Microtiter enzyme-linked immunosorbent assay for immunoglobulin g cholera antitoxin in humans: sensitivity and specificity

Serum samples were obtained from 92 informed, community volunteers before and 10, 21, and 28 days after they ingested 10(3) to 10(6)Vibrio cholerae of Inaba or Ogawa serotype and classical or El Tor biotype as part of a cholera vaccine development program. Pre- and postchallenge sera were examined for neutralizing antibody to cholera toxin by the rabbit skin permeability factor and adrenal cell techniques. Immunoglobulin G-binding antibodies to cholera toxin were quantitated by enzyme-linked immunosorbent assay (ELISA) in serum diluted 1:200. The results obtained in these cholera volunteers were compared with a negative control population comprising 30 people who ingested enteropathogenic Escherichia coli or E. coli which produced heat-stable but not heat-labile enterotoxin. Although all three antitoxin assays correlated closely with each other in both groups of volunteers, ELISA was more sensitive than either neutralization assay in detecting both subclinical and overt cholera infections. Seroconversion was demonstrated by ELISA in 58 of 66 (88%) volunteers who excreted V. cholerae, including 50 of 54 (93%) with clinical cholera, compared with 47 of 66 (71%) and 52 of 66 (79%) by the rabbit skin permeability factor and adrenal cell techniques, respectively. Although ELISA does not measure the toxin-neutralizing activity of antibodies directly, it provides a practical alternative to the rabbit skin permeability factor and adrenal cell assays.

The type III effectors NleE and NleB from enteropathogenic E. coli and OspZ from Shigella block nuclear translocation of NF-kappaB p65

Many bacterial pathogens utilize a type III secretion system to deliver multiple effector proteins into host cells. Here we found that the type III effectors, NleE from enteropathogenic E. coli (EPEC) and OspZ from Shigella, blocked translocation of the p65 subunit of the transcription factor, NF-kappaB, to the host cell nucleus. NF-kappaB inhibition by NleE was associated with decreased IL-8 expression in EPEC-infected intestinal epithelial cells. Ectopically expressed NleE also blocked nuclear translocation of p65 and c-Rel, but not p50 or STAT1/2. NleE homologues from other attaching and effacing pathogens as well OspZ from Shigella flexneri 6 and Shigella boydii, also inhibited NF-kappaB activation and p65 nuclear import; however, a truncated form of OspZ from S. flexneri 2a that carries a 36 amino acid deletion at the C-terminus had no inhibitory activity. We determined that the C-termini of NleE and full length OspZ were functionally interchangeable and identified a six amino acid motif, IDSY(M/I)K, that was important for both NleE- and OspZ-mediated inhibition of NF-kappaB activity. We also established that NleB, encoded directly upstream from NleE, suppressed NF-kappaB activation. Whereas NleE inhibited both TNFalpha and IL-1beta stimulated p65 nuclear translocation and IkappaB degradation, NleB inhibited the TNFalpha pathway only. Neither NleE nor NleB inhibited AP-1 activation, suggesting that the modulatory activity of the effectors was specific for NF-kappaB signaling. Overall our data show that EPEC and Shigella have evolved similar T3SS-dependent means to manipulate host inflammatory pathways by interfering with the activation of selected host transcriptional regulators.

Bicarbonate-mediated stimulation of RegA, the global virulence regulator from Citrobacter rodentium

The global virulence regulatory protein RegA, an AraC-like regulator, controls the expression of more than 60 genes in the mouse enteric pathogen Citrobacter rodentium. In the presence of bicarbonate, RegA activates the transcription of a number of virulence determinants and inhibits the expression of a series of housekeeping genes. To elucidate the molecular mechanism by which bicarbonate stimulates RegA activity, we carried out biophysical and mutational analyses. Our data indicate that RegA exists as a dimer in solution regardless of bicarbonate concentration. A leucine zipper, located in the region downstream of the N-terminal domain, is responsible for dimerisation. The N-terminal arm itself is involved in modulating the response to bicarbonate, which appears to bind to a region comprising a series of beta-sheets within the N-terminal domain. The presence of bicarbonate relieves the autoinhibition of RegA activity by its N-terminal arm. RegA is the first example of a bacterial virulence regulator that utilises the light switch mechanism, previously described for the Escherichia coli AraC protein, to respond to a gut-associated effector that controls its activity.

Characterisation of atypical enteropathogenic E. coli strains of clinical origin

BACKGROUND

Enteropathogenic E. coli (EPEC) is a prominent cause of diarrhoea, and is characterised in part by its carriage of a pathogenicity island: the locus for enterocyte effacement (LEE). EPEC is divided into two subtypes according to the presence of bundle-forming pili (BFP), a fimbrial adhesin that is a virulence determinant of typical EPEC (tEPEC), but is absent from atypical EPEC (aEPEC). Because aEPEC lack BFP, their virulence has been questioned, as they may represent LEE-positive Shiga toxin-producing E. coli (STEC) that have lost the toxin-encoding prophage, or tEPEC that have lost the genes for BFP. To determine if aEPEC isolated from humans in Australia or New Zealand fall into either of these categories, we undertook phylogenetic analysis of 75 aEPEC strains, and compared them with reference strains of EPEC and STEC. We also used PCR and DNA hybridisation to determine if aEPEC carry virulence determinants that could compensate for their lack of BFP.

RESULTS

The results showed that aEPEC are highly heterogeneous. Multilocus sequence typing revealed that 61 of 75 aEPEC strains did not belong to known tEPEC or STEC clades, and of those that did, none expressed an O:H serotype that is frequent in tEPEC or STEC strains associated with disease. PCR for each of 18 known virulence-associated determinants of E. coli was positive in less than 15% of strains, apart from NleB which was detected in 30%. Type I fimbriae were expressed by all aEPEC strains, and 12 strains hybridised with DNA probes prepared from either bfpA or bfpB despite being negative in the PCR for bfpA.

CONCLUSION

Our findings indicate that clinical isolates of aEPEC obtained from patients in Australia or New Zealand are not derived from tEPEC or STEC, and suggest that functional equivalents of BFP and possibly type I fimbriae may contribute to the virulence of some aEPEC strains.

Shiga toxin-producing Escherichia coli strains negative for locus of enterocyte effacement

Most Shiga toxin-producing Escherichia coli (STEC) infections that are associated with severe sequelae such as hemolytic uremic syndrome (HUS) are caused by attaching and effacing pathogens that carry the locus of enterocyte effacement (LEE). However, a proportion of STEC isolates that do not carry LEE have been associated with HUS. To clarify the emergence of LEE-negative STEC, we compared the genetic composition of the virulence plasmids pO113 and pO157 from LEE-negative and LEE-positive STEC, respectively. The complete nucleotide sequence of pO113 showed that several plasmid genes were shared by STEC O157:H7. In addition, allelic profiling of the ehxA gene demonstrated that pO113 belongs to a different evolutionary lineage than pO157 and that the virulence plasmids of LEE-negative STEC strains were highly related. In contrast, multilocus sequence typing of 17 LEE-negative STEC isolates showed several clonal groups, suggesting that pathogenic LEE-negative STEC has emerged several times throughout its evolution.

Shiga toxin-producing Escherichia coli strains negative for locus of enterocyte effacement

Most Shiga toxin-producing Escherichia coli (STEC) infections that are associated with severe sequelae such as hemolytic uremic syndrome (HUS) are caused by attaching and effacing pathogens that carry the locus of enterocyte effacement (LEE). However, a proportion of STEC isolates that do not carry LEE have been associated with HUS. To clarify the emergence of LEE-negative STEC, we compared the genetic composition of the virulence plasmids pO113 and pO157 from LEE-negative and LEE-positive STEC, respectively. The complete nucleotide sequence of pO113 showed that several plasmid genes were shared by STEC O157:H7. In addition, allelic profiling of the ehxA gene demonstrated that pO113 belongs to a different evolutionary lineage than pO157 and that the virulence plasmids of LEE-negative STEC strains were highly related. In contrast, multilocus sequence typing of 17 LEE-negative STEC isolates showed several clonal groups, suggesting that pathogenic LEE-negative STEC has emerged several times throughout its evolution.

