Introduction
Health care-associated infections (HAI) are acquired by patients during the process of receiving care and represent the most common adverse event affecting patient safety worldwide.1 The HAIs can be classified into central line-associated bloodstream infections, catheter-associated urinary tract infections, surgical site infections and ventilator-associated pneumonia.2 The term “surgical wound infection” was replaced by “surgical-site infection” by the Surgical Wound Infection Task Force in the year 1992.3 Surgical Site Infection(SSI) by definition refers to an infection which occurs within 30 days after the surgery or within 1 year when an an implant is left in place after the surgery and involving the incision or deep tissues at the operated site or infections involving organ or body space other than the incision, which was opened or manipulated during an operation.4 SSIs are classified by The Centre for Disease Control (CDC), USA into superficial incisional SSI, deep incisional SSI, and organ/space SSI .3 Recent work by the World Health Organization (WHO) shows that SSI affects up to one third of patients who have undergone a surgical procedure is in low- and middle-income countries where the endemic burden of HAI is also significantly higher than in high-income nations. 1 SSI is the leading cause of all HAIs in developing countries.5
SSIs are a frequent cause of morbidity and mortality among inpatients of hospitals.6 SSIs lead to an increased economic burden on the healthcare systems, including additional postoperative hospital stay and costs.7 According to the WHO and the CDC, SSIs are considered as one of the most preventable HAIs.8 Despite usage of prophylactic antibiotics both pre- and postoperatively along with various other preventive measures such as sterilization methods, use of barriers, improved operating room ventilation, improved surgical techniques SSIs are still a serious problem among postoperative patients.5 This has been mainly attributed to the increasing emergence of antibiotic resistance due to irrational use of antibiotics, this inappropriate choice of antibiotics increases selection pressure favouring emergence of pathogenic drug resistant bacteria.5 The incidence of postoperative SSI is seen to vary widely between patients, procedures, surgeons, hospitals and geographical locations.9 In developing countries the problem is more complicated due to overcrowded hospitals, poor infection control practices, and inappropriate use of antibiotics.10 Due to lack of standardized diagnosis, absence of surveillance and notification system in many developing countries there is lack of data on the global epidemiology of SSI.5
Usually these infections are caused either by exogenous and/or endogenous micro organisms which enter the operative wound either during the surgery causing primary infection or after the surgery leading to secondary infection.11 The risk of SSIs are also significantly influenced by a number of patient related factors, procedure related factors , another important factor is the virulence and the invasiveness of the organism involved.11 Numerous bacteriological studies reveal that gram-positive and gram-negative bacteria both play a role in the infection of surgical wounds.3 The most common among these bacteria is Staphylococcus aureus (31.58%) followed by Klebsiella pneumoniae (26.31%), Pseudomonas aeruginosa (15.79%), Escherichia coli (10.53%), Acinetobacter (10.53%) and Proteus mirabilis (5.26%). 3 Most of these bacteria are multi-drug resistant posing a major problem for surgeons. 3 For proper management of the patients it is very essential to know which pathogen has caused the infection and also its antibiotic susceptibility.12 Especially in the situation where empirical treatment has to be started without the benefit of the Gram-stain or culture and sensitivity results, knowledge regarding the most likely organisms and their prevailing antibiotic sensitivity pattern will be helpful.13
Therefore the information regarding the common organisms causing SSI and their antibiotic susceptibility pattern will be helpful in choosing the most effective antibiotics early on and thereby help in preventing further life-threatening infections. Given this scenario where the vital knowledge of the most probable microorganism and also their existing antibiotic susceptibility pattern will be helpful in preventing SSI. The present study was undertaken to know about the aerobic bacteriological profile and antibiotic susceptibility pattern of surgical site infections in our hospital.
