Paradoxical High-Level Spiramycin Resistance and Erythromycin Susceptibility due to 23S rRNA Mutation in Streptococcus constellatus.

Objectives: The aim of the study was to characterize phenotypically and genotypically an uncommon mechanism of resistance to macrolides, lincosamides, and streptogramins (MLS) in a Streptococcus milleri group clinical isolate. Materials and Methods: The isolate UCN96 was recovered from an osteoradionecrosis wound, and was identified using the matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and the partial sequencing of the sodA gene. Antimicrobial susceptibility testing were carried out by the disk diffusion method and minimal inhibitory concentrations (MICs) were determined by the broth microdilution technique. PCR screening was performed for MLS resistance genes described in Gram-positive bacteria. Specific mutations in the ribosomal proteins L3-, L4-, and L22-encoding genes were also screened and those in domain V of the 23S rRNA gene (rrl). The number of mutated copies of the rrl gene was determined using amplification-refractory mutation system quantitative-polymerase chain reaction (qPCR) analysis. Results: The clinical isolate UCN96 was unambiguously identified as Streptococcus constellatus. It was susceptible to all macrolides and lincosamides (ML) antibiotics except spiramycin (MIC >256 mg/L) while it was also resistant to streptogramins. Screening for all acquired resistance genes was negative and no mutation was found in genes coding for L3, L4, and L22 ribosomal proteins. Of interest, a single mutation, A2062C (according to Escherichia coli numbering), was detected in the domain V of 23S rRNA. Conclusion: Mutations at the position 2062 of 23S rRNA have been detected once in Streptococcus pneumoniae, and not yet in other Streptococcus spp. This mechanism is very likely uncommon in Gram-positive bacteria because different copies of 23S rRNA operons should be mutated for development of such a resistance pattern.

Clinical characteristics and treatment outcomes in a cohort of patients with pyogenic and amoebic liver abscess.

BACKGROUND: We describe the clinical features of a cohort of patients with liver abscesses and investigate relationships between clinical, radiological and microbiological findings and mortality. METHODS: Retrospective review of pyogenic (PLA) or amoebic liver abscesses (ALA) diagnosed and treated at a major infectious diseases department in London over 9 years. RESULTS: One hundred forty-one patient records were identified; 132 (93.6%) had PLA and 9 (6.4%) ALA. No organism was identified in 38.6% (51/132); a single bacterial species was isolated in 47.0% (62/132) of PLA, ≥ 2 in 14.4% (19/132). There was weak evidence of variation in abscess size by type of microorganism, with streptococcal PLA typically larger (p = 0.03 for Streptococcus milleri group, p = 0.05 for non-milleri streptococci). Patients with ALA were younger (median 41, IQR 37-51 years) than those with PLA (median 68, IQR 50.5-78 years) (p = 0.003) and all were male (9/9, 100%, (p = 0.03)), with a history of recent travel in the majority (6/9, 66.7% (p = 0.003)). C-reactive protein was higher in ALA than in PLA (p = 0.06). In the entire cohort, loculation (HR = 2.51 (95% CI 1.00-6.32), p = 0.04) and baseline ALP (HR = 4.78 (95% CI 1.19-19.2) per log10 increase, p = 0.03) were associated with mortality. 16S ribosomal RNA (rRNA) analysis was used in a subset of culture-negative cases and increased the diagnostic yield by 13%. CONCLUSIONS: Clinical or radiological features cannot be used to distinguish between PLA and ALA, or help identify the bacterial cause of PLA. However, ALA is more common in young, male patients with a history of travel. 16S rRNA analysis of abscess fluid has a role in improving microbiological diagnosis in culture-negative cases.

The Yin and Yang of Streptococcus Lung Infections in Cystic Fibrosis: a Model for Studying Polymicrobial Interactions.

