European Journal of Cardiovascular Medicine

Staphylococci are one of the major groups of bacteria inhabiting mammals’ skin, skin glands and mucous membranes.  Staphylococcus comprises 53 recognised species and 28 subspecies, most of which are found in only lower mammals. The staphylococci most frequently associated with human infection are S. aureus, S. epidermidis and S. saprophyticus. S. aureus causes a wide range of major and minor infections in man and animals and is characterised by its ability to clot blood by the action of its enzyme coagulase. Hence called Coagulase-positive staphylococcus. There are other species of staphylococci which lack this enzyme and hence are called Coagulase-negative Staphylococci (CoNS). The CoNS species as a group constituted a major component of the normal microbial flora of humans¹. In the past, CoNS were generally considered contaminants with little significance². 

CoNS species constitute a major component of the normal microflora of humans¹. Over the last two decades, the rule of CoNS species in causing nosocomial infections has been recognised and well documented, especially for S. epidermidis. The infection rate has been correlated with the increased use of prosthetic and indwelling devices and the growing number of immunocompromised patients in hospitals. CoNS are a major cause of foreign body infections caused by bacteria adhesion to biomaterials

The need exists for the accurate identification of CoNS so that precise delineation of the clinical disease produced by this group of bacteria and the determination of the etiological agent can be done.  S. epidermidis has been documented as a pathogen in numerous cases of bacteraemia, native and prosthetic valve endocarditis, surgical wounds, urinary tract infections, cerebrospinal fluid, prosthetic joint, peritoneal dialysis, ophthalmologic and intravascular catheter-related infections.   S. saprophyticus is an important pathogen in urinary tract infections.  S. haemolyticus is another most frequently encountered CoNS species.

Other CoNS species have also been implicated in a variety of infections—S. Capitis has been implicated in endocarditis, septicaemia, and catheter infections; S. warneri in endocarditis and osteomyelitis; and S. simulans in septicaemia and osteomyelitis. S. haemolytic associated with native valve endocarditis, septicaemia, peritonitis, urinary tract infections, and wound, bone and joint infections³.

Most CoNS infections are nosocomial, and their antibiogram pattern showed multi-drug resistance, including methicillin.   A high incidence of resistance to methicillin is seen in S. epidermidis that is methicillin-resistant S. epidermidis (MRSE).  Drug resistance is highest in nosocomial infections because, in hospitals, frequent contact with antibiotics leads to the elimination of sensitive organisms from the flora and their replacement with resistance strains acquired by cross-infection.   CoNS will continue to be an infective agent in the future, and studies on CoNS will be helpful in formulating and adapting specific antibiotic policies for treating CoNS infections and restricting further emergence of drug resistance strains in future.

AIMS AND OBJECTIVES: Isolation of bacteria and its species from the clinical samples and evaluation of antibiotic susceptibility.

Inclusion Criteria:

The following clinical samples were collected from the patients of S.V.R.R.G.G. Hospital and Govt. Maternity Hospital, Tirupati.

1. Pus and wound swabs.
   2. Urine from catheterised patients.
   3. Blood from septicaemia, PUO, and endocarditis patients.
2. Swabs from the patients' ears, conjunctiva, cervix, and IV cannula tips.

 Exclusion Criteria:

1. Patients age less than 10 years.
2. Patients who are not willing.

Based on cultural characteristics, strains resembling Staphylococcal characteristics were processed further to differentiate from micrococci by following tests.

1. Gram staining
2. Catalase test
3. Oxidation – fermentation test

With these tests, micrococci were excluded, and staphylococcal strains were taken for study. A coagulase test confirmed coagulase-negative Staphylococci (CoNS).

ANTIBIOTIC SUSCEPTIBILITY TESTING:

By Kirby-Bauer disc diffusion method.

Media & Reagents:

1. Mueller – Hinton Agar
2. Mc Farland 0.5 standard
3. Ruler and Calipers
4. Antibiotic discs

124 strains of CoNS isolated from various clinical samples were studied. All these strains were isolated and identified and were subjected to antimicrobial susceptibility tests.

