Effects of Sublethal Temperature Stress on the Growth, Survival and Culturability of Listeria Monocytogenes

Survival and growth of Listeria monocytogenes L56 (JMR isolate) was studied in trypticase soy broth grown at 37°C before being subjected to three selected sublethal stress of temperatures (55°C, 28°C and 4°C) using log and stationary phase as inoculums using two-plating systems; TSA with and without 4% NaCl (TSAS). The influence of morphological changes and listerial motility as affected by sublethal stress of temperatures were also determined using Scanning Electron Microscopy (SEM) and motility media, respectively. A standard growth curve of L. monocytogenes at 37°C was established using plate counts showed that the log and stationary phase of the organism were achieved after 12 and 19 hours, respectively. It was observed that viable bacterial population (CFU/ml) after log and stationary phase were 108 and 109, respectively. From the growth curve, the generation time of L. monocytogenes at 37°C was 60 min. The bacterial growth rates obtained from culturability on culture plates assessed using two-system media, TSA with and without 4% NaCl concentration (TSAS) were assessed by their generation time. Cells of L. monocytogenes grown in exponential phase cultures demonstrated biphasic survival curves at 55°C and 4°C in both media. In contrast, survival curves at 28°C were not biphasic. The growth rates of L. monocytogenes grown in stationary phase cultures were also assessed by their generation time. The addition of sodium chloride enhanced heat resistance of microorganism. It has been proven that biphasic curve and tailing with/without shoulder from thennal inactivation curves in this study were associated with the occurrence of microbial injury. During the exponential phase of L. monocytogenes, the percentage injury at 55°C, 28°C and 4°C were ranged between 3.21% to 28.49%, 2.47% to 4.38%, and 4.34% to 8.61%, respectively. Whilst, during the stationary phase of L. monocytogenes, the percentage injury at 55°C, 28°C and 4°C were ranged between 2.05% to 4.15%, 1.44% to 3.06%, and 1.07 to 4.25%, respectively. L. monocytogenes cells were able to survive throughout the sublethal stress of temperatures and undergone morphological changes to adapt to new temperatures. In this study, results from Scanning Electron Microscopy (SEM) revealed three different analyses of temperature-stressed cells which were average mean of cells length, distribution of cells length, and minimum versus maximum cells length. The study demonstrated cells of both log and stationary phase showed a significant variation of morphology. Cells of log phase became elongated only at 55°C, not at 28°C and 4°C whereas cells of stationary phase were shorter and more coccoidal rather than elongated as in log phase cells. However, cells at 28°C were more intact than cells at other temperatures for most of the observations. In conjunction with SEM results, the variation of listerial morphology and the effect of listerial motility would be a part of microbial adaptation towards sublethal stress of temperatures. The loss of motility in stationary phase cells strongly suggested that listerial motility play a role in survival of the organism under temperature stress. The stationary phase cells of L. monocytogenes were more resistant than exponential phase cells exhibited by increased of generation times, lower percentage injury and most of the cells became coccoid

Antifungal Activity of Lactic Acid Bacteria Isolated from Soil Rhizosphere on Fusarium Species Infected Chilli Seeds

Lactic acid bacteria (LAB) are known to inhibit the growth of fungi and LAB cells or its  can be used as biocontrol against plant pathogens. The aim of this study was to evaluate the efficacy of selected LAB strains isolated from rhizospheric soil against Fusarium spp. These fungi were isolated from infected different plant parts and identified as F. oxysporum strain KAML01, Fusarium sp. CID124, Fusarium sp. fus 124 and F. proliferatum with 99 % similarity using Internal Transcribed Spacer (ITS) analysis. Five LAB strains were showed strong antifungal activity against the Fusarium spp. were evaluated using dual overlay method. Isolates MSS1 and FCF11 were 100% similarity with Lactobacillus plantarum and isolate MSS5 99% was similarity with Pediococcus pentoceous using 16S rDNA sequence analysis. Inhibition of Fusarium sp. CID124 fungal biomass in the de Man, Rogosa and Sharpe Broth (MRSB) was significantly greater (P ≤ 0.05) by cells of P. pentosaceus (97.43%) compared to inhibition of Fusarium sp. CID124 fungal biomass by Cell Free Supernatant (CFS) of Lb. acidophilus ATCC314 (91.8%) using biomass dry method in Malt Extract Broth (MEB) medium. Fusarium spp. infected to seeds of three cultivars, Cili Kulai, Red spicy-0639 and GAAC-SEED-5005 and then, treated with CFS-LAB. All treated seeds with CFS-LAB showed good germination in the range of 82.6 to 93.3% compared to seed germination 53.3 to 70.0% of chili seeds infected with Fusarium spp. The percentage germination of chilli seeds was strongly suppressed when infected with Fusarium sp. CID124. This infection had significant (P≤0.05) reduction of seed germination to 53.3 % compared to other Fusarium spp. Finally, the pathogenicity effect of Fusarium sp. CID124-CS  was highly virulent on seeds germination of chilli.

