Detection of virulence factors in Pseudomonas aeruginosa strains isolated from contact lens-associated corneal ulcers

A microbiological survey approach to understanding the virulence factors of Pseudomonas species in healthcare sinks

BACKGROUND

Hospital water is involved in both the prevention and spread of healthcare-associated infections (HCAIs). Handwashing is key to reducing the transmission of pathogens, yet numerous outbreaks have been found to be caused by organisms within sinks, taps and showers. Pseudomonas aeruginosa and increasingly non-aeruginosa Pseudomonas cause waterborne HCAI, however, little is known about the virulence potential of Pseudomonas species found within hospital environments.

METHODS

Swabs were taken from 62 sinks within two newly opened wards at Great Ormond Street Hospital, samples were taken before and after the wards opened to understand the impact of patient occupancy on sink micro-organisms. Culturable bacteria were identified by MALDI-TOF and virulence factors assessed through phenotypic methods.

RESULTS

A total of 106 bacterial isolates were recovered including 24 Pseudomonas isolates. Of these 25% were identified as P. oleovorans, 21% P. aeruginosa, 17% P. composti, 13% P. alicalipha, 8% P. monteilii, 4% P. putida, 4% P. stutzeri and 8% could only be identified to genus level by MALDI-TOF. Differences were seen in both the number of Pseudomonas isolates and virulence production between the two wards, overall 25% of the Pseudomonas isolates produced pigment, 58% were capable of haemolysis, 87.5% were able to swim, 83.3% were capable of twitching motility, 33.3% produced alkaline protease and 8.3% produced gelatinase.

CONCLUSIONS

Results suggest that patients may be back-contaminating sinks with colonizing organisms which has ongoing implications for infection prevention and control. Additionally, this work highlights the ability of non-aeruginosa Pseudomonas to produce virulence factors traditionally associated with P. aeruginosa.

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Genomic and metabolic versatility of Pseudomonas aeruginosa contributes to its inter-kingdom transmission and survival

Pseudomonas aeruginosa is one of the most versatile bacteria with renowned pathogenicity and extensive drug resistance. The diverse habitats of this bacterium include fresh, saline and drainage waters, soil, moist surfaces, taps, showerheads, pipelines, medical implants, nematodes, insects, plants, animals, birds and humans. The arsenal of virulence factors produced by P. aeruginosa includes pyocyanin, rhamnolipids, siderophores, lytic enzymes, toxins and polysaccharides. All these virulent elements coupled with intrinsic, adaptive and acquired antibiotic resistance facilitate persistent colonization and lethal infections in different hosts. To date, treating pulmonary diseases remains complicated due to the chronic secondary infections triggered by hospital-acquired P. aeruginosa. On the contrary, this bacterium can improve plant growth by suppressing phytopathogens and insects. Notably, P. aeruginosa is one of the very few bacteria capable of trans-kingdom transmission and infection. Transfer of P. aeruginosa strains from plant materials to hospital wards, animals to humans, and humans to their pets occurs relatively often. Recently, we have identified that plant-associated P. aeruginosa strains could be pathologically similar to clinical isolates. In this review, we have highlighted the genomic and metabolic factors that facilitate the dominance of P. aeruginosa across different biological kingdoms and the varying roles of this bacterium in plant and human health.

Prevalence and Virulence of Commensal Pseudomonas Aeruginosa Isolates from Healthy Individuals in Southern Vietnam (2018-2020)

Understanding the colonization of Pseudomonas aeruginosa (P. aeruginosa) in healthy humans is useful for future prevention and treatment of P. aeruginosa infection. This study aimed to investigate the prevalence and risk factors of of P. aeruginosa colonization in healthy humans. At the same time, the virulence of the isolated P. aeruginosa was also studied. In the study, 609 Vietnamese volunteers (310 females and 299 males, age range of 2 to 73 years), who had no acute infection or disease symptoms participated at the time of sample collection. Samples were taken from the throat, nostrils, and outer ears. P. aeruginosa was found in 19 participants (3.12%, 95% CI: 0.017−0.045), mainly from the throat (11/19, 57.89%). Participants with a history of sinusitis were 11.57 times more likely to be colonized with P. aeruginosa than participants without a history of sinusitis (OR: 11.57, 95% CI: 4.08−32.76, p-value < 0.0001, Fisher’s Exact test). Age and sex were not significantly associated with P. aeruginosa colonization. Among 16 P. aeruginosa isolates used in virulence tests, 100% (16/16) were positive for the synthesis of biofilm, pyocyanin, and siderophores; 93.75% (15/16) isolates were positive for the synthesis of gelatinase and protease; and 50% (8/16) isolates were positive for lipase. There were no differences in the pattern and range of virulence factors of P. aeruginosa isolates taken from participants with and without sinusitis history. P. aeruginosa colonized 3.12% of participants, and its presence was associated with sinusitis history.