Table. 1. Specimen-wise isolation of CoNS

A greater number of CoNS were isolated from the pus and wound swabs (33.9%), followed by urine (32.3%) and blood (21.8%).

Table. 2. Species incidence of CoNS

58. epidermidis was the predominant species (58.9%) among the different species of CoNS isolated followed by S. saprophyticus (21.8%) and S. hemolyticus (15.3%). S. hominis and S. xylosus were isolated in 2 samples each and S. warneri was isolated from 1 sample.

Table. 3. Antibiotic susceptibility pattern of CoNS

Number of CoNS strains tested: 124

*used only for 40 urine isolates.

All strains were sensitive to vancomycin.

Most of the strains were resistant to Penicillin and Co-trimoxazole.

The majority of strains were sensitive to Amikacin and Ceftriaxone.

In the case of Amoxyclav, 61 strains were found to be sensitive, and 63 strains were found to be resistant.

The CoNS species constitute a major component of humans' normal microflora. In the past, CoNS were generally considered to be contaminants having little clinical significance. Over the last two decades, the role of CoNS species in causing nosocomial infections has been recognised and well-documented, especially for the species S.epidermidis, which accounts for 50-80%.

In this study, 124 CoNS were isolated from various clinical specimens, and the results were compared with those of other studies. The majority of strains isolated were from pus and wound swabs (33.9%), followed by urine (32.3%) and blood (21.8%).  The remaining were from IV cannula and urinary catheter tips (6.5%), cervical swabs (2.4%), conjunctival swabs (2.4%) and oral swabs (0.8%).

A significant association was found between slime production and multiple antibiotic resistance. The present study correlated with the results of Deighton and U. Mohan et.al.

Table 4: Comparative study of incidence of S.epidermidis

Jayanthi Pathak⁴ studied 106 strains. Out of which 20 strains were from urine samples. 18 (90%) strains were identified as S. saprophyticus and 2 as S. epidermidis. 70 strains (66%) were methicillin-resistant. U. Mohan et.al.,⁵ studied 192 strains. S. saprophyticus (15.6%) was the second important species isolated mostly from urine specimens.  The present study correlated well with the studies of Jayanthi Pathak et.al and U. Mohan et.al.

A significant association was found between slime production and multiple antibiotic resistance. The present study correlated well with Deighton MA et al. and U. Mohan et al.'s results. All strains were sensitive to vancomycin. Most of the strains were resistant to penicillin (93.5%) and Co-trimoxazole (92.7%). Most strains were sensitive to Amikacin (68.5%) and Ceftriaxone (66.9%). In the case of Amoxyclav, 49.2% of strains were sensitive, and 50.8% were found to be resistant.

In the present study, 124 strains of CoNS isolated from various clinical samples were studied. More number of isolates were from pus (42) followed by Urine (40) and blood (27). S. epidermidis was the predominant species (58.9%) among the different species CoNS isolated followed by S. saprophyticus (21.8%) and S. hemolyticus (15.3%). From pus and wound swabs (36/42) S. epidermidis was the predominant species. In the urine sample, S.saprophyticus was the predominant species.  From blood samples S. epidermidis and S. hemolyticus were the major species.

Among the 124 CoNS isolated, 66.1% of strains were methicillin-resistant, and 33.9% were methicillin-sensitive. All strains were sensitive to vancomycin, and many strains were resistant to penicillin (93.5%) and Co-trimoxazole (92.3%).

Globally, it is found that CoNS strains are increasingly becoming drug-resistant. Hospital authorities must adapt antibiotic policy depending upon the culture and sensitivity report, as methicillin-resistant staphylococcal strains are difficult to treat. Preventive measures should be taken by the hospital authorities to eradicate the nasal carrier state of methicillin-resistant staphylococci. Clinicians will have to adopt restrictive antibiotic policies. In this study, no vancomycin-resistant strain was found.

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