Abstract

Introduction: Surgical site infection (SSI) is second most common hospital acquired infection. The rate of SSI ranges from 2.5% to 41.9% globally. The identification of bacterial pathogens and their antibiotic susceptibility testing is required for successful treatment of SSI.

Objective: To study the bacterial pathogens in patients with SSI and their antibiotic susceptibility pattern.

Results: Out of 107 samples collected from post operative cases with symptomatic wound infection, 60(56.07%) samples showed single isolates where as 13(12.14%) samples showed multiple isolates and 34(31.77%) did not show any bacterial growth. Out of 86 isolates, 29(33.7%) isolates are Gram positive organisms and 57(66.3%) isolates are Gram Negative organisms, among Gram positive isolates Staphylococcus aureus (MSSA) (44.8%) is predominant pathogen and in Gram negative isolates Escherichia coli (42.1%) is the predominant pathogen. In the present study Gram positive organisms showed high susceptibility to vancomycin and linezolid (100%) followed by gentamicin (79.3%) and Gram negative organisms showed high susceptibility to polymyxin B (94.7%) followed by imipenem (75.4%).

Conclusion: The study gives an insight into bacterial pathogens and their antibiotic sensitivity patterns isolated from SSI and there should be surveillence of SSI which helps to reduce the rate of SSI as well appropriate use of antibiotics.

Keywords: Hospital acquired infections, Surgical site infections (SSI), Antibiotic sensitivity testing, Gram positive bacteria, Gram negative bacteria.

As a part of innate immunity the main function of intact skin in humans is to control the microbes that are resident on the skin surface and also it prevents the underlying tissues from colonization or invasion by pathogens.

If due to any condition (wounds) where there is exposure of subcutaneous tissue due to loss of integrity of skin it provides good environment for colonization and proliferation of microorganisms and so any wound is at risk of developing infection.^[1]

Infections occurring in the wound are major barriers for healing which shows impact on patients, which may prolong the hospital stay and effects the quality of life^[2] and wound healing requires a healthy environment which will result in normal healing process and also with minimal scar formation.^[3]

SSI which was previously termed as post operative wound infections was termed by US center for disease control in order to prevent the confusion between infection at site of surgical incision and infection at the site of traumatic wound^[4] and SSI can be defined as proliferation of pathogenic microorganisms at the site of surgical incision which may involve skin and subcutaneous fat (superficial), Musculofacial layers (deep) in an organ/cavity.^[5]

Hospital acquired infections are common type of nosocomial infections in surgical patients^[6] and SSI is the second most common hospital acquired infection.^[7] Generally SSI occur within 30 days after the procedure but in cases of any added implants the duration of SSI may also extend upto one year from the operation procedure.^[8]

Despite efforts to prevent these SSI, the data of National Centre for Health Statistics^[9] and National Healthcare Safety Network^[10] suggests that 2,50,000 to 1 million SSI complicate 26.6 million inpatient surgical procedures performed annually in USA and this impact of SSI have been estimated to be 3.7 million hospital days and also excess cost of 1.6 billion dollars.^[7]

The rate of SSI ranges from 2.5% to 41.9% globally^[11]and the risk of acquiring hospital acquired infection is high in patients undergoing surgery and also 77% of death of patients with hospital acquired infections are related to SSI.^[12]

Hospital acquired infections are complicated by the increasing prevalence of some multi drug resistant organisms like Methicillin resistant Staphylococcus aureus (MRSA), Coagulase Negative Staphylococci, Vancomycin Resistant Enterococci (VRE), Escherichia coli, Acinetobacter baumanii, Pseudomonas aeruginosa^[13] which increase the mortality and morbidity.

Materials and Methods

This is a prospective observational study carried out after approval by institutional ethics committee for a period of one year (from August 2017 to August 2018) and a total of 107 samples were collected from either gender and different age groups after taking intra operative and post operative details. Samples were collected from SSI from patients with complaint of pain, swelling, discharge, delayed or non healing wound at surgical site.

Two swabs were collected from each subject from the surgical site following standard procedure. One swab was kept in a sterile test tube and the other in sterile nutrient broth( in order to maintain the viability of organisms) and they were immediately transported to microbiology laboratory and these specimens were inoculated onto Nutrient agar, Blood agar, Chocolate agar, MacConkey agar within 30minutes to 1 hour after collection and these are incubated at 35^oc-37^oc aerobically and are observed for growth after 24hrs and the plates which did not show growth after 24hrs are re-incubated for other 48hrs.

