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Biofilm formation by staphylococci in health-related environments and recent reports on their control using natural compounds

Yong YY, Dykes GA, Choo WS

Crit Rev Microbiol, 2019 Mar;45(2):201-222.
PMID: 30786799 DOI: 10.1080/1040841X.2019.1573802

Staphylococci are Gram-positive bacteria that are ubiquitous in the environment and able to form biofilms on a range of surfaces. They have been associated with a range of human health issues such as medical device-related infection, localized skin infection, or direct infection caused by toxin production. The extracellular material produced by these bacteria resists antibiotics and host defence mechanism which complicates the treatment process. The commonly reported Staphylococcus species are Staphylococcus aureus and S. epidermidis as they inhabit human bodies. However, the emergence of other staphylococci, such as S. haemolyticus, S. lugdunensis, S. saprophyticus, S. capitis, S. saccharolyticus, S. warneri, S. cohnii, and S. hominis, is also of concern and they have been associated with biofilm formation. This review critically assesses recent cases on the biofilm formation by S. aureus, S. epidermidis, and other staphylococci reported in health-related environments. The control of biofilm formation by staphylococci using natural compounds is specifically discussed as they represent potential anti-biofilm agents which may reduce the burden of antibiotic resistance.
Fulltext Inhibition of attachment of oral bacteria to immortalized human gingival fibroblasts (HGF-1) by tea extracts and tea components

Wang Y, Chung FF, Lee SM, Dykes GA

BMC Res Notes, 2013;6:143.
PMID: 23578062 DOI: 10.1186/1756-0500-6-143

Tea has been suggested to promote oral health by inhibiting bacterial attachment to the oral cavity. Most studies have focused on prevention of bacterial attachment to hard surfaces such as enamel.
Potential mechanisms for the effects of tea extracts on the attachment, biofilm formation and cell size of Streptococcus mutans

Wang Y, Lee SM, Dykes GA

Biofouling, 2013;29(3):307-18.
PMID: 23528127 DOI: 10.1080/08927014.2013.774377

Tea can inhibit the attachment of Streptococcus mutans to surfaces and subsequent biofilm formation. Five commercial tea extracts were screened for their ability to inhibit attachment and biofilm formation by two strains of S. mutans on glass and hydroxyapatite surfaces. The mechanisms of these effects were investigated using scanning electron microscopy (SEM) and phytochemical screening. The results indicated that extracts of oolong tea most effectively inhibited attachment and extracts of pu-erh tea most effectively inhibited biofilm formation. SEM images showed that the S. mutans cells treated with extracts of oolong tea, or grown in medium containing extracts of pu-erh tea, were coated with tea components and were larger with more rounded shapes. The coatings on the cells consisted of flavonoids, tannins and indolic compounds. The ratio of tannins to simple phenolics in each of the coating samples was ∼3:1. This study suggests potential mechanisms by which tea components may inhibit the attachment and subsequent biofilm formation of S. mutans on tooth surfaces, such as modification of cell surface properties and blocking of the activity of proteins and the structures used by the bacteria to interact with surfaces.
A statistical approach for modelling the physical process of bacterial attachment to abiotic surfaces

Wang Y, Lee SM, Gentle IR, Dykes GA

Biofouling, 2020 11;36(10):1227-1242.
PMID: 33412938 DOI: 10.1080/08927014.2020.1865934

A statistical approach using a polynomial linear model in combination with a probability distribution model was developed to mathematically represent the process of bacterial attachment and study its mechanism. The linear deterministic model was built based on data from experiments investigating bacterial and substratum surface physico-chemical factors as predictors of attachment. The prediction results were applied to a normal-approximated binomial distribution model to probabilistically predict attachment. The experimental protocol used mixtures of Streptococcus salivarius and Escherichia coli, and mixtures of porous poly(butyl methacrylate-co-ethyl dimethacrylate) and aluminum sec-butoxide coatings, at varying ratios, to allow bacterial attachment to substratum surfaces across a range of physico-chemical properties (including the surface hydrophobicity of bacterial cells and the substratum, the surface charge of the cells and the substratum, the substratum surface roughness and cell size). The model was tested using data from independent experiments. The model indicated that hydrophobic interaction was the most important predictor while reciprocal interactions existed between some of the factors. More importantly, the model established a range for each factor within which the resultant attachment is unpredictable. This model, however, considers bacterial cells as colloidal particles and accounts only for the essential physico-chemical attributes of the bacterial cells and substratum surfaces. It is therefore limited by a lack of consideration of biological and environmental factors. This makes the model applicable only to specific environments and potentially provides a direction to future modelling for different environments.
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.
Growth in the presence of specific antibiotics induces biofilm formation by a Campylobacter jejuni strain sensitive to them but not in resistant strains

