Tryptone Glucose Yeast Extract Agar Research Articles

Facultative thermophilic microorganisms in potato products in retort packaging

Thermally treated potato products in retort packaging with an extended shelf-life (up to 90 days before opening) at room temperature (20 ± 1 °C) from two Latvian vegetable processing companies (A and B) were analysed in this research. The aim of this research was to determine the presence of thermotolerant microbial contamination in thermally treated potato products in retort packaging, to ensure their safety and suitability for immediate consumption. Samples from three production batches were used. The total plate count was determined, and a microscopic examination of potato product samples was performed. Microscopic examination of microorganisms showed the presence of microbial vegetative forms in potato products from company B, but the standard investigation did not register them; therefore, Tryptone Glucose Yeast Extract Agar (TGYA), TGYA enriched with 1 % starch solution and TGYA enriched with 5 % starch solution were used for potential microorganism isolation. Samples were incubated at 25 °C; 37 °C; 41.5 °C; 50 °C; 55 °C and 60 °C temperatures under aerobic and anaerobic conditions, incubation time 12, 24 and 48 h. Facultative thermophilic Bacillus licheniformis bacteria which produce thermotolerant spores were isolated from thermally treated potato products in retort packaging from company B. The average colony count in company B samples was 1.27´100 CFU/g (SD = 78.25). The presence of microorganisms was not detected in potato products produced at company A, while facultative thermophilic and thermotolerant microorganisms were found in potato products produced at company B. DOI: http://dx.doi.org/10.5755/j01.ct.66.1.12363

Deinococcus mumbaiensissp. nov., a radiation-resistant pleomorphic bacterium isolated from Mumbai, India

A radiation-resistant, Gram-negative and pleomorphic bacterium (CON-1) was isolated from a contaminated tryptone glucose yeast extract agar plate in the laboratory. It was red pigmented, nonmotile, nonsporulating, and aerobic, and contained MK-8 as respiratory quinone. The cell wall of this bacterium contained ornithine. The major fatty acids were C16:0, C16:1, C17:0, C18:1 and iso C18:0. The DNA of CON-1 had a G+C content of 70 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that CON-1 exhibited a maximum similarity (94.72%) with Deinococcus grandis. Based on the genotypic, phenotypic and chemotaxonomic characteristics, the bacterium CON-1 was identified as a new species of the genus Deinococcus, for which the name Deinococcus mumbaiensis sp. nov. is proposed. The type strain of D. mumbaiensis is CON-1 (MTCC 7297(T)=DSM 17424(T)).

Prevalence and characterization of Clostridium perfringens from spices in Argentina

Spices can present high microbial counts and Clostridium perfringens, Bacillus cereus, Salmonella and Shigella, among others have been isolated from spices. C. perfringens is an important pathogen agent causing, among other diseases, enteritis in humans caused by C. perfringens enterotoxin (CPE) which causes human food poisoning and enterotoxemia in domestic animals. The aims of the present work were (i) to establish the hygienic sanitary quality of some spices in San Luis, Argentina; (ii) to determine the presence of C. perfringens in these spices by means of the most probable number (MPN) and count on plate methods; (iii) to characterize the enterotoxigenic strains of C. perfringens by PCR and immunological methods such as reverse passive latex agglutination (RPLA) and (iv) to type by PCR C. perfringens strains isolated. A total of 115 samples of spices, 67 of which were purchased in local retail stores and 48 domestically collected were analysed. Total aerobe counts on tryptone glucose yeast extract agar medium of the 115 samples were between <10 and 10 6 CFU/g. The colifecal counts using Mac Conkey broth of the 115 samples were <4–10 3 CFU/g, with 28 samples (24.34%) exceeding the limit established by the Spanish Alimentary Code (10 CFU/g) while 2 samples (1.73%) had a sulfite reducing anaerobe load above standard limits. A total of 14 C. perfringens strains (12.17%) were isolated and characterized from 115 samples by the standard biochemical tests. Four of which (28.60%) turned out to be enterotoxigenic by PCR and RPLA. In order to type C. perfringens strains based on their main toxins, the 14 strains were analysed by PCR. All strains belonged to type A. All RPLA positive strains were cpe + by PCR. The percentage of enterotoxigenic strains was more elevated that those reported in other studies for this type of sample. These results indicate that sanitary conditions in different production stages of species must be improved to reduce health hazards. The high percentage (24.34%) of samples with colifecal values above standard limits is an indication of deficient sanitary conditions. These results suggest the need to provide legislation on the sanitary and hygienic quality of spices in our country.

