Effectiveness of mupirocin and polymyxin B in experimental Staphylococcus aureus, Pseudomonas aeruginosa, and Serratia marcescens keratitis

A Comparative Review on Current and Future Drug Targets Against Bacteria & Malaria

Long before the discovery of drugs like 'antibiotic and anti-parasitic drugs', the infectious diseases caused by pathogenic bacteria and parasites remain as one of the major causes of morbidity and mortality in developing and underdeveloped countries. The phenomenon by which the organism exerts resistance against two or more structurally unrelated drugs is called multidrug resistance (MDR) and its emergence has further complicated the treatment scenario of infectious diseases. Resistance towards the available set of treatment options and poor pipeline of novel drug development puts an alarming situation. A universal goal in the post-genomic era is to identify novel targets/drugs for various life-threatening diseases caused by such pathogens. This review is conceptualized in the backdrop of drug resistance in two major pathogens i.e. "Pseudomonas aeruginosa" and "Plasmodium falciparum". In this review, the available targets and key mechanisms of resistance of these pathogens have been discussed in detail. An attempt has also been made to analyze the common drug targets of bacteria and malaria parasite to overcome the current drug resistance scenario. The solution is also hypothesized in terms of a present pipeline of drugs and efforts made by scientific community.

In vitro Pharmacodynamics and PK/PD in Animals

In the last decade, considerable advancements have been made to identify the pharmacokinetic/pharmacodynamic (PK/PD) index that defines the antimicrobial activity of polymyxins. Dose-fractionation studies performed in hollow-fiber models found that altering the dosing schedule had little impact on the killing or suppression of resistance emergence, alluding to AUC/MIC as the pharmacodynamic index that best describes polymyxin's activity. For in vivo efficacy, the PK/PD index that was the most predictive of the antibacterial effect of colistin against P. aeruginosa and A. baumannii was ƒAUC/MIC.

Microbiological risk assessment for personal care products

Regulatory decisions regarding microbiological safety of cosmetics and personal care products are primarily hazard-based, where the presence of a potential pathogen determines decision-making. This contrasts with the Food industry where it is a commonplace to use a risk-based approach for ensuring microbiological safety. A risk-based approach allows consideration of the degree of exposure to assess unacceptable health risks. As there can be a number of advantages in using a risk-based approach to safety, this study explores the Codex Alimentarius (Codex) four-step Microbiological Risk Assessment (MRA) framework frequently used in the Food industry and examines how it can be applied to the safety assessment of personal care products. The hazard identification and hazard characterization steps (one and two) of the Codex MRA framework consider the main microorganisms of concern. These are addressed by reviewing the current industry guidelines for objectionable organisms and analysing reports of contaminated products notified by government agencies over a recent 5-year period, together with examples of reported outbreaks. Data related to estimation of exposure (step three) are discussed, and examples of possible calculations and references are included. The fourth step, performed by the risk assessor (risk characterization), is specific to each assessment and brings together the information from the first three steps to assess the risk. Although there are very few documented uses of the MRA approach for personal care products, this study illustrates that it is a practicable and sound approach for producing products that are safe by design. It can be helpful in the context of designing products and processes going to market and with setting of microbiological specifications. Additionally, it can be applied reactively to facilitate decision-making when contaminated products are released on to the marketplace. Currently, the knowledge available may only allow a qualitative or semi-quantitative rather than fully quantitative risk assessment, but an added benefit is that the disciplined structuring of available knowledge enables clear identification of gaps to target resources and if appropriate, instigate data generation.

A proof-of-concept model for the identification of the key events in the infection process with specific reference to Pseudomonas aeruginosa in corneal infections

BACKGROUND

It is a common medical practice to characterise an infection based on the causative agent and to adopt therapeutic and prevention strategies targeting the agent itself. However, from an epidemiological perspective, exposure to a microbe can be harmless to a host as a result of low-level exposure or due to host immune response, with opportunistic infection only occurring as a result of changes in the host, pathogen, or surrounding environment.

METHODS

We have attempted to review systematically the key host, pathogen, and environmental factors that may significantly impact clinical outcomes of exposure to a pathogen, using Pseudomonas aeruginosa eye infection as a case study.

RESULTS AND DISCUSSION

Extended contact lens wearing and compromised hygiene may predispose users to microbial keratitis, which can be a severe and vision-threatening infection. P. aeruginosa has a wide array of virulence-associated genes and sensing systems to initiate and maintain cell populations at the corneal surface and beyond. We have adapted the well-known concept of the epidemiological triangle in combination with the classic risk assessment framework (hazard identification, characterisation, and exposure) to develop a conceptual pathway-based model that demonstrates the overlapping relationships between the host, the pathogen, and the environment; and to illustrate the key events in P. aeruginosa eye infection.

CONCLUSION

This strategy differs from traditional approaches that consider potential risk factors in isolation, and hopefully will aid the identification of data and models to inform preventive and therapeutic measures in addition to risk assessment. Furthermore, this may facilitate the identification of knowledge gaps to direct research in areas of greatest impact to avert or mitigate adverse outcomes of infection.

