Ease of biofilm accumulation, and efficacy of sanitizing treatments in removing the biofilms formed, on coupons made of materials commonly used in blueberry packing environment

Using Bio-inline Reactor to Evaluate Sanitizer Efficacy in Removing Dual-species Biofilms Formed by Escherichia coli O157:H7 and Listeria monocytogenes

The efficacy of a sanitizer in biofilm removal may be influenced by a combination of factors such as sanitizer exposure time and concentration, bacterial species, surface topography, and shear stresses. We employed an inline biofilm reactor to investigate the interactions of these variables on biofilm removal with chlorine. The CDC bioreactor was used to grow E. coli O157:H7 and L. monocytogenes biofilms as a single species or with Ralstonia insidiosa as a dual-species biofilm on stainless steel, PTFE, and EPDM coupons at shear stresses 0.368 and 2.462 N/m2 for 48 hours. Coupons were retrieved from a CDC bioreactor and placed in an inline biofilm reactor and 100, 200, or 500 ppm of chlorine was supplied for 1- and 4 min. Bacterial populations in the biofilms were quantified pre- and posttreatment by plating on selective media. After chlorine treatment, reduction (Log CFU/cm2) in pathogen populations obtained from three replicates was analyzed for statistical significance. A 1-min chlorine treatment (500 ppm), on dual-species E. coli O157:H7 biofilms grown at high shear stress of 2.462 N/m2 resulted in significant E. coli O157:H7 reductions on SS 316L (2.79 log CFU/cm2) and PTFE (1.76 log CFU/cm2). Similar trend was also observed for biofilm removal after a 4-min chlorine treatment. Single species E. coli O157:H7 biofilms exhibited higher resistance to chlorine when biofilms were developed at high shear stress. The effect of chlorine in L. monocytogenes removal from dual-species biofilms was dependent primarily on the shear stress at which they were formed rather than the surface topography of materials. Besides surface topography, shear stresses at which biofilms were formed also influenced the effect of sanitizer. The removal of E. coli O157:H7 biofilms from EPDM material may require critical interventions due to difficulty in removing this pathogen. The inline biofilm reactor is a novel tool to evaluate the efficacy of a sanitizer in bacterial biofilm removal.

Variations in the motility and biofilm formation abilities of Escherichia coli O157:H7 during noodle processing

Motility and biofilm formation help to protect bacteria from host immune responses and facilitate tolerance of environmental stimuli to improve their adaptability. However, few reports have investigated the adaptability of bacteria that live in food substrates undergoing food processing-induced stress. In this study, variations in the surface morphology, bacterial count, motility, and biofilm formation abilities of Escherichia coli O157:H7 NCTC12900 were investigated during noodle processing, including the kneading, squeezing, resting, and sheeting phases. The results showed that bacterial surface morphology, count, and motility were impaired in the squeezing phase, whereas biofilm biomass continuously increased across all processing phases. Twenty-one genes and sRNAs were measured using RT-qPCR to reveal the mechanisms underlying these changes. Of these, the genes adrA, csrA, flgM, flhD, fliM, ydaM, and the sRNA McaS were significantly upregulated, whereas the genes fliA, fliG, and the sRNAs CsrC, DsrA, GcvB, and OxyS were evidently repressed. According to the correlation matrix results based on the reference gene adrA, we found that csrA, GcvB, McaS, and OxyS were the most relevant genes and sRNAs for biofilm formation and motility. For each of them, their overexpressions was found to inhibit bacterial motility and biofilm formation to varying degrees during noodle processing. Among these, 12900/pcsrA had the highest inhibitory potential against motility, yielding a minimum of 11.2 mm motility diameter in the resting phase. Furthermore, 12900/pOxyS showed the most significant inhibitory effect against biofilm formation, yielding a minimum biofilm formation value of 5% of that exhibited the wild strain in the sheeting phase. Therefore, we prospect to find an effective and feasible novel approach to weaken bacterial survival during food processing by regulating the genes or sRNAs related to motility and biofilm formation.

Antimicrobial effects of automobile screenwashes against Legionella pneumophila

AIMS

Legionella pneumophila (Lp), a human pathogen, has been detected in windscreen wiper fluid reservoirs (WWFRs) where commercial screenwashes (CSWs) are commonly added. Limited information is available on CSWs against planktonic Lp; however, responses of sessile Lp and planktonic Lp pre-acclimated in nutrient-limited water to CSWs remain unknown. This study thus investigates the antibacterial effects of CSWs on sessile and starved planktonic Lp, in comparison with unstarved Lp.

