Introduction: Postoperative wound infection or surgical site infection (SSI), a common post-operative complication, while seemingly infrequent and almost never lethal, contributes to morbidity and mortality, delays incisional healing and thereby generates large marginal care expenses. The magnitude of SSIs and emergence of antibiotic resistant bacterial strains are likely to increase.

Objective: To study about the bacteriological profile of the postoperative wound samples and their antibiogram in B&B Hospital, Gwarko, Lalitpur.

Methods: A total of 388 postoperative wound samples were collected and processed at Microbiology laboratory, B&B Hospital, over a period of 6 months, from April to October 2014. The bacteriological agents were isolated, identified by culture and biochemical tests and their antibiotic susceptibility pattern were determined using standard protocols.

Results: Out of 388 samples (351 swabs and 37 aspirates), 235 samples (182 single isolates and 53 multiple isolates) were culture positive. High infection rate was found in males (62.5%) than females (53.1%) and in the age group 30-40 years (25.5%). The prevalence of wound infections was not significantly affected by gender and age (P>0.05). The majority of the organisms were isolated from surgical sites after orthopedic surgery (63.01%), and from orthopedic ward (25.7%). 292 isolates of 10 different bacterial species were obtained. The predominant isolates were Pseudomonas spp. (33.9%), followed by Escherichia coli and Staphylococcus aureus. Other isolates were Acinetobacter spp., Klebsiella spp., Enterobacter spp., Coagulase Negative Staphylococci, Proteus mirabilis, Nonhemolytic Streptococci and Citrobacter spp. The most effective antibiotic for Gram positive isolates was Oxacillin (96.1%) followed by Chloramphenicol (85.2%) and, Ceftriaxone and Cefoperazone Sulbactam (66.7% each). Similarly, against Gram negative bacteria, Imipenem was most effective (74.8%), followed by Amikacin (58.8%). A total of 2.2% of S. aureus was Methicillin resistant S. aureus (MRSA).

Conclusion: Routine microbial analysis of surgical site infections and their antibiogram is recommended so as to guide clinician for the treatment of surgical site infections.

• Postoperative wound infection

• Isolates

• Antibiotics

• Surgery

Amatya J, Rijal M, Baidya R (2015) Bacteriological Study of the Postoperative Wound Samples and Antibiotic Susceptibility Pattern of the Isolates in B&B Hospital. JSM Microbiology 3(1): 1019.

Wound is a discontinuity or break of the surface of the body. Wound is a breach in the normal tissue continuum, resulting in a variety of cellular and molecular sequelae [1]. Infection of a wound may be defined as invasion of organisms through tissues following a breakdown of local and systemic host defenses [2]. Wound infection has probably been a major complication of surgery and trauma [3].

Postoperative wound infections or Surgical Site Infections (SSIs) are defined as infections that occur at incision site within thirty days after surgery. SSI may be defined as invasion and multiplication of microorganisms in body tissue which may be clinically in apparent, or result in local cellular injury because of competitive metabolism, toxins, intracellular replication or antigen-antibody response [4]. SSI accounts for 15% of all nosocomial infections and among surgical patients, represents the most common nosocomial infection [5].

Most postoperative wound infections are hospital acquired, varies from one hospital to another and they cause significant post-operative morbidity, mortality and prolonged hospital stay, leading directly or indirectly to an enormous increase in the hospitalization cost and to the emergence of new health hazards for the community [6]. These infections complicate illness, because anxiety, increase patient discomfort, delayed healing and can lead to death [7].

The occurrence of a postoperative infection is dependent upon the interaction of patient- or host-related factors, such as host immunity, nutritional status, comorbid conditions; procedurerelated factors, including the presence of foreign bodies and tissue trauma associated with the procedure; microbial properties, such as ability to adhere to tissue or foreign bodies and innate virulence, and appropriate and timely antimicrobial prophylaxis [8]. The risk of developing an SSI is largely determined by three factors: the amount, type of microbial contamination of the wound and host susceptibility [9].

