Evaluation of PCR methods for rapid identification and differentiation of Streptococcus uberis and Streptococcus parauberis

Antimicrobial resistance patterns of Streptococcus uberis isolates from bovine milk in Chiba prefecture, Japan: association between multidrug resistance and clonal complex 996

Streptococcus uberis is one of major pathogens causing bovine mastitis. However, there is poor information on antimicrobial resistance (AMR) among the Japanese isolates. To provide treatment information for the mastitis caused by S. uberis in Japan, we aimed to clarify AMR patterns of the isolates from bovine milk mainly in Chiba. AMR phenotyping/genotyping [blaZ-erm(A)-erm(B)-mef(A)-linB-lnuD-tet(M)-tet(O)-tet(K)-tet(L)-tet(S)] and multilocus sequence typing were performed to analyze relationships between AMR patterns and clonal complexes (CCs). Resistance to tetracycline-, macrolide-, and lincosamide-classes was mainly associated with possession of tet(O), tet(S), erm(B), linB, and lnuD genes. CC996 was significantly associated with multidrug resistance (P<0.0001). These findings will aid Chiba farm animal clinics in treating bovine mastitis.

Survey of Genotype Diversity, Virulence, and Antimicrobial Resistance Genes in Mastitis-Causing Streptococcus uberis in Dairy Herds Using Whole-Genome Sequencing

Streptococcus uberis is one of the primary causative agents of mastitis, a clinically and economically significant disease that affects dairy cattle worldwide. In this study, we analyzed 140 S. uberis strains isolated from mastitis milk samples collected from 74 cow herds in the Czech Republic. We employed whole-genome sequencing to screen for the presence of antimicrobial resistance (AMR) genes and genes encoding virulence factors, and to assess their genetic relationships. Our analysis revealed the presence of 88 different sequence types (STs), with 41% of the isolates assigned to global clonal complexes (GCCs), the majority of which were affiliated with GCC5. The STs identified were distributed across the major phylogenetic branches of all currently known STs. We identified fifty-one putative virulence factor genes, and the majority of isolates carried between 27 and 29 of these genes. A tendency of virulence factors and AMR genes to cluster with specific STs was observed, although such clustering was not evident within GCCs. Principal component analysis did not reveal significant diversity among isolates when grouped by GCC or ST prevalence. The substantial genomic diversity and the wide array of virulence factors found in S. uberis strains present a challenge for the implementation of effective anti-mastitis measures.

Diversity of Streptococcus spp. and genomic characteristics of Streptococcus uberis isolated from clinical mastitis of cattle in Bangladesh

Introduction

Streptococci are the major etiology in mastitis in dairy cattle, a cause of huge economic losses in the dairy industries. This study was aimed to determine the diversity of Streptococcus spp. isolated from clinical mastitis of cattle reared in Bangladesh.

Methods

A total of 843 lactating cattle reared in four prominent dairy farms and one dairy community were purposively included in this study where 80 cattle were positive to clinical mastitis (CM) based on gross changes in the udder (redness, swelling, and sensitive udder) and/or milk (flakes and/or clots). Milk samples were collected from all the eighty cattle with clinical mastitis (CCM) and twenty five apparently healthy cattle (AHC). Samples were enriched in Luria Bertani broth (LB) and one hundred microliter of the enrichment culture was spread onto selective media for the isolation of Staphylococcus spp., Streptococcus spp., Enterococcus spp., Escherichia coli and Corynebacterium spp., the major pathogen associated with mastitis. Isolates recovered from culture were further confirmed by species specific PCR.

Results and Discussion

Out of 105 samples examined 56.2% (59/105), 17.14% (18/105), 9.52% (10/105) and 22.9% (24/105) samples were positive for Staphylococcus, Streptococcus, Enterococcus faecalis and E. coli, respectively. This study was then directed to the determination of diversity of Streptococcus spp. through the sequencing of 16S rRNA. A total of eighteen of the samples from CCM (22.5%) but none from the AHC were positive for Streptococcus spp. by cultural and molecular examination. Sequencing and phylogenetic analysis of 16S rRNA identified 55.6, 33.3, 5.6 and 5.6% of the Streptococcus isolates as Streptococcus uberis, Streptococcus agalactiae, Streptococcus hyovaginalis and Streptococcus urinalis, respectively. Considering the high prevalence and worldwide increasing trend of S. uberis in mastitis, in-depth molecular characterization of S. uberis was performed through whole genome sequencing. Five of the S. uberis strain isolated in this study were subjected to WGS and on analysis two novel ST types of S. uberis were identified, indicating the presence of at least two different genotypes of S. uberis in the study areas. On virulence profiling, all the isolates harbored at least 35 virulence and putative virulence genes probably associated with intramammary infection (IMI) indicating all the S. uberis isolated in this study are potential mastitis pathogen. Overall findings suggest that Streptococcus encountered in bovine mastitis is diverse and S. uberis might be predominantly associated with CM in the study areas. The S. uberis genome carries an array of putative virulence factors that need to be investigated genotypically and phenotypically to identify a specific trait governing the virulence and fitness of this bacterium. Moreover, the genomic information could be used for the development of new genomic tools for virulence gene profiling of S. uberis.

Ascorbic Acid-Mediated Modulation of Antibiotic Susceptibility of Major Bovine Mastitis Pathogens

This study aimed to investigate the effects of ascorbic acid on antibiotic susceptibility of major bovine mastitis pathogens, including Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis, Streptococcus agalactiae, and Escherichia coli. Minimum inhibitory concentrations (MICs) were determined by E-test method. The presence of 10 mM ascorbic acid decreased the MICs of penicillin and ampicillin while increased the MICs of erythromycin, kanamycin, streptomycin, and ciprofloxacin for all tested strains. Besides, ascorbic acid specifically reduced the MICs of tetracycline for gram-positive bacteria and chloramphenicol for gram-negative bacteria. This study highlights that ascorbic acid is a potential modulator of antibiotic activity against the major bovine mastitis pathogens.

Multilocus Sequence Genotype Heterogeneity in Streptococcus uberis Isolated from Bovine Mastitis in the Czech Republic

Simple Summary

Bovine mastitis is a serious problem for dairy farmers, resulting in great economic losses. A large number of antimicrobials are used to treat mastitis, contributing to the spread of resistance. Streptococcus uberis is an important environmental pathogen responsible for a significant proportion of subclinical (asymptomatic) and clinical intramammary infections in many countries. This pathogen is present in the environment of cows, colonising multiple body sites of the cow, including the mammary gland. Isolates may produce virulence factors that enable the bacteria to infect the mammary gland, resist the defence mechanisms of the mammary gland, and persist inside the gland. S. uberis isolates differ in virulence and the level of antimicrobial resistance, posing a challenge to controlling S. uberis infection. Therefore, it is necessary to study the biology and genetics of this pathogen to be able to help farmers and veterinarians to implement effective targeted measures against S. uberis mastitis.

