Bacillus cereus endophthalmitis

Endophthalmitis Caused by Bacillus cereus: Clinical Characteristics, Outcomes and Antibiotic Susceptibility

Bacillus cereus endophthalmitis is a severe vision-threatening disease. This study aimed to analyze the clinical characteristics, antibiotic susceptibility, and risk factors for poor final visual acuity (VA) and enucleation or evisceration (ENEV) outcomes of B. cereus endophthalmitis patients. We retrospectively reviewed 52 cases (52 eyes) of culture-proven B. cereus endophthalmitis at Zhongshan Ophthalmic Center from January 2013 to December 2023. The mean age of the patients was 38.1 ± 20.1 years, and males composed the majority (90.4%) of the sample size; laborers (32.7%) and farmers (19.2%) were the primary occupations of the patients. All cases were caused by ocular trauma. Forty-one of 51 eyes (80.4%) had a final VA worse than the ability to count fingers (CFs), and 15 of the 52 total eyes (28.8%) underwent ENEV. Binary logistic forward (LR) regression analysis demonstrated that red eye (odds ratio [OR], 13.13; 95% confidence interval [CI], 1.58-108.80; p = 0.017), eye pain (OR, 22.87; 95% CI, 1.00-522.72; p = 0.050), and corneal edema/ulcer (OR, 13.13; 95% CI, 1.58-108.80; p = 0.017) were significant risk factors for poor VA outcomes. Conjunctival sac purulent discharge (OR, 10.08; 95% CI, 2.11-48.12, p = 0.004) and white blood cell (WBC) count (OR, 1.35; 95% CI, 1.06-1.72, p = 0.016) were significant risk factors for ENEV outcomes. B. cereus showed susceptibility rates of 100.0% to vancomycin and ofloxacin; 98.0% to levofloxacin; 93.3% to ciprofloxacin; 87.5% to imipenem; and 78.9% to tobramycin. The susceptibility to azithromycin and clindamycin was 66.7% and 50.0%, respectively. In contrast, B. cereus was resistant to penicillin (susceptibility at 3.8%), cefuroxime (5.6%), and cefoxitin (37.1%).

Identification of Genetic Markers for the Detection of Bacillus thuringiensis Strains of Interest for Food Safety

Bacillus thuringiensis (Bt), belonging to the Bacillus cereus (Bc) group, is commonly used as a biopesticide worldwide due to its ability to produce insecticidal crystals during sporulation. The use of Bt, especially subspecies aizawai and kurstaki, to control pests such as Lepidoptera, generally involves spraying mixtures containing spores and crystals on crops intended for human consumption. Recent studies have suggested that the consumption of commercial Bt strains may be responsible for foodborne outbreaks (FBOs). However, its genetic proximity to Bc strains has hindered the development of routine tests to discriminate Bt from other Bc, especially Bacillus cereus sensu stricto (Bc ss), well known for its involvement in FBOs. Here, to develop tools for the detection and the discrimination of Bt in food, we carried out a genome-wide association study (GWAS) on 286 complete genomes of Bc group strains to identify and validate in silico new molecular markers specific to different Bt subtypes. The analyses led to the determination and the in silico validation of 128 molecular markers specific to Bt, its subspecies aizawai, kurstaki and four previously described proximity clusters associated with these subspecies. We developed a command line tool based on a 14-marker workflow, to carry out a computational search for Bt-related markers from a putative Bc genome, thereby facilitating the detection of Bt of interest for food safety, especially in the context of FBOs.

INCIDENCE AND RISK FACTORS OF POSTOPERATIVE ENDOPHTHALMITIS AFTER PRIMARY SURGICAL REPAIR COMBINED WITH INTRAOCULAR FOREIGN BODY REMOVAL

PURPOSE

To analyze the incidence and risk factors of postoperative endophthalmitis after primary surgical repair and intraocular foreign body (IOFB) removal within 24 hours of injury.

METHODS

The records of all patients treated surgically for open globe injury and IOFB removal at the Eye Hospital of Shandong First Medical University between January 1, 2015, and June 30, 2020, were retrospectively reviewed. Variables included time from injury to operation, cause of injury, details of surgical repair, and follow-up. The incidence and risk factors of endophthalmitis after IOFB removal were studied.

RESULTS

During 5 years, 99 patients with IOFB were reviewed. Of these, 19 patients were diagnosed with endophthalmitis on admission, and 5 were suspected of having endophthalmitis during operation. Fifty-four cases had no clinical signs of endophthalmitis on admission and during operation and were treated with operation within 24 hours after the injury. Two patients (2 of 54; 3.70%) developed endophthalmitis after IOFB removal, and the causative agent in both cases was Bacillus cereus.

CONCLUSION

The incidence of infectious endophthalmitis after primary surgical repair combined with IOFB removal (≤24 hours) was 3.70% in patients who received a series of standard treatments, and B. cereus infection might be a risk factor.

Immune Inhibitor A Metalloproteases Contribute to Virulence in Bacillus Endophthalmitis

Endophthalmitis is a devastating infection that can cause blindness. Over half of Bacillus endophthalmitis cases result in significant loss of useful vision. Bacillus produces many virulence factors that may contribute to retinal damage and robust inflammation. We analyzed Bacillus immune inhibitor A (InhA) metalloproteases in the context of this disease, hypothesizing that InhAs contribute to Bacillus intraocular virulence and inflammation. We analyzed phenotypes and infectivity of wild type (WT), InhA1-deficient (ΔinhA1), InhA2-deficient (ΔinhA2), or InhA1, A2, and A3-deficient (ΔinhA1-3) Bacillus thuringiensis. In vitro analysis of growth, proteolysis, and cytotoxicity were compared. WT and InhA mutants were similarly cytotoxic to retinal cells. Mutants ΔinhA1 and ΔinhA2 entered log phase growth earlier than WT. Proteolysis by the ΔinhA1-3 mutant was decreased, but this strain grew similar to WT in vitro. Experimental endophthalmitis was initiated by intravitreally infecting C57BL/6J mice with 200 CFU of B. thuringiensis WT or InhA mutants. Eyes were analyzed for intraocular Bacillus and myeloperoxidase concentrations, retinal function loss, and gross histological changes. Eyes infected with ΔinhA1 or ΔinhA2 strains contained greater numbers of bacteria than eyes infected with WT throughout the infection course. Eyes infected with single mutants had inflammation and retinal function loss similar to eyes infected with WT strain. Eyes infected with ΔinhA1-3 cleared the infection. RT-PCR results suggested that there may be compensatory expression of the other InhAs in the single InhA mutant. These results indicate that together, the InhA metalloproteases contribute to the severity of infection and inflammation in Bacillus endophthalmitis.

Bacillus cereus Induces Severe Infections in Preterm Neonates: Implication at the Hospital and Human Milk Bank Level

Human breast milk (HBM) is a source of essential nutrients for infants and is particularly recommended for preterm neonates when their own mother's milk is not available. It provides protection against infections and decreases necrotizing enterocolitis and cardiovascular diseases. Nevertheless, HBM spoilage can occur due to contamination by pathogens, and the risk of a shortage of HBM is very often present. B. cereus is the most frequent ubiquitous bacteria responsible for HBM being discarded. It can contaminate HBM at all stages, from its collect point to the storage and delivery. B. cereus can induce severe infection in newborns with very low birth weight, with sometimes fatal outcomes. Although the source of contamination is rarely identified, in some cases, HBM was suspected as a potential source. Even if the risk is low, as infection due to B. cereus in preterm infants should not be overlooked, human milk banks follow strict procedures to avoid contamination, to accurately identify remaining bacteria following pasteurization and to discard non-compliant milk samples. In this review, we present a literature overview of B. cereus infections reported in neonates and the suspected sources of contamination. We highlight the procedures followed by the human milk banks from the collection of the milk to its microbiological characterization in Europe. We also present improved detection and decontamination methods that might help to decrease the risk and to preserve the public's confidence in this vital biological product for infants whose mothers cannot breastfeed.

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.

Antimicrobial guide to posterior segment infections

PURPOSE

This review article is meant to serve as a reference guide and to assist the treating physician in making an appropriate selection and duration of an antimicrobial agent.

METHODS

Literature review.

