Experimental Bacillus cereus post-traumatic endophthalmitis and treatment with ciprofloxacin

Phosphatidylinositol-specific phospholipase C can decrease Müller cell viability and suppress its phagocytic activity by modulating PI3K/AKT signaling pathway

Bacillus cereus endophthalmitis is a devastating eye infection that causes rapid blindness through the release of extracellular tissue-destructive exotoxins. The phagocytic and antibacterial functions of ocular cells are the keys to limiting ocular bacterial infections. In a previous study, we identified a new virulence gene, plcA-2 (different from the original plcA-1 gene), that was strongly associated with the plcA gene of Listeria monocytogenes. This plcA gene had been confirmed to play an important role in phagocytosis. However, how the Bc-phosphatidylinositol-specific phospholipase C (PI-PLC) proteins encoded by the plcA-1/2 genes affect phagocytes remains unclear in B. cereus endophthalmitis. Here, we found that the enzymatic activity of Bc-PI-PLC-A2 was approximately twofold higher than that of Bc-PI-PLC-A1, and both proteins inhibited the viability of Müller cells. In addition, PI-PLC proteins reduced phagocytosis of Müller cells by decreasing the phosphorylation levels of key proteins in the PI3K/AKT signaling pathway. In conclusion, we showed that PI-PLC proteins contribute to inhibit the viability of and suppress the phagocytosis of Müller cells, providing new insights into the pathogenic mechanism of B. cereus endophthalmitis.

Roles of CCL2 and CCL3 in intraocular inflammation during Bacillus endophthalmitis

Bacillus cereus (B. cereus) endophthalmitis is a vision-threatening bacterial infection. Uncontrolled inflammatory responses are the hallmark of this disease which cause irreversible damage to the retina. We recently reported C-X-C chemokines as a vital modulators which impacted the pathogenesis of this disease. Here, we investigated the impact of two highly upregulated C-C chemokines, CCL2 and CCL3, on intraocular inflammation this disease. B. cereus was injected into the eyes of C57BL/6J (WT), CCL2-/-, and CCL3-/- mice to induce endophthalmitis. Infected eyes were examined for bacterial growth, retinal function, and inflammation. Bacterial growth in CCL2-/- and CCL3-/- mice were similar, but retained retinal function was greater in CCL2-/- and CCL3-/- eyes compared to that of C57BL/6J eyes. The retinal architecture of infected eyes of CCL2-/- mice were conserved for a longer period of time than in infected CCL3-/- eyes. Infected CCL2-/- and CCL3-/- eyes had less inflammation than did infected C57BL/6J eyes. Based on these results, we assessed the efficacies of intravitreal anti-CCL2 or anti-CCL3 with or without the antibiotic gatifloxacin. Compared to infected untreated eyes, there was significantly less inflammation and greater retention of retinal function in eyes treated with anti-CCL2 or anti-CCL3 with gatifloxacin. This study showed that B. cereus endophthalmitis in CCL2-/- mice had a better clinical outcome than in CCL3-/- mice. Intravitreal administration of anti-CCL2 and anti-CCL3 with gatifloxacin significantly reduced inflammation and provided protection of retinal function. These results suggest that CCL2 and CCL3 are prospective anti-inflammatory targets that should be tested along with other antibiotics for treating Bacillus and perhaps other forms of endophthalmitis.

Antibiotic resistance, biofilm formation, and virulence factors of isolates of staphylococcus pseudintermedius from healthy dogs and dogs with keratitis

