Displaying publications 21 - 37 of 37 in total

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  1. The influence of dissolved oxygen level and medium on biofilm formation by Campylobacter jejuni
    Teh AHT, Lee SM, Dykes GA
    Food Microbiol, 2017 Feb;61:120-125.
    PMID: 27697161 DOI: 10.1016/j.fm.2016.09.008
    Campylobacter jejuni survival in aerobic environments has been suggested to be mediated by biofilm formation. Biofilm formation by eight C. jejuni strains under both aerobic and microaerobic conditions in different broths (Mueller-Hinton (MH), Bolton and Brucella) was quantified. The dissolved oxygen (DO) content of the broths under both incubation atmospheres was determined. Biofilm formation for all strains was highest in MH broth under both incubation atmospheres. Four strains had lower biofilm formation in MH under aerobic as compared to microaerobic incubation, while biofilm formation by the other four strains did not differ under the 2 atm. Two strains had higher biofilm formation under aerobic as compared to microaerobic atmospheres in Bolton broth. Biofilm formation by all other strains in Bolton, and all strains in Brucella broth, did not differ under the 2 atm. Under aerobic incubation DO levels in MH > Brucella > Bolton broth. Under microaerobic conditions levels in MH = Brucella > Bolton broth. Levels of DO in MH and Brucella broth were lower under microaerobic conditions but those of Bolton did not differ under the 2 atm. Experimental conditions and especially the DO of broth media confound previous conclusions drawn about aerobic biofilm formation by C. jejuni.
  2. Modulation of cell surface hydrophobicity and attachment of bacteria to abiotic surfaces and shrimp by Malaysian herb extracts
    Hui YW, Dykes GA
    J Food Prot, 2012 Aug;75(8):1507-11.
    PMID: 22856578 DOI: 10.4315/0362-028X.JFP-12-062
    The use of simple crude water extracts of common herbs to reduce bacterial attachment may be a cost-effective way to control bacterial foodborne pathogens, particularly in developing countries. The ability of water extracts of three common Malaysian herbs (Andrographis paniculata, Eurycoma longifolia, and Garcinia atroviridis) to modulate hydrophobicity and attachment to surfaces of five food-related bacterial strains (Bacillus cereus ATCC 14576, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 10145, Salmonella Enteritidis ATCC 13076, Staphylococcus aureus ATCC 25923) were determined. The bacterial attachment to hydrocarbon assay was used to determine bacterial hydrophobicity. Staining and direct microscopic counts were used to determine attachment of bacteria to glass and stainless steel. Plating on selective media was used to determine attachment of bacteria to shrimp. All extracts were capable of either significantly ( P < 0.05) increasing or decreasing bacterial surface hydrophobicity, depending on the herb extract and bacteria combination. Bacterial attachment to all surfaces was either significantly (P < 0.05) increased or decreased, depending on the herb extract and bacteria combination. Overall, hydrophobicity did not show a significant correlation (P > 0.05) to bacterial attachment. For specific combinations of bacteria, surface material, and plant extract, significant correlations (R > 0.80) between hydrophobicity and attachment were observed. The highest of these was observed for S. aureus attachment to stainless steel and glass after treatment with the E. longifolia extract (R = 0.99, P < 0.01). The crude water herb extracts in this study were shown to have the potential to modulate specific bacterial and surface interactions and may, with further work, be useful for the simple and practical control of foodborne pathogens.
  3. Sonication reduces the attachment of Salmonella Typhimurium ATCC 14028 cells to bacterial cellulose-based plant cell wall models and cut plant material
    Tan MSF, Rahman S, Dykes GA
    Food Microbiol, 2017 Apr;62:62-67.