The isolates were then identified by colony morphology, Gram’s stain and conventional biochemical tests used for Gram positive and Gram negative bacteria. Antibiotic susceptibility pattern of the isolates was studied by Kirby bauer disc diffusion technique following Clinical Laboratory Standards Institute (CLSI) guidelines^12,13 and the diameter of zone of inhibition was measured and interpreted as sensitive(S), intermediate (I) and resistant (R) after incubation at 35^oc-37^oc for 18-24 hrs using antibiotic discs (Himedia Labs) Control strains like Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Pseudomonas aeruginosa (ATCC 27853) were included in the study and the study findings are being explained in words, percentages and tables. ESBL detection in gram negative isolates was performed after screening by checking for presence of resistance against ceftriaxone, cefotaxime, ceftazidime, cefpodoxime and conformed by combined disc diffusion test using cefotaxime (30mcg) and ceftazidime (30mcg) antibiotic disc (Himedia labs) with and without clavulanic acid (10mcg) and MRSA detection was done by E-test using MHA with 2% Nacl with 0.5McFarland density according to CLSI guidelines.^[12],^[13]

Results

In present study a total number of 4642 (100%) surgical procedures were done in our institute during the study period out of which 107(2.30%) (Table 1) samples were collected from symptomatic SSI cases and out of the samples collected from post operative cases, 60(56.07%) samples showed growth of single isolates whereas 13(12.14%) samples showed multiple isolates and 34(31.77%) did not show any bacterial growth after 48hrs of aerobic incubation. (Table 2).

In the present study out of 86 isolates, 29(33.7%) isolates were gram positive organisms and 57(66.3%) isolates were gram negative organisms (Table 3). Gram negative organisms were more frequently isolated than Gram positive organisms.

Out of 29 Gram positive isolates, Staphylococcus aureus (MSSA) (44.8%) is the predominant pathogen followed by MRSA (31.03%), Coagulase Negative Staphylococci and Enterococcus species (10.3%), Streptococcus pyogenes (3.44%) respectively. (Table 4). Out of 57 Gram negative isolates, 24(42.1%) showed Escherichia coli followed by Klebsiella species 17(29.8%), Pesudomonas aeruginosa 15(26.3%), Acinetobacter baumanii 1(1.8%) respectively (Table 5). In the present study out of 86 isolates, 57(66.3%) were isolated from superficial SSI and 29(33.7%) from Deep or organ/space SSI and in superficial SSI among gram positives MSSA (15.78%) is predominant pathogen and among gram negatives Escherichia coli (26.31%) is predominant pathogen and from deep or organ /space SSI also MSSA (13.78%) is predominant pathogen among gram positives and Escherichia coli (31.03%) is predominant pathogen among gram negatives (Table 6).

In the present study, Gram positive organisms showed high susceptibility to vancomycin and linezolid (100%) followed by gentamicin (79.3%), tetracycline (75.9%), neomycin (55.2%), co-amoxyclav (48.3%), erythromycin, oxacillin, ceftriaxone and cephalothin (44.8%), cotrimoxazole (34.5%), ciprofloxacin (27.6%), penicillin (3.4%) (Table 7) whereas Gram negative organisms showed high susceptibility to polymyxin B(94.7%) followed by imipenem (75.4%), amikacin (73.7%), meropenem (71.96%), gentamicin (64.9%), piperacillin-tazobactam (52.6%), neomycin (49.1%), cefaperazone-sulbactam (43.8%), ciprofloxacin (40.3%), co-amoxyclav (33.3%), cotrimoxazole (26.3%), ceftriaxone, ceftazidime (10.5%), cephalothin (7%) respectively (Table 8). In the present study out of 86 isolates, 23(26.7%) are multidrug resistant and 8(9.3%) are carbapenem resistant (Table 9) and among 57 gram negative isolates 25(43.9%) were ESBL producers (Table 10) and overall rate of HAI in our institute is 1.9%.

Table 1: Shows total number of surgical procedures done during study period, no. of symptomatic SSI and rate of Hospital Acquired Infection (HAI) in our institute.

Table 2: Shows number of isolates from clinical specimens.

Table 3: Shows number of Gram positive and Gram negative organisms isolated from clinical specimens.

Table 4: Shows different types of Gram positive organisms.

Table 5: Shows different types of Gram negative organisms.

Table 7: Showing the antibiotic susceptibility pattern of gram positive organisms to various antibiotics.

Table 8: Showing the antibiotic susceptibility pattern of gram negative organisms to various antibiotics.