Postoperative wound infections and their antimicrobial susceptibility pattern in a tertiary care hospital in salem, india

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ISSN Print: 2278 – 2648 IJRPP | Vol 3 | Issue 1 | Jan–Mar - 2014
ISSN Online: 2278-2656 Journal Home page: www.ijrpp.com
Research article Open Access
Postoperative wound infections and their antimicrobial susceptibility pattern in a tertiary care hospital in salem, India.
J.Lalithambigai*, A.Kavitha, R. Indra Priyadharsini, K.R.Rajesh.
Department of Microbiology, Vinayaka Mission’s Kirupanada Variyar Medical College and Hospital (VMKVMC & H), Seeragapadi, Salem-636308, India.
* Corresponding author: J. Lalithambigai
E-mail id: j.lalithambigai4@gmail.com
Abstract
Background: Surgical site infection (SSI) is defined as an infection that occurs at an incision site within 30 days after surgery. Postoperative wound infections have been an important cause of morbidity and cost burden for the patients.
Aim & Objectives: To isolate and identify the bacteria causing postoperative wound infections and to determine the antimicrobial susceptibility pattern.
Materials & Methods: One hundred and ten pus samples and wound swabs were collected from clinically suspected post-operative wound infection in Vinayaka Mission’s Kirupanada Variyar Medical College and Hospital, Salem from November 2011 to October 2012. The samples were processed as per standard guidelines. Antimicrobial susceptibility testing was performed as per CLSI guidelines.
Results: Out of 110 pus samples and wound swabs, 41 samples (37.27%) were culture positive, out of which 5 samples showed more than 1 isolate. Sixty nine samples (62.72%) were culture negative. The common organisms isolated were Staphylococcus aureus 18(39.13%), Escherichia coli 10(21.73%), Klebsiella pneumoniae 8(17.39%) and Pseudomonas aeruginosa 7(15.21%). Most of the Staphylococcus aureus exhibited resistance to cefoxitin, cefazolin and gram negative bacilli showed resistance commonly to first and second generation cephalosporins.
Conclusion: Staphylococcus aureus was the most frequently isolated pathogen from post- operative wound infections. Antibiotic susceptibility pattern of various isolates help to assist the clinician in appropriate selection of empirical antibiotics especially against hospital acquired infections.
Key words: Post –Operative wound infections, Antimicrobial susceptibility pattern, Gram negative organisms, Gram positive organisms.
INTRODUCTION
Besides skin and soft tissue infections that occur primarily as a result of a break in the skin surface,
wound infections can occur as complications of surgery, trauma and bites or diseases that interrupt a
International Journal of Research in Pharmacology & Pharmacotherapeutics

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mucosal or skin surface1. Postoperative wound infections can be caused through two major sources: exogenous and endogenous2. Surgical site infection (SSI) is the most common nosocomial infections in surgical patients and defined as infections occurring within 30 days after surgical operations and affecting either the incision or deep tissue at operation site3. The development of surgical site infection (SSI) is related to three factors firstly, the degree of microbial contamination of the wound during surgery; secondly, the duration of the procedure, and thirdly, host factors such as diabetes, malnutrition, obesity, immune suppression, advanced age and a number of underlying disease states. Factors leading to higher risk of infection have been described and prophylaxis with antibiotics will definitely curtail/ prevent surgical wound infection4. Postoperative wound infection delays recovery, increased hospital stay and may produce long lasting sequelae5. As a result of indiscriminate use of antimicrobial agents, significant changes occur in microbial genetic ecology, so spread of antimicrobial resistance is now a global problem6.The aim of the study was to isolate and identify the bacteria causing postoperative wound infections, to determine their antimicrobial susceptibility pattern.
MATERIALS AND METHOD
This prospective study was designed to determine the distribution of the bacterial pathogens and their antimicrobial susceptibility pattern from suspected cases of postoperative wound infections. All the 110 samples were obtained from postoperative patients who were admitted to the VMKVMC and Hospital, Salem between November 2011 to October 2012. The 76 pus samples and 34 wound swabs were collected under aseptic precautions and were transported to laboratory without delay.
The samples were subjected to Gram staining and cultured on nutrient agar, blood agar and MacConkey agar. Organisms were identified based on the cultural characteristics and by standard biochemical tests7.
All the isolates were tested for antimicrobial susceptibility by the disc diffusion technique according to the Clinical and Laboratory Standards Institute (CLSI) guidelines8.
RESULTS
A total number of 46 isolates were obtained from 110 pus samples and wound swabs which were collected from clinically suspected postoperative wound infections. 41(37.27%) samples were culture positive, out of which 46 isolates were obtained. Five samples showed more than 1 isolate. 69(62.72%) samples were culture negative.
Figure 1: Distributions of the sex in culture positive samples.
The males constituted 56% (n=23) while females constituted 44% (n=18) of the total number of 41 culture positive samples.
Female 44%
Male 56%