Microbial Adherence to Contact Lenses and Pseudomonas aeruginosa as a Model Organism for Microbial Keratitis

Microbial keratitis (MK), the infection of the cornea, is a devastating disease and the fifth leading cause of blindness and visual impairment around the world. The overwhelming majority of MK cases are linked to contact lens wear combined with factors which promote infection such as corneal abrasion, an immunocompromised state, improper contact lens use, or failing to routinely disinfect lenses after wear. Contact lens-related MK involves the adherence of microorganisms to the contact lens. Therefore, this review discusses the information currently available regarding the disease pathophysiology, the common types of microorganisms causing MK, physical and organic mechanisms of adhesion, material properties which are involved in adhesion, and current antimicrobial strategies. This review also concludes that Pseudomonas aeruginosa is a model organism for the investigation of contact lens microbial adherence due to its prevalence in MK cases, its extremely robust adhesion, antimicrobial-resistant properties, and the severity of the disease it causes.

Plant-associated Pseudomonas aeruginosa strains harbour multiple virulence traits critical for human infection

Introduction. Pseudomonas aeruginosa causes fatal infections in immunocompromised individuals and patients with pulmonary disorders.Gap Statement. Agricultural ecosystems are the vast reservoirs of this dreaded pathogen. However, there are limited attempts to analyse the pathogenicity of P. aeruginosa strains associated with edible plants.Aim. This study aims to (i) elucidate the virulence attributes of P. aeruginosa strains isolated from the rhizosphere and endophytic niches of cucumber, tomato, eggplant and chili;and (ii) compare these phenotypes with that of previously characterized clinical isolates.Methodology. Crystal-violet microtitre assay, swarm plate experiment, gravimetric quantification and sheep blood lysis were performed to estimate the biofilm formation, swarming motility, rhamnolipid production and haemolytic activity, respectively, of P. aeruginosa strains. In addition, their pathogenicity was also assessed based on their ability to antagonize plant pathogens (Xanthomonas oryzae, Pythium aphanidermatum, Rhizoctonia solani and Fusarium oxysporum) and kill a select nematode (Caenorhabditis elegans).Results. Nearly 80 % of the plant-associated strains produced rhamnolipid and exhibited at least one type of lytic activity (haemolysis, proteolysis and lipolysis). Almost 50 % of these strains formed significant levels of biofilm and exhibited swarming motility. The agricultural strains showed significantly higher and lower virulence against the bacterial and fungal pathogens, respectively, compared to the clinical strains. In C. elegans, a maximum of 40 and 100% mortality were induced by the agricultural and clinical strains, respectively.Conclusion. This investigation shows that P. aeruginosa in edible plants isolated directly from the farm express virulence and pathogenicity. Furthermore, clinical and agricultural P. aeruginosa strains antagonized the tested fungal phytopathogens, Pythium aphanidermatum, Rhizoctonia solani and Fusarium oxysporum. Thus, we recommend using these fungi as simple eukaryotic model systems to test P. aeruginosa pathogenicity.

In Vitro Antimicrobial Activity of a New Ophthalmic Solution Containing Hexamidine Diisethionate 0.05% (Keratosept)

PURPOSE

To assess the in vitro antimicrobial activity of a new commercial ophthalmic solution containing hexamidine diisethionate 0.05% (Keratosept).

METHODS

Staphylococcus aureus American Type Culture Collection (ATCC 43300), Pseudomonas aeruginosa ATCC 27853, 3 ocular bacterial isolates (1 Staphylococcus epidermidis, 1 S. aureus, and 1 P. aeruginosa), and 5 Candida species were used. The bacterial and fungal isolates were cultured on Columbia blood agar base and Sabouraud-dextrose agar plates, respectively, and incubated overnight at 37°C. Suspensions were prepared in a sterile saline solution with optical density equal to 0.5 McFarland standard (∼10 CFU/mL). Isolate suspensions were made in Keratosept solution to obtain a concentration of 10 CFU/mL. The suspensions were then distributed in conical tubes with a final volume of 1 mL and incubated at 37°C. After 1, 5, 10, 15, 20, 25, 30 minutes, and 24 hours, 10 μL of each suspension was removed, seeded on Columbia blood agar base and Sabouraud-dextrose agar plates and then incubated for 24 hours at 37°C.

RESULTS

After 1-minute incubation, there was no growth on the plates seeded with S. aureus ATCC 43300, S. aureus clinical isolate, S. epidermidis clinical isolate, and all 5 Candida species tested. Conversely, Keratosept solution failed to kill the Pseudomonas isolates after 30 minutes exposure and needed 24 hours to eradicate the organisms.

CONCLUSIONS

Keratosept ophthalmic solution showed in vitro antimicrobial activity against S. epidermidis, S. aureus, and Candida species. Results suggest that it may be a potential candidate for the treatment of staphylococcal and Candida infections of the ocular surface and have some role in antimicrobial prophylaxis before intravitreal injections.

