Identification of Staphylococcus aureus, S. intermedius and S. hyicus by PCR amplification of coa and nuc genes

Identificação de Staphylococcus aureus, S. intermedius e S. hyicus através de seqüências dos genes coa e nuc

FOOD MICROBIOLOGY

Identification of Staphylococcus aureus, S. intermedius and S. hyicus by PCR amplification of coa and nuc genes

Identificação de Staphylococcus aureus, S. intermedius e S. hyicus através de seqüências dos genes coa e nuc

Wladimir Padilha da Silva^I; Jorge Adolfo Silva^II; Márcia Raquel Pegoraro de Macedo^I; Márcia Ribeiro de Araújo^I; Márcia Magalhães Mata^I; Eliezer Avila Gandra^I

^ILaboratório de Microbiologia de Alimentos, Departamento de Ciências e Tecnologia Agro-industrial, Faculdade de Agronomia Eliseu Maciel, Universidade Federal de Pelotas, Pelotas, RS, Brasil

^IILaboratório de Biotecnologia de Alimentos, Departamento de Ciências e Tecnologia Agro-industrial, Faculdade de Agronomia Eliseu Maciel, Universidade Federal de Pelotas, Pelotas, RS, Brasil

^{Correspondence}

ABSTRACT

Sixty-five strains of coagulase positive staphylococci (Staphylococcus aureus, S. intermedius and S. hyicus) were identified at species level by PCR amplification of the coa gene, specific for S. aureus, and of the nuc gene, specific for S. intermedius and for S. hyicus.

Key words: coagulase positive staphylococci, PCR, coa gene, nuc gene.

RESUMO

Sessenta e cinco cepas de estafilococos coagulase positiva foram identificadas em nível de espécie, através da amplificação, por PCR, de seqüências do gene coa, específicas para S. aureus, e do gene nuc, específicas para S. intermedius e para S. hyicus.

Palavras-chave: estafilococos coagulase positiva, PCR, gene coa, gene nuc.

INTRODUCTION

S. aureus, S. hyicus and S. intermedius are species of staphylococcus associated with food intoxication outbreaks (5) that present very similar phenotypic characteristics, which makes the identification and differentiation through traditional culture techniques defficult (5,7). Despite the recommendation for the use of methods based on the polymerase chain reaction (PCR) to select pathogens among other bacterial species (2), very limited research using molecular methods to differentiate S. aureus, S. hyicus and S. intermedius has been reported. This work ained to evaluate the amplification of the gene sequences of coa and nuc for the identification of S. aureus, S. intermedius and S. hyicus.

MATERIALS AND METHODS

Sixty-five strains previously characterized as coagulase positive staphylococci (CPS) and identified as S. aureus (55 strains), S. intermedius (4 strains) and S. hyicus (6 strains) were used. The genomic DNA extraction from all strains was done according to the protocol proposed by Matthews et al. (6). The primers used in the PCR were: COAG2 and COAG3, specific for the coa gene of S. aureus; NUC1 and NUC2, specific for the nuc gene of S. intermedius and NUC3 and NUC4, specific for the nuc gene of S. intermedius (Table 1).

The PCR reactions were prepared with 20 nM of extracted DNA, 1 µM of each primer, 200 µM of each triphosphate desoxinucleotide (dNTP, Gibco BRL), 1 U of Taq DNA Polymerase (Pharmacia, 5 U.µL^-1), 2 mM of MgCl₂ (Pharmacia) and 4 µL of 10 X buffer (Pharmacia), making a total volume of 40 µL. The program consisted of 50 seconds at 95ºC, 2 minutes at 55ºC (for primers COAG) or at 42ºC (for primers NUC) and 4 minutes at 72ºC, for 40 cycles (4). The electrophoresis was performed in agarose gel (p/v) stained with 0.5 mg.mL^-1 of ethidium bromide. The size of the amplified fragments was determined under UV light, through comparison with the molecular weight standard (1 Kb Plus DNA Ladder or 100 bp DNA Ladder, Gibco BRL).