METHODS AND RESULTS

Lp biofilms were produced on glass and WWFR materials of high-density polyethylene (HDPE) and polypropylene (PP). Planktonic Lp with and without acclimation in tap water were prepared. Log reductions in cell counts averaged 0.4-5.0 for ten brands of CSWs against sessile Lp and 1.0-3.9 and 0.9-4.9, respectively, against starved and unstarved planktonic Lp for five CSWs. Both biofilm formation and acclimation in tap water enhanced Lp resistance to CSWs. Significantly different log-reduction values among CSW brands were observed for sessile Lp on HDPE and planktonic Lp regardless of acclimation (p<0.05).

CONCLUSIONS

Biofilm formation, starvation acclimation, and CSW brand are crucial factors influencing Lp response to CSWs.

SIGNIFICANCE AND IMPACT OF STUDY

This study advances the knowledge of Lp reaction in anthropogenic water systems with CSWs.

Effect of Pre-Exposure to Chlorine Dioxide on the Susceptibility of Fecal Coliforms to Antibiotics

Adaptive exposure to sub-lethal concentrations of sanitizers was previously reported to offer cross-protection to bacteria against antibiotics. This study was undertaken to determine whether the pre-exposure of fecal coliforms to suboptimal concentrations of a chemical sanitizer, chlorine dioxide (ClO₂), alters their susceptibility to certain antibiotics. Fecal coliforms isolated from fresh fruit packing facilities (n = 12) were adapted in ½ or ¼ of the manufacturer-recommended concentration of ClO₂. The susceptibility of the adapted and non-adapted cells to 13 different antibiotics was determined by observing the changes in their minimal inhibitory concentrations (MICs). The results showed that preadaptation to the suboptimal concentrations of ClO₂, in general, either decreased or did not change the MICs of the antibiotics against selected fecal coliform isolates, with only two exceptions; preadaptation increased the MICs of kanamycin against two of the fecal coliform isolates, and of nalidixic acid against one of the fecal coliform isolates. The results suggest that the use of ClO₂ has a relatively low risk of inducing the resistance of fecal coliforms to antibiotics.

Biofilm-Forming Ability of Microbacterium lacticum and Staphylococcus capitis Considering Physicochemical and Topographical Surface Properties

Biofilm characteristics of Microbacterium lacticum D84 (M. lacticum) and Staphylococcus capitis subsp. capitis (S. capitis) on polytetrafluoroethylene and AISI-304 stainless steel at early- (24, 48 h) and late-stage (144, 192 h) biofilm formation were investigated. M. lacticum biofilm structure was more developed compared to S. capitis, representing vastly mature biofilms with a strongly developed amorphous matrix, possibly extracellular polymeric substances (EPSs), at late-stage biofilm formation. S. capitis showed faster growth behavior but still resulted in a relatively flat biofilm structure. Strong correlations were found between several roughness parameters and S. capitis surface coverage (r ≥ 0.98), and between total surface free energy (γs) and S. capitis surface coverage (r = 0.89), while M. lacticum remained mostly unaffected. The pronounced ubiquitous biofilm characteristics make M. lacticum D84 a suitable model for biofilm research. Studying biofilm formation of these bacteria may help one understand bacterial adhesion on interfaces and hence reduce biofilm formation in the food industry.

Effect of different disinfection treatments on the adhesion and separation of biofilm on stainless steel surface

Attachment and separation of sulfate-reducing bacteria (SRB) biofilm on stainless steel (SS) in simulated cooling water with and without different sterilization treatments was investigated by calculation of surface energy, theoretical work of adhesion and analysis of Scanning Electron Microscope/Energy Dispersive Spectrometer. Two types of biocides, glutaraldehyde and Polyhexamethylene guanidine (PHMG), and electromagnetic treatment were used in this paper. The results show that PHMG had the best bactericidal performance, followed by glutaraldehyde, and electromagnetic treatment was the lowest one. The theoretical work of adhesion was used to quantitatively evaluate the adhesion of biofilm on the surface of the metal. Theoretical work of adhesion between biofilm and SS in simulated cooling water increased with time. The theoretical adhesion work and adhesive capacity of biofilm to SS surface increased after treating with glutaraldehyde while decreasing after treating with PHMG and electromagnetic field. As the theoretical adhesion work decreased, the biofilm was gradually removed from the stainless steel surface. On the contrary, the biofilm adhered more firmly. The results of SEM were also consistent with the calculation results of theoretical adhesion work. The results obtained indicated that electromagnetic treatment had the lowest effect in sterilization but the best in biofilm separation.