Abstract

The ubiquitous occurrence and high heterogeneity of Streptococcus uberis strains cause difficulties in the development and implementation of effective control strategies in dairy herds. In this study, S. uberis strains from 74 farms, obtained predominantly from subclinical, acute, and chronic recurrent mastitis, as well as from udder surface swabs and milk from healthy udders, were analysed for their genetic diversity using multilocus sequence typing (MLST). Isolates were tested for the presence of the genes encoding the virulence factors using polymerase chain reaction. Antibiotic susceptibility testing was performed using a microdilution assay including 14 antimicrobials. The virulence profiles and antimicrobial (AMR) profiles of the isolates were assembled and the overall heterogeneity was evaluated. Among the 124 isolates, 89 MLST genotypes, 7 different virulence profiles, and 12 AMR profiles were identified. The large number of different MLST allelic profiles in this study points to the high heterogeneity of strains in dairy herds in the Czech Republic. Isolates of a certain MLST genotype may possess a different set of virulence factor genes. We detected up to three different resistance profiles within a single MLST genotype. The results of our study showed that fully susceptible isolates coexisted with resistant or even multiresistant isolates in the same herd. Multiple genotypes within a herd were detected on many farms (up to seven MLST genotypes and four AMR profiles in one herd). This heterogenic population structure might suggest that environmental transmission is the predominant route of infection in herds in the Czech Republic.

Occurrence of virulence-associated genes in Streptococcus uberis and Streptococcus parauberis isolated from bovine mastitis

Streptococcus uberis is one of the most important mastitis-causing pathogens. Although the pathogenesis and virulence factors required for the intramammary infection development are not yet well established, several putative virulence-associated genes have been described. This work aimed to investigate the presence of ten known and putative virulence-associated genes in S. uberis isolated from subclinical or clinical mastitis and its closely related species Streptococcus parauberis in 135 dairy farms in the Czech Republic. The PCR analysis detected that all the examined isolates possessed at least four virulence genes and most isolates carried eight out of ten virulence genes. All S. uberis isolates were positive for the oppF, gapC and sua genes. Among the most prevalent virulence-associated genes skc (98%) and pauA (97%) were also found. The hasA and hasB genes were always present together in 94% of the isolates. The genes cfu and lbp were detected in 6% and 2%, respectively. In the S. uberis isolates, 14 different virulence gene profiles were observed. The most frequent profile was hasA + hasB + sua + skc + pauA + gapC + oppF with variable hasC, observed in 86% of the tested isolates, occurring in 127 out of 135 farms. S. parauberis was identified very sporadically and, although it is closely related to S. uberis, only a rare occurrence of the examined virulence-associated genes was found.

Immunomodulatory Effects of Herbal Compounds Quercetin and Curcumin on Cellular and Molecular Functions of Bovine-Milk-Isolated Neutrophils toward Streptococcus agalactiae Infection

Herbal phytochemicals featuring active ingredients including quercetin and curcumin have shown potential in treating human and animal diseases. The current study investigated their potential function in vitro for host immunomodulation associated with Streptococcus agalactiae subclinical bovine mastitis via milk-isolated neutrophils. Our results showed a positive influence on cellular migration, reactive oxygen species (ROS) generation, phagocytosis, and bacterial killing as well as neutrophil extracellular traps (NETs) release. This study also highlighted several important molecular aspects of quercetin and curcumin in milk-isolated neutrophils. Gene expression analyses by RT-PCR revealed significant changes in the expression of proinflammatory cytokines (IL1B, IL6, and TNF), ROS (CYBA), phagocytosis (LAMP1), and migration (RAC). The expression levels of apoptotic genes or proteins in either pro-apoptosis (CASP3 and FAS) or anti-apoptosis (BCL2, BCL2L1, and CFLAR) were significantly manipulated by the effects of either quercetin or curcumin. A principal component analysis (PCA) identified the superior benefit of quercetin supplementation for increasing both cellular and molecular functions in combating bacterial mastitis. Altogether, this study showed the existing and potential benefits of these test compounds; however, they should be explored further via in vivo studies.

Antimicrobial Resistance Profiles and Genes in Streptococcus uberis Associated With Bovine Mastitis in Thailand

Streptococcus uberis is recognized as an environmental mastitis pathogen in dairy cattle. The varied success rate of antibiotic treatment for S. uberis intramammary infection may be associated with the antimicrobial resistance (AMR) of these bacteria. This observational study aimed to analyze 228 S. uberis strains associated with bovine mastitis in northern Thailand from 2010 to 2017. AMR and AMR genes were determined by the minimum inhibitory concentration (MIC) using a microdilution method and polymerase chain reaction, respectively. The majority of S. uberis strains were resistant to tetracycline (187/228, 82.02%), followed by ceftiofur (44/228, 19.30%), and erythromycin (19/228, 8.33%). The MIC50 and MIC90 of ceftiofur in 2017 were 2–4-fold higher than those in 2010 (P < 0.01). Resistance to tetracycline and ceftiofur significantly increased between 2010 and 2017 (P < 0.05). The most common gene detected in S. uberis was tetM (199/228, 87.28%), followed by ermB (151/228, 66.23 %) and blaZ (15/228, 6.58 %). The association between tetracycline resistance and tetM detection was statistically significant (P < 0.01). The detection rates of tetM significantly increased, while the detection rates of tetO and ermB significantly decreased during 2010–2017. AMR monitoring for bovine mastitis pathogens, especially S. uberis, is necessary to understand the trend of AMR among mastitis pathogens, which can help create an AMR stewardship program for dairy farms in Thailand.

Vancomycin resistant Streptococcus equi subsp. equi isolated from equines suffering from respiratory manifestation in Egypt

Background and Aim:

Upper respiratory tract infections are common in horses and can be caused by a variety of pathogens, mainly Streptococcus equi subsp. equi, which are a significant equine pathogen causing major health issues as well as financial losses to the equine industry. This study aimed to determine the prevalence of Streptococcal bacteria in equines in Egypt, and characterize vancomycin-resistant S. equi subsp. equi phenotypically and genotypically.