Canine bacterial keratitis is a common infection that can potentially threaten vision. Staphylococcus pseudintermedius (S. pseudintermedius) is an opportunistic pathogen that has been isolated from the canine conjunctival sac but there are only a few reports on the role of this bacterium in canine keratitis. This study focused on the distribution rate of S. pseudintermedius in the canine conjunctival sac, and the antibiotic resistance, biofilm-producing ability, and dissemination of virulence factors in strains of S. pseudintermedius isolated from healthy dogs and dogs with keratitis. The study included 35 healthy dogs and 40 dogs with keratitis. Bacterial species were confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI–TOF MS). Strains of S. pseudintermedius were screened for resistance against nine different antibiotics by the Kirby–Bauer assay. The ability to produce biofilm was investigated by microtiter plate assay (MtP) and amplification of icaA and icaD genes. Virulence factors in the strains were also evaluated. A total of 132 aerobic bacteria were isolated from the 119 samples in the study. Among them, 67 bacterial strains were isolated from 70 eyes of healthy dogs, and 65 bacterial strains were isolated from 49 eyes of dogs with keratitis. The prevalence of S. pseudintermedius, which was the most frequent bacterial isolate in both the groups, was 20.9% in the healthy group and 23.08% in the keratitis group. Most of the isolates of S. pseudintermedius were sensitive to rifampin (96.6%), oxacillin (100%), and neomycin (96.6%), and resistant to tetracycline (96.6%). Virulence factors such as lip (96.6%), hlgB (96.6%), and hlgA (96.6%) were found in most of the isolates, and 89.66% of isolates were classed as biofilm producers. In conclusion, S. pseudintermedius was the common bacterium in the conjunctivital sac of the healthy dogs and dogs with keratitis in Yangzhou, China, and the presence of virulence factors and biofilm-formation ability were high in the strains isolated from the dogs with keratitis.

Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis

Intraocular bacterial infections are a danger to the vision. Researchers use animal models to investigate the host and bacterial factors and immune response pathways associated with infection to identify viable therapeutic targets and to test drugs to prevent blindness. The intravitreal injection technique is used to inject organisms, drugs, or other substances directly into the vitreous cavity in the posterior segment of the eye. Here, we demonstrated this injection technique to initiate infection in the mouse eye and the technique of quantifying intraocular bacteria. Bacillus cereus was grown in brain heart infusion liquid media for 18 hours and resuspended to a concentration 100 colony forming units (CFU)/0.5 µL. A C57BL/6J mouse was anesthetized using a combination of ketamine and xylazine. Using a picoliter microinjector and glass capillary needles, 0.5 µL of the Bacillus suspension was injected into the mid vitreous of the mouse eye. The contralateral control eye was either injected with sterile media (surgical control) or was not injected (absolute control). At 10 hours post infection, mice were euthanized, and eyes were harvested using sterile surgical tweezers and placed into a tube containing 400 µL sterile PBS and 1 mm sterile glass beads. For ELISAs or myeloperoxidase assays, proteinase inhibitor was added to the tubes. For RNA extraction, the appropriate lysis buffer was added. Eyes were homogenized in a tissue homogenizer for 1-2 minutes. Homogenates were serially diluted 10-fold in PBS and track diluted onto agar plates. The remainder of the homogenates were stored at -80 °C for additional assays. Plates were incubated for 24 hours and CFU per eye was quantified. These techniques result in reproducible infections in mouse eyes and facilitate quantitation of viable bacteria, the host immune response, and omics of host and bacterial gene expression.

Poor prognostic factors in post-traumatic endophthalmitis following open globe injury

AIM

To demonstrate prognostic factors for poor visual outcome in patients with post-traumatic endophthalmitis (PTE) following open globe injury.

METHODS

A retrospective study was conducted on 66 patients (66 eyes) with PTE following open globe injury from 2005 to 2015. Potential factors accounting for good and poor visual outcome were statistically analyzed by Chi-square test and Logistic regression model.

RESULTS

In 66 cases, 39 cases (59%) had a poor visual outcome. Univariate and multivariate Logistic regression analysis identified retained intraocular foreign body (IOFB) as the only factor significantly associated with poor visual outcome [adjusted odds ratio, 4.62; 95% confidence interval (1.04-20.53); P=0.04]. The most common causative agents were gram-positive organisms (83%), of which Bacillus cereus (33%), was the most common pathogen. All cases received intravitreal antibiotic injections. Oral ciprofloxacin was the most used systemic antibiotic (33%). Pars plana vitrectomy was performed in 83% (55/66) of cases. At 6mo follow-up, mean BCVA was 1.74±0.72 logMAR units.

CONCLUSION

In patients with PTE following open globe injury, the only predictor of poor visual outcome is the presence of IOFB. Bacillus cereus is the most isolated microorganism.

