Evaluation of Petrifilm™ method for enumerating aerobic bacteria in Crottin goat's cheese / Evaluación de PetrifilmTM para la enumeración de bacterias aerobias en queso de cabra Crottin

The PetrifilmTM Aerobic Count Plate (ACP) developed by 3M laboratories, is a ready-to-use culture medium system, useful for the enumeration of aerobic bacteria in food. PetrifilmTMwas compared with a standard method in several different food products with satisfactory results. However, many studies showed that bacterial counts in PetrifilmTM were significantly lower than those obtained with conventional methods in fermented food. The purpose of this study was to compare the PetrifilmTM method for enumerating aerobic bacteria with a conventional method (PCA) in Crottin goat's cheese. Thirty samples were used for the colony count. The mean count and standard deviation were 7.18 ± 1.17 log CFU g-1 on PCA and 7.11 ± 1.05 log CFU g-1 on PetrifilmTM. Analysis of variance revealed no significant differences between both methods (t = 1.33, P = 0.193). The Pearson correlation coefficient (0.971, P=0.0001) indicated a strong linear relationship between the PetrifilmTM and the standard method. The results showed that PetrifilmTM is suitable and a convenient alternative to this standard method for the enumeration of aerobic flora in goat soft cheese.

PetrifilmTM Aerobic Count Plate (ACP) desarrollado por 3M es un sistema listo para usar, empleado para el recuento de bacterias aerobias en alimentos. PetrifilmTMfue comparado con los métodos estándar en diferentes productos alimenticios con resultados satisfactorios. Sin embargo, en alimentos fermentados, algunos estudios mostraron que el recuento de bacterias aerobias en PetrifilmTM fue significativamente menor que aquellos obtenidos con los métodos convencionales (PCA). El propósito de este estudio fue comparar el método PetrifilmTM para el recuento de bacterias aerobias con un método convencional en queso de cabra Crottin. Se usaron 30 muestras para el recuento de colonias. Las medias y desviaciones estándar fueron 7,18 ± 1,17 log UFC g-1 en PCA y 7,11 ± 1,05 log UFC g-1 en PetrifilmTM. El análisis de varianza mostró que no había diferencia significativa entre ambos métodos (t = 1,33, P = 0,193). El coeficiente de correlación fue 0,971 ( P = 0,0001) indicando una fuerte correlación lineal. Los resultados muestran a PetrifilmTM como un método apropiado y una alternativa conveniente a los métodos estándar para la cuantificación de flora aeróbica en queso blando de cabra.

Behavior of Yersinia enterocolitica and Salmonella typhimurium in Crottin goat's cheese.

In order to evaluate the behavior of Yersinia enterocolitica and Salmonella typhimurium in Crottin goat's cheese, inoculated products stored at 5, 15 and 25 degrees C were analysed together with chemical and microbiological characteristics of the cheese. In general, low counts of microorganisms were detected. None of the samples showed the presence of Escherichia coli, Salmonella spp. or Y. enterocolitica. In the inoculation tests, Y. enterocolitica and S. typhimurium were inhibited during storage; nevertheless, these bacteria survived for extensive periods. The counts at the end of the experiments at 5 and 15 degrees C were high, indicating that contamination with high bacterial numbers represents a potential health hazard. The primary mathematical models used to analyse the behavior of Y. enterocolitica and S. typhimurium were the Vitalistic, Gompertz's empirical and Churchill's model. The mean square error was calculated for the three models in order to evaluate the goodness-of-fit of each one. For Y. enterocolitica, the Vitalistic model was the best at the three temperatures. For S. typhimurium, there was no significant difference between the three models at 5 and 15 degrees C; the Churchill model was clearly the best at 25 degrees C. These results confirm that, in order to predict the risk of transmission of pathogenic microorganisms in foods using mathematical models, it is essential to analyse their behavior in specific foods.

Evaluation of Petrifilm method for enumerating aerobic bacteria in Crottin goat cheese.