Materials and Methods
This retrospective study was carried out on 320 culture positive samples received over a one year period from January 2019 to December 2019 in the department of Microbiology from Surgery, Orthopaedics & Obstetrics and Gynaecology (OBG) departments of KIMS Hospital. Tissue, Discharge and swabs received from the surgical wounds of patients were analysed. Microbiological profile of the aerobic isolates and its antibiotic susceptibility pattern was collected from the maintained records in the department of microbiology and analysis was done. The samples were processed as per standard microbiological methods. Two swabs were collected. One swab used for smear preparation and Gram stain. The second swab was used for aerobic bacterial culture by inoculation on various culture media like blood agar, chocolate agar, MacConkey agar, thioglycollate broth etc. The isolates were identified by relevant biochemical tests.14 The isolates were subjected to antibiotic susceptibility testing on Mueller‑Hinton agar plates by Kirby-Bauer disc diffusion method, as per CLSI guidelines. Screening for Methicillin Resistant Staphylococcus Aureus (MRSA) was done using cefoxitin (30 μg) disc. Resistance to ceftazidime (30 μg) disk was used as a screening method for detection of Extended Spectrum Beta Lactamase (ESBL) confirmed by double disk synergy test.15
Results
From January 2019 to December 2019 combined from departments of General Surgery, Orthopaedics & OBG samples from 320 patients with SSIs were processed to yield a total of 324 aerobic bacterial isolates. Among the 320 patients with SSIs 171(53.44%) were females & 149(46.56%) were males. Out of the 320 samples monomicrobial growth was seen in 316 (98.75%) samples whereas polymicrobial growth was seen in 04 samples (1.25%). Out of the 324 isolates Gram negative bacilli constituted 239(73.77%) of the isolates with Escherichia coli predominating. The Gram positive cocci constituted 26.23% with Staphylococcus aureus 68(20.98%) predominating followed by Coagulase Negative Staphylococcus (CONS) which accounted for 17(5.25%). Organisms isolated are seen inTable 1.
Department wise the number of cases 101(31.17%) were 138(42.6%) from General Surgery department, 113(34.8%) were from OBG department & 73(22.6%) were from Orthopaedics department. Among the 138 isolates from Surgery department the predominant isolate was Escherichia coli with 67(48.6%) & this accounts for 66.3% of the total Escherichia coli isolates in the entire study. Out of the 113 isolates from OBG department the predominant isolate was Staphylococcus aureus with 38(33.6%) & accounting for 55.9% of the total Staphylococcus aureus isolates across all 3 departments. Out of the 73 isolates from Orthopaedics department the predominant isolate was Staphylococcus aureus with 19(26%) & accounting for 27.9% of the total Staphylococcus aureus isolates. Department wise distributions of isolates are seen in Table 2.
Table 1
List of organisms isolated in the study
Table 2
Department wise distribution of isolation of the bacteria
Antibiotic susceptibility pattern- In this study 14(20.6%) of the Staphylococcus aureus were found to be methicillin resistant. Of the Staphylococcus aureus isolates 32% were resistant to ampicillin, 28% were resistant to amoxy-clavulanic acid, 35.3% were resistant to erythromycin, 60.3% were resistant to ciprofloxacin, , and 81% were sensitive to cefepime, 94% were sensitive to vancomycin, 97% were sensitive to amikacin, 99% were sensitive to linezolid & 100% were sensitive to gentamicin. Four (24%) isolates of CONS were found to be methicillin resistant. The resistance rates for CONS were 76% were resistant to ampicillin, 35% were resistant to ciprofloxacin, 53% were resistant to cefepime and, 82% were sensitive to erythromycin, 94% were sensitive to amikacin, 100 % were sensitive to vancomycin & linezolid.
Of the Escherichia coli isolates 88% were resistant to ampicillin,53% were resistant to amoxy-clavulanic acid, 88% were resistant to ciprofloxacin, 84% were resistant to cephazolin,68% were resistant to cephaperazone, 57% were resistant to cefepime, 57% were sensitive to gentamicin, 80% were sensitive to amikacin, 95% were sensitive to piperacillin & 100% were sensitive to imipenem. Out of 101 Escherichia isolates 82(81.2%) were found to be ESBL (Extended Spectrum Beta Lactamase) producers. Among the Citrobacter species 96% were resistant to ampicillin, 71% were resistant to amoxy-clavulanic acid, 48% were resistant to ciprofloxacin, 90% were resistant to cephazolin,75% were resistant to amikacin, 50% were resistant to cefepime, 75% were sensitive to gentamicin, 63% were sensitive to cephaperazone, 54% were sensitive to piperacillin. Out of 48 Citrobacter isolates 37(77.1%) were found to be ESBL producers. Among Klebsiella species 85% were resistant to amoxy-clavulanic acid, 66% were resistant to ciprofloxacin,76% were resistant to cephazolin, 68% were resistant to cephaperazone, 44% were resistant to cefepime, 93% sensitive to ampicillin 66% were sensitive to gentamicin, 71% were sensitive to amikacin, 59% were sensitive to piperacillin & 100% were sensitive to imipenem. Out of 41 Klebsiella isolates 29(70.7%) were found to be ESBL producers.
