Browsing by Author "Teh, Koon Hoong"

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    Biofilm formation by Campylobacter jejuni in controlled mixed-microbial populations : a thesis presented in partial fulfillment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 2008) Teh, Koon Hoong
    Poultry meat consumption in New Zealand has been increasing since 1975 with the highest peak reported in 2006. The total poultry meat consumption was 36.5 kg per capita in the year ending September 2006. Consumption of contaminated food with raw poultry can lead to campylobacteriosis, which is a food-borne disease that causes gastroenteritis in humans and it is a major problem in New Zealand. There were 12,776 reported cases of campylobacteriosis in 2007, which accounts for 65.9% of the overall notified diseases. Campylobacteriosis can lead to Guillain-Barré syndrome in some patients, an autoimmune disorder of the peripheral nervous system. Campylobacteriosis is caused by consumption of either Campylobacter jejuni or Campylobacter coli. Campylobacter spp. have been found in commercially raised poultry being infected predominantly by C. jejuni. C. jejuni has been found associated with biofilms of other bacterial species in the watering supplies and plumbing systems of animal husbandry facilities and animalprocessing plants. A biofilm is an assemblage of microbial cells that is associated with a surface and the cells are enclosed in a matrix of polysaccharides, which provides a survival advantage to the bacteria in the film. In this study, the ability to form biofilm was measured in a laboratory assay using microtitre plates. C. jejuni strains in monoculture were shown to attach to the abiotic surface and form biofilms to various degrees, thus potentially enhancing their survivability in the poultry environment. C. jejuni was also shown to have the ability to attach and survive in mixed-microbial populations. Biofilm formation may play a role in the epidemiology of C. jejuni infections. Enterococcus faecalis and Staphylococcus simulans may play a role in the biofilm formation in the poultry environment as both of these microorganisms were able to form, and harbour C. jejuni in their biofilms. Pseudomonas aeruginosa seemed to inhibit biofilm formation and C. jejuni in the mixed-microbial population. Further studies are required to establish control measures against the formation of biofilms containing C. jejuni in poultry processing plants and farms in New Zealand to reduce the reservoir of contamination and thus reduce the incidence of campylobacteriosis.
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    Enzymes produced by bacteria within biofilms of dairy origin and their effect on dairy products : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy, Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Teh, Koon Hoong
    Prior to the current study, there was no scientific evidence that enzymes produced by bacteria within biofilms in milk transport tanker could have a detrimental effect on the quality of dairy products. Bacteria attached to the internal surfaces of milk tankers were isolated, identified, and characterized in terms of their ability to produce heat-stable enzymes (protease and lipase) and to form biofilms. Twelve of the bacterial isolates were identified by 16s DNA sequencing as belonging to the genera Bacillus, Staphylococcus, Streptococcus, Pseudomonas, and Serratia. Six of the dairy bacterial isolates were evaluated for their ability to produce proteolysis in milk when growing within either single culture or co-culture biofilms in an in vitro model system that simulated the upper part of a milk tanker during a typical summer’s day of milk collection in New Zealand. Proteolysis per cfu decreased as the temperature of incubation increased (20-37 °C), and proteolysis per cfu was generally higher within biofilms compared with the corresponding planktonic cultures. Lipolysis by bacteria within biofilms in the in vitro model was investigated using single or co-culture biofilms or planktonic cultures of four dairy bacteria and a known lipase-producing bacterium. The hydrolysis of p-nitrophenol palmitate was at least 10 times higher by bacteria within biofilms (0.01 to 8.35 nU/CFU) than in planktonic cultures (0.01 to 0.07 nU/CFU). The effect of proteases on UHT skim milk was determined by exposing sterile skim milk to a multispecies biofilm formed on an in vitro model of a milk tanker. The amount of free peptides which indicated proteolysis in the UHT milk was monitored over five months of storage. Free peptides were higher in UHT milk that had been made from milk exposed to the multispecies biofilm, than in UHT milk that had been made from milk that had not been exposed to the biofilm. Enzymes that are secreted from biofilms into raw milk during transportation can potentially reduce the quality of dairy products. Improvements at this early stage of dairy manufacture may reduce economic loss in the dairy industry.