Inhibitory Effect of Ophthalmic Solutions against SARS-CoV-2: A Preventive Action to Block the Viral Transmission?

In 2020, a global pandemic was declared following the spread of SARS-CoV-2, the pathogen responsible for COVID-19. The risk of infection is high due to the ease of transmission, which can occur orally, through droplets, or via contact with contaminated surfaces and objects. It has also been demonstrated that the ocular surface can constitute a transmission route, especially in hospital settings, where health care workers can become a dangerous source of infection. In order to increase prevention and reduce the spread of the virus on the ocular surface, the antiviral activity of already-marketed eye drops against SARS-CoV-2 was evaluated. Iodim, Ozodrop, Septavis, and Dropsept were tested against SARS-CoV-2 in plaque-assay experiments at different stimulation times. Furthermore, the expression levels of early and late genes were evaluated through molecular assays. Results indicated that three of the four ophthalmic solutions showed a considerable dose-dependent inhibition of viral replication, highlighting their use as potential antiviral drugs against SARS-CoV-2 and preventing other ocular infections.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.

Antimicrobial Effects of Thymosin Beta-4 and Ciprofloxacin Adjunctive Therapy in Pseudomonas aeruginosa Induced Keratitis

Prior work has indicated that thymosin beta 4 (Tβ4) administered with ciprofloxacin markedly improves disease outcome for Pseudomonas aeruginosa (PA)-induced keratitis. As a result, the goal of the current study was to elucidate mechanisms by which Tβ4 mitigates the corneal response; specifically, regarding its bactericidal influence and potential synergy with ciprofloxacin. An in vitro approach was carried out using minimum inhibitory concentration (MIC) assays to assess bactericidal activity against PA. In addition, antimicrobial peptide (AMP) production was evaluated at the mRNA levels using human corneal epithelial cells in response to lipopolysaccharide (LPS) challenge. The results of the MIC assays did not show direct bactericidal activity with Tβ4 alone, although ciprofloxacin exhibited significant killing at concentrations far lower than clinically dosed. Tβ4, however, displayed an indirect effect on bacterial killing, as shown by an upregulation of AMPs and related molecules. The cumulative data from this study indicate an indirect bactericidal role of Tβ4, as well as a synergistic relationship with ciprofloxacin. Furthermore, ciprofloxacin alone was found to influence cellular functions that otherwise have yet to be reported. These results highlight a mechanism of intracellular communication for Tβ4 and further strengthen its development as an adjunct therapy with antibiotics for corneal infections.

A Novel Vitamin E TPGS-Based Formulation Enhances Chlorhexidine Bioavailability in Corneal Layers

Keratitis is a severe condition characterized by inflammation of the cornea following a local trauma. The most common ocular disease is the bacterial one, which requires an antibiotic treatment. The major limitation of this therapy is the resistance of the antibiotic. For this reason, alternative procedures have been developed and consist of antimicrobial molecules. One of the most used is the chlorhexidine gluconate, which has shown activity versus Gram-positive and Gram-negative bacteria and fungi. In addition to its efficiency, chlorhexidine shows low toxicity levels for mammalian cells and is a low-cost molecule. Despite its multiple benefits, chlorhexidine, if used at concentrations higher than 0.02% (w/w), can cause local eye irritation. Additionally, its poor penetrability through the cornea makes necessary frequent instillation of eye drops for a prolonged time. Due to these limitations, alternative drug delivery strategies are required. Here, we report a novel formulation based on the combination of d-alpha-tocopherol polyethylene glycol 1000 succinate with chlorhexidine, which results in higher accumulation of the drug in human corneas measured by liquid chromatography and strong antimicrobial activity. Moreover, this formulation does not cause any toxic effect on human cells and is well tolerated by rabbit eyes. Therefore this novel formulation represents a good candidate for the treatment of keratitis that overcomes the risk of antibiotic resistance.

In vitro antimicrobial activity of a new ophthalmic solution containing povidone-iodine 0.6% (IODIM® )

PURPOSE

To assess the in vitro antimicrobial activity of a new commercial ophthalmic solution containing povidone-iodine 0.6% (IODIM^® ).

METHODS

Staphylococcus aureus ATCC 43300, Pseudomonas aeruginosa ATCC 27853, three ocular bacterial isolates (1 S. epidermidis, 1 S. aureus, 1 P. aeruginosa) and five Candida species were used. The bacterial and fungal isolates were cultured on Columbia blood agar base plates and Sabouraud-dextrose agar plates, respectively and incubated overnight at 37°C. Bacterial and fungal suspensions in sterile saline solution were prepared to an optical density equal to 0.5 McFarland standard (approximately 10⁸ CFU/ml). Suspensions of the isolates were made in IODIM^® solution to obtain a final concentration of 10⁶ CFU/ml. The suspensions were then distributed in conical tubes in a final volume of 1 ml and incubated at 37°C. At different time-points (1, 5, 10, 15, 20, 25, 30 min and 24 hr), 10 μl of each suspension was removed, seeded on Columbia blood agar base and Sabouraud-dextrose agar plates and then incubated for 24 hr at 37°C. Positive and negative controls were included in all experiments.