RESULTS

Infections of the posterior segment require prompt medical or surgical therapy to reduce the risk of permanent vision loss. While numerous options exist to treat these infections, doses and alternative therapies, especially with contraindications for first-line therapy, are often elusive. Antimicrobial agents to treat posterior segment infections can be administered via various routes, including topical, intravitreal, intravenous, and oral.

CONCLUSIONS

Although there are many excellent review articles on the management of endophthalmitis, we take the opportunity in this review to comprehensively summarize the appropriate antimicrobial regimen of both common and rare infectious etiologies of the posterior segment, using evidence from clinical trials and large case series.

Characterization of Bacillus cereus in Dairy Products in China

Bacillus cereus is a common and ubiquitous foodborne pathogen with an increasing prevalence rate in dairy products in China. High and unmet demands for such products, particularly milk, raise the risk of B. cereus associated contamination. The presence of B. cereus and its virulence factors in dairy products may cause food poisoning and other illnesses. Thus, this review first summarizes the epidemiological characteristics and analytical assays of B. cereus from dairy products in China, providing insights into the implementation of intervention strategies. In addition, the recent achievements on the cytotoxicity and mechanisms of B. cereus are also presented to shed light on the therapeutic options for B. cereus associated infections.

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.

Bacillus S-Layer-Mediated Innate Interactions During Endophthalmitis

Bacillus endophthalmitis is a severe intraocular infection. Hallmarks of Bacillus endophthalmitis include robust inflammation and rapid loss of vision. We reported that the absence of Bacillus surface layer protein (SLP) significantly blunted endophthalmitis severity. Here, we further investigated SLP in the context of Bacillus-retinal cell interactions and innate immune pathways to explore the mechanisms by which SLP contributes to intraocular inflammation. We compared phenotypes of Wild-type (WT) and SLP deficient (ΔslpA) Bacillus thuringiensis by analyzing bacterial adherence to and phagocytosis by human retinal Muller cells and phagocytosis by mouse neutrophils. Innate immune receptor activation by the Bacillus envelope and purified SLP was analyzed using TLR2/4 reporter cell lines. A synthetic TLR2/4 inhibitor was used as a control for this receptor activation. To induce endophthalmitis, mouse eyes were injected intravitreally with 100 CFU WT or ΔslpA B. thuringiensis. A group of WT infected mice was treated intravitreally with a TLR2/4 inhibitor at 4 h postinfection. At 10 h postinfection, infected eyes were analyzed for viable bacteria, inflammation, and retinal function. We observed that B. thuringiensis SLPs contributed to retinal Muller cell adherence, and protected this pathogen from Muller cell- and neutrophil-mediated phagocytosis. We found that B. thuringiensis envelope activated TLR2 and, surprisingly, TLR4, suggesting the presence of a surface-associated TLR4 agonist in Bacillus. Further investigation showed that purified SLP from B. thuringiensis activated TLR4, as well as TLR2 in vitro. Growth of WT B. thuringiensis was significantly higher and caused greater inflammation in untreated eyes than in eyes treated with the TLR2/4 inhibitor. Retinal function analysis also showed greater retention of A-wave and B-wave function in infected eyes treated with the TLR2/4 inhibitor. The TLR2/4 inhibitor was not antibacterial in vitro, and did not cause inflammation when injected into uninfected eyes. Taken together, these results suggest a potential role for Bacillus SLP in host-bacterial interactions, as well as in endophthalmitis pathogenesis via TLR2- and TLR4-mediated pathways.

A Pyrrhic Victory: The PMN Response to Ocular Bacterial Infections

Some tissues of the eye are susceptible to damage due to their exposure to the outside environment and inability to regenerate. Immune privilege, although beneficial to the eye in terms of homeostasis and protection, can be harmful when breached or when an aberrant response occurs in the face of challenge. In this review, we highlight the role of the PMN (polymorphonuclear leukocyte) in different bacterial ocular infections that invade the immune privileged eye at the anterior and posterior segments: keratitis, conjunctivitis, uveitis, and endophthalmitis. Interestingly, the PMN response from the host seems to be necessary for pathogen clearance in ocular disease, but the inflammatory response can also be detrimental to vision retention. This "Pyrrhic Victory" scenario is explored in each type of ocular infection, with details on PMN recruitment and response at the site of ocular infection. In addition, we emphasize the differences in PMN responses between each ocular disease and its most common corresponding bacterial pathogen. The in vitro and animal models used to identify PMN responses, such as recruitment, phagocytosis, degranulation, and NETosis, are also outlined in each ocular infection. This detailed study of the ocular acute immune response to infection could provide novel therapeutic strategies for blinding diseases, provide more general information on ocular PMN responses, and reveal areas of bacterial ocular infection research that lack PMN response studies.

S-layer Impacts the Virulence of Bacillus in Endophthalmitis

Purpose

Bacillus causes a sight-threating infection of the posterior segment of the eye. The robust intraocular inflammatory response in this disease is likely activated via host innate receptor interactions with components of the Bacillus cell envelope. S-layer proteins (SLPs) of some Gram-positive pathogens contribute to the pathogenesis of certain infections. The potential contributions of SLPs in eye infection pathogenesis have not been considered. Here, we explored the role of a Bacillus SLP (SlpA) in endophthalmitis pathogenesis.

Methods

The phenotypes and infectivity of wild-type (WT) and S-layer deficient (ΔslpA) Bacillus thuringiensis were compared. Experimental endophthalmitis was induced in C57BL/6J mice by intravitreally injecting 100-CFU WT or ΔslpA B. thuringiensis. Infected eyes were analyzed by bacterial counts, retinal function analysis, histology, and inflammatory cell influx. SLP-induced inflammation was also analyzed in vitro. Muller cells (MIO-M1) were treated with purified SLP. Nuclear factor-κB (NF-κB) DNA binding was measured by ELISA and expression of proinflammatory mediators from Muller cells was measured by RT-qPCR.

Results

Tested phenotypes of WT and ΔslpA B. thuringiensis were similar, with the exception of absence of the S-layer in the ΔslpA mutant. Intraocular growth of WT and ΔslpA B. thuringiensis was also similar. However, eyes infected with the ΔslpA mutant had significantly reduced inflammatory cell influx, less inflammatory damage to the eyes, and significant retention of retinal function compared with WT-infected eyes. SLP was also a potent stimulator of the NF-κB pathway and induced the expression of proinflammatory mediators (IL6, TNFα, CCL2, and CXCL-1) in human retinal Muller cells.

Conclusions

Taken together, our results suggest that SlpA contributes to the pathogenesis of Bacillus endophthalmitis, potentially by triggering innate inflammatory pathways in the retina.

Recent actuality about Bacillus cereus and human milk bank: a new sensitive method for microbiological analysis of pasteurized milk

Three cases of Bacillus cereus infection or colonization occurred in the same region in France, and milk from the milk bank was suspected as a possible common source of contamination. All Batches delivered to the three cases complied with the requirements of the bacteriological reference method recommended by good practices guidelines. Still, a retrospective analysis with a more sensitive method showed one batch to contain B. cereus, however straincomparison revealed no epidemiological link betweenisolates from patients and those from the milk. Consequently, in accordance with the precautionary principle, we developed a new sensitive method for the screening of pasteurized milk for pathogenic bacteria. From January 1 to August 31, 2017, 2526 samples of pasteurized milk were prospectively included in the study. We showed that a 20 mL sample of pasteurized milk incubated for 18 h at 37 °C under aerobic conditions was favoring the detection of B. Cereus. The nonconformity rate was 6.3% for the reference method and 12.6% for the improved method (p < 0.0001). Nonconformity was due to the presence of B. cereus in 88.5% of cases for the improved method and 53% of cases for the reference method (p < 0.0001). Thus our new method is improves the microbiological safety of the product distributed and only moderately increases the rate of bacteriological nonconformity .

TLR4 modulates inflammatory gene targets in the retina during Bacillus cereus endophthalmitis

Background

Endophthalmitis is a serious intraocular infection that frequently results in significant inflammation and vision loss. Because current therapeutics are often unsuccessful in mitigating damaging inflammation during endophthalmitis, more rational targets are needed. Toll-like receptors (TLRs) recognize specific motifs on invading pathogens and initiate the innate inflammatory response. We reported that TLR4 contributes to the robust inflammation which is a hallmark of Bacillus cereus endophthalmitis. To identify novel, targetable host inflammatory factors in this disease, we performed microarray analysis to detect TLR4-dependent changes to the retinal transcriptome during B. cereus endophthalmitis.