Materials and Methods:

S. equi subsp. equi was isolated from internal nares of horses. All strains were confirmed by polymerase chain reaction-based detection of Streptococcus genus-specific 16S rRNA, sodA and seeI genes. Antibiotic susceptibility was determined phenotypically using the disk diffusion method. Genotypic detection of antibiotic resistance genes was performed by analyzing as b-lactamase resistance (blaZ), tetracycline resistance (tetK), vancomycin resistance (vanA), and chloramphenicol resistance (fexA).

Results:

Eight streptococcal isolates were confirmed as S. equi subsp. equi. The genotypic characterization of antibiotic resistance showed resistance to vanA and tetK, with a frequency of 87.5% and 12.5%, respectively, while the frequency of sensitivity was 100% for blaz gene and fexA gene.

Conclusion:

In this study, we assessed vancomycin-resistant S. equi subsp. equi from equines suffering from respiratory manifestation in Egypt.

Sequence characterisation and novel insights into bovine mastitis-associated Streptococcus uberis in dairy herds

Streptococcus uberis is one of the most frequent mastitis-causing pathogens isolated from dairy cows. Further understanding of S. uberis genetics may help elucidate the disease pathogenesis. We compared the genomes of S. uberis isolates cultured from dairy cows located in distinctly different geographic regions of Australia. All isolates had novel multi locus sequence types (MLST) indicating a highly diverse population of S. uberis. Global clonal complexes (GCC) were more conserved. GCC ST86 and GCC ST143 represented 30% of the total isolates (n = 27) and were clustered within different geographic regions. Core genome phylogeny revealed low phylogenetic clustering by region, isolation source, and MLST. Identification of putative sortase (srtA) substrates and generation of a custom putative virulence factor database revealed genes which may explain the affinity of S. uberis for mammary tissue, evasion of antimicrobial efforts and disease pathogenesis. Of 27 isolates, four contained antibiotic resistance genes including an antimicrobial resistance cluster containing mel/mef(A), mrsE, vatD, lnuD, and transposon-mediated lnuC was also identified. These are novel genes for S. uberis, which suggests interspecies lateral gene transfer. The presence of resistance genes across the two geographic regions tested within one country supports the need for a careful, tailored, implementation and monitoring of antimicrobial stewardship.

Discrimination of major and minor streptococci incriminated in bovine mastitis by MALDI-TOF MS fingerprinting and 16S rRNA gene sequencing

The current work investigated the discriminatory potential of MALDI-TOF MS fingerprinting towards most-relevant major (Streptococcus agalactiae, S. dysgalactiae, S. uberis) and minor (S. canis, S. parauberis, S. salivarius, S. equinus and S. gallolyticus) streptococci involved in bovine mastitis (BM), in comparison to 16S rRNA gene sequencing (GS)-based identification. The MALDI-TOF MS-generated spectral fingerprints were recruited for eliciting a detailed proteomic map that demonstrated clear variability for inter- and intra-species-specific biomarkers. Besides, a phyloproteomic dendrogram was evolved and comparatively analyzed against the phylogenetic one obtained from 16S rRNA GS in order to assess the differentiation of streptococci of bovine origin based on variability of protein fingerprints versus the variation of 16S rRNA gene homology. Results showed that the discrimination of BM-implicated streptococci can be obtained by both approaches; however MALDI-TOF MS was superior, achieving more variability at both intra- and sub-species levels. MALDI-TOF MS spectral analytics revealed that Streptococcus spp. exhibited three genus-specific biomarkers (peaks with m/z values at 2112, 4452 and 5955) and all streptococci exhibited spectral variability at both species and subspecies levels. Remarkably, MALDI-TOF MS fingerprinting was found to be at least as robust as 16S rRNA GS-based identification, allowing much cheaper and faster analysis, and additionally exhibiting high reliability for characterization of BM-implicated streptococci, thus proving to be a powerful tool that can be used independently within dairy diagnostics.

Molecular epidemiology of Streptococcus uberis intramammary infections: Persistent and transient patterns of infection in a dairy herd

A longitudinal observational study was carried out to explore transmission dynamics and duration of infection of Streptococcus uberis. Quarter milk samples were collected aseptically for bacterial culture from all lactating cows once a month over a 10-mo period. Molecular typing of S. uberis mastitis was performed using pulsed-field gel electrophoresis (PFGE). Molecular typing was used to determine episodes of S. uberis intramammary infection (IMI). Comparisons of spontaneous cure among PFGE types were performed using Fisher's exact chi-squared tests. Differences of duration among PFGE types and between periods of lactation were tested with Kaplan-Meier survival curves and Cox's proportional hazard model. Among a total of 851 quarter samples, 145 milk samples were detected with S. uberis presence. Based on results of PFGE, 66 episodes of S. uberis IMI were determined. From the 8 main PFGE types (A-H), PFGE type D, E, F1, F2, G, and H had only one episode indicating no evidence for transmission, subsequently defined as environmental S. uberis strains. In contrast, PFGE types A1, A2, B, C1, and C2 had at least 2 infection episodes caused by the same strain in different quarters or cows, indicating that these strains would be able to transmit to other quarters or cows. These strains were defined as contagious strains. The majority of IMI were attributable to PFGE type A1 (55%), B (17%), and A2 (11%). Spontaneous cures were observed in 35 IMI episodes. Of these 35 IMI cures, 91.4% were in IMI with duration of infection of 1 mo, n = 25, and 2 mo, n = 6. The remaining 8.6% was in IMI with duration of infection >2 mo, n = 4. Based on results from Cox's proportional hazard model, environmental S. uberis episodes were likely to have spontaneous cure with shorter duration compared with contagious S. uberis with PFGE type B (hazard ratio = 8.4). Quarters infected with S. uberis strain PFGE type A in early lactation were more likely to persist compared with those infected in late lactation (hazard ratio = 7.57). In conclusion, the majority of S. uberis IMI in this herd were transient and showed spontaneous cure. In addition to environmental S. uberis IMI, at least 3 types of contagious IMI S. uberis can be defined as (1) short duration of IMI and likely to have spontaneous cure, (2) long duration and unlikely to have spontaneous cure, and (3) wide range of duration of IMI either transient or persistent where spontaneous cure may occur depending on host defense capacity.