    PMID: 27889167 DOI: 10.1016/j.fm.2016.10.009
    This study investigated the removal of bacterial surface structures, particularly flagella, using sonication, and examined its effect on the attachment of Salmonella Typhimurium ATCC 14028 cells to plant cell walls. S. Typhimurium ATCC 14028 cells were subjected to sonication at 20 kHz to remove surface structures without affecting cell viability. Effective removal of flagella was determined by staining flagella of sonicated cells with Ryu's stain and enumerating the flagella remaining by direct microscopic counting. The attachment of sonicated S. Typhimurium cells to bacterial cellulose-based plant cell wall models and cut plant material (potato, apple, lettuce) was then evaluated. Varying concentrations of pectin and/or xyloglucan were used to produce a range of bacterial cellulose-based plant cell wall models. As compared to the non-sonicated controls, sonicated S. Typhimurium cells attached in significantly lower numbers (between 0.5 and 1.0 log CFU/cm2) to all surfaces except to the bacterial cellulose-only composite without pectin and xyloglucan. Since attachment of S. Typhimurium to the bacterial cellulose-only composite was not affected by sonication, this suggests that bacterial surface structures, particularly flagella, could have specific interactions with pectin and xyloglucan. This study indicates that sonication may have potential applications for reducing Salmonella attachment during the processing of fresh produce.
  4. Transfer of Campylobacter and Salmonella from Poultry Meat onto Poultry Preparation Surfaces
    Sarjit A, Dykes GA
    J Food Prot, 2017 May 01;80(5):750-757.
    PMID: 28358259 DOI: 10.4315/0362-028X.JFP-16-414
    Thermophilic Campylobacter and Salmonella enterica are major causes of gastrointestinal foodborne infection. Survival of these pathogens on food-associated surfaces is a risk contributing to their spread through the food system. This study examined the transfer of two strains each of C. jejuni, C. coli, Salmonella Enteritidis, and Salmonella Typhimurium from chicken meat to a knife or scissors used on either a plastic or wooden cutting board. Each strain of Campylobacter and Salmonella at ∼108 CFU mL-1 was inoculated (5 mL) onto 25 g of chicken meat with skin and allowed to attach (for 10 min). The meat was then cut (20 times per implement) into 1-cm2 pieces with either a knife or scissors on either a plastic or wooden cutting board. The numbers of pathogens transferred from meat onto cutting implements and cutting board surfaces were enumerated. The surfaces were subsequently either rinsed with water or rinsed with water and wiped with a kitchen towel to mimic commonly used superficial cleaning practices for these implements, and the numbers of pathogens were enumerated again. The bacterial numbers for both pathogens were determined on thin-layer agar. The attachment of the Salmonella strains to chicken meat (∼7.0 to 7.8 log CFU cm-2) was higher than the attachment of the Campylobacter strains (∼4.6 to 6.6 log CFU cm-2). All four Salmonella strains transferred in higher numbers (∼1.9 to 6.3 log CFU cm-2) to all surfaces than did the Campylobacter strains (∼1.1 to 3.9 log CFU cm-2). The transfer rates of both pathogens from the chicken meat to all the surfaces examined varied substantially between ∼0 and 21.1%. The highest rate of transfer (∼21.1%) observed was for C. coli 2875 when transferred from the chicken meat to the scissors. Most cleaning treatments reduced the numbers of both pathogens (∼0.3 to 4.1 log CFU cm-2) transferred to all the surfaces. Our study gives insights into the risks associated with the transfer of Campylobacter and Salmonella from poultry to the surfaces used in poultry preparation.
  5. Fulltext Identification of potential Campylobacter jejuni genes involved in biofilm formation by EZ-Tn5 Transposome mutagenesis
    Teh AHT, Lee SM, Dykes GA
    BMC Res Notes, 2017 May 12;10(1):182.
    PMID: 28499399 DOI: 10.1186/s13104-017-2504-1
    BACKGROUND: Biofilm formation has been suggested to play a role in the survival of Campylobacter jejuni in the environment and contribute to the high incidence of human campylobacteriosis. Molecular studies of biofilm formation by Campylobacter are sparse.