Results

C57BL/6 J and TLR4^−/− mouse eyes were infected with B. cereus and retinas were harvested at 4 h postinfection, a time representing the earliest onset of neutrophil infiltration. Genes related to acute inflammation and inflammatory cell recruitment including CXCL1 (KC), CXCL2 (MIP2-α), CXCL10 (IP-10), CCL2 (MCP1), and CCL3 (MIP1-α)) were significantly upregulated 5-fold or greater in C57BL/6 J retinas. The immune modulator IL-6, intercellular adhesion molecule ICAM1, and the inhibitor of cytokine signal transduction SOCS3 were upregulated 25-, 11-, and 10-fold, respectively, in these retinas. LIF, which is crucial for photoreceptor cell survival, was increased 6-fold. PTGS2/COX-2, which converts arachidonic acid to prostaglandin endoperoxide H2, was upregulated 9-fold. PTX3, typically produced in response to TLR engagement, was induced 15-fold. None of the aforementioned genes were upregulated in TLR4^−/− retinas following B. cereus infection.

Conclusions

Our results have identified a cohort of mediators driven by TLR4 that may be important in regulating pro-inflammatory and protective pathways in the retina in response to B. cereus intraocular infection. This supports the prospect that blocking the activation of TLR-based pathways might serve as alternative targets for Gram-positive and Gram-negative endophthalmitis therapies in general.

Electronic supplementary material

The online version of this article (10.1186/s12886-018-0764-8) contains supplementary material, which is available to authorized users.

Treatment of Bacillus cereus endophthalmitis with endoscopy-assisted vitrectomy

To evaluate the use of endoscopy-assisted vitrectomy in patients with sight-threatening Bacillus cereus endophthalmitis.A retrospective analysis was conducted in 15 eyes with Bacillus cereus endophthalmitis. Patients were divided into 2 groups: endoscopy-assisted vitrectomy (5 eyes) and conventional vitrectomy (10 eyes). The following clinical data were recorded and analyzed: sex, age, latent period, symptom duration, follow-up time, visual acuity pre- and postsurgery, recurrence of endophthalmitis, incidence of phithisis bulbi, and incidence of enucleation.In the conventional vitrectomy group, postoperative visual acuity ranged from no light perception in 5 patients (50%), light perception in 3 patients (30%), 20/1000 in 1 patient (10%), and 20/50 in 1 patient (10%). In the endoscopy-assisted vitrectomy group, postoperative visual acuity ranged from no light perception in 2 patients (40%), light perception in 1 patient (20%), and hand movements in 2 patients (40%). There was no statistically significant difference between the 2 groups in terms of the final postoperative visual acuity (F = 0.006, P = .937). There is no difference between the 2 groups in terms of the incidence of enucleation. The median symptom duration was 4 hours (range: 2-6 hours) in the conventional group and 9 hours (range: 7-11 hours) in the endoscopy-assisted vitrectomy group. The difference in the symptom duration between the 2 groups was statistically significant (P = .002).There is no statistical significant difference between the 2 groups in terms of visual acuity and incidence of enucleation. Therefore, endoscopy-assisted vitrectomy can be considered as an alternative treatment for treatment of B cereus endophthalmitis particularly for cases when symptom duration was more than 6 hours.

The role of pili in Bacillus cereus intraocular infection

Bacterial endophthalmitis is a potentially blinding intraocular infection. The bacterium Bacillus cereus causes a devastating form of this disease which progresses rapidly, resulting in significant inflammation and loss of vision within a few days. The outer surface of B. cereus incites the intraocular inflammatory response, likely through interactions with innate immune receptors such as TLRs. This study analyzed the role of B. cereus pili, adhesion appendages located on the bacterial surface, in experimental endophthalmitis. To test the hypothesis that the presence of pili contributed to intraocular inflammation and virulence, we analyzed the progress of experimental endophthalmitis in mouse eyes infected with wild type B. cereus (ATCC 14579) or its isogenic pilus-deficient mutant (ΔbcpA-srtD-bcpB or ΔPil). One hundred CFU were injected into the mid-vitreous of one eye of each mouse. Infections were analyzed by quantifying intraocular bacilli and retinal function loss, and by histology from 0 to 12 h postinfection. In vitro growth and hemolytic phenotypes of the infecting strains were also compared. There was no difference in hemolytic activity (1:8 titer), motility, or in vitro growth (p > 0.05, every 2 h, 0-18 h) between wild type B. cereus and the ΔPil mutant. However, infected eyes contained greater numbers of wild type B. cereus than ΔPil during the infection course (p ≤ 0.05, 3-12 h). Eyes infected with wild type B. cereus experienced greater losses in retinal function than eyes infected with the ΔPil mutant, but the differences were not always significant. Eyes infected with ΔPil or wild type B. cereus achieved similar degrees of severe inflammation. The results indicated that the intraocular growth of pilus-deficient B. cereus may have been better controlled, leading to a trend of greater retinal function in eyes infected with the pilus-deficient strain. Although this difference was not enough to significantly alter the severity of the inflammatory response, these results suggest a potential role for pili in protecting B. cereus from clearance during the early stages of endophthalmitis, which is a newly described virulence mechanism for this organism and this infection.

CLINICAL PRESENTATION, MICROBIOLOGIC PROFILE AND FACTORS PREDICTING OUTCOMES IN BACILLUS ENDOPHTHALMITIS

PURPOSE

To describe the clinical presentation, microbiologic profile, and factors predicting outcomes in Bacillus endophthalmitis.

METHODS

Retrospective interventional case series. Eighty-six patients with culture-proven Bacillus endophthalmitis, from January 2001 to December 2015, underwent vitrectomy/vitreous biopsy and intravitreal antibiotic with or without steroid as appropriate. The undiluted vitreous biopsy was subjected to microbiologic evaluation. The duration of symptoms, presenting visual acuity, organisms isolated, influence of intravitreal dexamethasone with intravitreal antibiotics, and type of initial intervention were examined for any clinical and statistical correlation in terms of odds ratio with the final visual outcome.

RESULTS

Trauma was the commonest etiology (n = 75; 87.2%). Mixed infection with other bacteria was seen in 11 patients. All Bacillus species were sensitive to gentamicin followed by ciprofloxacin (n = 85; 98.83%) and vancomycin (n = 81; 94.18%). Odds in favor of a favorable visual outcome were seen with clinical treatment within 48 hours of the symptoms (OR 25.47, 95% CI 2.45-254.16, P = 0.006), better presenting vision (OR 31.21, 95% CI 2.96-323.64, P = 0.004), and absence of polymicrobial infection (OR 18.03, 95% CI 0.9-344.4, P = 0.05). Only 20% of all treated patients regained ambulatory vision, and one fifth of all of them developed phthisis.

CONCLUSION

Patients diagnosed with Bacillus endophthalmitis merit aggressive vitreous intervention guided by the culture-sensitivity report. Despite early and appropriate treat ment, the outcomes are generally poor.

Prevalence, virulence factor genes and antibiotic resistance of Bacillus cereus sensu lato isolated from dairy farms and traditional dairy products

Background

B. cereus are of particular interest in food safety and public health because of their capacity to cause food spoilage and disease through the production of various toxins. The aim of this study was to determine the prevalence, virulence factor genes and antibiotic resistance profile of B. cereus sensu lato isolated from cattle grazing soils and dairy products in Ghana. A total of 114 samples made up of 25 soil collected from cattle grazing farm land, 30 raw milk, 28 nunu (yoghurt-like product) and 31 woagashie (West African soft cheese). Ninety-six B. cereus sensu lato isolates from 54 positive samples were screened by PCR for the presence of 8 enterotoxigenic genes (hblA, hblC, hblD, nheA, nheB, nheC, cytK and entFM), and one emetic gene (ces). Phenotypic resistance to 15 antibiotics were also determined for 96 B. cereus sensu lato isolates.