Wound infection can be caused by different group of organisms like bacteria, virus, fungi and protozoa and may co-exist as polymicrobial communities especially in wound margins and in chronic wounds [10]. In many cases there is a mixed infection with more than one bacterial species [11]. It is difficult to list all the pathogens that may be found in wound isolates. Those listed are the more commonly isolated pathogens from wounds, abscess, burns, and draining sinuses. Organisms generally encountered in wound infections and abscesses are as follows [12]:

Gram positive bacteria

Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes, S. faecalis, S. pneumoniae, CoNS, etc.

Gram negative bacteria

Pseudomonas aeruginosa, Escherichia coli and other coliform, Proteus spp., Klebsiella spp., Morganella spp., Enterobacter spp., Citrobacter spp., Providencia spp., etc.

Today, MRSA has emerged as one of the most important nosocomial pathogens. Prompt diagnosis of MRSA infection is, therefore, important for patients, health care givers and for epidemiological purposes [13].

The magnitude of SSIs and emergence of antibiotic resistant bacterial strains are likely to increase. Therefore a better understanding of the spectrum of pathogens causing SSI and their susceptibility pattern is important for prompt management of patients, as antimicrobial therapy significantly influences the outcome of the patients with SSI. This study would help to establish guidelines for the management of SSIs and contribute to planning of surveillance, prevention and control of this group of infections.

The study was conducted over a period of 6 months, from April to October 2014 in the microbiology laboratory of B&B Hospital. A total of 388 pus samples were collected for culture and antibiotic susceptibility testing, from the patients of different wards of the hospital and processed following the standard laboratory techniques. The surgical wounds included in the study were from the patients who had undergone different surgical procedure at different sites.

The samples collected for the study were wound swab on a sterile cotton swab or aspirated pus in syringe from the surgical wounds. The sample was inoculated on to Nutrient agar (NA), Mac Conkey Agar (MA) and Blood Agar (BA) plates and incubated at 37 °C for 24 hours aerobically. After incubation, identification of bacterium from positive cultures was done with a standard microbiological technique which includes studying the colonial morphology, Gram stain and biochemical reactions. The antibiotic sensitivity testing of all isolates was performed by modified Kirby-Bauer’s disc diffusion method on Mueller Hinton agar using antibiotics as per CLSI guidelines. All the culture media, biochemical media and antibiotics used were from Hi Media. Each of the strain of S. aureus was screened for Oxacillin resistance using control of ATCC strain for MRSA testing.

Out of 388 samples (351 swabs and 37 aspirates), 235 samples (182 single isolates and 53 multiple isolates) were culture positive (Table 1)

Table 1: Pattern of growth in different types of samples.

Table 2: Pattern of bacterial isolates in pus sample collected from different wards.

Table 3: Distribution of bacterial isolates with the type of surgery.

Note: GI- Gastrointestinal surgery; Gyn - Gynecological surgery; Neuro - Neurological surgery; Ortho - Orthopedic surgery; Others- Debridement, Incision and drainage, etc

High infection rate was found in males (62.5%) than females (53.1%) and in the age group 30- 40 years (25.5%). The prevalence of wound infections was not significantly affected by gender and age (P>0.05).

Highest number of samples, 134 (34.5%) were collected from the orthopedic ward, followed by the surgical ward, postoperative ward, neurological ward, CCU, annex, Gynae, Pediatric, Medicine Ward and ICU. 292 isolates of 10 different bacterial species were obtained from 235 growth positive samples. Gram positive organisms were 18.5% and Gram negative bacilli were 81.5%. The predominant isolates were Pseudomonas spp. (33.9%), followed by E. coli (17.5%) and S. aureus (15.8%). Other isolates were Acinetobacter spp., Klebsiella spp., Enterobacter spp., CoNS, P. mirabilis, NHS and Citrobacter spp.

The most effective antibiotic for the Gram positive isolates was Oxacillin (96.1%) followed by Chloramphenicol (85.2%) (Table 4)

Table 4: Antibiotic susceptibility pattern of Gram positive bacterial isolates.

Imipenem (74.8%) was found to be the drug of choice for gram negative. Bacterial wound isolates, followed by Amikacin (58.8%) (Table 5)

Table 5: Antibiotic susceptibility pattern of Gram negative bacterial isolates.

