Emerg Infect DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention20031055287435609-063210.3201/eid1601.090632DispatchHuman Group A Streptococci Virulence Genes in Bovine Group C StreptococciHuman GAS Virulence Genes in Bovine GCSRatoMárcia G.BexigaRicardoNunesSandro F.VilelaCristina L.Santos-SanchesIldaUniversidade Nova de Lisboa, Caparica, Portugal (M.G. Rato, I. Santos-Sanches)Universidade Técnica de Lisboa, Lisbon, Portugal (R. Bexiga, S.F. Nunes, C.L. Vilela)Cambridge University, Cambridge, UK (S.F. Nunes)Address for correspondence: Ilda Santos-Sanches, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal; email: isanches@fct.unl.pt12010161116119

Phage-encoded virulence genes of group A streptococci were detected in 10 (55.6%) of 18 isolates of group C streptococci that had caused bovine mastitis. Bovine isolates carried other genetic determinants, such as composite transposon Tn1207.3/Φ10394.4 (100%) and antimicrobial drug resistance genes erm(B)/erm(A) (22.2%), linB (16.6%), and tet(M)/tet(O) (66.7%), located on mobile elements.

Keywords: Bovine mastitislysogenyprophagessuperantigensStreptococcus pyogenesStreptococcus dysgalactiae subsp. dysgalactiaebacteriavirusesdispatch

Strains of Streptococcus dysgalactiae subsp. dysgalactiae are described as α-hemolytic or nonhemolytic (Lancefield group C) and associated only with animal infections (bovine mastitis), a disease with major economic consequences for the dairy industry (1). Group A streptococci (GAS)–specific phage-associated virulence determinants encoding pyrogenic exotoxins or superantigens (speM, ssa), which are strongly associated with severe diseases such as scarlet fever, streptococcal toxic shock syndrome, and rheumatic fever, have been described among human group C streptococci (GCS) or group G streptococci (GGS) (S. dysgalactiae subsp. equisimilis) (2) but not among α-hemolytic GCS (S. dysgalactiae subsp. dysgalactiae) of bovine origin. In contrast, M protein or M-like proteins were found in human GGS/GCS (S. dysgalactiae subsp. equisimilis) and in animal GCS (S. dysgalactiae subsp. dysgalactiae) but only in β-hemolytic strains (3).

Composite transposons and other genetic determinants also considered to be located in specific mobile elements such as macrolide (either encoding methylases [erm genes] or efflux pumps [mef genes]) and tetracycline resistance determinants (tet genes) have been found among streptococcal species of human origin. We studied a collection of field isolates of bovine GCS S. dysgalactiae subsp. dysgalactiae to search for genetic determinants, particularly those carried by mobile elements known to be transferred among human GAS and GGS/GCS.

The Study

We studied 18 α-hemolytic S. dysgalactiae subsp. dysgalactiae field isolates of Lancefield group C that had caused bovine subclinical mastitis. Isolates were obtained from 304 milk samples of 248 cows from 8 farms in Portugal that were included in the study. Detailed information regarding isolation methods and identification of field isolates by biochemical methods was described in a study of the subclinical mastitis–associated pathogen S. uberis (4). To confirm identification of S. dysgalactiae subsp. dysgalactiae, the 16S rRNA gene was amplified by PCR and sequenced (5). SmaI/cfr9I-digested DNA banding patterns were obtained by pulsed-field gel electrophoresis for clone identification as described (4).

All genes analyzed by PCR are shown in the Appendix Table. The emm gene subtyping was performed as described (www.cdc.gov/ncidod/biotech/strep/M-ProteinGene_typing.htm). Primers used and conditions for PCR were essentially as described elsewhere (Appendix Table).

Samples without DNA and strains lacking (negative) or carrying (positive) specific genes were used as controls in the PCR. Results were consistent in 2 or 3 PCRs that included these controls. Sequencing of all virulence gene amplicons was performed with the same primers used for amplification (STAB-Vida, Lisbon, Portugal). All sequences were compared with sequences in GenBank by using the BLAST alignment tool (www.ncbi.nlm.nih.gov/BLAST).

Antimicrobial drug resistance against macrolides (erythromycin), lincosamides (pirlimycin), and tetracycline was determined as described (10). Macrolide resistance phenotypes identified were M (resistance to macrolides) and MLSB (resistance to macrolides, lincosamides and streptogramins B).