Effects of hydrophilic and lipophilic emulsifier concentrations on the characteristics of Germander essential oil nanoemulsions prepared using the nanoprecipitation technique

The Germanders (Teucrium polium L.) essential oil exhibits antioxidant and bactericidal activities against a wide range of microorganisms; however, its water insolubility, susceptibility to environmental stresses, and intense flavors limit its uses in food formulations. As a solution, in the present study, nanoemulsions of Germanders (Mentha pulegium) essential oil were prepared using a bottom-up nanoprecipitation technique. A central composite design based on the response surface methodology was implemented to investigate the effects of selected lipophilic and hydrophilic emulsifier concentrations. The proposed second-order polynomial models, with relatively high coefficients of determination, could efficiently predict alterations in response parameters due to emulsifier concentrations. The results revealed that both lipophilic and hydrophilic emulsifiers had significantly affected all characteristics of the synthesized essential oil nanoemulsions. Multi-goal optimization analysis suggested that 7.8% and 4.8% concentrations of Span 80 and Tween 80, respectively, could yield the most desirable Germanders essential oil nanoemulsions, with a mean particle size of 78.56 nm, PDI of 0.1722, DPPH radical scavenging of 83.69%, Staphylococcus aureus and Salmonella enterica growth inhibition zones of 10.5 mm and 12.7 mm, respectively. The validity of the models was confirmed by the absence of substantial variations between experimental data and modeling results. While the prepared Germander essential oil nanoemulsions demonstrated acceptable physical properties, they exhibited relatively limited chemical stability during storage at 5°C for 30 days

Surface modification via alginate-based edible coating for enhanced osmotic dehydration mass transfer of ginger slices

Ginger has a high moisture content, which makes it highly susceptible to spoilage. Therefore, the shelf life can be extended through drying. In the drying process, osmotic dehydration is applied as pre-treatment due to its simple operation and energy-saving process for removing moisture from food. However, large solute gain during the osmotic dehydration has become the major challenge of this process as it has a negative impact on the final product. The edible coating is the key step to circumventing this issue. Alginate is a potential candidate for the coating material to enhance the mass transfer kinetics of the osmotic dehydration process. This study investigated the surface modification of ginger slices caused by the cross-linker calcium chloride and plasticizer glycerol on alginate coating using a Scanning Electron Microscope. Furthermore, the kinetics of water loss and solute gain were evaluated and modelling aspects were conducted. It was observed that the surface roughness of ginger coated with a combination of alginate, glycerol and calcium ions has reduced. This facilitated the mass transfer process, which was observed to have a high water loss and a lower solute gain. The Peleg model presented the best fitting model of mass transfer kinetics during osmotic dehydration of ginger slices. From this work, it can be deduced that alginate-based coating can be a promising pre-treatment step in the osmotic dehydration process

Antimicrobial resistance of Escherichia coli isolated of ulam from supermarkets and wet markets in Kuala Terengganu, Malaysia