The most effective drugs against Pseudomonas spp. was Imipenem (87.9%), followed by Amikacin (64.6%), Gentamicin (54.5%) (Table 6)

Table 6: Antibiotic susceptibility pattern of Pseudomonas spp.

The most effective antibiotic against S. aureus was Oxacillin (97.8%), followed by Chloramphenicol (89.1%).

Methicillin resistant S. aureus (MRSA) was found to be 1 (2.2%) which was resistant to Oxacillin, and was found to be sensitive to Vancomycin (Table 7)

Table 7: Antibiotic susceptibility pattern of S. aureus.

This study was carried out to gain insight into the distribution and carriage rate of bacterial flora that could be of potential health risk in a hospital facility mainly of the surgical units. Out of 388 samples studied, 235 (60.6%) samples showed growth and 153 (39.4%) samples showed no growth with 182 (77.4%) single isolate and 53 (22.6%) multiple isolates. Our study agreed with the study carried out by Bhatt and Lakhey [14], in Nepal, who reported that 60% swabs of total 200 samples showed positive growth. However, Banjara et al. [15], in TUTH reported that rate of surgical wound infection was 4.7% (189/3988). The result agrees with the study carried out by Anguzu and Olila [16], in Uganda, out of 59.6% positive growth samples, 72.7% had pure growth while 27.3% had mixed growth. Of the 388 samples collected, 307 (79.1%) were male patients and 81 (20.9%) were female patients. The growth was found to be higher in male patients 192 (62.5%) than in female patients 43 (53.1%).

The prevalence of wound infections was not significantly affected by gender (P>0.05). In the study of Nwachukwu et al. [9], in Nigeria, 68.8% were males and 31.11% were females. Anguzu and Olila [16] have also found the similar result with 59.6% male and 40.4% female patients. Thus, this study complies with all of the above study that male patients were more affected than female patients. The reason may be that males are highly exposed to external environment than female.

In our study, pus samples were collected from patients ranging in age from 1 month to 85 years old. Out of 235 culture positive samples, highest number of samples was from the age group (30-40) years, followed by the age group 20-30, 10-20 and 40-50. The patients in the age groups 70-80 and above 80 were relatively found to be less affected. The prevalence of wound infection was not significantly affected by age. Similar results were obtained in the study carried out by Kumari [17] (21-30 years), in Bir Hospital, and Raza et al. [18] (21-40 years) in Nepal. It was found that SSI is prevalent mostly in the working age group. People in the age group 20-40 years are thought to be more leisurely active age which may explain why most wound patients were of this group. Above 70 years old, people are generally less actively involved in various types of work, so may be less prone to accidents and the resulting wound infections.

Majority of the organisms were isolated from surgical sites after orthopedic surgery (63.01%), and from orthopedic ward (25.7%). In this study, a total of 292 isolates of 10 different bacterial species were obtained, of which 54 (18.5%) were Gram positive and 238 (81.5%) were Gram negative bacteria. The predominant isolates were Pseudomonas spp. (33.9%), followed by E. coli (17.5%) and S. aureus (15.8%). Other isolates were Acinetobacter spp., Klebsiella spp., Enterobacter spp., CoNS, P. mirabilis, NHS and Citrobacter spp.

Banjara et al. [15] at TUTH showed that high rate of Gram negative bacteria are found in HAI. In the study carried out by Kumari [17], a total of 253 bacterial species were isolated of which 98 (38.8%) were Gram positive and 155 (61.2%) were Gram negative bacteria. A similar result was obtained in the study of Ranjan et al. [19] on postoperative wound infection, in India, where P. aeruginosa was isolated as the predominant species (29.6%), followed by E. coli (20.3%), Klebsiella spp. (16.6%), S. aureus (14.3%), Proteus spp. (6.3%) and C. freundii (0.6%). Similarly, the study carried out by Manyahi [20] in Tanzania, demonstrated the predominance of gram negative bacterial isolates in SSIs, P. aeruginosa being the commonest isolated organism followed by S. aureus, Klebsiella pneumoniae, P. mirabilis and Acinetobacter baumannii. However, in the study carried out by Zafar et al. [10] in Lahore, S. aureus was isolated as the predominant species (41.28%), followed by Pseudomonas spp. (18.35%).

