Single culture media in infectious keratitis

Raman spectroscopy may allow rapid noninvasive screening of keratitis and conjunctivitis

Keratitis and conjunctivitis are the most common ocular diseases, their symptoms are similar and easy to confuse, however infectious conjunctivitis is highly contagious. If misdiagnosed, it may worsen the disease and pose a threat to public health.This is a preclinical study to propose a method for rapid and accurate screening of keratitis and conjunctivitis by combining tear Raman spectroscopy with deep learning models that may be applied to clinical applications in the future.The tears of 16 cases of keratitis patients, 13 cases of conjunctivitis patients and 46 cases of healthy subjects were collected, and their Raman spectra were compared and analyzed. By adding different decibels of Gaussian white noise to expand the data, the performance of the tear Raman spectra with a large sample size in the deep learning model was discussed. Principal component analysis (PCA), partial least squares (PLS) and maximum correlation minimum redundancy (mRMR) were used for feature extraction. The processed data were imported into convolutional neural network (CNN) and recurrent neural network (RNN) depth models for classification. After the data were enhanced and processed by PLS, the highest classification accuracy of healthy subjects and keratitis patients, healthy subjects and conjunctivitis patients, and keratitis and conjunctivitis patients reached 94.8%, 95.4%, and 92.7%, respectively. The results of this study show that the use of large sample tear Raman spectra data combined with PLS feature extraction and depth learning algorithms may have great potential in clinical screening of keratitis and conjunctivitis.

Diagnostic armamentarium of infectious keratitis: A comprehensive review

Infectious keratitis (IK) represents the leading cause of corneal blindness worldwide, particularly in developing countries. A good outcome of IK is contingent upon timely and accurate diagnosis followed by appropriate interventions. Currently, IK is primarily diagnosed on clinical grounds supplemented by microbiological investigations such as microscopic examination with stains, and culture and sensitivity testing. Although this is the most widely accepted practice adopted in most regions, such an approach is challenged by several factors, including indistinguishable clinical features shared among different causative organisms, polymicrobial infection, long diagnostic turnaround time, and variably low culture positivity rate. In this review, we aim to provide a comprehensive overview of the current diagnostic armamentarium of IK, encompassing conventional microbiological investigations, molecular diagnostics (including polymerase chain reaction and mass spectrometry), and imaging modalities (including anterior segment optical coherence tomography and in vivo confocal microscopy). We also highlight the potential roles of emerging technologies such as next-generation sequencing, artificial intelligence-assisted platforms. and tele-medicine in shaping the future diagnostic landscape of IK.

Corneal Culture in Infectious Keratitis: Effect of the Inoculation Method and Media on the Corneal Culture Outcome

Background: To compare two different methods of corneal culture in infectious keratitis: multiple sampling for direct inoculation and enrichment (standard method) and a single sample via transport medium for indirect inoculation (indirect inoculation method). Methods: Prospective inclusion of patients fulfilling predefined criteria of infectious keratitis undergoing corneal culture according to both studied methods in a randomized order. Results: The standard method resulted in a significantly higher proportion of positive culture outcomes among the 94 included episodes of infectious keratitis (61%; 57/94) than the indirect inoculation method (44%; 41/94) (p = 0.002) and a significantly higher proportion of microorganisms than the indirect inoculation method, with a Cohen’s kappa of 0.38 (95% CI: 0.28–0.49) for agreement between the methods. Subanalysis of culture results showed that direct inoculation on gonococcal agar only combined with the indirect inoculation method resulted in a similar rate of culture positive patients and proportion of detected microorganisms to the standard method. Conclusion: Indirect inoculation of one corneal sample cannot replace direct inoculation of multiple corneal samples without loss of information. A combination of directly and indirectly inoculated samples can reduce the number of corneal samples by four without statistically significant differences in culture outcome or in the proportion of detected microorganisms.

