Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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Item Air-liquid interface biofilm formation of pseudomonads and the impact of traditional clean-in-place on biofilm removal(Elsevier Ltd, 2026-02-28) Muthuraman S; Palmer J; Flint SPseudomonads are common psychrotrophic spoilage bacteria associated with dairy, poultry, and meat processing environments. They can multiply at low temperatures, 4–7 °C, producing thermostable spoilage enzymes. Pseudomonads form strong biofilms by producing higher EPS (Extracellular polymeric substances) at low temperatures. This study focused on the biofilm formation of pseudomonads at the air-liquid interface and their EPS removal. Two strong biofilm-forming isolates, (Pseudomonas lundensis) 3SM and (Pseudomonas cedrina) 20SM were allowed to form biofilms on stainless steel coupons in a CDC reactor under a continuous flow of nutrients at 4 °C over a week. The cell counts reached approximately 7.5 log CFU/cm2. The biofilms formed at the air-liquid interface showed more visible biofilms, polysaccharides, and higher cell counts than those submerged in liquid. Cleaning the biofilms using 1 % NaOH at 70 °C resulted in viable bacterial cells below the detection limit. However, residual material termed biofilm “footprints” was present after cleaning and were analysed with SEM and FTIR. The SEM observations showed tightly packed robust biofilm cells before cleaning. Coupons treated with 55 °C water showed an upper layer of degraded cells. After treatment with 70 °C NaOH, organic material was still visible under SEM. Based on the FTIR observations, the EPS extracted from the control and treated coupons showed that the amount of biomolecules reduced after cleaning with NaOH, but the footprints still existed. The biofilm footprints led to the early appearance of biofilms at the air-liquid interface compared to new coupons exposed to strong biofilm-forming isolates. Cleaning with caustic can eliminate the cells, but the EPS from biofilms of pseudomonads is not completely removed, resulting in a possibility of regrowth when the new inoculum is introduced.Item Global expansion of Vibrio parahaemolyticus threatens the seafood industry: Perspective on controlling its biofilm formation(Elsevier Ltd, 2022-03-15) Wang D; Flint SH; Palmer JS; Gagic D; Fletcher GC; On SLWAs global warming increases the geographical range and frequency of Vibrio parahaemolyticus infections, its formation of biofilms providing bacteria greater resistance to stress and contributing to the persistence of pathogens, is threatening the seafood industry. V. parahaemolyticus has a number of advantages leading to biofilm formation. This study reviews recent advances in understanding V. parahaemolyticus biofilm formation on biotic and abiotic surfaces, discusses research gaps in the mechanism of biofilm formation and examines promising biofilm control strategies to overcome current limitations of chemical disinfectant. This information will deepen our understanding of V. parahaemolyticus biofilm formation, as well as help design and optimize V. parahaemolyticus biofilm control strategies for the seafood industry.Item Biofilm formation, sodium hypochlorite susceptibility and genetic diversity of Vibrio parahaemolyticus(Elsevier BV, 2023-01-16) Wang D; Fletcher GC; On SLW; Palmer JS; Gagic D; Flint SHVibrio parahaemolyticus is a marine oriented pathogen; and biofilm formation enables its survival and persistence on seafood processing plant, complicating the hygienic practice. The objectives of this study are to assess the ability of V. parahaemolyticus isolated from seafood related environments to form biofilms, to determine the effective sodium hypochlorite concentrations required to inactivate planktonic and biofilm cells, and to evaluate the genetic diversity required for strong biofilm formation. Among nine isolates, PFR30J09 and PFR34B02 isolates were identified as strong biofilm forming strains, with biofilm cell counts of 7.20, 7.08 log10 CFU/cm2, respectively, on stainless steel coupons after incubation at 25 °C. Free available chlorine of 1176 mg/L and 4704 mg/L was required to eliminate biofilm cells of 1.74-2.28 log10 CFU/cm2 and > 7 log10 CFU/cm2, respectively, whereas 63 mg/L for planktonic cells, indicating the ineffectiveness of sodium hypochlorite in eliminating V. parahaemolyticus biofilm cells at recommended concentration in the food industry. These strong biofilm-forming isolates produced more polysaccharides and were less susceptible to sodium hypochlorite, implying a possible correlation between polysaccharide production and sodium hypochlorite susceptibility. Genetic diversity in mshA, mshC and mshD contributed to the observed variation in biofilm formation between isolates. This study identified strong biofilm-forming V. parahaemolyticus strains of new multilocus sequence typing (MLST) types, showed a relationship between polysaccharide production and sodium hypochlorite resistance.