Comparison of Established Diagnostic Methodologies and a Novel Bacterial smpB Real-Time PCR Assay for Specific Detection of Haemophilus influenzae Isolates Associated with Respiratory Tract Infections

Direct Real-Time PCR for the Detection and Serotyping of Haemophilus influenzae without DNA Extraction

To monitor the burden and changes in Haemophilus influenzae (Hi) disease, direct real-time PCR (drt-PCR) assays have been developed for Hi detection in monoplex form and its six serotypes in triplex form, directly from cerebrospinal fluid (CSF) specimens. These assays target the phoB gene for the species detection (Hi-phoB) and serotype-specific genes in region II of the capsule biosynthesis locus (Hi-abf and Hi-cde), identified through comparative analysis of Hi and non-Hi whole-genome sequences. The lower limit of detection (LLD) is 293 CFU/mL for the Hi-phoB assay and ranged from 11 to 130 CFU/mL for the triplex serotyping assays. Using culture as a reference method, the sensitivity and specificity of Hi-phoB, Hi-abf, and Hi-cde were 100%. Triplex serotyping assays also showed 100% agreement for each serotype compared to their corresponding monoplex serotyping assay. These highly sensitive and specific drt-PCR assays do not require DNA extraction and thereby reduce the time, cost, and handling required to process CSF specimens. Furthermore, triplex drt-PCR assays combine the detection of three serotypes in a single reaction, further improving testing efficiency, which is critical for laboratories that process high volumes of Hi specimens for surveillance and diagnostic purposes.

Ear microbiota and middle ear disease: a longitudinal pilot study of Aboriginal children in a remote south Australian setting

BACKGROUND

Otitis media (OM) is a major disease burden in Australian Aboriginal children, contributing to serious long-term health outcomes. We report a pilot analysis of OM in children attending an outreach ear and hearing clinic in a remote south Australian community over a two-year period. Our study focuses on longitudinal relationships between ear canal microbiota characteristics with nasopharyngeal microbiota, and clinical and treatment variables.

RESULTS

Middle ear health status were assessed in 19 children (aged 3 months to 8 years) presenting in remote western South Australia and medical interventions were recorded. Over the two-year study period, chronic suppurative OM was diagnosed at least once in 7 children (37%), acute OM with perforation in 4 children (21%), OM with effusion in 11 children (58%), while only 1 child had no ear disease. Microbiota analysis of 19 children (51 sets of left and right ear canal swabs and nasopharyngeal swabs) revealed a core group of bacterial taxa that included Corynebacterium, Alloiococcus, Staphylococcus, Haemophilus, Turicella, Streptococcus, and Pseudomonas. Within-subject microbiota similarity (between ears) was significantly greater than inter-subject similarity, regardless of differences in ear disease (p = 0.0006). Longitudinal analysis revealed changes in diagnosis to be associated with more pronounced changes in microbiota characteristics, irrespective of time interval. Ear microbiota characteristics differed significantly according to diagnosis (P (perm) = 0.0001). Diagnoses featuring inflammation with tympanic membrane perforation clustering separately to those in which the tympanic membrane was intact, and characterised by increased Proteobacteria, particularly Haemophilus influenzae, Moraxella catarrhalis, and Oligella. While nasopharyngeal microbiota differed significantly in composition to ear microbiota (P (perm) = 0.0001), inter-site similarity was significantly greater in subjects with perforated tympanic membranes, a relationship that was associated with the relative abundance of H. influenzae in ear samples (rs = - 0.71, p = 0.0003). Longitudinal changes in ear microbiology reflected changes in clinical signs and treatment.

CONCLUSIONS

Children attending the ear and hearing clinic in a remote Aboriginal community present with a broad spectrum of OM conditions and severities, consistent with other remote Aboriginal communities. Ear microbiota characteristics align with OM diagnosis and change with disease course. Nasopharyngeal microbiota characteristics are consistent with the contribution of acute upper respiratory infection to OM aetiology.

Patients with Chronic Obstructive Pulmonary Disease harbour a variation of Haemophilus species

H. haemolyticus is often misidentified as NTHi due to their close phylogenetic relationship. Differentiating between the two is important for correct identification and appropriate treatment of infective organism and to ensure any role of H. haemolyticus in disease is not being overlooked. Speciation however is not completely reliable by culture and PCR methods due to the loss of haemolysis by H. haemolyticus and the heterogeneity of NTHi. Haemophilus isolates from COPD as part of the AERIS study (ClinicalTrials - NCT01360398) were speciated by analysing sequence data for the presence of molecular markers. Further investigation into the genomic relationship was carried out using average nucleotide identity and phylogeny of allelic and genome alignments. Only 6.3% were identified as H. haemolyticus. Multiple in silico methods were able to distinguish H. haemolyticus from NTHi. However, no single gene target was found to be 100% accurate. A group of omp2 negative NTHi were observed to be phylogenetically divergent from H. haemolyticus and remaining NTHi. The presence of an atypical group from a geographically and disease limited set of isolates supports the theory that the heterogeneity of NTHi may provide a genetic continuum between NTHi and H. haemolyticus.

Understanding the impact of antibiotic therapies on the respiratory tract resistome: a novel pooled-template metagenomic sequencing strategy

Determining the effects of antimicrobial therapies on airway microbiology at a population-level is essential. Such analysis allows, for example, surveillance of antibiotic-induced changes in pathogen prevalence, the emergence and spread of antibiotic resistance, and the transmission of multi-resistant organisms. However, current analytical strategies for understanding these processes are limited. Culture- and PCR-based assays for specific microbes require the a priori selection of targets, while antibiotic sensitivity testing typically provides no insight into either the molecular basis of resistance, or the carriage of resistance determinants by the wider commensal microbiota. Shotgun metagenomic sequencing provides an alternative approach that allows the microbial composition of clinical samples to be described in detail, including the prevalence of resistance genes and virulence traits. While highly informative, the application of metagenomics to large patient cohorts can be prohibitively expensive. Using sputum samples from a randomised placebo-controlled trial of erythromycin in adults with bronchiectasis, we describe a novel, cost-effective strategy for screening patient cohorts for changes in resistance gene prevalence. By combining metagenomic screening of pooled DNA extracts with validatory quantitative PCR-based analysis of candidate markers in individual samples, we identify population-level changes in the relative abundance of specific macrolide resistance genes. This approach has the potential to provide an important adjunct to current analytical strategies, particularly within the context of antimicrobial clinical trials.