Technical note: Development of multiplex PCR assays for the molecular characterization of Streptococcus uberis strains isolated from bovine mastitis

Streptococcus uberis is an important causative agent for clinical and subclinical mastitis in dairy cattle. The aim of this study was to develop 2 multiplex PCR assays (mPCR) for the simultaneous detection of virulence factors and housekeeping genes for use when investigating the genetic variability and distribution of Strep. uberis virulence factors. The tuf, cpn60, pauA, sodA, sua, oppF, and gapC genes were grouped in assay 1 (mPCR1) and the hasA, hasB, and hasC genes were included in assay 2 (mPCR2). The detection limits were 11.8 pg and 5.9 pg of DNA for mPCR1 and mPCR2, respectively. The 2 mPCR assays were validated with 56 Strep. uberis strains isolated from mastitis milk samples collected from different bovine herds in northern Italy. Results revealed that gapC and oppF were detected in 98.2% of the strains, whereas sua and hasC genes were detected in 94.6 and 89.2% of the strains, respectively. The most common pattern was gapC+, oppF+, cpn60+, sua+, sodA+, pauA+, tuf+, hasA+, hasB+, and hasC+, which appeared in 59% of the strains analyzed. The molecular assays developed in the present study represent a powerful tool for the evaluation of virulence pattern distribution in Strep. uberis strains associated with intramammary infections.

Genotyping and antimicrobial resistance of Streptococcus uberis isolated from bovine clinical mastitis

A genotypic characterization of Streptococcus uberis isolated from clinical mastitis (CM) in dairy cows, and the association of Strep. uberis genotypes and antimicrobial susceptibility (AMS) was performed. A total of 89 isolates identified as Strep. uberis from 86 dairy cows with CM in 17 dairy herds of Southeastern Brazil were genotyped using random amplified polymorphic DNA (RAPD) analysis. After genotyping, two clusters (I and II) were created according to RAPD types. A commercial broth microdilution test was used to determine the susceptibility of Strep. uberis isolates to 8 antimicrobials (ampicillin, ceftiofur, cephalothin, erythromycin, penicillin, penicillin+novobiocin, pirlimycin and tetracycline). For each antimicrobial, we determined the minimal inhibitory concentrations that inhibit 50% (MIC₅₀) and 90% (MIC₉₀) of Strep. uberis strains. Differences in AMS among genotypic clusters were evaluated using mixed regression models. Overall, a great polymorphism (56 RAPD-types) was found among Strep. uberis isolates, although a higher genetic similarity (based on the PCR bands features) was observed within herds after genotypic clustering. No differences in AMS were observed among clusters. Strep. uberis isolated from bovine CM were resistant to most antimicrobials, with the exception of cephalothin and penicillin+novobiocin.

Identification and typing of Vagococcus salmoninarum using genomic and proteomic techniques

This study reports on the characterization of Vagococcus salmoninarum using phenotypic, serological, antigenic, genetic and proteomic methods. All strains of V. salmoninarum were resistant to most of the antimicrobials tested, and only 10% of strains were sensitive to florfenicol. Serological analysis demonstrated a high antigenic homogeneity within the species. No cross-reaction was detected with other fish pathogenic species causing streptococcosis (Lactococcus garvieae, Streptococcus parauberis, Streptococcus iniae, Streptococcus agalactiae, Carnobacterium maltaromaticum) using serum against V. salmoninarum CECT 5810. Electrophoretic analysis of cell surface proteins and immunoblot supported the antigenic homogeneity within V. salmoninarum strains. Moreover, limited diversity was detected using genomic (RAPD, ERIC-PCR and REP-PCR) and MALDI-TOF-MS analyses. The phenotypic, genomic and proteomic methods tested allowed the rapid differentiation of V. salmoninarum from the other species causing streptococcosis. However, MALDI-TOF-MS is the most promising method for typing and characterization of V. salmoninarum.

Antibacterial Effect of Copper on Microorganisms Isolated from Bovine Mastitis

The antimicrobial properties of copper have been recognized for several years; applying these properties to the prevention of diseases such as bovine mastitis is a new area of research. The aim of the present study was to evaluate in vitro the antimicrobial activity of copper on bacteria isolated from subclinical and clinical mastitis milk samples from two regions in Chile. A total of 327 microorganisms were recovered between March and September 2013, with different prevalence by sample origin (25 and 75% from the central and southern regions of Chile, respectively). In the central region, Escherichia coli and coagulase negative Staphylococci (CNS) were the most frequently detected in clinical mastitis cases (33%), while in the southern region S. uberis, S. aureus, and CNS were detected with frequencies of 22, 21, and 18%, respectively. Antibiotic susceptibility studies revealed that 34% of isolates were resistant to one or more antibiotics and the resistance profile was different between bacterial species and origins of isolation of the bacteria. The minimum inhibitory concentration of copper (MIC-Cu) was evaluated in all the isolates; results revealed that a concentration as low as 250 ppm copper was able to inhibit the great majority of microorganisms analyzed (65% of isolates). The remaining isolates showed a MIC-Cu between 375 and 700 ppm copper, and no growth was observed at 1000 ppm. A linear relationship was found between the logarithm of viable bacteria number and time of contact with copper. With the application of the same concentration of copper (250 ppm), CNS showed the highest tolerance to copper, followed by S. uberis and S. aureus; the least resistant was E. coli. Based on these in vitro results, copper preparations could represent a good alternative to dipping solutions, aimed at preventing the presence and multiplication of potentially pathogenic microorganisms involved in bovine mastitis disease.

Molecular identification key of the family Streptococcaceae

The gene order conservation (GOC) between the species of family Streptococcaceae was analysed. The rate of GOC in the strains belonging to the same species is 70% or more. When we compared different species belonging to the same genus, the rate of GOC was 30-47% while it was below 20% when the species were from different genera. A molecular identification key was established for identifying those genera and species within the family Streptococcaceae which have an already known full genome sequence (24 Streptococcus and 2 Lactococcus species). Identical genome parts of the species belonging to the same genus were used for determination of genera. These are the sections surrounding the replication origin dnaA, the sequence from gene phaB to the gene accA, and the sequence of alr acpS secA. Sections around the genes pepX, leuS and rplM were used for identifying the species. The gene order analysis and data in molecular identification key showed that S. uberis and S. parauberis also belong to the same species, and our suggestion for their new names is S. uberis subsp. uberis and S uberis subsp. parauberis. Based on this data, a new definition of bacterial species is proposed: two isolates belong to the same species if the order of the genes in their genomes is almost identical.