Evaluation of media for enumerating heat-stressed, benzoate-resistant Zygosaccharomyces bailii

A study was undertaken to determine the efficacy of yeast malt extract agar (YMA), acidified YMA (YMAA), acidified tryptone glucose yeast extract agar (TGYA) and Zygosaccharomyces bailii agar (ZBA) for enumerating two strains of Z. bailii (FRR 2227 and FRR 3680) grown and heated in blueberry syrup containing 0, 300 and 600 μg ml sodium benzoate. Cells were heated at 50, 51 or 52 °C for 0, 15, 30 or 45 min before spread plating diluted samples on enumeration media and incubating at 30 °C for 5 days. Strain FRR 3680 exhibited higher heat resistance than did strain FRR 2227. Regardless of the sodium benzoate concentration in growth and heating media, or the temperature and time of heating, non-selective YMA supported recovery of the highest number of viable cells, followed by TGYA for strain FRR 2227 and TGYA or ZBA for strain FRR 3680. YMAA supported the lowest recovery of heat-stressed cells. The concentration of sodium benzoate in the growth medium did not have a significant effect on tolerance of strain FRR 3680 to heat; however, tolerance of strain FRR 2227 to heat decreased when cells were grown in blueberry syrup containing increased concentrations of sodium benzoate. Regardless of the sodium benzoate concentration in the growth medium, both strains exhibited increased sensitivity when heated in blueberry syrup containing increased concentrations of sodium benzoate. Overall, TGYA was judged best among selective media for enumerating Z. bailii because of its ability to support colony development by heat-stressed cells and because of the ease of counting and differentiating colonies.

Improved selective medium for enumeration of benzoate-resistant, heat-stressed Zygosaccharomyces bailii

The efficacy of acidified (0.5% acetic acid) tryptone glucose yeast extract agar (TGYA), acidified malt extract agar (MEAA) and Zygosaccharomyces bailiiselective medium (ZBA) to recover seven strains of Z. bailiifrom a mixture of mayonnaise and water (1:1, w:v, mayonnaise:water) heated at 50 and 51°C for up to 45 min was determined. Cells not subjected to heat treatment were recovered in equal numbers on TGYA, ZBA and non-selective yeast malt agar (YMA). Recovery on MEAA was inferior. YMA supported the highest recovery of unheated and heat stressed cells, followed by TGYA and ZBA. Lowest recovery of heated cells was observed on MEAA. The ability of heated Z. bailiicells to recover on acidified (0.5% acetic acid) tryptone fructose yeast extract agar (TFYA), acidified (0.3% acetic acid) tryptone glucose yeast extract agar (TGYAC), acidified (0.5% acetic acid) tryptone yeast extract agar containing sodium benzoate (300 μg ml −1) (TGYACB), acidified (0.3% acetic acid) fructose yeast extract agar (TFYAC) and ZBA containing 0.3% acetic acid (ZBAC) compared with recovery on YMA was investigated. Regardless of the strain, performance of media for recovering heated-stressed cells of Z. bailiiwas YMA=TGYAC=TFYAC>TFYA>TGYA>TGYACB>ZBAC>ZBA. Overall, TGYAC and TFYAC were judged best among selective media for recovering unheated and heat-stressed Z. bailii. However, the ability of these media to inhibit colony formation by several other yeasts, not particularly resistant to acids, is less than adequate. A medium that supports the growth of all healthy and heat-injured cells of Z. bailiibut not other yeast species has yet to be perfected.