    RESULTS: We attempted to identify genes that may be involved in biofilm formation in seven C. jejuni strains through construction of mutants using the EZ-Tn5 Transposome system. Only 14 mutants with reduced biofilm formation were obtained, all from one strain of C. jejuni. Three different genes of interest, namely CmeB (synthesis of multidrug efflux system transporter proteins), NusG (transcription termination and anti-termination protein) and a putative transmembrane protein (involved in membrane protein function) were identified. The efficiency of the EZ::TN5 transposon mutagenesis approach was strain dependent and was unable to generate any mutants from most of the strains used.

    CONCLUSIONS: A diverse range of genes may be involved in biofilm formation by C. jejuni. The application of the EZ::TN5 system for construction of mutants in different Campylobacter strains is limited.

  6. Fulltext Role of Fimbriae, Flagella and Cellulose on the Attachment of Salmonella Typhimurium ATCC 14028 to Plant Cell Wall Models
    Tan MS, White AP, Rahman S, Dykes GA
    PLoS One, 2016;11(6):e0158311.
    PMID: 27355584 DOI: 10.1371/journal.pone.0158311
    Cases of foodborne disease caused by Salmonella are frequently associated with the consumption of minimally processed produce. Bacterial cell surface components are known to be important for the attachment of bacterial pathogens to fresh produce. The role of these extracellular structures in Salmonella attachment to plant cell walls has not been investigated in detail. We investigated the role of flagella, fimbriae and cellulose on the attachment of Salmonella Typhimurium ATCC 14028 and a range of isogenic deletion mutants (ΔfliC fljB, ΔbcsA, ΔcsgA, ΔcsgA bcsA and ΔcsgD) to bacterial cellulose (BC)-based plant cell wall models [BC-Pectin (BCP), BC-Xyloglucan (BCX) and BC-Pectin-Xyloglucan (BCPX)] after growth at different temperatures (28°C and 37°C). We found that all three cell surface components were produced at 28°C but only the flagella was produced at 37°C. Flagella appeared to be most important for attachment (reduction of up to 1.5 log CFU/cm2) although both cellulose and fimbriae also aided in attachment. The csgD deletion mutant, which lacks both cellulose and fimbriae, showed significantly higher attachment as compared to wild type cells at 37°C. This may be due to the increased expression of flagella-related genes which are also indirectly regulated by the csgD gene. Our study suggests that bacterial attachment to plant cell walls is a complex process involving many factors. Although flagella, cellulose and fimbriae all aid in attachment, these structures are not the only mechanism as no strain was completely defective in its attachment.
  7. Fulltext Stochasticity of bacterial attachment and its predictability by the extended derjaguin-landau-verwey-overbeek theory
    Chia TW, Nguyen VT, McMeekin T, Fegan N, Dykes GA
    Appl Environ Microbiol, 2011 Jun;77(11):3757-64.
    PMID: 21478319 DOI: 10.1128/AEM.01415-10
    Bacterial attachment onto materials has been suggested to be stochastic by some authors but nonstochastic and based on surface properties by others. We investigated this by attaching pairwise combinations of two Salmonella enterica serovar Sofia (S. Sofia) strains (with different physicochemical and attachment properties) with one strain each of S. enterica serovar Typhimurium, S. enterica serovar Infantis, or S. enterica serovar Virchow (all with similar physicochemical and attachment abilities) in ratios of 0.428, 1, and 2.333 onto glass, stainless steel, Teflon, and polysulfone. Attached bacterial cells were recovered and counted. If the ratio of attached cells of each Salmonella serovar pair recovered was the same as the initial inoculum ratio, the attachment process was deemed stochastic. Experimental outcomes from the study were compared to those predicted by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Significant differences (P < 0.05) between the initial and the attached ratios for serovar pairs containing S. Sofia S1296a for all different ratios were apparent for all materials. For S. Sofia S1635-containing pairs, 7 out of 12 combinations of serovar pairs and materials had attachment ratios not significantly different (P > 0.05) from the initial ratio of 0.428. Five out of 12 and 10 out of 12 samples had attachment ratios not significantly different (P > 0.05) from the initial ratios of 1 and 2.333, respectively. These results demonstrate that bacterial attachment to different materials is likely to be nonstochastic only when the key physicochemical properties of the bacteria were significantly different (P < 0.05) from each other. XDLVO theory could successfully predict the attachment of some individual isolates to particular materials but could not be used to predict the likelihood of stochasticity in pairwise attachment experiments.