Molecular epidemiology of recurrent clinical mastitis due to Streptococcus uberis: evidence of both an environmental source and recurring infection with the same strain

This study was undertaken because clinicians and farmers have observed that a considerable number of cows diagnosed with Streptococcus uberis mastitis have recurrences of mastitis in the same or a different quarter. The study was an attempt to answer whether these recurring cases were due to treatment failure (in which case a search would have begun for a better treatment for Strep. uberis mastitis) or due to reinfection with a different strain of Strep. uberis. Using pulsed-field gel electrophoresis (PFGE), we determined that the majority of recurrences (20 of 27) were caused by a new strain of Strep. uberis, indicating that treatment of the initial infection had been successful. A small number of recurrences (5 of 27) were caused by the initial strain, indicating persistence. The remaining 2 recurrences occurred in a new quarter but with the initial strain of Strep. uberis, indicating either spread between quarters or reactivation of a previous subclinical infection. Analysis of the PFGE profiles failed to reveal any strain-specific propensity to persist, because strains causing recurrences occurred in most of the major clusters.

Prevalence and different characteristics of two serotypes of Streptococcus parauberis isolated from the farmed olive flounder, Paralichthys olivaceus (Temminck and Schlegel), in Korea

The prevalence of two serotypes of Streptococcus parauberis isolated from the olive flounder, Paralichthys olivaceus, was evaluated in a total of 29 isolates between 2003 and 2010 in Korea. Streptococcus parauberis isolates were divided into two serologically distinct types (serotype 1 and serotype 2), except for one strain (S1091), using an agglutination assay with rabbit antiserum, and serotype 1 was identified as the dominant type (24 of 29 isolates) in this study. To identify the characteristics of the two serotypes of S. parauberis, we conducted a biochemical test using the API 20 Strep kit, a transmission electron microscopy (TEM) assay, sequence analysis of 16S-23S rRNA intergenic spacer region (ISR) and a pathogenicity test. In TEM, both serotypes possessed polysaccharide capsule layers around the cell surface when bacterial cells were treated with a homologous serotype of rabbit antiserum. However, we were unable to discriminate serotype-specific biochemical characteristics and genetic characteristics of 16S-23S rRNA ISR between the two serotypes. In the pathogenicity test, the serotype 1 strains induced significantly higher mortality than the serotype 2 strains in olive flounder when experimentally inoculated via the intraperitoneal route.

Mastitis diagnostics and performance monitoring: a practical approach

In this paper a review is given of frequently used mastitis diagnostic methods in modern dairy practice. Methods used at the quarter, cow, herd and regional or national level are discussed, including their usability for performance monitoring in udder health. Future developments, such as systems in which milk-derived parameters are combined with modern analytical techniques, are discussed. It is concluded that, although much knowledge is available and science is still developing and much knowledge is available, it is not always fully exploited in practice.

Identification and antimicrobial resistance of Streptococcus uberis and Streptococcus parauberis isolated from bovine milk samples

The conventional identification of Streptococcus uberis/parauberis group (n = 137) in clinical and subclinical bovine mastitis samples originating from 111 different farms was compared with identification based on 16 and 23S rRNA gene HindIII RFLP patterns used as operational taxonomic units in numerical analyses. On the basis of ribopattern analysis only 2 isolates belonged to S. parauberis, which is thus not a frequent cause of bovine intramammary infections in Finland. According to in vitro antimicrobial susceptibility testing, Streptococcus uberis is susceptible to beta-lactam antibiotics. The prevalence of erythromycin (15.6%) and oxytetracycline (40.6%) resistance of clinical S. uberis isolates was higher than reported previously among subclinical isolates. The 2 subclinical S. parauberis isolates were susceptible to all the antimicrobials tested.

Gene content differences across strains of Streptococcus uberis identified using oligonucleotide microarray comparative genomic hybridization

Streptococcus uberis is one of the principal causative agents of bovine mastitis. The organism is typically considered an environmental pathogen. In this study, two multilocus sequence typing (MLST) schemes and whole genome DNA microarrays were used to evaluate the degree and nature of genome flexibility between S. uberis strains. The 21 isolates examined in this study arise from a collection of 232 international isolates for which previous epidemiological and preliminary genotyping data existed. The microarray analysis resulted in an estimate of the core genome for S. uberis, consisting of 1530 ORFs, among 1855 tested, representing 82.5% of the S. uberis 0140J genome. The remaining ORFs were variable in gene content across the 21 tested strains. A total of 26 regions of difference (RDs), consisting of three or more contiguous ORFs, were identified among the variable genes. Core genes mainly encoded housekeeping functions, while the variable genes primarily fell within categories such as protection responses, degradation of small molecules, laterally acquired elements, and two component systems. Recombination detection procedures involving the MLST loci suggested S. uberis is a highly recombinant species, precluding accurate phylogenetic reconstructions involving these data. On the other hand, the microarray data did provide limited support for an association of gene content with strains found in multiple cows and/or multiple herds, suggesting the possibility of genes related to bovine transmissibility or host-adaptation.

PCR amplification of species specific sequences of 16S rDNA and 16S–23S rDNA intergenic spacer region for identification of Streptococcus phocae

Streptococcus phocae, a bacterial pathogen of seals, could reliably be identified by PCR amplification using oligonucleotide primers designed according to species specific segments of the previously sequenced 16S rRNA gene and the 16S-23S rDNA intergenic spacer region of this species. The PCR mediated assay allowed an identification of S. phocae isolated from harbor and gray seals and from Atlantic salmons. No cross-reaction could be observed with 13 different other streptococcal species and subspecies and with Lactococcus garvieae strains investigated for control purposes.

Molecular identification of Arcanobacterium bialowiezense and Arcanobacterium bonasi based on 16S-23S rRNA intergenic spacer region sequences

In the present study, the 16S-23S rDNA intergenic spacer region (ISR) of Arcanobacterium (A.) bialowiezense DSM 17162, A. bonasi DSM 17163, A. bernardiae DSM 9152, A. haemolyticum DSM 20595, A. hippocoleae DSM 15539, A. phocae DSM 10002, A. pluranimalium DSM 13483 and A. pyogenes DSM 20630 was amplified, sequenced and compared with the corresponding 16S rRNA gene sequences yielding comparable phylogenetic relationships. The ISR sequence of A. bialowiezense and A. bonasi allowed the design of species-specific oligonucleotide primers which could successfully be used for PCR-mediated identification of previously characterized A. bialowiezense and A. bonasi isolated from infections of the European bison. The presented molecular identification might help to improve a future diagnosis of both newly described bacterial pathogens.