Among the NFGNB(Non Fermenting Gram Negative Bacilli) 63% were sensitive to ampicillin, 96% were sensitive to amoxy-clavulanic acid, 71% were sensitive to ciprofloxacin, 42% were resistant to cephazolin, 50% were resistant to cephaperazone, 42% were resistant to cefepime, 87% were sensitive to gentamicin, 67% were sensitive to amikacin, & 63% were sensitive to imipenem.
Among Pseudomonas aeruginosa 43% were resistant to piperacillin, 29% were resistant to ciprofloxacin, 28% were resistant to ceftazidime, 79% were sensitive to ofloxacin, and 93% were sensitive to levofloxacin. 57% were sensitive to gentamicin, 86% were sensitive to aztreonam & amikacin, 95% were sensitive to piperacillin & 100% were sensitive to piperacillin-tazobactum & imipenem.
Among Enterobacter species 100% were sensitive to ampicillin, amoxy-clavulanic acid, cefotaxime, ceftazidime, cephaperazone & ciprofloxacin, 71% were sensitive to ceftriaxone, 71% were resistant to piperacillin, & 86% were resistant to amikacin. Proteus species 100% were sensitive to ampicillin & amoxy-clavulanic acid, 67% were sensitive to ciprofloxacin & ceftriaxone, 100% were resistant to cephaperazone. Among Providencia species 100% were sensitive to piperacillin with tazobactum. 100% were resistant to ceftriaxone, ceftazidime, amikacin, ciprofloxacin & cephazolin.
Discussion
The results of this study provide an overview of the current microbiology, both the aerobic bacteriological profile and also the present antibiotic susceptibility pattern in SSIs in our setup. From the 320 patients in our study we obtained 324 bacterial isolates.
In this study majority of the infections were monomicrobial infections (98.75%) as in other studies. Polymicrobial infections (1.25%) were of a small proportion only which corresponds to various other studies where monomicrobial infections were dominant.11, 12, 16, 17
In this study overall predominance of gram negative bacilli was seen with 73.77%, correlating with another study where gram negative bacilli predominated with 73.1%.17 This could be attributed to diverse habitat of Gram negative bacteria including inanimate surfaces in hospitals, multidrug resistant patterns portrayed and possible contamination from intestinal tract during surgery.5 This is also in concordance with various other studies where gram negative bacteria were dominant.9, 10, 16 A systematic review also concluded that surgical site infections are caused predominantly by gram negative bacilli and found Escherichia coli as the common predominant isolate.18
In the present study, out of 320 culture positive samples, 149(46.56%) specimens were from male patients and 171 (53.44%) were from female patients. The infection was found to be higher in female patients as in another study which concluded that it was statistically insignificant.19
In our study Escherichia coli was the predominant isolate being isolated from 101 patients constituting 31.2% of the isolates. Among the gram negative bacilli Escherichia coli was followed by Citrobacter species n=48(14.8%), Klebsiella species n=41 (12.7%) and NFGNB n=24 (7.4%). Escherichia coli was the predominant isolate in studies by several authors with isolation rates of 23.1%17, 33.33%7, 42.3%20 & 58%21.
