A Study on surgical Site Infections, their bacteriological profile and antimicrobial susceptibility pattern

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.


Introduction
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 o c-37 o c 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 o c-37 o c 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.

Discussion
SSI is a problem in both developing countries as well as in developed countries inspite of introduction of various infection control practices and antibiotic regimens into surgical practice. 14,15 Management of patients with SSI either with gram positive organisms or gram negative organisms depend on selection of effective and appropriate antibiotic or regimen against the organisms as antibiotics play an important role in both prophylaxis and treatment of infectious diseases. 16,17 According to Nandita pal et al 18 23.3% showed single isolates whereas 36.7% showed multiple isolates.Mama et al 19 reported single isolates in 91.6% whereas multiple isolates in 8.4% and also reported that 87.4% samples were culture positive and 12.6% samples did not show any bacterial growth. In the present study the growth of single isolates are most frequent (56.07%) than multiple isolates (12.14%).

Conclusion
The study gives insight into bacterial pathogens and their antibiotic susceptibility patterns isolated from SSI in a tertiary care hospital.
Surveillance of SSI along with feedback from surgeons will help to reduce the SSI rate and this surveillance system should be developed in all hospitals and also guidelines for antibiotic use among surgical patients should also be developed and strictly followed which may provide the estimate of incidence of SSI.
From the present study it was observed that microorganisms, both gram positive and gram negatives became resistant to more commonly used drugs like penicillin, cephalosporins and even quinolones which are cost effective. We are now left with few reserve drugs like carbapenems which should be used judisiously.
New technological advances (eg: Minimally invasive procedures) and emergence of antibiotic resistant organisms (eg: MRSA) led to additional challenges in prevention, identification and treatment of SSI.
Although there are many programmes centered to basic key principles of surgical care and antibiotic prophylaxis, there are still some unresolved issues regarding some aspects in antibiotic prophylaxis in surgical care patients like drug dose in obese patients, specific timings of antibiotic administration, role of anti MRSA prophylaxis etc. To conclude there is still much to learn about pathophysiology, prevention and surveillance of SSI even after 150 years of discoveries of Louis pasteur and Joseph lister.

Conflicts of Interest:
None.