Teh AHT, Lee SM, Dykes GA

J Glob Antimicrob Resist, 2019 09;18:55-58.
PMID: 31163253 DOI: 10.1016/j.jgar.2019.05.020

OBJECTIVE: Campylobacter jejuni (C. jejuni) are among the most frequently identified bacteria associated with human gastroenteritis worldwide. Exposure to antibiotics may induce or inhibit biofilm formation in some bacterial species. Little work has been reported on the influence of antibiotics on biofilm formation by C. jejuni.
METHODS: This study investigated the effect of six different classes of antibiotics with different modes of action (ampicillin, ciprofloxacin, erythromycin, nalidixic acid, rifampicin and tetracycline) on biofilm formation in vitro by seven C. jejuni from poultry with different antibiotic resistance profiles.
RESULTS: The results indicated that in the presence of most of the tested antibiotics, biofilm formation by C. jejuni strains, which are resistant to them, was reduced but biofilm formation in sensitive strains was increased.
CONCLUSION: The ability of certain antibiotics to induce biofilm formation by a tested C. jejuni strain is of concern, with respect to the effective control of disease caused by this pathogen; however, further work is required to confirm how widespread this feature is.
Fulltext Association of some Campylobacter jejuni with Pseudomonas aeruginosa biofilms increases attachment under conditions mimicking those in the environment

Teh AHT, Lee SM, Dykes GA

PLoS One, 2019;14(4):e0215275.
PMID: 30970009 DOI: 10.1371/journal.pone.0215275

Campylobacter jejuni is a microaerophilic bacterial species which is a major food-borne pathogen worldwide. Attachment and biofilm formation have been suggested to contribute to the survival of this fastidious bacteria in the environment. In this study the attachment of three C. jejuni strains (C. jejuni strains 2868 and 2871 isolated from poultry and ATCC 33291) to different abiotic surfaces (stainless steel, glass and polystyrene) alone or with Pseudomonas aeruginosa biofilms on them, in air at 25°C and under static or flow conditions, were investigated using a modified Robbins Device. Bacteria were enumerated and scanning electron microscopy was carried out. The results indicated that both C. jejuni strains isolated from poultry attached better to Pseudomonas aeruginosa biofilms on abiotic surfaces than to the surfaces alone under the different conditions tested. This suggests that biofilms of other bacterial species may passively protect C. jejuni against shear forces and potentially oxygen stress which then contribute to their persistence in environments which are detrimental to them. By contrast the C. jejuni ATCC 33291 strain did not attach differentially to P. aeruginosa biofilms, suggesting that different C. jejuni strains may have alternative strategies for persistence in the environment. This study supports the hypothesis that C. jejuni do not form biofilms per se under conditions they encounter in the environment but simply attach to surfaces or biofilms of other species.
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.
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.
The influence of antibiotic resistance gene carriage on biofilm formation by two Escherichia coli strains associated with urinary tract infections

Teh AH, Wang Y, Dykes GA

Can J Microbiol, 2014 Feb;60(2):105-11.
PMID: 24498987 DOI: 10.1139/cjm-2013-0633