Rabbit-specific fimbriae, Ral, alter the patterns of in vitro adherence and intestinal colonisation of rabbits by human-specific enteropathogenic E. coli

Enteropathogenic Escherichia coli (EPEC) poses a significant threat to human health, causing diarrhoea in children worldwide, and is a leading cause of infant mortality in developing countries. The pathogenic effects of EPEC and other attaching-effacing (A/E) bacteria result from adhesion to the intestinal mucosa by a variety of mechanisms, including fimbrial adhesins, which are believed to contribute to the host and tissue specificity of EPEC by their interaction with specific receptors on cell surfaces. In this study we investigated the contribution of a fimbrial adhesin, Ral, of rabbit-specific EPEC (REPEC) to host specificity by introducing Ral into derivatives of human-specific EPEC (hEPEC) strain, E2348/69, in which expression of the fimbrial adhesin, Bfp, had been interrupted. Although unable to cause diarrhoeal disease in rabbits, Ral-bearing hEPEC strains colonised rabbit intestine more efficiently and showed altered intestinal localisation when compared to an isogenic Ral-negative strain. These findings suggest that Ral enhances the initial interaction between a DeltabfpA mutant of hEPEC and rabbit intestine and may influence tissue specificity, but is not sufficient on its own to transform hEPEC into a rabbit pathogen. This study affords new insights into the complex mechanisms which determine the host range of bacterial pathogens.

Virulence regulation in Citrobacter rodentium: the art of timing

The mouse enteric pathogen Citrobacter rodentium, like its human counterpart, enteropathogenic Escherichia coli, causes attaching and effacing lesions in the intestinal epithelium of its host. This phenotype requires virulence factors encoded by the locus for enterocyte effacement (LEE) pathogenicity island. For timely expression of these virulence determinants at the site of infection and for efficient delivery of some virulence factors into epithelial cells, C. rodentium utilizes a positive regulatory loop involving the LEE‐encoded regulatory proteins Ler, GrlA and GrlR to control LEE expression. Several transcription factors not encoded by LEE, some of which respond to specific environmental signals, also participate in this regulatory loop. Recently, we identified a non‐LEE encoded, AraC‐like regulatory protein, RegA, which plays a key role in the ability of C. rodentium to colonize the intestine. RegA functions by activating the transcription of a number of horizontally acquired operons encoding virulence‐associated factors, such as autotransporters, fimbriae, a dispersin‐like protein and its transporter. In addition, RegA represses transcription of a number of housekeeping genes. Importantly, RegA requires a gut‐specific environmental signal, bicarbonate, to exert its effects on gene expression. In our proposed model, when C. rodentium senses bicarbonate ions in the gastrointestinal tract, RegA directs the bacterium to reduce the production of proteins involved in normal cellular functions, while enhancing the production of factors required for colonization and virulence.

Effects of Lactobacillus GG treatment during pregnancy on the development of fetal antigen-specific immune responses

BACKGROUND

Several clinical trials suggest that probiotics may have a role in the prevention of eczema. The optimal timing and mechanisms underlying this intervention are not clear. In particular it is not known whether such treatment works during pregnancy or whether postnatal exposure is important.

OBJECTIVE

We investigated whether the probiotic Lactobacillus rhamnosus strain GG (LGG) influences fetal immune responses when administered to pregnant women, as a possible mechanism for its protective effects against the development of eczema.

METHODS

Peripheral blood mononuclear cell from 11 adults treated with LGG, and cord blood mononuclear cells (CBMCs) from 73 women participating in a randomized controlled trial of LGG treatment were cultured with heat-killed LGG, ovalbumin (OVA) or without stimulus. Cells were analysed by flow cytometry and real-time PCR for markers of dendritic cell (DC) phenotype, T cell proliferation and regulation. Cytokine secretion was analysed in culture supernatants by multiplex cytokine assay.

RESULTS

LGG treatment of adults led to systemic immune responses suggestive of antigen-specific tolerance including reduced CD4(+) T cell proliferation to heat-killed LGG (30% reduction; P=0.03). LGG treatment of pregnant women did not influence CD4(+) T cell proliferation, forkhead box P3 expression, DC phenotype or cytokine secretion in CBMCs cultured with heat-killed LGG or OVA.

CONCLUSION

LGG treatment of pregnant women fails to influence fetal antigen-specific immune responses. This suggests that modulation of fetal immune responses may not be a major mechanism by which probiotics such as LGG prevent eczema.

Pneumococcal meningitis threshold model: A potential tool to assess infectious risk of new or existing inner ear surgical interventions

HYPOTHESIS

A minimal threshold of Streptococcus pneumoniae is required to induce meningitis in healthy animals for intraperitoneal (hematogenous), middle ear, and inner ear inoculations, and this threshold may be altered via recent inner ear surgery.

BACKGROUND

There has been an increase in the number of reported cases of cochlear implant-related pneumococcal meningitis since 2002. The pathogenesis of pneumococcal meningitis is complex and not completely understood. The bacteria can reach the central nervous system (CNS) from the upper respiratory tract mucosa via either hematogenous route or via the inner ear. The establishment of a threshold model for all potential routes of infection to the CNS in animals without cochlear implantation is an important first step to help us understand the pathogenesis of the disease in animals with cochlear implantation.

METHODS

Fifty-four otologically normal adult Hooded Wistar rats (27 receiving cochleostomy and 27 controls) were inoculated with different amounts of bacterial counts via three different routes (intraperitoneal, middle ear, and inner ear). Rats were monitored during 5 days for signs of meningitis. Blood, cerebrospinal fluid, and middle ear swabs were taken for bacterial culture, and brains and cochleae were examined for signs of infection.

RESULTS

The threshold of bacterial counts required to induce meningitis is lowest in rats receiving direct inner ear inoculation compared with both intraperitoneal and middle ear inoculation. There is no change in threshold between the group of rats with cochleostomy and the control (Fisher's exact test, p < 0.05).

CONCLUSION

A minimal threshold of bacteria is required to induce meningitis in healthy animals and is different for three different routes of infection (intraperitoneal, middle ear, and inner ear). Cochleostomy performed 4 weeks before the inoculation did not reduce the threshold of bacteria required for meningitis in all three infectious routes. This threshold model will also serve as a valuable tool, assisting clinicians to quantitatively analyze if the presence of a cochlear implant or other CNS prostheses alter the risk of meningitis.

Characterisation of Shiga toxin-producing Escherichia coli O157 strains isolated from humans in Argentina, Australia and New Zealand

Background

Shiga toxin-producing Escherichia coli (STEC) is an important cause of bloody diarrhoea (BD), non-bloody diarrhoea (NBD) and the haemolytic uraemic syndrome (HUS). In Argentina and New Zealand, the most prevalent STEC serotype is O157:H7, which is responsible for the majority of HUS cases. In Australia, on the other hand, STEC O157:H7 is associated with a minority of HUS cases. The main aims of this study were to compare the phenotypic and genotypic characteristics of STEC O157 strains isolated between 1993 and 1996 from humans in Argentina, Australia and New Zealand, and to establish their clonal relatedness.

