Relationship of in vitro susceptibility to moxifloxacin and in vivo clinical outcome in bacterial keratitis

A comparison of antimicrobial regimen outcomes and antibiogram development in microbial keratitis: a prospective cohort study in Alexandria, Egypt

INTRODUCTION

Antimicrobial resistance in microbial keratitis has not been previously explored in Alexandria. We aim to recommend effective therapies through identification of etiological agents, determination of antimicrobial susceptibilities, and comparing outcomes of empiric topical antimicrobials.

METHODS

In this 2022 prospective cohort conducted in Alexandria Main University Hospital cornea clinic, antimicrobial susceptibilities of isolated microorganisms from corneal scrapings were detected and antibiograms were developed. Bacterial (BK), fungal (FK), or mixed fungal/bacterial keratitis (MFBK) patients on empiric regimens were compared for ulcer healing, time-to-epithelialization, best-corrected visual acuity, interventions, and complications.

RESULTS

The prevalent microorganisms in 93 positive-cultures were coagulase-negative staphylococci (CoNS, 30.1%), Pseudomonas aeruginosa (14%), and Aspergillus spp. (12.9%). CoNS were susceptible to vancomycin (VAN, 100%) and moxifloxacin (MOX, 90.9%). Gram-negative bacteria showed more susceptibility to gatifloxacin (90.9%) than MOX (57.1%), and to gentamicin (GEN, 44.4%) than ceftazidime (CAZ, 11.8%). Methicillin-resistance reached 23.9% among Gram-positive bacteria. Fungi exhibited 10% resistance to voriconazole (VRC). Percentages of healed ulcers in 49 BK patients using GEN + VAN, CAZ + VAN and MOX were 85.7%, 44.4%, and 64.5%, respectively (p = 0.259). Their median time-to-epithelialization reached 21, 30, and 30 days, respectively (log-rank p = 0.020). In 51 FK patients, more ulcers (88.9%) healed with natamycin (NT) + VRC combination compared to VRC (39.1%) or NT (52.6%) (p = 0.036). Their median time-to-epithelialization was 65, 60, and 22 days, respectively (log-rank p < 0.001). The VRC group required more interventions (60.9%) than NT + VRC-treated group (11.1%) (p = 0.018). In 23 MFBK patients, none healed using NT + CAZ + VAN, while 50% healed using VRC + CAZ + VAN (p = 0.052). Regimens had comparable visual outcomes and complications.

CONCLUSION

Based on the higher detected susceptibility, we recommend empiric MOX in suspected Gram-positive BK, gatifloxacin in Gram-negative BK, and GEN + VAN in severe BK. Due to better outcomes, we recommend NT + VRC in severe FK.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT05655689. Registered December 19, 2022- Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT05655689?cond=NCT05655689.&draw=2&rank=1.

Progressive ulcerative keratitis in dogs in the United Kingdom: Microbial isolates, antimicrobial sensitivity, and resistance patterns

OBJECTIVES

The objective of the study was to identify bacterial pathogens and their antimicrobial sensitivity profile associated with cases of canine progressive ulcerative keratitis.

MATERIALS AND METHODS

Analysis of microbial culture and sensitivity results from dogs with progressive ulcerative keratitis presenting to a UK referral practice between December 2018 and August 2020.

RESULTS

Positive bacterial cultures were obtained from 80/148 (54%) of the canine ulcers sampled with 99 bacterial isolates cultured. Streptococcus canis (n = 29), Pseudomonas aeruginosa (n = 19), and Staphylococcus pseudintermedius (n = 16) were the most common isolates. Pseudomonas aeruginosa was more likely to be isolated whether the ulcer was clinically malacic at the time of sampling (OR = 10.1, p < .001). Ulcers treated prior to culture with fusidic acid were 7.6 times more likely to be positive than those treated with any other antimicrobial(s). Bacterial isolates demonstrated resistance against neomycin (85%), fusidic acid (78%), and tetracycline (68%). Conversely, isolates were most likely to be sensitive to gentamicin (88%), ofloxacin (77%), ciprofloxacin (73%), and chloramphenicol (64%). Antimicrobial combinations of chloramphenicol or gentamicin with a fluoroquinolone (ofloxacin or ciprofloxacin) or chloramphenicol combined with gentamicin were the most effective on in vitro analysis (over 90% susceptibility of all isolates).

CONCLUSION

The most common bacterial species associated with canine progressive ulcerative keratitis in a UK referral population were S. canis, P. aeruginosa, and S. pseudintermedius. Combination antimicrobial therapy is recommended pending culture and sensitivity results given the varied antimicrobial susceptibility profiles and significant bacterial in vitro resistance to antimicrobial monotherapy.

Staphylococcal Enterotoxins Promote Virulence in Bacterial Keratitis

Purpose

Staphylococcus aureus is an important cause of corneal infections (keratitis). To better understand the virulence mechanisms mediating keratitis, a recent comparative genomics study revealed that a set of secreted enterotoxins were found with higher prevalence among ocular versus non-ocular S. aureus clinical infection isolates, suggesting a key role for these toxins in keratitis. Although well known to cause toxic shock syndrome and S. aureus food poisoning, enterotoxins have not yet been shown to mediate virulence in keratitis.

Methods

A set of clinical isolate test strains, including a keratitis isolate that encodes five enterotoxins (sed, sej, sek, seq, ser), its corresponding enterotoxin deletion mutant and complementation strain, a keratitis isolate devoid of enterotoxins, and the non-ocular S. aureus strain USA300 along with its corresponding enterotoxin deletion and complementation strains, were evaluated for cellular adhesion, invasion and cytotoxicity in a primary corneal epithelial model as well as with microscopy. Additionally, strains were evaluated in an in vivo model of keratitis to quantify enterotoxin gene expression and measure disease severity.

Results

We demonstrate that, although enterotoxins do not impact bacterial adhesion or invasion, they do elicit direct cytotoxicity in vitro toward corneal epithelial cells. In an in vivo model, sed, sej, sek, seq, ser were found to have variable gene expression across 72 hours of infection and test strains encoding enterotoxins resulted in increased bacterial burden as well as a reduced host cytokine response.

Conclusions

Our results support a novel role for staphylococcal enterotoxins in promoting virulence in S. aureus keratitis.

Simultaneous control of infection and inflammation with keratin-derived antibacterial peptides targeting TLRs and co-receptors

Controlling infection-driven inflammation is a major clinical dilemma because of limited therapeutic options and possible adverse effects on microbial clearance. Compounding this difficulty is the continued emergence of drug-resistant bacteria, where experimental strategies aiming to augment inflammatory responses for enhanced microbial killing are not applicable treatment options for infections of vulnerable organs. As with corneal infections, severe or prolonged inflammation jeopardizes corneal transparency, leading to devastating vision loss. We hypothesized that keratin 6a-derived antimicrobial peptides (KAMPs) may be a two-pronged remedy capable of tackling bacterial infection and inflammation at once. We used murine peritoneal neutrophils and macrophages, together with an in vivo model of sterile corneal inflammation, to find that nontoxic and prohealing KAMPs with natural 10- and 18-amino acid sequences suppressed lipoteichoic acid (LTA)- and lipopolysaccharide (LPS)-induced NFκB and IRF3 activation, proinflammatory cytokine production, and phagocyte recruitment independently of their bactericidal function. Mechanistically, KAMPs not only competed with bacterial ligands for cell surface Toll-like receptor (TLR) and co-receptors (MD2, CD14, and TLR2) but also reduced cell surface availability of TLR2 and TLR4 through promotion of receptor endocytosis. Topical KAMP treatment effectively alleviated experimental bacterial keratitis, as evidenced by substantial reductions of corneal opacification, inflammatory cell infiltration, and bacterial burden. These findings reveal the TLR-targeting activities of KAMPs and demonstrate their therapeutic potential as a multifunctional drug for managing infectious inflammatory disease.

Enhancing efficacy of existing antibacterials against selected multiple drug resistant bacteria using cinnamic acid-coated magnetic iron oxide and mesoporous silica nanoparticles

Developing new antibacterial drugs by using traditional ways is insufficient to meet existing challenges; hence, new strategies in the field of antibacterial discovery are necessary. An alternative strategy is to improve the efficacy of currently available antibiotics. Herein, the antibacterial efficacy of drugs (Cefixime, Sulfamethoxazole, and Moxifloxacin) and drug-loaded cinnamic acid-coated magnetic iron oxide and mesoporous silica nanoparticles (NPs) was elucidated versus Gram-negative bacteria (Pseudomonas aeruginosa, Klebsiella pneumoniae, neuropathogenic Escherichia coli K1 and Serratia marcescens) and Gram-positive bacteria (Methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pyogenes, Streptococcus pneumoniae, and Bacillus cereus). NPs were synthesized by co-precipitation and the Stöber method, and characterized by Fourier transform-infrared spectroscopy, Zetasizer, and Atomic force microscopy. Lactate dehydrogenase (LDH) assays were accomplished to determine drug cytotoxicity against human cells. Spherical NPs in the range of 118-362 nm were successfully synthesized. Antibacterial assays revealed that drugs conjugated with NPs portray enhanced bactericidal efficacies against multiple drug resistant bacteria compared to the drugs alone. Of note, Cefixime-conjugated NPs against Escherichia coli K1 and Methicillin- resistant Staphylococcus aureus, resulted in the complete eradication of all bacterial isolates tested at significantly lower concentrations compared to the antibiotics alone. Likewise, conjugation of Moxifloxacin resulted in the complete elimination of E. coli K1 and MRSA. Of note, nano-formulated drugs presented negligible cytotoxicity against human cells. These results depict potent, and enhanced efficacy of nano-formulated drugs against medically important bacteria and can be used as alternatives to current antibiotics. Future in vivo studies and clinical studies are warranted in prospective years to realize these expectations.

