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Terrones-Fernandez I, Casino P, López A, Peiró S, Ríos S, Nardi-Ricart A, García-Montoya E, Asensio D, Marqués AM, Castilla R, Gamez-Montero PJ, Piqué N. Improvement of the Pour Plate Method by Separate Sterilization of Agar and Other Medium Components and Reduction of the Agar Concentration. Microbiol Spectr 2023; 11:e0316122. [PMID: 36625633 PMCID: PMC9927588 DOI: 10.1128/spectrum.03161-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 12/12/2022] [Indexed: 01/11/2023] Open
Abstract
Although the pour plate method is widely employed in microbiological quality control, it has certain drawbacks, including having to melt the culture medium before seeding. In this study, the preparation of the culture medium was modified by using a lower concentration of agar (10 g/L), which was separated from the nutrients during sterilization. The new protocol was assessed in media frequently used in microbiological quality control of food, cosmetics, and pharmaceutical products, with tryptic soy agar (TSA), Sabouraud 4% dextrose agar (SDA), and violet red bile glucose agar (VRBG). In comparison with the conventionally produced media, the modifications significantly improved the growth of Saccharomyces cerevisiae in SDA, Staphylococcus aureus, Salmonella enterica subsp. enterica serovar Typhimurium, and Candida albicans in TSA and Escherichia coli ATCC 8739 and ATCC 25922 and S. Typhimurium in VRBG. The modified VRBG was also more selective for Pseudomonas aeruginosa. Regarding physicochemical properties, a significantly lower pH was observed in TSA and VRBG and lower strength values in TSA. Sterilizing agar separately from the other components of the medium and reducing the agar concentration to 10 g/L can improve microorganism growth and enhance the selectivity of differential media in the pour plate method. These modifications could facilitate the automation of this culture technique. IMPORTANCE In the era of rapid microbiological methods, there is a need to improve long-established culture techniques. Drawbacks of the pour plate method include having to melt each medium separately before seeding. For this technique, we demonstrate that separating the agar from the other components of commonly used media during sterilization and reducing the agar concentration to 10 g/L can enhance microbial growth. The new protocol could have advantages in routine laboratory practice because less agar is required and the same molten agar suspension can be used to prepare different media. Moreover, these modifications could facilitate the automation of the pour plate method.
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Affiliation(s)
- I. Terrones-Fernandez
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD), Barcelona, Catalonia, Spain
- CATMech. Department of Fluid Mechanics, Universitat Politecnica de Catalunya, Terrassa, Catalonia, Spain
| | - P. Casino
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD), Barcelona, Catalonia, Spain
| | - A. López
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD), Barcelona, Catalonia, Spain
| | - S. Peiró
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD), Barcelona, Catalonia, Spain
| | - S. Ríos
- Department of Genetics, Microbiology and Statistics, Biology Faculty, Universitat de Barcelona, Barcelona, Catalonia, Spain
- Department of Biochemistry and Biotechnology, Human Nutrition Unit, Universitat Rovira i Virgili, Reus, Catalonia, Spain
| | - A. Nardi-Ricart
- Department of Pharmacy and Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona, Catalonia, Spain
| | - E. García-Montoya
- Department of Pharmacy and Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona, Catalonia, Spain
- Pharmacotherapy, Pharmacogenetics and Pharmaceutical Technology Research Group, Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Catalonia, Spain
| | - D. Asensio
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD), Barcelona, Catalonia, Spain
| | - A. M. Marqués
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
| | - R. Castilla
- CATMech. Department of Fluid Mechanics, Universitat Politecnica de Catalunya, Terrassa, Catalonia, Spain
| | - P. J. Gamez-Montero
- CATMech. Department of Fluid Mechanics, Universitat Politecnica de Catalunya, Terrassa, Catalonia, Spain
| | - N. Piqué
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
- Institut de Recerca en Nutrició i Seguretat Alimentària de la UB (INSA-UB), Universitat de Barcelona, Barcelona, Catalonia, Spain