Results

About 72% (18 of 25 soil), 47% (14 of 30 raw milk), 35% (10 of 28 nunu) and 39% (12 of 31 woagashi) were positive for B. cereus sensu lato with mean counts (log₁₀ cfu/g) of 4.2 ± 1.8, 3.3 ± 2.0, 1.8 ± 1.4 and 2.6 ± 1.8 respectively. The distribution of enterotoxigenic genes revealed that 13% (12/96 isolates) harboured all three gene encoding for haemolytic enterotoxin HBL complex genes (hblA, hblC and hblD), 25% (24/96 isolates) possessed no HBL gene, whereas 63% (60/96 isolates) possessed at least one of the three HBL genes. All three genes encoding for non-haemolytic enterotoxin (nheA, nheB and nheC) were detected in 60% (57/96) isolates, 14% (13/96) harboured only one gene, 19% (18/96) whereas 8% possessed none of the NHE genes. The detection rates of cytk, entFM, and ces genes were 75, 67 and 9% respectively. Bacillus cereus s. l. isolates were generally resistant to β-lactam antibiotics such as ampicillin (98%), oxacillin (92%), penicillin (100%), amoxicillin (100%), and cefepime (100%) but susceptible to other antibiotics tested.

Conclusions

Bacillus cereus s. l. is prevalent in soil, raw milk and dairy products in Ghana. However, loads are at levels considered to be safe for consumption. Various enterotoxin genes associated with virulence of B. cereus are widespread among the isolates.

CXCL1, but not IL-6, significantly impacts intraocular inflammation during infection

During intraocular bacterial infections, the primary innate responders are neutrophils, which may cause bystander damage to the retina or perturb the clarity of the visual axis. We hypothesized that cytokine IL-6 and chemokine CXCL1 contributed to rapid neutrophil recruitment during Bacillus cereus endophthalmitis, a severe form of intraocular infection that is characterized by explosive inflammation and retinal damage that often leads to rapid vision loss. To test this hypothesis, we compared endophthalmitis pathogenesis in C57BL/6J, IL-6^-/-, and CXCL1^-/- mice. Bacterial growth in eyes of CXCL1^-/-, IL-6^-/-, and C67BL/6J mice was similar. Retinal function retention was greater in eyes of IL-6^-/- and CXCL1^-/- mice compared with that of C57BL/6J, despite these eyes having similar bacterial burdens. Neutrophil influx into eyes of CXCL1^-/- mice was reduced to a greater degree compared with that of eyes of IL6^-/- mice. Histology confirmed significantly less inflammation in eyes of CXCL1^-/- mice, but similar degrees of inflammation in IL6^-/- and C57BL/6J eyes. Because inflammation was reduced in eyes of infected CXCL1^-/- mice, we tested the efficacy of anti-CXCL1 in B. cereus endophthalmitis. Retinal function was retained to a greater degree and there was less overall inflammation in eyes treated with anti-CXCL1, which suggested that anti-CXCL1 may have therapeutic efficacy in limiting inflammation during B. cereus endophthalmitis. Taken together, our results indicate that absence of IL-6 did not affect overall pathogenesis of endophthalmitis. In contrast, absence of CXCL1, in CXCL1^-/- mice or after anti-CXCL1 treatment, led to an improved clinical outcome. Our findings suggest a potential benefit in targeting CXCL1 to control inflammation during B. cereus and perhaps other types of intraocular infections.

Comparative Bioinformatics and Experimental Analysis of the Intergenic Regulatory Regions of Bacillus cereus hbl and nhe Enterotoxin Operons and the Impact of CodY on Virulence Heterogeneity

Bacillus cereus is a food contaminant with greatly varying enteropathogenic potential. Almost all known strains harbor the genes for at least one of the three enterotoxins Nhe, Hbl, and CytK. While some strains show no cytotoxicity, others have caused outbreaks, in rare cases even with lethal outcome. The reason for these differences in cytotoxicity is unknown. To gain insight into the origin of enterotoxin expression heterogeneity in different strains, the architecture and role of 5′ intergenic regions (5′ IGRs) upstream of the nhe and hbl operons was investigated. In silico comparison of 142 strains of all seven phylogenetic groups of B. cereus sensu lato proved the presence of long 5′ IGRs upstream of the nheABC and hblCDAB operons, which harbor recognition sites for several transcriptional regulators, including the virulence regulator PlcR, redox regulators ResD and Fnr, the nutrient-sensitive regulator CodY as well as the master regulator for biofilm formation SinR. By determining transcription start sites, unusually long 5′ untranslated regions (5′ UTRs) upstream of the nhe and hbl start codons were identified, which are not present upstream of cytK-1 and cytK-2. Promoter fusions lacking various parts of the nhe and hbl 5′ UTR in B. cereus INRA C3 showed that the entire 331 bp 5′ UTR of nhe is necessary for full promoter activity, while the presence of the complete 606 bp hbl 5′ UTR lowers promoter activity. Repression was caused by a 268 bp sequence directly upstream of the hbl transcription start. Luciferase activity of reporter strains containing nhe and hbl 5′ IGR lux fusions provided evidence that toxin gene transcription is upregulated by the depletion of free amino acids. Electrophoretic mobility shift assays showed that the branched-chain amino acid sensing regulator CodY binds to both nhe and hbl 5′ UTR downstream of the promoter, potentially acting as a nutrient-responsive roadblock repressor of toxin gene transcription. PlcR binding sites are highly conserved among all B. cereus sensu lato strains, indicating that this regulator does not significantly contribute to the heterogeneity in virulence potentials. The CodY recognition sites are far less conserved, perhaps conferring varying strengths of CodY binding, which might modulate toxin synthesis in a strain-specific manner.

Unexpected Roles for Toll-Like Receptor 4 and TRIF in Intraocular Infection with Gram-Positive Bacteria

Inflammation caused by infection with Gram-positive bacteria is typically initiated by interactions with Toll-like receptor 2 (TLR2). Endophthalmitis, an infection and inflammation of the posterior segment of the eye, can lead to vision loss when initiated by a virulent microbial pathogen. Endophthalmitis caused by Bacillus cereus develops as acute inflammation with infiltrating neutrophils, and vision loss is potentially catastrophic. Residual inflammation observed during B. cereus endophthalmitis in TLR2(-/-) mice led us to investigate additional innate pathways that may trigger intraocular inflammation. We first hypothesized that intraocular inflammation during B. cereus endophthalmitis would be controlled by MyD88- and TRIF-mediated signaling, since MyD88 and TRIF are the major adaptor molecules for all bacterial TLRs. In MyD88(-/-) and TRIF(-/-) mice, we observed significantly less intraocular inflammation than in eyes from infected C57BL/6J mice, suggesting an important role for these TLR adaptors in B. cereus endophthalmitis. These results led to a second hypothesis, that TLR4, the only TLR that signals through both MyD88 and TRIF signaling pathways, contributed to inflammation during B. cereus endophthalmitis. Surprisingly, B. cereus-infected TLR4(-/-) eyes also had significantly less intraocular inflammation than infected C57BL/6J eyes, indicating an important role for TLR4 in B. cereus endophthalmitis. Taken together, our results suggest that TLR4, TRIF, and MyD88 are important components of the intraocular inflammatory response observed in experimental B. cereus endophthalmitis, identifying a novel innate immune interaction for B. cereus and for this disease.

Bacillus cereus in personal care products: risk to consumers

Bacillus cereus is ubiquitous in nature and thus occurs naturally in a wide range of raw materials and foodstuffs. B. cereus spores are resistant to desiccation and heat and able to survive dry storage and cooking. Vegetative cells produce several toxins which on ingestion in sufficient numbers can cause vomiting and/or diarrhoea depending on the toxins produced. Gastrointestinal disease is commonly associated with reheated or inadequately cooked foods. In addition to being a rare cause of several acute infections (e.g. pneumonia and septicaemia), B. cereus can also cause localized infection of post-surgical or trauma wounds and is a rare but significant pathogen of the eye where it may result in severe endophthalmitis often leading to loss of vision. Key risk factors in such cases are trauma to the eye and retained contaminated intraocular foreign bodies. In addition, rare cases of B. cereus-associated keratitis (inflammation of the cornea) have been linked to contact lens use. Bacillus cereus is therefore a microbial contaminant that could adversely affect product safety of cosmetic and facial toiletries and pose a threat to the user if other key risk factors are also present. The infective dose in the human eye is unknown, but as few as 100 cfu has been reported to initiate infection in a susceptible animal model. However, we are not aware of any reports in the literature of B. cereus infections in any body site linked with use of personal care products. Low levels of B. cereus spores may on occasion be present in near-eye cosmetics, and these products have been used by consumers for many years. In addition, exposure to B. cereus is more likely to occur through other routes (e.g. dustborne contamination) due to its ubiquity and resistance properties of spores. The organism has been recovered from the eyes of healthy individuals. Therefore, although there may be a perceived hazard, the risk of severe eye infections as a consequence of exposure through contaminated near-eye cosmetics is judged to be vanishingly small. It is unlikely that more stringent microbiological standards for near-eye cosmetics will have any impact on the risk of severe eye infections caused by B. cereus, as these are not linked to use of personal care products.