RESULTS

After 5-min incubation, there was no bacterial growth on any plate. Conversely, IODIM^® failed to kill the Candida isolates after 30 min' exposure and needed 24 hr to eradicate the organisms.

CONCLUSION

IODIM^® ophthalmic solution showed in vitro antimicrobial activity against S. epidermidis, S. aureus, P. aeruginosa and Candida species. Results suggest that it may be a potential candidate for the treatment of ocular surface infections and antimicrobial prophylaxis before intravitreal injections.

Genetic features of Pseudomonas aeruginosa isolates associated with eye infections referred to Farabi Hospital, Tehran, Iran

BACKGROUND

Pseudomonas is the most common cause of microbial keratitis especially in people who use contact lens. The virulence of Pseudomonas aeruginosa in different eye infections is associated with different virulence factors .

METHODS

In this study, 54 P. aeruginosa isolates including 39 isolates from keratitis and 15 isolates from conjunctivitis were evaluated for their ability to form biofilm, production of protease, elastase, alkaline protease and their antibiotic-resistant patterns. The distribution of the exoS and exoU genes in the test strains were determined using PCR assays.

RESULTS

Most of the eye infections (90.74%) were seen in people who used contact lenses, and in most of patients (72.22%), the infection was presented as keratitis. None of the isolates were resistant to a single antibiotic as tested. Multidrug resistance (MDR) was detected in two isolates (3.5%) which were resistant to more than one category of antibiotics. The exoU⁺/exoS⁺ isolates were in majority although in total, compared to exoS, there were more exoU in a greater number of samples. Most of the strains produce elastase but among all of ocular isolates, only 5.8% of the strains showed alkaline protease activity. Most of the ocular isolates were not capable of producing biofilm.

CONCLUSIONS

In our study, a high prevalence of virulence factors was observed in P. aeruginosa isolates from contact lens wearer with keratitis. As the P. aeruginosa isolates from different infection origins and different geographic region may have different virulence factors, having a better perception of these differences could help to improve development of clinical instructions for the control of keratitis.

Phylogenetic study of metallo-β-lactamase producing multidrug resistant Pseudomonas aeruginosa isolates from burn patients

The present study was carried out to understand the clonal relationship using enterobacteriaceae repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) among metallo-β-lactamase (MBL) producing multidrug resistant Pseudomonas aeruginosa isolates from burn victims and their susceptibility to commonly used anti-pseudomonal agents. In the present study 94 non-duplicate P. aeruginosa strains from the wound samples of burn patients were included. Identification of the isolates was done by biochemical methods and antibiotic sensitivity was done by disc diffusion method following CLSI (Clinical Laboratory Standard Institute) guidelines. By using imipenem (IPM)-EDTA disk diffusion/double disc synergy method carbapenem resistant organisms were tested for MBL. To define the clonal relationship ERIC-PCR was used. Of the 94 isolates, 18 (19.14%) were found resistant to IPM and MBL production was shown 11 (11.70%) by the IPM-EDTA disc diffusion method. From dendrogram of the ERIC-PCR profile four major clusters were obtained (A, B, C and D). Cluster B contained the majority of the isolates (6 strains 1, 4, 8, 9, 10 and 11). This study using ERIC-PCR of randomly collected isolates exhibits high genetic diversity which rules out cross contamination frequency.

Esculentin-1a(1-21)NH2: a frog skin-derived peptide for microbial keratitis

Pseudomonas aeruginosa is the primary bacterial pathogen causing contact lens related keratitis. Available ophthalmic agents have reduced efficacy and antimicrobial peptides (AMPs) hold promise as future antibiotics. Here we investigated the in vitro and in vivo anti-Pseudomonal activity of esculentin-1a(1-21)NH2, derived from a frog skin AMP. The data revealed a minimum inhibitory concentration between 2 and 16 μM against reference strains or drug-resistant clinical isolates of P. aeruginosa without showing toxicity to human corneal epithelial cells up to 50 μM. At 1 μM the peptide rapidly killed bacterial cells and this activity was fully retained in 150 mM sodium chloride and 70 % (v/v) human basal tears, particularly against the virulent ATCC 19660 strain. Furthermore, its dropwise administration at 40 μM to the ocular surface in a murine model of P. aeruginosa keratitis (three times daily, for 5 days post-infection) resulted in a significant reduction of infection. The mean clinical score was 2.89 ± 0.26 compared to 3.92 ± 0.08 for the vehicle control. In addition, the corneal level of viable bacteria in the peptide treated animals was significantly lower with a difference of 4 log10 colony counts, compared to 7.7 log10 cells recovered in the control. In parallel, recruitment of inflammatory cells was reduced by half compared to that found in the untreated eyes. Similar results were obtained when esculentin-1a(1-21)NH2 was applied prior to induction of keratitis. Overall, our findings highlight esculentin-1a(1-21)NH2 as an attractive candidate for the development of novel topical pharmaceuticals against Pseudomonas keratitis.

