Salmonella and the food industry ‐ methods for isolation, identification and enumeration

Rapid estimation of Salmonella enterica contamination level in ground beef - Application of the time-to-positivity method using a combination of molecular detection and direct plating

Little progress has been made in decreasing the incidence rate of salmonellosis in the US over the past decade. Mitigating the contribution of contaminated raw meat to the salmonellosis incidence rate requires rapid methods for quantifying Salmonella, so that highly contaminated products can be removed before entering the food chain. Here we evaluated the use of Time-to-Positivity (TTP) as a rapid, semi-quantitative approach for estimating Salmonella contamination levels in ground beef. Growth rates of 14 Salmonella strains (inoculated at log 1 to -2 CFU/g) were characterized in lean ground beef mTSB enrichments and time-to-detection was determined using culture and molecular detection methods. Enrichments were sampled at five timepoints and results were used to construct a prediction model of estimated contamination level by TTP (superscript indicates time in hours) defined as TTP⁴: ≥5 CFU/g; TTP⁶: ≤5, ≥1 CFU/g; TTP⁸: ≤1, ≥0.01 CFU/g; with samples negative at 8 h estimated ≤0.01 CFU/g. Model performance measures showed high sensitivity (100%) and specificity (83% and 93% for two detection methods) for samples with a TTP⁴, with false negative rates of 0%.

Atividade de desinfetantes frente a sorotipos de Salmonella isolados de granjas avícolas

RESUMO O objetivo com este trabalho foi avaliar in vitro a eficácia de desinfetantes comumente utilizados e biodegradáveis na sanitização de aviários frente a sorotipos de Salmonella spp. isolados de granjas de aves no Estado do Paraná, Brasil.Os experimentos foram realizados utilizando o tempo de contato de 20 minutos e os desinfetantes testados emtrês concentrações:a recomendada pelo fabricante,metade da concentração recomendada e o dobro da mesma,bem como na presença e ausência de matéria orgânica. Em geral, todos os desinfetantes foram capazes de causar a redução significativa nas contagens dos micro-organismos em relação ao grupo controle. Na ausência de matéria orgânica, os desinfetantes a base de ácidos orgânicos apresentaram os melhores resultados frente ao sorotipo S. Gallinarum biovar Gallinarum, e os desinfetantes a base de glutaraldeído e hipoclorito de sódio frente aos sorotipos S. Typhimurium e S. Intantis. Na presença de matéria orgânica, como comumente se encontra o ambiente avícola, pôde-se observar que todos os desinfetantes apresentaram sua eficácia diminuída, sendo o a base de ácidos orgânicos o que apresentou as menores contagens de unidades formadoras de colônias (UFC). O desinfetante a base de ácidos orgânicos mostrou-se uma potencial alternativa de uso na avicultura, pela eficácia no controle dos sorotipos de Salmonella isoladas de granjas avícolas.

ISOLAMENTO DE SALMONELLA: COMPARAÇÃO DAS ETAPAS DE PRÉ- ENRIQUECIMENTO E ENRIQUECIMENTO DIRETO DE AMOSTRAS DE FEZES ARMAZENADAS POR 24 E 96 HORAS

RESUMO Este trabalho foi desenvolvido para avaliar comparativamente o isolamento de Salmonella sorotipos Enteritidis (SE) e Typhimurium (STM) a partir do enriquecimento direto (ED) ou processamento com pré-enriquecimento (PE) de amostras de fezes de aves adultas, armazenadas em água peptonada tamponada a 1% (APT) por 24 ou 96h a 4º C. Utilizou-se os caldos de enriquecimento Rapapport-Vassiliadis novobiocina (RVN), tetrationato-novobiocina (TN) e selenitonovobiocina (SN) e os meios para plaqueamento ágar verde brilhante (VB), ágar de MacConkey (MC), ágar de Hektoen (HE), ágar Salmonella-Shigella (SS), ágar xilose lisina desoxicolato (XLD) e ágar xilose lisina tergitol 4 (XLT4). O procedimento bacteriológico incluiu as etapas de pré-enriquecimento, enriquecimento em caldo seletivo, plaqueamento, testes bioquímicos presuntivos e confirmação sorológica com utilização de soros polivalentes anti-antígenos somáticos e anti-antígenos flagelares de Salmonella. Não houve diferença estatisticamente significativa (p > 0,05) para as amostras armazenadas por 24h submetidas tanto ao PE quanto ao ED. Entretanto, em armazenagem por 96h o número de isolamentos nas amostras submetidas ao PE foi estatisticamente superior às submetidas ao ED (p < 0,05). Quanto aos caldos enriquecedores, não houve diferença estatística de número de isolamentos (p > 0,05) entre os caldos SN e TN, mas o caldo RVN mostrou-se estatisticamente superior aos demais (p < 0,05). Para os meios de plaqueamento, o XLD destacou-se por promover maior número de recuperações, embora sem significado estatístico (p > 0,05) para as amostras estocadas por 24h. Entre os dois sorotipos de Salmonella (SE e STM) não houve diferença estatística no número de recuperações (p > 0,05).