  8. Fulltext Pectin and Xyloglucan Influence the Attachment of Salmonella enterica and Listeria monocytogenes to Bacterial Cellulose-Derived Plant Cell Wall Models
    Tan MS, Rahman S, Dykes GA
    Appl Environ Microbiol, 2016 01 15;82(2):680-8.
    PMID: 26567310 DOI: 10.1128/AEM.02609-15
    Minimally processed fresh produce has been implicated as a major source of foodborne microbial pathogens globally. These pathogens must attach to the produce in order to be transmitted. Cut surfaces of produce that expose cell walls are particularly vulnerable. Little is known about the roles that different structural components (cellulose, pectin, and xyloglucan) of plant cell walls play in the attachment of foodborne bacterial pathogens. Using bacterial cellulose-derived plant cell wall models, we showed that the presence of pectin alone or xyloglucan alone affected the attachment of three Salmonella enterica strains (Salmonella enterica subsp. enterica serovar Enteritidis ATCC 13076, Salmonella enterica subsp. enterica serovar Typhimurium ATCC 14028, and Salmonella enterica subsp. indica M4) and Listeria monocytogenes ATCC 7644. In addition, we showed that this effect was modulated in the presence of both polysaccharides. Assays using pairwise combinations of S. Typhimurium ATCC 14028 and L. monocytogenes ATCC 7644 showed that bacterial attachment to all plant cell wall models was dependent on the characteristics of the individual bacterial strains and was not directly proportional to the initial concentration of the bacterial inoculum. This work showed that bacterial attachment was not determined directly by the plant cell wall model or bacterial physicochemical properties. We suggest that attachment of the Salmonella strains may be influenced by the effects of these polysaccharides on physical and structural properties of the plant cell wall model. Our findings improve the understanding of how Salmonella enterica and Listeria monocytogenes attach to plant cell walls, which may facilitate the development of better ways to prevent the attachment of these pathogens to such surfaces.
  9. Fulltext Does Campylobacter jejuni form biofilms in food-related environments?
    Teh AH, Lee SM, Dykes GA
    Appl Environ Microbiol, 2014 Sep;80(17):5154-60.
    PMID: 24928882 DOI: 10.1128/AEM.01493-14
    Campylobacter jejuni is one of the most frequent causes of bacterial gastrointestinal food-borne infection worldwide. This species is part of the normal flora of the gastrointestinal tracts of animals used for food production, including poultry, which is regarded as the primary source of human Campylobacter infections. The survival and persistence of C. jejuni in food processing environments, especially in poultry processing plants, represent significant risk factors that contribute to the spread of this pathogen through the food chain. Compared to other food-borne pathogens, C. jejuni is more fastidious in its growth requirements and is very susceptible to various environmental stressors. Biofilm formation is suggested to play a significant role in the survival of C. jejuni in the food production and processing environment. The aims of this minireview were (i) to examine the evidence that C. jejuni forms biofilms and (ii) to establish the extent to which reported and largely laboratory-based studies of C. jejuni biofilms provide evidence for biofilm formation by this pathogen in food processing environments. Overall existing studies do not provide strong evidence for biofilm formation (as usually defined) by most C. jejuni strains in food-related environments under the combined conditions of atmosphere, temperature, and shear that they are likely to encounter. Simple attachment to and survival on surfaces and in existing biofilms of other species are far more likely to contribute to C. jejuni survival in food-related environments based on our current understanding of this species.
  10. Fulltext Characterization of Shiga Toxigenic Escherichia coli O157 and Non-O157 Isolates from Ruminant Feces in Malaysia
    Perera A, Clarke CM, Dykes GA, Fegan N
    Biomed Res Int, 2015;2015:382403.