Results

Seventy-three O157 STEC strains, isolated from HUS (n = 36), BD (n = 20), NBD (n = 10), or unspecified conditions (n = 7) in Argentina, Australia and New Zealand, were analysed. The strains were confirmed to be E. coli O157 by biochemical tests and serotyping. A multiplex polymerase chain reaction (PCR) was used to amplify the stx₁, stx₂ and rfb_O157 genes and a genotyping method based on PCR-RFLP was used to determine stx₁ and stx₂ variants. This analysis revealed that the most frequent stx genotypes were stx₂/stx_{2c (vh-a)} (91%) in Argentina, stx₂ (89%) in New Zealand, and stx₁/stx₂ (30%) in Australia. No stx₁-postive strains were identified in Argentina or New Zealand. All strains harboured the eae gene and 72 strains produced enterohaemolysin (EHEC-Hly). The clonal relatedness of strains was investigated by phage typing and pulsed-field gel electrophoresis (PFGE). The most frequent phage types (PT) identified in Argentinian, Australian, and New Zealand strains were PT49 (n = 12), PT14 (n = 9), and PT2 (n = 15), respectively. Forty-six different patterns were obtained by XbaI-PFGE; 37 strains were grouped in 10 clusters and 36 strains showed unique patterns. Most clusters could be further subdivided by BlnI-PFGE.

Conclusion

STEC O157 strains isolated in Argentina, Australia, and New Zealand differed from each other in terms of stx-genotype and phage type. Additionally, no common PFGE patterns were found in strains isolated in the three countries. International collaborative studies of the type reported here are needed to detect and monitor potentially hypervirulent STEC clones.

Bicarbonate-mediated transcriptional activation of divergent operons by the virulence regulatory protein, RegA, from Citrobacter rodentium

Regulation of virulence gene expression plays a central role in the pathogenesis of enteric bacteria as they encounter diverse environmental conditions in the gastrointestinal tract of their hosts. In this study, we investigated environmental regulation of two putative virulence determinants adcA and kfc by RegA, an AraC/XylS-like regulator, from Citrobacter rodentium, and identified bicarbonate as the environmental signal which induced transcription of adcA and kfc through RegA. Primer extension experiments showed that adcA and kfc were divergently transcribed from sigma(70) promoters. In vivo and in vitro experiments demonstrated that bicarbonate facilitated and stabilized the binding of RegA to an operator located between the two promoters. The interaction of RegA with its DNA target resulted in the formation of a nucleosome-like structure, which evidently displaced the histone-like proteins, H-NS and StpA, from the adcA and kfc promoter regions, leading to transcriptional derepression. In addition, our results indicated that RegA also behaved as a Class I activator by directly stimulating transcription initiation by RNA polymerase. This is the first report to describe the molecular mechanism by which an environmental chemical stimulates transcription of virulence-associated genes of an enteric pathogen through an AraC/XlyS-like activator.

Reactive oxygen species are the major antibacterials against Salmonella Typhimurium purine auxotrophs in the phagosome of RAW 264.7 cells

Intramacrophage survival appears to be a pathogenic trait common to Salmonellae and definition of the metabolic requirements of Salmonella within macrophages might provide opportunities for novel therapeutic interventions. We show that loss of PurG function in Salmonella enterica serovar Typhimurium SL1344 leads to death of the bacterium in RAW264.7 cells, which was due to unavailability of purine nucleotides but not thiamine in the phagosome of RAW264.7 cells. Phagosomal escape of purG mutant restored growth, suggesting that the phagosomal environment, but not the cytosol, is toxic to Salmonella purine auxotrophs. NADPH oxidase inhibition restored the growth of purG mutant in RAW264.7 cells, implying that the Salmonella-containing vacuole acquires reactive oxygen species (ROS) that are lethal to purine auxotrophs. Under purine limiting conditions, purG mutant was unable to repair the damage caused by hydrogen peroxide or UV irradiation, suggesting that ROS-mediated DNA damage may have been responsible for the attenuated phenotype of purG mutant in RAW264.7 cells and in mice. These studies highlight the possibility of utilizing the Salmonella purine nucleotide biosynthetic pathway as a prospective therapeutic target and also underline the importance of metabolic pathways in assembling a comprehensive understanding of the host-pathogen interactions inside phagocytic cells.

Meningitis after cochlear implantation

The risk is low, and preventive measures can reduce this further

A C-terminal class I PDZ binding motif of EspI/NleA modulates the virulence of attaching and effacing Escherichia coli and Citrobacter rodentium

Enteropathogenic Escherichia coli induces characteristic attaching-effacing (A/E) lesions on the intestinal mucosa during infection. The locus of enterocyte effacement is essential for A/E lesion formation and encodes a type III secretion system that translocates multiple effector proteins into the host cell. Following translocation, EspI/NleA localizes to the Golgi. Using the yeast two-hybrid system (Y2HS) and PSD-95/Disk-large/ZO-1 (PDZ)-domain protein array overlays, we identified 15 putative host-interacting partners of EspI. All but two of the target proteins contained PDZ domains. Examination of the EspI amino acid sequence revealed a C-terminal consensus class I PDZ binding motif. Deletion of the last 7 amino acids of EspI to generate EspI(DeltaC7) abrogated the Y2HS interaction between EspI and 5 of the 6 putative host cell target proteins tested. Deletion of the EspI PDZ binding motif also resulted in delayed trafficking of EspI to the Golgi. Using a mouse model of infection, we showed that Citrobacter rodentium expressing truncated EspI(DeltaC7) was attenuated when in competition with C. rodentium expressing full-length EspI. Overall, these results suggested that EspI may modulate the virulence of A/E pathogens by binding host PDZ-domain proteins.

Assessment of the protective effect of pneumococcal vaccination in preventing meningitis after cochlear implantation

OBJECTIVES

To examine if a 23-valent pneumococcal capsular polysaccharide vaccine (PPV23) reduces the risk of meningitis in healthy rats after cochlear implantation.

DESIGN

Interventional animal study.

INTERVENTIONS

Thirty-six rats (18 immunized and 18 unimmunized) received cochlear implantations and were then infected with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) in numbers sufficient to induce meningitis.

RESULTS

The rats with implants that received PPV23 were protected from meningitis when the bacteria were delivered via the hematogenous and middle-ear routes (Fisher exact test P<.05). However, the protective effect of the vaccine in the rats with implants was only moderate when the bacteria were inoculated directly into the inner ear.

CONCLUSIONS

Our animal model clearly demonstrates that immunization can protect healthy rats with a cochlear implant from meningitis caused by a vaccine-covered serotype. This finding supports the notion that all current and future implant recipients should be vaccinated against S pneumoniae.

The rise and rise of enteropathogenic Escherichia coli

First described in 1885, Escherichia coli gradually achieved recognition as a cause of diarrhoea. Strains of E. coli which belonged to a limited number of O-serogroups and had been associated with outbreaks of diarrhoea in hospitalised children were designated 'enteropathogenic' E. coli (EPEC) to distinguish them from E. coli strains that cause other types of infection. The discovery that some strains of E. coli can produce toxins or invade epithelial cells in a similar fashion to established pathogens, such as Vibrio cholerae and Shigella species, shed new light on E. coli virulence. As EPEC do not exhibit either of these properties, however, their pathogenicity was brought into question. Further studies revealed that EPEC constitute a distinctive group of pathogenic bacteria that display characteristic adherence to cultured epithelial cells and produce distinctive histopathological changes, termed 'attaching-effacing lesions', in the intestinal epithelium. The ability to evoke these lesions, which are essential for virulence, is associated with a series of linked genes, known as the locus for enterocyte effacement, on the bacterial chromosome. In addition, the pathogenicity of some EPEC strains is associated with the presence of a plasmid-encoded, bundle-forming pilus. Naturally occurring strains of EPEC which lack this pilus are known as atypical EPEC and are an emerging cause of diarrhoea throughout the world.

