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  Table of Contents    
ORIGINAL ARTICLE  
Year : 2016  |  Volume : 59  |  Issue : 1  |  Page : 47-49
Rare and unusual isolates of viridans streptococci from the human oral cavity


1 Department of Microbiology, M.M. Patel Public Charitable Trust's, Ashwini Medical College and Hospital, Kumbhari, Solapur, Maharashtra, India
2 Department of Microbiology, Maharashtra Institute of Medical Sciences and Research, Latur, Maharashtra, India
3 Department of Physiotherapy, MIP College of Physiotherapy, Latur, Maharashtra, India

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Date of Web Publication9-Mar-2016
 

   Abstract 

Context: The genus Streptococcus consists of more than 65 species. The taxonomic classification of these members is not well-defined. Among the viridans group streptococci (VGS), there are major taxonomic changes by the addition of many new species; whereas, most of the new strains are of animal origin and only a few have been reported to be isolated from humans. Rare and unusual species of VGS such as Streptococcus thoraltensis, S. pluranimalium and S. hyointestinalis are normally associated with different animals. Their isolation from human being is not yet reported. Aim: To find out the rare and unusual species of viridans group streptococci from human oral cavity. Settings and Design: A case-controlled study carried out at hospital-based dental services in a tertiary care hospital. Materials and Methods: Subgingival plaque samples of the tooth were collected from 80 patients (34 with periodontitis and 46 without periodontitis) undergoing tooth extraction. Cultures were subcultured onto special media such as Tryptone Soya blood Agar supplemented with strepto supplement and Mutans-Sanguis Agar. Identification of strains and antimicrobial susceptibilities were measured as minimum inhibitory concentration using Vitek 2 (BioMérieux, Paris, France) automated system. Results: We have identified three strains of VGS - S. thoraltensis, S. pluranimalium and S. hyointestinalis from subgingival plaque samples from patients with periodontitis. S. thoraltensis and S. pluranimalium were found to be resistant to most of the antibiotics. Conclusions: To the best of our knowledge, this is the first report of isolation of these rare and unusual strains from the human oral cavity.

Keywords: Oral cavity, Streptococcus hyointestinalis, Streptococcus pluranimalium, Streptococcus thoraltensis, subgingival plaque

How to cite this article:
Dhotre S, Suryawanshi N, Nagoba B, Selkar S. Rare and unusual isolates of viridans streptococci from the human oral cavity. Indian J Pathol Microbiol 2016;59:47-9

How to cite this URL:
Dhotre S, Suryawanshi N, Nagoba B, Selkar S. Rare and unusual isolates of viridans streptococci from the human oral cavity. Indian J Pathol Microbiol [serial online] 2016 [cited 2019 Nov 14];59:47-9. Available from: http://www.ijpmonline.org/text.asp?2016/59/1/47/174817



   Introduction Top


The human oral cavity is colonized by a wide range of bacteria, and more than 700 species of different bacterial species have been detected so far. [1] The majority of the bacterial species found in the oral cavity belongs to the viridans group of streptococci (VGS). Streptococci constitute the major microbial flora around the teeth, mainly in the dental plaque that forms above the gingival crest. Although species of VGS are commensal in human beings, they also have a pathogenic potential to cause a variety of infections. Whereas, some are true pathogens which not only spread from one host to the other but can cause infection in nonimmune individuals. [2]

Isolation of some of the rare and unusual isolates of streptococci such as Streptococcus hyointestinalis recovered from the swine gut, S. pluranimalium from cattle, goats, cats and birds, [3] and S. thoraltensis from the intestinal tract of swine, have never been reported from the oral cavity of human beings, except for one isolate of S. thoraltensis from human subgingival plaque in our earlier report. [4]

In the present study, we report the isolation of these rare and unusual isolates from the human oral cavity. To the best of our knowledge, it is the first report of their isolation from human source.


   Materials and methods Top


In this study, 80 patients (34 with periodontitis and 46 without periodontitis) undergoing tooth extraction were screened. Subgingival plaque samples of the tooth were collected from the gingival area of buccal and lingual tooth surfaces of affected tooth using sterile curettes into sterile transport media.

The samples were processed for isolation of VGS. Cultures with bacterial growth were Gram-stained and subcultured onto special media such as, Tryptone Soya blood Agar supplemented with strepto supplement (nalidixic acid 3.750 mg, nemomycin sulfate 1.060 mg and polymixin B sulfate 8500 units for 500 ml media) and Mutans-Sanguis Agar (HiMedia Laboratories, Mumbai, India). Cultures with growth were further subjected to standard biochemical identification using automated Vitek 2 (BioMérieux, Paris, France) system, to complete the strain identification. Antimicrobial susceptibilities were measured as minimum inhibitory concentration (MIC) by automated Vitek 2 system and reported the strain as sensitive or resistant based on MIC values to respective antimicrobial agents as per the guidelines of Clinical Laboratory Standard Institutes. [5]


   Results Top


A total of 260 VGS strains belonging to seven phenotypic groups and few strains of undifferentiated Streptococci were isolated from the subgingival plaque of patients undergoing tooth extraction. Of 260 VGS strains, three species namely S. thoraltensis, S. pluranimalium and S. hyointestinalis were found to be isolated for the first time from the subgingival plaque of three patients with periodontitis undergoing tooth extraction.

