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An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium
Published on: July 22, 2011
Confirmation of presumptive Salmonella colonies contaminated with Proteus swarming using the polymerase chain
Rosalba Gutiérrez Rojo1, Edith Torres Chavolla
1Laboratorio de Microbiología Molecular, Unidad de Biotecnología, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco. rgutierrez@ciatej.net.mx
Abstract:
In Mexico, zero tolerance regulation is practiced regarding Salmonella in food products. the presence of which is verified by the procedure described in NOM 114-SSA-1994. During the period between August 2002 and March 2003, 245 food samples were tested using this procedure in the Central Laboratories of the Department of Health for the State of Jalisco (CEESLAB). Of these 245 samples, 35 showed presumptive colonies contaminated with Proteus swarm cells even after selective isolation. These swarm cells make Salmonella recovery and biochemical identification difficult due to the occurance of atypical biochemical profiles which generally correspond to that of Proteus. Out of the 35 samples contaminated with Proteus, 65 presumptive colonies were isolated. These colonies were analyzed using both normative microbiological method and Polymerase Chain Reaction (PCR). The PCR method detected two positive samples while normative microbiological method was not able to identify. In order to determine the extent of interference of Proteus swarming on the Salmonella-specific PCR band amplification, Salmonella ser. Typhimurium was grown in the presence of Proteus swarming. These results show that Proteus swarming did not interfere with Salmonella PCR-amplification, although the appearance of Sanlmonella was altered such that the black precipitate was no observed in the presence of Proteus swarming. Ours result indicate that the PCR method used in this study may be successfully applied to confirm presumptive Salmnonella colonies contaminated with Proteus swarming.
Insights
In Mexico, Polymerase Chain Reaction (PCR) successfully identified Salmonella in food samples contaminated with Proteus swarming. This method offers a reliable alternative to traditional techniques when Proteus interference is present.
Area of Science:
- Food Safety
- Microbiology
- Molecular Diagnostics
Background:
- Mexico enforces strict zero-tolerance regulations for Salmonella in food products.
- Traditional microbiological methods for Salmonella detection can be hindered by the presence of interfering bacteria like Proteus.
Purpose of the Study:
- To evaluate the effectiveness of Polymerase Chain Reaction (PCR) for detecting Salmonella in food samples contaminated with Proteus swarming.
- To compare PCR with the normative microbiological method (NOM 114-SSA-1994) in the presence of Proteus interference.
Main Methods:
- Analysis of 245 food samples using the NOM 114-SSA-1994 procedure.
- Isolation and analysis of presumptive Salmonella colonies, including those contaminated with Proteus.
- Application of both normative microbiological methods and PCR for identification.
- Experimental verification of Proteus swarming interference on Salmonella PCR amplification.
Main Results:
- 35 out of 245 samples showed presumptive colonies contaminated with Proteus.
- The normative microbiological method failed to identify Salmonella in Proteus-contaminated samples.
- PCR successfully detected Salmonella in two samples where the microbiological method failed.
- Proteus swarming did not interfere with Salmonella PCR amplification, though it altered the visual appearance of the Salmonella colonies.
Conclusions:
- The PCR method is a viable and effective tool for confirming presumptive Salmonella colonies, even when contaminated with Proteus swarming.
- PCR offers an advantage over traditional methods in challenging food safety scenarios involving bacterial interference.