Automated ribotyping and antibiotic resistance determining of Bacillus spp from conjunctiva of diabetic patients

OBJECTIVE(S)

We aimed to characterize the phenotype and genotype of Bacillus spp isolated from diabetic patients' eyes, by studying the drug sensitivity patterns with a disc-diffusion method.

MATERIALS AND METHODS

Fifty eyes of 25 patients with type II diabetes mellitus, with at least 10 years of diabetes history, were included in the study. We analyzed the eyes for the presence of Bacillus spp.; presumptive isolates were identified by morphological, and biochemical tests, and confirmed by the VITEK system. Automated EcoRI ribotyping was performed with a RiboPrinter(®) Microbial Characterization System. We determined the antibiotic resistance of the isolates by the Kirby-Bauer disc diffusion test.

RESULTS

Seven out of 25 patients were on insulin treatment; 7 on oral anti-diabetic medication; and 11 on combination therapy of insulin and oral medications. Among the 28 Bacillus spp isolates, 14 were B. cereus, 11 were B. pumilus, 2 were B. mojavensis and 1 was B. subtilis. Almost all the strains were either resistant or multiresistant, particularly towards cefuroxime, methicillin, and ceftazidime.

CONCLUSION

Diabetic patients seem to be more prone to B. cereus infections than healthy individuals. It would be greatly beneficial to understand and recognize the prevalence of microorganisms and their resistance patterns for better outcome in ocular surgeries.

Antimicrobial and acetylcholinesterase inhibitory activities of Buddleja salviifolia (L.) Lam. leaf extracts and isolated compounds

ETHNOPHARMACOLOGICAL RELEVANCE

Buddleja salviifolia leaves are used for the treatment of eye infections and neurodegenerative conditions by various tribes in South Africa.

AIM OF STUDY

This study was designed to isolate the phenolic constituents from the leaf extracts of Buddleja salviifolia and evaluate their antimicrobial and acetylcholinesterase (AChE) activities.

MATERIAL AND METHODS

Three phenolic compounds were isolated from the ethyl acetate fraction of a 20% aqueous methanol leaf extract of Buddleja salviifolia using Sephadex LH-20 and silica gel columns. Structure elucidation of the isolated compounds was carried out using spectroscopic techniques: mass spectrometry (ESI-TOF-MS) and NMR (1D and 2D). The extracts and isolated compounds were evaluated for antimicrobial and acetylcholinesterase activities using the microdilution technique. The bacteria used for the antimicrobial assays were Gram-positive Bacillus subtilis and Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumoniae.

RESULTS

The isolated compounds were characterized as: 4'-hydroxyphenyl ethyl vanillate (1) a new natural product, acteoside (2) and quercetin (3). The crude extract, fractions and the isolated compounds from the leaves of the plant exhibited a broad spectrum of antibacterial activity. The EtOAc fraction exhibited good activity against Bacillus subtilis and Staphylococcus aureus with MIC values ranging from 780.0 to 390.0 µg/mL. Isolated compound 2 exhibited good activity against Staphylococcus aureus with an MIC value of 62.5 µg/mL. The hexane and DCM fractions of leaves showed the best activity against Candida albicans with MIC and MFC values of 390.0 µg/mL. In the AChE inhibitory test, among the tested extracts, the hexane fraction was the most potent with an IC50 value of 107.4 µg/mL, whereas for the isolated compounds, it was compound (3) (quercetin) with an IC50 value of 66.8 µg/mL.

CONCLUSIONS

Activities demonstrated by the extracts and isolated compounds support the ethnopharmacological use of Buddleja salviifolia against eye infections and neurodegenerative diseases.

Bacterial endophthalmitis in the age of outpatient intravitreal therapies and cataract surgeries: host-microbe interactions in intraocular infection

Bacterial endophthalmitis is a sight threatening infection of the interior structures of the eye. Incidence in the US has increased in recent years, which appears to be related to procedures being performed on an aging population. The advent of outpatient intravitreal therapy for management of age-related macular degeneration raises yet additional risks. Compounding the problem is the continuing progression of antibiotic resistance. Visual prognosis for endophthalmitis depends on the virulence of the causative organism, the severity of intraocular inflammation, and the timeliness of effective therapy. We review the current understanding of the pathogenesis of bacterial endophthalmitis, highlighting opportunities for the development of improved therapeutics and preventive strategies.

Efficacy of vitrectomy in improving the outcome of Bacillus cereus endophthalmitis

PURPOSE

To evaluate the efficacy of vitrectomy with vancomycin for the treatment of experimental Bacillus cereus endophthalmitis.

METHODS

Endophthalmitis was initiated in rabbits via intravitreal injection of 100 colony-forming unit B. cereus. Treatment groups included 25-gauge transconjunctival sutureless vitrectomy with intravitreal vancomycin (1 mg) or vancomycin alone. Groups were treated at 4, 5, or 6 hours after infection. At 48 hours (for 4-hour and 5-hour groups) or 36 hours (for the 6-hour group) after infection, eyes were analyzed by electroretinography, histology, and inflammatory cell counts.

RESULTS

Treatment with vitrectomy/vancomycin at 4 hours resulted in significantly greater retinal function compared with that of vancomycin alone. Intraocular inflammation after treatment at 4 hours was minimal for both the treatment groups. Treatment with vitrectomy/vancomycin or vancomycin alone at 5 hours or 6 hours after infection resulted in similar levels of retinal function loss (i.e., >90%) and significant intraocular inflammation.

CONCLUSION

These results demonstrate that vitrectomy may be of therapeutic benefit in the treatment of B. cereus endophthalmitis but only during the early stages of infection.

Role of Toll-like receptor (TLR) 2 in experimental Bacillus cereus endophthalmitis

Bacillus cereus causes a uniquely rapid and blinding intraocular infection, endophthalmitis. B. cereus replicates in the eye, synthesizes numerous toxins, and incites explosive intraocular inflammation. The mechanisms involved in the rapid and explosive intraocular immune response have not been addressed. Because Toll-like receptors (TLRs) are integral to the initial recognition of organisms during infection, we hypothesized that the uniquely explosive immune response observed during B. cereus endophthalmitis is directly influenced by the presence of TLR2, a known gram-positive pathogen recognition receptor. To address this hypothesis, we compared the courses of experimental B. cereus endophthalmitis in wild type C57BL/6J mice to that of age-matched homozygous TLR2(-/-) mice. Output parameters included analysis of bacterial growth, inflammatory cell (PMN) infiltration, cytokine/chemokine kinetics, retinal function testing, and histology, with N≥4 eyes/assay/time point/mouse strain. B. cereus grew at similar rates to10(8) CFU/eye by 12 h, regardless of the mouse strain. Retinal function was preserved to a greater degree in infected TLR2(-/-) eyes compared to that of infected wild type eyes, but infected eyes of both mouse strains lost significant function. Retinal architecture was preserved in infected TLR2(-/-) eyes, with limited retinal and vitreal cellular infiltration compared to that of infected wild type eyes. Ocular myeloperoxidase activities corroborated these results. In general, TNFα, IFNγ, IL6, and KC were detected in greater concentrations in infected wild type eyes than in infected TLR2(-/-) eyes. The absence of TLR2 resulted in decreased intraocular proinflammatory cytokine/chemokine levels and altered recruitment of inflammatory cells into the eye, resulting in less intraocular inflammation and preservation of retinal architecture, and a slightly greater degree of retinal function. These results demonstrate TLR2 is an important component of the initial ocular response to B. cereus endophthalmitis.

