Ability of chlorhexidine, octenidine, polyhexanide and chloroxylenol to inhibit metabolism of biofilm-forming clinical multidrug-resistant organisms

Purpose

This in vitro study was designed to determine if standard antiseptics used for skin and environmental surface cleansing can disrupt the metabolic activity (as a measure of viability) of multidrug-resistant gram-negative bacteria, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus isolates within their native biofilms.

Methods

Sixty clinical isolates of multidrug-resistant bacteria were selected for testing in different chlorhexidine gluconate, octenidine, polyhexanide and chloroxylenol concentrations. Metabolic inhibition of biofilm for each clinical isolate was analysed using a biofilm viability assay.

Results

Chlorhexidine gluconate (mean = 83.8% ± 9.8%) and octenidine (mean = 84.5% ± 6.8%) showed the greatest efficacy against biofilms of the tested microorganisms, with the greatest efficacies against MRSA. The antiseptics demonstrated the least efficacy against biofilms of Pseudomonas aeruginosa.

Conclusion

Chlorhexidine gluconate and octenidine showed the greatest level of bacterial metabolic inhibition and were statistically equivalent. Polyhexanide was more effective than chloroxylenol, but both were inferior to chlorhexidine gluconate and octenidine against the tested organisms.

Natural isothiocyanates express antimicrobial activity against developing and mature biofilms of Pseudomonas aeruginosa

BACKGROUND

The antimicrobial properties of natural isothiocyanates (ITCs) found in plants such as nasturtium (Tropaeolum majus) and horseradish (Armoracia rusticana), and the need of new chemotherapeutic options for treatment of infections caused by multidrug-resistant and biofilm-forming Gram-negative bacteria such as Pseudomonas aeruginosa (Pa), led us to evaluate the effects of three major ITCs, allylisothiocyanate (AITC), benzylisothiocyanate (BITC), and phenylethyl-isothiocyanate (PEITC), and a mixture (ITCM) adapted to the ITC composition after release of active components out of natural sources.

MATERIAL/METHODS

Out of 105Pa isolates 27 isolates with increased biofilm formation were selected for testing. The effects of ITCs on Pa were evaluated regarding (1) planktonic bacterial proliferation, (2) biofilm formation, (3) metabolic activity in mature biofilms, and (4) synergism of ITCs and antibiotics.

RESULTS

(1) Each ITC had anti-Pa activity. Mean minimum inhibitory concentrations (MICs) were (μg/ml, mean±standard deviation): AITC 103±6.9; BITC, 2145±249; PEITC 29,423±1652; and ITCM, 140±5. (2) Treating bacteria with PEITC and ITCM in concentrations below the MIC significantly inhibited biofilm formation. Particularly, ITCM reduced biofilm mass and bacterial proliferation. (3) ITCs significantly inhibited metabolic activity in mature biofilms. (4) Combining ITCs with meropenem synergistically increased antimicrobial efficacy on Pa biofilms.

CONCLUSIONS

ITCs represent a promising group of natural anti-infective compounds with activity against Pa biofilms.

MRSA decolonization failure-are biofilms the missing link?

BACKGROUND

Device-associated infections due to biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) have been recently associated with the failure of antibiotic treatment and decolonization measures. The goal of our study was to evaluate the extent to which the formation of biofilms influenced the efficacy of topical decolonization agents or disinfectants such as mupirocin (MUP), octenidine (OCT), chlorhexidine (CHG), polyhexanide (POL), and chloroxylenol (CLO).

METHODS

Bacterial killing in biofilms by the disinfectants and MUP was determined as the reduction [%] in metabolic activity determined by a biofilm viability assay that uses kinetic analysis of metabolic activity. The test substances were diluted in water with standardized hardness (WSH) at 25 °C at the standard concentration as well as half the standard concentration to demonstrate the dilution effects in a practical setting. The tested concentrations were: CHG 1%, 2%; OCT 0.1%, 0.05%; PH 0.04%, 0.02%; and CLO 0.12%, 0.24%. A test organism suspension, 1 mL containing ~1 × 109 bacterial cells/mL, and 1 mL of sterile WSH were mixed and incubated for six different exposure times (15 s, 1, 3, 5, 10 and 20 min) after the test substance was added. Additionally, the bactericidal effects of all substances were tested on planktonic bacteria and measured as the log10 reduction.

RESULTS

The disinfectants OCT and CHG showed good efficacy in inhibiting MRSA in biofilms with reduction rates of 94 ± 1% and 91 ± 1%, respectively. POL, on the other hand, had a maximum efficacy of only 81 ± 7%. Compared to the tested disinfectants, MUP showed a significantly lower efficacy with <20% inhibition (p < .05). Bactericidal effects were the greatest for CHG (log10 reduction of 9.0), followed by OCT (7.7), POL (5.1), and CLO (6.8). MUP, however, showed a very low bactericidal effect of only 2.1. Even when the exposure time was increased to 24 h, 2% MUP did not show sufficient bactericidal effect.

CONCLUSIONS

Our data provide evidence that OCT and CHG are effective components for disinfection of MRSA-biofilms. On the other hand, exposure to MUP at the standard concentrations in topical preparations did not effectively inhibit MRSA-biofilms and also did not show adequate bactericidal effects. Combining an MUP-based decolonization regimen with a disinfectant such as OCT or CHG could decrease decolonization failure.

Swarming phenomena, basis of a method to identify motile bacteria densitometrically

The swarming phenomenon of 18 strains was tested with the intention to identify motile, swarming bacteria. Not all bacteria which are motile in liquid are able to swarm on semisolid nutrient broth, but all swarming bacteria show characteristic swarming developments, resulting in different swarming zones which could be scanned densitometrically. The densitograms are fully reproducible for the same strain and show similarities between strains of one species.