Raw vegetables were highly exposed to microbial contamination by handling at harvest or during postharvest processing. Nowadays, emerging issues threatening public health are bacterial resistance to antibiotics due to the excessive usage and misuse of antibiotics in agriculture. In this study, antibiotic susceptibility profiles of 23 Escherichia coli strains were tested by the standard disk diffusion method. Sixteen antimicrobial agents namely amikacin, amoxycillin/cluvanic acid, ampicillin, ampicillin/sulbactam, chloramphenicol, ceftriaxone, ciproflaxacin, ceftazidime, cephalotin, cefoperazone, gentamicin, kanamycin, nalidixic acid, streptomycin, tetracycline and trimethoprim were included in this study. In this study, 78.3% of the E. coli isolates were found to be resistant to cephalotin and it was the highest compared with the other antibiotics. It was found that 87% of isolates exhibited resistance to at least one antibiotic. E. coli showed high resistance to ampicillin (52.2%) and tetracycline (52.2%). In contrast, ceftriaxone and ceftazidime were found to be (100%) effective in restraining the growth of E. coli isolates. The highest multiple antibiotic resistance index (MAR) index was 0.48. Multiple resistance was observed in 47.8% of isolates with resistance to three to seven antibiotics. In conclusion, ulam could be the potential source of this antibiotic resistance of E. coli, and it may pose health threats to consumers

Preliminary Assessment of Antifungal Activity of Lactic Acid Bacteria From Selected Malaysian Traditional Fermented Food

Candida albicans, naturally a part of a healthy gut and oral microflora, is an opportunistic pathogen that commonly infects humans. However, current antifungal agents are made of synthetic drugs that cause varied adverse effects in patients. This drives efforts to look for natural and safer alternatives to antifungal agents. Fermented food has been studied for its ability to produce lactic acid bacteria with antimicrobial properties. This study examined the antifungal activity of lactic acid bacteria isolated from four traditional Malaysian fermented foods. Pickled chilies, pickled garlic, pickled maman, and tapai were prepared by using homemade recipes and fermented at 4°C. Lactic acid bacteria were isolated from the fermented food during a two-week fermentation on three selective growth agars. During fermentation, bacterial cells were counted at intervals. Growth trends for pickled garlic and pickled chilies presented an exponential phase between days 0 – 4, followed by stationary and death phases between days 8 – 14. Meanwhile, pickled maman and tapai showed continuous growth throughout the 14 days. Antifungal potential of the lactic acid bacteria was assessed via dual agar diffusion assay by spotting pickled water of each fermented food on De Man, Rogosa, Sharpe agar placed above a layer of Sabouraud Dextrose agar with pre-inoculated C. albicans, followed by measurement of the zone of inhibition. Pickled maman produced 1.2 ± 0.05 mm inhibition. In conclusion, pickled maman and tapai produced lactic acid bacteria throughout the two-week fermentation. Based on the dual agar diffusion, pickled maman showed an antifungal potential against C. albicans

Microbial inactivation using pulsed light - a review

The use of pulse light to inactivate microbes has recently attracted interest of many researchers. Consequently, there are various reports on the efficacy and advantages of pulsed light in microbial inactivation; and also the potentiality of pulsed light systems being adopted for industrial use in this regards. Here, we review some of the works done in relation to microbial inactivation with pulse light, with emphasis on the role played by pulse light parameters such as fluence, spectral range, pulse power, pulse width, pulse frequency, etc. We focussed in particular on factors that make pulsed light systems more effective than their continuous wave counterpart and also proffer suggestions on possible areas for improvement in future study. The use of pulsed lasers in inactivating microbes was briefly appraised. Also, prospects and challenges in the use of pulsed light for inactivation were highlighted

Lactic Acid Bacteria Producing Sorbic Acid and Benzoic Acid Compounds from Fermented Durian Flesh (Tempoyak) and Their Antibacterial Activities Against Foodborne Pathogenic Bacteria