Drug resistance profile and biofilm forming potential of Pseudomonas aeruginosa isolated from contact lenses in Karachi-Pakistan

Background

The contaminated contact lens provides Pseudomonas aeruginosa an ideal site for attachment and biofilm production. Continuous contact of the eye to the biofilm-infested lens can lead to serious ocular diseases, such as keratitis (corneal ulcers). The biofilms also prevent effective penetration of the antibiotics, which increase the chances of antibiotic resistance.

Methods

For this study, 22 Pseudomonas aeruginosa isolates were obtained from 36 contact lenses and 14 contact lens protective fluid samples. These isolates were tested against eight commonly used antibiotics using Kirby-Bauer disk diffusion method. The biofilm forming potential of these isolates was also evaluated using various qualitative and quantitative techniques. Finally, a relationship between biofilm formation and antibiotic resistance was also examined.

Results

The isolates of Pseudomonas aeruginosa tested were found resistant to most of the antibiotics tested. Qualitative and quantitative biofilm analysis revealed that most of the isolates exhibited strong biofilm production. The biofilm production was significantly higher in isolates that were multi-drug resistant (p < 0.0001).

Conclusion

Our study indicates that multi-drug resistant, biofilm forming Pseudomonas aeruginosa isolates are mainly involved in contact lens associated infections. This appears to be the first report from Pakistan, which analyzes both antibiotic resistance profile and biofilm forming potential of Pseudomonas aeruginosa isolates from contact lens of the patients with contact lens associated infections.

TREM-2 promotes host resistance against Pseudomonas aeruginosa infection by suppressing corneal inflammation via a PI3K/Akt signaling pathway

PURPOSE

To explore the role of triggering receptor expressed on myeloid cells 2 (TREM-2) in Pseudomonas aeruginosa (PA) keratitis.

METHODS

BALB/c mice were routinely infected with PA and evaluated at various postinfection time points for corneal expression of TREM-2, by real-time PCR, Western blot, and flow cytometry. Next, BALB/c and C57BL/6 mice were respectively treated with TREM-2 siRNA or agonistic anti-TREM-2 antibody, to determine the role of TREM-2 in PA keratitis. Bacterial load and neutrophil infiltration were tested by plate count and myeloperoxidase assay, respectively. Th1-/Th2-type and proinflammatory cytokine expression were tested by real-time PCR and ELISA after in vivo and in vitro silencing of TREM-2. Moreover, phosphorylated Akt levels were tested by Western blot in murine macrophages after treatment with agonistic anti-TREM-2 antibody. mRNA levels of proinflammatory cytokines were examined in murine macrophages after TREM-2 activation and lipopolysaccharide stimulation, following pretreatment with inhibitors for PI3K or Akt, to determine whether PI3K/Akt is required in TREM-2-mediated immune modulation. In addition, BALB/c mice were treated with wortmannin and analyzed for bacterial load and proinflammatory cytokine expression.

RESULTS

TREM-2 expression was elevated in the infected BALB/c corneas at 3 or 5 days postinfection. Silencing of TREM-2 accelerated disease progression by enhancing bacterial load and corneal inflammation, whereas activation of TREM-2 promoted host resistance to PA keratitis. PI3K/Akt signaling is required in the TREM-2-mediated immune modulation, and inhibition of PI3K resulted in worsened disease after PA corneal infection.

CONCLUSIONS

TREM-2 promoted host resistance to PA infection by suppressing corneal inflammation via activation of the PI3K/Akt pathway.

Phenotypic and molecular characterization of antimicrobial resistance and virulence factors in Pseudomonas aeruginosa clinical isolates from Recife, State of Pernambuco, Brazil