Pneumococcal meningitis: development of a new animal model

HYPOTHESIS

The rat is a suitable animal to establish a model for the study of pneumococcal meningitis postcochlear implantation.

BACKGROUND

There has been an increase in the number of cases of cochlear implant-related meningitis. The most common organism identified was Streptococcus pneumoniae. Whether cochlear implantation increases the risk of pneumococcal meningitis in healthy subjects without other risk factors remains to be determined. Previous animal studies do not focus on the pathogenesis and risk of pneumococcal meningitis postimplantation and are based on relatively small animal numbers, making it difficult to assess the cause-and-effect relationship. There is, therefore, a need to develop a new animal model allowing direct examination of the pathogenesis of meningitis in the presence of a cochlear implant.

METHODS

Eighteen nonimplanted rats were infected with 1 x 10 and 1 x 10 colony-forming units (CFU) of a clinical isolate of S. pneumoniae via three different inoculation routes (middle ear, inner ear, and i.p.) to examine for evidence of meningitis during 24 hours. Six implanted rats were infected with the highest amount of bacteria possible for each route of inoculation (4 x 10 CFU i.p., 3 x 10 CFU middle ear, and 1 x 10 CFU inner ear) to examine for evidence of meningitis with the presence of an implant. The histological pattern of cochlear infections for each of the three different inoculating routes were examined.

RESULTS

Pneumococcal meningitis was evident in all 6 implanted animals for each of the three different routes of inoculation. Once in the inner ear, bacteria were found to enter the central nervous system via either the cochlear aqueduct or canaliculi perforantes of the osseous spiral lamina, reaching the perineural and perivascular space then the internal acoustic meatus. The rate, extent, and pattern of infection within the cochleae depended on the route of inoculation. Finally, there was no evidence of pneumococcal meningitis observed in 18 nonimplanted rats inoculated at a lower concentration of S. pneumoniae when observed for 24 hours postinoculation.

CONCLUSION

Meningitis in implanted rats after inoculation with a clinical isolate of S. pneumoniae is possible via all three potential routes of infection via the upper respiratory tract. The lack of meningitis observed in the 18 nonimplanted rats suggests that longer postinoculation monitoring periods are required to ensure whether or not meningitis will develop. Based on this work, we have developed a new animal model that will allow quantitative risk assessment of meningitis postcochlear implantation, and the assessment of the efficacy of potential interventional strategies in future studies.

Contribution of a novel gene, rpeA, encoding a putative autotransporter adhesin to intestinal colonization by rabbit-specific enteropathogenic Escherichia coli

Rabbit-specific enteropathogenic Escherichia coli (REPEC) is an attaching and effacing pathogen of young rabbits. Using signature-tagged mutagenesis, we identified several known colonization factors of REPEC as well as a gene predicted to encode a novel autotransporter protein. This novel gene was termed rpeA for REPEC plasmid-encoded autotransporter.

Threshold shift: effects of cochlear implantation on the risk of pneumococcal meningitis

OBJECTIVES

The study goals were to examine whether cochlear implantation increases the risk of meningitis in the absence of other risk factors and to understand the pathogenesis of pneumococcal meningitis post cochlear implantation.

STUDY DESIGN AND SETTING

Four weeks following surgery, 54 rats (18 of which received a cochleostomy alone, 18 of which received a cochleostomy and acute cochlear implantation using standard surgical techniques, and 18 of which received a cochlear implant) were infected with Streptococcus pneumoniae via three different routes of bacterial inoculation (middle ear, inner ear, and intraperitoneal) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges.

RESULTS

The presence of a cochlear implant reduced the threshold of bacteria required to cause pneumococcal meningitis from all routes of infection in healthy animals.

CONCLUSION

The presence of a cochlear implant increases the risk of pneumococcal meningitis regardless of the route of bacterial infection.

SIGNIFICANCE

Early detection and treatment of pneumococcal infection such as otitis media may be required, as cochlear implantation may lead to a reduction of infectious threshold for meningitis.

Effects of inner ear trauma on the risk of pneumococcal meningitis

OBJECTIVE

To examine the risk of pneumococcal meningitis in healthy rats that received a severe surgical trauma to the modiolus and osseous spiral lamina or the standard insertion technique for acute cochlear implantation.

DESIGN

Interventional animal studies.

SUBJECTS

Fifty-four otologically normal adult Hooded-Wistar rats.

INTERVENTIONS

Fifty-four rats (18 of which received a cochleostomy alone; 18, a cochleostomy and acute cochlear implantation using standard surgical techniques; and 18, a cochleostomy followed by severe inner ear trauma) were infected 4 weeks after surgery with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges in cochlear implant recipients with meningitis.

RESULTS

Severe trauma to the osseous spiral lamina and modiolus increased the risk of pneumococcal meningitis when the bacteria were given via the middle or inner ear (Fisher exact test, P<.05). However, the risk of meningitis did not change when the bacteria were given via the hematogenous route. Acute electrode insertion did not alter the risk of subsequent pneumococcal meningitis for any route of infection.

CONCLUSIONS

Severe inner ear surgical trauma to the osseous spiral lamina and modiolus can increase the risk of pneumococcal meningitis. Therefore, every effort should be made to ensure that cochlear implant design and insertion technique cause minimal trauma to the bony structures of the inner ear to reduce the risk of pneumococcal meningitis.

Protective effects of local administration of ciprofloxacin on the risk of pneumococcal meningitis after cochlear implantation

OBJECTIVES

To determine whether ciprofloxacin retains its antimicrobial activity after storage with Healon at ambient temperature and at 37 degrees C over 5 weeks and then to establish whether the application of ciprofloxacin/Healon onto scala tympani electrode arrays reduces the risk of meningitis in implanted rats inoculated with S. pneumoniae.

STUDY DESIGN

In vitro laboratory and in vivo animal studies

METHODS

The antibacterial activity of three concentrations of ciprofloxacin/Healon (7.5, 75, and 750 microg/mL) was examined over 5 weeks at both ambient temperature (23 degrees C) and body temperature (37 degrees C). Thirty-six rats (18 implanted with ciprofloxacin [750 mg/mL]/Healon-coated electrode array and 18 without the coating) were infected with S. pneumoniae 4 weeks after implantation by way of three different routes of infection (hematogenous, middle ear, and inner ear) and observed for the development of meningitis.

RESULTS

The antibacterial activity of ciprofloxacin/Healon was maintained over 5 weeks at both 23 degrees C and 37 degrees C. The implanted rats with the ciprofloxacin/Healon-coated electrode array were protected from meningitis when the bacteria were given by way of the hematogenous route (Fisher's exact test, P = .008) but not when the bacteria were inoculated directly into the middle or inner ear. However, the time to develop meningitis was significantly longer in rats implanted with a coated array, irrespective of the route of inoculation (P < .05, log rank test).

CONCLUSION

Our animal model demonstrated that a ciprofloxacin-coated electrode array can protect healthy implanted rats from meningitis when the route of infection is hematogenous and can delay the onset of meningitis when bacteria are inoculated directly into the middle or inner ear.

