Endophthalmitis: Microbiology and Organism Identification Using Current and Emerging Techniques

Comparative evaluation of 16S rRNA metagenomic sequencing in the diagnosis and understanding of bacterial endophthalmitis

OBJECTIVE

To evaluate the usefulness of metagenomic analysis in the search for causative organisms of bacterial endophthalmitis.

METHODS AND ANALYSIS

Twenty-one consecutive treatment-naïve patients (13 men and 8 women; mean age, 60.8±19.8 years) with suspected endophthalmitis were recruited. Vitrectomy was performed to diagnose and treat endophthalmitis. Bacterial culture and metagenomic analysis of the vitreous body were performed. Extracted DNA was analysed using 16S rRNA sequences, and libraries were sequenced on an Illumina MiSeq sequencer. To compare the bacterial composition in each case, α and β diversities were determined.

RESULTS

Patients were categorised into three groups: endophthalmitis cases with matching predominant organisms according to metagenomic analysis and bacterial culture, those with negative results for bacterial culture and those with negative results in both cases. In 7 of 15 culture-negative cases, results from metagenomic analysis could detect pathogens. The diversity of bacterial populations was significantly lower in the group with positive results for predominant bacteria according to culture and metagenomic analysis. All patients with uveitis were included in the group for which the causative pathogen could not be determined by culture or metagenomic analysis. The structures of bacterial populations significantly differed between the positive and negative groups by culture and metagenomic analysis.

CONCLUSIONS

Metagenomic analysis could be useful for prompt detection of causative pathogens, for precise diagnosis of infection, and as a marker of inflammation processes such as uveitis.

Laboratory Investigations in Infectious Uveitis

Laboratory investigations can play a significant role in the diagnosis and decision-making of infectious uveitis. Though direct demonstration of the infective organism remains the gold standard of diagnosis, it is not always possible with ocular tissues. Recent advancements in molecular techniques have made it possible to overcome these limitations and to identify the genomic DNA of pathogens associated with infectious uveitis. Techniques such as next-generation sequencing can analyze all DNA-based lifeforms, regardless of whether they are bacteria, fungi, viruses, or parasites and have been used in the laboratory diagnosis of intraocular inflammation. On the other hand, serological tests, though they dominate the diagnostic landscape of various infectious etiologies in uveitis in routine clinical practice, have varied specificities and sensitivities in different infectious uveitis. In this review, we focus on various methods of laboratory diagnosis of infectious uveitis and discuss the recent advances in molecular diagnosis and their role in various infectious clinical entities.

Thermosensitive Intravitreal In Situ Implant of Cefuroxime Based on Poloxamer 407 and Hyaluronic Acid

The main method of treatment and prevention of endophthalmitis is a combination of intravitreal and topical administration of antibiotics, such as cefuroxime moxifloxacin or vancomycin. However, this method is ineffective due to the rapid elimination of the drug. This problem can be solved with the help of intravitreal in situ injection systems, which are injected with a syringe into the vitreous body and provide prolonged action of the drug at the focus of inflammation. Under the influence of temperature, the liquid drug undergoes a phase transition and turns into a gel after injection. This ensures its prolonged action. The study aimed to develop an intravitreal in situ cefuroxime delivery system for the treatment of endophthalmitis based on a thermosensitive biodegradable composition of poloxamer 407 and hyaluronic acid. A combination of poloxamer Kolliphor® P407, Kolliphor® P188, and PrincipHYAL® hyaluronic acids of different molecular weights was used as a delivery system. The potency of cefuroxime solid dispersion with polyvinylpyrrolidone-10000, polyethylene glycol-400, and polyethylene glycol-1500 in a 1:2 ratio was studied for prolonged action compared to cefuroxime substance. The experimental formulations were studied for the parameters of gelation temperature in a long-term test (4 months), pH, and release of cefuroxime using dialysis bags. To study the distribution parameter in the vitreous body, an in vitro model (1/13) was developed, which was a hollow agar sphere filled with 1% (w/v) polyacrylate gel. For the superior formulations, a HET-CAM test (chorioallantoic membrane test) was performed to determine the absence of irritant effects. According to the study results, a formulation containing a solid dispersion of cefuroxime:PEG-400 (1:2), the matrix of which contained 18% (w/v) Kolliphor® P407 poloxamer, 3% (w/v) Kolliphor® P188 poloxamer, and 0.5% (w/v) hyaluronic acid (1400-1800), was selected. This sample had an average gelation temperature of 34.6 °C, pH 6.7 ± 0.5, and a pronounced prolonged effect. Only 7.6% was released in 3 h of the experiment, whereas about 38% of cefuroxime was released in 72 h. No irritant effect on the chorioallantoic membrane was observed for any formulations studied.