Background and Objective: Antibacterial compounds produced by lactic acid bacteria are believed to replace functions of chemical preservatives. The objectives of this study were to identify lactic acid bacteria, which produced antibacterial compounds, from fermented durian flesh (tempoyak) and to assess antibacterial activities of the isolates. Material and Methods: Two bacterial identification techniques were used, including API 50 CHL kit with supplementary medium and matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF/MS). Results and Conclusion: Four various lactic acid bacteria strains of Lactobacillus buchneri, Lactobacillus plantarum, Lactobacillus brevis I and Lactobacillus acidophilus I were identified using API 50 CHL Kit and five various others of Lactobacillus paracasei DSM 2649, Lactobacillus buchneri DSM 20057T, Lactobacillus parabuchneri DSM 57069, Lactobacillus paracasei DSM 20020 and Lactobacillus farcimini CIP 103136T using MALDI-TOF/MS. Cell-free supernatant extracted from Lactobacillus plantarum, Lactobacillus buchneri, Lactobacillus brevis I and Lactobacillus acidophilus I included strong inhibitory effects against Vibrio cholera O1 (Inaba type), Vibrio cholera O139 (Bengal type), Vibrio parahaemolyticus ATCC 17802, Escherichia coli ATCC 11795, Escherichia coli O157, Salmonella typhimurium ATCC 14028 and a total of 23 serotypes of Salmonella spp. associated with outbreaks of food poisoning from raw chicken, egg shell and water samples. Only Lactobacillus buchneri DSM 20057T was identified by MALDI-TOF/MS as a strain producing sorbic and benzoic acids. This strain can potentially be used as food preservative to decrease growth of foodborne pathogenic bacteria

Microbiological evaluation on raw materials and food contact surfaces of ‘keropok lekor’ premises in Kuala Nerus, Terengganu and their prevalence of antibiotic resistant bacteria

‘Keropok lekor’ is a popular street food and widely available in Terengganu. However, there is limited study on the microbiological status of sources of contamination from ‘keropok lekor’ premises in Terengganu. Microbiological quality of raw materials and food contact surfaces were determined by Total Plate Count, coliform count, Staphylococcus spp. and Vibrio spp. count. The presumptive of Escherichia coli, Staphylococcus aureus and Vibrio spp. were further identified by phenotypic identification such as IMViC tests and API20 NE identification system. The antibiotic resistance of the identified bacteria was determined using disc diffusion method. Escherichia coli and Vibrio were predominant microorganisms isolated from raw materials, whereas Staphylococcus was the predominant microorganism on food contact surfaces. The boiling process of ‘keropok lekor’ at 100°C was significantly (p < 0.05) reduced the Total Plate Counts, coliform, Staphylococcus spp. and Vibrio spp. count for safe consumption. The identified antibiotic resistance of E. coli, S. aureus and Vibrio spp. showed that the bacteria were within controllable emergence strains, whereby the present antibiotics used are able to suppress the growth. Regular monitoring programme is essential to further improve the microbiological quality of raw materials and food contact surfaces

Candida albicans skin infection in diabetic patients: An updated review of pathogenesis and management

Candida species, commensal residents of human skin, are recognized as the cause of cutaneous candidiasis across various body surfaces. Individuals with weakened immune systems, particularly those with immunosuppressive conditions, are significantly more susceptible to this infection. Diabetes mellitus, a major metabolic disorder, has emerged as a critical factor inducing immunosuppression, thereby facilitating Candida colonization and subsequent skin infections. This comprehensive review examines the prevalence of different types of Candida albicans-induced cutaneous candidiasis in diabetic patients. It explores the underlying mechanisms of pathogenicity and offers insights into recommended preventive measures and treatment strategies. Diabetes notably increases vulnerability to oral and oesophageal candidiasis. Additionally, it can precipitate vulvovaginal candidiasis in females, Candida balanitis in males, and diaper candidiasis in young children with diabetes. Diabetic individuals may also experience candidal infections on their nails, hands and feet. Notably, diabetes appears to be a risk factor for intertrigo syndrome in obese individuals and periodontal disorders in denture wearers. In conclusion, the intricate relationship between diabetes and cutaneous candidiasis necessitates a comprehensive understanding to strategize effective management planning. Further investigation and interdisciplinary collaborative efforts are crucial to address this multifaceted challenge and uncover novel approaches for the treatment, management and prevention of both health conditions, including the development of safer and more effective antifungal agents