Transcriptional regulation of the yghJ-pppA-yghG-gspCDEFGHIJKLM cluster, encoding the type II secretion pathway in enterotoxigenic Escherichia coli

The gene cluster gspCDEFGHIJKLM codes for various structural components of the type II secretion pathway which is responsible for the secretion of heat-labile enterotoxin by enterotoxigenic Escherichia coli (ETEC). In this work, we used a variety of molecular approaches to elucidate the transcriptional organization of the ETEC type II secretion system and to unravel the mechanisms by which the expression of these genes is controlled. We showed that the gspCDEFGHIJKLM cluster and three other upstream genes, yghJ, pppA, and yghG, are cotranscribed and that a promoter located in the upstream region of yghJ plays a major role in the expression of this 14-gene transcriptional unit. Transcription of the yghJ promoter was repressed 168-fold upon a temperature downshift from 37 degrees C to 22 degrees C. This temperature-induced repression was mediated by the global regulatory proteins H-NS and StpA. Deletion mutagenesis showed that the promoter region encompassing positions -321 to +301 relative to the start site of transcription of yghJ was required for full repression. The yghJ promoter region is predicted to be highly curved and bound H-NS or StpA directly. The binding of H-NS or StpA blocked transcription initiation by inhibiting promoter open complex formation. Unraveling the mechanisms of regulation of type II secretion by ETEC enhances our understanding of the pathogenesis of ETEC and other pathogenic varieties of E. coli.

Atypical enteropathogenic Escherichia coli infection and prolonged diarrhea in children

Some clinical isolates of enteropathogenic Escherichia coli (EPEC) lack bundle-forming pili and are termed atypical EPEC. The aim of this study was to determine if atypical EPEC are pathogens by comparing the clinical features of patients infected with atypical EPEC with those of children infected with other causative agents of diarrhea. Fecal samples obtained from children attending the Royal Children's Hospital in Melbourne for investigation of diarrhea were examined for adenovirus, rotavirus, Campylobacter spp., Salmonella spp., protozoa, and pathogenic E. coli. Clinical data were obtained by using a standardized pro forma and analyzed separately. Patients infected with atypical EPEC experienced mild, nondehydrating, and noninflammatory diarrhea that was not particularly associated with fever, vomiting, or abdominal pain. However, the duration of diarrhea in patients infected with atypical EPEC was significantly longer than that caused by the other species or where no pathogens were identified. Infection with atypical EPEC is associated with prolonged diarrhea.

Probiotic use in clinical practice: what are the risks?

Probiotics have been advocated for the prevention and treatment of a wide range of diseases, and there is strong evidence for their efficacy in some clinical scenarios. Probiotics are now widely used in many countries by consumers and in clinical practice. Given the increasingly widespread use of probiotics, a thorough understanding of their risks and benefits is imperative. In this article we review the safety of probiotics and discuss areas of uncertainty regarding their use. Although probiotics have an excellent overall safety record, they should be used with caution in certain patient groups-particularly neonates born prematurely or with immune deficiency. Because of the paucity of information regarding the mechanisms through which probiotics act, appropriate administrative regimens, and probiotic interactions, further investigation is needed in these areas. Finally, note that the properties of different probiotic species vary and can be strain-specific. Therefore, the effects of one probiotic strain should not be generalized to others without confirmation in separate studies. Careful consideration should be given to these issues before patients are advised to use probiotic supplements in clinical practice.

Essential role of the type III secretion system effector NleB in colonization of mice by Citrobacter rodentium

Attaching and effacing (A/E) pathogens are a significant cause of gastrointestinal illness in humans and animals. All A/E pathogens carry a large pathogenicity island, termed the locus for enterocyte effacement (LEE), which encodes a type III secretion system that translocates several effector proteins into host cells. To identify novel virulence determinants in A/E pathogens, we performed a signature-tagged mutagenesis screen in C57BL/6 mice by using the mouse A/E pathogen Citrobacter rodentium. Five hundred seventy-six derivatives of C. rodentium were tested in pools of 12 mutants. One attenuated mutant carried a transposon insertion in nleB, which encodes a putative effector of the LEE-encoded type III secretion system (T3SS). nleB is present in a genomic pathogenicity island that also encodes another putative effector, NleE, immediately downstream. Using translational fusions with beta-lactamase (TEM-1), we showed that both NleB and NleE were translocated into host cells by the LEE-encoded T3SS of enteropathogenic Escherichia coli. In addition, deletion of the gene encoding NleB in C. rodentium resulted in reduced colonization of mice in single infections and reduced colonic hyperplasia. In contrast, the deletion of other non-LEE-encoded effector genes in C. rodentium, nleC, nleD, or nleE, had no effect on host colonization or disease. These results suggest that nleB encodes an important virulence determinant of A/E pathogens.

Homologues of insecticidal toxin complex genes in Yersinia enterocolitica biotype 1A and their contribution to virulence

Yersinia enterocolitica is an enteric pathogen that consists of six biotypes: 1A, 1B, 2, 3, 4, and 5. Strains of the latter five biotypes can carry a virulence plasmid, known as pYV, and several well-characterized chromosomally encoded virulence determinants. Y. enterocolitica strains of biotype 1A lack the virulence-associated markers of pYV-bearing strains and were once considered to be avirulent. There is growing epidemiological, clinical, and experimental evidence, however, to suggest that some biotype 1A strains are virulent and can cause gastrointestinal disease. To identify potential virulence genes of pathogenic strains of Y. enterocolitica biotype 1A, we used genomic subtractive hybridization to determine genetic differences between two biotype 1A strains: an environmental isolate, Y. enterocolitica IP2222, and a clinical isolate, Y. enterocolitica T83. Among the Y. enterocolitica T83-specific genes we identified were three, tcbA, tcaC, and tccC, that showed homology to the insecticidal toxin complex (TC) genes first discovered in Photorhabdus luminescens. The Y. enterocolitica T83 TC gene homologues were expressed by Y. enterocolitica T83 and were significantly more prevalent among clinical biotype 1A strains than other Yersinia isolates. Inactivation of the TC genes in Y. enterocolitica T83 resulted in mutants which were attenuated in the ability to colonize the gastrointestinal tracts of perorally infected mice. These results indicate that products of the TC gene complex contribute to the virulence of some strains of Y. enterocolitica biotype 1A, possibly by facilitating their persistence in vivo.

Restriction of DNA encoding selectable markers decreases the transformation efficiency of Helicobacter pylori

Helicobacter pylori populations recovered from the human stomach display extensive recombination and quasispecies development, and this suggests frequent exchange of DNA between different strains in vivo. In vitro, however, most H. pylori strains display restriction to the uptake of non-self DNA, as measured using selectable markers, regardless of their competency for transformation with self DNA. We have examined the effect of different selectable markers on double-crossover recombination efficiencies in three reference strains (1061, 26695 & SS1) and one clinical isolate (CHP1) of H. pylori. All strains were efficiently transformable to kanamycin or chloramphenicol resistance by using self-genomic DNA from isogenic mutants bearing the aphA3 or cat cassettes, respectively. However, strains 26695 and CHP1 showed a 3-5-log reduction in transformation efficiency by non-self recombinant DNA containing aphA3, when compared to cat. Strain 1061 readily accepted either cassette, and strain SS1 was poorly tolerant of any non-self DNA. Genome-wide random mutagenesis of these strains was only achievable with a selectable marker that allowed high transformation efficiency. Digestion of 32P-labelled cassettes by H. pylori lysates mirrored the transformation results and indicated that in some strains these cassettes are the targets of enzymatic restriction.

The H-NS protein represses transcription of the eltAB operon, which encodes heat-labile enterotoxin in enterotoxigenic Escherichia coli, by binding to regions downstream of the promoter

Heat-labile enterotoxin, a major virulence determinant of enterotoxigenic Escherichia coli, is encoded by the eltAB operon. To elucidate the molecular mechanism by which the heat-stable nucleoid-structural (H-NS) protein controls transcription of eltAB, the authors constructed an eltAB-lacZ transcriptional fusion and performed beta-galactosidase analysis. The results showed that H-NS protein exerts fivefold repression on transcription from the eltAB promoter at 37 degrees C and 10-fold repression at 22 degrees C. Two silencer regions that were required for H-NS-mediated repression of eltAB expression were identified, both of which were located downstream of the start site of transcription. One silencer was located between +31 and +110, the other between +460 and +556, relative to the start site of transcription, and they worked cooperatively in repression. DNA sequences containing the silencers were predicted to be curved by in silico analysis and bound H-NS protein directly in vitro. Repression of eltAB transcription by H-NS was independent of promoter strength, and the presence of H-NS protein did not affect promoter opening in vitro, indicating that repression was achieved by inhibiting promoter clearance or blocking transcription elongation, probably via DNA looping between the two silencers.

