Prevalence and antimicrobial susceptibility pattern of Coagulase-negative Staphylococcus

Begum, et al.: Coagulase-Negative Staphylococci Int. J. Med. Public health [www.ijmedph.org] | October–December 2011 | Vol 1 | Issue 4 60 of such resistance between species have led to call for restricted use of glycopeptides. The objective of this study was to determine the incidence of CoNS species from different clinical samples and their resistance patterns so as to provide these data on the prevailing strains in the hospital. MATERIALS AND METHODS Bacterial strains: 113 strains of CoNS recovered from cultures of clinical specimens over a period of six months from November 2004 to April 2005 from hospitalized patients were studied. Coagulase-negative Staphylococcus was identifi ed based on the conventional scheme of identifi cation proposed by Kloos and Schleifer[8]. Clinical signifi cance was based on repeated isolation of the same organism from the same site. Antimicrobial susceptibility testing was done on MuellerHinton agar according to standard procedures[9]. Methicillin resistance was screened by both oxacillin and cefoxitin discs. Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis ATCC 12228 strains were used as controls. Results were interpreted as per CLSI guidelines [10] .


INTRODUCTION
Coagulase-negative staphylococcus (CoNS) is a heterogeneous group of adaptable and opportunistic pathogens whose adaptability to persist and multiply in a variety of environments causes a wide spectrum of diseases in humans.Often identifi cation of Staphylococcus is limited to a rapid screening test for Staphylococcus aureus and non Staphylococcus aureus isolates are simply designated as CoNS.
We should not disregard any of these organisms until their clinical signifi cance is resolved and since they are of such resistance between species have led to call for restricted use of glycopeptides.
The objective of this study was to determine the incidence of CoNS species from different clinical samples and their resistance patterns so as to provide these data on the prevailing strains in the hospital.

MATERIALS AND METHODS
Bacterial strains: 113 strains of CoNS recovered from cultures of clinical specimens over a period of six months from November 2004 to April 2005 from hospitalized patients were studied.Coagulase-negative Staphylococcus was identifi ed based on the conventional scheme of identifi cation proposed by Kloos and Schleifer [8] .Clinical signifi cance was based on repeated isolation of the same organism from the same site.
Antimicrobial susceptibility testing was done on Mueller-Hinton agar according to standard procedures [9] .Methicillin resistance was screened by both oxacillin and cefoxitin discs.Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis ATCC 12228 strains were used as controls.Results were interpreted as per CLSI guidelines [10] .

RESULTS
The distribution of 113 CoNS isolates according to species and clinical material sources are presented in Table 1.Data showed S.epidermidis to be the most common CoNS species (n=55) and blood cultures yielded the highest number of isolates (n=30).ICU was the most important source of CoNS isolates contributing 44 isolates followed by post operative surgical wards.

RESISTANCE TO ANTIMICROBIALS
The resistance patterns of the isolates to twenty different antibiotics are presented in Table 2.
Among the β-lactams, maximum resistance was seen with penicillin (91%) followed by ampicillin (72%).Resistance to methicillin was seen in 48% of the CoNS isolates.With the cephalosporins, 68% were resistant to cephalexin and 65% to cephotaxime.
In the macrolides group, 83% of the isolates showed resistance to erythromycin.While within the fl uoroquinolones, resistance to ciprofl oxacin and ofl oxacin were found in 60% and 50.4% of the CoNS isolates respectively.With reference to aminoglycosides, higher percentage (80%) of resistance was seen for gentamicin when compared to amikacin (48.6%).Cotrimaxazole and nitrofurantoin were used only for urinary isolates and 75% were resistant to both the drugs.42 % of the isolates were resistant to rifampicin.While all CoNS strains were sensitive to oxazolidones (linezolid), with glycopeptides 100% sensitivity was found to vancomycin and only 97.3% to teicoplanin.64% of S.epidermidis , 78% of S.haemolyticus and 50% of S.saprophyticus were multiple resistant to 3 or more of the following group of agents: β-lactams, aminoglycosides, macrolides, quinolones and trimethoprim.(Table 3)

DISCUSSION
This study showed that S. epidermidis was the most common CoNS species comprising 43% of all isolates similar to that of other reports [11][12][13][14][15][16] .CoNS was reported as an important cause of blood stream infections and the second most common source after wound swabs in a hospital in Lebanon and Kuwait [17][18] .
Although there exists about 33 CoNS species, only a few of them have been associated with an increase in hospital acquired infections due to the use of invasive elements [19] .In a survey with dialysis patients carried out in 2002, 40 to 60% of the infections were caused by CoNS species.for the empiric treatment of serious Staphylococcal infections [2,6,15] .Subsequent resistance to vancomycin was reported in some strains of S.haemolyticus [23][24][25] .Staphylococcus haemolyticus is known to be unique among Coagulasenegative Staphylococci in being predisposed to develop glycopeptide resistance and especially to teicoplanin for which MICs are increased [26] .Three of our S.haemolyticus isolates expressed resistance to teicoplanin.

CONCLUSION
The increasing importance of CoNS nowadays may be due in part to the growing appreciation of this group of organisms as opportunistic pathogens and to the increase in the use of transient or permanent medical devices, such as intravascular catheters and prosthetic devices, in seriously ill and immunocompromised patients (i.e., intensive care patients, premature newborns, and cancer and transplant patients).CoNS infections often can be life-threatening in these patients.
Although Staphylococcus epidermidis accounts for most CoNS infections, many other species have been identifi ed in association with human infections.CoNS species identifi cation, which is still diffi cult for most clinical laboratories, is necessary in order to establish epidemiological trends, confi rm treatment failures, or determine the cause of specifi c infections.In another study among catheter related blood stream infections -96% were S. epidermidis [21] .Similarly in another study, of the isolated CoNS strains, 51% were S.epidermidis , 18% S.haemolyticus , 16% S. saprophyticus [22] .The results obtained in our study were similar coinciding with the fact that the most frequently isolated CoNS strain was S.epidermidis followed by S.haemolyticus .
High incidence of methicillin resistance in the Staphylococci is a common problem in many institutions [1,3,12] .The 48 % incidence of methicillin resistance observed in this study was almost equal to that noted in S.aureus , isolated in the same hospital during the same study period.
Methicillin resistance in Staphylococci necessitated the use of the glycopeptides vancomycin and recently teicoplanin

Table 1 : Distribution of CoNS in clinical specimens
Begum, et al.: Coagulase-Negative Staphylococci