Sean Gorman

Clinical relevance of the ESKAPE pathogens.

In recent years, the Infectious Diseases Society of America has highlighted a faction of antibiotic-resistant bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) – acronymically dubbed ‘the ESKAPE pathogens’ – capable of ‘escaping’ the biocidal action of antibiotics and mutually representing new paradigms in pathogenesis, transmission and resistance. This review aims to consolidate clinically relevant background information on the ESKAPE pathogens and provide a contemporary summary of bacterial resistance, alongside pertinent microbiological considerations necessary to face the mounting threat of antimicrobial resistance.

Formation of Propionibacterium acnes biofilms on orthopaedic biomaterials and their susceptibility to antimicrobials

Failure to treat and eradicate prosthetic hip infection with systemic antibiotic regimens is usually due to the fact that the infection is associated with biofilm formation and that bacterial cells growing within a biofilm exhibit increased resistance to antimicrobial agents. In this in vitro study, we investigated the susceptibility of prosthetic hip Propionibacterium acnes and Staphylococcus spp. isolates growing within biofilms on polymethylmethacrylate (PMMA) bone cement to a range of antibiotics. All P. acnes isolates in the biofilm mode of growth demonstrated considerably greater resistance to cefamandole, ciprofloxacin and vancomycin. In contrast, only four of the eight P. acnes isolates demonstrated an increase in resistance to gentamicin. All ten Staphylococcus spp. isolates in the biofilm mode of growth exhibited large increases in resistance to gentamicin and cefamandole with eight of the ten isolates also exhibiting an increase in resistance to vancomycin. However, only three of the ten Staphylococcus spp. isolates exhibited an increase in resistance to ciprofloxacin. Biofilms were also formed on three different titanium alloys and on PMMA bone cement using P. acnes, Staphylococcus epidermidis and Staphylococcus aureus strains to determine if the underlying biomaterial surface had an effect on biofilm formation and the antimicrobial susceptibility of the bacteria growing within biofilms. Although differences in the rate at which the three strains adhered to the different biomaterials were apparent, no differences in biofilm antibiotic resistance between the biomaterials were observed. In the light of these results, it is important that the efficacy of other antibiotics against P. acnes and Staphylococcus spp. prosthetic hip isolates growing within biofilms on orthopaedic biomaterials be determined to ensure optimal treatment of orthopaedic implant infection.

Antibiofilm activities of 1-alkyl-3-methylimidazolium chloride ionic liquids

Microbial biofilms are ubiquitous in nature and represent the predominant mode of growth of microorganisms. A general characteristic of biofilm communities is that they tend to exhibit significant tolerance to antimicrobial challenge compared with planktonic bacteria of the same species The antibiofilm activity of a series of 1-alkyl-3-methylimidazolium chloride ionic liquids has been evaluated against a panel of clinically significant microbial pathogens, including MRSA. A comparison of antimicrobial activity against planktonic bacteria and established biofilms is presented. In general, these ionic liquids possess potent, broad spectrum antibiofilm activity.

Staphylococcus epidermidis device-related infections: pathogenesis and clinical management

Staphylococcus epidermidis, the most frequently isolated coagulase-negative staphylococcus, is the leading cause of infection related to implanted medical devices (IMDs). This is directly related to its capability to establish multilayered, highly structured biofilms on artificial surfaces. At present, conventional systemic therapies using standard antimicrobial agents represent the main strategy to treat and prevent medical device-associated infections. However, device-related infections are notoriously difficult to treat and bacteria within biofilm communities on the surface of IMDs frequently outlive treatment, and removal of the medical device is often required for successful therapy. Importantly, major advances in this research area have been made, leading to a greater understanding of the complexities of biofilm formation of S. epidermidis and resulting in significant developments in the treatment and prevention of infections related to this member of the coagulase-negative group of staphylococci. This review will examine the pathogenesis of the clinically significant S. epidermidis and provide an overview of the conventional and emerging antibiofilm approaches in the management of medical device-associated infections related to this important nosocomial pathogen.

Improved detection of infection in hip replacements

Our aim was to determine if the detection rate of infection of total hip replacements could be improved by examining the removed prostheses. Immediate transfer of prostheses to an anaerobic atmosphere, followed by mild ultrasonication to dislodge adherent bacteria, resulted in the culture of quantifiable numbers of bacteria, from 26 of the 120 implants examined. The same bacterial species were cultured by routine microbiological techniques from only five corresponding tissue samples. Tissue removed from 18 of the culture-positive implants was suitable for quantitative tissue pathology and inflammatory cells were present in all samples. Furthermore, inflammatory cells were present in 87% of tissue samples taken from patients whose implants were culture-negative. This suggests that these implants may have been infected by bacteria which were not isolated by the techniques of culture used. The increased detection of bacteria from prostheses by culture has improved postoperative antibiotic therapy and should reduce the need for further revision.