Identification of Streptococcus uberis multilocus sequence types highly associated with mastitis

Multilocus sequence typing analysis of Streptococcus uberis has identified a cluster of isolates associated with clinical and subclinical mastitis and a cluster associated with cows with low somatic cell counts in their milk. Specific groups of genotypes (global clonal complex [GCC] sequence type 5s [ST5s] and GCC ST143s) were highly associated (P = 0.006) with clinical and subclinical mastitis and may represent a lineage of virulent isolates, whereas isolates belonging to GCC ST86 were associated with low-cell-count cows. This study has, for the first time, demonstrated the occurrence of identical sequence types (ST60 and ST184) between different continents (Australasia and Europe) and different countries (Australia and New Zealand). The standardized index of association and the empirical estimation of the rate of recombination showed substantial recombination within the S. uberis population in Australia, consistent with previous multilocus sequence type analyses.

Evaluation of tandem repeats for MLVA typing of Streptococcus uberis isolated from bovine mastitis

BACKGROUND

Streptococcus uberis is a common cause of bovine mastitis and recommended control measures, based on improved milking practice, teat dipping and antibiotic treatment at drying-off, are poorly efficient against this environmental pathogen. A simple and efficient typing method would be helpful in identifying S.uberis sources, virulent strains and cow to cow transmission. The potential of MLVA (Multiple Loci VNTR Analysis; VNTR, Variable Number of Tandem Repeats) for S. uberis mastitis isolates genotyping was investigated.

RESULTS

The genomic sequence of Streptococcus uberis (strain 0104J) was analyzed for potential variable number tandem repeats (VNTRs). Twenty-five tandem repeats were identified and amplified by PCR with DNA samples from 24 S. uberis strains. A set of seven TRs were found to be polymorphic and used for MLVA typing of 88 S. uberis isolates. A total of 82 MLVA types were obtained with 22 types among 26 strains isolated from the milk of mastitic cows belonging to our experimental herd, and 61 types for 62 epidemiologically unrelated strains, i.e. collected in different herds and areas.

CONCLUSION

The MLVA method can be applied to S. uberis genotyping and constitutes an interesting complement to existing typing methods. This method, which is easy to perform, low cost and can be used in routine, could facilitate investigations of the epidemiology of S. uberis mastitis in dairy cows.

Conventional Identification of Streptococcus uberis Isolated from Bovine Mastitis in Argentinean Dairy Herds

The objective of this study was to evaluate a conventional scheme for identifying Streptococcus uberis strains isolated from bovine mastitis. Seventy-five gram-positive, catalase-negative cocci were collected from cows with mastitis from 19 dairy herds located in the east-central region of Argentina. Five American Type Culture Collection strains and bovine isolates were identified by the API 20 Strep system and by restriction fragment length polymorphism analysis of 16S rDNA. A conventional scheme based on 11 biochemical tests was selected for identification of Strep. uberis strains: the Christie-Atkins-Munch-Petersen reaction; hydrolysis of Arg, esculin, and sodium hippurate; growth in inulin, mannitol, raffinose, salicin, and sorbitol; and growth at 45 degrees C and in 6.5% NaCl. Reference strains and 25 bovine isolates were classified accurately to the species level by the conventional scheme in a blind assay. Each reference strain and each bovine isolate were identified as belonging to the same species following these 3 methods. The remaining 50 isolates identified as Strep. uberis by the API 20 Strep system and 16S rDNA RFLP were assayed by the conventional scheme. This scheme correctly identified 47 (94%) of 50 isolates as Strep. uberis by comparing their biochemical profile with that of the reference strain. Three (6%) of the 50 isolates were classified as Strep. uberis by the API 20 Strep system and by 16S rDNA RFLP and were identified as Enterococcus faecalis by the conventional scheme. Thirty percent of the Strep. uberis strains showed biochemical profiles identical to the Strep. uberis American Type Culture Collection 27958 strain. Seventy percent of the Strep. uberis strains demonstrated variability compared with the reference strain, resulting in 19 different biochemical profiles. The conventional scheme proposed in this study resulted in a relatively low number of misidentifications and could biochemically identify not only typical, but also atypical Strep. uberis strains. This conventional scheme can be considered an adequate method for identifying Strep. uberis strains isolated from bovine mastitis because of its affordable cost in developing countries, and it may contribute to determining the frequency of isolation of Strep. uberis strains in Argentinean dairy herds.

First insights into the evolution of Streptococcus uberis: a multilocus sequence typing scheme that enables investigation of its population biology

Intramammary infection with Streptococcus uberis is a common cause of bovine mastitis throughout the world. Several procedures to differentiate S. uberis isolates have been proposed. However, all are prone to interlaboratory variation, and none is suitable for the description of the population structure. We describe here the development of a multilocus sequence typing (MLST) scheme for S. uberis to help address these issues. The sequences of seven housekeeping gene fragments from each of 160 United Kingdom milk isolates of S. uberis were determined. Between 5 and 17 alleles were obtained per locus, giving the potential to discriminate between 1.3 x 10(7) sequence types. In this study, 57 sequence types (STs) were identified. Statistical comparisons between the maximum-likelihood trees constructed by using the seven housekeeping gene fragments showed that the congruence was no better than that between each tree and trees of random topology, indicating there had been significant recombination within these loci. The population contained one major lineage (designated the ST-5 complex). This dominated the population, containing 24 STs and representing 112 isolates. The other 33 STs were not assigned to any clonal complex. All of the isolates in the ST-5 lineage carried hasA, a gene that is essential for capsule production. There was no clear association between ST or clonal complex and disease. The S. uberis MLST system offers researchers a valuable tool that allows further investigation of the population biology of this organism and insights into the epidemiology of this disease on a global scale.

