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.

Genetic relationships among Aedes aegypti (Diptera: Culicidae) populations from Argentina using random amplified polymorphic DNA polymerase chain reaction markers.

Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) polymorphism was analyzed in five Aedes aegypti (L.) populations from Argentina and one from Puerto Rico to estimate levels of intraspecific polymorphism and genetic relatedness. Allele frequencies were estimated assuming that RAPD products segregate as dominants and that genotype frequencies at those loci are in Hardy-Weinberg equilibrium. Mean expected heterozygosity (He) was 0.350; F(ST) values were significant at all loci except one, supporting the usefulness of the fragments used here to discriminate among populations. Rogers' genetic similarity between samples ranged from 0.806 to 0.621. The population from Puerto Rico was the most different from the Argentina populations. Considering that Ae. aegypti eggs, larvae, and pupae can be transported easily, relationships among the Argentinian populations may reflect the routes and intensity of commercial transit.

Allozymic polymorphism in Aedes aegypti populations from Argentina.

In Argentina, reinfestation with Aedes aegypti was registered in 1986. At present, the mosquito is well established in 10 provinces, from Buenos Aires up to the country's northern frontiers. This paper presents estimates of genetic variability in Ae. aegypti populations from central Argentina and determinations of genetic distances among them. We analyzed allozymic frequencies at 11 loci in samples from 3 localities. The proportion of polymorphic loci varied between 27.3 and 63.6. Expected mean heterozygosity ranged from 0.090 to 0.161 and Rogers' similarity among samples ranged between 0.909 and 0.958. The lack of relationship between genetic and geographic distances is in agreement with a recent colonization of the studied area. The mean Wright's coefficient FST value (0.065) indicates low levels of genetic differentiation among populations from different localities. Given the recent reinfestation with this mosquito in Argentina, the high levels of polymorphism found could indicate multiple introductions of representative samples from genetically different subpopulations.

Genetic structure of Aedes albifasciatus (Diptera: Culicidae) populations in central Argentina determined by random amplified polymorphic DNA-polymerase chain reaction markers.

The floodwater mosquito, Aedes albifasciatus (Macquart), is the main vector of western equine encephalomyelitis virus in Argentina. Previous studies on the genetic structure of this species using allozymes showed low levels of polymorphism, absence of subpopulations at distinct habitats, and moderate differentiation among localities separated up to 500 km. To examine gene flow using other genetic methods, we analyzed random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) polymorphism in 28 presumptive loci of Ae. albifasciatus from 6 populations in central Argentina. Allele frequencies were estimated assuming that RAPD products segregate as dominants and that genotype frequencies at those loci are in Hardy-Weinberg equilibrium. Expected heterozygosity ranged between 0.19 and 0.31, approximately 3 times the value obtained on the basis of the 16 allozymic loci studied previously. Four of the populations formed a single panmictic unit. Allele frequencies in populations occupying different phytogeographic regions gave significant FST values at 5 loci. Effective migration rates among populations estimated from FST ranged from 2.3 to 9.0. The results support the existence of a north-south cline.

Temporal variation of allozyme frequencies in Aedes albifasciatus (Diptera: Culicidae) from Argentina.

Aedes albifasciatus is a floodwater mosquito widely distributed in Argentina. It is important from economic and medical points of view. A 4-year survey of seasonal variation in allele frequencies in a population of this species was undertaken to determine possible changes in the genetic structure and their correlation with environmental conditions. Significant temporal variation was detected at most of the loci, but it did not follow a cyclic or seasonal pattern. Multivariate analysis of principal components showed a remarkable homogeneity of samples collected from December 1993 to April 1995 and a clear differentiation of the November 1991, March 1992, and November 1993 samples. This variation could be correlated with the magnitude of rainfall occurring in the area. Passive transport of larvae by water streams and river freshets produced by floods would have mixed larvae from breeding sites with different allele frequencies, causing the genetic differentiation observed.

Gene flow in Aedes albifasciatus (Diptera:Culicidae) from central Argentina.

To estimate gene flow among populations of the floodwater mosquito Aedes albifasciatus, allozymic frequencies were analyzed at 16 loci in samples from 6 localities in central Argentina. Expected mean heterozygosity ranged from 0.057 to 0.137. FST was significant for 5 of 11 polymorphic loci; mean value was 0.024, which gave an Nm of 50.96. Levels of genetic identity among samples were high (IN between 0.9815 and 0.9988) even between populations 500 km apart. However, there was a significant correlation between genetic and geographic distance, which indicated that although the 6 populations were at approximate equilibrium because of gene flow, this was restricted by distance. The distribution of allele frequencies possibly reflected the present status of a single large population occupying this region in the past. When geological change separated breeding areas, a moderate level of gene flow may have resulted in the current genetic structure of the populations.

Genetic structure of Aedes albifasciatus (Diptera:Culicidae) from a marsh ecosystem in Córdoba, Argentina.

Allozymic variability was analyzed for 8 samples of the floodwater mosquito Aedes albifasciatus (Macquart) obtained in October and November 1993 from marsh and pasture habitats along the Mar Chiquita ecosystem in central Argentina. Expected mean heterozygosity among 17 loci was low. Fls values were negative for all polymorphic loci, and mean FST values were low, indicating high levels of gene exchange and the absence of subpopulations within the 25-km-wide study area. Genetic homogeneity throughout the area suggests that outcrossing occurs frequently as a result of dispersal among sampled sites.