Rapid, non-invasive screening of keratitis based on Raman spectroscopy combined with multivariate statistical analysis

This study proposes a multivariate statistical analysis method based on Raman spectroscopy and different dimensionality reduction methods combined with the support vector machine (SVM) algorithm for rapid, non-invasive, high-accuracy classification of keratitis screenings. In this experiment, tear samples from 19 subjects with keratitis and 27 healthy subjects were detected, Raman spectra of the two groups of subjects were compared and analysed, and we found that their spectral intensities were different at 1005 cm^-1 and 1155 cm^-1 Principal component analysis (PCA) and partial least squares (PLS) were used for feature extraction, which greatly reduced the dimensionality of the high-dimensional spectral data. Then, the above two feature extraction methods were used as input to an SVM to build the discriminant diagnosis model. The average accuracy obtained from the PCA-SVM and PLS-SVM models was 77.86 % and 100 %, respectively. Our results suggest that tear Raman spectroscopy combined with multivariate statistical analysis has great potential in screening for keratitis. We expect this technology to could lead to the development of a portable, non-invasive and highly accurate keratitis screening device.

Does the sampling instrument influence corneal culture outcome in patients with infectious keratitis? A retrospective study comparing cotton tipped applicator with knife blade

Objective

This study aimed to compare the efficacy of a cotton tipped applicator and a knife blade in obtaining corneal samples in patients with infectious keratitis.

Methods and analysis

This is a retrospective cohort study of patients with suspected infectious keratitis during 2004–2014. Samples for corneal culture were obtained by a cotton tipped applicator and a knife blade, and directly inoculated on GC agar, blood agar and Sabouraud agar.

Results

In all, 355 patients were included. Corneal sampling by cotton tipped applicator yielded a significantly higher rate of patients with positive corneal culture, 156/355 (43.9%), compared with knife blade, 111/355 (31.3%) (p<0.001). On a patient level, the culture results obtained by the cotton tipped applicator and the knife blade were identical in 269/355 (76%) of the patients. The overall agreement between the two instruments on microbial level was 0.66 (Cohen’s kappa 95% CI 0.60 to 0.72).

Conclusion

Corneal sampling by cotton tipped applicator generated a higher rate of positive corneal cultures and a higher proportion of isolated microbes than by knife blade. Future studies with randomised sampling order are needed to establish which instrument, cotton tipped applicator or knife blade, is the most effective in sampling microbes for direct inoculation in patients with infectious keratitis.

Clinical features and microbiological in bacterial keratitis in a tertiary referral hospital

OBJECTIVE

To describe the clinical features, bacterial agents, and antibiotic sensitivity of bacterial keratitis in the Ophthalmology Department at the University Hospital Fundación Jiménez Díaz (HUFJD) in Madrid.

MATERIALS AND METHODS

A retrospective observational descriptive study using clinical records and reports of corneal scrapings in patients with bacterial keratitis at the HUFJD conducted between 2009 and 2014.

RESULTS

In a sample of 160 patients, gram-positive bacteria were the most prevalent with 64.3% (n=103). Coagulase negative staphylococcus (20.6%), Staphylococcus aureus (19.4%), and Pseudomonas aeruginosa (12.5%) were the most frequent bacteria. The most common risk factor was the use of contact lenses, followed by disease of the ocular surface, and previous ocular surgeries. The antibiotics to which the bacteria were most commonly susceptible were gentamicin (n=114), cotrimoxazole (n=107), vancomycin (n=106), and ciprofloxacin (n=97). The antibiotics to which the bacteria were most commonly resistant were ampicillin (n=59) and erythromycin (n=45).

CONCLUSIONS

In the initial management of bacterial keratitis, the sensitivity and resistance of bacteria to antibiotics should be taken into account. Based on our findings, the use of aminoglycosides, vancomycin and fluoroquinolones is recommended, and, although widely used today, the discontinuation of erythromycin.

Impression membrane for the diagnosis of microbial keratitis

PURPOSE

To evaluate a corneal impression membrane (CIM) for isolation of bacteria, fungi and acanthamoeba in suspected microbial keratitis.