Macrolide and lincosamide resistance genes of environmental streptococci from bovine milk

Environmental streptococcus isolates from bovine milk were identified to the species and strain level and screened for resistance to macrolide and lincosamide antibiotics by phenotypic and genotypic methods. Isolates were tested for resistance to erythromycin and pirlimycin by broth microdilution assays. Presence of ribosomal methylase genes (ermA, ermB, ermC) and efflux pump genes (mefA/E, msrA/C) was detected by polymerase chain reaction (PCR). Resistance to pirlimycin (minimum inhibitory concentration (MIC) = 8microg/ml) was detected in 6 of 13 Enterococcus isolates that were identified as E. faecium by API20Strep typing. msrC was detected in 10 enterococcal isolates but the detection of msrC was not associated with phenotypic resistance. msrC negative isolates were reclassified as Enterococcus mundtii based on sequencing of housekeeping genes. Resistance to erythromycin and pirlimycin (MIC > 16microg/ml) was detected in 4 of 4 Streptococcus dysgalactiae and 12 of 20 Streptococcus uberis isolates and was encoded by ermB. All Streptococcus isolates tested negative for ermA, ermC, mefA/E and msrA/C. Among ermB positive streptococci, three alleles were identified based on a 527 bp gene fragment. Each allele was detected in at least two herds. The same alleles have also been detected in other bacterial species from bovine and non-bovine hosts and farm soil, suggesting a theoretical potential for horizontal transfer of macrolide resistance genes on dairy farms.

Ribotyping of Streptococcus uberis from a dairy's environment, bovine feces and milk

Streptococcus uberis is a major cause of bovine mastitis and infections commonly result from environmental exposure to the pathogen. To identify specific sources of mastitis-causing S. uberis strains, samples were collected monthly from the environment and feces of dry cows in a grazing herd. Environmental and fecal strains of S. uberis were compared to those found in milk. S. uberis was detected in 63% of 94 environmental samples, including water, soil, plant matter, bedding material, flies, and hay, in 23% of 107 fecal samples, and in 4% of 787 milk samples. Automated PvuII ribotyping revealed 48 ribotypes among 266 isolates. Per sample, up to five ribotypes were detected. The distribution of ribotypes did not differ significantly among environmental, fecal and milk samples. Specific environmental sources or strains of udder-pathogenic S. uberis were not identified. Fecal shedding was not persistent and did not differ between dry-off and calving. The proportion of fecal samples containing S. uberis was highest during the summer grazing season. S. uberis was common in farm soil (31 of 35 samples) but not in non-farm soil (0 of 11 samples). We hypothesize that fecal shedding of S. uberis may play a role in maintenance of S. uberis populations in the dairy ecosystem.

Multilocus sequence typing of Streptococcus uberis provides sensitive and epidemiologically relevant subtype information and reveals positive selection in the virulence gene pauA

Control of the bovine mastitis pathogen Streptococcus uberis requires sensitive and epidemiologically meaningful subtyping methods that can provide insight into this pathogen's epidemiology and evolution. Development of a multilocus sequence typing (MLST) scheme based on six housekeeping and virulence genes allowed differentiation of 40 sequence types among 50 S. uberis isolates from the United States (n = 30) and The Netherlands (n = 20). MLST was more discriminatory than EcoRI or PvuII ribotyping and provided subtype data with better epidemiological relevance, e.g., by discriminating isolates with identical ribotypes obtained from different farms. Phylogenetic analyses of MLST data revealed indications of reticulate evolution between genes, preventing construction of a core phylogeny based on concatenated DNA sequences. However, all individual gene phylogenies clearly identified a distinct pauA-negative subtaxon of S. uberis for which housekeeping alleles closely resembled those of Streptococcus parauberis. While the average GC content for five genes characterized was between 0.38 and 0.40, pauA showed a considerably lower GC content (0.34), suggesting acquisition through horizontal transfer. pauA also showed a higher nonsynonymous/synonymous rate ratio (dN/dS) (1.2) compared to the other genes sequenced (dN/dS < 0.12), indicating positive selection in this virulence gene. In conclusion, our data show that (i) MLST provides for highly discriminatory and epidemiologically relevant subtyping of S. uberis; (ii) S. uberis has a recombinatorial population structure; (iii) phylogenetic analysis of MLST data reveals an S. uberis subtaxon resembling S. parauberis; and (iv) horizontal gene transfer and positive selection contribute to evolution of certain S. uberis genes, such as the virulence gene pauA.

Identification of Streptococcus canis isolated from milk of dairy cows with subclinical mastitis

Streptococcus canis was isolated from 31 milk samples from 11 cows in a dairy herd (with 49 lactating cows) affected by subclinical mastitis in north Rhine-Westphalia, Germany. Thirty-one isolates from the infected udder quarters were further characterized for their phenotypic and molecular properties. Most isolates (83.9%) produced alpha-galactosidase, and all were negative for beta-d-glucuronidase. Amplification of the 16S rRNA gene by the PCR method and digestion with the restriction enzymes RsaI, MspI, and AvaII yielded species-specific patterns. Additional identification by species-specific amplification of the 16S rRNA gene, the 16S-23S rRNA gene intergenic spacer region, the CAMP factor-encoding gene cfg, and the internal fragments of the sodA gene was consistent with S. canis. Macrorestriction analysis of the chromosomal DNA by pulsed-field gel electrophoresis showed that the S. canis isolates originated from a single clone or were very closely related.

Multiplex polymerase chain reaction for identification and differentiation of Streptococcus equi subsp. zooepidemicus and Streptococcus equi subsp. equi

The closely related streptococcal species Streptococcus equi subsp. zooepidemicus and S. equi subsp. equi were identified by polymerase chain reaction using oligonucleotide primers designed according to species-specific parts of the superoxide dismutase A encoding gene sodA. A further differentiation of both subspecies could be performed by amplification of the genes seeH and seeI encoding the exotoxins SeeH and SeeI, respectively, which could be detected for S. equi subsp. equi but not for S. equi subsp. zooepidemicus. A further simplification of the identification and differentiation of both subspecies was conducted by sodA-seeI multiplex polymerase chain reaction.

Determination of species-specific sequences of superoxide dismutase A encoding gene sodA and chaperonin 60 encoding gene cpn60 for identification and phylogenetic analysis of Streptococcus phocae

Species-specific PCR tests, based on the manganese-dependent superoxide dismutase A encoding gene (sodA) and the chaperonin 60 encoding gene (cpn60), were developed for the identification of Streptococcus phocae, a bacterial pathogen of seals. The selection of both oligonucleotide primer pairs was performed after amplification and sequencing of internal parts of both genes using universal oligonucleotide primers. The sequence studies of both genes additionally confirmed that S. phocae could taxonomically be classified to the pyogenic group of the genus Streptococcus.