The results of antimicrobial susceptibility showed that S. hyointestinalis was sensitive to all antimicrobial agents that were included in the Gram-positive Vitek 2 Streptococcus MIC panel. S. pluranimalium was resistant to ampicillin, erythromycin, azithromycin, clarithromycin, levofloxacin, ofloxacin and clindamycin. However, S. thoraltensis was resistant to ampicillin, cefepime, ceftriaxone and cefotaxime [Table 1].
Table 1: Antibiotic susceptibility pattern of three rare VGS isolated from subgingival plaque of patients undergoing tooth extraction


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   Discussion Top


Among the VGS isolates, we had identified few strains that were unusual and uncommon in human clinical samples; namely S. thoraltensis, S. pluranimalium and S. hyointestinalis from the subgingival plaque of these patients. It has been reported that species not yet identified from human sources have been transmitted from nonhuman sources to humans has caused documented infections; [3] similarly these novel species of VGS isolated in this study may have been transmitted from nonhuman sources. In the light of these findings and the fact that VGS can cause life-threatening systemic infections like infective endocarditis, it is important to identify the individual species accurately.

These are nonhuman species that have been commonly isolated from several animal species, but their isolation has never been reported from human subgingival plaque except for S. thoraltensis, one strain of which has been previously reported in our earlier study. [4]

In the present study, for the first time, they have been isolated from three (3.75%) subgingival plaque samples. In contrast to most streptococcal species, which are associated with only one or a few phylogenetically related animal hosts, these isolates were found to be associated with different animal species. [6],[7]

The knowledge regarding identification and relationship among viridans Streptococci isolates increases by use of phenotypic and molecular methods. The Vitek 2 system seems to represent an accurate and acceptable mean for performing characterization/identification of many bacterial species; [8] studies by Wallet et al. [9] and Haanperä et al. [10] have reported excellent performances of the new Vitek 2 cards, due to the improvisation and the extension of its database, mainly for nonfermenting bacteria and Streptococcaceae, allowing their use in routine practice with a highly acceptable level of identification accuracy.

As isolation of these rare and unusual species of streptococci from human clinical samples has never been reported in literature so far; their isolation from human oral flora is a suggestive of astounding complexity and diversity of the human oral flora, with more than 700 species of the aerobic and anaerobic microflora, correctly mapping these organisms is an invincible task, moreover correct identification of the VGS up to the species level is difficult, as conventional tests and commercially available devices and systems have not incorporated all the taxonomic changes in the identification procedures. [7]

Our antimicrobial susceptibility results [Table 1] indicate that S. pluranimalium and S. thoraltensis were resistant to several antimicrobial agents that are included in the Gram-positive Vitek 2 Streptococcus MIC panel. S. thoraltensis isolate from human subgingival plaque in our earlier report [4] was resistant to ampicillin, cefotaxime and ceftriaxone. However, S. thoraltensis isolate in the present study was found to be resistant to cefepime in addition to ampicillin, cefotaxime and ceftriaxone. This resistance pattern of these isolates is a cause of concern; as this resistance pattern along with these new etiologic agents will complicate the management of infections if any due to these pathogens of animal origin.


   Conclusion Top


The results of the present study provide a new insight in the field of oral microbiology as this habitat of these rare and unusual isolates is abstruse. Although these isolates have been reported to cause a variety of infections in animals, their role in causation of infections in human beings and their pathogenic significance in the human oral cavity cannot be underestimated. Further detailed studies with special reference to their pathogenic significance in human beings by detecting virulent genes/factors will help in achieving more useful and concrete conclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Paster BJ, Olsen I, Aas JA, Dewhirst FE. The breadth of bacterial diversity in the human periodontal pocket and other oral sites. Periodontol 2000 2006;42:80-7.  Back to cited text no. 1
    
2.
Kilian M. Streptococcus and Lactococcus. In: Balows A, Duerden BI, editors. Topley and Wilson's Microbiology and Microbial Infections. New York: Arnold; 1998. p. 634-67.  Back to cited text no. 2
    
3.
Facklam R. What happened to the streptococci : o0 verview of taxonomic and nomenclature changes. Clin Microbiol Rev 2002;15:613-30.  Back to cited text no. 3
    
4.
Dhotre SV, Suryawanshi NM, Nagoba BS. Isolation of Streptococcus thoraltensis from human oral cavity. Indian J Dent 2014;5(Suppl) :140-1.  Back to cited text no. 4
    
5.
Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing; Twenty-second Informational Supplement. CLSI document M100-S22. Vol. 32. Wayne PA : Clinical and Laboratory Standards Institute; 2012.  Back to cited text no. 5
    
6.
Devriese LA. A Review of Streptococcal ecovars associated with different animal species : e0 pidemiological significance of serogroups and biotypes. J Appl Bacteriol 1991;71:478-83.  Back to cited text no. 6
    
7.
Devriese LA, Kilpper-Balz R, Schleifer KH. Streptococcus hyointestinalis sp. nov. from the gut of swine. Int J Syst Bacteriol 1988;38:440-1.  Back to cited text no. 7
    
8.
Barry J, Brown A, Ensor V, Lakhani U, Petts D, Warren C, et al. Comparative evaluation of the VITEK 2 Advanced Expert System (AES) in five UK hospitals. J Antimicrob Chemother 2003;51:1191-202.  Back to cited text no. 8
    
9.
Wallet F, Loïez C, Renaux E, Lemaitre N, Courcol RJ. Performances of VITEK 2 colorimetric cards for identification of gram-positive and gram-negative bacteria. J Clin Microbiol 2005;43:4402-6.  Back to cited text no. 9
    
10.
Haanperä M, Jalava J, Huovinen P, Meurman O, Rantakokko-Jalava K. Identification of alpha-hemolytic streptococci by pyrosequencing the 16S rRNA gene and by use of VITEK 2. J Clin Microbiol 2007;45:762-70.  Back to cited text no. 10
    

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Correspondence Address:
Basavraj Nagoba
Maharashtra Institute of Medical Sciences and Research, Latur - 413 531, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0377-4929.174817

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