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Year : 2013  |  Volume : 56  |  Issue : 3  |  Page : 258-260
Speciation of coagulase negative Staphylococcal isolates from clinically significant specimens and their antibiogram

1 Department of Microbiology, JJM Medical College, Davangere, Karnataka, India
2 Department of Microbiology, Basaveshwara Medical College, Chitradurga, Karnataka, India

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Date of Web Publication24-Oct-2013


Background: Despite their frequency as contaminants, coagulase-negative Staphylococci (CONS) have become important nosocomial pathogens, accounting for 9% of all nosocomial infections. These infections are difficult to treat because of the risk factors and the multiple drug resistance nature of these organisms. Materials and Methods: One hundred and two consecutive CONS were isolated from various clinical samples like blood, pus, urine, urine catheter tip and gastric lavage. Most of the blood samples were from patients with risk factors (immunocompromised or on medical devices). After confirming the isolates as CONS, species-level identification was performed by simple, non-expensive conventional methods and antibiotic sensitivity testing was also carried out. Results: Of 102 CONS isolates, 100 isolates could be identified to the species level. Among the 100 isolates, epidermidis was the most common species isolated, seen in 32%, followed by S. hemolyticus (18%), S. lugdunensis (12%), S. hominis (10%), S. saprophyticus (8%), S. capitis (6%), S. caprae (4%), S. xylosus (4%), S. cohni and S. warneri (3% each). In the present study, 56% of the isolates were methicillin-resistant CONS. Most of the isolates showed resistance to ampicillin and amoxyclav (89% each), followed by ceftriaxone (52%), cotrimoxazole (46%), cefotaxime (32%), gentamicin (25%), amikacin (21%). Conclusion: The increased pathogenic potential and multiple-drug resistance demonstrates the need to adopt simple, reliable and non-expensive methods for identifying and determining the antibiotic sensitivity of CONS.

Keywords: Antibiotic sensitivity test, CONS, S. epidermidis

How to cite this article:
Usha M G, Shwetha D C, Vishwanath G. Speciation of coagulase negative Staphylococcal isolates from clinically significant specimens and their antibiogram . Indian J Pathol Microbiol 2013;56:258-60

How to cite this URL:
Usha M G, Shwetha D C, Vishwanath G. Speciation of coagulase negative Staphylococcal isolates from clinically significant specimens and their antibiogram . Indian J Pathol Microbiol [serial online] 2013 [cited 2020 Jun 5];56:258-60. Available from: http://www.ijpmonline.org/text.asp?2013/56/3/258/120383

   Introduction Top

Coagulase-negative Staphylococci (CONS), which are the normal skin flora, have emerged as predominant pathogens in hospital-acquired infections. [1] The clinical significance of species other than S. epidermidis has been increasingly recognized in the recent years. [2]

Blood stream infections (BSI's) are the major causes of morbidity and mortality. [3] Studies revealed that CONS were the third most common cause of BSI's. [4] As the pathogenic significance increases, it becomes important to learn about the epidemiology and pathogenic potential of individual species. [5] S. epidermidis and S. hemolyticus are resistant to multiple antibiotics. [6]

The present study was carried out to identify the prevalent species of CONS and their antibiogram.

   Materials and Methods Top

The present study was performed after obtaining the Institutional Ethical Committee clearance.

A total of 102 non-repeat CONS were isolated and studied over a period of 9 months from January 2012 to September 2012 from different clinically significant specimens such as blood, pus, urine, urine catheter tip and gastric lavage. Most of the blood samples were from patients with medical devices and immunocompromised status. The isolates were considered clinically significant when isolated in pure culture, and repeatedly.

The isolates were identified as CONS by colony morphology, Gram stain, catalase test and coagulase test (slide and tube coagulase). Bacitracin susceptibility was performed to exclude Micrococci and Stomatococcus species. [7]

The conventional tests that are simple, easy to perform and non-expensive were chosen from the scheme of Kloos and Schleifer and Koneman et al. These include the ornithine decarboxylase test, nitrate reduction test, Voges-Proskauer test, urease test and fermentation of sucrose, lactose, maltose, mannose, mannitol, xylose and trehalose. Susceptibility to novobiocin and polymyxin B was performed as per the standard procedure. [8],[9]

The antibiotic sensitivity testing was performed on Muller-Hinton agar by the Kirby-Bauer disc diffusion method [10] using a panel of nine antibiotics, which includes ampicillin (A), amoxyclav (Amc), ceftriaxone (Ci), cotrimoxazole (Co), cefotaxime (Ce), gentamicin (G), amikacin (Ak) and vancomycin (Va). Cefoxitin (Cn-30 μg) was used to identify methicillin-resistant coagulase negative Staphylococci (MRCONS).

   Results Top

Of the 102 CONS isolates, 54 were from blood samples, 32 from pus samples, 2 from throat swabs, 12 from urine samples and one each from the urine catheter tip and gastric lavage samples. Of the 54 blood samples, 34 were from patients with intravascular catheters (peripheral venous/central vein/arterial) and patients in the Intensive Care Unit setting, on peritonial/hemodialysis, prolonged hospital stay, etc. The simple conventional methods identified 100 isolates (98.04%) correctly to a species level out of the 102 CONS isolates. The remaining two isolates (1.96%) could not be identified to the species level.

