Lipopolysaccharide structure modulates cationic biocide susceptibility and crystalline biofilm formation in Proteus mirabilis.

Chlorhexidine (CHD) is a cationic biocide used ubiquitously in healthcare settings. Proteus mirabilis, an important pathogen of the catheterized urinary tract, and isolates of this species are often described as "resistant" to CHD-containing products used for catheter infection control. To identify the mechanisms underlying reduced CHD susceptibility in P. mirabilis, we subjected the CHD tolerant clinical isolate RS47 to random transposon mutagenesis and screened for mutants with reduced CHD minimum inhibitory concentrations (MICs). One mutant recovered from these screens (designated RS47-2) exhibited ~ 8-fold reduction in CHD MIC. Complete genome sequencing of RS47-2 showed a single mini-Tn5 insert in the waaC gene involved in lipopolysaccharide (LPS) inner core biosynthesis. Phenotypic screening of RS47-2 revealed a significant increase in cell surface hydrophobicity and serum susceptibility compared to the wildtype, and confirmed defects in LPS production congruent with waaC inactivation. Disruption of waaC was also associated with increased susceptibility to a range of other cationic biocides but did not affect susceptibility to antibiotics tested. Complementation studies showed that repression of smvA efflux activity in RS47-2 further increased susceptibility to CHD and other cationic biocides, reducing CHD MICs to values comparable with the most CHD susceptible isolates characterized. The formation of crystalline biofilms and blockage of urethral catheters was also significantly attenuated in RS47-2. Taken together, these data show that aspects of LPS structure and upregulation of the smvA efflux system function in synergy to modulate susceptibility to CHD and other cationic biocides, and that LPS structure is also an important factor in P. mirabilis crystalline biofilm formation.

Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity.

Carbon nanomaterials have gained significant interest over recent years in the field of electrochemistry, and they may be limited in their use due to issues with their difficulty in dispersion. Enzymes are prime components for detecting biological molecules and enabling electrochemical interactions, but they may also enhance multiwalled carbon nanotube (MWCNT) dispersion. This study evaluated a MWCNT and diamine oxidase enzyme (DAO)-functionalised screen-printed electrode (SPE) to demonstrate improved methods of MWCNT functionalisation and dispersion. MWCNT morphology and dispersion was determined using UV-Vis spectroscopy (UV-Vis) and scanning electron microscopy (SEM). Carboxyl groups were introduced onto the MWCNT surfaces using acid etching. MWCNT functionalisation was carried out using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), followed by DAO conjugation and glutaraldehyde (GA) crosslinking. Modified C-MWNCT/EDC-NHS/DAO/GA was drop cast onto SPEs. Modified and unmodified electrodes after MWCNT functionalisation were characterised using optical profilometry (roughness), water contact angle measurements (wettability), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) (vibrational modes and elemental composition, respectively). The results demonstrated that the addition of the DAO improved MWCNT homogenous dispersion and the solution demonstrated enhanced stability which remained over two days. Drop casting of C-MWCNT/EDC-NHS/DAO/GA onto carbon screen-printed electrodes increased the surface roughness and wettability. UV-Vis, SEM, Raman and EDX analysis determined the presence of carboxylated MWCNT variants from their non-carboxylated counterparts. Electrochemical analysis demonstrated an efficient electron transfer rate process and a diffusion-controlled redox process. The modification of such electrodes may be utilised for the development of biosensors which could be utilised to support a range of healthcare related fields.

A traditional Ugandan Ficus natalensis bark cloth exhibits antimicrobial activity against methicillin-resistant Staphylococcus aureus.

AIMS: Surgical site, soft tissue and wound infections are some of the most prominent causes of healthcare-associated infections (HCAIs). Developing novel antimicrobial textiles and wound dressings may help alleviate the risk of developing HCAIs. We aimed to determine the antimicrobial efficacy of natural Ugandan bark cloth derived exclusively from the Ficus natalensis tree. METHODS AND RESULTS: Antimicrobial contact and disc diffusion assays, coupled with time-kill kinetic assays, demonstrated that bark cloth inhibited the growth of a clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strain and acted as a bactericidal agent causing a seven-log reduction in bacterial viability. Scanning electron microscopy was used to reveal morphological changes in the bacterial cell ultrastructure when exposed to bark cloth, which supported a proposed mechanism of antimicrobial activity. CONCLUSIONS: The observed antimicrobial properties, combined with the physical characteristics elicited by bark cloth, suggest this product is ideally suited for wound and other skin care applications. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report where a whole bark cloth product made by traditional methods has been employed as an antimicrobial fabric against MRSA. Bark cloth is a highly sustainable and renewable product and this study presents a major advance in the search for natural fabrics which could be deployed for healthcare applications.

Rhenium and yttrium ions as antimicrobial agents against multidrug resistant Klebsiella pneumoniae and Acinetobacter baumannii biofilms.

Antimicrobial resistance presents major global concerns to patient health. In this study, metal ions of molybdenum, rhenium, yttrium and thallium were tested against bacteria in planktonic and biofilm form using one strain of Klebsiella pneumoniae and Acinetobacter baumannii. The antimicrobial efficacy of the metal ions was evaluated against the planktonic bacterial strains using minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations, whilst the efficacy of the metal ions against biofilms was tested using a crystal violet biofilm assay. Live Dead staining was used to visualize the antimicrobial activity elicited by the metal ions on the bacterial cell. The results showed that higher concentrations of the metals were required to inhibit the growth of biofilms (72·9 mg l-1 to 416·7 mg l-1 ), in comparison to their planktonic counterparts. MICs of the metal ions (<46·9 mg l-1 ) (planktonic cells) did not affect biofilm formation. Overall, rhenium and yttrium were effective antimicrobial agents. Molybdenum demonstrated the greatest level of biotoxicity. When taking into account these results and the known toxicity of thallium, it is possible that rhenium or yttrium ions could be developed as effective biocidal formulations in order to prevent transmission in healthcare environments. SIGNIFICANCE AND IMPACT OF THE STUDY: The metal ions, molybdenum, rhenium, thallium and yttrium were tested against both Klebsiella pneumoniae and Acinetobacter baumannii in planktonic and biofilm forms. This research demonstrated that all the metal ions may be effective antimicrobial agents. However, molybdenum induced high levels of cytotoxicity, whilst, there was no significant difference in the toxicity of the other metal ions tested. When considering the results for the antimicrobial efficacy and biotoxicity of the metal ions, in conjunction with the known toxicity of thallium in certain chemical compositions, it was concluded that overall rhenium or yttrium ions may be effective antimicrobial agents, one potential application may be utilizing these metal ions in hospital surface cleaning formulations.