The Petrifilm Aerobic Count Plate (ACP) developed by 3M laboratories, is a ready-to-use culture medium system, useful for the enumeration of aerobic bacteria in food. Petrifilm was compared with a standard method in several different food products with satisfactory results. However, many studies showed that bacterial counts in Petrifilm were significantly lower than those obtained with conventional methods in fermented food. The purpose of this study was to compare the Petrifilm method for enumerating aerobic bacteria with a conventional method (PCA) in Crottin goat's cheese. Thirty samples were used for the colony count. The mean count and standard deviation were 7.18 +/- 1.17 log CFU g(-1) on PCA and 7.11 +/- 1.05 log CFU g(-1) on Petrifilm. Analysis of variance revealed no significant differences between both methods (t = 1.33, P = 0.193). The Pearson correlation coefficient (0.971, P = 0.0001) indicated a strong linear relationship between the Petrifilm and the standard method. The results showed that Petrifilm is suitable and a convenient alternative to this standard method for the enumeration of aerobic flora in goat soft cheese.

Evaluation of Petrifilm method for enumerating aerobic bacteria in Crottin goat cheese.

The Petrifilm Aerobic Count Plate (ACP) developed by 3M laboratories, is a ready-to-use culture medium system, useful for the enumeration of aerobic bacteria in food. Petrifilm was compared with a standard method in several different food products with satisfactory results. However, many studies showed that bacterial counts in Petrifilm were significantly lower than those obtained with conventional methods in fermented food. The purpose of this study was to compare the Petrifilm method for enumerating aerobic bacteria with a conventional method (PCA) in Crottin goats cheese. Thirty samples were used for the colony count. The mean count and standard deviation were 7.18 +/- 1.17 log CFU g(-1) on PCA and 7.11 +/- 1.05 log CFU g(-1) on Petrifilm. Analysis of variance revealed no significant differences between both methods (t = 1.33, P = 0.193). The Pearson correlation coefficient (0.971, P = 0.0001) indicated a strong linear relationship between the Petrifilm and the standard method. The results showed that Petrifilm is suitable and a convenient alternative to this standard method for the enumeration of aerobic flora in goat soft cheese.

[Indicators of contamination and their relation to the presence of Escherichia coli in ready-to-eat foods]. / Indicadores de contaminación y su relación con la presencia de Escherichia coli en alimentos listos para consumo.

The relationship between indicator microorganism counts and the presence of Escherichia coli was determined in ready-to-eat food in food stores. Aerobic counts (CA), total coliforms (CT) and molds and yeast (ML) were registered in each food sample as well as the presence of E. coli in food, surface and hand samples. There was a high percentage of E. coli in cooked food (46% in 1 g), in raw food (31% in 0.1 g), in surfaces (37%) and in hands (21%). Significant correlations were found in CT, CA and ML in cooked food (P = 0.0001); no significant correlations were found in raw food (P > 0.01). The CT count in cooked food with E. coli was significantly higher than CT count in cooked food without E. coli (median 5.00 cfu/g and 1.54 cfu/g, respectively). Meanwhile, no significant differences were found in raw food.

Indicadores de contaminación y su relación con la presencia de Escherichia coli en alimentos listos para consumo / Indicator microorganisms and their relationship to the presence of Escherichia coli in ready-to-eat food

Se determinó la relación entre indicadores de contaminación y la presencia de Escherichia coli en alimentos listos para consumo en locales de venta directa al público, en Córdoba, Argentina. Se tomaron 60 muestras de alimentos, 16 de superficies y 14 de manos. Se determinaron bacterias mesófilas aerobias (CA), coliformes totales (CT), mohos y levaduras (ML) en alimentos y la presencia de E.coli en alimentos, superficies y manos. Se detecto E.coli en el 46 por ciento de los alimentos cocidos en 1 g de muestra y en el 31 por ciento de los alimentos crudos en 0,1 g de muestra. También se encontró E.coli en el 37 por ciento de las muestras de superficies y en el 21 por ciento de las provenientes de manos. Se encontraron correlaciones significativas al comparar de a pares CT, CA y ML en los alimentos cocidos (P=0,0001); en los crudos no se observaron correlaciones (P>0,01). El nivel de CT en alimentos cocidos que presentaban E.coli resultó significativamente más alto que el nivel de CT en los alimentos cocidos sin E.coli (mediana 5,00 ufc/g y 1,54 ufc/g, respectivamente). Los alimentos crudos con o sin presencia de E.coli no mostraron diferencias significativas en los niveles de CT.

