G. Moschetti

Molecular evaluation of microbial diversity occurring in different types of Mozzarella cheese

Aims:u2002The microbial community of different types of unripened Pasta Filata cheese was investigated by culture‐independent methods with the aim of rapidly achieving knowledge about cheese microbiota and discriminating traditional and industrial cheeses.

Microbial succession during ripening of Naples-type salami, a southern Italian fermented sausage

Studies were carried out on the microbiological and physico-chemical changes which occurred during the ripening of five batches of Naples-type salami, manufactured without starter cultures. Salami were sampled internally and externally, and the following microbial groups were studied: lactic acid bacteria, Micrococcaceae and yeasts. The results obtained indicated that lactobacilli constituted the predominant flora, both on the surface and in the interior of the pieces throughout the ripening period. Micrococcaceae and yeasts were also found in considerable number in both locations. Characterisation of 191 lactic isolates indicated that the salami microflora was dominated by homofermentative lactobacilli; approximately 63% of them could be identified as Lactobacillus sake; 40% showing the traits of a racemase negative variant of this species, once referred to Lactobacillus bavaricus. Yeast population mainly comprised Debaryomyces strains. All the colonies grown on mannitol salt and Kranep agar were catalase-positive cocci; novobiocin-resistant staphylococci were the only Micrococcaceae found. The API Staph identification system did not prove to be reliable: 82% of the isolates remained unidentified. To achieve improved characterisation, cluster analysis was subsequently performed on this group, corroborating the existence of a fairly homogeneous group representing an intermediate variety between Staphylococcus xylosus and Staphylococcus saprophyticus that was isolated during the whole ripening process.

PCR-DGGE fingerprints of microbial succession during a manufacture of traditional water buffalo mozzarella cheese

Aims:u2002 To monitor the process and the starter effectiveness recording a series of fingerprints of the microbial diversity occurring at different steps of mozzarella cheese manufacture and to investigate the involvement of the natural starter to the achievement of the final product.

Random amplified polymorphic DNA and amplified ribosomal DNA spacer polymorphism : powerful methods to differentiate Streptococcus thermophilus strains

Streptococci from different collections and dairy materials were characterized by conventional and molecular methods. After amplification of the 16S–23S rDNA spacer region, all the strains referable to the genus Streptococcus exhibited a single polymerase chain reaction (PCR) product, allowing their differentiation from enterococci. Cleaving this PCR product with Hae III, two different restriction patterns could be observed, allowing Streptococcus salivarius DSM 20560T, Strep. thermophilus NCDO 822 and two strains of Streptococcus spp. to be gathered in one group and all the other strains in another. In order to achieve strain typing, all the cultures were investigated by random amplified polymorphic DNA (RAPD)‐PCR analysis employing two selected primers. The results were treated by cluster analysis, appearing significantly consistent with both the taxonomic position and the origin of the strains. Pulsed‐field gel electrophoresis (PFGE) of Sma I digests of the genomic DNA from 11 representative strains with decreasing levels of RAPD similarity allowed their diversity to be confirmed, even though RAPD‐PCR proved to be less discriminating than PFGE analysis. The results are discussed with reference to the capability of the analytical procedures used to aid both identification and strain typing of streptococci, as well as the taxonomic structure of the species Strep. thermophilus.

Detection and characterization of a bacteriocin, garviecin L1-5, produced by Lactococcus garvieae isolated from raw cow's milk

Aims: The identification of a bacteriocin‐producing lactococcal strain isolated from raw cow’s milk is reported, along with production conditions, physical and chemical properties, and mode of action of the bacteriocin.