Treatment of experimental Bacillus cereus endophthalmitis using intravitreal moxifloxacin with or without dexamethasone

PURPOSE

To evaluate the effects of intravitreal moxifloxacin with or without dexamethasone on experimental Bacillus cereus endophthalmitis.

METHODS

The right eyes of 21 New Zealand albino rabbits weighing 2-3 kg were used in this study. Each eye was inoculated with 1×10(6) colony-forming units of B. cereus microorganisms via intravitreal injection into the vitreous cavity, and an experimental model of B. cereus endophthalmitis was formed. The rabbits were separated into 3 groups: Group 1 was given 0.1 mL of balanced saline solution intravitreally, group 2 was given 50 μg of moxifloxacin, and group 3 was given 50 μg of moxifloxacin plus 400 μg of dexamethasone 24 h after the inoculation. Vitreous aspirates were taken for microbiological examination on the 3rd day. Clinical inflammation scores were evaluated on days 1, 7, and 14. The rabbits were killed on the 14th day, and the eyes were enucleated for histopathological examination.

RESULTS

On the 7th day, only the vitreous scores of the treatment groups were significantly low compared with those of the control group (P<0.05). On day 14, the clinical scores of vitreous inflammation were 2.43±0.79, 1.43±0.53, and 1.29±0.49 in Groups 1, 2, and 3, respectively. The clinical scores of the treatment groups were significantly lower compared with those of the control group on day 14 (P<0.05). Histopathological scores were 2.43±0.79, 1.43±0.53, and 1.43±0.79 for the iris and 2.14±0.69, 1.57±0.53, and 1.14±0.38 for the vitreous in Groups 1, 2, and 3, respectively. Apart from the conjunctiva, the histopathological scores of the other tissues in the treatment groups were significantly lower compared with those of the control group (P<0.05). No significant differences were found in the histopathological or clinical scores among the treatment groups (P>0.05). Microbiological scores at day 14 were 151±6.43, 125.43±13.44, and 131.14±16.99 for Groups 1, 2, and 3, respectively. The microbiological scores of the treatment groups were significantly lower compared with those of the control group (P<0.05).

CONCLUSIONS

Intravitreal moxifloxacin injection is effective in experimental B. cereus endophthalmitis. The addition of intravitreal dexamethasone may not significantly affect treatment efficacy.

Early murine immune responses from endotracheal exposures to biotechnology-related Bacillus strains

An immunology-based in vivo screening regime was used to assess the potential pathogenicity of biotechnology-related microbes. Strains of Bacillus cereus (Bc), Bacillus subtilis (Bs), Bacillus thuringiensis (Bt), and Bt commercial products (CPs) were tested. Balb/c mice were endotracheally instilled with purified spores, diluted CP, or vegetative cells (VC) (live or dead). Exposed mice were evaluated for changes in behavioral and physical symptoms, bacterial clearance, pulmonary granulocytes, and pulmonary and circulatory pyrogenic cytokines (interleukins (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α), as well as acute phase biomarkers (fibrinogen and serum amyloid A). Except for some differences in clearance rates, no marked effects were observed in mice exposed to any spore at 10(6) or 10(7) colony forming units (cfu). In contrast, live Bc or Bt VCs (10(5) or 10(6) cfu) produced shock-like symptoms (lethargy, hunched appearance, ruffled fur, and respiratory distress), and 11-200-fold elevations in pyrogenic cytokines at 2-h post-exposure. In the study, 4-h effects included increased lethargy, ocular discharge, and 1.5-4-fold rise in circulatory acute phase markers, but no indications of recovery. Bs VC did not produce any changes in symptoms or biomarkers. After 2 or 4 h of exposure to dead VC, increases of only plasma IL-1? and TNF-α (4.6- and 12.4-fold, respectively) were observed. These findings demonstrate that purified spores produced no marked effects in mice compared to that of metabolically active bacteria. This early screening regime was successful in distinguishing the pathogenicity of the different Bacillus species, and might be useful for assessing the relative hazard potential of other biotechnology-related candidate strains.

Bacillus cereus, a volatile human pathogen

Bacillus cereus is a Gram-positive aerobic or facultatively anaerobic, motile, spore-forming, rod-shaped bacterium that is widely distributed environmentally. While B. cereus is associated mainly with food poisoning, it is being increasingly reported to be a cause of serious and potentially fatal non-gastrointestinal-tract infections. The pathogenicity of B. cereus, whether intestinal or nonintestinal, is intimately associated with the production of tissue-destructive exoenzymes. Among these secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and proteases. The major hurdle in evaluating B. cereus when isolated from a clinical specimen is overcoming its stigma as an insignificant contaminant. Outside its notoriety in association with food poisoning and severe eye infections, this bacterium has been incriminated in a multitude of other clinical conditions such as anthrax-like progressive pneumonia, fulminant sepsis, and devastating central nervous system infections, particularly in immunosuppressed individuals, intravenous drug abusers, and neonates. Its role in nosocomial acquired bacteremia and wound infections in postsurgical patients has also been well defined, especially when intravascular devices such as catheters are inserted. Primary cutaneous infections mimicking clostridial gas gangrene induced subsequent to trauma have also been well documented. B. cereus produces a potent beta-lactamase conferring marked resistance to beta-lactam antibiotics. Antimicrobials noted to be effective in the empirical management of a B. cereus infection while awaiting antimicrobial susceptibility results for the isolate include ciprofloxacin and vancomycin.

Differential transfer dynamics of pAW63 plasmid among members of the Bacillus cereus group in food microcosms

AIM

To assess the dynamics of plasmid transfer between Bacillus thuringiensis and B. cereus in various food microcosms using the B. thuringiensis pAW63 and Staphylococcus aureus pUB110 plasmids as models.

METHODS AND RESULTS

The conjugative behaviour of pAW63, which resembles the B. anthracis virulence plasmid pXO2, and the mobilization of pUB110 were investigated using kinetics studies performed in reference LB (lysogeny broth) medium, full-cream and skimmed milks, soya milk and rice milk. Transfers of pAW63 and pUB110 were found to occur in the five tested media, with higher frequencies observed in food matrices, most notably in full-cream milk, skimmed milk and soya milk, where the mean transfer frequencies reached 10(-3) transconjugants per recipient cell. The most notable observations were that the higher transfer frequencies obtained in foodstuffs compared to those observed in LB were because of an earlier onset of conjugation in combination with a higher transfer rate and/or a longer mating period.

CONCLUSION

These results indicate that not only the potential for plasmid transfer but also the overall timing of conjugation is affected by each of these food matrices.

SIGNIFICANCE AND IMPACT OF THE STUDY

This new approach to study plasmid transfer provides insights for a better understanding of conjugation in food microcosms from both animal and vegetable origins among members of the B. cereus group.

Bacillus cereus-induced permeability of the blood-ocular barrier during experimental endophthalmitis

PURPOSE

The purpose of this study was to determine to what extent blood-retinal barrier (BRB) permeability occurred during experimental Bacillus cereus endophthalmitis and whether tight junction alterations were involved in permeability.

METHODS

Mice were intravitreally injected with 100 colony-forming units of B. cereus, and eyes were analyzed at specific times after infection for permeability to fibrin and albumin, quantitation of intraocular plasma constituent leakage, production of inflammatory cytokines, and alterations in tight junction protein localization and expression at the level of the retinal pigment epithelium.

RESULTS

B. cereus induced the leakage of albumin and fibrin into the aqueous and vitreous humor by 8 hours after infection. BRB permeability occurred as early as 4 hours and increased 13.30-fold compared with uninfected controls by 8 hours. Production of proinflammatory cytokines IL-6, MIP-1alpha, IL-1beta, and KC increased over the course of infection. In the retina, ZO-1 disruption began by 4 hours and was followed by decreasing occludin and ZO-1 expression at 4 and 8 hours, respectively. Tubulin condensation and RPE65 degradation occurred by 12 hours. A quorum-sensing mutant B. cereus strain caused BRB permeability comparable to that of wild-type B. cereus. Wild-type and mutant B. cereus sterile supernatants induced blood-ocular barrier permeability similarly to that of wild-type infection.