    PMID: 26539484 DOI: 10.1155/2015/382403
    Shiga toxigenic Escherichia coli (STEC) O157 and several other serogroups of non-O157 STEC are causative agents of severe disease in humans world-wide. The present study was conducted to characterize STEC O157 and non-O157 serogroups O26, O103, O111, O121, O45, and O145 in ruminants in Malaysia. A total of 136 ruminant feces samples were collected from 6 different farms in Peninsular Malaysia. Immunomagnetic beads were used to isolate E. coli O157 and non-O157 serogroups, while PCR was used for the detection and subtyping of STEC isolates. STEC O157:H7 was isolated from 6 (4%) feces samples and all isolates obtained carried stx 2c, eaeA-γ1, and ehxA. Non-O157 STEC was isolated from 2 (1.5%) feces samples with one isolate carrying stx 1a, stx 2a, stx 2c, and ehxA and the other carrying stx 1a alone. The presence of STEC O157 and non-O157 in a small percentage of ruminants in this study together with their virulence characteristics suggests that they may have limited impact on public health.
  11. Fulltext Genome sequencing and annotation of Cellulomonas sp. HZM
    Chua P, Har ZM, Austin CM, Yule CM, Dykes GA, Lee SM
    Genom Data, 2015 Sep;5:40-1.
    PMID: 26484221 DOI: 10.1016/j.gdata.2015.05.009
    We report the draft genome sequence of Cellulomonas sp. HZM, isolated from a tropical peat swamp forest. The draft genome size is 3,559,280 bp with a G + C content of 73% and contains 3 rRNA sequences (single copies of 5S, 16S and 23S rRNA).
  12. Fulltext Genome sequencing and annotation of Aeromonas sp. HZM
    Chua P, Har ZM, Austin CM, Yule CM, Dykes GA, Lee SM
    Genom Data, 2015 Sep;5:38-9.
    PMID: 26484220 DOI: 10.1016/j.gdata.2015.05.008
    We report the draft genome sequence of Aeromonas sp. strain HZM, isolated from tropical peat swamp forest soil. The draft genome size is 4,451,364 bp with a G + C content of 61.7% and contains 10 rRNA sequences (eight copies of 5S rRNA genes, single copy of 16S and 23S rRNA each). The genome sequence can be accessed at DDBJ/EMBL/GenBank under the accession no. JEMQ00000000.
  13. Determination of quarantine period in African catfish (Clarias gariepinus) fed with pig (Sus sp.) offal to assure compliance with halal standards
    Wan Norhana MN, Dykes GA, Padilah B, Ahmad Hazizi AA, Masazurah AR
    Food Chem, 2012 Dec 1;135(3):1268-72.
    PMID: 22953853 DOI: 10.1016/j.foodchem.2012.05.083
    Pig (Sus sp.) and pig by-products are considered as najasa (impurities) in Islam and forbidden in Muslim consumer products. Animals fed on najasa are categorised as al-jallālah (contaminated animals) which are allowed to be consumed as long as they have been quarantined for a certain period of time. During this quarantine period the animals will have undergone a natural purification process or istihālah. African catfish (Clarias gariepinus) are commonly consumed in Malaysia and may be fed on najasa. This study was carried out to estimate the istihālah period for catfish after feeding with pig offal, based on the absence of pig DNA in catfish gut and to suggest the quarantine period in catfish fed with pig offal. The results indicated that the maximum istihālah period could reach 36h in the stomach, 6h in the midgut and less than 2h in the hindgut although in many cases shorter periods were observed. Based on these results it is estimated that the minimum quarantine period for catfish fed with pig offal is 1.5days.
  14. Fulltext Draft Genome Sequences of Six Enterococcus faecalis Strains Isolated from Malaysian Clinical and Environmental Origins
    Daniel DS, Gan HM, Lee SM, Dykes GA, Rahman S
    Genome Announc, 2017 Jun 15;5(24).
    PMID: 28619812 DOI: 10.1128/genomeA.00553-17
    Enterococcus faecalis is known to cause a variety of nosocomial infections, including urinary tract infections. Antibiotic resistance and virulence properties in this species are of public concern. The draft genome sequences of six E. faecalis strains isolated from clinical and environmental sources in Malaysia are presented here.