Ocular drug delivery - a look towards nanobioadhesives

IMPORTANCE OF THE FIELD

A major challenge emanating in the design of topical ophthalmic preparations is their short precorneal residence time. Retention of a drug delivery system in the front of the eye is thus desirable. One solution identified to address this concern is a retentive system that can preferably be delivered in a liquid drop form and ultimately remain attached to the corneal tissue owing to incorporation of a bioadhesive component. Forward-thinking approaches are required to achieve advancements in this approach for the attainment of an effective drug concentration at the site of action. Accordingly, several investigators have identified the benefits of nanotechnology-based drug delivery systems for ophthalmic drug delivery.

AREAS COVERED IN THIS REVIEW

A concerted effort was made to review critically all 'nanobioadhesives', that is, nanosystems designed for ocular drug delivery with the goal of attaining prolonged ocular retention, in a systematic, chronological manner, from their reported point of inception to the present.

WHAT THE READER WILL GAIN

A perspective on possible future trends in this growing field of ocular drug delivery is formulated.

TAKE HOME MESSAGE

The importance of and need for new developments in the field of ocular nanobioadhesives is emphasized.

Animal models of bacterial keratitis

Bacterial keratitis is a disease of the cornea characterized by pain, redness, inflammation, and opacity. Common causes of this disease are Pseudomonas aeruginosa and Staphylococcus aureus. Animal models of keratitis have been used to elucidate both the bacterial factors and the host inflammatory response involved in the disease. Reviewed herein are animal models of bacterial keratitis and some of the key findings in the last several decades.

Liberação intraocular de ofloxacina associada a lente de contato biossintética em ceratite bacteriana experimental em cães

Avaliou-se a concentração de ofloxacina liberada por uma lente de contato de membrana de celulose biossintética, para tratamento de ceratite bacteriana experimental em cães, pela inoculação de Staphylococcus aureus intraestromal. Comparou-se o tratamento com a lente de contato biossintética impregnada com ofloxacina à terapia tópica convencional. Realizou-se avaliação microbiológica e dosagem de ofloxacina no humor aquoso por meio do método de cromatografia líquida de alto rendimento (HPLC). Houve diferença estatística na contagem de colônias bacterianas entre os olhos com ceratite e os demais grupos, no primeiro dia de coleta. O biomaterial, impregnado com ofloxacina, promoveu liberação gradual durante o período de avaliação, aos três e sete dias; no terceiro dia, o grupo tratado com a lente de contato obteve mediana de 3,72μg/mL, enquanto o grupo tratado com colírio resultou em 49,56μg/mL. Apesar do valor inferior, o grupo com lente de contato atingiu a concentração inibitória mínima, sendo eficaz no controle da infecção bacteriana.

Corneal virulence of Pseudomonas aeruginosa elastase B and alkaline protease produced by Pseudomonas putida

PURPOSE

To measure the specific virulence contributions of two Pseudomonas aeruginosa proteases, elastase B and alkaline protease, when expressed separately by Pseudomonas putida in a rabbit model of bacterial keratitis.

METHODS

P. putida KT2440 was transformed with plasmids that enabled the extracellular production of either elastase or alkaline protease. Protease expression was confirmed by zymography and immunoblotting. P. putida expressing elastase, alkaline protease, or vector alone was injected intrastromally (10(3) colony forming units [CFU]) into rabbit corneas (n=6). Infected eyes were graded by slit-lamp examination (SLE) at 20, 24, 28, and 32 hr postinfection (PI). Rabbits were sacrificed at 33 hr PI, and the log CFU (+/-SEM) per cornea was determined.

RESULTS

SLE scores for eyes infected with P. putida producing elastase were significantly higher than those infected with vector alone at all time points (p<or=0.008). SLE scores for eyes infected with P. putida producing alkaline protease were not significantly higher than the control (p>or=0.1), but small erosions formed in 33% of corneas. At both 24 and 28 hr PI, the SLE scores for corneas infected with P. putida producing elastase were significantly higher than those infected with P. putida producing alkaline protease (p<or=0.002).

CONCLUSIONS

Elastase production by P. putida caused significant increases in SLE scores whereas expression of alkaline protease caused limited corneal erosions. This suggests that the production of elastase during P. aeruginosa keratitis enhances ocular pathology, whereas alkaline protease production contributes to limited corneal erosion.

Methicillin-resistant Staphylococcus aureus infectious keratitis following refractive surgery

PURPOSE

To elucidate risk factors, clinical course, visual outcomes, and treatment of culture-proven methicillin-resistant Staphylococcus aureus (MRSA) infectious keratitis following refractive surgery.

DESIGN

Interventional case series.

METHODS

Multicenter chart review of 13 cases of MRSA keratitis following refractive surgery and literature review.