CONCLUSIONS

These results indicate that BRB permeability occurs during the early stages of experimental B. cereus endophthalmitis, beginning as early as 4 hours after infection. Disruption of tight junctions at the level of the retinal pigment epithelium may contribute to barrier breakdown. Quorum-sensing dependent factors may not significantly contribute to BRB permeability.

A role for tumor necrosis factor-alpha in experimental Bacillus cereus endophthalmitis pathogenesis

PURPOSE

To determine the contribution of tumor necrosis factor-alpha (TNFalpha) in the pathogenesis of experimental Bacillus cereus endophthalmitis.

METHODS

Experimental B. cereus endophthalmitis was induced in wild-type control (B6.129F1) and age-matched homozygous TNFalpha knockout mice (TNFalpha(-/-), B6.129S6-Tnf(tm1Gk1)/J). At various times after infection, eyes were analyzed by electroretinography and were harvested for quantitation of bacteria, myeloperoxidase, proinflammatory cytokines and chemokines, and histologic analysis.

RESULTS

B. cereus replicated more rapidly in the eyes of TNFalpha(-/-) mice than in the eyes of B6.129F1 mice. Retinal function decreased more rapidly in TNFalpha(-/-) mice than in B6.129F1 mice. Retinal layers were not as structurally intact at 6 and 12 hours after infection in TNFalpha(-/-) eyes as in B6.129F1 eyes. Histologic analysis suggested less polymorphonuclear leukocyte (PMN) infiltration into the vitreous of TNFalpha(-/-) mice than of B6.129F1 mice. B6.129F1 eyes also had greater myeloperoxidase concentrations than did eyes of TNFalpha(-/-) mice. In general, concentrations of proinflammatory cytokines and chemokines (IL-1beta, KC, IL-6, and MIP-1alpha) were greater in eyes of TNFalpha(-/-) mice than of B6.129F1 mice.

CONCLUSIONS

TNFalpha is important to intraocular pathogen containment by PMNs during experimental B. cereus endophthalmitis. In the absence of TNFalpha, fewer PMNs migrated into the eye, facilitating faster bacterial replication and retinal function loss. Although greater concentrations of proinflammatory cytokines were synthesized in the absence of TNFalpha, the resultant inflammation was diminished, and an equally devastating course of infection occurred.

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.

Bacterial endophthalmitis: therapeutic challenges and host-pathogen interactions

Endophthalmitis is an infection of the posterior segment of the eye that frequently results in loss of vision. This devastating result occurs despite prompt and often aggressive therapeutic and surgical intervention. Over the past decade, research has centered on determining the bacterial and host factors involved in this potentially blinding disease. The initial focus on the bacterial factors responsible for intraocular virulence has recently expanded into analysis the inflammatory response to infection, including the molecular and cellular interactions between the pathogen and host. This review discusses the epidemiology and therapeutic challenges posed by endophthalmitis, as well as recent findings from the analysis of interactions between the host and pathogen. Based on these findings, a model for the pathogenesis of endophthalmitis is presented. A more comprehensive understanding of the molecular and cellular interactions taking place between pathogen and host during endophthalmitis will expose possible therapeutic targets designed to arrest the infection and prevent vision loss.

Virulence factor profiles and antimicrobial susceptibilities of ocular bacillus isolates

Bacillus causes one of the most rapidly blinding intraocular infections: endophthalmitis. In this study, Bacillus spp. were isolated from ocular infection cases, taxonomically characterized by riboprint analysis, and screened for the presence of putative virulence factors. The ability of these isolates to kill retinal and corneal cells was examined, as were antibiotic susceptibility profiles. The majority of isolates belonged to the B. cereus taxonomic group of microorganisms and were identified as B. cereus (53%) or B. thuringiensis (26%). Toxins were identified in most B. thuringiensis and B. cereus isolates. Most B. cereus and B. thuringiensis killed corneal and retinal cells within 6 h. All isolates were susceptible to most antibiotics tested, with quinolones and vancomycin being the most potent. These findings represent the first report of B. thuringiensis as an important ocular pathogen, demonstrates the potential ocular toxicity of B. cereus and B. thuringiensis isolates, and identifies antibiotics whose efficacy against Bacillus were superior to those used clinically.

Plasmid exchanges among members of the Bacillus cereus group in foodstuffs

The Bacillus cereus sensu lato group is genetically very close and possesses a remarkable plasmid gene pool that encodes a variety of functions such as virulence and self-transfer capabilities. The potential for horizontal transfer among the various subspecies of this group, which includes the human opportunistic pathogens B. cereus sensu stricto and B. anthracis as well as the biopesticide B. thuringiensis, has led to growing concerns regarding food safety and public health. In this study, the conjugative behaviour of B. thuringiensis strains was compared in LB medium, milk and rice pudding using the pXO16 and pAW63 conjugative systems, as well as the mobilisable plasmid pC194, in bi- and triparental matings. Conjugation and mobilisation of these plasmids were shown to occur at significant levels in both food products, attaining the highest transfer frequencies in milk, with an approximately ten-fold increase in conjugative transfer in this growth medium as compared to liquid LB. Furthermore, the ability of an emetic strain of B. cereus to function as either plasmid donor or recipient partner in heterologous biparental matings with B. thuringiensis was demonstrated in these food matrices.

A comparative study ofBacillus cereus,Bacillus thuringiensis andBacillus anthracis extracellular proteomes

Bacillus cereus, Bacillus thuringiensis and Bacillus anthracis are closely related species that share a similar genetic background but occupy different ecological niches. Virulence plasmids bearing genes coding for toxins, may explain, at least partly, this specialization. We have compared by 2-DE in the early stationary phase of growth the extracellular proteomes of three strains of these species that have lost their virulence plasmids. Proteins expected to be secreted or to belong to the cell wall or to the cytosol were found in the three proteomes. For the cell wall and cytosolic proteins located in the extracellular space, the three proteomes were similar. Cytosolic proteins included enolase, GroEL, PdhB, PdhD, SodA and others. Cell surface proteins were mainly autolysins, proteases, nucleotidases and OppAs. In contrast, the secreted proteins profiles of B. cereus and B. thuringiensis were quite different from that of B. anthracis. B. cereus and B. thuringiensis extracellular proteomes both contained large amounts of secreted degradative enzymes and toxins, including nine proteases, three phospholipases, two haemolysins and several enterotoxins. Most of the genes encoding these enzymes and toxins are controlled by the transcriptional activator PlcR. The extracellular proteome of the pXO1-, pXO2- B. anthracis 9131 strain contained only one secreted protein: the metalloprotease InhA1, also found in the proteomes of the two other strains and possibly involved in antibacterial peptide degradation.

Conjugative plasmid pAW63 brings new insights into the genesis of the Bacillus anthracis virulence plasmid pXO2 and of the Bacillus thuringiensis plasmid pBT9727

BACKGROUND

Bacillus cereus, Bacillus anthracis and Bacillus thuringiensis belong to the genetically close-knit Bacillus cereus sensu lato group, a family of rod-shaped Gram-positive bacteria. pAW63 is the first conjugative plasmid from the B. cereus group to be completely sequenced.

RESULTS

The 71,777 bp nucleotide sequence of pAW63 reveals a modular structure, including a 42 kb tra region encoding homologs of the Type IV secretion systems components VirB11, VirB4 and VirD4, as well as homologs of Gram-positive conjugation genes from Enterococcus, Lactococcus, Listeria, Streptococcus and Staphylococcus species. It also firmly establishes the existence of a common backbone between pAW63, pXO2 from Bacillus anthracis and pBT9727 from the pathogenic Bacillus thuringiensis serovar konkukian strain 97-27. The alignment of these three plasmids highlights the presence of well conserved segments, in contrast to distinct regions of high sequence plasticity. The study of their specific differences has provided a three-point reference framework that can be exploited to formulate solid hypotheses concerning the functionalities and the molecular evolution of these three closely related plasmids. This has provided insight into the chronology of their divergence, and led to the discovery of two Type II introns on pAW63, matching copies of the mobile element IS231L in different loci of pXO2 and pBT9727, and the identification on pXO2 of a 37 kb pathogenicity island (PAI) containing the anthrax capsule genes.