METHODS

Consecutive patients presenting with suspected microbial keratitis were included. For each patient, samples were collected in a random order using a surgical blade and a 4-mm-diameter polytetrafluoroethylene CIM disc, and transported in brain heart infusion broth. Risk factors, best corrected visual acuity (BCVA), size, location, depth and healing time of the ulcer were recorded. The microbial isolation rate was used to compare sampling methods.

RESULTS

130 patients were included (mean age 62.6 years, SD 19.0). An antimicrobial had been used prior to presentation in 36 (27.7%) patients. Mean major and minor ulcer diameters were 2.1 mm (SD 2.0) and 1.6 mm (SD 1.7). Mean healing time was 12.4 days (SD 13.6). BCVA at presentation and following healing was 0.7 (SD 0.7) and 0.62 (SD 0.7) (p=0.34). There were 66 isolates (50.8%); 53 (40.8%) using a CIM and 35 (26.9%) using a blade (p=0.02). ITALIC! Staphylococcus aureus and coagulase-negative staphylococci were the commonest isolates. Isolation rate was not influenced by organism type, although in four cases ITALIC! Acanthamoeba spp. were isolated; three using CIM and one a blade.

CONCLUSIONS

In this study, the isolation of microorganisms from cases of suspected microbial keratitis was significantly higher using a CIM than a surgical blade. A CIM may be a useful alternative or addition for sample collection in microbial keratitis.

The corneal ulcer one-touch study: a simplified microbiological specimen collection method

PURPOSE

To determine if a new, single-sample device (ESwab; Copan Diagnostics, Inc) can simplify the traditional multi-sample approach to specimen collection in infectious keratitis.

DESIGN

Prospective, diagnostic test evaluation.

METHODS

In this institutional study, patients with suspected infectious keratitis meeting traditional criteria for diagnostic corneal specimen collection and culture were randomized to the order of first specimen collection method: ESwab or a sample directly plated for growth on chocolate agar. This was followed by standard samples for blood agar, Gram stain, Sabouraud agar, thioglycolate broth, and brain heart infusion broth in all cases. The specimens collected using the 2 approaches were analyzed separately by the laboratory in a masked fashion. The main outcome measure was positive growth on cultured media.

RESULTS

Eighty-one eyes from 80 consecutive patients were sampled. Culture positivity rate for the multi-sample method and ESwab was 70% and 69%, respectively, with a 75% agreement rate. ESwab sensitivity was 84% (95% confidence interval [CI]: 72%-93%), with a specificity of 67% (95% CI: 45%-84%). Positive and negative predictive values of the ESwab were 86% (95% CI: 74%-94%) and 64% (95% CI: 43%-82%), respectively. There was no difference in positive culture reports with respect to the order of specimen collection technique used.

CONCLUSIONS

The single-sample ESwab method is a more accessible and less cumbersome approach to corneal culturing for ophthalmologists, particularly those in the community setting who do not have access to the full set of traditional culture materials. Culture results using this single-sample approach were comparable to the multi-sample method.

Role of liquid culture media in the laboratory diagnosis of microbial keratitis

PURPOSE

To determine whether liquid culture media are helpful in the diagnosis of infectious keratitis.

DESIGN

Retrospective noncomparative case series.

SUBJECTS AND METHODS

This is a retrospective review of microbiology records of 114 corneal scraping samples from infectious keratitis patients. Samples were processed by corneal smear microscopy (potassium hydroxide with calcofluor white and Gram stains) and culture examination (5% sheep blood agar, sheep blood chocolate agar, Sabouraud dextrose agar, brain heart infusion, thioglycolate broth, and Robertson's cooked meat broth. Cases where at least 1 liquid medium was taken were included in the study and all cases were required to have significant growth in culture as per the institutional criteria. Results of smear examination and culture growth were analyzed.