The cereus matter of Bacillus endophthalmitis

Bacillus cereus (B. cereus) endophthalmitis is a devastating intraocular infection primarily associated with post-traumatic injuries. The majority of these infections result in substantial vision loss, if not loss of the eye itself, within 12-48 h. Multifactorial mechanisms that lead to the innate intraocular inflammatory response during this disease include the combination of robust bacterial replication, migration of the organism throughout the eye, and toxin production by the organism. Therefore, the window of therapeutic intervention in B. cereus endophthalmitis is quite narrow compared to that of other pathogens which cause this disease. Understanding the interaction of bacterial and host factors is critical in understanding the disease and formulating more rational therapeutics for salvaging vision. In this review, we will discuss clinical and research findings related to B. cereus endophthalmitis in terms of the organism's virulence and inflammogenic potential, and strategies for improving of current therapeutic regimens for this blinding disease.

Controlled Release of Vancomycin From a Thermoresponsive Hydrogel System for the Prophylactic Treatment of Postoperative Acute Endophthalmitis

Purpose

To investigate the efficacy of a poly(ethylene glycol) diacrylate and poly(N-isopropylacrylamide) based thermo-responsive hydrogel drug delivery system (DDS) to deliver prophylactic vancomycin (VAN) following ocular surgery.

Methods

VAN was encapsulated in a hydrogel DDS and characterized in terms of initial burst, release kinetics, bioactivity, and cytotoxicity. Long-Evans rats received an intravitreal injection of Staphylococcus aureus to produce acute endophthalmitis in four experimental groups. One of four treatments were then applied: (1) bolus subconjunctival injection of VAN, (2) blank DDS, (3) saline treatment, and (4) subconjunctival injection of VAN DDS. Animals were scored for infection (0–3) at 12, 24, 48, and 72 hours, and eyes were harvested at 24 and 48 hours for histology.

Results

Following a 36% initial burst, VAN release from the DDS continued at a steady rate for 2 weeks plateauing at 84% after 504 hours. Bioactivity was maintained for all release samples and cytotoxicity analysis for the DDS revealed cell viability >90%. Not until after 12 hours did any of the groups show evidence of infection; however, at 24 hours, animals that received the VAN DDS had significantly lower infection scores (0 ± 0) than those that received a bolus VAN injection, blank DDS, or saline (1.5 ±1.5, 2.3 ± 0.87, and 2.9 ± 0.25; respectively). At 48 and 72 hours, the VAN DDS and bolus VAN treatment groups performed comparably and showed significantly better infection scores than the control groups.

Conclusions

This DDS appears to have promise as a vehicle for short term, prophylactic antibiotic delivery.

Translational Relevance

This DDS may prevent the development of postoperative endophthalmitis.

Prophylactic intravitreal antibiotics reduce the risk of post-traumatic endophthalmitis after repair of open globe injuries

PURPOSE

To investigate efficacy of prophylactic intravitreal antibiotics in reducing incidence of endophthalmitis after repair of open globe injuries. At King Abdulaziz University Hospital, a standard protocol of intravenous vancomycin and ceftazidime was used in all cases.

METHODS

Charts of 353 patients who presented between January 2010 and January 2014 with open globe injury were retrospectively reviewed. In addition, the standard protocol in this cohort included prophylactic intravitreal antibiotics in high-risk cases at time of primary repair. High-risk cases were identified based on the presence of one or more of the following risk factors: dirty wound, retained intra-ocular foreign body (IOFB), rural setting, delayed primary repair of >24 hr and ruptured lens capsule. Rate of endophthalmitis in this recent cohort was compared with that of a previous cohort admitted for primary repair between May 1996 and May 2008 (641 patients). In the previous cohort, protocol did not include prophylactic intravitreal antibiotics.

RESULTS

Rates of clinically suspected endophthalmitis and culture-positive endophthalmitis were higher in previous cohort (24 of 641 eyes; 3.7% and 12 of 641 eyes; 1.9%, respectively) compared to recent cohort (six of 353 eyes; 1.7% and two of 353 eyes; 0.6%, respectively). In high-risk groups, rates of suspected endophthalmitis and culture-positive endophthalmitis were higher in previous cohort (19 of 345 eyes; 5.5% and 12 of 345 eyes; 3.5%, respectively) compared to the recent cohort (five of 200 eyes; 2.5% and two of 200 eyes; 1.0%, respectively).