Recent advances in bacteriophage therapy: how delivery routes, formulation, concentration and timing influence the success of phage therapy

Objectives  Bacteriophages are bacteria‐specific viruses that infect and, in the case of obligately lytic phages, destroy their host bacteria. Phage therapy has been used therapeutically to combat bacterial infections since their discovery. This paper reviewed recent in‐vivo phage therapy studies, with a distinct focus on the effect of delivery routes, phage concentration and timing of administration on the success of the therapy.

Evaluation of a poly(vinyl pyrollidone)-coated biomaterial for urological use

The associated problems of bacterial biofilm formation and encrustation that may cause obstruction or blockage of urethral catheters and ureteral stents often hinders the effective use of biomaterials within the urinary tract. In this in vitro study, we have investigated the surface properties of a hydrophilic poly(vinyl pyrollidone) (PVP)-coating applied to polyurethane and determined its suitability for use as a urinary tract biomaterial by comparing its lubricity and ability to resist bacterial adherence and encrustation with that of uncoated polyurethane and silicone. The PVP-coated polyurethane was significantly more hydrophilic and more lubricious than either uncoated polyurethane or silicone. Adherence of a hydrophilic Escherichia coli isolate to PVP-coated polyurethane and uncoated polyurethane was similar but significantly less than adherence to silicone. Adherence of a hydrophobic Enterococcus faecalis isolate to PVP-coated polyurethane and silicone was similar but was significantly less than adherence to uncoated polyurethane. Struvite encrustation was similar on the PVP-coated polyurethane and silicone but significantly less than on uncoated polyurethane. Furthermore, hydroxyapatite encrustation was significantly less on the PVP-coated polyurethane than on either uncoated polyurethane or silicone. The results suggest that the PVP-coating could be useful in preventing complications caused by bacterial biofilm formation and the deposition of encrustation on biomaterials implanted in the urinary tract and, therefore, warrants further evaluation.

The Potential of Antimicrobial Peptides as Biocides

Antimicrobial peptides constitute a diverse class of naturally occurring antimicrobial molecules which have activity against a wide range of pathogenic microorganisms. Antimicrobial peptides are exciting leads in the development of novel biocidal agents at a time when classical antibiotics are under intense pressure from emerging resistance, and the global industry in antibiotic research and development stagnates. This review will examine the potential of antimicrobial peptides, both natural and synthetic, as novel biocidal agents in the battle against multi-drug resistant pathogen infections.

Eradication of Pseudomonas aeruginosa biofilms by atmospheric pressure non-thermal plasma.

Bacteria exist, in most environments, as complex, organised communities of sessile cells embedded within a matrix of self-produced, hydrated extracellular polymeric substances known as biofilms. Bacterial biofilms represent a ubiquitous and predominant cause of both chronic infections and infections associated with the use of indwelling medical devices such as catheters and prostheses. Such infections typically exhibit significantly enhanced tolerance to antimicrobial, biocidal and immunological challenge. This renders them difficult, sometimes impossible, to treat using conventional chemotherapeutic agents. Effective alternative approaches for prevention and eradication of biofilm associated chronic and device-associated infections are therefore urgently required. Atmospheric pressure non-thermal plasmas are gaining increasing attention as a potential approach for the eradication and control of bacterial infection and contamination. To date, however, the majority of studies have been conducted with reference to planktonic bacteria and rather less attention has been directed towards bacteria in the biofilm mode of growth. In this study, the activity of a kilohertz-driven atmospheric pressure non-thermal plasma jet, operated in a helium oxygen mixture, against Pseudomonas aeruginosa in vitro biofilms was evaluated. Pseudomonas aeruginosa biofilms exhibit marked susceptibility to exposure of the plasma jet effluent, following even relatively short (∼10′s s) exposure times. Manipulation of plasma operating conditions, for example, plasma operating frequency, had a significant effect on the bacterial inactivation rate. Survival curves exhibit a rapid decline in the number of surviving cells in the first 60 seconds followed by slower rate of cell number reduction. Excellent anti-biofilm activity of the plasma jet was also demonstrated by both confocal scanning laser microscopy and metabolism of the tetrazolium salt, XTT, a measure of bactericidal activity.

Comparative assessment of ureteral stent biomaterial encrustation

Long-term use of ureteral stents is hindered by the inherent problem of biomaterial encrustation which may lead to stone formation and attendant problems. The wide variety of polymeric biomaterials currently used for stent fabrication suggests that no single material is significantly superior to the others at resisting encrustation. A model representing upper urinary tract conditions was employed to compare the long-term struvite and hydroxyapatite encrustation of five materials currently used in the fabrication of ureteral stents. Silicone was least prone to struvite encrustation, followed by polyurethane, silitek, percuflex and hydrogel-coated polyurethane, in rank order. Similarly, silicone was least prone to hydroxyapatite encrustation, followed by silitek, polyurethane, percuflex and hydrogel-coated polyurethane. This study has shown that the problem of encrustation may limit the long-term use of ureteral stent biomaterials and suggests directions for improvement of biomaterials in this regard.