Short Tryptamine-Based Peptoids as Potential Therapeutics for Microbial Keratitis: Structure-Function Correlation Studies

Peptoids are peptidomimetics that have attracted considerable interest as a promising class of antimicrobials against multi-drug-resistant bacteria due to their resistance to proteolysis, bioavailability, and thermal stability compared to their corresponding peptides. Staphylococcus aureus is a significant contributor to infections worldwide and is a major pathogen in ocular infections (keratitis). S. aureus infections can be challenging to control and treat due to the development of multiple antibiotic resistance. This work describes short cationic peptoids with activity against S. aureus strains from keratitis. The peptoids were synthesized via acid amine-coupling between naphthyl-indole amine or naphthyl-phenyl amine with different amino acids to produce primary amines (series I), mono-guanidines (series II), tertiary amine salts (series III), quaternary ammonium salts (series IV), and di-guanidine (series V) peptoids. The antimicrobial activity of the peptoids was compared with ciprofloxacin, an antibiotic that is commonly used to treat keratitis. All new compounds were active against Staphylococcus aureus S.aureus 38. The most active compounds against S.aur38 were 20a and 22 with MIC = 3.9 μg mL−1 and 5.5 μg mL−1, respectively. The potency of these two active molecules was investigated against 12 S. aureus strains that were isolated from microbial keratitis. Compounds 20a and 22 were active against 12 strains with MIC = 3.2 μg mL−1 and 2.1 μg mL−1, respectively. There were two strains that were resistant to ciprofloxacin (Sa.111 and Sa.112) with MIC = 128 μg mL−1 and 256 μg mL−1, respectively. Compounds 12c and 13c were the most active against E. coli, with MIC > 12 μg mL−1. Cytoplasmic membrane permeability studies suggested that depolarization and disruption of the bacterial cell membrane could be a possible mechanism for antibacterial activity and the hemolysis studies toward horse red blood cells showed that the potent compounds are non-toxic at up to 50 μg mL−1.

Potential new fluoroquinolone treatments for suspected bacterial keratitis

Topical fluoroquinolones (FQs) are an established treatment for suspected microbial keratitis. An increased FQ resistance in some classes of bacterial pathogens is a concern. Some recently developed FQs have an extended spectrum of activity, making them a suitable alternative for topical ophthalmic use. For example, the new generation FQs, avarofloxacin, delafloxacin, finafloxacin, lascufloxacin, nadifloxacin, levonadifloxacin, nemonoxacin and zabofloxacin have good activity against the common ophthalmic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae and several of the Enterobacteriaceae. However, because there are no published ophthalmic break-point concentrations, the susceptibility of an isolated micro-organism to a topical FQ is extrapolated from systemic break-point data and wild type susceptibility. The purpose of this review is to compare the pharmacokinetics and pharmacodynamics of the FQs licensed for topical ophthalmic use with the same parameters for new generation FQs. We performed a literature review of the FQs approved for topical treatment and the new generation FQs licensed to treat systemic infections. We then compared the minimum inhibitory concentrations (MIC) of bacterial isolates and the published concentrations that FQs achieved in the cornea and aqueous. We also considered the potential suitability of new generation FQs for topical use based on their medicinal properties. Notably, we found significant variation in the reported corneal and aqueous FQ concentrations so that reliance on the reported mean concentration may not be appropriate, and the first quartile concentration may be more clinically relevant. The provision of the MIC for the microorganism together with the achieved lower (first) quartile concentration of a FQ in the cornea could inform management decisions such as whether to continue with the prescribed antimicrobial, increase the frequency of application, use a combination of antimicrobials or change treatment.

Spectrum of bacterial keratitis in North India: A retrospective analysis of six years at a tertiary care eye center

Purpose

To analyze the pattern of bacterial pathogens causing infective keratitis and their resistance to the recommended antibiotics over six years.

Methods

It was a retrospective study of 9,357 cases of bacterial keratitis from January 2015 to December 2020, at a tertiary care ophthalmic center. A total of 9,547 corneal specimens were obtained from the study subjects. Demographic details of the patients, pathogenic bacteria isolated, and their antimicrobial susceptibility were noted and analyzed.

Results

Bacterial pathogens were identified in 23.52% of the specimens. The most common isolates were coagulase-negative Staphylococci (60.75%), followed by Pseudomonas aeruginosa (14.23%), Staphylococcus aureus (13.92%), gram negative bacilli of the family Enterobacterales (8.64%), Streptococcus spp. (1.72%), Acinetobacter spp. (0.13%), and other non-fermenting gram-negative bacilli (0.57%). In Staphylococci, 55-80% of isolates were resistant to erythromycin, and 40-70% to fluoroquinolones, while no resistance was observed against vancomycin. 40-60% of isolates of P. aeruginosa were resistant to cephalosporins, 40-55% to fluoroquinolones, and 30-60% to aminoglycosides. Also, 40-80% of isolates of Enterobacterales were resistant to cephalosporins, and 50-60% to fluoroquinolones. Most gram-negative isolates were susceptible to carbapenems and polymyxin B.

Conclusion

To the best of our knowledge, our study is the largest compilation of microbiological profile of bacterial keratitis from North India. It highlights the current trend of the bacterial pathogens that cause infectious keratitis. Staphylococci and Pseudomonas were found to be the most common pathogens. Increased resistance was seen against some of the commonly prescribed empirical antibiotics. Such evidence is useful for restructuring the empirical prescription practices from time to time.

Antimicrobial Activity of a Triple Antibiotic Combination Toward Ocular Pseudomonas aeruginosa Clinical Isolates

Purpose

Pseudomonas aeruginosa is a leading cause of corneal infections. Recently, we discovered an antimicrobial drug combination, polymyxin B/trimethoprim (PT) + rifampin, that displayed impressive efficacy toward P. aeruginosa in both in vitro and in vivo studies. As such, this combination was further evaluated as a potential keratitis therapeutic through testing the combination's efficacy against a diverse set of P. aeruginosa clinical isolates.

Methods

Minimum inhibitory concentrations (MICs) of moxifloxacin, levofloxacin, erythromycin, tobramycin, PT, polymyxin B (alone), trimethoprim (alone), and rifampin were determined for 154 ocular clinical P. aeruginosa isolates, 90% of which were derived from corneal scrapings. Additionally, the efficacy of PT + rifampin was evaluated utilizing fractional inhibitory concentration (FIC) testing.

Results

While 100% of isolates were resistant to erythromycin (average MIC 224 ± 110 µg·mL⁻¹) and trimethoprim (alone) (206 ± 67.3 µg·mL⁻¹), antibiotic resistance was generally found to be low: moxifloxacin (2% of isolates resistant; average MIC 1.08 ± 1.61 µg·mL⁻¹), levofloxacin (3.9%; 1.02 ± 2.96 µg·mL⁻¹), tobramycin (1%; 0.319 ± 1.31 µg·mL⁻¹), polymyxin B (0%; 0.539 ± 0.206 µg·mL⁻¹), PT (0%; 0.416 ± 0.135 µg·mL⁻¹), and rifampin (0%; 23.4 ± 6.86 µg·mL⁻¹). Additionally, FIC testing revealed that PT + rifampin eradicated 100% of isolates demonstrating additive or synergistic activity in 95% of isolates (average FIC index 0.701 ± 0.132).

Conclusions

The drug combination of PT + rifampin was effective against a large panel of clinically relevant P. aeruginosa strains and, as such, may represent a promising therapeutic for P. aeruginosa keratitis.

Translational Relevance

This work furthers the preclinical development of a novel antibiotic combination for the treatment of corneal infections (bacterial keratitis).

A Systematic Review of Multi-decade Antibiotic Resistance Data for Ocular Bacterial Pathogens in the United States

INTRODUCTION

Since 2009, the Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) surveillance study has been assessing in vitro antibiotic resistance for bacterial isolates sourced from ocular infections in the US. The main goal of this systematic review was to compare in vitro resistance data for ocular pathogens from published US studies with the most recently published data from the ARMOR study (2009-2018) and, where possible, to evaluate trends in bacterial resistance over time over all studies.