RESULTS

Thirteen eyes of 12 patients, nine of whom were either healthcare workers or exposed to a hospital surgical setting, developed MRSA keratitis following refractive surgery. All patients presented with a decrease in visual acuity and complaints of pain or irritation in the affected eye. Common signs on slit-lamp biomicroscopy were corneal epithelial defects, focal infiltrates with surrounding edema, conjunctival injection, purulent discharge, and hypopyon. All patients were diagnosed with infectious keratitis on presentation and treated with two antibiotics. All eyes were culture-positive for MRSA.

CONCLUSIONS

According to a computerized MEDLINE literature search, this is the first case series of MRSA infectious keratitis following refractive surgery, the first reports of MRSA keratitis after refractive surgery in patients with no known exposure to a healthcare facility, the first report of MRSA keratitis after a laser in situ keratomileusis (LASIK) enhancement, and the first reports of MRSA keratitis after prophylaxis with fourth-generation fluoroquinolones. MRSA keratitis is a serious and increasing complication following refractive surgery. Patients with exposure to a healthcare environment should be considered at additional risk for developing MRSA keratitis. However, in addition, surgeons should now be vigilant for community-acquired MRSA. Prompt identification with culturing and appropriate treatment of MRSA keratitis after refractive surgery is important to improve visual rehabilitation.

The corneal response to infection withStaphylococcus aureusin the absence of interleukin‐4

Interleukin-4 (IL-4) has previously been implicated in a protective response to Staphylococcus aureus corneal infection. Consequently, the specific role of IL-4 during S. aureus corneal infection was investigated using IL-4 gene knockout mice. The eyes of IL-4-/- mice and wild-type mice were challenged topically with S. aureus and examined at 24 h post-infection. Keratitis was examined clinically and histologically. Bacterial and polymorphonuclear leucocytes (PMN) numbers were enumerated and cytokine and chemokine levels determined by enzyme-linked immunosorbent assay. Exogenous IL-4 was administered to both IL-4-/- and wild-type mice and clinical parameters were determined. A lack of IL-4 resulted in a significant increase in clinical scores, pathology, bacterial load and neutrophil numbers. The absence of IL-4 also resulted in an upregulation of interferon (IFN)-gamma and a downregulation of IL-6, IL-10 and the chemokines KC and macrophage inflammatory protein-2. Administration of exogenous IL-4 to IL-4-/- mice was protective but time-dependent. This study highlights the protective role of IL-4 during S. aureus infection and emphasizes the balance between IL-4 and IFN-gamma in achieving bacterial control and maintaining the integrity of the cornea. This information may lead to the development of novel therapeutic strategies potentially improving the prognosis for infection of this unique avascular site.

The effect of freeze-drying with different cryoprotectants and gamma-irradiation sterilization on the characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-glycolide) nanoparticles

In the present study, the influence of freeze-drying with several cryoprotective agents and gamma (gamma)-irradiation sterilization on the physicochemical characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles was evaluated. Nanoparticles were prepared by W/O/W emulsification solvent evaporation followed by high-pressure homogenization. They were freeze-dried in the presence of 5.0% (w/v) mannitol, trehalose or glucose, with 5.0% (w/v) or 15.0% (w/v) dextran as cryoprotectants. The nanoparticles were irradiated at a dose of 25 kGy using a 60Co source. The following physicochemical properties of the formulations were investigated: the ratio of particle size before (initial) and after freeze-drying, the ease of reconstitution of the nanoparticle suspensions and the drug-release profiles of irradiated and non-irradiated nanoparticles. The antibacterial activity against Pseudomonas aeruginosa was measured. The freeze-drying process induced a significant increase in particle size when no cryoprotectant was employed. Similar results were observed when cryoprotectants were added to the formulation. Only when mannitol was used was no significant size increase measured. Moreover, for formulations with dextran, reconstitution after freeze-drying was difficult by manual agitation and particle size could not be determined because of aggregation. After gamma-sterilization no significant difference in mean particle size was observed, but reconstitution was more difficult and drug release was influenced negatively. Ciprofloxacin HCl incorporated in the nanoparticles was still effective against the micro-organism selected after freeze-drying and gamma-sterilization.

Factorial design, physicochemical characterisation and activity of ciprofloxacin-PLGA nanoparticles

Poly(lactide-co-glycolide) nanoparticles incorporating ciprofloxacin HCl were prepared by means of a W/O/W emulsification solvent evaporation method. The stabiliser selected was poly(vinylalcohol). A 2(4) full factorial design based on four independent variables was used to plan the experiments and the variable parameters were the number of homogenisation cycles, addition of boric acid to the inner water phase containing the drug, ciprofloxacin concentration in the inner water phase and oil:outer water phase ratio. The effects of these parameters on the particle size, zeta potential, drug loading efficiency and drug release were investigated. Also the effect of gamma irradiation on the particle size and drug release was evaluated and DSC and XRD analyses of the compounds and the nanoparticles were performed. The activity on two series of microorganisms, Pseudomonas aeruginosa and Staphylococcus aureus, was examined.