INTRODUCTION: The emergence of carbapenem resistance mechanisms in Pseudomonas aeruginosa has been outstanding due to the wide spectrum of antimicrobial degradation of these bacteria, reducing of therapeutic options. METHODS: Sixty-one clinical strains of P. aeruginosa isolated from five public hospitals in Recife, Pernambuco, Brazil, were examined between 2006 and 2010, aiming of evaluating the profiles of virulence, resistance to antimicrobials, presence of metallo-β-lactamase (MBL) genes, and clonal relationship among isolates. RESULTS: A high percentage of virulence factors (34.4% mucoid colonies; 70.5% pyocyanin; 93.4% gelatinase positives; and 72.1% hemolysin positive) and a high percentage of antimicrobial resistance rates (4.9% pan-resistant and 54.1% multi-drug resistant isolates) were observed. Among the 29 isolates resistant to imipenem and/or ceftazidime, 44.8% (13/29) were MBL producers by phenotypic evaluation, and of these, 46.2% (6/13) were positive for the blaSPM-1 gene. The blaIMP and blaVIM genes were not detected. The molecular typing revealed 21 molecular profiles of which seven were detected in distinct hospitals and periods. Among the six positive blaSPM-1 isolates, three presented the same clonal profile and were from the same hospital, whereas the other three presented different clonal profiles. CONCLUSIONS: These results revealed that P. aeruginosa is able to accumulate different resistance and virulence factors, making the treatment of infections difficult. The identification of blaSPM-1 genes and the dissemination of clones in different hospitals, indicate the need for stricter application of infection control measures in hospitals in Recife, Brazil, aiming at reducing costs and damages caused by P. aeruginosa infections.

An outbreak of acute post-cataract surgery Pseudomonas sp. endophthalmitis caused by contaminated hydrophilic intraocular lens solution

OBJECTIVE

To report the investigation for the source of infection and the clinical course and treatment response of 11 cases of acute post-cataract surgery endophthalmitis that developed during an outbreak.

DESIGN

Retrospective, consecutive, interventional case series.

PARTICIPANTS

Eleven patients who developed acute postoperative endophthalmitis after an uneventful cataract surgery with intraocular lens implantation from September 6 to 29, 2010, at a tertiary eye care center in South India.

METHODS

Aqueous aspirates, vitreous aspirates, and environmental surveillance specimens were sampled. All specimens were subjected to smear and culture. Positive cultures were subjected to antibiotic susceptibility. Genotypic diversity was determined by polymerase chain reaction (PCR) with enterobacterial repetitive intergenic consensus (ERIC) primers of each strain and was used to establish the clonal relationship between clinical and environmental isolates. The clinical patterns were analyzed.

MAIN OUTCOME MEASURES

Positive microbiology, molecular diagnostic similarity among the culture positive endophthalmitis cases, and surveillance specimens.

RESULTS

Aqueous and vitreous samples showed gram-negative bacilli in the smears of 8 of 11 eyes, and cultures grew Pseudomonas aeruginosa in 5 of 11 eyes. Among the samples from various surveillance specimens cultured, only the hydrophilic acrylic intraocular lenses and their solution grew P. aeruginosa, with antibiotic susceptibility pattern identical to the clinical isolates. The isolates from the patients and the intraocular lens solution revealed matching patterns similar to an American Type Culture Collection (ATCC) strain of P. aeruginosa on ERIC-PCR. The intraocular lenses of the same make were discontinued at our hospital, and the endophthalmitis did not recur. The final visual acuity improved to ≥ 20/50 in 8 of 11 patients (72.7%). One patient developed retinal detachment, but was treated successfully, and 2 other patients progressed to phthisis bulbi.

CONCLUSIONS

Positive microbiology and the ERIC-PCR results proved that contamination of hydrophilic intraocular lenses and the preservative solution was the source of infection in this outbreak. Early detection and a planned approach during the outbreak helped us to achieve good visual and anatomic outcomes, even though the offending organism was identified as P. aeruginosa.

Antibiotic susceptibility patterns of pseudomonas corneal ulcers in contact lens wearers

PURPOSE

To evaluate the resistance or susceptibility of Pseudomonas aeruginosa, the most common pathogen in contact lens keratitis and corneal ulcer, to different antibiotic regimens.

MATERIALS AND METHODS

This cross-sectional study included all patients with recently diagnosed contact lens corneal ulcer whose culture results were positive for P. aeruginosa, from March 2009 to March 2010. The empirical antibiotic therapy was changed to appropriate antibiotics according to the culture results, provided that satisfactory clinical improvement was not achieved with the initial antibiotic regimen. The overall sensitivity or resistance of P. aeruginosa to the most commonly used antibiotics was assessed based on the results of the antibiograms.

RESULTS

Fifty-two patients (43 females and 9 males) were included. Forty-five patients (86%) were wearing cosmetic contact lenses, while 7 patients (14%) were using therapeutic contact lenses. Thirty-nine patients (75%) were hospitalized and13 patients (25%) were followed up through an outpatient clinic. Thirty patients (58%) had central ulcers, whereas 22 patients (42%) had peripheral ulcers. Twelve patients (23%) had hypopyon in their first exam. The mean time to diagnose the ulcer after the last time wearing was 2 days (range: 12 hours to 5 days). AMT was required for 10 patients (19%). Based on the antibiograms, PA was shown to be sensitive in 100% of cases to ceftazidime and ciprofloxacin. Amikacin, imipenem, and gentamicin were the second most effective antibiotics.

CONCLUSION

P. aeruginosa was highly sensitive to ceftazidime, ciprofloxacin, and amikacin. All cases were resistant to cefazolin. Resistance to multiple antibiotics might be a significant concern in patients with corneal ulcers. In referral centers dealing with corneal ulcers, the initial antibiotic regimens should be changed from time to time to prevent this phenomenon.