Among these 100 identified CONS isolates, S. epidermidis was the most frequently isolated (32%), followed by S. hemolyticus (18%), S. lugdunensis (12%), S. hominis (10%), S. saprophyticus (8%), S. capitis (6%), S. caprae (4%), S. xylosus (4%), S. cohni and S. warneri (3% each). [Table 1] shows the species-wise distribution of CONS in the different clinical specimens.

Of the 34 blood samples from high-risk patients, the most commonly isolated species was S. hemolyticus, seen in 10 patients (29.42%), followed by S. epidermidis in nine patients (26.48%), S. lugdunensis in three patients (8.82%), S. hominis in three patients (8.82%), S. capitis in two patients (5.88%), S. caprae in two patients (5.88%), S. cohni in one patients (2.94%), S. xylosus in one patient (2.94%) and S. warneri in one patient (2.94%). The remaining two patients (5.88%) could not be identified. Among the remaining 20 blood specimens from immunocompetant or without any medical devices patients, the most common species identified was S. epidermidis, seen in 10 (50%) isolates, followed by S. hemolyticus in three (15%) isolates, S. caprae in two (10%) isolates, and one (05%) isolate each of S. lugdunensis, S. hominis, S. saprophyticus, S. capitis and S. warneri. [Table 2] shows the distribution of species of CONS in blood specimens among patients with predisposing factors and in patients without risk factors.
Table 1: Species-wise distribution of CONS in the various clinical specimens

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Table 2: Distribution of species in the blood specimens

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The incidence of CONS was high among males (59%) compared with females (41%). CONS BSI's were commonly seen in neonates compared with the other infections that are common in the age group between 30 and 40 years.

In the present study, the susceptibility pattern of CONS species against antimicrobial agents showed that 56% of the isolates were MRCONS. Majority of the CONS species were resistant to ampicillin and amoxyclav (89% each), followed by ceftriaxone (52%), cotrimoxazole (46%), cefotaxime (32%), gentamicin (25%) and amikacin (21%). None of the CONS species showed resistance to vancomycin.

   Discussion Top

Although the pathogenic role of CONS is now well established, the clinical significance of the various species is still being defined. We should not disregard any of the organisms until their clinical significance is resolved. [11] In the hospital microbiology laboratory, non-aureus isolates are simply reported as CONS without speciation. Because there is increasing pathogenecity of these organisms, CONS should be identified to the species level by simple, reliable and preferably inexpensive methods. [12]

In our study, the most commonly isolated species was S. epidermidis, similar to other studies as shown by Subadra Singh et al, where the rate of isolation was 40%. [7] Sheik et al.[13] and Asangi et al.[14] also showed that S. epidermidis is the most commonly isolated species from clinical specimens, seen in 19.40% and 44.8%, respectively. The next most common species in our study was S. hemolyticus, seen in 18%, similar results were seen in other studies also. [8],[13] But, in other studies, it was S. saprophyticus that was the second most common species [7],[15] and S. hominis in the study by Manikandan et al. [16]

The CONS infection was more common in males (59%) than in females (41%) in the present study, which is shown in another study as well. [14] When the different age groups were compared, the incidence of CONS was high from the blood specimen of neonates (38.88%) and the most common age group affected was between 30 and 40 years from the other specimens.

In our study, the species most common in blood samples were S. epidermdis, S. hemolyticus and S. hominis, which is similar to the study by Weinstein et al.,who evaluated Microscan rapid and Dried overnight Gram positive panels versus a conventional reference method. [5] The rate of isolation from the blood specimen was high in our study compared with other studies. [6],[13] This could be due to a higher number of blood samples tested for CONS and testing of more patients with predisposing factors (in situ medical devices or immunocompromised status), although the level of contamination may also be high in BSI. It can be very difficult to draw blood from venipuncture or critically ill patients; therefore a certain level of contamination is unavoidable. [6] This increased incidence of CONS from foreign body infections is due to the strong adherence to polymer surfaces (by polysaccharide adhesins), which leads to early colonization and biofilm formation. Biofilm may function as a penetration barrier to antibiotics and hence the high level of resistance. [17]

The incidence of methicillin resistance was 56% in this study, and many other studies have documented a still higher resistance. [3],[14] None of the isolates showed resistance to vancomycin in our study. However, others have noted a reduced susceptibility to vancomycin. [4],[6]

   Conclusions Top

Recently, CONS have emerged as a potential pathogen, especially BSI's. There is also an increased resistance among these isolates and glycopeptides have become the drug of choice in the treatment of these infections. Hence, there is a need for accurate identification of these isolates to a species level and their antibiotic sensitivity pattern to avoid decreased susceptibility to glycopeptides. In this study, the most common species identified was S. epidermidis. Resistance to ampicillin and amoxyclav was high and none of the isolates showed resistance to vancomycin.