Comparison of two commercial preparations of buffered peptone water for the recovery and growth of Salmonella bacteria from foods

This study compared the performance of two commercial preparations of buffered peptone water. Performance was assessed in terms of ability to resuscitate and recover low numbers of stressed cells, buffering capacity, growth of Salmonella bacteria in pure culture and growth of Salmonella in food pre-enrichments. Although both the preparations of BPW had similar chemical compositions, differences in their recovery performance were found. Brand A recovered significantly higher numbers of heat-injured Salmonella (mean = 0.57 log10 cfu ml(-1) difference) in pure culture compared with brand B when dealing with very low inoculum levels. Although brand B had higher buffering capacity, the pH at the end of the pre-enrichment was found to be similar in both media, even in foods such as milk powder which showed the greatest decline in pH. Both brands were comparable in their ability to grow unstressed Salmonella from different food types. In unstressed cell studies, similar cell numbers were recovered at the end of a 24 h incubation period from both media, although brand B yielded a higher biomass. In the food study with unstressed cells, performance was related more to the food type and the likely association between this and the level and type of competitor organisms present, rather than to the brand of medium used.

Comparison of methods for the recovery and detection of low levels of injured Salmonella in ice cream and milk powder

This study compared the ability of four rapid methods and a standard cultural method to detect low levels of heat-injured cells of Salmonella typhimurium in ice cream and skimmed milk powder. The detection of Salmonella in samples contaminated with low levels (< 10 cfu 25 g-1) was significantly greater with the novel broth method than with the other methods (P </= 0.01). At contamination levels > 10 cfu 25 g-1, there was no significant difference between the methods except for the novel broth method and a dipstick-based immunoassay (P </= 0.05). The novel broth method, S.P.R.I.N.T. Salmonella, which incorporates a specifically formulated peptone and Oxyrase(R) combination followed by the timed release of selective agents into the recovery medium, was shown to improve the rate of detection of low numbers of injured cells of Salmonella after 24 h enrichment.

Comparação de Meios de Enriquecimento e de Plaqueamento Utilizados na Pesquisa de Salmonella em Carcaças de Frango e Fezes de Aves

Este trabalho foi desenvolvido para avaliar, comparativamente, os caldos de enriquecimento Rapapport-novobiocina (RVN), selenito-cistinanovobiocina (SCN) e tetrationato-novobiocina (TN) e os meios para plaqueamento ágar Hektoen (HE), ágar MacConkey (MC), ágar Salmonella-Shigella (SS), ágar verde brilhante (VB) e ágar xilose lisina desoxicolato (XLD), utilizados no isolamento de Salmonella em carcaças de frango e fezes de aves. O procedimento bacteriológico consistiu das etapas de pré-enriquecimento, enriquecimento em caldos seletivos, plaqueamento, testes bioquímicos presuntivos e confirmação sorológica com soros polivalentes anti antígenos somáticos e flagelares de Salmonella.. As fezes foram experimentalmente contaminadas com 8 sorotipos de Salmonella (Agona, Anatum, Enteritidis, Havana, Infantis, Owakam, Schwazengrund e Typhimurium) e a concentração final foi aproximadamente de 1,2 x 10² ufc/g. As fezes foram inoculadas nos caldos enriquecedores e a partir daí, seguiu-se o mesmo procedimento utilizado para as carcaças. Os resultados referentes às carcaças de frango não foram estatisticamente diferentes (p>0,01) para os caldos e as placas. Todavia, verificou-se superioridade numérica em relação aos caldos SCN e TN sobre o caldo RVN, e em relação ao ágar XLD sobre os demais. Verificou-se também que com o emprego de dois caldos de enriquecimento e de dois meios para plaqueamento pode-se obter maior positividade. Quanto ao exame das fezes, o caldo TN mostrou-se superior aos demais (p>0,01), não havendo diferença (p>0,01) de resultados para os meios de plaqueamento. Os resultados sugerem que a utilização de mais de um meio de enriquecimento e de plaqueamento poderia aumentar as chances de isolamento de Salmonella.

Salmonellae, salmonellosis, and dairy foods: a review

Salmonellae continue to be a major concern for the dairy industry because these bacteria have caused recent outbreaks of illness and have been isolated from various dairy products in the market place. Salmonellae are generally not heat resistant and normally grow at 35 to 37 degrees C, but they can grow at much lower temperatures, provided that the incubation time is suitably extended. To minimize problems, foods should be held at or below 2 to 5 degrees C at all times. Both conventional and rapid methods are available to isolate salmonellae from dairy foods and to identify the bacteria. Salmonellae behave differently in different kinds of cheese: they survived in ripening Cheddar cheese for up to 7 mo at 13 degrees C and for 10 mo at 7 degrees C; in coldpack cheese food for several weeks, depending on the pH and preservative used; and in Domiati cheese 13 to 36 d, depending on the manufacturing process used. When Mozzarella cheese was made, temperatures of stretching and molding (60 degrees C) killed all salmonellae present, but, in cottage cheese, survival of the pathogen depended on the cooking temperature of curd. Spray drying of skim milk killed substantial numbers of salmonellae, but some survivors remained. Butter readily supported growth of salmonellae at room temperature, and neither freezing nor refrigeration for brief periods eliminated salmonellae from butter. Use of appropriate hygienic procedures, e.g., Hazard Analysis Critical Control Point system, during processing should reduce the likelihood of salmonellosis outbreaks associated with dairy foods.

Slow rehydration for detection of Salmonella spp. in feeds and feed ingredients

Rehydration and equilibration (4 h) of feeds and feed ingredients at water/sample ratios (vol/wt) of 1.4 to 3.2 did not markedly increase recovery of Salmonella spp. in the slurry when analyzed by standard cultural and direct enrichment methods. Of 143 naturally contaminated samples examined, equilibration increased levels of detection from 106 to 109 positive samples by the standard cultural method and from 103 to 112 by direct enrichment. Results suggest that nonhomogeneous distribution of low incident numbers of salmonellae in test samples rather than an equilibration-dependent response provided for the observed heterogeneity in recovery patterns. The novel equilibration approach is of limited application and requires validation on an individual food basis.