Invasion of epithelial cells by locus of enterocyte effacement-negative enterohemorrhagic Escherichia coli

The majority of enterohemorrhagic Escherichia coli (EHEC) strains associated with severe disease carry the locus of enterocyte effacement (LEE) pathogenicity island, which encodes the ability to induce attaching and effacing lesions on the host intestinal mucosa. While LEE is essential for colonization of the host in these pathogens, strains of EHEC that do not carry LEE are regularly isolated from patients with severe disease, although little is known about the way these organisms interact with the host epithelium. In this study, we compared the adherence properties of clinical isolates of LEE-negative EHEC with those of LEE-positive EHEC O157:H7. Transmission electron microscopy revealed that LEE-negative EHEC O113:H21 was internalized by Chinese hamster ovary (CHO-K1) epithelial cells and that intracellular bacteria were located within a membrane-bound vacuole. In contrast, EHEC O157:H7 remained extracellular and intimately attached to the epithelial cell surface. Quantitative gentamicin protection assays confirmed that EHEC O113:H21 was invasive and also showed that several other serogroups of LEE-negative EHEC were internalized by CHO-K1 cells. Invasion by EHEC O113:H21 was significantly reduced in the presence of the cytoskeletal inhibitors cytochalasin D and colchicine and the pan-Rho GTPase inhibitor compactin, whereas the tyrosine kinase inhibitor genistein had no significant impact on bacterial invasion. In addition, we found that EHEC O113:H21 was invasive for the human colonic cell lines HCT-8 and Caco-2. Overall these studies suggest that isolates of LEE-negative EHEC may employ a mechanism of host cell invasion to colonize the intestinal mucosa.

Detection of enterohaemorrhagic Escherichia coli in patients attending hospital in Melbourne, Australia

AIMS

The objectives of this study were (i) to determine the prevalence of enterohaemorrhagic Escherichia coli (EHEC) in adults and children with diarrhoea attending hospital in Melbourne, and (ii) to evaluate diagnostic assays for the detection of EHEC.

METHODS

EHEC were sought in 860 faecal samples (655 from children) using direct plating, a cytotoxicity assay and an enzyme immunoassay for Shiga toxin (Stx), and PCR for virulence-associated genes of EHEC.

RESULTS

EHEC were isolated from 14 of 858 (1.6%) faecal samples (excluding repeat isolates from one patient). Isolation rates in children (1.7%) and adults (1.5%) were similar. EHEC was detected 2.5 times more frequently in samples that contained blood, but this was not statistically significant. EHEC isolates were heterogeneous in terms of serotype and virulence profile, although all produced EHEC haemolysin. Of the screening assays used, direct plating on EHEC agar, assays for Stx in MacConkey broth inoculated with faeces, and detection of the genes for Stx and EHEC haemolysin were highly sensitive and specific.

CONCLUSIONS

EHEC are an infrequent cause of diarrhoea in Melbourne. EHEC can readily be isolated from faeces by screening enrichment broth cultures for Stx using PCR or enzyme immunoassay, followed by isolation of the bacteria on EHEC agar.

Escherichia coli and community-acquired gastroenteritis, Melbourne, Australia

As part of a study to determine the effects of water filtration on the incidence of community-acquired gastroenteritis in Melbourne, Australia, we examined fecal samples from patients with gastroenteritis and asymptomatic persons for diarrheagenic strains of Escherichia coli. Atypical strains of enteropathogenic E. coli (EPEC) were the most frequently identified pathogens of all bacterial, viral, and parasitic agents in patients with gastroenteritis. Moreover, atypical EPEC were more common in patients with gastroenteritis (89 [12.8%] of 696) than in asymptomatic persons (11 [2.3%] of 489, p < 0.0001). Twenty-two random isolates of atypical EPEC that were characterized further showed marked heterogeneity in terms of serotype, genetic subtype, and carriage of virulence-associated determinants. Apart from the surface protein, intimin, no virulence determinant or phenotype was uniformly present in atypical EPEC strains. This study shows that atypical EPEC are an important cause of gastroenteritis in Melbourne.

A newly discovered verotoxin variant, VT2g, produced by bovine verocytotoxigenic Escherichia coli

A new verotoxin (VT) variant, designated vt2g, was identified from a bovine strain of verocytotoxigenic Escherichia coli (VTEC) serotype O2:H25. When vt2g was aligned with published sequences of vt2 and vt variants, it exhibited the highest DNA sequence homology with vt2 and vt2c. However, vt2g was not detected by vt2-specific primers and probes, although it was partially neutralized by an antiserum to the VT2A subunit. VT2g was cytotoxic for Vero and HeLa cells and was not activated by mouse intestinal mucus. The vt2g gene was detected in 3 of 409 (0.7%) bovine VTEC strains, including serotypes O2:H25, O2:H45 and Ont:H-.

Contribution of long polar fimbriae to the virulence of rabbit-specific enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) is a major of cause of diarrhea among children in developing countries. Although EPEC is a human specific pathogen, some related strains are natural pathogens of animals, including laboratory-bred rabbits. We have identified two chromosomal loci in rabbit-specific EPEC (REPEC) O15:H- strain 83/39, which are predicted to encode long polar fimbriae (LPF). lpf(R154) was identical to a fimbrial gene cluster, lpf(O113), identified previously in enterohemorrhagic E. coli (EHEC) O113:H21. The second locus, lpf(R141), comprised a novel sequence with five predicted open reading frames, lpfA to lpfE, that encoded long fine fimbriae in nonfimbriated E. coli ORN103. The predicted products of lpf(R141) shared identity with components of the lpfABCC'DE gene cluster from EHEC O157:H7, and the fimbriae were similar in morphology and length to LPF from EHEC O157:H7. Interruption of lpf(R141) resulted in significant attenuation of REPEC 83/39 for rabbits with respect to the early stages of colonization and severity of diarrhea. However, there was no significant difference in the number of bacteria shed at later time points or in overall body weight and mortality rate of rabbits infected with lpf(R141) mutant strains or wild-type REPEC 83/39. Although rabbits infected with the lpf(R141) mutants did not develop severe diarrhea, there was evidence of attaching and effacing histopathology, which was indistinguishable in morphology, location, and extent compared to rabbits infected with wild-type REPEC 83/39. The results suggested that lpf(R141) contributes to the early stages of REPEC-mediated disease and that this is important for the development of severe diarrhea in susceptible animals.

Pathogenicity of Yersinia enterocolitica biotype 1A

Yersinia enterocolitica strains of biotype 1A lack the known virulence determinants of strains in other categories, including the Yersinia virulence plasmid (pYV), and several chromosomal markers of pathogenicity. For this reason, and also because Y. enterocolitica strains of biotype 1A are frequently isolated from the environment or asymptomatic individuals, these bacteria are often assumed to be avirulent. On the other hand, there is a considerable body of clinical, epidemiological and experimental evidence to indicate that at least some strains of Y. enterocolitica biotype 1A are able to cause gastrointestinal symptoms which resemble those caused by pYV-bearing strains. The availability of a number of experimental systems, including cell culture and animal models of infection, provides an opportunity to identify and characterise the essential virulence determinants of biotype 1A strains.