Urinary tract infections (UTI) caused by uropathogenic Escherichia coli are one of the most common forms of human disease. In this study, the effect of the presence of newly acquired antibiotic resistance genes on biofilm formation of UTI-associated E. coli strains was examined. Two clinical UTI-associated E. coli strains (SMC18 and SMC20) carrying different combinations of virulence genes were transformed with pGEM-T, pGEM-T::KmΔAmp, or pGEM-T::Km to construct ampicillin-resistant (Km(S)Amp(R)), kanamycin-resistant (Km(R)Amp(S)), or ampicillin- and kanamycin-resistant (Km(R)Amp(R)) strains. Transformed and wild-type strains were characterized for biofilm formation, bacterial surface hydrophobicity, auto-aggregation, morphology, and attachment to abiotic surfaces. Transformation with a plasmid carrying an ampicillin resistance gene alone decreased (p < 0.05) biofilm formation by SMC18 (8 virulence marker genes) but increased (p < 0.05) biofilm formation by SMC20 (5 virulence marker genes). On the other hand, transformation with a plasmid carrying a kanamycin resistance gene alone or both ampicillin and kanamycin resistance genes resulted in a decrease (p < 0.05) in biofilm formation by SMC18 but did not affect (p > 0.05) the biofilm formation by SMC20. Our results suggest that transformation of UTI-associated E. coli with plasmids carrying different antibiotic resistance gene(s) had a significant impact on biofilm formation and that these effects were both strain dependent and varied between different antibiotics.
Fulltext Draft Genome Sequences of Three Multiantibiotic-Resistant Campylobacter jejuni Strains (2865, 2868, and 2871) Isolated from Poultry at Retail Outlets in Malaysia

Teh AH, Lee SM, Dykes GA

Genome Announc, 2016;4(3).
PMID: 27151799 DOI: 10.1128/genomeA.00331-16

Campylobacter jejuni is a frequent cause of human bacterial gastrointestinal foodborne disease worldwide. Antibiotic resistance in this species is of public health concern. The draft genome sequences of three multiantibiotic-resistant C. jejuni strains (2865, 2868, and 2871) isolated from poultry at retail outlets in Malaysia are presented here.
The Influence of Prior Modes of Growth, Temperature, Medium, and Substrate Surface on Biofilm Formation by Antibiotic-Resistant Campylobacter jejuni

Teh AH, Lee SM, Dykes GA

Curr Microbiol, 2016 Dec;73(6):859-866.
PMID: 27623781

Campylobacter jejuni is one of the most common causes of bacterial gastrointestinal food-borne infection worldwide. It has been suggested that biofilm formation may play a role in survival of these bacteria in the environment. In this study, the influence of prior modes of growth (planktonic or sessile), temperatures (37 and 42 °C), and nutrient conditions (nutrient broth and Mueller-Hinton broth) on biofilm formation by eight C. jejuni strains with different antibiotic resistance profiles was examined. The ability of these strains to form biofilm on different abiotic surfaces (stainless steel, glass, and polystyrene) as well as factors potentially associated with biofilm formation (bacterial surface hydrophobicity, auto-aggregation, and initial attachment) was also determined. The results showed that cells grown as sessile culture generally have a greater ability to form biofilm (P
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.
Acetic acid induces pH-independent cellular energy depletion in Salmonella enterica

Tan SM, Lee SM, Dykes GA

Foodborne Pathog Dis, 2015 Mar;12(3):183-9.
PMID: 25562466 DOI: 10.1089/fpd.2014.1853

Weak organic acids are widely used as preservatives and disinfectants in the food industry. Despite their widespread use, the antimicrobial mode of action of organic acids is still not fully understood. This study investigated the effect of acetic acid on the cell membranes and cellular energy generation of four Salmonella strains. Using a nucleic acid/protein assay, it was established that acetic acid did not cause leakage of intracellular components from the strains. A scanning electron microscopy study further confirmed that membrane disruption was not the antimicrobial mode of action of acetic acid. Some elongated Salmonella cells observed in the micrographs indicated a possibility that acetic acid may inhibit DNA synthesis in the bacterial cells. Using an ATP assay, it was found that at a neutral pH, acetic acid caused cellular energy depletion with an ADP/ATP ratio in the range between 0.48 and 2.63 (p<0.05) that was apparent for the four Salmonella strains. We suggest that this effect was probably due solely to the action of undissociated acid molecules. The antimicrobial effect of acetic acid was better under acidic conditions (ADP/ATP ratio of 5.56 ± 1.27; p<0.05), where the role of both pH and undissociated acid molecules can act together. We concluded that the inhibitory effect of acetic acid is not solely attributable to acidic pH but also to undissociated acid molecules. This finding has implication for the use of acetic acid as an antimicrobial against Salmonella on food products, such as chicken meat, which can buffer its pH.
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.
Attachment of bacterial pathogens to a bacterial cellulose-derived plant cell wall model: a proof of concept

