Sequencing and Functional Annotation of Avian Pathogenic Escherichia coli Serogroup O78 Strains Reveal the Evolution of E. coli Lineages Pathogenic for Poultry via Distinct Mechanisms

Avian pathogenic Escherichia coli (APEC) causes respiratory and systemic disease in poultry. Sequencing of a multilocus sequence type 95 (ST95) serogroup O1 strain previously indicated that APEC resembles E. coli causing extraintestinal human diseases. We sequenced the genomes of two strains of another dominant APEC lineage (ST23 serogroup O78 strains χ7122 and IMT2125) and compared them to each other and to the reannotated APEC O1 sequence. For comparison, we also sequenced a human enterotoxigenic E. coli (ETEC) strain of the same ST23 serogroup O78 lineage. Phylogenetic analysis indicated that the APEC O78 strains were more closely related to human ST23 ETEC than to APEC O1, indicating that separation of pathotypes on the basis of their extraintestinal or diarrheagenic nature is not supported by their phylogeny. The accessory genome of APEC ST23 strains exhibited limited conservation of APEC O1 genomic islands and a distinct repertoire of virulence-associated loci. In light of this diversity, we surveyed the phenotype of 2,185 signature-tagged transposon mutants of χ7122 following intra-air sac inoculation of turkeys. This procedure identified novel APEC ST23 genes that play strain- and tissue-specific roles during infection. For example, genes mediating group 4 capsule synthesis were required for the virulence of χ7122 and were conserved in IMT2125 but absent from APEC O1. Our data reveal the genetic diversity of E. coli strains adapted to cause the same avian disease and indicate that the core genome of the ST23 lineage serves as a chassis for the evolution of E. coli strains adapted to cause avian or human disease via acquisition of distinct virulence genes.     

Adolescents’ and caregivers’ perceptions of caregiver-provided testing and HIV self-testing using oral mucosal transudate tests in Zimbabwe: a short report

ABSTRACT

Uptake of HIV testing remains lower among children and adolescents compared to adults. This study explored adolescents’ perceptions of HIV self-testing (HIVST) and caregivers’ perceptions of testing their children using an oral mucosal transudate (OMT) rapid HIV test (caregiver-provided testing). We conducted 31 interviews with adolescents aged 16–18 years and caregivers of children aged 2–15 years who received an OMT test. Participants described barriers to HIV testing including lack of privacy and the potential for discrimination by community members towards children and adolescents who received an HIV test. Most participants felt caregiver-provided testing and HIVST could address these barriers through increased privacy. Some participants expressed worry about their ability to correctly perform the OMT and their anxious reactions to a positive result. Counseling and assistance from health care workers were viewed as ways to alleviate concerns. Concerns shaped participants’ preferences for facility-based HIVST and caregiver-provided testing. Findings demonstrate HIVST performed by adolescents and caregiver-provided testing could increase the uptake of HIV testing. Concerns related to being able to test correctly and the availability of post-test counseling must be addressed in any future delivery mechanisms.     

Role of intimin-tir interactions and the tir-cytoskeleton coupling protein in the colonization of calves and lambs by Escherichia coli O157:H7

Intimin facilitates intestinal colonization by enterohemorrhagic Escherichia coli O157:H7; however, the importance of intimin binding to its translocated receptor (Tir) as opposed to cellular coreceptors is unknown. The intimin-Tir interaction is needed for optimal actin assembly under adherent bacteria in vitro, a process which requires the Tir-cytoskeleton coupling protein (TccP/EspF(U)) in E. coli O157:H7. Here we report that E. coli O157:H7 tir mutants are at least as attenuated as isogenic eae mutants in calves and lambs, implying that the role of intimin in the colonization of reservoir hosts can be explained largely by its binding to Tir. Mutation of tccP uncoupled actin assembly from the intimin-Tir-mediated adherence of E. coli O157:H7 in vitro but did not impair intestinal colonization in calves and lambs, implying that pedestal formation may not be necessary for persistence. However, an E. coli O157:H7 tccP mutant induced typical attaching and effacing lesions in a bovine ligated ileal loop model of infection, suggesting that TccP-independent mechanisms of actin assembly may operate in vivo.     

Familial silence surrounding HIV and non-disclosure of HIV status to older children and adolescents

Increasing numbers of children with HIV are surviving to adolescence and beyond, many of whom are orphaned. Disclosure of childrens' and adolescents' HIV status has been shown to improve adherence and retention in HIV treatment programmes. We investigated caregiving arrangements and intra-familial experience of HIV and its relationship to HIV disclosure to older children and adolescents. Children aged 6–15 years, newly diagnosed with HIV infection or previously diagnosed but not engaged in HIV care, were recruited from seven primary care clinics in Harare, Zimbabwe. Their caregivers responded to a nurse-led questionnaire. Family history of HIV, disclosure of HIV status to the child and reasons for non-disclosure were ascertained. The association between sociodemographics, caregiving, family HIV history and other characteristics and non-disclosure of HIV status to the child was determined using univariate and multivariate logistic regression. We recruited 385 participants, median age?=?11 years (IQR: 9–13); 52% were female. Disclosure had occurred in 79% of children aged 11–15 years and 19% of children aged 6–10 years. Age under 11 years (adjusted OR [aOR]?=?18.89, 95% confidence interval [CI]?=?10.64–33.55; p?p?=?0.001, being unaware of the parents’ HIV status [aOR]=?32.42, 95% CI?=?13.19–79.71; p?p?=?0.007, were independently associated with non-disclosure. Disclosure outside of the family occurred infrequently and included friends of family (7%), school teacher (8%), school headmaster (4%) and church pastor (6%). High non-disclosure rates were present as well as a lack of discussion about HIV within the family. Disclosure outside of family was low reflecting difficulty in caregivers’ ability to discuss HIV with their child or surrounding community. HIV programmes need to support families in the disclosure process.     