The pattern of organisms causing SSIs in the current study was in contrast with some of the previous studies which reported S. aureus as the most common SSI bacterial pathogen. The possible reason for variation in the studies could be attributed to differences in the populations investigated; diversity of surgical procedures performed on the study participants, as well as timing of specimen collections. There are multiple factors that could have contributed to the high proportion of infections due to Gram negative pathogens in this study.

In this study, direct smear Gram staining and culture were positively correlated (rxy = 0.99) which was consistent with the results of the study conducted by Kumari [17] at Bir Hospital.

Gram positive isolates were 96.1% sensitive to Oxacillin, followed by Chloramphenicol (85.2%) and 100% resistant towards Penicillin. Imipenem was found to be the drug of choice for gram negative bacterial wound isolates which were 74.8% sensitive, followed by Amikacin (58.8%). The Gram negative bacterial isolates were found to be 100% sensitive towards Colistin. In the study carried out by Parajuli et al. [21] in Nepal, Gentamicin (82.83%) and Cloxacillin (72.72%) were the most effective antibiotics, while Cotrimoxazole (38.38%) was found to be the least effective drug for Gram positive isolates. Similarly, in the study of Kumari [17], the Gram negative isolates were sensitive to Imipenem (97.62%), Amikacin (82.14%) and Gentamicin (52.38%), while least effective was Amoxyclav (14.29%) and Ceftriaxone (23.81%).

Methicillin resistant S. aureus (MRSA) was found to be 1 (2.2%) which was resistant to Oxacillin, and was found to be sensitive to Vancomycin (100%). %). S. aureus was found to be 59.74% resistant to Oxacillin and 100% sensitive to Vancomycin [21].

This study shows that Gram negative bacteria are more common than Gram positive bacteria in the postoperative wound samples. Among Gram negative bacteria, Pseudomonas spp. and E. coli, and among Gram positive bacteria, S. aureus was found to be the most predominant isolates respectively. So, they should be considered as serious problem and precautions should be taken to minimize the wound contamination by using appropriate antibiotics with continuous surveillance to monitor antimicrobial susceptibility pattern of the common isolates found in SSI.

From the 388 samples processed in this study, 292 isolates of 10 different bacterial species were obtained from the 235 growth positive samples. The majority of the organisms were isolated from surgical sites after orthopedic surgery (63.01%), and from orthopedic ward (25.7%). Gram negative bacteria were found to be more predominant in the postoperative wound samples compared to the gram positive organisms. Pseudomonas spp. (33.9%) was one of the major organisms isolated, followed by E. coli, S. aureus, Acinetobacter spp. and Klebsiella spp. The most effective antibiotic for Gram positive isolates was Oxacillin followed by Chloramphenicol. Similarly, against Gram negative bacteria, Imipenem was most effective, followed by Amikacin. Methicillin resistant S. aureus (MRSA) was found to be 1 (2.2%) which was resistant to Oxacillin, and was found to be sensitive to Vancomycin (100%). So Vancomycin could be the drug of choice for MRSA. Thus, this study concludes that wound infection remains an ongoing problem. Although complete eradication of wound infection is not possible precautions should be taken to minimize the wound contamination by using appropriate antibiotics with continuous surveillance to monitor antimicrobial susceptibility pattern of the common isolates found in SSI. In this study, Pseudomonas spp. and Acinetobacter spp., the organisms associated with nosocomial infections, was found to be predominant, thus, hospital disinfection and treatment protocols should be practiced vigorously and monitored regularly to keep the incidences in control. Besides, the prime focus for the problem-solving approach should be given to the personal hygiene of the patients and that of the health workers as well because studies have reported that hands of health care workers and patients can play a role in transfer of Gram negative bacteria during cross infection.

We acknowledge the cooperation rendered by the staffs of the Microbiology department of St. Xavier’s College, Microbiology laboratory of B&B Hospital and all the patients.