METHODS

A literature search was conducted using MEDLINE®, BIOSIS Previews®, and EMBASE^® databases (1/1/1995-6/30/2021). Data were extracted from relevant studies and antibiotic susceptibility rates for common ocular pathogens (Staphylococcus aureus, coagulase-negative staphylococci [CoNS], Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae), longitudinal changes in susceptibility, and multidrug resistance (MDR) were compared descriptively.

RESULTS

Thirty-two relevant studies were identified. High in vitro resistance was found among S. aureus and CoNS to fluoroquinolones, macrolides, and methicillin/oxacillin across studies, with high rates of MDR noted, specifically among methicillin-resistant staphylococci. Data from studies pre-dating or overlapping the early years of ARMOR reflected increasing rates of S. aureus resistance to fluoroquinolones, macrolides, methicillin/oxacillin, and aminoglycosides, while the ARMOR data suggested slight decreases in resistance to these classes between 2009 and 2018. Overall, methicillin-resistant S. aureus (MRSA) prevalence peaked from 2005 to 2015 with a possible decreasing trend in more recent years.

DISCUSSION AND CONCLUSIONS

Data from local and regional US datasets were generally consistent with data from the national ARMOR surveillance study. Continued surveillance of ocular bacterial pathogens is needed to track trends such as methicillin resistance and MDR prevalence and any new emerging antibiotic resistance phenotypes. Susceptibility data from ARMOR can inform initial choice of therapy, especially in practice areas where local antibiograms are unavailable.

Double-masked, sham and placebo-controlled trial of corneal cross-linking and topical difluprednate in the treatment of bacterial keratitis: Steroids and Cross-linking for Ulcer Treatment Trial (SCUT II) study protocol

Introduction

Although antibiotics are successful at achieving microbiological cure in infectious keratitis, outcomes are often poor due to corneal scarring. Ideal treatment of corneal ulcers would address both the infection and the inflammation. Adjunctive topical steroid treatment may improve outcomes by reducing inflammation. Corneal cross-linking (CXL) is a novel prospective therapy that may simultaneously reduce both inflammatory cells and bacterial pathogens. The purpose of this study is to determine differences in 6-month visual acuity between standard medical therapy with antibiotics versus antibiotics with adjunctive early topical steroid therapy versus antibiotic treatment plus CXL and early topical steroids.

Methods and analysis

This international, randomised, sham and placebo-controlled, three-arm clinical trial randomises patients with smear positive bacterial ulcers in a 1:1:1 fashion to one of three treatment arms: (1) topical 0.5% moxifloxacin plus topical placebo plus sham CXL; (2) topical 0.5% moxifloxacin plus difluprednate 0.05% plus sham CXL; or (3) the CXL group: topical 0.5% moxifloxacin plus difluprednate 0.05% plus CXL.

Ethics and dissemination

We anticipate that both adjunctive topical steroids and CXL will improved best spectacle corrected visual acuity and also reduce complications such as corneal perforation and the need for therapeutic penetrating keratoplasty. This study will comply with the NIH Data Sharing Policy and Policy on the Dissemination of NIH-Funded Clinical Trial Information and the Clinical Trials Registration and Results Information Submission rule. Our results will be disseminated via ClinicalTrials.gov website, meetings and journal publications. Our data will also be available on reasonable request.

Trial registration number

NCT04097730.

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Hybrid derivative of cathelicidin and human beta defensin-2 against Gram-positive bacteria: A novel approach for the treatment of bacterial keratitis

Bacterial keratitis (BK) is a major cause of corneal blindness globally. This study aimed to develop a novel class of antimicrobial therapy, based on human-derived hybrid host defense peptides (HyHDPs), for treating BK. HyHDPs were rationally designed through combination of functional amino acids in parent HDPs, including LL-37 and human beta-defensin (HBD)-1 to -3. Minimal inhibitory concentrations (MICs) and time-kill kinetics assay were performed to determine the concentration- and time-dependent antimicrobial activity and cytotoxicity was evaluated against human corneal epithelial cells and erythrocytes. In vivo safety and efficacy of the most promising peptide was examined in the corneal wound healing and Staphylococcus aureus (ATCC SA29213) keratitis murine models, respectively. A second-generation HyHDP (CaD23), based on rational hybridization of the middle residues of LL-37 and C-terminal of HBD-2, was developed and was shown to demonstrate good efficacy against methicillin-sensitive and methicillin-resistant S. aureus [MIC = 12.5-25.0 μg/ml (5.2-10.4 μM)] and S. epidermidis [MIC = 12.5 μg/ml (5.2 μM)], and moderate efficacy against P. aeruginosa [MIC = 25-50 μg/ml (10.4-20.8 μM)]. CaD23 (at 25 μg/ml or 2× MIC) killed all the bacteria within 30 min, which was 8 times faster than amikacin (25 μg/ml or 20× MIC). After 10 consecutive passages, S. aureus (ATCC SA29213) did not develop any antimicrobial resistance (AMR) against CaD23 whereas it developed significant AMR (i.e. a 32-fold increase in MIC) against amikacin, a commonly used treatment for BK. Pre-clinical murine studies showed that CaD23 (0.5 mg/ml) achieved a median reduction of S. aureus bioburden by 94% (or 1.2 log10 CFU/ml) while not impeding corneal epithelial wound healing. In conclusion, rational hybridization of human-derived HDPs has led to generation of a potentially efficacious and safe topical antimicrobial agent for treating Gram-positive BK, with no/minimal risk of developing AMR.

In Vitro Antibiotic Resistance among Bacteria from the Cornea in the Antibiotic Resistance Monitoring in Ocular MicRoorganisms Surveillance Study

PURPOSE

This study aimed to report on in vitro susceptibility patterns among corneal isolates collected in the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study.

METHODS

Each year, from 2009 to 2019, Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae isolates cultured from patients with ocular infections at participating ARMOR sites were submitted to a central laboratory for species confirmation and antibiotic susceptibility testing. In this analysis of corneal isolates, odds ratios for concurrent resistance were based on sample proportions, one-way ANOVA was used to evaluate resistance by patient age, and Cochran-Armitage tests were used to examine changes in antibiotic resistance over time.

RESULTS

A total of 1499 corneal isolates were collected from 61 sites over the 11-year period. Overall, 34.5% (148 of 429) of S. aureus and 41.9% (220 of 525) of CoNS isolates were methicillin resistant and had higher odds ratios for concurrent resistance to azithromycin (17.44 and 5.67), ciprofloxacin (39.63 and 12.81), and tobramycin (19.56 and 19.95), respectively, relative to methicillin-susceptible isolates (P < .001, all); also, a high proportion of methicillin-resistant S. aureus (85.1%) and methicillin-resistant CoNS (81.8%) were multidrug resistant (at least three classes of antibiotics). Resistance among S. pneumoniae isolates was highest for azithromycin (33.1%), whereas P. aeruginosa and H. influenzae isolates demonstrated low resistance overall. Among staphylococci, antibiotic resistance differed by patient age (S. aureus: F = 6.46, P < .001; CoNS: F = 4.82, P < .001), and few small changes in resistance (≤3.60% per year), mostly decreases, were observed over time.

CONCLUSIONS

Although rates of in vitro antibiotic resistance among presumed keratitis isolates obtained in ARMOR seemed stable between 2009 and 2019, resistance among staphylococci and pneumococci remains high (and should be considered when treating keratitis).

Antimicrobial resistance of ocular microbes and the role of antimicrobial peptides

Isolation of antimicrobial-resistant microbes from ocular infections may be becoming more frequent. Infections caused by these microbes can be difficult to treat and lead to poor outcomes. However, new therapies are being developed which may help improve clinical outcomes. This review examines recent reports on the isolation of antibiotic-resistant microbes from ocular infections. In addition, an overview of the development of some new antibiotic therapies is given. The recent literature regarding antibiotic use and resistance, isolation of antibiotic-resistant microbes from ocular infections and the development of potential new antibiotics that can be used to treat these infections was reviewed. Ocular microbial infections are a global public health issue as they can result in vision loss which compromises quality of life. Approximately 70 per cent of ocular infections are caused by bacteria including Chlamydia trachomatis, Staphylococcus aureus, and Pseudomonas aeruginosa and fungi such as Candida albicans, Aspergillus spp. and Fusarium spp. Resistance to first-line antibiotics such as fluoroquinolones and azoles has increased, with resistance of S. aureus isolates from the USA to fluoroquinolones reaching 32 per cent of isolates and 35 per cent being methicillin-resistant (MRSA). Lower levels of MRSA (seven per cent) were isolated by an Australian study. Antimicrobial peptides, which are broad-spectrum alternatives to antibiotics, have been tested as possible new drugs. Several have shown promise in animal models of keratitis, especially treating P. aeruginosa, S. aureus or C. albicans infections. Reports of increasing resistance of ocular isolates to mainstay antibiotics are a concern, and there is evidence that for ocular surface disease this resistance translates into worse clinical outcomes. New antibiotics are being developed, but not by large pharmaceutical companies and mostly in university research laboratories and smaller biotech companies. Antimicrobial peptides show promise in treating keratitis.