Identification of Salmonella enterica serovar Dublin-specific sequences by subtractive hybridization and analysis of their role in intestinal colonization and systemic translocation in cattle

Salmonella enterica serovar Dublin is a host-restricted serovar associated with typhoidal disease in cattle. In contrast, the fowl-associated serovar S. enterica serovar Gallinarum is avirulent in calves, yet it invades ileal mucosa and induces enteritis at levels comparable to those induced by S. enterica serovar Dublin. Suppression subtractive hybridization was employed to identify S. enterica serovar Dublin strain SD3246 genes absent from S. enterica serovar Gallinarum strain SG9. Forty-one S. enterica serovar Dublin fragments were cloned and sequenced. Among these, 24 mobile-element-associated genes were identified, and 12 clones exhibited similarity with sequences of known or predicted function in other serovars. Three S. enterica serovar Dublin-specific regions were homologous to regions from the genome of Enterobacter sp. strain 638. Sequencing of fragments adjacent to these three sequences revealed the presence of a 21-kb genomic island, designated S. enterica serovar Dublin island 1 (SDI-1). PCR analysis and Southern blotting showed that SDI-1 is highly conserved within S. enterica serovar Dublin isolates but rarely found in other serovars. To probe the role of genes identified by subtractive hybridization in vivo, 24 signature-tagged S. enterica serovar Dublin SD3246 mutants lacking loci not present in Salmonella serovar Gallinarum SG9 were created and screened by oral challenge of cattle. Though attenuation of tagged SG9 and SD3246 Salmonella pathogenicity island-1 (SPI-1) and SPI-2 mutant strains was detected, no obvious defects of these 24 mutants were detected. Subsequently, a ΔSDI-1 mutant was found to exhibit weak but significant attenuation compared with the parent strain in coinfection of calves. SDI-1 mutation did not impair invasion, intramacrophage survival, or virulence in mice, implying that SDI-1 does not influence fitness per se and may act in a host-specific manner.     

Identification of enterohemorrhagic Escherichia coli O26:H- genes required for intestinal colonization in calves

Enterohemorrhagic Escherichia coli (EHEC) infections in humans are an important public health problem and are commonly acquired via contact with ruminant feces. The serogroups that are predominantly associated with human infection in the United States and Europe are O157 and O26. Serotypes O157:H7 and O26:H- differ in their virulence and tissue tropism in calves and therefore may colonize calves by distinct mechanisms. The mechanisms underlying EHEC intestinal colonization and pathogenesis are poorly understood. Signature-tagged mutagenesis was used to identify 59 genes of EHEC O26:H- that are required for the intestinal colonization of calves. Our results indicate important roles for locus of enterocyte effacement (LEE)-encoded type III secreted proteins in intestinal colonization. In addition, colonization is facilitated by cytotoxins, putative type III secreted proteins unlinked to the LEE, a putative fimbrial operon, and numerous genes involved in central metabolism and transport and genes of unknown function. Our data also imply that the elaboration of type I fimbriae by EHEC O26:H- is disadvantageous for persistence within the bovine intestines. These observations have important implications for the design of vaccines to control these important zoonotic pathogens.     

Genotypic heterogeneity of Pasteurella gallinarum as shown by ribotyping and 16S rRNA sequencing

Forty-five strains mainly isolated from chickens in Zimbabwe and Denmark, two pig and three rat isolates all identified as Pasteurella gallinarum by conventional phenotypic tests were characterized by ribotyping, and selected strains were subsequently analysed by 16S rRNA gene sequencing. High genotypic diversity was observed, the number of ribotypes totalling 24. A major group of 47 isolates including the type strain of P. gallinarum clustered at 56% similarity and included 21 ribotypes. Ribotyping showed that some genotypes of P. gallinarum seem to be globally distributed. The three isolates from rodents did not share even a single common ribotype fragment with strains from birds and the pig isolates. Two avian isolates from Denmark and Zimbabwe and the pig strain showed from 97.6 to 99.8% 16S rRNA sequence similarity with the type strain of P. gallinarum and with type strains of Pasteurella volantium and Pasteurella avium . Two rat strains showed 98.6% 16S rRNA gene sequence similarity with each other, but were only related with P. gallinarum at 93% similarity. These isolates showed the highest similarity with [ Actinobacillus ] muris at 96.4 to 95.0% similarity. We suggest that conventional identification of P. gallinarum consequently should consider the source of isolation to obtain a correct diagnosis, and that isolation from animals other than fowl should be confirmed by genotypic analysis such as 16S rRNA gene sequence comparison.