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Figure 2: Distributions of age in surgical site infections.
The most commonly affected age group patients were 51-60 followed by 41-50 whereas 21-30 age group of patients were least affected.
Figure 3: Percentage distributions of isolated organisms.
The predominant organism among gram positive cocci (45.65%) was Staphylococcus aureus (39%). The predominant organism among gram negative bacilli (54.34%) was Escherichia coli (22%) followed by Klebsiella pneumoniae (18%), Pseudomonas aeruginosa (15%).
Antibacterial susceptibility pattern of gram positive cocci and gram negative bacilli to various antibiotics are shown in the table 1 and table 2.
Age group
0
2
4
6
8
10
12
14
16
0-10
11-20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
No .of cases
18(39%)
10(22%)
8(18%)
7(15%)
2(4%)
1(2%)
Staphylococcus aureus
Escherichia coli
Klebsiella pneumoniae
Pseudomonas aeruginosa
CONS
Enterococcus species

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Table 1: Antibacterial sensitivity pattern of gram positive cocci.
Antibiotics
Bacterial isolates (sensitivity pattern% )
S.aureus
n(%)
CONS#
n(%)
Enterococus species
n(%)
Penicillin (10U)
5(27.77)
1(50)
0
Cefoxitin (30μg)
8(44.44)
2(100)
-
Gentamicin (10μg)
16(88.88)
1(100)
1(100)*
Erythromycin (15μg)
15(83.33)
1(100)
1(100)
Clindamycin (2μg)
15(83.33)
1(100)
1(100)
Cefazolin (30μg)
5(27.77)
2(50)
0
Cotrimoxazole
(1.25/23.75μg)
10(55.55)
2(50)
1(100)
Ciprofloxacin (5μg)
10(55.55)
2(100)
0
Levofloxacin (5μg)
15(83.33)
2(100)
1(100)
Vancomycin (30μg)
18(100)
2(100)
1(100)
Linezolid (30μg)
18(100)
2(100)
1(100)
Teicoplanin (30μg)
18(100)
2(100)
1(100)
*For High Level Gentamicin (HLG) (120μg)
# Coagulase –negative staphylococci
The gram positive cocci showed 100% sensitivity to vancomycin, teicoplanin and linezolid. Staphylococcus aureus showed resistant to penicillin, cefazolin (72.73%) followed by cefoxitin (55.56%).
Table 2: Antibacterial sensitivity pattern of gram negative bacilli.
Antibiotics
Bacterial isolates (Sensitivity pattern %)
Escherichia coli
n(%)
Klebsiella
pneumoniae
n(%)
P.aeruginosa
n(%)
Ampicillin (10μg)
3(30)
0
2(28.57)
Amoxy-clav (20/10μg)
7(70)
6(75)
6(85.71)
Cefazolin (30μg)
3(30)
2(25)
2(28.57)
Cefuroxime (30μg)
5(50)
4(50)
2(28.57)
Cefotaxime (30μg)
6(60)
5(62.5)
5(71.42)
Cefepime (30μg)
6(60)
5(62.5)
5(71.42)
Ciprofloxacin (5μg)
6(60)
5(62.5)
4(57.14)
Levofloxacin (5μg)
9(90)
8(100)
6(85.71)
Amikacin (30μg)
9(90)
7(87.5)
6(85.71)
Cotrimoxazole
(1.25/23.75μg)
7(70)
4(50)
3(42.85)
Imipenem (10μg)
10(100)
8(100)
7(100)
Piperacillin tazobactum
(100/10μg)
10(100)
8(100)
6(85.71)