In the present study the second most common isolate was Staphylococcus aureus n=68(21%). This correlates with other studies where the isolation rates for Staphylococcus aureus were as follows…21.51%5, 26.2%19, 27.7%10, 29%12, 29.16%13. Among these studies few have Staphylococcus aureus as their predominant isolate.10, 12, 13, 19
CONS was isolated from n=17 (5.3%) which correlates with other studies where the isolation rates for CONS were as follows…3.8%17, 7.53%5 & 8.64%16. Few other studies have shown higher rates of isolation of CONS. 19.8 % 22, 21.4 %.19
The other dominant organisms in our study were Klebsiella species, Citrobacter species, NFGNB and Pseudomonas aeruginosa. Klebsiella species was isolated from n=41(12.65%). This correlates with other studies where the isolation rates for Klebsiella species were as follows...12.5%17 & 11.7%12. The various rates in other studies are 8.5%23, 20.4%24, 27.8%.6 Few studies have shown Klebsiella to be predominant isolate with 29.03 %5 & 55 %25. Citrobacter species was isolated from n=48(14.81%) corresponding to another study with an isolation rate of 16 %.6 NFGNB was isolated from n=24(7.41%). It is one of the lesser common isolates in our study. Pseudomonas aeruginosa was isolated from n=14(4.81%) corresponding to various other studies with isolation rates of 5.1 % 9, 5.8 %.17 In one particular study Pseudomonas was a predominant isolate with 29.31%.20 Enterobacter species was isolated from n=7(2.16%). Proteus species was isolated from n=3(0.92%), Providencia species was isolated from n=1(0.3%) Department wise as in the overall study, Escherichia coli was the predominant isolate in General Surgery department, whereas in Orthopaedics & OBG departments Staphylococcus aureus was the predominant isolate. This may be due to the variation in nature of surgeries. In General Surgery due to intra-abdominal & rectal surgeries endogenous flora may be the main contaminant due to which Escherichia coli could be predominant. In Orthopaedics department based on the nature of surgeries accompanied with the usage of implants, skin contaminants are more common due to which Staphylococcus aureus may predominate. In a study done on implant surgeries in Orthopaedics department Staphylococcus aureus was the predominant isolate with 44.4%.27 In OBG department, in our study Staphylococcus aureus was the predominant isolate with 33.6% & accounted for 55.9% of total isolated Staphylococci corresponding with a study where Staphylococcus aureus was the predominant isolate with 36.6% & accounted for 57.7% of total isolated Staphylococci.21
In our study 21% of the Staphylococcus aureus were methicillin resistant similar to another study which reported that 25% of Staphylococcus aureus isolated from cases of surgical site infection were methicillin resistant. 20 The various findings about MRSA isolation rates by other authors are 10.5%17, 15.7%11, 39.7%12. A few others have very high rates of MRSA like 54.4%28 & 86.4%.9
In our study the rate of methicillin resistance among CONS was 24% corresponding to another study where the rate of methicillin resistance among CONS was 21.05% 16.
The overall rate of methicillin resistance among the Staphylococci was found to be 21.2%.
Among Escherichia coli 81.1% were found to be ESBL producers & among Klebsiella species 70.7% were found to be ESBL producers. Overall among Escherichia coli & Klebsiella ESBL producers were found to be 71.1%, corresponding to another study with an ESBL rate of 64 %. 22
For Staphylococcus aureus amikacin, gentamicin, cefepime, linezolid & vancomycin were found to be highly effective antibiotics; a pattern of high resistance was observed against the penicillins & fluoroquinolones. The degree of resistance was comparably higher among the gram negative bacilli showing high resistance against the penicillins, cephalosporins & fluoroquinolones but demonstrated good sensitivity to amikacin, gentamicin & carbapenems. Amikacin, piperacillin-tazobactum, aztreonam & carbapenems were found to be the most effective antibiotics for Pseudomonas species.
Conclusion
This study shows that Escherichia coli and Staphylococcus aureus are the predominant organisms associated with surgical site infections. A very high rate of ESBL producers was observed. Overall the gram negative bacilli showed a high rate of drug resistance against the commonly used antibiotics. Several measures can be taken to decrease the antibiotic resistance like infection control measures, restricting the use of the broad spectrum antibiotics, rational use of antibiotics, prescribing only specific antibiotic therapy after evaluating the sensitivity pattern of isolates and cycling of antibiotics. Simple measures like appropriate hand hygiene can go a long way in bringing down the rate of SSI as well as slowing down the further spread of the resistant hospital strains.
Acknowledgements
Authors acknowledge the immense help received from the scholars whose articles are cited and included in references of this manuscript. The authors are also grateful to authors / editors / publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.
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