CONCLUSION

Prophylactic intravitreal antibiotics reduce risk of endophthalmitis after repair of open globe injuries.

Risk Factors for Culture-Positive Endophthalmitis after Repair of Open Globe Injuries

Purpose

To identify risk factors for the development of culture-positive endophthalmitis after repair of open globe injuries.

Methods

We retrospectively reviewed the medical records of 629 consecutive patients with open globe injuries admitted to King Abdulaziz University Hospital between May 1996 and January 2008.

Results

Endophthalmitis developed in 12 (1.9%) patients. The following factors were significantly associated with endophthalmitis by univariate analysis: delayed presentation (>24 hours) (p=0.008), rural address (p=0.013), and dirty wound (p=0.012). Logistic regression analysis identified dirty wound to be associated with the development of endophthalmitis (odds ratio = 11.6; 95% confidence interval [CI] = 2.67–50.6). On logistic regression analysis, presence of retained intraocular foreign body (IOFB) in association with rural address (odds ratio = 11.0; 95% CI = 1.44–83.3) or dirty wound (odds ratio = 9.2; 95% CI = 1.22–69.1) was associated with development of endophthalmitis. Endophthalmitis was a significant negative predictor for final good visual outcome (p=0.00261) and was significantly associated with hypotony (p=0.033).

Conclusions

Delayed presentation, rural address, and dirty wound were associated with development of endophthalmitis. Retained IOFB in association with rural address or dirty wound was associated with a particularly high risk of endophthalmitis.

Modeling intraocular bacterial infections

Bacterial endophthalmitis is an infection and inflammation of the posterior segment of the eye which can result in significant loss of visual acuity. Even with prompt antibiotic, anti-inflammatory and surgical intervention, vision and even the eye itself may be lost. For the past century, experimental animal models have been used to examine various aspects of the pathogenesis and pathophysiology of bacterial endophthalmitis, to further the development of anti-inflammatory treatment strategies, and to evaluate the pharmacokinetics and efficacies of antibiotics. Experimental models allow independent control of many parameters of infection and facilitate systematic examination of infection outcomes. While no single animal model perfectly reproduces the human pathology of bacterial endophthalmitis, investigators have successfully used these models to understand the infectious process and the host response, and have provided new information regarding therapeutic options for the treatment of bacterial endophthalmitis. This review highlights experimental animal models of endophthalmitis and correlates this information with the clinical setting. The goal is to identify knowledge gaps that may be addressed in future experimental and clinical studies focused on improvements in the therapeutic preservation of vision during and after this disease.

Association of Genotyping of Bacillus cereus with Clinical Features of Post-Traumatic Endophthalmitis

Bacillus cereus is the second most frequent cause of post-traumatic bacterial endophthalmitis. Although genotyping of B. cereus associated with gastrointestinal infections has been reported, little is known about the B. cereus clinical isolates associated with post-traumatic endophthalmitis. This is largely due to the limited number of clinical strains available isolated from infected tissues of patients with post-traumatic endophthalmitis. In this study, we report successful isolation of twenty-four B. cereus strains from individual patients with different disease severity of post-traumatic endophthalmitis. Phylogenetic analysis showed that all strains could be categorized into three genotypes (GTI, GTII and GTIII) and the clinical score showed significant differences among these groups. We then further performed genotyping using the vrrA gene, and evaluated possible correlation of genotype with the clinical features of B. cereus-caused post-traumatic endophthalmitis, and with the prognosis of infection by conducting follow-up with patients for up to 2 months. We found that the disease of onset and final vision acuity were significantly different among the three groups. These results suggested that the vrrA gene may play a significant role in the pathogenesis of endophthalmitis, and genotyping of B. cereus has the potential for predicting clinical manifestation and prognosis of endophthalmitis. To the best of our knowledge, this is the first report of isolation of large numbers of clinical isolates of B. cereus from patients with endophthalmitis. This work sets the foundation for future investigation of the pathogenesis endophthalmitis caused by B. cereus infection.