Characterization of strains of Leuconostoc mesenteroides by analysis of soluble whole-cell protein pattern, DNA fingerprinting and restriction of ribosomal DNA

Of 215 leuconostocs isolated from field grass, natural whey cultures and water‐buffalo milk, 178 were identified as Leuconostoc mesenteroides ssp. mesenteroides while 37 strains could not be identified Biochemical characterization allowed seven groups to be defined. Representative strains of each group and different habitat and nine reference strains were selected for further analyses. Protein profiles appeared suitable for species discrimination, but did not differentiate between the three subspecies of Leuc. mesenteroides. The technique also showed some differences among equivocal strains. DNA fingerprinting for most strains of Leuc. mesenteroides ssp. mesenteroides examined showed a different restriction pattern from that of the type strain. Ribotyping was not useful for discriminating species and subspecies of the genus Leuconostoc: Leuc. mesenteroides ssp. mesenteroides and ssp. dextranicum showed the same ribopattern as Leuc. lactis while Leuc. mesenteroides ssp. cremoris exhibited a pattern distinct from all the other species examined. On the basis of ARDRA‐PCR, two main groups could be distinguished: the larger group included Leuc. mesenteroides, Leuc. lactis, Leuc. pseudomesenteroides and some unidentifiable strains; the second one included Leuc. citreum, Leuc. fallax, Weissella paramesenteroides and some unidentified strains.

Antilisterial activity of thermophilin 347, a bacteriocin produced by Streptococcus thermophilus

Streptococcus thermophilus 347 isolated from yogurt produces a bacteriocin referred as thermophilin 347. The bacteriocin was evidenced in the neutralized, filtered and catalase treated culture supernatant fluid of the producer strain. After partial purification, thermophilin 347 exhibited a bactericidal effect against Listeria monocytogenes and several closely related lactic acid bacteria. The activity of thermophilin 347 was lost after protease treatment but was maintained after heating at 100 degrees C for 1 h; after autoclaving at 121 degrees C for 15 min the activity was reduced by 50%. SDS-PAGE of partially purified thermophilin 347 was used to detect bacteriocin activity corresponding to an apparent molecular mass between 2.5 and 6.2 KDa.

Genotyping of Lactobacillus delbrueckii subsp. bulgaricus and determination of the number and forms of rrn operons in L. delbrueckii and its subspecies

Three different approaches (whole-cell protein profiles, DNA fingerprinting combined with pulsed-field gel electrophoresis and analysis of rDNA genes) were used to characterize thirty-one strains of Lactobacillus delbrueckii subsp. bulgaricus from different dairy products, and three type strains belonging to L. delbrueckii subsp. delbrueckii, L. delbrueckii subsp. lactis and L. delbrueckii subsp. bulgaricus. Moreover, the number and different forms of rrn operons in L. delbrueckii and its subspecies were defined. At the strain typing level, Notl macrorestriction analysis permitted grouping of the 32 strains of L. delbrueckii subsp. bulgaricus into 23 restriction patterns, providing a high degree of discriminatory power. Among whole-cell protein profiles, PCR analysis of rDNA genes and ribotyping, the latter method seemed to be the most reliable approach to characterizing the subspecies belonging to L. delbrueckii. Ribotyping combined with enzymes such as HindIII and EcoRI showed that at least six rrn operons were present in L. delbrueckii and its subspecies; two forms of rrn operons were present in the subspecies lactis and bulgaricus and four forms were present in the subspecies delbrueckii.

Antimicrobial activity of Staphylococcus xylosus from Italian sausages against Listeria monocytogenes

One hundred and twenty‐five isolates of Micrococcaceae from Italian salami were tested for antagonistic activities against Listeria monocytogenes. Four isolates, identified as Staphylococcus xylosus, inhibited the growth of all five strains of L. monocytogenes tested. The antagonistic substances produced by strains 39A and 41A were inactivated by some proteases, whereas those from strains 1E and 27E were inactivated only by esterase and lipase. They are neither bacteriophages, nor lytic enzymes like lysostaphin.

Characterization of lactic acid bacteria strains on the basis of neutral volatile compounds produced in whey.

G. MAURIELLO, L. MOIO, G. MOSCHETTI, P. PIOMBINO, F. ADDEO AND S. COPPOLA. 2001.