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The gram negative bacilli showed 100% sensitivity to imipenem, pipercillin tazobactum whereas Pseudomonas aeruginosa showed 85.71% sensitivity to pipercillin tazobactum. All gram negative isolates showed more than 85% sensitivity to levofloxacin, amikacin and more than 60% sensitivity to amoxy- clav, cefotaxime, cefepime. A majority of the isolates showed more than 70% resistant to ampicillin and cefazolin.
Discussion
Inspite of proper application of the basic principles in surgical wound care, a number of patients develop infections needing proper identification of the organisms for appropriate management9. A changing pattern of isolated organism and their antimicrobial sensitivity; (it varies from hospital to hospital and region to region) is a usual feature. Many a time patients’ lives are lost after extensive surgery, owing to microbial infections and improper treatment. Thus, the study is clinically relevant in the present scenario by not only observing the spectrum of microorganisms isolated from surgical patients (nosocomial infections) but also in evaluating their antimicrobial susceptibility pattern4.
In our study 37.27% samples showed growth on culture and it was comparable with study done by Anbumani et al10, where 47% of samples were culture positive. The predominance of males 56% (n=23) in culture positive cases is probably due to more exposure to the environment and more chances of exposure to accidents. This was similar to the study done by Siguan et al9 (57.3%). But it was comparably low to other studies done by Shriyan et al2, Verma et al4 which showed 72% and 71% of predominance in males respectively. In this study, postoperative wound infection was common in 51-60 years of age group of people. This result correlates with the study done by Isibor et al5 where more than 50 years of age group people were commonly affected. Isibor et al5 reported high rates of infected wounds may be due to decline in immunological competence among people in older age groups.
In our study Staphylococcus aureus was the most frequently isolated pathogenic bacteria from postoperative wound infections which was similar to the other studies done by Shriyan et al2, Noroozi et al3, Isibor et al5, Siguan et al9, Anbumani et al10. The predominance of S. aureus is however not surprising as it forms the bulk of the normal flora of the skin and nails5. Escherichia coli was the next common organisms causing wound infections followed by Klebsiella pneumoniae, Pseudomonas aeruginosa which was similar to other study done by Verma et al 2, Anbumani et al10 .This confirms that most wound infections arising from abdominal procedures are presently acquired from patients own faecal flora5.
In our study, Staphylococcus aureus showed 100% sensitivity to vancomycin, linezolid, teicoplanin followed by gentamicin (88.88), erythromycin and levofloxacin (83.33%) and reduced sensitivity to penicillin, cefazolin (27.77%), cefoxitin (44.44%). But the study done by Goswani et al6 had shown variable susceptibility pattern with penicillin (29.82%), methicillin (29.17%), cefazolin (31.25%), ciprofloxacin (41.67%) and levofloxacin (66.67%). In a study done by Shriyan et al2, Staphylococcus aureus showed 100% sensitivity to vancomycin, linezolid, teicoplanin followed by gentamicin (98.2%) which was similar to this study. More than 50% of the E.coli and Klebsiella pneumoniae were resistant to ampicillin, cefazolin and cefuroxime, while only few (<30%) were resistant to the combination of amoxicillin with clavulanic acid and majority were susceptible to third generation cephalosporin – cefotaxime (60%), imipenem and piperacillin with tazobactum (100%) which was similar to the study done by Anbumani et al10. Pseudomonas aeruginosa isolates were susceptible to imipenem (100%), piperacillin with tazobactum and levofloxacin (85.71%), cefotaxime (71.42%) which was similar to the study done by Anbumani et al10.
The susceptibility data collected in this study shows that some antibiotics would have very limited usefulness for the prophylaxis or the empirical treatment of wound infections. For instance, most of the gram- negative bacilli were found to be resistant to ampicillin and cefazolin while the majority of staphylococcal strains were resistant to cefoxitin.
According to the study done by Giacometti et al11, preoperative prophylaxis can decrease the incidence of surgical wound infection. Cefazolin which is used for surgical prophylaxis in hospitals has now become increasingly ineffective to common wound pathogens, methicillin – resistant S. aureus and P. aeruginosa. A close collaboration between surgeons

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and microbiologists is needed10,11. On the basis of our results, antimicrobial agents or drug combinations with wider spectra of activity like gentamicin, erythromycin, levofloxacin for gram positive cocci and amoxy-clav, amikacin, levofloxacin for gram negative bacilli are desirable for preoperative prophylaxis or treatment of surgical infection.
Postoperative wound infection in any hospital depends on the hospital environment and irrational use of antibiotics. Antibiotic resistance can be controlled by appropriate antimicrobial prescription, prudent infection control, new treatment alternatives and continued surveillance6. So updating the antibiogram periodically and comparative studies in the same hospital over years will further reduce the rate of postoperative wound infections to a considerable extent.
This study gives us an insight to the current state of causative organisms of post-operative wound infections and their sensitivity pattern, discourages the indiscriminate use of antibiotics and continued surveillance to prevent further development of bacterial drug resistance. An effective national & state level antibiotic policy along with infection control measures and draft guidelines should be introduced to preserve the effectiveness of antibiotics and for better patient management.
Acknowledgement
We would like to thank the hospital for providing facility and financial assistance to make this study possible.
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