Morphological features in eyes with endophthalmitis after cataract surgery - histopathology and optical coherence tomography assessment

PURPOSE

To assess the ocular damage that occurs in eyes with postoperative endophthalmitis after cataract surgery (PE) based on optical coherence tomography (OCT) retinal scans of PE eyes and histological specimens of eyes removed due to PE.

METHODS

Case-control study and case series. Fifty-one patients who had previously developed PE were clinically examined with OCT scans of the retina of both eyes. Histological specimens of 10 removed PE eyes were studied.

RESULTS

The OCT scans showed that PE eyes had a statistically significantly higher frequency of hyperdense elements on the internal limiting membrane (ILM) of the retina (14 eyes versus 3 eyes, p = 0.015) and a higher degree of retinal atrophy temporal to the fovea (13 eyes versus 1 eye, p = 0.013) compared to fellow eyes. The histopathological analyses showed the formation of epiretinal membranes, derangement of all retinal layers with a reduced number of nuclei in the nuclear layers, loss of photoreceptor outer segments and massive retinal gliosis.

CONCLUSIONS

Optical coherence tomography scans of the retina and histopathology analyses provide insights in the pathological process occurring in PE.

Toward improving therapeutic regimens for Bacillus endophthalmitis

PURPOSE

Bacillus cereus causes the most virulent and refractory form of endophthalmitis. The authors analyzed the effectiveness of early treatment with vancomycin or gatifloxacin, with or without dexamethasone, for experimental B. cereus endophthalmitis.

METHODS

Rabbit eyes were injected intravitreally with 100 colony-forming units of B. cereus. At 2, 4, or 6 hours after infection, eyes were injected intravitreally with 0.1 mL gatifloxacin (0.3%), vancomycin (1.0%), either antibiotic plus dexamethasone, dexamethasone alone (1.0%), or PBS. Eyes were analyzed by electroretinography, bacterial quantitation, and antibiotic penetration analysis. Drug toxicity toward Müller cells, retinal pigment epithelium, and cones was also analyzed.

RESULTS

Eyes treated at 2 hours with vancomycin or gatifloxacin, with or without dexamethasone, maintained higher ERG amplitudes than the dexamethasone alone and PBS control groups. Eyes treated with antibiotic plus dexamethasone at 6 hours had reduced retinal function compared to antibiotic treatment alone. With the exception of vancomycin with or without dexamethasone at 6 hours, all antibiotic treatments sterilized eyes. Only gatifloxacin reached aqueous concentrations greater than the minimal inhibitory concentration for B. cereus when measured at 8 hours. Neither gatifloxacin nor vancomycin was toxic to retinal cells in vitro.

CONCLUSIONS

Early intravitreal injection of vancomycin or gatifloxacin improved the therapeutic outcome of B. cereus endophthalmitis. The addition of dexamethasone to antibiotic treatment did not provide a therapeutic benefit over antibiotics alone and appeared to reduce the antibiotic efficacy of vancomycin 6 hours after infection. In this model, delay in treatment past 6 hours significantly reduced the potential for salvaging useful vision.

Clinical Case Notes. Three cases of post-traumatic endophthalmitis caused by unusual bacteria

Three cases of post-traumatic endophthalmitis caused by unusual bacteria are presented. The pathogens identified were: (i) Bacillus cereus and Citrobacter freundii; (ii) Pseudomonas fluorescens; and (iii) Chryseobacterium meningosepticum and Stenotrophomonas maltophilia. Two of these pathogens have not previously been reported to cause endophthalmitis. The available literature regarding the individual cases is summarized and a brief discussion of post-traumatic endophthalmitis is presented, with reference to a recently published large series at the authors' institution.

Infective endophthalmitis caused by Bacillus cereus after cataract extraction surgery

We describe a 72-year-old Chinese man who developed fulminant Bacillus cereus endophthalmitis 36 h after an uneventful surgery for cataract extraction. Clinical progression of disease was extremely rapid, in spite of early vitrectomy and intravitreal injection of antibiotics. Results of Gram staining showed gram-positive bacilli, and the culture was positive for B. cereus. Endophthalmitis is rare after cataract surgery (cumulative probability within 1 year, approximately 0.08%), and cases caused by B. cereus are even less common. The prognosis and plan of treatment are discussed.

