Staphylococci from Dental Personnel

Maria Lúcia PEREIRA1
Luiz Simeão do CARMO1
Marcelo Quiroga SOUKI2
Elisângela José dos SANTOS1
Maria Auxiliadora Roque de CARVALHO2
Merlin S. BERGDOLL3

1Fundação Ezequiel Dias, Belo Horizonte, MG, Brasil
2ICB, Universidade Federal de Minas Gerais, MG, Brasil
3Food Research Institute, University of Wisconsis-Madison, Madison, WI, USA


Braz Dent J (1999) 10(1): 1-60 ISSN 0103-6440

| Introduction | Material and Methods | Results and Discussion | Conclusions | Acknowledgments | References |


Thirty dental students and five professors were cultured in nares, throat, and hands for the presence of staphylococci. Twenty-four students and two professors were colonized with staphylococci that were classified as S. aureus. Twelve students and one professor were colonized with staphylococci that produced enterotoxin. Care needs to be taken to avoid contaminating patients during dental examination, particularly during any type of surgery.


Key Words: dental personnel, staphylococci, enterotoxin.


Introduction

    Transfer of disease-causing microorganisms from medical personnel to patients is a problem in any type of health establishment. Although it is particularly troublesome in hospitals where patients are there because of health problems, it is also of concern in dental clinics where patients are normally healthy individuals (Autio et al., 1980; Reader et al., 1994; Horiba et al., 1995). Dissemination of microorganisms during operative procedures represents a hazard for both patients and dental practitioners as it is not unusual for either the medical personnel or the patients to be colonized with disease-forming organisms, such as staphylococci (Wyman et al., 1978; Alacam et al., 1995), that can be carried in the nasal passages, throat, or on the hands (Zelante et al., 1982; Salvador et al., 1989; Molinari and Molinari, 1992; Pereira et al., 1994). Although it is possible for both coagulase-positive and -negative staphylococci species to cause disease, especially in hospitals, they normally do not cause problems in dental practice unless they produce an infection after dental surgery. If disease-producing staphylococci are transferred to the patient during a dental procedure, such as conventional endodontic treatment, tooth extraction or other surgery, an infection may result; the more virulent the staphylococci, the more serious the infection. Virulence and pathogenicity of staphylococci are closely related to a wide range of extracellular enzymes and toxins linked with their ability to colonize within the host and to induce lysis of phagocytic cells.
    Although staphylococcal enterotoxins (SE) are well known for their role in food poisoning, primarily due to food contamination by food handlers, few studies have been done on the importance of SE-producing staphylococci in dental practice.
    The purpose of this study was to evaluate dental personnel for coagulase-positive and -negative staphylococci with an emphasis on Staphylococcus aureus and enterotoxin production.


Material and Methods

    First, second, and third year dental students in clinical practice and professors from the Dental School of Minas Gerais of the Federal University responsible for teaching them were examined. Ten students from each group and five professors were evaluated for the presence of staphylococci. Their nares, throats, and hands were cultured using sterile swabs that were placed in a tube of tryptic soy broth (TSB, Biobrás, Montes Claros) containing 10% NaCl and incubated for 24 hours at 37ºC.
    The cultures were streaked on Baird-Parker agar (Biobrás, Montes Claros) and incubated for 48 hours at 37ºC. Five typical colonies (jet black to dark grey, smooth, convex, entire margins, off-white edge, and may show an opaque zone and/or a clear halo beyond the opaque zone) and three atypical colonies (gray and mucoid) were selected for further testing.
    Each colony was transferred to two test tubes containing 1 ml of brain heart infusion broth (BHI, Biobrás, Montes Claros) and incubated for 24 hours at 37ºC. Tests for coagulase and thermonuclease production, anaerobic fermentation of glucose and mannitol, and production of hemolysin using sheep blood were conducted (Vanderzant and Splittstoesser, 1992).
    Inocula were prepared by incubating the staphylococci in BHI overnight at 37ºC and the enterotoxin production was performed by the membrane-over-agar plate method described by Robbins et al. (1974).
    Two methods were used for enterotoxin detection: the optimum-sensitivity-plate (OSP) gel diffusion method (Robbins et al., 1974) and the reversed passive latex agglutination assay (RPLA) that is sensitive to about 0.5 ng of enterotoxin, according to Igarashi et al. (1986).