Tan MS, Wang Y, Dykes GA

Foodborne Pathog Dis, 2013 Nov;10(11):992-4.
PMID: 23941519 DOI: 10.1089/fpd.2013.1536

This study aimed to establish, as a proof of concept, whether bacterial cellulose (BC)-derived plant cell wall models could be used to investigate foodborne bacterial pathogen attachment. Attachment of two strains each of Salmonella enterica and Listeria monocytogenes to four BC-derived plant cell wall models (namely, BC, BC-pectin [BCP], BC-xyloglucan [BCX], and BC-pectin-xyloglucan [BCPX]) was investigated. Chemical analysis indicated that the BCPX composite (31% cellulose, 45.6% pectin, 23.4% xyloglucan) had a composition typical of plant cell walls. The Salmonella strains attached in significantly (p<0.05) higher numbers (~6 log colony-forming units [CFU]/cm(2)) to the composites than the Listeria strains (~5 log CFU/cm(2)). Strain-specific differences were also apparent with one Salmonella strain, for example, attaching in significantly (p<0.05) higher numbers to the BCX composite than to the other composites. This study highlights the potential usefulness of these composites to understand attachment of foodborne bacteria to fresh produce.
Fulltext Attachment of Salmonella strains to a plant cell wall model is modulated by surface characteristics and not by specific carbohydrate interactions

Tan MS, Moore SC, Tabor RF, Fegan N, Rahman S, Dykes GA

BMC Microbiol, 2016 09 15;16:212.
PMID: 27629769 DOI: 10.1186/s12866-016-0832-2

BACKGROUND: Processing of fresh produce exposes cut surfaces of plant cell walls that then become vulnerable to human foodborne pathogen attachment and contamination, particularly by Salmonella enterica. Plant cell walls are mainly composed of the polysaccharides cellulose, pectin and hemicelluloses (predominantly xyloglucan). Our previous work used bacterial cellulose-based plant cell wall models to study the interaction between Salmonella and the various plant cell wall components. We demonstrated that Salmonella attachment was favoured in the presence of pectin while xyloglucan had no effect on its attachment. Xyloglucan significantly increased the attachment of Salmonella cells to the plant cell wall model only when it was in association with pectin. In this study, we investigate whether the plant cell wall polysaccharides mediate Salmonella attachment to the bacterial cellulose-based plant cell wall models through specific carbohydrate interactions or through the effects of carbohydrates on the physical characteristics of the attachment surface.
RESULTS: We found that none of the monosaccharides that make up the plant cell wall polysaccharides specifically inhibit Salmonella attachment to the bacterial cellulose-based plant cell wall models. Confocal laser scanning microscopy showed that Salmonella cells can penetrate and attach within the tightly arranged bacterial cellulose network. Analysis of images obtained from atomic force microscopy revealed that the bacterial cellulose-pectin-xyloglucan composite with 0.3 % (w/v) xyloglucan, previously shown to have the highest number of Salmonella cells attached to it, had significantly thicker cellulose fibrils compared to other composites. Scanning electron microscopy images also showed that the bacterial cellulose and bacterial cellulose-xyloglucan composites were more porous when compared to the other composites containing pectin.
CONCLUSIONS: Our study found that the attachment of Salmonella cells to cut plant cell walls was not mediated by specific carbohydrate interactions. This suggests that the attachment of Salmonella strains to the plant cell wall models were more dependent on the structural characteristics of the attachment surface. Pectin reduces the porosity and space between cellulose fibrils, which then forms a matrix that is able to retain Salmonella cells within the bacterial cellulose network. When present with pectin, xyloglucan provides a greater surface for Salmonella cells to attach through the thickening of cellulose fibrils.
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.
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.
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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