Clinical profile and outcome in Bacillus endophthalmitis

OBJECTIVE

To study the clinical presentation, microscopic and organismal culture correlation of vitreous, and species-specific outcome in Bacillus endophthalmitis

DESIGN

Retrospective noncomparative case series.

INTERVENTION

Thirty-one culture proven Bacillus endophthalmitis patients between January 1991 and February 1998 underwent vitrectomy and intravitreal antibiotic injection. Lensectomy was combined when considered essential, and on a few occasions intravitreal dexamethasone was added. The patients also received topical and systemic antibiotics. The undiluted vitreous biopsy was the source for microbiologic evaluation (microscopy and culture sensitivity).

MAIN OUTCOME MEASURES

The duration of symptoms, the presenting visual acuity, and influence of intravitreal dexamethasone with intravitreal antibiotics were examined for any statistical correlation with the final visual acuity.

RESULTS

Trauma was the major cause of infection. Vitreous biopsy microscopy demonstrated gram-positive bacillus in 28 of 31 cases, and polymicrobial infection was seen in 12 instances. All Bacillus species were sensitive to gentamicin, followed by vancomycin and ciprofloxacin. Clinical treatment within 7 days of symptoms, use of intravitreal vancomycin, and absence of polymicrobial infection were associated with better visual outcome.

CONCLUSIONS

With appropriate treatment that essentially consists of vitrectomy and intravitreal antibiotics, patients with Bacillus endophthalmitis are likely to benefit in many instances. Gram-positive bacilli detected on vitreous microscopy should be empirically treated as Bacillus species unless otherwise proved.

Subretinal fluid levels of topical, oral, and combined administered ciprofloxacin in humans

AIMS

To investigate the subretinal fluid (SRF) penetration of ciprofloxacin following topical, oral, and combined administration.

METHODS

34 patients undergoing conventional retinal reattachment surgery were randomly assigned to three groups. Twelve patients received topical ciprofloxacin, 11 patients received oral ciprofloxacin, and the other 11 patients received combined drug administration. SRF drug level was measured by using high performance liquid chromatography method.

RESULTS

The highest drug concentrations of all tested modes were attained following combined administration and lowest following topical administration (p<0.001). The SRF drug concentration following oral administration was also significantly higher than that of topical administration (p<0.001). Concentrations after oral and combined administration did not differ significantly (p = 0.217).

CONCLUSIONS

Topical ciprofloxacin can penetrate SRF. Ocular bioavailability of ciprofloxacin in SRF after oral and combined administration is equivalent.

Epidemiology and pathogenesis of Bacillus cereus infections

Bacillus cereus is a causative agent in both gastrointestinal and in nongastrointestinal infections. Enterotoxins, emetic toxin (cereulide), hemolysins, and phoshpolipase C as well as many enzymes such as beta-lactamases, proteases and collagenases are known as potential virulence factors of B. cereus. A special surface structure of B. cereus cells, the S-layer, has a significant role in the adhesion to host cells, in phagocytosis and in increased radiation resistance. Interest in B. cereus has been growing lately because it seems that B. cereus-related diseases, in particular food poisonings, are growing in number.

Penetration of topical, oral, and combined administered ofloxacin into the subretinal fluid

AIMS

To assess the subretinal fluid (SRF) levels of ofloxacin following topical, oral or combined administration.

METHODS

31 patients undergoing conventional retinal reattachment surgery were randomly assigned to three groups. Nine patients received topical ofloxacin, 11 patients received oral ofloxacin, and the other 11 patients received combined administration. Collected SRF samples were analysed for drug level by using high performance liquid chromatography.

RESULTS

SRF drug levels after oral and combined administration were significantly higher than that after topical administration (p=0.0002 and p=0.0002, respectively) while there was no significant difference between oral and combined administration (p=0.0844).

CONCLUSIONS

Ocular bioavailability of ofloxacin in SRF after oral and combined administration is equivalent. The addition of oral ofloxacin to topical therapy increased drug SRF penetration sixfold.