Trends in Antibiotic Resistance Among Ocular Microorganisms in the United States From 2009 to 2018

Question

What are the antibiotic resistance profiles and trends among common ocular pathogens across the United States?

Findings

In this cross-sectional study of more than 6000 ocular isolates of Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae collected between 2009 and 2018, methicillin resistance and multidrug resistance were prevalent among staphylococci. Antibiotic resistance profiles were mostly unchanged during 10 years.

Meaning

These in vitro antibiotic resistance data may assist clinicians in selecting appropriate antibiotics for treatment of ocular infections.

Importance

Antibiotic resistance in ocular infections can affect treatment outcomes. Surveillance data on evolving antibacterial susceptibility patterns inform the treatment of such infections.

Objective

To assess overall antibiotic resistance profiles and trends among bacterial isolates from ocular sources collected during 10 years.

Design, Setting, and Participants

This cross-sectional study of longitudinal data from the ongoing, nationwide, prospective, laboratory-based surveillance study, the Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) study, included clinically relevant isolates of Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae cultured from patients with ocular infections at US centers from January 1, 2009, to December 31, 2018.

Main Outcomes and Measures

Minimum inhibitory concentrations were determined for various combinations of antibiotics and species. Odds ratios (ORs) were determined for concurrent antibiotic resistance; analysis of variance and χ² tests were used to evaluate resistance rates by patient age and geographic region; Cochran-Armitage tests identified changing antibiotic susceptibility trends over time.

Results

A total of 6091 isolates (2189 S aureus, 1765 CoNS, 590 S pneumoniae, 767 P aeruginosa, and 780 H influenzae) from 6091 patients were submitted by 88 sites. Overall, 765 S aureus (34.9%) and 871 CoNS (49.3%) isolates were methicillin resistant and more likely to be concurrently resistant to macrolides (azithromycin: S aureus: OR, 18.34 [95% CI, 13.64-24.67]; CoNS: OR, 4.59 [95% CI, 3.72-5.66]), fluoroquinolones (ciprofloxacin: S aureus: OR, 22.61 [95% CI, 17.96-28.47]; CoNS: OR, 9.73 [95% CI, 7.63-12.40]), and aminoglycosides (tobramycin: S aureus: OR, 18.29 [95% CI, 13.21-25.32]; CoNS: OR, 6.28 [95% CI, 4.61-8.56]) compared with methicillin-susceptible isolates (P < .001 for all). Multidrug resistance was observed among methicillin-resistant S aureus (577 [75.4%]) and CoNS (642 [73.7%]) isolates. Antibiotic resistance among S pneumoniae isolates was highest for azithromycin (214 [36.3%]), whereas P aeruginosa and H influenzae isolates showed low resistance overall. Differences in antibiotic resistance were found among isolates by patient age (S aureus: F = 28.07, P < .001; CoNS: F = 11.46, P < .001) and geographic region (S aureus: F = 8.03, P < .001; CoNS: F = 4.79, P = .003; S pneumoniae: F = 8.14, P < .001; P aeruginosa: F = 4.32, P = .005). Small changes in antibiotic resistance were noted over time (≤2.5% per year), with decreases in resistance to oxacillin/methicillin (oxacillin: −2.16%; 95% CI, −3.91% to −0.41%; P < .001) and other antibiotics among S aureus isolates, a decrease in ciprofloxacin resistance among CoNS (−1.38%; 95% CI, −2.24% to −0.52%; P < .001), and an increase in tobramycin resistance among CoNS (0.71%; 95% CI, –0.29% to 1.71%; P = .03). Besifloxacin retained consistently low minimum inhibitory concentrations.

Conclusions and Relevance

Antibiotic resistance may be prevalent among staphylococcal isolates, particularly among older patients. In this study, a few small differences in antibiotic resistance were observed by geographic region or longitudinally.

Multifunctional Monoclonal Antibody Targeting Pseudomonas aeruginosa Keratitis in Mice

A worrisome trend in the study and treatment of infectious disease noted in recent years is the increase in multidrug resistant strains of bacteria concurrent with a scarcity of new antimicrobial agents to counteract this rise. This is particularly true amongst bacteria within the Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) designation. P. aeruginosa is one of the most common causes of bacterial keratitis. Therefore, it is of vital importance to characterize new antimicrobial agents with anti-Pseudomonal activity for use with the ocular surface. MEDI3902 is a multifunctional antibody that targets the P. aeruginosa persistence factor Psl exopolysaccharide, and the type 3 secretion protein PcrV. We initially assessed this antibody for ocular surface toxicity. The antimicrobial activity of the antibody was then tested by treating mice with established P. aeruginosa keratitis with both topical and intravenous treatment modalities. MEDI3902, was shown to be non-toxic to the ocular surface of mice when given topically. It was also effective compared to the control antibody at preventing P. aeruginosa keratitis with a one-time treatment at the time of infection. Both topical and intravenous administration of MEDI3902 has been proved significant in treating established keratitis infections as well, speeding the resolution of infection significantly more than that of the control IgG. We report the first use of a topical immunotherapeutic multifunctional agent targeting Psl and type 3 secretion on the ocular surface as an antimicrobial agent. While MEDI3902 has been shown to prevent Pseudomonas biofilm formation in keratitis models when given prophylactically intravitally, we show that MEDI3902 has the capability to also treat an active infection when given intravenously to mice with Pseudomonas keratitis. Our data indicate antibodies are well tolerated and nontoxic on the ocular surface. They reduce infection in mice treated concurrently at inoculation and reduced the signs of cornea pathology in mice with established infection. Taken together, these data indicate treatment with monoclonal antibodies directed against Psl and PcrV may be clinically effective in the treatment of P. aeruginosa keratitis and suggest that the design of further antibodies to be an additional tool in the treatment of bacterial keratitis.

Efficacy of a Novel Ophthalmic Antimicrobial Drug Combination Toward a Large Panel of Staphylococcus aureus Clinical Ocular Isolates From Around the World

PURPOSE

Staphylococcus aureus is a leading cause of keratitis requiring urgent antimicrobial treatment. However, rising antibiotic resistance has rendered current ophthalmic antibiotics increasingly ineffective. First, a diverse, ocular S. aureus strain set was evaluated for resistance to 6 commonly used ophthalmic antibiotics. Next, a recently discovered antimicrobial drug combination containing polymyxin B/trimethoprim (PT) + rifampin that displayed impressive efficacy toward S. aureus in both in vitro and in vivo studies was evaluated as a potential novel keratitis therapeutic through testing this combination's efficacy against the clinical strain set.

METHODS

A total of 163 S. aureus isolates were collected either commercially or from the Flaum Eye Institute, University of Rochester. The minimum inhibitory concentrations of moxifloxacin, levofloxacin, vancomycin, erythromycin, tobramycin, rifampin, and PT were determined for the entire strain set to establish the incidence of resistance to current treatment options among a contemporary clinical isolate set and compared with the performance of PT + rifampin.

RESULTS

Among all 163 isolates tested, high rates of antibiotic resistance were found toward erythromycin (69% resistance), moxifloxacin (33%), levofloxacin (40%), and tobramycin (17%). Conversely, the entire strain set, including multidrug resistant isolates, was sensitive to PT + rifampin, demonstrating the potency of this combination.

CONCLUSIONS

We established that antibiotic resistance is pervasive among clinical S. aureus isolates, underscoring the concern for the effectiveness of current ophthalmic antibiotics. The drug combination of PT + rifampin, however, eradicated 100% of isolates tested, demonstrating the ability to overcome existing circulating resistance factors, and as such, might represent a promising therapeutic for S. aureus keratitis.

Using minimum inhibitory concentration values of common topical antibiotics to investigate emerging antibiotic resistance: A retrospective study of 134 dogs and 20 horses with ulcerative keratitis

OBJECTIVES

To identify the minimum inhibitory concentration (MIC) distribution for commonly used topical antibiotics from isolates of dogs and horses with ulcerative bacterial keratitis, and to investigate changes in MIC values over time and following treatment with topical fluoroquinolones.

ANIMALS STUDIED

One hundred thirty-four client-owned dogs and 20 client-owned horses with bacterial ulcerative keratitis.

PROCEDURE

Minimum inhibitory concentration values for 14 topical antibiotics were reported for canine and equine cases of bacterial ulcerative keratitis between 2013 and 2018. Changes in MIC values over time and after treatment with topical fluoroquinolones were reported.

RESULTS

The three most common bacterial genera isolated were Staphylococcus, Streptococcus, and Pseudomonas. Together, these represented 79.4% of canine cases and 77.4% of equine cases. Overall, isolates from horses tended to have lower MIC values, as did Pseudomonas isolates from both dogs and horses, compared to other bacterial genera, especially Staphylococcus spp. The MIC values of erythromycin and trimethoprim sulfa for Staphylococcus spp., and the MIC value of moxifloxacin for Pseudomonas significantly increased over time. Previous topical fluoroquinolone use was associated with a significant increase in the MIC value of ofloxacin in canine and equine Staphylococcus isolates and current topical fluoroquinolone use was associated with significant increases in the MIC values of ciprofloxacin, moxifloxacin, and ofloxacin in canine Staphylococcus isolates.