RESULTS

Out of 114 cases, 44 (38.59%) were bacterial, 62 (54.38%) fungal, and 8 (7.01%) were mixed (bacteria + fungus) infection. Thirty-eight out of 44 cases of bacterial keratitis (86.36%) were diagnosed by solid media alone (criterion 1) and 6 of 44 (13.63%) required liquid media for diagnosis (P < .001). In fungal keratitis, 61 of 62 cases (98.38%) were diagnosed using solid media alone (criterion 1) while 1 case required liquid media for diagnosis. In mixed infection, none of the cases required liquid media for diagnosis of fungal component; however, all 8 cases required liquid media for establishing bacterial component.

CONCLUSIONS

Liquid culture media increase the chance of isolation of bacteria in pure bacterial and/or mixed infection; however, their role in isolating fungus is limited. Owing to overlap in clinical diagnosis of bacterial and fungal keratitis, we recommend inclusion of both solid and liquid culture media in the laboratory diagnosis of nonviral keratitis.

Prevalence and spectrum of bacterial co-infection during fungal keratitis

AIMS

To estimate the propensity of keratomycosis for parallel or secondary bacterial infection and to explore affinities among fungal and bacterial co-isolates.

METHODS

A retrospective review of laboratory records over 24 years yielded 152 episodes of culture positive fungal keratitis. After collating 65 corneal specimens having bacterial co-isolates, polymicrobial co-infection was defined as detection of concordant bacteria on smear and culture or on two or more different media.

RESULTS

30 (20%) keratomycoses met laboratory criteria for polymicrobial infection. The risk of bacterial co-infection was 3.2 (95% confidence interval, 1.7 to 5.8) times greater with yeast keratitis than with filamentous fungal keratitis.

CONCLUSIONS

Bacterial co-infection occasionally complicates fungal keratitis, particularly candidiasis.

Broth cultures yield vs traditional approach in the workup of infectious keratitis

PURPOSE

To elucidate whether BACTEC Peds Plus F broth, usually used for culturing body fluids in paediatric departments, can be used for corneal cultures from cases with clinically suspected infectious keratitis, and to compare yields between this method and traditional methods (blood agar, chocolate agar, a fungal media, and swab transport media).

METHODS

All cases with newly diagnosed, nonviral, clinically suspected infectious keratitis with no prior antibiotic therapy, were cultured both in the BACTEC Peds Plus F broth and the traditional method. McNemar's test was used for pairwise comparisons of the rates of positive growth between the two groups.

RESULTS

In total, 30 eyes were included in this study. The growth rates for the traditional method and the BACTEC broth were similar (50.0 and 53.33%, respectively, P=1.0). The overall growth rate for the two methods combined was 73.33%, which is 45.29% higher than the reported yield in the literature (average of 50.47%).

CONCLUSIONS

Our results show that BACTEC Peds Plus F broth can be used successfully in the work-up of clinically suspected infectious keratitis. The method has, apparently, several advantages over the 'Traditional method:' time-savings, as only one medium needs to be inoculated, transportation to the laboratory is simpler as there is no need for immediate incubation, and there is no need to keep and maintain a supply of fresh agar media. This method is especially suitable for office settings and remote clinics, but also can be used in hospital setting, as an adjunct, when available, to increase the growth yield.

Culture Plate Temperature and Delayed Incubation Effect on Bacterial Recovery

PURPOSE

To discover if initial culturing conditions (plate temperature and time delay to incubation) adversely influence the recovery of organisms associated with bacterial keratitis.

METHODS

The rate of temperature equilibration of culture plates taken from a refrigerator and placed in an incubator and left on the desk was evaluated with a digital thermometer. A standard inoculum for each of five organisms (S. aureus, S. pneumoniae, P. aeruginosa, E. aerogenes, K. oxytoca) isolated from human bacterial keratitis was spread evenly on blood agar plates at refrigerator (Tcold; 4 degrees C), room (Troom; 24 degrees C), and incubator (Twarm; 37 degrees C) temperatures. The plates were then kept at room temperature for 0, 1, 3, 5, and 8 hours before overnight incubation at 37 degrees C (S. pneumoniae under microaerophilic conditions), and the number of colony-forming units was counted.