   References Top

1.Badwi JA, Memon AH, Soomro AA. Coagulase Negative Staphylococci (CONS) is the contaminant in the clinical specimen. Med Channel 2012;19:23-7.  Back to cited text no. 1
2.Makki AR, Sharma S, Duggirala A, Prashanth K, Garg P, Das T. Phenotypic and Genotypic Characterization of Coagulase Negative Staphylococci (CoNS) Other thanStaphylococcus epidermidis Isolated from Ocular Infections. Invest Ophthalmol and VisSci 2011;52:9018-22.  Back to cited text no. 2
3.Wisplinghoff H, Bischoff T, Tallent SM, Seifert H, Wenzel P, Edmond MB. Nosocomial Bloodstream Infections in US Hospitals: Analysis of 24,179 Cases from a ProspectiveNationwide Surveillance Study. Clin Infect Dis 2004;39:309-17.  Back to cited text no. 3
4.Diekema DJ, Pfaller MA, Schmitz FJ, Smayevsky J, Bell J, Jones RN, et al. Survey of Infections Due to StaphylococcusSpecies: Frequency of Occurrenceand Antimicrobial Susceptibility of IsolatesCollected in the United States, Canada, LatinAmerica, Europe, and the Western PacificRegion for the SENTRY AntimicrobialSurveillance Program, 1997-1999. Clin Infect Dis 2001;32(suppl2):S114-32.  Back to cited text no. 4
5.Weinstein MP, Mirrett S, Pelt LV, McKinnon M, Zimmer BL, Kloos W, et al. Clinical importance of identifying coagulase negative staphylococci isolated from blood cultures: Evaluation of microscan rapid and dried overnight gram-positive panel versus a conventional reference method. J Clin Microbiol 1998;36:2089-92.  Back to cited text no. 5
6.Natoli S, Fontana C, Favaro M, Bergamini A, Testore GP, Minelli S, et al. Characterization of coagulase-negative staphylococcal isolates from blood with reduced susceptibility to glycopeptides and therapeutic options. BMC Infect Dis 2009;9:83.  Back to cited text no. 6
7.Singh S, Banerjee G, Agarwal SK, Kumar M, Singh RK. Simple method for speciation of clinically significant Coagulase Negative Staphylococci and its antibiotic sensitivity/resistant pattern in NICU of tertiary care centre. Biomed Res 2008;19:97-101.  Back to cited text no. 7
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9.Winn WC, Allen SD, Janda WM, Koneman EW, Procop CW, Schreckenberger PC, et al. Gram positive cocci Part I: Starphylococci and related Gram positive cocci. In:Koneman's colour atlas and textbook of diagnostic Microbiology. 6 th ed. USA: Lippincott Williams and Wilkins; 2006. p. 623-73.  Back to cited text no. 9
10.Miles RS, Amyes SG.Laboratory control of antimicrobial therapy. In: Collee JG, Fraser AG, Marmion BP, Simmons A, editors. Mackie and Mc Cartney practical Medical Microbiology. 14 th ed. New York:Churchill Livingston;1996. p. 151-78.  Back to cited text no. 10
11.Hebert GA, CrowderCG, Hancock GA, Jarvis WR, Thornsberry C. Characteristics of Coagulase Negative Staphylococci That Help Differentiate These Species and Other Members of the Family Micrococcaceae. J Clin Microbiol 1988;26:1939-49.  Back to cited text no. 11
12.Ieven M, Verhoeven J, Pattyn SR, Goossens H. Rapid and Economical Method for Species Identification of Clinically Significant Coagulase-Negative Staphylococci. J Clin Microbiol 1995;33:1060-3.  Back to cited text no. 12
13.Sheikh AF, Mehdinejad M. Identification and determination of coagulase negative staphylococci species and antimicrobial susceptibility pattern of isolates from clinical specimens. Afr J Microbiol Res 2012;6:1669-74.  Back to cited text no. 13
14.Asangi SY, Mariraj J, Sathyanarayan MS, Nagabhushan R. Speciation of clinically significant Coagulase Negative Staphylococci and their antibiotic resistant pattern in a tertiary care hospital. Int J Biol Med Res 2011;2:735-9.  Back to cited text no. 14
15.Goyal R, Singh NP, Kumar A, Kaur I, Singh M, Sunita N, et al. Simple and economical method for speciation and resistotyping of clinically significant coagulase negative staphylococci. Indian J Med Microbiol 2006;24:201-4.  Back to cited text no. 15
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16.Manikandan P, Bhaskar M, Revathy R, John RK, Narendran K, Narendran V. Speciation of Coagulase Negative Staphylococcus causing Bacterial Keratitis. Indian J Ophthalmol 2005;53:59-60.  Back to cited text no. 16
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17.Kloos WE, Bannerman TL. Update on clinical significance of coagulase negative staphylococci. Clin Microbiol Rev 1994;7:117-40.  Back to cited text no. 17

Correspondence Address:
M G Usha
Department of Microbiology, JJM Medical College, Davangere, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.120383

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