CONCLUSION

Patients previously or currently treated with topical fluoroquinolones, particularly in Staphylococcus infections, may require alternative antibiotics or additional antibiotic classes other than fluoroquinolones. Bacterial culture with MIC susceptibility testing should be highly recommended when a Staphylococcal infection is suspected.

Minimum inhibitory concentrations and resistance for selected antimicrobial agents (including imipenem, linezolid and tigecycline) of bacteria obtained from eye infections

Objective: To determine bacteria obtained from eye infections, both resistance and minimal inhibitory concentration (MIC) to gatifloxacin, moxifloxacin, tigecycline, linezolid and imipenem, in vitro. Methods: A cross-sectional descriptive study was undergone with 50 samples from 50 eyes of patients diagnosed with keratitis or endophthalmitis, who came to a consultation at the Fundación Oftalmológica de Santander (Floridablanca, Colombia) from August to November 2014. The MICs of the isolated microorganisms were established through Etest® strips (BioMérieux SA, Marcy-l'Etoile - France). Results: Of the 50 samples in total, 17 different bacteria species or groups were isolated. The main isolate for gram-positives was Methicillin Resistant Coagulase-Negative Staphylococcus (17 samples), and for gram-negatives was Pseudomonas aeruginosa (6 samples). The susceptibility percentages sorted from highest to lowest for gram-positive isolates (n=38) were: imipenem 90.3%, linezolid 87.9%, tigecycline 78.1%, gatifloxacin 68.8% and moxifloxacin 68.8%. For gram-negative isolates (n=12), they were: imipenem 72.7%, gatifloxacin 70%, moxifloxacin 66.7% (no reference cut-off points were found for Pseudomonas aeruginosa), tigecycline 22.2%, and linezolid 0% (as expected according to its inhibition spectrum). Conclusions: Although fourth generation fluoroquinolones are currently the preferred initial empirical monotherapy in our practice, given the increasing bacterial resistance, in cases in which gram-positive bacteria were isolated in the initial staining imipenem, linezolid or tigecycline could be used as an alternative. On the other hand, for cases of gram-negative bacteria, no antimicrobial susceptibility exceeded 80%, so using two antimicrobials looking for a synergy between them could be a better option. Abbreviations: S = Susceptibility, IS = Intermediate susceptibility, R = Resistance.

Klebsiella pneumoniae-induced multiple invasive abscesses: A case report and literature review

RATIONALE

Klebsiella pneumoniae infection can induce multiple invasive abscesses, and the invasive infection is severe and life-threatening.

PATIENT CONCERNS

A 69-year-old previously healthy Chinese male presented with fever, chill, backache, and ocular pain.

DIAGNOSIS

The blood culture results indicated Klebsiella pneumoniae of the K1 serotype. Multiple invasive abscesses in liver, lung, eye, soft tissue, and central nervous system were identified by imaging examination. Subsequently, the patient experienced right ocular pain accompanied by visual disturbance. Tyndall sign was strongly positive, and lens opacity was observed by the ophthalmologist.

INTERVENTIONS

Full-dose and long-term treatment with meropenem was performed. Intraventricular injection of glass and anterior chamber puncture with antibiotics were performed twice. The patient also underwent an evacuation of the brain abscess.

OUTCOMES

The patient's headache and lumbar backache were relieved, his ophthalmodynia disappeared, and his vision recovered after nearly 3 months of treatment.

LESSONS

Imaging examination is very important for severe Klebsiella pneumoniae infection. The choice of antibiotics is complex, and the antimicrobial regimen should be adjusted according to the assessment of illness and the therapeutic effect. Surgical intervention must be considered for patients with multiple invasive abscesses.

Antimicrobial susceptibility and minimal inhibitory concentration of bacteria isolated from the eyes of dogs with keratoconjunctivitis sicca

ABSTRACT: The objective of this study was to evaluate the antimicrobial susceptibility profile of bacteria isolated from the eyes of dogs with keratoconjunctivitis sicca (KCS). We evaluated 65 dogs diagnosed with KCS and 30 healthy dogs (Control Group). Conjunctival swab samples were collected after KCS was diagnosed. Microbiological examinations were performed, including aerobic culture, antimicrobial susceptibility testing and minimum inhibitory concentration (MIC) determination for chloramphenicol, tobramycin, ofloxacin and moxifloxacin. MICs of the fifteen most resistant strains of Staphylococcus pseudintermedius (Staphylococcus intermedius Group, SIG) and the fifteen most resistant strains of gram-negative bacteria were determined. By percentage, the microorganisms exhibited the highest susceptibility to polymyxin B, tobramycin and chloramphenicol and the lowest to tetracycline. Three multi-drug-resistant strains of SIG were detected: one displayed isolated susceptibility to cefazolin, another to vancomycin, and another to polymyxin B and amikacin. The species of bacteria isolated from the eyes of dogs with KCS presented variable susceptibility to the antibiotics tested. We found evidence of the emergence of quinolone-resistant strains of SIG and further evidence of increased ocular prevalence. These findings reinforce the need to identify the bacteria involved and their antimicrobial susceptibility profile, as secondary infections can serve as exacerbating and perpetuating factors in KCS.

Development of a Broad-Spectrum Antimicrobial Combination for the Treatment of Staphylococcus aureus and Pseudomonas aeruginosa Corneal Infections

Staphylococcus aureus and Pseudomonas aeruginosa are two of the most common causes of bacterial keratitis and corresponding corneal blindness. Accordingly, such infections are predominantly treated with broad-spectrum fluoroquinolones, such as moxifloxacin. Yet, the rising fluoroquinolone resistance has necessitated the development of alternative therapeutic options. Herein, we describe the development of a polymyxin B-trimethoprim (PT) ophthalmic formulation containing the antibiotic rifampin, which exhibits synergistic antimicrobial activity toward a panel of contemporary ocular clinical S. aureus and P. aeruginosa isolates, low spontaneous resistance frequency, and in vitro bactericidal kinetics and antibiofilm activities equaling or exceeding the antimicrobial properties of moxifloxacin. The PT plus rifampin combination also demonstrated increased efficacy in comparison to those of either commercial PT or moxifloxacin in a murine keratitis model of infection, resulting in bacterial clearance of 70% in the animals treated. These results suggest that the combination of PT and rifampin may represent a novel antimicrobial agent in the treatment of bacterial keratitis.

Update on the Management of Infectious Keratitis

Infectious keratitis is a major global cause of visual impairment and blindness, often affecting marginalized populations. Proper diagnosis of the causative organism is critical, and although culture remains the prevailing diagnostic tool, newer techniques such as in vivo confocal microscopy are helpful for diagnosing fungus and Acanthamoeba. Next-generation sequencing holds the potential for early and accurate diagnosis even for organisms that are difficult to culture by conventional methods. Topical antibiotics remain the best treatment for bacterial keratitis, and a recent review found all commonly prescribed topical antibiotics to be equally effective. However, outcomes remain poor secondary to corneal melting, scarring, and perforation. Adjuvant therapies aimed at reducing the immune response associated with keratitis include topical corticosteroids. The large, randomized, controlled Steroids for Corneal Ulcers Trial found that although steroids provided no significant improvement overall, they did seem beneficial for ulcers that were central, deep or large, non-Nocardia, or classically invasive Pseudomonas aeruginosa; for patients with low baseline vision; and when started early after the initiation of antibiotics. Fungal ulcers often have worse clinical outcomes than bacterial ulcers, with no new treatments since the 1960s when topical natamycin was introduced. The randomized controlled Mycotic Ulcer Treatment Trial (MUTT) I showed a benefit of topical natamycin over topical voriconazole for fungal ulcers, particularly among those caused by Fusarium. MUTT II showed that oral voriconazole did not improve outcomes overall, although there may have been some effect among Fusarium ulcers. Given an increase in nonserious adverse events, the authors concluded that they could not recommend oral voriconazole. Viral keratitis differs from bacterial and fungal cases in that it is often recurrent and is common in developed countries. The Herpetic Eye Disease Study (HEDS) I showed a significant benefit of topical corticosteroids and oral acyclovir for stromal keratitis. HEDS II showed that oral acyclovir decreased the recurrence of any type of herpes simplex virus keratitis by approximately half. Future strategies to reduce the morbidity associated with infectious keratitis are likely to be multidimensional, with adjuvant therapies aimed at modifying the immune response to infection holding the greatest potential to improve clinical outcomes.

The Utility of Repeat Culture in Fungal Corneal Ulcer Management: A Secondary Analysis of the MUTT-I Randomized Clinical Trial

PURPOSE

To determine whether patients who had a positive repeated culture was predictive of worse clinical outcome than those who achieved microbiological cure at 6 days in the Mycotic Ulcer Treatment Trial I (MUTT-I).