Polymerase chain reaction mediated identification of Streptococcus uberis and Streptococcus parauberis using species-specific sequences of the genes encoding superoxide dismutase A and chaperonin 60*

Streptococcus uberis, a well-known bacterial pathogen associated with bovine mastitis, appears to be biochemically and serologically almost indistinguishable from the closely related species Streptococcus parauberis. In the present study, species-specific oligonucleotide primers were designed using internal parts of the genes sodA, encoding superoxide dismutase A, and cpn60 encoding chaperonin 60 of S. uberis and S. parauberis, respectively. The two oligonucleotide primer pairs allowed a rapid and reliable PCR-mediated identification and differentiation of both species. These studies, performed with S. uberis and S. parauberis reference cultures and clinical isolates from routine diagnostics, revealed that the occurrence of S. parauberis as causative agent of bovine mastitis appears to be rare. In addition the sodA and cpn60 sequence data confirmed that both species could taxonomically be classified to the pyogenic group of genus Streptococcus.

Identification of Streptococcus dysgalactiae strains of Lancefield's group C, G and L by polymerase chain reaction

Streptococcus dysgalactiae serogroup C, G and L strains were investigated by polymerase chain reaction (PCR) using oligonucleotide primers designed according to species-specific parts of the 16S-23S rDNA intergenic spacer region. The oligonucleotide primers with specificity for the 16S-23S rDNA intergenic spacer region allowed a correct identification of all S. dysgalactiae serogroups C, G and L strains investigated. No cross-reactivities could be observed with any of the control strains indicating the usefulness of PCR-technology to identify the serologically heterogeneous species S. dysgalactiae.

Inter- and intraspecies variations of the 16S-23S rDNA intergenic spacer region of various streptococcal species

The 16S-23S rDNA intergenic spacer regions (ISR) of different streptococcal species and subspecies were amplified with primers derived from the highly conserved flanking regions of the 16S rRNA and 23S rRNA genes. The single sized amplicons showed a uniform pattern for S. agalactiae, S. dysgalactiae subsp. dysgalactiae (serogroup C), S. dysgalactiae subsp. equisimilis (serogroup G), S. dysgalactiae subsp. dysgalactiae (serogroup L), S. canis, S. phocae, S. uberis, S. parauberis, S. pyogenes and S. equi subsp. equi, respectively. The amplicons of S. equi subsp. zooepidemicus, S. porcinus and S. suis appeared with 3, 5 and 3 different sizes, respectively. ISR of selected strains of each species or subspecies investigated were sequenced and multiple aligned. This allowed a separation of ISR into regions, with 7 regions for S. agalactiae, S. dysgalactiae subsp. dysgalactiae (serogroup C), S. dysgalactiae subsp. equisimilis (serogroup G), S. dysgalactiae subsp. dysgalactiae (serogroup L), S. canis, S. phocae, S. pyogenes and S. suis, 8 regions for S. uberis and S. parauberis and mostly 9 regions for S. equi subsp. equi, S. equi subsp. zooepidemicus and S. porcinus. Region 4, encoding the transfer RNA for alanine (tRNA(Ala)), was present and identical for all isolates investigated. The size and sequence of ISR appears to be a unique marker for streptococci of various species and subspecies and could be used for bacterial identification. In addition the size and sequence variations of ISR of S. equi subsp. zooepidemicus, S. porcinus and S. suis allows a molecular typing of isolates of these species possibly useful in epidemiological aspects.

The hyaluronic acid capsule of Streptococcus uberis is not required for the development of infection and clinical mastitis

The frequency at which the genes responsible for capsule biosynthesis occurred in field isolates of Streptococcus uberis was determined. Of the two genotypes detected (hasABC and hasC), the capsular genotype (hasABC) was more common. This genotype was present at a higher frequency in a population isolated from mastitis cases than in a population isolated from cattle bedding. The virulence of a mutant strain of S. uberis (TRF0-6) that lacked the ability to produce a hyaluronic acid capsule due to an insertion within its single copy of hasA (P. N. Ward, T. R. Field, W. G. F. Ditcham, E. Maguin, and J. A. Leigh, Infect. Immun. 69:392-399, 2001) was compared to that of the capsular parental strain (0140J). Strains TRF0-6 and 0140J infected all mammary gland quarters following experimental challenge. The wild type and the mutant induced overt signs of disease in four out of four and in six out of eight mammary gland quarters, respectively. Both the wild type and the hasA mutant were resistant to killing by bovine neutrophils following cultivation in bovine milk. The ability to withstand the bactericidal action of neutrophils following growth in milk was therefore independent of the capsule and coincided with the ability of supernatants from such cultures to prevent the bactericidal action of neutrophils. This investigation revealed that, in the absence of the capsule, S. uberis is able to withstand the bactericidal effect of bovine neutrophils and induce mastitis in dairy cows.

Rapid identification, differentiation, and proposed new taxonomic classification of Bifidobacterium lactis

Identification of Bifidobacterium lactis and Bifidobacterium animalis is problematic because of phenotypic and genetic homogeneities and has raised the question of whether they belong to one unique taxon. Analysis of the 16S-23S internally transcribed spacer region of B. lactis DSM10140(T), B. animalis ATCC 25527(T), and six potential B. lactis strains suggested two distinct clusters. Two specific 16S-23S spacer rRNA gene-targeted primers have been developed for specific detection of B. animalis. All of the molecular techniques used (B. lactis or B. animalis PCR primers, enterobacterial repetitive intergenic consensus PCR) demonstrated that B. lactis and B. animalis form two main groups and suggest a revision of the strains assigned to B. animalis. We propose that B. lactis should be separated from B. animalis at the subspecies level.

16S-23S rDNA intergenic spacer region polymorphism of Lactococcus garvieae, Lactococcus raffinolactis and Lactococcus lactis as revealed by PCR and nucleotide sequence analysis

The intergenic spacer region (ISR) between the 16S and 23S rRNA genes was tested as a tool for differentiating lactococci commonly isolated in a dairy environment. 17 reference strains, representing 11 different species belonging to the genera Lactococcus, Streptococcus, Lactobacillus, Enterococcus and Leuconostoc, and 127 wild streptococcal strains isolated during the whole fermentation process of "Fior di Latte" cheese were analyzed. After 16S-23S rDNA ISR amplification by PCR, species or genus-specific patterns were obtained for most of the reference strains tested. Moreover, results obtained after nucleotide analysis show that the 16S-23S rDNA ISR sequences vary greatly, in size and sequence, among Lactococcus garvieae, Lactococcus raffinolactis, Lactococcus lactis as well as other streptococci from dairy environments. Because of the high degree of inter-specific polymorphism observed, 16S-23S rDNA ISR can be considered a good potential target for selecting species-specific molecular assays, such as PCR primer or probes, for a rapid and extremely reliable differentiation of dairy lactococcal isolates.