Pseudomonas aeruginosa growth in Refresh Plus®

PURPOSE

To assess Pseudomonas aeruginosa growth in Refresh Plus(®), a unit-dose preservative-free ophthalmic solution indicated for the treatment of dry eye and after laser-assisted in situ keratomileusis (LASIK) surgery, which contains carboxymethylcellulose 0.5% as its active ingredient.

METHODS

Multiple test tubes of Refresh Plus were inoculated with 3 clinical ocular isolates of P. aeruginosa to achieve a target concentration of ∼100 colony-forming units (CFU)/mL. The tubes were incubated at 25°C and samples were aseptically removed at 6, 12, and 24 h. The samples were cultured to enumerate the population at each time point.

RESULTS

After 6 h incubation, the number of CFU/mL was 3,200 for isolate 1, 2,000 for isolate 2, and 6,480 CFU/mL for isolate 3. For all 3 organisms tested, the number of CFU/mL after 12 and 24 h incubation was >10(6) CFU/mL.

CONCLUSIONS

Under the conditions of this experiment, Refresh Plus appears to support P. aeruginosa growth, suggesting that if the solution in a unit-dose vial of Refresh Plus were contaminated with P. aeruginosa during use, the organism would survive and replicate in the solution over time. Noncompliance with the manufacturer's recommendations (i.e., reuse of an open vial) may result in contamination of the solution with P. aeruginosa, which may cause severe keratitis.

Evaluation of tumour necrosis factor-alpha and interleukin-1beta in an experimental pyelonephritis model induced with planktonic and biofilms cells of Pseudomonas aeruginosa

Urinary tract infections may induce severe inflammation, transient impairment in renal function and scar formation, ranging in severity from acute symptomatic pyelonephritis to chronic pyelonephritis, and have the potential to lead to renal failure and death. In the present study, the relationship between production of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), neutrophil recruitment, bacterial colonization and tissue damage was investigated using a mouse model of acute ascending pyelonephritis induced with planktonic and biofilm cells of Pseudomonas aeruginosa. Neutrophil influx correlated with rise in TNF-alpha and IL-1beta, indicating an association between these cytokines and neutrophil infiltration. However, biofilm cells of P aeruginosa induced higher levels of TNF-alpha and IL-1beta leading to higher neutrophil infiltration causing tissue damage, assessed in terms of malondialdehyde, lactate dehydrogenase and glutathione content, which may have contributed to bacterial persistence compared with their planktonic counterparts. The results of the present investigation suggest that exaggerated cytokine production during P aeruginosa-induced pyelonephritis causes tissue damage operative through neutrophil recruitment leading to bacterial persistence in host tissues. The findings of the present study may be relevant for the better understanding of disease pathophysiology and for the future developments of preventive strategies against pyelonephritis based on anti-inflammatory intervention.

Detection of virulence factors in Serratia strains isolated from contact lens-associated corneal ulcers

PURPOSE

This paper reports on the microbiological findings pertaining to three Serratia isolates from soft contact lens-related corneal ulcers, which represent a complication of contact lens wear reported with increasing frequency.

METHODS

Bacterial identification and antibiotic susceptibility testing were performed using the Vitek system. Serratia's ability to form biofilm, produce gelatinase, elastase and alkaline protease, and invade human corneal epithelial (HCE) cells was investigated. The isolates' susceptibility to the following disinfectants was tested: (a) ReNu MultiPlus(®) , containing polyaminopropyl biguanide 0.0001%; (b) Opti-Free Express(®) , containing polyquaternium-1 0.001% and myristamidopropyldimethylamine 0.0005%; (c) Opti-Free Replenish(®) , containing polyquaternium-1 0.001% and myristamidopropyldimethylamine 0.0005%, and (d) Oxysept Comfort(®) , a one-step 3% hydrogen peroxide-catalase system.

RESULTS

Two Serratia marcescens and one Serratia liquefaciens were identified. All the strains were susceptible to aminoglycosides and fluoroquinolones. No isolate formed biofilm or significantly invaded HCE cells; all produced alkaline protease and gelatinase, but not elastase. Opti-Free Express(®) and Opti-Free Replenish(®) were active against S. liquefaciens, but failed to kill the S. marcescens isolates within the minimum recommended time (6 hours). ReNu MultiPlus(®) needed 6 hours to kill one strain of S. marcescens, which is 2 hours more than recommended. Conversely, Oxysept Comfort(®) was always effective within the minimum recommended time (6 hours).

CONCLUSIONS

The ability to produce alkaline protease and gelatinase may play a major role in the pathogenesis of contact lens-related Serratia keratitis. Several types of contact lens solutions may be ineffective in eradicating Serratia from contaminated contact lens cases within the minimum recommended time. Only exposure to Oxysept Comfort(®) was always effective against Serratia in this study.