DESIGN

Secondary analysis from a multicenter, double-masked, randomized clinical trial.

METHODS

setting: Multiple hospital sites of the Aravind Eye Care System, India.

STUDY POPULATION

Patients with culture-positive filamentous fungal ulcers and visual acuity of 20/40 to 20/400 reexamined 6 days after initiation of treatment.

INTERVENTION

Corneal scraping and cultures were obtained from study participants at day 6 after enrollment.

MAIN OUTCOME MEASURES

We assessed 3-month best spectacle-corrected visual acuity (BSCVA), 3-month infiltrate/scar size, corneal perforation, and re-epithelialization rates stratified by culture positivity at day 6.

RESULTS

Of the 323 patients with smear-positive ulcers enrolled in MUTT-I, 299 (92.6%) were scraped and cultured 6 days after enrollment. Repeat culture positivity was 31% (92/299). Among patients who tested positive at enrollment, those with positive 6-day cultures had significantly worse 3-month BSCVA (0.39 logMAR; 95% confidence interval [CI]: 0.24-0.44; P < .001), had larger 3-month scar size (0.39 mm; 95% CI: 0.06-0.73; P = .02), were more likely to perforate or require therapeutic penetrating keratoplasty (odds ratio: 6.27; 95% CI: 2.73-14.40; P < .001), and were slower to re-epithelialize (hazard ratio: 0.33; 95% CI: 0.21-0.50; P < .001) than those with a negative 6-day culture result.

CONCLUSIONS

Early microbiological cure on culture is a predictor of clinical response to treatment.

Clinical utility of antimicrobial susceptibility measurement plate covering formulated concentrations of various ophthalmic antimicrobial drugs

PURPOSE

The purpose of this study was to evaluate the clinical utility of SG17, an ophthalmic antimicrobial susceptibility measurement plate.

DESIGN

This was a multicenter, retrospective, observational study.

PATIENTS AND METHODS

Using clinical isolates from patients with ocular infections, drug susceptibility testing using the Clinical Laboratory and Standards Institute standards was routinely conducted at five facilities. The minimum inhibitory concentrations of the isolated strains were determined using SG17 at the Research Foundation for Microbial Diseases of Osaka University. The records of antimicrobial drugs used and the therapeutic course were evaluated for all cases. The susceptibility results from SG17 and routine methods used at each facility were compared.

RESULTS

A total of 112 bacterial strains were isolated from 92 patients. Of these cases, keratitis was the most common (52.2%), followed by conjunctivitis (21.7%) and others (26.1%). Principal signs and symptoms resolved in all patients, indicating that therapeutic effects had been achieved. With SG17, drug susceptibility was determined in 98.9% of isolates compared with 30.4% of isolates determined using conventional methods. By adapting the Clinical Laboratory and Standards Institute standards to SG17 results, we found that 91.3% of patients were susceptible and 7.6% were resistant. In five patients, drugs with a resistant evaluation were initially administered with no effect, and the patients were then switched to drugs with a susceptible evaluation with final resolution, indicating agreement of clinical results with SG17.

CONCLUSION

SG17 can be used to determine drug susceptibility to antimicrobial agents currently used in ophthalmic practice. SG17 is useful for selecting antimicrobial drugs.

Role of steroids in the treatment of bacterial keratitis

Bacterial keratitis can lead to severe visual impairment from corneal ulceration, subsequent scarring, and possible perforation. The mainstay of treatment is topical antibiotics, whereas the use of adjunctive topical corticosteroid drops remains a matter of debate. Herein, we review the rationale for and against the use of topical corticosteroids and we assess their effectiveness and safety in the published randomized controlled trials that have evaluated their role as adjunctive therapy for bacterial corneal ulcers. In the largest study to date, the Steroids for Corneal Ulcers Trial, topical corticosteroid drops were neither helpful nor harmful for the 500 participants as a whole. However, subgroup analyses suggested that topical corticosteroids may be beneficial upon early administration (within 2–3 days after starting antibiotics) for more central corneal ulcers with poorer vision at presentation, for invasive Pseudomonas strains, and for non-Nocardia ulcers. These results are discussed within the limitations of the study.

Proteomics in the Study of Bacterial Keratitis

Bacterial keratitis is a serious ocular infection that can cause severe visual loss if treatment is not initiated at an early stage. It is most commonly caused by Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, or Serratia species. Depending on the invading organism, bacterial keratitis can progress rapidly, leading to corneal destruction and potential blindness. Common risk factors for bacterial keratitis include contact lens wear, ocular trauma, ocular surface disease, ocular surgery, lid deformity, chronic use of topical steroids, contaminated ocular medications or solutions, and systemic immunosuppression. The pathogenesis of bacterial keratitis, which depends on the bacterium-host interaction and the virulence of the invading bacterium, is complicated and not completely understood. This review highlights some of the proteomic technologies that have been used to identify virulence factors and the host response to infections of bacterial keratitis in order to understand the disease process and develop improved methods of diagnosis and treatment. Although work in this field is not abundant, proteomic technologies have provided valuable information toward our current knowledge of bacterial keratitis. More studies using global proteomic approaches are warranted because it is an important tool to identify novel targets for intervention and prevention of corneal damage caused by these virulent microorganisms.

Predisposing Factors, Microbial Characteristics, and Clinical Outcome of Microbial Keratitis in a Tertiary Centre in Hong Kong: A 10-Year Experience

Purpose. To study the risk factors, microbial profile, antibiotic susceptibility pattern, and outcome for microbial keratitis over the past 10 years in a tertiary center in Hong Kong. Methods. All cases with corneal scraping performed in Queen Mary Hospital, Hong Kong from January 2004 to December 2013 were included. Clinical outcome was defined as poor if the final visual acuity (VA) was abnormal or worse than presenting VA, a major complication occurred, or therapeutic keratoplasty was required. Results. 347 scrapes were performed in the 10-year period growing 130 microorganisms (32.3% culture positive rate). Contact lens use was the commonest risk factor. The commonest isolates were coagulase-negative Staphylococcus and Pseudomonas aeruginosa. Fluoroquinolone susceptibility was tested in 47 Gram-negative bacteria with 93.6% susceptibility (100% for Pseudomonas). 90.7% of cases had good visual outcome. Multivariate logistic regression showed age (p = 0.03), trauma (p = 0.006), and ulcer size >3 mm (p = 0.039) to be independently associated with poor outcome. Conclusion. There was no shifting trend in the isolate distribution or emergence of resistant strains in our study. Contact lens wear was the commonest risk factor, with Pseudomonas being the most frequent isolate in this group. It remained 100% susceptible to fluoroquinolones and 97% cases had good visual outcome.

Topical corticosteroids as adjunctive therapy for bacterial keratitis

BACKGROUND

Bacterial keratitis is a serious ocular infectious disease that can lead to severe visual disability. Risk factors for bacterial corneal infection include contact lens wear, ocular surface disease, corneal trauma, and previous ocular or eyelid surgery. Topical antibiotics constitute the mainstay of treatment in cases of bacterial keratitis, whereas the use of topical corticosteroids as an adjunctive therapy to antibiotics remains controversial. Topical corticosteroids are usually used to control inflammation using the smallest amount of the drug. Their use requires optimal timing, concomitant antibiotics, and careful follow-up.

OBJECTIVES

The objective of the review was to assess the effectiveness and safety of corticosteroids as adjunctive therapy for bacterial keratitis. Secondary objectives included evaluation of health economic outcomes and quality of life outcomes.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 6), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to July 2014), EMBASE (January 1980 to July 2014), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to July 2014), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 14 July 2014. We also searched the Science Citation Index to identify additional studies that had cited the only trial included in the original version of this review, reference lists of included trials, earlier reviews, and the American Academy of Ophthalmology guidelines. We also contacted experts to identify any unpublished and ongoing randomized trials.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that had evaluated adjunctive therapy with topical corticosteroids in people with bacterial keratitis who were being treated with antibiotics.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by The Cochrane Collaboration.

MAIN RESULTS

We found four RCTs that met the inclusion criteria of this review. The total number of included participants was 611 (612 eyes), ranging from 30 to 500 participants per trial. One trial was included in the previous version of the review, and we identified three additional trials through the updated searches in July 2014. One of the three smaller trials was a pilot study of the largest study: the Steroids for Corneal Ulcers Trial (SCUT). All trials compared the treatment of bacterial keratitis with topical corticosteroid and without topical corticosteroid and had follow-up periods ranging from two months to one year. These trials were conducted in the USA, Canada, India, and South Africa.All trials reported data on visual acuity ranging from three weeks to one year, and none of them found any important difference between the corticosteroid group and the control group. The pilot study of the SCUT reported that time to re-epithelialization in the steroid group was 53% slower than the placebo group after adjusting for baseline epithelial defect size (hazard ratio (HR) 0.47; 95% confidence interval (CI) 0.23 to 0.94). However, the SCUT did not find any important difference in time to re-epithelialization (HR 0.92; 95% CI 0.76 to 1.11). For adverse events, none of the three small trials found any important difference between the two treatment groups. The investigators of the largest trial reported that more patients in the control group developed intraocular pressure (IOP) elevation (risk ratio (RR) 0.20; 95% CI 0.04 to 0.90). One trial reported quality of life and concluded that there was no difference between the two groups (data not available). We did not find any reports regarding economic outcomes.Although the four trials were generally of good methodological design, all trials had considerable losses to follow-up (10% or more) in the final analyses. Further, three of the four trials were underpowered to detect treatment effect differences between groups and inconsistency in outcome measurements precluded meta-analyses for most outcomes relevant to this review.