1. Pintu, Ahmed K. Aids to short practice of surgery. 2nd edition. Aids publication. 2001; 13-17.
2. Leaper DJ. Wound Infection. Russell RCG, William NS, Bulstrode CJK, editors. In: Bailey & Love’s Short Practice of Surgery; 24th edition. London: Arnold. 2004; 118-132.
3. Pradhan GBN, Agrawal J. Comparative study of postoperative wound infection following emergency lower segment caesarean section with and without the topical use of fusidic acid. Nepal Med Col J. 2009; 11: 189-191.
4. Ramesh A, Dharini R. Surgical site infections in a teaching Hospital. Clinio Microbiological and Epidemiological profile. Int J Biol Med Res. 2012; 3: 2050-2053.
5. Watanabe A, Kohnoe S, Shimabukuro R, Yamanaka T, Iso Y, Baba H, et al. Risk factors associated with surgical site infection in upper and lower gastrointestinal surgery. Surg Today. 2008; 38: 404-412.
6. Bratzler DW. The Surgical Infection Prevention and Surgical Care Improvement Projects: promises and pitfalls. Am Surg. 2006; 72: 1010-1016.
7. NINSS. Surveillance of Surgical Site Infection in English Hospitals: a national surveillance and quality improvement programme. Public Health Laboratory Service. 2002.  
8. An APIC Guide. Guide to the Elimination of Orthopedic Surgical Site Infections. 2010.
9. Nwachukwu NC, Orija FA, Okike UM. Antibiotic susceptibility pattern of bacterial isolates from surgical wounds in Abia State University Teaching Hospital (ABSUTH), Aba-Nigeria. Res J Med and Med Sci. 2009; 4: 575-579.
10. Zafar A, Anwar N, Hasan E. Bacteriology of infected wounds- A study conducted at Children hospital Lahore. E:/Biomedica. 2007; 23.
11. Collee JG, Fraser AG, Marmion BP, Simmons A. Mackie and McCartney Practical Medical Microbiology, 14th edition. Churchill Livingstone, New York. 2007
12. Cheesbrough M. District laboratory Practice in tropical Countries. Part 2, Cambridge University Press, London. 2000; 26-196
13. Sanjaya KR, Nagedra Prasad MN, Vijaya Kumar GS. A study on isolation and detection of drug resistance gram negative bacilli with special importance to postoperative wound infection. J Microbiol Antimicrobials. 2010; 2: 8-75.
14. Bhatt CP, Lakhey M. The Distribution of pathogens Causing Wound Infection and Their Antibiotic Susceptibility Pattern. J. Nepal Health Res. Counc. 2007; 5: 22-26
15. Banjara MR, Sharma AP, Joshi AB, Tuladhar NR, Ghimire P, Bhatt DR. Surgical wound infections in patients of Tribhuvan University Teaching Hospital. J Nepal Health Res Counc. 2003; 1: 41-45
16. Anguzu JR, Olila D. Drug sensitivity patterns of bacterial isolates from septic post-operative wounds in a regional referral hospital in Uganda. Afr Health Sci. 2007; 7: 148-154.
17. Kumari K. Pattern of Bacterial isolates and antibiogram from open wound infection among the indoor patients of Bir Hospital. A Dissertation submitted to the Central Department of Microbiology, Tribhuvan University, Kathmandu, Nepal. 2008
18. Raza MS, Chander A, Ranabhat A. Antimicrobial Susceptibility Patterns of the Bacterial Isolates in Post-Operative Wound Infections in a Tertiary Care Hospital, Kathmandu, Nepal. Open J Med Microbiol. 2013; 3: 159-163.
19. Ranjan KP, Ranjan N, Bansal SK, Arora DR. Prevalence of Pseudomonas aeruginosa in post-operative wound infection in a referral hospital in Haryana, India. J Lab Physicians. 2010; 2: 74-77.
20. Manyahi J. Bacteriological spectrum of postoperative wound infections and their antibiogram in a tertiary hospital, Dar es Salaam, Tanzania. A dissertation submitted to Muhimbili University of Health and Allied Sciences. 2012.
21. Parajuli P, Basnyat SR, Shrestha R, Shah PK, Gurung P. Identification and Antibiotic Susceptibility Pattern of Aerobic Bacterial Wound Isolates in Scheer Memorial Hospital. JSM Microbiology. 2014; 2: 1011.