We detected bacteriophage-associated virulence genes speM, speK, speC, spd1, and speL. Overall, speM was found in 10 (55.6%) of 18 bovine GCS isolates, speK in 9 (50%), speC and spd1 in 6 (33%), and speL in 4 (22.2%). All but 1 of the PCR products showed expected sizes (Appendix Table). Tn1207.3/Φ10394.4 composite transposon left junction amplicon showed a size of 380 bp instead of 453–6,807 bp as described for GAS (9). No amplification was observed for the right junction of this genetic element.

The emm gene encoding the antiphagocytic M surface protein was not amplified in any of the 18 bovine GCS isolates; therefore, no emm types were obtained. Subsets of isolates were erythromycin and pirlimycin resistant (MLSB phenotype) and contained erm(B) or erm(A) genes (22.2%) or erythromycin susceptible and pirlimycin resistant and contained the linB gene (16.6%). All isolates were tetracycline resistant with a subset (66.7%) carrying tet(M) or tet(O) tetracycline resistance determinants. Distribution of bacteriophage-associated virulence genes and other characteristics of strains are shown in Figure 1.

Dendrogram and pulsed-field gel electrophoresis (PFGE) profiles of group C streptococci (Streptococcus dysgalactiae subsp. dysgalactiae) subclinical mastitis isolates from 8 dairy herds, Portugal. PFGE type-subtype, virulence genotype, antimicrobial drug resistance phenotypes, and genotypes of each isolate are indicated. The dendrogram was produced by using Dice coefficients and unweighted pair group method using arithmetic averages. Default clustering settings of 0.00% optimization (i.e., the relative distance an entire lane is allowed to shift in matching attempts) and 1.5% band position tolerance were used. *All isolates were negative for speA, ssa, speH, speJ, speI, and slaA genes and for Tn1207.3/Φ10394.4 element right junction tested by PCR; **All isolates were negative for mefA, tet(T), tet(W), tet(L), tet(Q), tet(S) and tet(K) genes tested by PCR; TET, resistance only to tetracycline; MLSB-TET, resistance to macrolides, lincosamides, streptogramin B, and TET; L-TET, susceptibility to macrolides and resistance to lincosamides (L phenotype) and TET; Tn1207.3 LJ, Tn1207.3/Φ10394.4 element left junction. Clusters are shown in roman numerals on the right.

Sequences of all virulence genes were compared by using the BioEdit sequence alignment editor (www.mbio.ncsu.edu/BioEdit/bioedit.html). One different allele was found for each of the following gene sequences: spd1 (among 6 strains), speC (among 6 strains), and speL (among 4 strains). Two alleles were found for speK (among 9 strains) (speK-1 and speK-2), and 4 alleles were found for speM gene sequences (among 10 strains) (speM-1, speM-2, speM-3, and speM-4). Bovine alleles had sizes of 386 bp (spd1), 222 bp (speC), 444 bp (speL), 232 bp (speK), and 357 bp (speM). Examples of alignments between bovine virulence gene alleles with sequences from GenBank (only most similar ones) are shown in Figure 2.

Alignments of bovine group C streptococci (Streptococcus dysgalactiae subsp. dysgalactiae) alleles of virulence genes from 8 dairy herds, Portugal, with sequences from the National Center for Biotechnology (Bethesda, MD, USA) database showing base differences between sequences. The alignments were created by using BioEdit sequence alignment editor (www.mbio.ncsu.edu/BioEdit/bioedit.html). Nucleotide differences are shown in boldface. A) spd1 (99% maximum identity); B) speK (99% maximum identity); C) speC (99% maximum identity); D) speL–szeM (99% maximum identity); E) speL (97% maximum identity; F) speM alleles 1, 2, and 3–szeL (98%–99% maximum identity); G) speM allele 4 (98% maximum identity). S. equi. zoo., S. equi subsp. zooepidemicus.

Conclusions

Using PCR, we determined that bovine GCS S. dysgalactiae subsp. dysgalactiae strains (55.6%) carried >1 GAS-specific bacteriophage virulence-associated genes (spd1, speC, speK, speL, and speM). This finding suggested that bacteriophages may also play a role in the genetic plasticity and virulence of animal GCS.