AUTHORS' CONCLUSIONS

There is inadequate evidence as to the effectiveness and safety of adjunctive topical corticosteroids compared with no topical corticosteroids in improving visual acuity, infiltrate/scar size, or adverse events among participants with bacterial keratitis. Current evidence does not support a strong effect of corticosteroid, but may be due to insufficient power to detect a treatment effect.

Intraocular penetration of systemic antibiotics in eyes with penetrating ocular injury

PURPOSE

To determine whether penetrating scleral or corneal injury can enhance intraocular penetration of systemic moxifloxacin, vancomycin, and ceftazidime.

METHODS

Thirty rabbits were divided into 3 groups for each antibiotic and then further subdivided to receive either scleral or corneal injury to the right eye. The left eye served as a control. Intravenous antibiotics were given following injury, and eyes were subsequently enucleated. Vitreous antibiotic concentration was determined by high-performance liquid chromatography analysis. Plasma concentration was measured for comparison.

RESULTS

Intravitreal moxifloxacin concentration was unchanged by injury. Minimum inhibitory concentration (MIC90) was achieved in the vitreous against the most common gram-positive endophthalmitis-causing organisms. Intravitreal vancomycin levels were not enhanced by injury and did not reach the MIC90 for gram-positive organisms commonly causing intraocular infection. Intravitreal ceftazidime was increased in the injured eyes, 67% and 73% higher in scleral and corneal injury eyes. It reached MIC90 of many gram-negative bacteria.

CONCLUSIONS

Intravitreal antibiotic penetration of systemic antibiotics with or without penetrating ocular injury varies depending on the antibiotic. For prevention or treatment of gram-positive-bacteria-causing endophthalmitis, intravitreal vancomycin is necessary and provides the most reliable coverage. Systemic ceftazidime can be used for many gram-negative bacteria, but intravitreal injection is recommended for better coverage, especially for more-potent organisms. Systemic moxifloxacin can be considered for most gram-positive and -negative infections due to its excellent intraocular penetration and broad coverage, but the patient's previous history of its topical use and increasing resistance patterns must be considered.

Challenges of ophthalmic care in the developing world

Global blindness exacts an enormous financial and social cost on developing countries. Reducing the prevalence of blindness globally requires a set of strategies that are different from those typically used in developed countries. This was the subject of the 2013 Knapp symposium at the American Ophthalmological Society Annual Meeting, and this article summarizes the presentations of epidemiologists, health care planners, and ophthalmologists. It explores a range of successful strategies from the multinational Vision 2020 Initiative to disease-specific schemes in cataract, trachoma control, infectious corneal ulceration, cytomegalovirus retinitis, and retinopathy of prematurity. In each example, the importance of an attitudinal change set toward public health becomes clear. There is reason for optimism in the struggle against global blindness in large measure because of innovative programs such as those described here.

Cytotoxic clinical isolates of Pseudomonas aeruginosa identified during the Steroids for Corneal Ulcers Trial show elevated resistance to fluoroquinolones

Background

To determine the relationship between type three secretion genotype and fluoroquinolone resistance for P. aeruginosa strains isolated from microbial keratitis during the Steroids for Corneal Ulcers Trial (SCUT) and for two laboratory strains, PA103 and PAO1.

Methods

Confirmed P. aeruginosa isolates from the SCUT were divided into exoU(+) or exoU(−). The exoU(+) strains contained the gene encoding ExoU, a powerful phospholipase toxin delivered into host cells by the type three secretion system. Isolates were then assessed for susceptibility to fluoroquinolone, cephalosporin, and aminoglycoside antibiotics using disk diffusion assays. Etest was used to determine the MIC of moxifloxacin and other fluoroquinolones. Laboratory isolates in which the exoU gene was added or deleted were also tested.

Results

A significantly higher proportion of exoU(+) strains were resistant to ciprofloxacin (p = 0.001), gatifloxacin (p = 0.003), and ofloxacin (p = 0.002) compared to exoU(−) isolates. There was no significant difference between exoU(+) or exoU(−) negative isolates with respect to susceptibility to other antibiotics except gentamicin. Infections involving resistant exoU(+) strains trended towards worse clinical outcome. Deletion or acquisition of exoU in laboratory isolates did not affect fluoroquinolone susceptibility.

Conclusions

Fluoroquinolone susceptibility of P. aeruginosa isolated from the SCUT is consistent with previous studies showing elevated resistance involving exoU encoding (cytotoxic) strains, and suggest worse clinical outcome from infections involving resistant isolates. Determination of exoU expression in clinical isolates of P. aeruginosa may be helpful in directing clinical management of patients with microbial keratitis.

The steroids for corneal ulcers trial (SCUT): secondary 12-month clinical outcomes of a randomized controlled trial

PURPOSE

To determine whether topical corticosteroids as adjunctive therapy for bacterial keratitis improves long-term clinical outcomes.

DESIGN

Randomized, placebo-controlled, double-masked clinical trial.

METHODS

This multicenter trial compared 1.0% prednisolone sodium phosphate to placebo in the treatment of bacterial keratitis among 500 patients with culture-positive ulcers receiving 48 hours of moxifloxacin before randomization. The primary endpoint was 3 months from enrollment, and 399 patients were evaluated at 12 months. The outcomes examined were best spectacle-corrected visual acuity (BSCVA) and scar size at 12 months. Based on previous results, regression models with adjustments for baseline status and/or causative organism were used for analysis.

RESULTS

No significant differences in clinical outcomes by treatment group were seen with the prespecified regression models (BSCVA: -0.04 logMAR, 95% CI, -0.12 to 0.05, P = .39; scar size: 0.03 mm, 95% CI, -0.12 to 0.18, P = .69). A regression model including a Nocardia-treatment arm interaction found corticosteroid use associated with a mean 1-line improvement in BSCVA at 12 months among patients with non-Nocardia ulcers (-0.10 logMAR, 95% CI, -0.19 to -0.02, P = .02). No significant difference was observed in 12-month BSCVA for Nocardia ulcers (0.18 logMAR, 95% CI, -0.04 to 0.41, P = .16). Corticosteroids were associated with larger mean scar size at 12 months among Nocardia ulcers (0.47 mm, 95% CI, 0.06-0.88, P = .02) and no significant difference was identified by treatment for scar size for non-Nocardia ulcers (-0.06 mm, 95% CI, -0.21 to 0.10, P = .46).

CONCLUSIONS

Adjunctive topical corticosteroid therapy may be associated with improved long-term clinical outcomes in bacterial corneal ulcers not caused by Nocardia species.

Combination effect of antibiotics against bacteria isolated from keratitis using fractional inhibitory concentration index

PURPOSE

To study the in vitro interaction of fluoroquinolones such as levofloxacin (LVFX), gatifloxacin (GFLX), or moxifloxacin (MFLX) in combination with tobramycin (TOB) or cefmenoxime (CMX) against clinical isolates of bacteria from keratitis.

METHODS

The activity of each drug alone was determined by an agar dilution method. Checkerboard synergy testing was then performed against 47 isolates, including Staphylococcus species, Streptococcus species, and Pseudomonas aeruginosa. Antimicrobial combinations were classified as synergistic, additive, indifferent, or antagonistic, according to their fractional inhibitory concentration.

RESULTS

The average fractional inhibitory concentration indexes of combined use of LVFX/CMX or GFLX/CMX in Staphylococcus species and Streptococcus species, and LVFX/CMX, GFLX/CMX, MFLX/CMX in gram-negative rods were low. The additive activity of the following drug combinations were seen in more than 70% of isolates: LVFX/CMX and GFLX/CMX against gram-positive cocci and LVFX/CMX, GFLX/CMX, MFLX/CMX against gram-negative rods. No consistent synergistic or antagonistic effect was observed with the combinations used.

CONCLUSION

The combination of LVFX/CMX or GFLX/CMX was predominantly additive for all tested isolates.

Fusarium keratitis in Brazil: genotyping, in vitro susceptibilities, and clinical outcomes

Background

The purpose of this paper is to describe clinical characteristics and determine correlations between clinical outcomes and antifungal susceptibility among molecularly characterized ocular Fusarium isolates in Brazil.

