|Year : 2017 | Volume
| Issue : 2 | Page : 277-278
Changing epidemiology of coagulase-negative staphylococci in normal flora of skin
Vikas Gautam1, Nandini Sethuraman2, Ramanpreet Kaur3, Suchet Sachdev4, Neelam Marwaha4, Pallab Ray1
1 Department of Medical Microbiology, Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Medical Microbiology, Postgraduate Institute of Medical Education and Research, Chandigarh; Department of Microbiology, Apollo Hospitals, Chennai, Tamil Nadu, India
3 Department of Medical Microbiology, Postgraduate Institute of Medical Education and Research, Chandigarh; Department of Microbiology, Tagore Hospital and Heart Care Centre, Jalandhar, Punjab, India
4 Department of Transfusion Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh, India
|Date of Web Publication||5-Jul-2017|
Department of Medical Microbiology, Research Block-A, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
Source of Support: None, Conflict of Interest: None
Coagulase negative staphylococci (CoNS) have recently emerged as important pathogens causing nosocomial blood stream infections. To evaluate the prevalence of CoNS in cutaneous normal flora, skin swabs were collected from voluntary blood donors and processed for culture and identification using matrix assisted laser desorption ionisation-time of flight (MALDI-TOF). CoNS were isolated from 96% of blood donors, most commonly Staphylococcus hominis (86%), followed by Staphylococcus epidermidis (22%) and Staphylococcus haemolyticus (9%). There has been a shift in the prevalent species of CoNS in the community in India, from the earlier known S. epidermidis towards resistant species such as S. hominis and S. haemolyticus. Routine and rapid speciation of CoNS in clinical isolates with MALDI-TOF should be used effectively to manage these resistant species.
Keywords: Coagulase negative, normal flora, staphylococci, Staphylococcus epidermidis, Staphylococcus haemolyticus
|How to cite this article:|
Gautam V, Sethuraman N, Kaur R, Sachdev S, Marwaha N, Ray P. Changing epidemiology of coagulase-negative staphylococci in normal flora of skin. Indian J Med Microbiol 2017;35:277-8
|How to cite this URL:|
Gautam V, Sethuraman N, Kaur R, Sachdev S, Marwaha N, Ray P. Changing epidemiology of coagulase-negative staphylococci in normal flora of skin. Indian J Med Microbiol [serial online] 2017 [cited 2018 Feb 20];35:277-8. Available from: http://www.ijmm.org/text.asp?2017/35/2/277/209581
| ~ Introduction|| |
Coagulase negative staphylococci (CoNS) are a diverse group of Gram-positive cocci, commonly isolated from human skin as normal flora, and recently recognised as a significant cause of nosocomial bloodstream infections. This upsurge is associated with the increasing use of indwelling medical devices as well as rising number of critically ill patients. CoNS account for 12%–80% mortality in hospitalised patients and also 16% morbidity has been associated with CoNS bacteraemia. The multidrug resistant nature of the different CoNS species further aggravates the situation, limiting the treatment options for prevalent CoNS species. However, routine speciation is not commonly done in most laboratories. By doing so, we are closing the precious therapeutic window for patients with invasive diseases. The usual conception is that infections caused by CoNS are predominantly caused by Staphylococcus epidermidis. However, the scenario is not the same now as earlier. The other species such as Staphylococcus haemolyticus and Staphylococcus hominis are taking over S. epidermidis. This recent shift in epidemiology is responsible for diverting much more attention towards CoNS species identification. The relative abundance of different Staphylococcus species as normal flora of skin requires a re-evaluation. Hence, this study was taken up to evaluate the distribution of CoNS species in normal flora of a representative healthy population.
| ~ Materials and Methods|| |
To evaluate the prevalence of CoNS in normal flora, a fixed surface area of 24 cm 2 over the cubital fossa was swabbed in 100 voluntary blood donors attending the blood bank between February and December 2014 at our tertiary care centre. Sterile cotton swabs moistened with Butterfields' phosphate buffer were used for sampling the skin surface and the swabs were resuspended in the same buffer. They were processed in the laboratory within 2 h of collection and inoculated on 5% sheep blood agar and MacConkey agar. Different morphotypes of colonies were picked up following overnight incubation and identified to species level using matrix assisted laser desorption ionisation-time of flight (MALDI-TOF) (Microflex LT, Bruker Daltonik GmbH, Leipzig, Germany) using Bruker Biotyper software v2.0 with a cut-off score of ≥2. As the study was performed on human subjects, ethics approval was obtained from the Institute Ethics Committee (NK/314/res/2875).
| ~ Results|| |
The relative distribution of different Staphylococcus species in the normal flora of 100 healthy adult blood donors was studied [Table 1]. CoNS were isolated from 96% of donors. The most common CoNS isolate was S. hominis isolated from 86% of donors, followed by S. epidermidis (22%) and S. haemolyticus (9%).
|Table 1: Relative distribution of different Staphylococcus species in normal flora of healthy blood donors|
Click here to view
| ~ Discussion|| |
The microbial flora of skin is diverse between sites of a body and also within a site between individuals of a population. However, core microbiome consisting of most commonly shared species does exist. Traditional culture methods have been used in the 1960s and 1970s to characterise normal flora of skin, which showed S. epidermidis as the most common species of Staphylococcus in normal flora. However, there are very few studies in recent times demonstrating relative distribution of all cultivable species on skin in a large group of individuals. Hitherto, culture studies of the normal flora of skin have been more concentrated on the pathogenic species of Staphylococcus aureus.,, With the rising importance of CoNS in bacterial sepsis, we felt it pertinent to reevaluate the relative abundance of Staphylococcus species in a large number of individuals. We selected the antecubital fossa to sample major cultivable bacterial flora as it is the site most commonly used to draw blood for culture, and also it is one of the moist sites of the body where staphylococci predominate as the major bacterial genus. We chose swabbing of a fixed surface area of the skin over more invasive procedures because the relative abundance of organisms in the different layers throughout the thickness of skin remains fairly constant. Our study found that S. hominis was present in the antecubital fossae of 86% of individuals, whereas only 22% of individuals harboured S. epidermidis. This difference in distribution may be due to selective pressures even in the community due to widespread use of antibiotics in our country. S. haemolyticus, not described as a common commensal was the third most common commensal (9%). S. haemolyticus is a particularly difficult to treat species with high-level resistance to methicillin as well as vancomycin. Hence, CoNS speciation must be a routine in all the diagnostic laboratories.
Rapid bacterial identification methods like MALDI-TOF-MS can be especially beneficial in diagnosis and early initiation of therapy. Identification using MALDI-TOF is based on bacterial intrinsic ribosomal proteins and has been shown to yield accurate results in a short time frame and at a much lower cost than any other routinely available microbiological techniques.
| ~ Conclusion|| |
The epidemiology of coagulase negative staphylococci is shifting towards more drug resistant species. This underlies the need to rapidly identify clinical isolates of CoNS to species level using available robust methods such as MALDI-TOF.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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