The speL allele from bovine strains showed higher similarity with the szeM allele (99% maximum identity) from S. equi subsp. zooepidemicus than with the speL allele (97% maximum identity) from S. pyogenes. The szeM gene encodes a superantigen in S. equi subsp. zooepidemicus, which is primarily a pathogen of nonhuman animal species. This organism causes mastitis in cows and mares and is most frequently found in horses (14). We also observed that 3 of the speM alleles found among bovine strains (speM-1, speM-2, and speM-3) also showed higher similarity with superantigen-encoding gene szeL from S. equi subsp. zooepidemicus than with speM gene sequence from S. pyogenes. Another allele (speM-4) showed higher similarity with the sdm gene from S. dysgalactiae subsp. dysgalactiae than with the speM gene from S. pyogenes.

The remaining alleles (spd1, speC, speK-1, and speK-2) from the GCS S. dysgalactiae subsp. dysgalactiae bovine strains showed high similarity with S. pyogenes superantigen genes (98%–99% maximum identity). This finding supports our hypothesis that GAS prophages may play a role in the genetic plasticity of this pathogen. The speC and spd1 genes are known to be localized on the same GAS prophage (15), and both genes were detected in 6 bovine GCS S. dysgalactiae subsp. dysgalactiae isolates in our study.

None of 18 α-hemolytic group C S. dysglacatiae subsp. dysgalactiae bovine isolates in this study were typed by emm-typing because amplification products in the PCR specific for the M surface protein gene emm were not obtained. This result is consistent with those of a report that β-hemolytic, but not α-hemolytic, group C S. dysglacatiae subsp. dysgalactiae isolates of animal origin contained the emm gene (3).

Amplification (380-bp product) of the left junction of the composite transposon in bovine isolates suggests that this mobile element may be inserted in a similar location, the comEC locus, as mapped in S. pyogenes and S. dysglactiae subsp. equisimilis. Absence or unexpected PCR products specific for any of the junctions of this element have been reported in other studies and attributed to possible lack of homology between the target and primers used (9). Detection of the linB gene carried by a large conjugative plasmid (13) in 3 of 18 bovine GCS S. dysgalactiae subsp. dysgalactiae isolates is indicative of horizontal gene transfer.

Our findings indicate that α-hemolytic bovine GCS isolates, which are known to be environmental or contagious pathogens and a cause of bovine mastitis, may be reservoirs of virulence genes encoded by prophages of human-specific GAS. These genes encode exotoxins, superantigens, and streptodornases, which are responsible for GAS virulence and pathogenesis, and may be transferred to other streptococci of human origin by horizontal genetic transfer. Therefore, α-hemolytic isolates should not be disregarded as putative infectious disease agents in humans.

Supplementary MaterialAppendix Table

Genes analyzed by PCR and primers used, for group C streptococci, from 8 dairy herds, Portugal

Suggested citation for this article: Rato MG, Bexiga R, Nunes SF, Vilela CL, Santos-Sanches I. Human group A streptococci virulence genes in bovine group C streptococci. Emerg Infect Dis [serial on the Internet]. 2010 Jan [date cited]. Available from http://www.cdc.gov/EID/content/16/1/116.htm

This study was supported by grant POCTI/ESP/48407/2002 (Fundação para a Ciência e Tecnologia, Portugal) and Fundo Europeu de Desenvolvimento Regional Project PROC 60839 (Fundação Calouste Gulbenkian, Portugal, Project Faculdade de Medicina Veterinária de Lisboa/46; Bovine mastitis: epidemiology, prophylactic and therapeutic approaches; Centro de Investigação Interdisciplinar em Sanidade Animal/Faculdade de Medicina Veterinária, Universidade Técnica de Lisboa, Portugal). M.G.R. was supported by PhD grant SFRH/BD/32513/2006 (Fundação para a Ciência e Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior).

Ms Rato is a doctoral candidate in the Department of Life Sciences of the Faculty of Science and Technology, New University of Lisbon, Caparica, Portugal. Her research interests include epidemiology, antimicrobial drug resistance, and virulence mechanisms of streptococci from animal and human origin.

