) and in Caco-2 cells (11·5%). Most strains (87·5%) showed 'peripheral association' (PA) adherence phenotype to undifferentiated Caco-2 cells. Twenty-five (92·6%) of 27 strains invaded Caco-2 cells. The highest average value of invasion (9·6%) was observed among the eae-negative bovine strains from serotypes described in human disease. CONCLUSION: Healthy dairy cattle is a reservoir of STEC carrying virulence genes and properties associated with human disease. SIGNIFICANCE AND IMPACT OF THE STUDY: Although reports of human disease associated with STEC are scarce in Brazil, the colonization of the animal reservoir by potentially pathogenic strains offers a significant risk to our population.

Genetic relatedness of a non-motile variant O157 enteropathogenic Escherichia coli (EPEC) strain and E. coli strains belonging to pathogenic related groups.

The study was undertaken to determine the clonal relationship and the genetic diversity among Escherichia coli isolates by comparing a non-motile O157 variant with three O157:H7 EHEC isolates and one O55:H7 enteropathogenic E. coli (EPEC) strain. E. coli strains were characterized by sorbitol phenotype, multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, random amplification polymorphic DNA, and the presence of specific virulence genes (stx, E-hly and LEE genes). Sorbitol fermentation was observed in O157:H- (strain 116I), O55:H7 and O157:H7 (strain GC148) serotypes. stx1 or stx2 and E-hly genes were only detected among O157:H7 isolates. LEE typing revealed specific allele distribution: eaegamma, tirgamma, espAgamma, espBgamma associated with EPEC O55:H7 and EHEC O157:H7 strains (B1/1 and EDL 933), eaealpha, tiralpha, espAalpha, espBalpha related to the 116I O157:H- strain and the GC148 strain presented non-typable LEE sequences. Multilocus enzyme profiles revealed two main clusters associated with specific LEE pathotypes. E. coli strains were discriminated by random amplification of polymorphic DNA-polymerase chain reaction and pulsed-field gel electrophoresis methodologies. The molecular approaches used in this study allowed the determination of the genetic relatedness among E. coli strains as well as the detection of lineage specific group markers.

Phenotypic and genotypic characterisation of Escherichia coli strains serogrouped as enteropathogenic E. coli (EPEC) isolated from pasteurised milk.

Fifty-six Escherichia coli strains, serogrouped as EPEC, isolated from three different brands of pasteurised milk commercialised in Rio de Janeiro, Brazil, were tested for enteropathogenicity markers. Most of the strains (71.4%) were adherent to HEp-2 cells. The adherent strains were distributed among 7 EPEC serogroups (O26, O55, O111, O114, O125, O127, O128, O158). Although almost half of these strains (33.9%) presented unrecognisable adherence phenotypes, classical adherence patterns (localised-like, aggregative and diffuse adherence) described for E. coli and epidemiologically associated with diarrheagenic strains were observed. None of the strains showed typical localised adherence, usually associated with EPEC strains, but 4 of them displayed a localised-like adherence (LAL) phenotype, characterised by fewer and less compact microcolonies but that is still associated with diarrheagenic strains as well as strains of non-human origin. Indeed, 3 of these 4 strains were able to elicit the attaching-effacing lesion (FAS-positive), the central feature of EPEC pathogenesis, and hybridised with bfpA and eae DNA probes. The other LAL-positive strain hybridised with the bfpA probe but gave negative results for the eae probe and FAS assays. Interestingly, all LAL-positive strains produced amplicons of 200 bp in the PCR for bfpA, instead of the expected 326 bp fragment. PCR reactions for stx1 and stx2, two shiga-toxin-encoding genes, gave negative results. Typing of LEE-associated genes by PCR showed the profile eae (beta), tir (beta), espA (alpha) and espB (alpha) for one of the LAL-positive strain. The most prevalent adherence phenotype was the aggregative pattern which is observed in strains epidemiologically associated with persistent diarrhea. Additionally, one strain promoted complete detachment of the Hep-2 cell monolayer after 3 h of infection which might be related to the production of citotoxins, a feature that has been increasingly observed in clinical strains. The possession of EPEC-related O and H antigens is no longer deemed an essential characteristic of true pathogenic EPEC strains, emphasising the importance of routinely screen for virulence markers in E. coli strains isolated from foods. Our results are in accordance with data from the literature that demonstrate that environmental strains display atypical features but yet are capable of eliciting the classical A/E lesion and thus must be considered as potentially pathogenic. Further, our results demonstrate the potential of pasteurised milk as a vehicle for transmission of diarrheagenic E. coli in Brazil.