Performance of Selective Media for Enumerating Zygosaccharomyces bailii in Acidic Foods and Beverages

A study was undertaken to evaluate the performance of yeast-malt extract agar (YMA) (control medium) and three selective media, acidified YMA (AYMA), acidified tryptone-glucose-yeast extract agar (TGYA), and Zygosaccharomyces bailii selective agar (ZBA), for detecting and enumerating nine strains of Z. bailii grown in six commercial food products with aw and pH values ranging from 0.82 to 0.99 and 2.99 to 6.47, respectively. These media were also evaluated for their suitability for enumerating two strains of Z. bailii grown in blueberry syrup containing 0, 300, and 600 μg of sodium benzoate ml−1 and subsequently stored at 1 and −19°C. The nonselective enumeration medium (YMA) supported significantly (P ≤ 0.05) higher recovery of all strains of Z. bailii from the six food products compared to the three selective media; TGYA was the best selective medium, followed by ZBA. The performance of the selective media was dependent on the strain of Z. bailii and the food type. Recovery of cells of Z. bailii from blueberry syrup before storage or after storage at 1 or −19°C was equivalent on YMA, TGYA, and ZBA but inferior on AYMA, regardless of the benzoate concentration in the syrup in which the cells had grown. Cells in blueberry syrup held at −19°C exhibited a higher sensitivity to the acidic environment imposed by selective media compared to cells held at 1°C. Sensitivity to selective media was more apparent in cells grown in syrup containing no sodium benzoate compared to cells grown in syrup containing 300 or 600 μg of sodium benzoate ml−1. It is recommended that TGYA be used for enumerating Z. bailii in acidic foods with reduced aw, regardless of the presence of sodium benzoate in these foods or the reduced temperature at which they are held before being analyzed.

Media for preservative resistant yeasts: a collaborative study

An international collaborative study was carried out to determine the most effective medium for selective isolation and enumeration of preservative resistant yeasts. Such a medium should prevent the growth of other yeasts such as Saccharomyces cerevisiae that are tolerant to lower levels of commonly used food preservatives, and sensitive yeasts such as Rhodotomla species. The study compared two non-selective media that are in common use for cultivation of yeasts from foods, Malt Extract agar (MEA) and Tryptone Glucose Yeast extract agar (TGY) with media made selective for preservative resistant yeasts by the addition of 0.5% acetic acid to these two basal media (MEAA and TGYA). A fifth medium, Zygosaccharomyces bailii medium (ZBM) was also included in the study. These media were compared for their efficacy in selective isolation and enumeration of the preservative resistant yeasts Zygosaccharomyces bailii, Schizosaccharomyces pombe and Pichia membranaefaciens. MEA and TGY without acetic acid were used as control, non-selective media, and Rhodotorula glutinis was the preservative sensitive control culture. Seven laboratories in six countries took part in the study. Of the non-selective media, TGY generally gave the highest counts, and TGY amended with 0.5% acetic acid (TGYA) was the best medium for recovery of all three preservative-resistant yeasts. ZBM was found to be selective for Z. bailii, but counts of this yeast on ZBM were significantly lower than on TGYA. R. glutinis did not grow on any of the selective media.

A pigment-producing spoilage bacterium responsible for violet discoloration of refrigerated market milk and cream.

A psychrophilic strain of bacteria identified as Chromobacterium lividum was established as the causative agent of an outbreak of violet discoloration in refrigerated, pasteurized retail milk and cream. The organism was rod-shaped, gram-negative, and produced viscid colonies with abundant violet pigment on Tryptone glucose yeast extract agar. Growth was abundant at 4 C but none occurred at 37 C. Growth in milk was characterized by a dark violet ring at the surface after a few days, and the deep violet color gradually extended through the product in older cultures. Some proteolysis occurred. The pigment appeared to be similar to that of other known species of Chromobacterium and assisted in identification of the genus of the causative organism. The isolated strain of C. lividum was destroyed by exposure to 56 C for 5 min which suggested postpasteurization contamination as the source of the spoilage organism in commercial milk and cream.

A Pigment-producing Spoilage Bacterium Responsible for Violet Discoloration of Refrigerated Market Milk and Cream1

A psychrophilic strain of bacteria identified as Chromobacterium lividum was established as the causative agent of an outbreak of violet discoloration in refrigerated, pasteurized retail milk and cream. The organism was rod-shaped, gram-negative, and produced viscid colonies with abundant violet pigment on Tryptone glucose yeast extract agar. Growth was abundant at 4 C but none occurred at 37 C. Growth in milk was characterized by a dark violet ring at the surface after a few days, and the deep violet color gradually extended through the product in older cultures. Some proteolysis occurred. The pigment appeared to be similar to that of other known species of Chromobacterium and assisted in identification of the genus of the causative organism. The isolated strain of C. lividum was destroyed by exposure to 56 C for 5 min which suggested postpasteurization contamination as the source of the spoilage organism in commercial milk and cream.