Morphological bactericidal fast-acting effects of peracetic acid, a high-level disinfectant, against Staphylococcus aureus and Pseudomonas aeruginosa biofilms in tubing

Abstract

Background: The bactericidal effect of disinfectants against biofilms is essential to reduce potential endoscopy-related infections caused by contamination. Here, we investigated the bactericidal effect of a high-level disinfectant, peracetic acid (PAA), against Staphylococcus aureus and Pseudomonas aeruginosa biofilm models in vitro.

Methods: S. aureus and P. aeruginosa biofilms were cultured at 35 °C for 7 days with catheter tubes. The following high-level disinfectants (HLDs) were tested: 0.3% PAA, 0.55% ortho-phthalaldehyde (OPA), and 2.0% alkaline-buffered glutaraldehyde (GA). Biofilms were exposed to these agents for 1-60 min and observed after 5 min and 30 min by transmission and scanning electron microscopy. A Student's t test was performed to compare the exposure time required for bactericidal effectiveness of the disinfectants.

Results: PAA and GA were active within 1 min and 5 min, respectively, against S. aureus and P. aeruginosa biofilms. OPA took longer than 10 min and 30 min to act against S. aureus and P. aeruginosa biofilms, respectively (p < 0.01). Treatment with PAA elicited changes in cell shape after 5 min and structural damage after 30 min.

Conclusions: Amongst the HLDs investigated, PAA elicited the most rapid bactericidal effects against both biofilms. Additionally, treatment with PAA induced morphological alterations in the in vitro biofilm models, suggesting that PAA exerts fast-acting bactericidal effects against biofilms associated with endoscopy-related infections. These findings indicate that the exposure time for bactericidal effectiveness of HLDs for endoscope reprocessing in healthcare settings should be reconsidered.

Keywords: Bactericidal effectiveness; Electron microscopy; Exposure time; Peracetic acid; Pseudomonas aeruginosa biofilm; Staphylococcus aureus biofilm.

Fig. 1

Bactericidal effects of high-level disinfectants (HLDs). 0.3% peracetic acid (PAA), 2.0% glutaraldehyde (GA), and 0.55% ortho-phthalaldehyde (OPA) against (a) Staphylococcus aureus and (b) Pseudomonas aeruginosa biofilms in tubing. We used 0.1% sodium hypochlorite (NaClO) as a comparable standard formulation, with sterile distilled water (SDW) as a positive control

Fig. 2

Transmission electron photomicrographs: Staphylococcus aureus 209P (top) and Pseudomonas aeruginosa E7 (bottom) biofilm in tubing: (a, e) before treatment, (b, f) after a 5-min and (c, g) 30-min treatment with peracetic acid (PAA), and (d, h) after a 30-min treatment with glutaraldehyde (GA). Compared with GA, treatment with PAA resulted in gradual cell-structure collapse (S. aureus) and evident bleb-like bulges indicating cell damage (P. aeruginosa)

Fig. 3

Scanning electron photomicrographs: Staphylococcus aureus 209P (top) and Pseudomonas aeruginosa E7 (bottom) biofilm in tubing: (a, e) before treatment, (b, f) after a 5-min and (c, g) 30-min treatment with peracetic acid (PAA), and (d, h) after a 30-min treatment with glutaraldehyde (GA). Compared with GA, treatment with PAA resulted in gradual reduction in bacterial internal pressure, followed by destruction of mashed cell surfaces (S. aureus), reduced bacterial aggregation, and decreases in biofilm matrix components (P. aeruginosa)