Effects of iron depletion on antimicrobial activities against planktonic and biofilm Pseudomonas aeruginosa

Objectives

Iron plays an important role in the development of Pseudomonas aeruginosa biofilm. Here we evaluated effects of iron depletion on the antimicrobial activity of ceftazidime, tobramycin and ciprofloxacin against planktonic and biofilm Pseudomonas aeruginosa.

Methods

We tested the sensitivities of wild-type PAO1, type-IV pilus mutant PAO-ΔpilHIJK and the quorum-sensing mutant PAO-JP2 P. aeruginosa planktonic cultures and biofilms to antibiotics under iron-depleted conditions.

Key findings

In planktonic bacteria, the minimum concentration that inhibited visible growth (MIC) of ciprofloxacin was increased slightly in an iron-depleted environment in all three strains, whereas the MIC of tobramycin was similar in iron-depleted and control environments. The MIC of ceftazidime increased in the PAO-JP2 strain when iron was depleted. Tobramycin achieved the best bactericidal effect in biofilms. Viable counts were reduced by one log under iron-depleted conditions in all three strains when tobramycin reached 4 MIC and when ceftazidime and ciprofloxacin reached 8 MIC.

Conclusions

This study suggests that once the biofilm is formed, iron depletion may only slightly promote the bactericidal effect of antibiotics on PAO1, PAO-ΔpilHIJK and PAO-JP2. Although these changes were relatively small, iron as one of the environmental factors should not be ignored when evaluating bactericidal effect of antibiotics. The combination of an iron chelator and antibiotics may have therapeutic value under certain bacterial growth conditions.

Properties of PASP: a Pseudomonas protease capable of mediating corneal erosions

PURPOSE

To analyze PASP in terms of its gene distribution and expression, its corneal pathologic effects, its enzymatic properties, and the protectiveness of the immune response to this protease.

METHODS

Twenty-five strains of P. aeruginosa were analyzed for the PASP gene and secreted protein by PCR and Western blot analysis, respectively. Active recombinant (r)PASP (10 microg/20 microL) or heat-inactivated rPASP was intrastromally injected into rabbit corneas. Pathologic changes were monitored by slit lamp examination (SLE) and histopathology. Purified rPASP was assayed for cleavage of collagens and susceptibility to TLCK. Rabbit antibody to rPASP was produced and tested for enzyme inactivation, and actively immunized rabbits were challenged by intrastromal injection of active rPASP (5 microg).

RESULTS

All 25 strains of P. aeruginosa analyzed were positive for the PASP gene and protein. SLE scores of eyes injected with active rPASP were significantly higher than control eyes at all postinjection times (PI; P <or= 0.004). Histopathologic studies documented the destruction of the corneal epithelial layer and portions of the corneal stroma at 9 hours PI, and polymorphonuclear (PMN) leukocyte infiltration into the cornea by 24 hours after active rPASP injection. PASP cleaved type I and IV collagens and was susceptible to TLCK inhibition. PASP was present in the cytoplasm and periplasm, but only secreted PASP was enzymatically active. A high antibody titer (ELISA titer >or= 10,000) was produced, but this antibody did not protect against active rPASP challenge.

CONCLUSIONS

PASP is a commonly produced Pseudomonas protease that can cleave collagens and cause corneal erosions.

Comparison of virulence factors in Pseudomonas aeruginosa strains isolated from contact lens- and non-contact lens-related keratitis

Pseudomonas aeruginosa is one of the common pathogens associated with corneal infection, particularly in contact lens-related keratitis events. The pathogenesis of P. aeruginosa in keratitis is attributed to the production of virulence factors under certain environmental conditions. The aim of this study was to determine differences in the virulence factors of P. aeruginosa isolated from contact lens- and non-contact lens-related keratitis. Associations were assessed between type III secretion toxin-encoding genes, protease profiles, biofilm formation, serotypes and antibiotic-resistance patterns among 27 non-contact lens- and 28 contact lens-related P. aeruginosa keratitis isolates from Australia. Strains with a exoS +/exoU − genotype and a type I protease profile predominated in the non-contact lens-related keratitis isolates, whereas the exoS −/exoU + and a type II protease profile was associated with contact lens-related isolates (P<0.05). A strong biofilm formation phenotype was found to be associated with the possession of the exoU gene, and serotypes E, I and C. The exoS gene was strongly associated with serotypes G, A and B, while exoU was associated with serotypes E and C. Six out of fifty-five (11 %) clinical isolates were non-susceptible (intermediate-resistant or resistant) to ofloxacin and moxifloxacin. All resistant isolates were from non-contact lens-related keratitis. The results suggest that P. aeruginosa isolates from different infection origins may have different characteristics. A better understanding of these differences may lead to further development of evidence-based clinical guidelines for the management of keratitis.