Indicadores de contaminación y su relación con la presencia de Escherichia coli en alimentos listos para consumo / Indicator microorganisms and their relationship to the presence of Escherichia coli in ready-to-eat food

Se determinó la relación entre indicadores de contaminación y la presencia de Escherichia coli en alimentos listos para consumo en locales de venta directa al público, en Córdoba, Argentina. Se tomaron 60 muestras de alimentos, 16 de superficies y 14 de manos. Se determinaron bacterias mesófilas aerobias (CA), coliformes totales (CT), mohos y levaduras (ML) en alimentos y la presencia de E.coli en alimentos, superficies y manos. Se detecto E.coli en el 46 por ciento de los alimentos cocidos en 1 g de muestra y en el 31 por ciento de los alimentos crudos en 0,1 g de muestra. También se encontró E.coli en el 37 por ciento de las muestras de superficies y en el 21 por ciento de las provenientes de manos. Se encontraron correlaciones significativas al comparar de a pares CT, CA y ML en los alimentos cocidos (P=0,0001); en los crudos no se observaron correlaciones (P>0,01). El nivel de CT en alimentos cocidos que presentaban E.coli resultó significativamente más alto que el nivel de CT en los alimentos cocidos sin E.coli (mediana 5,00 ufc/g y 1,54 ufc/g, respectivamente). Los alimentos crudos con o sin presencia de E.coli no mostraron diferencias significativas en los niveles de CT. (AU)

Indicadores de contaminación y su relación con la presencia de Escherichia coli en alimentos listos para consumo. / [Indicators of contamination and their relation to the presence of Escherichia coli in ready-to-eat foods]

The relationship between indicator microorganism counts and the presence of Escherichia coli was determined in ready-to-eat food in food stores. Aerobic counts (CA), total coliforms (CT) and molds and yeast (ML) were registered in each food sample as well as the presence of E. coli in food, surface and hand samples. There was a high percentage of E. coli in cooked food (46

in 1 g), in raw food (31

in 0.1 g), in surfaces (37

) and in hands (21

). Significant correlations were found in CT, CA and ML in cooked food (P = 0.0001); no significant correlations were found in raw food (P > 0.01). The CT count in cooked food with E. coli was significantly higher than CT count in cooked food without E. coli (median 5.00 cfu/g and 1.54 cfu/g, respectively). Meanwhile, no significant differences were found in raw food.

Evaluation of two media and different plating techniques for enumeration of thermotolerant coliforms in river water.

Testing for evidence of faecal contamination in river water has been traditionally accomplished by enumeration of thermotolerant coliform bacteria. In this work, deoxycholate lactose and m-Endo Agar LES media were evaluated using different techniques. The colony count methods were pour plate technique on Deoxycholate Agar (DCL pour plate), spread plating on m-Endo Agar LES (ELS spread), and membrane filtration on m-Endo Agar LES (ELF filtration). Typical thermotolerant coliform colonies were analysed by conventional biochemical tests. The three matched pairs showed statistically significant differences (P < 0.05) by the Wilcoxon signed rank test. One hundred and twenty three isolates obtained on m-Endo Agar LES (65%) were confirmed as E. coli. Likewise, one hundred and twenty isolates obtained on Deoxycholate Agar (71%) were confirmed as E. coli. The results of this study showed that the matched DCL-ELF presented the smaller statistically significant difference (P = 0.042) so, DCL could be used as alternative to ELF.

Bacteriological stability and growth kinetics of Pseudomonas aeruginosa in bottled water.

Bacteriological stability of water bottled in plastic containers and the growth kinetics of Pseudomonas aeruginosa were determined. Samples of water from the source, water to be bottled, finished product and sterile water bottled in non-returnable and returnable containers were analysed for aerobic colony count, coliforms, Escherichia coli and Ps. aeruginosa. The samples were examined for up to 30 d storage. Aerobic colony count increased 6 d after bottling to between 10(3) and 10(5) cfu ml-1. Coliforms and E. coli were not found in any sample. Pseudomonas aeruginosa was isolated from commercial products bottled in returnable plastic containers due to the contamination from the containers and the subsequent multiplication utilizing trace nutrients. The predominant Ps. aeruginosa strains showed high doubling time (26 h) due to competition from the accompanying flora. In the absence of competing flora Ps. aeruginosa reached higher density than the maximum reached by aerobic flora, with a doubling time of only 3.6 h. After 30 d storage, this micro-organism was predominant.