Outbreaks of cholera-like diarrhoea caused by enterotoxigenic Escherichia coli in the Brazilian Amazon Rainforest.

The relationship between enteropathogens and severe diarrhoea in the Brazilian Amazon is poorly understood. In 1998, outbreaks of acute diarrhoea clinically diagnosed as cholera occurred in two small villages localized far from the main cholera route in the Brazilian rainforest. PCR was performed on some enteropathogens and heat-labile (LT) and/or heat-stable (STh) toxin genes, the virulence determinants of enterotoxigenic Escherichia coli (ETEC), were detected. Further characterization of ETEC isolates revealed the presence of two clones, one from each outbreak. One presenting serotype O167:H5 harboured LT-I and STh toxin genes and expressed the CS5CS6 colonization factor. The other, a non-typeable serotype, was positive for the LT-I gene and expressed the CS7 colonization factor. The current study demonstrates the importance of molecular diagnosis in regions such as the Amazon basin, where the enormous distances and local support conditions make standard laboratory diagnosis difficult. Here we also show that the mis-identified cholera cases were in fact associated with ETEC strains. This is the first report of ETEC, molecularly characterized as the aetiological agent of severe diarrhoea in children and adults in the Brazilian Amazon Rainforest.

Frequency and characteristics of diarrhoeagenic Escherichia coli strains isolated from children with and without diarrhoea in Rio de Janeiro, Brazil.

The frequency of diarrhoeagenic Escherichia coli (DEC) strains was investigated in 253 children up to 3 years old, with (patient group, PG, 199 children) and without (control group, CG, 54 children) diarrhoea, living in Rio de Janeiro, Brazil. DEC strains were detected in 70 (27.6%) children, including 54 (27.1%) with diarrhoea and 16 (29.6%) without diarrhoea. Enteroaggregative E. coli (EAEC) was the most frequent DEC category, accounting for 14.6% of the isolates in the PG and for 11.1% in the CG. E. coli strains carrying enteropathogenic E. coli (EPEC) virulence markers showed higher incidence in the CG (12.9%) than in the PG (8.0%). E. coli strains belonging to non-classical EPEC groups that carried eae only or eae and bfpA, designated as attaching-effacing E. coli (AEEC) were the most frequent (79.1%). Simultaneous presence of multiple EPEC virulence factors (EAF/eae/bfpA) were only detected among strains isolated from the PG. Enterotoxigenic E. coli (ETEC) strains were isolated from 5.5% of the children in the CG and from 3.5% of those in the PG. Most of the ETEC isolates were LT-probe positive (70%) and none carried both LT-I and ST-I probe sequences. One enteroinvasive E. coli (EIEC) strain was recovered from a child with diarrhoea. No stx-probe positive E. coli strains were detected. Overall, DEC strains were not found to be significantly associated with diarrhoea (p>0.05). However, the higher incidence of EAEC, the most frequent DEC category, among children with diarrhoea, suggests a potential role of EAEC as an important enteric pathogen in the community investigated.

Serobiotypes and virulence genes of Escherichia coli strains isolated from diarrheic and healthy rabbits in Brazil.