Divinatorins A-C, new neoclerodane diterpenoids from the controlled sage Salvia divinorum

Three new neoclerodane diterpenoids, divinatorins A-C (7-9), have been isolated from the leaves of Salvia divinorum. The compounds were identified by spectroscopic methods as derivatives of the antibiotic (-)-hardwickiic acid (10), which was also isolated, along with four other known terpenoids. Neither the crude extract nor 7-9 displayed antimicrobial activity.

Contribution of Efa1/LifA to the adherence of enteropathogenic Escherichia coli to epithelial cells

Enteropathogenic E. coli(EPEC) is an important diarrhoeal pathogen that induces characteristic lesions on the host intestine termed attaching and effacing (A/E) lesions. In this study we have examined the contribution of a large gene, efa1, which is present in all A/E pathogens, to the adherence phenotype of EPEC. An efa- derivative of EPEC JPN15 was constructed and this mutant was significantly less adherent to epithelial cells than the parent strain. The JPN15 efa- derivative was FAS-positive, produced EspA filaments and showed comparable levels of EspA secretion to JPN15. In addition, polyclonal antibodies raised to Efa1 partially inhibited the adherence of JPN15 to cultured epithelial cells. In further work, we showed that human and rabbit hosts infected with an A/E pathogen produced antibodies to Efa1 and we observed that the truncated form of efa1 present in EHEC O157:H7 was specific to that serotype. Generally efa1 was present in its entirety in the genomes of other A/E pathogens. Overall our data suggest that Efa1 has host cell binding activity, at least in tissue culture, and that it is produced during infection. These findings suggest that Efa1 may play a direct role in the pathogenesis of infections caused by A/E pathogens.

Acquired T-helper 1 lymphocyte anergy following infection with Mycobacterium ulcerans

We describe a patient with acquired T-helper lymphocyte anergy to mycobacteria following infection with Mycobacterium ulcerans. Before infection, the patient's peripheral blood mononuclear cells responded to in vitro stimulation with M. ulcerans by producing Th1 cytokines, but, after she developed an ulcer, the response was shifted toward production of Th2 cytokines. Immunomodulatory therapy may be an effective intervention for Buruli ulcer.

Identification of a novel fimbrial gene cluster related to long polar fimbriae in locus of enterocyte effacement-negative strains of enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a food-borne cause of bloody diarrhea and the hemolytic-uremic syndrome (HUS) in humans. Most strains of EHEC belong to a group of bacterial pathogens that cause distinctive lesions on the host intestine termed attaching-and-effacing (A/E) lesions. A/E strains of EHEC, including the predominant serotype, O157:H7, are responsible for the majority of HUS outbreaks worldwide. However, several serotypes of EHEC are not A/E pathogens because they lack the locus of enterocyte effacement (LEE) pathogenicity island. Nevertheless, such strains have been associated with sporadic cases and small outbreaks of hemorrhagic colitis and HUS. Of these LEE-negative organisms, O113:H21 is one of the most commonly isolated EHEC serotypes in many regions. Clinical isolates of LEE-negative EHEC typically express Shiga toxin 2 and carry an approximately 90-kb plasmid that encodes EHEC hemolysin, but in the absence of LEE, little is known about the way in which these pathogens colonize the host intestine. In this study we describe the identification of a novel fimbrial gene cluster related to long polar fimbriae in EHEC O113:H21. This chromosomal region comprises four open reading frames, lpfA to lfpD, and has the same location in the EHEC O113:H21 genome as O island 154 in the prototype EHEC O157:H7 strain, EDL933. In a survey of EHEC of other serotypes, homologues of lpfA(O113) were found in 26 of 28 LEE-negative and 8 of 11 non-O157:H7 LEE-positive EHEC strains. Deletion of the putative major fimbrial subunit gene, lpfA, from EHEC O113:H21 resulted in decreased adherence of this strain to epithelial cells, suggesting that lpf(O113) may function as an adhesin in LEE-negative isolates of EHEC.

Cytokine profiles of patients infected with Mycobacterium ulcerans and unaffected household contacts

Mycobacterium ulcerans, the cause of Buruli ulcer, is an environmental mycobacterium with a distinct geographic distribution. The reasons why only some individuals who are exposed to M. ulcerans develop ulcers are not known but are likely to reflect individual differences in the immune response to infections with this bacterium. In this study, we investigated cytokine profiles of peripheral blood mononuclear cells (PBMC) from 23 Buruli ulcer patients and 25 household contacts in a region of Australia where Buruli ulcer is endemic. The results showed that following stimulation with M. ulcerans or Mycobacterium bovis BCG, PBMC from Buruli ulcer patients mounted a Th2-type response, which was manifested by the production of mRNA for interleukin 4 (IL-4), IL-5, IL-6, and IL-10, whereas unaffected contacts responded mainly with the Th1 cytokines gamma interferon (IFN-gamma) and IL-12. For example, mRNA for IL-4 was detected in 18 of 23 patients but in only 3 of 25 control subjects (P < 0.0001). By contrast, PBMC from 21 of 25 unaffected individuals produced IFN-gamma compared with 3 of 23 patients (P < 0.0001). IFN-gamma release following stimulation with mycobacteria was markedly reduced in affected subjects. Frequencies of antibodies to M. ulcerans in serum samples from affected and unaffected subjects were similar, indicating that many of the control subjects had been exposed to this bacterium. Together, these findings suggest that a Th1-type immune response to M. ulcerans may prevent the development of Buruli ulcer in people exposed to M. ulcerans, but a Th-2 response does not.

Detection of a widespread clone of Pseudomonas aeruginosa in a pediatric cystic fibrosis clinic

Cross-infection by Pseudomonas aeruginosa between unrelated patients with cystic fibrosis (CF) is believed to be uncommon. After detecting a genotypically identical strain of P. aeruginosa in five unrelated children with CF dying from severe lung disease, we determined its prevalence within a large CF clinic using pulsed-field gel electrophoresis and random amplified polymorphic DNA assays. The clinical status of P. aeruginosa-infected patients was also determined. Between September and December 1999, 152 patients, aged 3.9-20.7 years, provided sputum for culture. P. aeruginosa was detected in 118 children of mean (SD) age 13.5 (3.8) years. The genotyping techniques were concordant, showing that 65 (55%) infected patients carried an indistinguishable or closely related strain. No distinctive antibiogram or environmental reservoir was found. Patients with the clonal strain were more likely than those with unrelated isolates to have been hospitalized in the preceding 12 months for respiratory exacerbations. This study demonstrates extensive spread of a single, clonal strain of P. aeruginosa in a large pediatric CF clinic. Whether this strain is also more virulent than sporadic isolates remains to be determined. As transmissible strains could emerge elsewhere, other CF clinics may also need to consider molecular methods of surveillance for cross-infection.

Enteric pathogens, intestinal permeability and nitric oxide production in acute gastroenteritis

BACKGROUND

Aboriginal children hospitalized with diarrheal disease in northern Australia have high rates of acidosis, hypokalemia and osmotic diarrhea, as well as abnormal small bowel permeability and elevated nitric oxide (NO) production.

METHODS

In a study of 291 diarrheal admissions and 84 controls, we examined the relationship of diarrheal severity outcomes with specific enteric pathogens. NO production was measured by urine nitrate plus nitrite excretion on a low nitrate diet, small bowel permeability by the lactulose:rhamnose ratio on a timed blood specimen and stool pathogens by standard microbiologic investigations and PCR.