ReferencesVieira VV, Teixeira LM, Zahner V, Momen H, Facklam RR, Steigerwalt AG, Genetic relationships among the different phenotypes of Streptococcus dysgalactiae strains.Int J Syst Bacteriol 1998;48:123143 10.1099/00207713-48-4-12319828425Igwe EI, Shewmaker PL, Facklam RR, Farley MM, van Beneden C, Beall B Identification of superantigen genes speM, ssa, and smeZ in invasive strains of beta-hemolytic group C and G streptococci recovered from humans.FEMS Microbiol Lett 2003;229:25964 10.1016/S0378-1097(03)00842-514680708Zhao J, Hayashi T, Saarinen S, Papageorgiou AC, Kato H, Imanishi K, Cloning, expression, and characterization of the superantigen streptococcal pyrogenic exotoxin G from Streptococcus dysgalactiae.Infect Immun 2007;75:17219 10.1128/IAI.01183-0617283088Rato MG, Bexiga R, Nunes SF, Cavaco LM, Vilela CL, Santos-Sanches I Molecular epidemiology and population structure of bovine Streptococcus uberis.J Dairy Sci 2008;91:454251 10.3168/jds.2007-090719038929Weisburg WG, Barns SM, Pelletier DA, Lane DJ 16S ribosomal DNA amplification for phylogenetic study.J Bacteriol 1991;173:6977031987160Pires R, Rolo D, Mato R, Feio de Almeida J, Johansson C, Henriques-Normark B, Resistance to bacitracin in Streptococcus pyogenes from oropharyngeal colonization and noninvasive infections in Portugal was caused by two clones of distinct virulence genotypes.FEMS Microbiol Lett 2009;296:23540 10.1111/j.1574-6968.2009.01642.x19486163Lintges M, Arlt S, Uciechowski P, Plümäkers B, Reinert RR, Al-Lahham A, A new closed-tube multiplex real-time PCR to detect eleven superantigens of Streptococcus pyogenes identifies a strain without superantigen activity.Int J Med Microbiol 2007;297:4718 10.1016/j.ijmm.2007.03.01517481952Green NM, Beres SB, Graviss EA, Allison JE, McGeer AJ, Vuopio-Varkila J, Genetic diversity among type emm28 group A Streptococcus strains causing invasive infections and pharyngitis.J Clin Microbiol 2005;43:408391 10.1128/JCM.43.8.4083-4091.200516081955Figueiredo TA, Aguiar SI, Melo-Cristino J, Ramirez M DNA methylase activity as a marker for the presence of a family of phage-like elements conferring efflux-mediated macrolide resistance in streptococci.Antimicrob Agents Chemother 2006;50:368994 10.1128/AAC.00782-0616954322Pires R, Rolo D, Gama-Norton L, Morais A, Lito L, Salgado MJ, Group A streptococci from carriage and disease in Portugal: evolution of antimicrobial resistance and T antigenic types during 2000–2002.Microb Drug Resist 2005;11:36070 10.1089/mdr.2005.11.36016359196Ng L-K, Martin I, Alfa M, Mulvey M Multiplex PCR for the detection of tetracycline resistant genes.Mol Cell Probes 2001;15:20915 10.1006/mcpr.2001.036311513555Aminov RI, Garrigues-Jeanjean N, Mackie RI Molecular ecology of tetracycline resistance: development and validation of primers for detection of tetracycline resistance genes encoding ribosomal protection proteins.Appl Environ Microbiol 2001;67:223 10.1128/AEM.67.1.22-32.200111133424Bozdogan B, Berrezouga L, Kuo MS, Yurek DA, Farley KA, Stockman BJ, A new resistance gene, linB, conferring resistance to lincosamides by nucleotidylation in Enterococcus faecium HM1025.Antimicrob Agents Chemother 1999;43:925910103201Alber J, El-Sayed A, Estoepangestie S, Lämmler C, Zschöck M Dissemination of the superantigen encoding genes seeL, seeM, szeL and szeM in Streptococcus equi subsp. equi and Streptococcus equi subsp. zooepidemicus.Vet Microbiol 2005;109:13541 10.1016/j.vetmic.2005.05.00115953700Banks DJ, Beres SB, Musser JM The fundamental contribution of phages to GAS evolution, genome diversification and strain emergence.Trends Microbiol 2002;10:51521 10.1016/S0966-842X(02)02461-712419616