RESUMO
AIMS: To evaluate the phage diversity in the environment of a dairy industry which manufactures a product fermented with a probiotic strain of Lactobacillus paracasei. METHODS AND RESULTS: Twenty-two Lact. paracasei phages were isolated from an industrial plant that manufactures a probiotic dairy product. Among them, six phages were selected based on restriction profiles, and two phages because of their notable thermal resistance during sample processing. Their morphology, host range, calcium dependency and thermal resistance were investigated. All phages belonged to the Siphoviridae family (B1 morphotype), were specific for Lact. casei and paracasei strains showing identical host spectrum, and only one phage was independent of calcium for completing its lytic cycle. Some of the phages showed an extraordinary thermal resistance and were protected by a commercial medium and milk. CONCLUSIONS: Phage diversity in a probiotic product manufacture was generated to a similar or greater extent than during traditional yogurt or cheese making. SIGNIFICANCE AND IMPACT OF THE STUDY: This work emphasizes probiotic phage infections as a new ecological situation beyond yogurt or cheese manufactures, where the balanced coexistence between phages and strains should be directed toward a favourable state, thus achieving a successful fermentation.
Assuntos
Bacteriófagos/isolamento & purificação , Indústria de Laticínios , Lactobacillus/virologia , Apoptose/efeitos dos fármacos , Bacteriófagos/genética , Bacteriófagos/crescimento & desenvolvimento , Cálcio/farmacologia , DNA Viral/análise , Eletroforese em Gel de Ágar , Microbiologia Ambiental , Manipulação de Alimentos , Temperatura Alta , Cinética , Microscopia Eletrônica , Mapeamento por Restrição , Esterilização/métodosRESUMO
Sixty-one natural phages (59 of Streptococcus thermophilus and 2 of Lactobacillus delbrueckii subsp. bulgaricus) were isolated from Argentinian dairy plants from November 1994 to July 2000. Specifically, 17 yogurt samples (18% of all samples) and 26 cheese samples (79%) contained phages lytic to S. thermophilus strains. The number of viral particles found in samples ranged from 10(2) to 10(9) PFU/ml. The phages belonged to Bradley's group B or the Siphoviridae family (morphotype B1). They showed high burst size values and remarkably short latent periods. The results of this study show that phages were found more frequently in cheesemaking processes than in yogurt-making processes. The commercial streptococcus strains appeared to propagate more phages, whereas the natural strains propagated fewer phage strains. These results suggest that the naturally occurring cultures are inherently more phage resistant.
Assuntos
Bacteriófagos/isolamento & purificação , Laticínios/virologia , Lactobacillus/virologia , Fagos de Streptococcus/isolamento & purificação , Animais , Bacteriófagos/classificação , Bacteriófagos/genética , Queijo/microbiologia , Queijo/virologia , Laticínios/microbiologia , Lactobacillus/genética , Fagos de Streptococcus/classificação , Fagos de Streptococcus/genética , Iogurte/microbiologia , Iogurte/virologiaRESUMO
Thermal and chemical resistance of five autochthonal bacteriophages of Streptococcus thermophilus, isolated from Cuartirolo cheese wheys and yogurt, was investigated. Times to obtain 99% inactivation of phages (T99) at 63 degrees C and 72 degrees C in three suspension media (enriched tryptic soy broth, reconstituted commercial nonfat skim milk, and tris magnesium gelatin buffer) were determined. The thermal resistance was dependent on the phages studied but not detectable counts (<10 PFU/ml) were only achieved by heating at 90 degrees C during 5 min. The data obtained for the three assayed media did not permit verifying significant differences among them. Sodium hypochlorite (100 ppm) provided a fast inactivation of bacteriophage particles (<10 PFU/ml after 5 min). Ethanol, at concentrations of 75% and 100%, was also effective for phage destruction. Isopropanol was slightly less effective than ethanol at the same concentrations. Peracetic acid (0.15%) was also a very effective agent for phage inactivation. The results showed that these autochthonal bacteriophages were not completely inactivated neither by normal pasteurization treatments nor by some biocides commonly used in disinfection, except sodium hypochlorite and peracetic acid. The practical implications of these findings have pointed out the necessity of recognizing the importance of establishing adequate conditions to assure effective thermal and chemical treatments in dairy plants and laboratory environments.
Assuntos
Bacteriófagos/isolamento & purificação , Laticínios/microbiologia , Microbiologia de Alimentos , Temperatura Alta , Streptococcus/virologia , 2-Propanol/farmacologia , Argentina , Bacteriófagos/patogenicidade , Cinética , Ácido Peracético/farmacologia , Hipoclorito de Sódio/farmacologiaRESUMO
Samples (32) of natural milk cultures used in the Santa Fe, Argentina, area for soft and semihard cheese production were examined. The microbial composition (including lactic acid microflora characterization) and technological parameters (acidifying and proteolytic activities) were evaluated. The cultures contained mainly thermophilic lactic acid bacteria, identified as Streptococcus salivarius subsp. thermophilus (96.8% of the total strains) and Enterococcus spp. The strains showed a low proteolytic activity. The isolates of S. salivarius subsp. thermophilus exhibited a widespread phage resistance. The nonlactic microflora comprised coliforms, yeasts, spore-forming bacteria and lactate fermentative bacteria. The samples showed an acidity level from 0.38 to 0.69% lactic acid (pH from 4.25 to 5.75). The acidifying activity was optimal at 45 degrees C. The advantages and disadvantages of the employment of natural milk starters are discussed.