Methods

Forty-one Fusarium isolates obtained from 41 eyes of 41 patients were retrieved from the ophthalmic microbiology laboratory at São Paulo Federal University and grown in pure culture. These isolates were genotyped and antifungal susceptibilities determined for each isolate using a broth microdilution method. The corresponding medical records were reviewed to determine clinical outcomes.

Results

The 41 isolates were genotypically classified as Fusarium solani species complex (36 isolates, 88%), Fusarium oxysporum species complex (two isolates, 5%), Fusarium dimerum species complex (one isolate, 2%) and two isolates that did not group into any of the species complexes. Final best corrected visual acuity varied from 20/20 to light perception and was on average 20/800 (logarithm of the minimum angle of resolution (LogMAR) 1.6). A history of trauma was the most common risk factor, being present in 21 patients (51%). Therapeutic penetrating keratoplasty was necessary in 22 patients (54%). Amphotericin B had the lowest minimum inhibitory concentration for 90% of isolates (MIC₉₀) value (2 μg/mL) and voriconazole had the highest (16 μg/mL). There was an association between a higher natamycin MIC and need for therapeutic penetrating keratoplasty (Mann–Whitney test, P < 0.005).

Conclusion

Trauma was the main risk factor, and therapeutic penetrating keratoplasty was necessary in 54% of patients. Amphotericin B had the lowest MIC₉₀ (2 μg/mL) of the three antifungal agents tested. There was an association between higher natamycin MIC levels and corneal perforation, emphasizing the need for antifungal susceptibility testing and tailoring of antifungal strategies.

Emerging moxifloxacin resistance in Pseudomonas aeruginosa keratitis isolates in South India

PURPOSE

To describe temporal trends in Pseudomonas aeruginosa resistance to moxifloxacin in keratitis isolates from South India.

METHODS

The Steroids for Corneal Ulcers Trial (SCUT) was a randomized, double-masked, placebo-controlled trial assessing outcomes in patients with culture positive bacterial corneal ulcers randomized to receive prednisolone phosphate or placebo. All patients received moxifloxacin, and susceptibility to moxifloxacin was measured at baseline using Etest. We investigated trends in moxifloxacin susceptibility of P. aeruginosa during 2007, 2008, and 2009 isolated in SCUT in South India.

RESULTS

There were 89 P. aeruginosa isolates during 2007, 2008, and 2009 in SCUT that were eligible for this study. There was an increase in the proportion of resistant isolates from 19% in 2007 to 52% in 2009 (p = 0.02, χ(2) test for trend). Logistic regression showed that there was a 2-fold increase in odds of resistance per 1 year increase during the study period (odds ratio 2.16, 95% confidence interval 1.09-4.26, p = 0.027).

CONCLUSIONS

We found a sharp increase in the proportion of isolates that were resistant to moxifloxacin from 2007 to 2009. Further work needs to be done to characterize the nature of this increase.

Fluoroquinolone treatment and susceptibility of isolates from bacterial keratitis

OBJECTIVE

To analyze the relationship between fluoroquinolone use at presentation and minimum inhibitory concentration in bacterial keratitis.

METHODS

The Steroids for Corneal Ulcers Trial was a randomized, double-masked, placebo-controlled trial assessing the effect of adjunctive topical corticosteroid treatment on outcomes in bacterial keratitis. After presentation, all patients were treated with moxifloxacin hydrochloride, 0.5%. We compare antibiotic use at presentation with minimum inhibitory concentration against moxifloxacin for all isolates. Separate analyses accounted for organism species and fluoroquinolone generation.

RESULTS

Topical fluoroquinolone use at presentation was reported in 92 of 480 cases (19.2%). Causative organisms in the 480 cases included Streptococcus pneumoniae (247 cases [51.5%]), Pseudomonas aeruginosa (109 cases [22.7%]), and Nocardia species (55 cases [11.5%]). Isolates from patients who reported fluoroquinolone use at presentation had a 2.01-fold-higher minimum inhibitory concentration (95% CI, 1.39-fold to 2.91-fold; P < .001). Fourth-generation fluoroquinolones were associated with a 3.48-fold-higher minimum inhibitory concentration than those isolates that were not exposed to pretreatment at enrollment (95% CI, 1.99-fold to 6.06-fold; P < .001).

CONCLUSION

This study provides evidence that prior use of fluoroquinolones is associated with antibiotic resistance.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00324168.

Moxifloxacin susceptibility mediates the relationship between causative organism and clinical outcome in bacterial keratitis

PURPOSE

Bacterial keratitis is a sight-threatening infection of the cornea that is one of the leading causes of blindness globally. In this report, we analyze the role of moxifloxacin susceptibility in the relationship between causative organisms and clinical outcome in bacteria keratitis.

METHODS

A mediation analysis is used to assess the role of moxifloxacin susceptibility in the relationship between causative organisms and clinical outcome in bacterial keratitis using data collected in a randomized, controlled trial.

RESULTS

In the Steroids for Corneal Ulcers Trial (SCUT), 500 corneal infections were treated with topical moxifloxacin. The outcome of 3-week best spectacle-corrected visual acuity was significantly associated with an organism (Streptococcus pneumoniae, Pseudomonas aeruginosa, etc., P = 0.008). An indirect effects mediation model suggests that MIC accounted for approximately 13% (95% confidence interval, 3%-24%, P = 0.015) of the effect of the organism on 3-week visual acuity.

CONCLUSIONS

Moxifloxacin mediates the relationship between causative organisms and clinical outcome in bacterial keratitis, and is likely on the causal pathway between the organism and outcome. (ClinicalTrials.gov number, NCT00324168.).

Pharmacological treatment for infectious corneal ulcers

INTRODUCTION

Cornea ulceration and infectious keratitis are leading causes of corneal morbidity and blindness. Infectious causes are among the most frequent and most severe. Management strategies for bacterial corneal ulcers have changed significantly over the last decades, however with a more limited progress in the treatment and management of nonbacterial, infectious ulcers.

AREAS COVERED

This paper provides an overview of the current principles, strategies and treatment choices for infectious corneal ulcers in adults.

EXPERT OPINION

Topical application with a broad-spectrum antimicrobial remains the preferred method for the pharmacological management of infectious corneal ulcers. Increasing reports of clinical failures and in vitro resistance to antibiotics to treat the most common infectious (bacterial) corneal ulcers are increasing concerns. New approaches for improvement in the pharmacological management of corneal ulcers should focus on strategies for a more rational and evidence-based use of current antimicrobials and development of products to modulate the host immune response and to neutralize microbial toxins and other immune modulators.

Infectious keratitis: secreted bacterial proteins that mediate corneal damage

Ocular bacterial infections are universally treated with antibiotics, which can eliminate the organism but cannot reverse the damage caused by bacterial products already present. The three very common causes of bacterial keratitis—Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pneumoniae—all produce proteins that directly or indirectly cause damage to the cornea that can result in reduced vision despite antibiotic treatment. Most, but not all, of these proteins are secreted toxins and enzymes that mediate host cell death, degradation of stromal collagen, cleavage of host cell surface molecules, or induction of a damaging inflammatory response. Studies of these bacterial pathogens have determined the proteins of interest that could be targets for future therapeutic options for decreasing corneal damage.

Nocardia keratitis: clinical course and effect of corticosteroids

PURPOSE

To compare the clinical course of Nocardia species keratitis with keratitis resulting from other bacterial organisms and to assess the effect of corticosteroids as adjunctive therapy using data collected from the Steroids for Corneal Ulcers Trial.

DESIGN

Subgroup analysis of a randomized controlled trial.

METHODS

setting: Multicenter randomized controlled trial. study population: Five hundred patients with bacterial keratitis randomized 1:1 to topical corticosteroid or placebo who had received at least 48 hours of topical moxifloxacin. intervention/observation procedure: Topical prednisolone phosphate 1% or placebo and clinical course of Nocardia keratitis. main outcome measures: Best spectacle-corrected visual acuity and infiltrate or scar size at 3 months from enrollment.

RESULTS

Of 500 patients enrolled in the trial, 55 (11%) had a Nocardia corneal ulcer. Patients with Nocardia ulcers had better presentation visual acuity compared with non-Nocardia ulcers (median Snellen visual acuity, 20/45, compared with 20/145; P < .001) and comparable 3-month visual acuity (median, 20/25, vs 20/40; P = .25). Nocardia ulcers had approximately 2 lines less of improvement in visual acuity compared with non-Nocardia ulcers (0.21 logarithm of the minimal angle of resolution; 95% confidence interval, 0.09 to 0.33 logarithm of the minimal angle of resolution; P = .001). This difference may reflect the better starting visual acuity in patients with Nocardia ulcers. In Nocardia ulcers, corticosteroids were associated with an average 0.4-mm increase in 3-month infiltrate or scar size (95% confidence interval, 0.03 to 0.77 mm; P = .03).

CONCLUSIONS

Nocardia ulcers responded well to treatment. They showed less overall improvement in visual acuity than non-Nocardia ulcers, but had better presentation acuity. Corticosteroids may be associated with worse outcomes.