  15. Fulltext Genetic diversity of Enterococcus faecalis isolated from environmental, animal and clinical sources in Malaysia
    Daniel DS, Lee SM, Gan HM, Dykes GA, Rahman S
    J Infect Public Health, 2017 02 21;10(5):617-623.
    PMID: 28254461 DOI: 10.1016/j.jiph.2017.02.006
    Enterococcus faecalis ranks as one of the leading causes of nosocomial infections. A strong epidemiological link has been reported between E. faecalis inhabiting animals and environmental sources. This study investigates the genetic diversity, antibiotic resistance and virulence determinants in E. faecalis from three sources in Malaysia. A total of 250 E. faecalis isolates were obtained consisting of 120 isolates from farm animals, 100 isolates from water sources and 30 isolates from hospitalized patients. Pulse-field gel electrophoresis-typing yielded 63 pulsotypes, with high diversity observed in all sources (D=≥0.901). No pulsotype was common to all the three sources. Each patient room had its own unique PFGE pattern which persisted after six months. Minimum inhibitory concentrations of Vancomycin, Gentamicin, Penicillin, Tetracycline, Nitrofurantoin, Levofloxacin, Ciprofloxacin and Fosfomycin were evaluated. Resistance to Tetracycline was most prevalent in isolates from farm animals (62%) and water sources (49%). Water isolates (86%) had a higher prevalence of the asa1 gene, which encodes for aggregation substance, whereas clinical (78%) and farm animal isolates (87%) had a higher prevalence of the esp gene, encoding a surface exposed protein. This study generates knowledge on the genetic diversity of E. faecalis with antibiotic resistance and virulence characteristics from various sources in Malaysia.
  16. Fulltext Public Health Risks of Multiple-Drug-Resistant Enterococcus spp. in Southeast Asia
    Daniel DS, Lee SM, Dykes GA, Rahman S
    Appl Environ Microbiol, 2015 Sep;81(18):6090-7.
    PMID: 26150452 DOI: 10.1128/AEM.01741-15
    Enterococci rank as one of the leading causes of nosocomial infections, such as urinary tract infections, surgical wound infections, and endocarditis, in humans. These infections can be hard to treat because of the rising incidence of antibiotic resistance. Enterococci inhabiting nonhuman reservoirs appear to play a critical role in the acquisition and dissemination of antibiotic resistance determinants. The spread of antibiotic resistance has become a major concern in both human and veterinary medicine, especially in Southeast Asia, where many developing countries have poor legislation and regulations to control the supply and excessive use of antimicrobials. This review addresses the occurrence of antibiotic-resistant enterococci in Association of Southeast Asian Nations countries and proposes infection control measures that should be applied to limit the spread of multiple-drug-resistant enterococci.
  17. Enhanced xylose recovery from oil palm empty fruit bunch by efficient acid hydrolysis
    Tan HT, Dykes GA, Wu TY, Siow LF
    Appl Biochem Biotechnol, 2013 Aug;170(7):1602-13.
    PMID: 23709290 DOI: 10.1007/s12010-013-0298-8
    Oil palm empty fruit bunch (EFB) is abundantly available in Malaysia and it is a potential source of xylose for the production of high-value added products. This study aimed to optimize the hydrolysis of EFB using dilute sulfuric acid (H2SO4) and phosphoric acid (H3PO4) via response surface methodology for maximum xylose recovery. Hydrolysis was carried out in an autoclave. An optimum xylose yield of 91.2 % was obtained at 116 °C using 2.0 % (v/v) H2SO4, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. A lower optimum xylose yield of 24.0 % was observed for dilute H3PO4 hydrolysis at 116 °C using 2.4 % (v/v) H3PO4, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. The optimized hydrolysis conditions suggested that EFB hydrolysis by H2SO4 resulted in a higher xylose yield at a lower acid concentration as compared to H3PO4.
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