RESULTS

Cold plates took at least 15 minutes in an incubator to attain room temperature, and up to an hour when left on the desk. Increased organism recovery was found comparing both Twarm and Troom plates (6.2 to 24.8% and 7.0 to 14.7%, respectively, P<0.001) to Tcold plates for all organisms except S. pneumoniae (P=0.057). Comparing Twarm plates to Troom plates demonstrated an increased recovery (P<0.001) for S. aureus. Delayed incubation resulted in decreased recovery for S. pneumoniae (P<0.001).

CONCLUSIONS

Culture plates should preferably be warmed at least to room temperature before inoculation, as well as promptly incubated to increase bacterial recovery from cases of septic keratitis.

Simplifying collection of corneal specimens in cases of suspected bacterial keratitis

Identification of the causative organisms in suspected bacterial keratitis traditionally involves collecting multiple corneal scrapes, which are plated directly onto different solid agar culture media. Difficulties have been reported with this practice, so the development of a simpler diagnostic method in suspected bacterial keratitis would be useful. It is unclear whether a single corneal scrape sent to the microbiology laboratory in a liquid transport culture medium (indirect method) is as reliable for the diagnosis of bacterial keratitis as inoculation of multiple scrapes directly onto agar plates (direct method). To investigate this, bacterial recovery was assessed following transfer and transport of different concentrations and types of bacteria from an artificially contaminated surgical blade into brain heart infusion (BHI). Bacterial recovery rates between the proposed (indirect) and standard (direct) method were then compared after the in vitro inoculation of pig corneas and following specimen collection in patients with presumed bacterial ulcerative keratitis. Recovery of bacteria from contaminated surgical blades was found to be the same from both solid and liquid culture media. There was no significant difference in the numbers of positive cultures from solid (direct) and liquid (indirect) culture media, both in the experimental pig cornea inoculation study (P = 0.34) and in experiments with patients with clinical infections (P = 0.4), with an 85.2% agreement between methods (kappa = 0.61, P < 0.0001). In conclusion, therefore, the collection of two corneal scrapes, one used for Gram staining and the other transported in BHI followed by plating and subculturing in an enrichment medium, provides a simple method for the investigation of presumed bacterial keratitis.

Bacterial keratitis: a prospective clinical and microbiological study

AIM

To define the clinical and microbiological profile of bacterial keratitis at the Jules Gonin Eye Hospital and to test the in vitro bacterial resistance.

METHODS

Patients presenting with bacterial keratitis were prospectively followed; clinical features (age, risk factors, visual acuity) and response to therapy were analysed. Bacteriological profile was determined and the sensitivity/resistance of isolated strains were tested towards 12 ocular antibiotics (NCCLS disc diffusion test).

RESULTS

85 consecutive patients (mean age 44.3 (SD 20.7) years) were prospectively enrolled from 1 March 1997 to 30 November 1998. The following risk factors were identified: contact lens wear, 36%; blepharitis, 21%; trauma, 20%; xerophthalmia, 15%; keratopathies, 8%; and eyelid abnormalities, 6%. The most commonly isolated bacteria were Staphylococcus epidermidis, 40%; Staphylococcus aureus, 22%; Streptococcus pneumoniae, 8%; others Streptococcus species, 5%; Pseudomonas, 9%; Moraxella and Serratia marcescens, 5% each; Bacillus, Corynebacterium, Alcaligenes xyloxidans, Morganella morganii, and Haemophilus influenza, 1% each. 1-15% of strains were resistant to fluoroquinolones, 13-22% to aminoglycosides, 37% to cefazolin, 18% to chloramphenicol, 54% to polymyxin B, 51% to fusidic acid, and 45% to bacitracin. Five of the 85 patients (5.8%) had a poor clinical outcome with a visual loss of one or more lines of visual acuity.

CONCLUSION

Fluoroquinolones appear to be the therapy of choice for bacterial keratitis, but, based upon these in vitro studies, some strains may be resistant.