The streptococci are increasingly recognized as a core component of the cystic fibrosis (CF) lung microbiome, yet the role that they play in CF lung disease is unclear. The presence of the Streptococcus milleri group (SMG; also known as the anginosus group streptococci [AGS]) correlates with exacerbation when these microbes are the predominant species in the lung. In contrast, microbiome studies have indicated that an increased relative abundance of streptococci in the lung, including members of the oral microflora, correlates with impacts on lung disease less severe than those caused by other CF-associated microflora, indicating a complex role for this genus in the context of CF. Recent findings suggest that streptococci in the CF lung microenvironment may influence the growth and/or virulence of other CF pathogens, as evidenced by increased virulence factor production by Pseudomonas aeruginosa when grown in coculture with oral streptococci. Conversely, the presence of P. aeruginosa can enhance the growth of streptococci, including members of the SMG, a phenomenon that could be exacerbated by the fact that streptococci are not susceptible to some of the frontline antibiotics used to treat P. aeruginosa infections. Collectively, these studies indicate the necessity for further investigation into the role of streptococci in the CF airway to determine how these microbes, alone or via interactions with other CF-associated pathogens, might influence CF lung disease, for better or for worse. We also propose that the interactions of streptococci with other CF pathogens is an ideal model to study clinically relevant microbial interactions.

The Streptococcus milleri population of a cystic fibrosis clinic reveals patient specificity and intraspecies diversity.

The genetic relatedness of Streptococcus milleri group isolates from the airways of cystic fibrosis patients was determined by using pulsed-field gel electrophoresis. This study reveals no evidence for patient-to-patient transmission in our patient population; however, within individual patients, complex inter- and intraspecies diversity and dynamics can be observed.

Characterization of Streptococcus milleri group isolates from expectorated sputum of adult patients with cystic fibrosis.

With the recent insights into the Streptococcus milleri group (SMG) as pulmonary pathogens in patients with cystic fibrosis (CF), we sought to characterize 128 isolates from the sputum of adults with CF, along with 45 isolates from patients with invasive diseases for comparison. The tests performed included Lancefield grouping; tests for hemolysis; tests for the production of hyaluronidase, chondroitin sulfatase, DNase, proteases, and hydrogen peroxide; and PCR for the detection of the intermedilysin gene (ily). We also generated biochemical profiles with the Rapid ID Strep 32 API system and tested cell-free supernatants for the presence of the signal molecule autoinducer-2 (AI-2) using a Vibrio harveyi bioassay with a subset of CF strains. The S. intermedius isolates from both strain collections were similar, while the S. constellatus and S. anginosus isolates yielded several biotypes that differed in prevalence between the two strain collections. Beta-hemolytic, Lancefield group C S. constellatus comprised 74.4% of the S. constellatus isolates from patients with CF but only 13.3% of the corresponding isolates from patients with invasive infections. This was the only S. constellatus biotype associated with pulmonary exacerbations. Hyaluronidase-positive S. anginosus was detected only among the isolates from patients with CF. Strain-to-strain variability in AI-2 expression was evident, with the mean values being the highest for S. anginosus, followed by S. constellatus and then S. intermedius. Cluster analysis and 16S rRNA sequencing revealed that the species of SMG could be accurately determined with a minimum of three phenotypic tests: tests for the Lancefield group, hyaluronidase production, and chondroitin sulfatase production. Furthermore, isolates from patients with invasive infections clustered with isolates from the sputum of patients with CF, suggesting that the respiratory tract isolates were equally pathogenic.

Gastrointestinal stromal tumor complicated by Streptococcus milleri bacteremia and liver abscess.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. Often discovered incidentally, GISTs can present with nonspecific abdominal symptoms or more overt symptoms of bleeding, obstruction, or perforation. Despite a myriad of clinical presentations, bacteremia associated with a GIST has not been described. In this report, we present an unusual clinical case that illustrates how GISTs can become infected, and demonstrate the importance of Streptococcus milleri bacteremia as an indicator of possible underlying gastrointestinal neoplasm.

Species-level molecular identification of invasive "Streptococcus milleri" group clinical isolates by nucleic acid sequencing in a centralized regional microbiology laboratory.

Organisms belonging to the "Streptococcus milleri" group are important invasive human pathogens. A detailed understanding of their pathogenesis in human infection has only recently been facilitated by the use of molecular methods to study this group of organisms.