RESULTS

The addition of diagnostic tests for diarrheagenic Escherichia coli to standard stool microbiologic testing increased the rate of specific diagnoses from 53% to 75%, but with multiple pathogens isolated from 34%. The most frequently isolated pathogens from diarrheal patients were enteroaggregative E. coli (28.9%), rotavirus (26.5%), enteropathogenic E. coli (17.2%), Salmonella spp. (10.7%), Cryptosporidium parvum (7.2%) and Strongyloides stercoralis (7.2%). High geometric mean permeability ratios (95% confidence intervals) occurred with rotavirus (19.6; 15.3 to 25.1), enteroaggregative E. coli (21.2; 15.3 to 29.3) and Cryptosporidium (23.0; 15.1 to 35.1) compared with 9.4 (6.8 to 13.1) for no pathogens. NO production was highest for Cryptosporidium (3.7; 2.3 to 6.1) compared with 0.6 (0.4 to 1.1) for no pathogens. Multiple regression analysis revealed significant associations (P < 0.001) for rotavirus with acidosis and osmotic diarrhea, for Strongyloides with wasting and hypokalemia and for Cryptospoidium with severe and prolonged diarrhea.

CONCLUSIONS

Cryptosporidium, Strongyloides, rotavirus and enteroaggregative E. coli are important contributors to the severe manifestations of acute gastroenteritis in Australian Aboriginal children.

Characterization and evidence of mobilization of the LEE pathogenicity island of rabbit-specific strains of enteropathogenic Escherichia coli

We have characterized the LEE pathogenicity islands (PAIs) of two rabbit-specific strains of enteropathogenic E. coli (REPEC), 83/39 (serotype O15:H-) and 84/110-1 (O103:H2), and have compared them to homologous loci from the human enteropathogenic and enterohaemorrhagic E. coli strains, E2348/69 and EDL933, and another REPEC strain, RDEC-1. All five PAIs contain a 34 kb core region that is highly conserved in gene order and nucleotide sequence. However, the LEE of 83/39 is significantly larger (59 540 basepairs) than those of the human strains, which are less than 44 kb, and has inserted into pheU tRNA. The regions flanking the 34 kb core of 83/39 contain homologues of two putative virulence determinants, efa1/lifA and senA. The LEE of 84/110-1 is approximately 85 kb and is located at pheV tRNA. Its core is almost identical to those of 83/39 and RDEC-1, apart from a larger espF gene, but its flanking regions contain trcA, a putative virulence determinant of EPEC. All three REPEC LEE PAIs contain a gene for an integrase, Int-phe. The LEE PAI of 84/110-1 is also flanked by short direct repeats (representing the 3'-end of pheV tRNA), suggesting that it may be unstable. To investigate this possibility, we constructed a LEE::sacB derivative of 84/110-1 and showed that the PAI was capable of spontaneous deletion. We also showed that Int-phe can mediate site-specific integration of foreign DNA at the pheU tRNA locus of E. coli DH1. Together these results indicate possible mechanisms of mobilization and integration of the LEE PAI.

Identification of a protein secretory pathway for the secretion of heat-labile enterotoxin by an enterotoxigenic strain of Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is an enteric pathogen that causes cholera-like diarrhea in humans and animals. ETEC secretes a heat-labile enterotoxin (LT), which resembles cholera toxin, but the actual mechanism of LT secretion is presently unknown. We have identified a previously unrecognized type II protein secretion pathway in the prototypic human ETEC strain, H10407 (serotype O78:H11). The genes for this pathway are absent from E. coli K-12, although examination of the K-12 genome suggests that it probably once possessed them. The secretory pathway bears significant homology at the amino acid level to the type II protein secretory pathway required by Vibrio cholerae for the secretion of cholera toxin. With this in mind, we determined whether the homologous pathway of E. coli H10407 played a role in the secretion of LT. To this end, we inactivated the pathway by inserting a kanamycin-resistance gene into one of the genes (gspD) of the type II secretion pathway by homologous recombination. LT secretion by E. coli H10407 and the gspD mutant was assayed by enzyme immunoassay, and its biological activity was assessed by using Y-1 adrenal cells. This investigation showed that the protein secretory pathway is functional and necessary for the secretion of LT by ETEC. Our findings have revealed the mechanism for the secretion of LT by ETEC, which previously was unknown, and provide further evidence of close biological similarities of the LT and cholera toxin.

Escherichia coli as a cause of diarrhea

Escherichia coli is the best-known member of the normal microbiota of the human intestine and a versatile gastrointestinal pathogen. The varieties of E. coli that cause diarrhea are classified into named pathotypes, including enterotoxigenic, enteroinvasive, enteropathogenic and enterohemorrhagic E. coli. Individual strains of each pathotype possess a distinct set of virulence-associated characteristics that determine the clinical, pathological and epidemiological features of the diseases they cause. In the present brief review, we summarize the key distinguishing features of the major pathotypes of diarrheagenic E. coli. Knowledge of the pathogenic mechanisms of these bacteria has led to the development of rational interventions for the treatment and prevention of E. coli-induced diarrhea. In addition, investigations into E. coli virulence are providing useful insights into the origins and evolution of bacterial pathogens more generally.

Nationwide study of haemolytic uraemic syndrome: clinical, microbiological, and epidemiological features

AIMS

To establish the incidence and aetiology of haemolytic uraemic syndrome (HUS) in Australia and compare clinical and microbial characteristics of sporadic and outbreak cases.

METHODS

National active surveillance through the Australian Paediatric Surveillance Unit with monthly case notification from paediatricians, July 1994 to June 1998. Children under 15 years presenting with microangiopathic haemolytic anaemia, thrombocytopenia, and acute renal impairment were identified.

RESULTS

Ninety eight cases were identified (incidence 0.64 per 10(5) children <15 years/annum and 1.35 per 10(5) children <5 years/annum). Eighty four were associated with diarrhoea (64 sporadic, 20 constituting an outbreak) and 14 were atypical. Shiga toxin producing Escherichia coli (STEC) O111:H- was the most common isolate in sporadic HUS and caused the outbreak. However O111:H- isolates from outbreak and sporadic cases differed in phage type and subtyping by DNA electrophoresis. STEC isolates from sporadic cases included O26:H-, O113:H21, O130:H11, OR:H9, O157:H-, ONT:H7, and ONT:H-. STEC O157:H7 was not isolated from any case. Only O111:H- isolates produced both Shiga toxins 1 and 2 and possessed genes encoding E coli attaching and effacing gene (intimin) and enterohemolysin. Outbreak cases had worse gastrointestinal and renal disease at presentation and more extrarenal complications.

CONCLUSIONS

Linking national surveillance with a specialised laboratory service allowed estimation of HUS incidence and provided information on its aetiology. In contrast to North America, Japan, and the British Isles, STEC O157:H7 is rare in Australia; however, non-O157:H7 STEC cause severe disease including outbreaks. Disease severity in outbreak cases may relate to yet unidentified virulence factors of the O111:H- strain isolated.

Brachyspira aalborgi infection in four Australian children

AIM

The clinical presentation of four children and adolescents (two males and two females with a mean age of 12.4 years; range 9-16 years) with colorectal spirochetosis is discussed.

RESULTS

Symptoms included persistent diarrhea (n = 2), rectal bleeding (n = 1) and abdominal pain (n = 2). In all patients, colorectal spirochetosis was an unanticipated finding on colonic histology, and the presence of spirochetes was confirmed by the use of electron microscopy. Spirochetes were identified as Brachyspira aalborgi by using PCR amplification of the bacterial 16S rRNA and nicotinamide adenine dinucleotide oxidase sequences in all four patients. No other enteric pathogens were found.

CONCLUSIONS

Although all patients appeared to respond to antibiotic treatment, the clinical significance of B. aalborgi as a human pathogen requires further investigation.