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CORRESPONDENCE
Year : 2014  |  Volume : 32  |  Issue : 4  |  Page : 460-461
 

Small colony variants of Staphylococcus aureus: Enemies with hidden weapons


1 Department of Microbiology, All India Institute of Medical Sciences, Phulwarisharif, Patna - 801 505, Bihar, India
2 Department of Microbiology, IMS, BHU, Varanasi, Uttar Pradesh, India

Date of Submission05-Sep-2013
Date of Acceptance20-Jan-2014
Date of Web Publication4-Oct-2014

Correspondence Address:
S Bhattacharyya
Department of Microbiology, All India Institute of Medical Sciences, Phulwarisharif, Patna - 801 505, Bihar
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0255-0857.142237

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How to cite this article:
Bhattacharyya S, Kumar D. Small colony variants of Staphylococcus aureus: Enemies with hidden weapons . Indian J Med Microbiol 2014;32:460-1

How to cite this URL:
Bhattacharyya S, Kumar D. Small colony variants of Staphylococcus aureus: Enemies with hidden weapons . Indian J Med Microbiol [serial online] 2014 [cited 2019 Nov 14];32:460-1. Available from: http://www.ijmm.org/text.asp?2014/32/4/460/142237


Dear Editor,

Small colony variants (SCV) of Staphylococcus aureus originate from wild-type strains by genetic mutation, resulting in loss of properties like α-cytotoxin (α-hemolysin) activity and auxotrophicity for thymidine and menadione or vitamin K. [1] These morphological variants are typified by a slow growth rate, absence of colony pigment, colony size approximately one-tenth that of wild-type strains and atypical biochemical characteristics, which make laboratory diagnosis very difficult. [2]

SCVs are auxotrophic for menadione and thymidine. Intra-cellular persistence shields them from host immunity and antibiotics. [3]

The differentiating features of SCV and wild-type S. aureus are enumerated in [Table 1]. [4]
Table 1: Differences between wild type S. aureus and SCV

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SCVs are associated with diseases like cystic fibrosis, osteomyelitis and wound infection. [5],[6] SCV of S. aureus can also be recovered in 17-49% cases of cystic fibrosis. There are also reports of device-related infections, like ventriculo-peritoneal shunt infections.

Diagnosis follows timely suspicion since colonies are slow-growing, and multiply at a rate one-ninth that of wild-type S. aureus. Accurate diagnosis rests upon detection of small, pinpoint, non-pigmented, non-haemolytic colonies in 5% Sheep blood agar reverting to normal phenotype in presence of vitamin K in media (Schaedler agar) and ambient 5% CO 2 . "Fried Egg" colonies (central raised and peripheral flat parts) are characteristic of Thymidine-auxotrophic SCV. Colonies are also catalase positive and delayed positive for tube coagulase. However, tube coagulase comes positive only after 18 h incubation.Molecular methods like detection of S. aureus-specific nuc or coa genes (by polymerase chain reaction) can also be attempted. Some authors have shown augmented growth on lawn culture around discs impregnated with 15 μl of vitamin K as diagnostic. Colonies of SCV S. aureus have been shown in [Figure 1].
Figure 1: SCV colonis on 5% sheep blood agar

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Treatment is difficult due to inherent resistance to aminoglycosides and cell-wall active antibiotics. Rifampicin, being active intra-cellularly, or its combination with cotrimoxazole is effective. Daptomycin injection for about 2 months is documented to be useful in deep-seated infections. [7]

SCVs of S. aureus represent underdiagnosed agents of persistent subclinical infections that need to be promptly diagnosed and treated. Further research is awaited regarding their pathogenesis and treatment guidelines.

The authors thank all workers whose research has been cited and mentioned in this study.

 
 ~ References Top

1.Melter O, Radojevic B. Small colony variants of Staphylococcus aureus--review. Folia Microbiol (Praha) 2010;55:548-58.  Back to cited text no. 1
    
2.Besier S, Smaczny C, von Mallinckrodt C, Krahl A, Ackermann H, Brade V, et al. Prevalence and clinical significance of Staphylococcus aureus small-colony variants in cystic fibrosis lung disease. J Clin Microbiol 2007;45:168-72.  Back to cited text no. 2
    
3.Sifri CD, Baresch-Bernal A, Calderwood SB, von Eiff C. Virulence of Staphylococcus aureus small colony variants in the Caenorhabditis elegans infection model. Infect Immun 2006;74:1091-6.  Back to cited text no. 3
    
4.Atalla H, Gyles C, Mallard B. Staphylococcus aureus small colony variants (SCVs) and their role in disease. Anim Health Res Rev 2011;12:33-45.  Back to cited text no. 4
    
5.Yagci S, Hascelik G, Dogru D, Ozcelik U, Sener B. Prevalence and genetic diversity of Staphylococcus aureus small-colony variants in cystic fibrosis patients. Clin Microbiol Infect 2013;19:77-84.  Back to cited text no. 5
    
6.Proctor RA, van Langevelde P, Kristjansson M, Maslow JN, Arbeit RD. Persistent and relapsing infections associated with small-colony variants of staphylococcus aureus. Clin Infect Dis 1995;20:95-102.  Back to cited text no. 6
    
7.Kipp F, Ziebuhr W, Becker K, Krimmer V, Höbeta N, Peters G, et al. Detection of Staphylococcus aureus by 16S rRNA directed in situ hybridisation in a patient with a brain abscess caused by small colony variants. J Neurol Neurosurg Psychiatry 2003;74:1000-2.  Back to cited text no. 7
    


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