A total of 178 Escherichia coli isolates from diarrheic and healthy rabbits in the São Paulo State (Brazil) were serobiotyped and investigated by PCR for the presence of virulence genes. Among the 90 (50.6%) isolates which possessed the eae gene, 74 were from diarrheic animals and all but one encoded intimin beta. Sixty five (72.2%) of the eae+ isolates had insertion of the locus of enterocyte effacement locus in the pheU locus, 11 (12.2%) in the selC and 14 (15.6%) did not insert in either of these loci. All isolates were negative for genes of the E. coli enterotoxins, Stx1, Stx2, CNF1, CNF2 and EHEC hemolysin. The O132:H2 serotype was dominant, being present in 63 isolates (70%) of the 90 eae+ isolates, and 57 of the 63 isolates of this serotype belonged to biotype 30. PCR detected the gene for AF/R2 fimbriae in 75 (83.3%) of the 90 eae+ isolates. Adherence to HeLa cells was best detected following 6h incubation and a positive fluorescence actin staining (FAS) test was given by 52 isolates. These data show that isolates of E. coli associated with diarrhea in rabbits in Brazil possess the genotype and phenotype typically associated with rabbit enteropathogenic E. coli (EPEC). We conclude that EPEC that possess the eae gene are a common cause of diarrhea in Brazilian rabbit farms and that the pathogenic eae+ AF/R2+ isolates of O132:H2:B30 serobiotype are especially predominant.

Bacteroides fragilis adherence to Caco-2 cells.

The ability of ten Bacteroides fragilis strains isolated from intestinal and non-intestinal infections, normal flora and environment to adhere to human colon carcinoma cells, Caco-2, was examined. The adherence capacity varied among the strains tested from strongly adherent (76-100%) to non- or weakly adherent (0-25%). Negative staining with Indian ink showed that all the strains were capsulated, although strain 1032 (strongly adherent and originated from bacteremia) had the highest rate of capsulated cells in the culture. All strains studied presented an electron-dense layer and no fimbrial structures in their surface after PTA negative staining. The analysis of the strains with ruthenium red showed the presence of an acidic polysaccharide and also surface vesicles in all of them. The strain 1032 presented an aggregative adherence pattern toward Caco-2 cells monolayers. It could be seen trapped by elongated microvilli and surrounded by extracellular material in the scanning electron microscope. Treatment with sodium periodate (100 mM/1 h) reduced significantly its adherence capacity and also the expression of an electron-dense layer and of the capsule, detected with PTA and Indian ink staining, respectively. We suggest that the capsular polysaccharide might mediate the adherence of the B. fragilis to Caco-2 cells.

The Amazonia variant of Vibrio cholerae: molecular identification and study of virulence genes

The pathogenic O1 Amazonia variant of Vibrio cholerae has been shown previously to have a cytotoxin acting on cultured Vero and Y-1 cells, and to lack important virulence factors such as the cholera toxin (Coelho et al. 1995a). This study extends the molecular analysis of the Amazonia strains, detecting the presence to the toxR gene, with a very similar sequence to that of the El Tor and classical biotypes. The outer membrane proteins are analysed, detecting a variation among the group of Amazonia strains, with three different patterns found. As a by-product of this work a polymerase chain reation fragment was sequenced, reading part of the sequence of the Lon protease of the Amazonia strains. The gene was not previously described in V. cholerae, but its sequences is present in the TIGR database specific for this species.

Preliminary report on the application of the coaggutination test for rapid diagnosis of cholera in the upper Solimöes river area in the Brazilian Amazon region

The conventional diagnosis of cholera depends on complex bacteriological procedures. Coagglutination is a simnple, rapid, inexpensive and efficient technique for the presumptive diagnosis of cholera. Of 840 fecal samples from suspected cases of cholera examined at Tabatinga (State of Amazonas, Brazil) 31 (3.6%) were confirmed by culture and 29 of then were also positive by the coagglutination test performed directly on the fecal enrichment broth (alkaline peptone water). About 90% of the positive coagglutination results were obtained after-5-h incubation at 37 grade C and the sensitivity, specificity and accuracy of the method were 93.5%, 99% and 98.8%, respectively. relative to the culture results, coagglutination yielded two false-negative and eight false-positive results. The coagglutination test for cholera can provide a rapid and reliable tool for epidemiological studies and for the planning of more effective measures against cholera