CONCLUSION

The complete sequence determination of pAW63 has led to a functional map of the plasmid yielding insights into its conjugative apparatus, which includes T4SS-like components, as well as its resemblance to other large plasmids of Gram-positive bacteria. Of particular interest is the extensive homology shared between pAW63 and pXO2, the second virulence plasmid of B. anthracis, as well as pBT9727 from the pathogenic strain B. thuringiensis serovar konkukian strain 97-27.

Effective antiprotease-antibiotic treatment of experimental anthrax

Background

Inhalation anthrax is characterized by a systemic spread of the challenge agent, Bacillus anthracis. It causes severe damage, including multiple hemorrhagic lesions, to host tissues and organs. It is widely believed that anthrax lethal toxin secreted by proliferating bacteria is a major cause of death, however, the pathology of intoxication in experimental animals is drastically different from that found during the infectious process. In order to close a gap between our understanding of anthrax molecular pathology and the most prominent clinical features of the infectious process we undertook bioinformatic and experimental analyses of potential proteolytic virulence factors of B. anthracis distinct from lethal toxin.

Methods

Secreted proteins (other than lethal and edema toxins) produced by B. anthracis were tested for tissue-damaging activity and toxicity in mice. Chemical protease inhibitors and rabbit immune sera raised against B. anthracis proteases were used to treat mice challenged with B. anthracis (Sterne) spores.

Results

B. anthracis strain delta Ames (pXO1^-, pXO2^-) producing no lethal and edema toxins secrets a number of metalloprotease virulence factors upon cultivation under aerobic conditions, including those with hemorrhagic, caseinolytic and collagenolytic activities, belonging to M4 and M9 thermolysin and bacterial collagenase families, respectively.

These factors are directly toxic to DBA/2 mice upon intratracheal administration at 0.5 mg/kg and higher doses. Chemical protease inhibitors (phosphoramidon and 1, 10-phenanthroline), as well as immune sera against M4 and M9 proteases of B. anthracis, were used to treat mice challenged with B. anthracis (Sterne) spores. These substances demonstrate a substantial protective efficacy in combination with ciprofloxacin therapy initiated as late as 48 h post spore challenge, compared to the antibiotic alone.

Conclusion

Secreted proteolytic enzymes are important pathogenic factors of B. anthrasis, which can be considered as effective therapeutic targets in the development of anthrax treatment and prophylactic approaches complementing anti-lethal toxin therapy.

Liver abscess due to Bacillus cereus: a case report

Bacillus cereus is a food-borne pathogen that causes a self-limiting gastroenteritis. We describe the case of a 72-year-old woman admitted to our hospital because of acute abdominal colic pain. Over a 2-day period, her clinical condition deteriorated rapidly, with the appearance of acute abdomen. Computed tomography investigation of the abdomen showed a liver abscess (diameter approximately 3 cm). At laparotomy, the abscess was found to be ruptured to the free peritoneal cavity. The final clinical diagnosis was acute peritonitis due to a ruptured liver abscess. Bacillus cereus was isolated from culture of the pus. Up to now, no case of liver abscess due to this organism has been reported.

Camelysin is a novel surface metalloproteinase from Bacillus cereus

Bacillus cereus frequently causes food poisoning or nosocomial diseases. Vegetative cells express the novel surface metalloproteinase camelysin (casein-cleaving metalloproteinase) during exponential growth on complex, peptide-rich media. Camelysin is strongly bound to the cell surface and can be solubilized only by detergents or butanol. Camelysin spontaneously migrates from the surface of intact bacterial cells to preformed liposomes. The complete sequence of the camelysin-encoding gene, calY, was determined by reverse PCR on the basis of the N-terminal sequence and some internal tryptic cleavage peptides. The calY gene codes for a polypeptide of 21.569 kDa with a putative signal peptide of 27 amino acids (2.513 kDa) preceding the mature protein (19.056 kDa). Although the predicted amino acid sequence of CalY does not exhibit a typical metalloprotease consensus sequence, high-pressure liquid chromatography-purified camelysin contains one zinc ion per protein molecule. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and tryptic peptide mass fingerprinting confirmed the identity of this zinc-binding protein as CalY. Disruption of the calY gene results in a strong decrease in the cell-bound proteolytic activity on various substrates.

Immunology of Staphylococcal biofilm infections in the eye: new tools to study biofilm endophthalmitis

Endophthalmitis is an important disease of the eye that is most frequently caused by postoperative and post-traumatic introduction of bacteria into the posterior segment of the eye. In the case of severe infections, visual acuity is greatly damaged or completely lost. Much work has focused on the ability of planktonic bacteria to cause infection and ocular damage while little work has focused on chronic infections in endophthalmitis mediated by the formation of bacterial biofilms on the surface of the lens. This review focuses on the interaction of Staphylococcus aureus and Staphylococcus epidermidis lens-associated biofilms in endophthalmitis. Additionally, this review highlights some relevant biofilm-immune system interactions and outlines a new in vivo mouse model to explore biofilm-related infections in endophthalmitis.

Bacterial endophthalmitis: epidemiology, therapeutics, and bacterium-host interactions

Endophthalmitis is a severe inflammation of the interior of the eye caused by the introduction of contaminating microorganisms following trauma, surgery, or hematogenous spread from a distant infection site. Despite appropriate therapeutic intervention, bacterial endophthalmitis frequently results in visual loss, if not loss of the eye itself. Although the pathogenicity of bacterial endophthalmitis has historically been linked with toxin production during infection, a paucity of information exists as to the exact mechanisms of retinal toxicity and the triggers for induction of the intraocular immune response. Recently, research has begun to examine the bacterial and host molecular and cellular events that contribute to ocular damage during endophthalmitis. This review focuses on the causative agents and therapeutic challenges of bacterial endophthalmitis and provides current data from the analysis of the role of bacterial virulence factors and host inflammatory interactions in the pathogenesis of eye infections. Based on these and related studies, a hypothetical model for the molecular pathogenesis of bacterial endophthalmitis is proposed. Identifying and understanding the basic mechanisms of these bacterium-host interactions will provide the foundation for which novel, information-based therapeutic agents are developed in order to prevent vision loss during endophthalmitis.

The cell envelope-bound metalloprotease (camelysin) from Bacillus cereus is a possible pathogenic factor

A novel membrane proteinase of the nosocomial important bacteria species Bacillus cereus (synonyms: camelysin, CCMP) was purified up to homogeneity as was shown by mass spectrometry in its amphiphilic form. Camelysin is a neutral metalloprotease with a molecular mass of 19 kDa. Its unique N-terminus Phe-Phe-Ser-Asp-Lys-Glu-Val-Ser-Asn-Asn-Thr-Phe-Ala-Ala-Gly-Thr-Leu-Asp-Leu-Thr-Leu-Asn-Pro-Lys-Thr-Leu-Val-Asp-(Ile-Lys-Asp)- was not detected in the protein data bases during BLAST searches, but in the partially sequenced genome of Bacillus anthracis, coding for an unknown protein. Cleavage sites of the membrane proteinase for the insulin A- and B-chains were determined by mass spectrometry and N-terminal sequencing. Camelysin prefers cleavage sites in front of aliphatic and hydrophilic amino acid residues (-OH, -SO3H, amido group), avoiding bulky aromatic residues. The internally quenched fluorogenic substrates of the matrix metalloproteases 2 and 7 were cleaved with the highest efficiency at the Leu-decrease-Gly or Leu-decrease-Ala bond with the smaller residue in the P1' position. The protein specificity is broad--all various kinds of casein were cleaved as well as acid-soluble collagen, globin and ovalbumin; intact insulin was destroyed only to a low extent. Actin, collagen type I, fibrinogen, fibrin, alpha2-antiplasmin and alpha1-antitrypsin were cleaved. The protease formed SDS-stable complexes with Glu-plasminogen and antithrombin III, visible after SDS electrophoresis by gold staining and Western blot. The CCMP-plasminogen complex caused a partial activation of plasminogen to plasmin. Camelysin interacts with proteins of the blood coagulation cascade and could facilitate the penetration of fibrin clots and of the extracellular matrix during bacterial invasion.