RESULTS AND DISCUSSION

It was verified that COAG2 and COAG3 primers showed specificity for S. aureus, as amplifications were obtained in all the reactions in which DNA from this species (3) was used (Fig. 1). These results are in accordance with Aarestrup et al. (1), who studied the amplification of sequences of the coa gene in 187 strains of S. aureus, 10 strains of S. intermedius, 3 strains of S. hyicus, 1 strain of S. delphini and 1 strain of S. schleiferi subspecies coagulans and verified the presence of bands only in S. aureus. The variability in the size of the amplified fragments with primers COAG2 e COAG3 may be due to the existence of structurally different gene forms of coagulase in S. aureus, allowing one strain to produce one or more of these variants (4). However, the reason for this polymorphism is not clear yet (4).

NUC1 and NUC2 primers demonstrated to be specific for S. hyicus, as there was amplification only when the DNA from this microorganism was used (Fig. 1). Although these results refer only six strains of S. hyicus, the observed specificity indicates that these primers have potential to be used in the differentiation between this species and S. aureus and S. intermedius.

A great variability in the size of the amplified fragments obtained with NUC3 and NUC4 primers was verified. However, the expected fragment (431 bp) was always obtained when the DNA from S. Intermedius was submitted to amplification (Fig. 1). This polymorphism may be related to the conditions used for the PCR, which could be enabling unspecific amplifications or, also allowing the primers to attach to other genes with similar sequences or partially homologous. Despite the small number of strains tested, these results showed that these primers have potential to be used in CPS identification and differentiation studies, but conditions of the reaction still need to be optimized.

ACKNOWLEDGEMENT

This work was supported by Capes and CNPq/Pibic schoolarship.

This paper corresponds to an "extended abstract" selected for oral presentation in the 22^nd Brazilian Congress of Microbiology, held in Florianópolis, SC, Brazil, in November 17-20, 2003

References

• 1. Aarestrup, F.M.; Wegener, H.C.; Rosdahl, V.T. Evaluation of phenotypic and genotypic methods for epidemiological typing of Staphylococcus aureus isolates from bovine mastitis in Denmark. Vet. Microbiol., 45:139-150, 1995.
• 2. Farber, J.M.; Gendel, S.M.; Tyler, K.D.; Boerlin, P.; Landry, W.L.; Fritschel, S.J.; Barrett, T.J. Molecular typing and differentiation. In: Compendium of methods for the microbiological examination of foods APHA, Washington, 2001. p.127-158.
• 3. Gandra, E.A. Identificação de Staphylococcus aureus, S. hyicus e S. intermedius através de testes bioquímicos e da amplificação por PCR de sequências dos genes coa e nuc. (Dissertação de mestrado, Universidade Federal de Pelotas). Pelotas, 2003, p.101.
• 4. Goh, S.H.; Byrne, S.K.; Zhang, J.L.; Chow, A.W. Molecular typing of Staphylococcus on the basis of coagulase gene polymorphism. J. Clin. Microbiol., 30:1642-1645, 1992.
• 5. Kloos, W.E.; Bannerman, T.L. Staphylococcus and Micrococcus In: Murray, P.R.; Baron, E.J.; Pfaller, M.A.; Tenover, F.C.; Yolken, R.H. Manual of Clinical Microbiology ASM, Washington, 1999. p.264-282.
• 6. Matthews, K.R.; Roberson, J.; Gillespie, B.E.; Luther, D.A.; Oliver, S.P. Identificação and differentiation of coagulase-negative Staphylococcus aureus by polymerase chain reaction. J. Food Prot., 60:686-688, 1997.
• 7. Roberson, J.R.; Fox, L.K.; Hancock, D.D.; Besser, T.E. Evaluation of methods for differentiation of coagulase-positive Staphylococci. J. Clin. Microbiol., 30:3217-3219, 1992.

Publication Dates

• Publication in this collection
  30 Nov 2004
• Date of issue
  Nov 2003