Results and Discussion

    Characteristics of both typical and atypical staphylococci varied (Table 1). Several of the typical colonies were negative for the hemolysis factor and others lacked other characteristics except glucose fermentation. Some atypical staphylococci were positive for all characteristics tested (result not shown in Table). The number of individuals colonized with staphylococci that were positive for all characteristics, except possibly hemolysin, are given in Table 2, as Staphylococcus aureus (A). The number of individuals colonized with staphylococci that tested positive for at least two of the three major characteristics of S. aureus, coagulase and thermonuclease production and anaerobic fermentation of mannitol, are given in Table 2 as S. aureus (B). They are listed as S. aureus because isolates from the same culture produced the same SE and represent the same strain (II 3- and 7-nasal, III 3-hand, Table 2). If they lacked two of these properties, they were not classified as S. aureus (III 1-hand, Table 1).
    Several papers have been published on the isolation of human carriers in Brazil (Iaria et al., 1980; Dametto et al., 1981; Zelante et al., 1982; Salvador et al., 1989; Pereira et al., 1994). In most cases the staphylococci were classified as S. aureus on the basis of coagulase production, which was the major characteristic for S. aureus classification before volume 2 of Bergey’s Manual of Systematic Bacteriology, published in 1986 (Kloos and Schleifer, 1986). Other species share this characteristic, hence, the mere production of coagulase cannot be used to classify staphylococci as S. aureus. However, most coagulase-positive staphylococci isolated from humans may be classified as S. aureus because the other coagulase-positive staphylococci are residents of animals and seldom isolated from humans. There are exceptions because two individuals were colonized with coagulase-positive staphylococci that did not fit the S. aureus (B) classification (Table 2). The use of bound coagulase and lecithinase as characteristics for classification, as was done by Salvador and Verri (1989), may be questioned as these are not listed as major identifying characteristics for S. aureus.
    The percentage of dental personnel colonized with typical S. aureus (A) (Table 2) was 54.3% which is greater than the 35.7% reported by Dametto and Zelante (1981), and much greater if only coagulase production was used to classify the staphylococci (26 + 2 of 35; 80.0%). If the 2nd classification is used, the percent colonization was 71.4% when only those colonized in the nares and/or throats are included. This compares to the 67.3% reported by Salvador et al. (1982) who used bound coagulase and lecithinase to classify staphylococci.
    A relatively high percentage (46.2%) of the strains classified as S. aureus (B) produced SE (Table 3), with only one strain not classified as S. aureus producing SE. This species is the one most likely to cause infections and if the staphylococci produce SE the result of any infection could be more serious. Only two other studies have been reported in which the staphylococci isolated in Brazil from human carriers were examined for SE production (Iaria et al., 1980; Pereira et al., 1994). In a study of hospital food handlers, only 12 (35.3%) of 34 examined were colonized with S. aureus, with only two (5.88%) of the food handlers colonized with SE-producing staphylococci (Iaria et al., 1980). In the other study, 32 (58.2%) of 55 food handlers were colonized with S. aureus, with 17 (30.9%) colonized with SE-producing staphylococci (Pereira et al., 1994), which compares to 37.1% of the 35 dental personnel colonized with SE-producing staphylococci.
    The saliva from the dental personnel was not examined in this study; however, others have found that saliva is an important carrier of S. aureus (Piochi and Zelante, 1973; Autio et al., 1980; Zelante et al., 1982). This was found to be particularly important in transfer of S. aureus to the dentist’s hands from the patients and subsequently to the dental equipment (Autio et al., 1980).
    In the present study, ten (28.6%) of the 35 dental personnel were positive for S. aureus on the hands with 4 (11.4%) of the 35 colonized with SE-producing staphylococci. Although the frequency of S. aureus on the hands was less frequent than in the nares and throat, this is of concern because of the transfer from the hands to dental equipment (Autio et al., 1980). A more serious problem is the antibiotic resistance of strains isolated from the hands, such as methicillin-resistant staphylococci (Cardoso and Teixeira, 1988; Horiba et al., 1995).
    The presence of staphylococci on the hands can be reduced and/or eliminated by careful washing of the hands and wearing of surgical gloves by dental personnel during examination of the patient (Stiles and Sheena, 1985; Field et al., 1996).


Conclusions

    1. The majority of dental personnel examined carried staphylococci that were classified as S. aureus, with many strains producing enterotoxin.
    2. Ten of the dental personnel carried staphylococci on their hands, which indicates the need for special care in the handling of dental equipment.


Acknowledgments

    This investigation was supported by Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) through Projects CBS-1129/93 and CAG-374/90. We wish to recognize the gift of the Brain Heart Infusion and other media by Biobrás-Bioquímica do Brazil, Montes Claros, State of Minas Gerais, Brazil.


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Correspondence:  Dra. Maria Lúcia Pereira, Fundação Ezequiel Dias, Caixa Postal 26, 30161-970 Belo Horizonte, MG, Brasil. Telefax: +55-31-371-9480. E-mail: funed@rodemge.gov.br/malu@ez-bh.com.br


Accepted October 22, 1998
Electronic publication: September, 1999


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