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Torrico M, Casino P, López A, Peiró S, Ríos M, Ríos S, Montes MJ, Guillén C, Nardi-Ricart A, García-Montoya E, Asensio D, Marqués AM, Piqué N. Improvement of Mueller-Kauffman Tetrathionate-Novobiocin (MKTTn) enrichment medium for the detection of Salmonella enterica by the addition of ex situ-generated tetrathionate. J Microbiol Methods 2022; 199:106524. [PMID: 35732231 DOI: 10.1016/j.mimet.2022.106524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/15/2022] [Accepted: 06/15/2022] [Indexed: 12/27/2022]
Abstract
The detection of Salmonella in food is based on the use of a selective enrichment broth such as Muller-Kauffman Tetrathionate-Novobiocin (MKTTn), in which tetrathionate plays a key role by providing Salmonella with a growth advantage. As sodium tetrathionate is unstable, it is generated in situ by the addition of iodine (Lugol's solution) before seeding. This step is cumbersome as the solution is easily spilled, compromising the performance of the medium and hindering the work of technicians. The aim of this study was to optimize MKTTn broth by generating tetrathionate ex situ through an external reaction between iodine and thiosulphate followed by lyophilization. Quality control procedures were performed to compare the modified and original media, testing pure productivity (enrichment with 50-120 CFU of Salmonella Thyphimurim ATCC 14028 and Salmonella Enteritidis ATCC 13076 and plating on Xylose Lysine Deoxycholate agar, XLD), mixed productivity (50-120 CFU of Salmonella strains and Pseudomonas aeruginosa and Escherichia coli at ≥104 CFU and XLD plating) and selectivity (≥104 CFU of P. aeruginosa and Enterococcus faecalis and plating on Tryptone Casein Soy agar, TSA). The modified MKTTn medium (S/L) performed comparably with the original medium in terms of growth of both Salmonella strains (>300 colonies in XLD), alone or with P. aeruginosa and E. coli. Quantitative assays showed no statistically significant differences in the number of colonies grown on XLD after 10-5 dilution (p = 0.7015 with S. Thyphimurim ATCC 14028 and p = 0.2387 with S. enteritidis ATCC 13076; ANOVA test). MKTTn medium (S/L) was also selective against E. coli (≤100 colonies) and E. faecalis (<10 colonies). These results suggest that adding tetrathionate as a lyophilisate (S/L) is a feasible alternative to the use of Lugol's solution for the preparation of MKTTn enrichment broth and does not affect the properties of the medium.
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Affiliation(s)
- M Torrico
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD). Josep Tura, 9H, polígon industrial Mas d'en Cisa, 08181 Sentmenat, Barcelona, Catalonia, Spain
| | - P Casino
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD). Josep Tura, 9H, polígon industrial Mas d'en Cisa, 08181 Sentmenat, Barcelona, Catalonia, Spain
| | - A López
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD). Josep Tura, 9H, polígon industrial Mas d'en Cisa, 08181 Sentmenat, Barcelona, Catalonia, Spain
| | - S Peiró
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD). Josep Tura, 9H, polígon industrial Mas d'en Cisa, 08181 Sentmenat, Barcelona, Catalonia, Spain; Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
| | - M Ríos
- Department of Genetics, Microbiology and Statistics, Biology Faculty, Universitat de Barcelona, Barcelona, Catalonia, Spain
| | - S Ríos
- Department of Genetics, Microbiology and Statistics, Biology Faculty, Universitat de Barcelona, Barcelona, Catalonia, Spain; Department of Biochemistry and Biotechnology, Human Nutrition Unit, Universitat Rovira i Virgili, Reus, Catalonia, Spain
| | - M J Montes
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
| | - C Guillén
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
| | - A Nardi-Ricart
- Department of Pharmacy and Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona, Catalonia, Spain
| | - E García-Montoya
- Department of Pharmacy and Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona, Catalonia, Spain; Pharmacotherapy, Pharmacogenetics and Pharmaceutical Technology research group, Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Catalonia, Spain
| | - D Asensio
- Department of Quality Control, Reactivos para Diagnóstico, S.L. (RPD). Josep Tura, 9H, polígon industrial Mas d'en Cisa, 08181 Sentmenat, Barcelona, Catalonia, Spain
| | - A M Marqués
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain
| | - N Piqué
- Microbiology Section, Department of Biology, Healthcare and Environment, Faculty of Pharmacy and Food Sciences, Universitat de Barcelona (UB), Barcelona, Catalonia, Spain; Institut de Recerca en Nutrició i Seguretat Alimentària de la UB (INSA-UB), Universitat de Barcelona, Barcelona, Catalonia, Spain.
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