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A study of sensitivity pattern analysis of surgical wound isolates in a tertiary care hospital.

BACKGROUND

It is important to have a clear understanding of the terms used for wound infection. Since 1985 the most commonly used terms have included wound contamination, wound colonisation, wound infection and more recently, critical colonisation. These terms can be defined as: Wound contamination: The presence of bacteria within a wound without any host reaction. [2] Wound colonisation: The presence of bacteria within the wound which do multiply or initiate a host reaction. [2] Critical colonisation: Multiplication of bacteria causing a delay in wound healing, usually associated with an exacerbation of pain not previously reported but still with no overt host reaction. [3,4] Wound infection: The deposition and multiplication of bacteria in tissue with an associated host reaction. [2]

Recognition of wound infection: The inflammatory response is a protective mechanism that aims to neutralise and destroy any toxic agents at the site of injury and restore tissue homeostasis. [5] There are a number of indicators of infection. These include the classical signs related to the inflammatory process and further more subtle changes as highlighted by Cutting and Harding. [6] The classical signs of infection include: Localised erythema, Localised pain, Localised heat, Cellulitis and Oedema. Further criteria include: Abscess, Discharge which may be viscous in nature, discoloured and purulent; Delayed healing not previously anticipated, Discolouration of tissues both within and at the wound margins, Friable, bleeding granulation tissue despite gentle handling and the non-adhesive nature of wound management materials used; Unexpected pain and/or tenderness either at the time change of dressing or reported by the patient as associated specifically with the wound even when the wound dressing is in place; Abnormal smell, Wound breakdown associated with wound pocketing/bridging at base of wound, i.e., when a wound that was assessed as healing starts to develop strips of granulation tissue in the base as opposed to a uniform spread of granulation tissue across the whole of the wound bed. The above criteria should be used as discriminating factors when the 'classic' signs of wound infection do not appear to be present but the presence of a wound infection is suspected. Surgical wounds are classified based on the presumed magnitude of the bacterial load at the time of surgery. [7]

According to WHO report 2002, prevalence rate of health care associated infection (HCAI) is 7.7% - 9% in developed countries and 10-11.8% in developing countries. The common HCAI as per CDC updated 2007 is UTI (32%) followed by postoperative wound infections (22%), nosocomial pneumonia (15%) and nosocomial septicaemia (14%). [1]

MATERIALS AND METHODS

Samples were collected from patients with suspected postoperative wound infection, using sterile cotton swabs. The wound was thoroughly irrigated with sterile normal saline until all visible debris had been washed away. Care was taken not to clean the wound with Betadine or any other antiseptic solution before swabbing the area. The area selected was the highly vascular granulation tissue rather than the yellow fibrous slough. The material was collected by pressing the swab over the clean wound surface to extract tissue fluid as this may contain the potential pathogen. [8,9] Two swabs were collected from each site. One swab was used for direct smear examination after Gram staining. The second swab was subjected to culture and antibiotic sensitivity testing by standard microbiological techniques. The swab was plated on Blood agar and MacConkey's agar. Blood agar plates were incubated in the candle jar (C[O.sub.2]) at 37[degrees]]c for 24 hours. A sterile report was given only after 48 hours of incubation. From the culture plates, Gram stained smears were made from different types of colonies after noting the colony characteristics. Identification of bacteria was carried out as described by Koneman's textbook of microbiology (sixth edition). [10] Antibiotic sensitivity testing of the isolates was done by the Stokes method for Staphylococcus and Kirby Bauer method for Gram-negative bacilli. The following antibiotic discs were used for sensitivity testing of Grampositive cocci: Penicillin (10 units), Erythromycin (15 mcg), Gentamicin (10 mcg), Vancomycin (30 mcg), Cefazolin (30 mcg). Oxacillin screen agar was used for Staphylococci. Ampicillin (10 mcg), Gentamicin (10 mcg), Cefazolin (30 mcg), Ceftriaxone (30 mcg), Amikacin (30 mcg), Ciprofloxacin (5 mcg) were used for sensitivity testing of Gram-negative bacilli. For Pseudomonas Ceftazidime (30 mcg) (HiMedia Laboratories Pvt. Ltd. Mumbai.) was also used. In 50 cases, a repeat swab was taken and processed as there was a delay in wound healing and poor response to treatment. All cases were followed up to the date of discharge. Condition of the wound was noted at the time of discharge from the hospital.

RESULTS

Total number of surgeries done during the one year period in the three surgical units was 1902 which comprised of 1074 elective and 828 emergency cases. One hundred and two suspected postoperative wounds were studied. Twenty-seven were of the 'clean' type of surgical wounds, thirty-two of the 'clean-contaminated', thirteen of the 'contaminated' and thirty of the 'dirty' cases. The incidence of postoperative wound infection was 5.36%. Among one hundred and two clinically suspected cases studied, bacteriologically proven surgical site infection was identified in thirty-six patients. The prevalence of infection being 35% (36/102). In the 'clean' surgical group, five patients developed infection, the prevalence was 18.5%. Prevalence of Infection in the 'clean-contaminated' group was 37.5% (12/32). In the 'contaminated' group, it was 38.5% (5/13) and in the 'dirty' group it was 47% (14/30). Lowest infection rate was seen in clean surgery followed by clean-contaminated, contaminated and dirty surgeries Out of the thirty-six infected cases, thirty-one cases showed infection with single organism and five cases showed mixed infection.

The pathogenic organisms isolated from the thirty-six cases of wound infection are given below. (Table 1a).

Staphylococcus aureus was isolated from 18 cases, Escherichia coli from 15 cases and Enterobacter from 2 cases. Klebsiella, Acinetobacter and Serratia was isolated from one case each. Pseudomonas aeruginosa was isolated from 4 cases. Five cases showed mixed infection. One case of mixed infection was with three organisms and four cases with two organisms (Table 1c).

The commonest microorganism causing wound infection in the study was Staphylococcus aureus. Staphylococcus aureus was isolated from cases of laparotomy (6), mastectomy (4), gastrectomy (1), abscess incision and drainage (1), APR for Ca rectum (2), paraumbilical hernia with appendicular abscess (1), Trendelenburg operation (1), appendicectomy (2). Fifteen out of the eighteen isolates of Staphylococcus aureus were MRSA. The three Methicillin sensitive Staphylococcus aureus were from the 'clean' surgical group. Seven MRSA were from the 'clean-contaminated', two from the 'contaminated' and six from the 'dirty' group.

Multidrug resistant Gram-negative bacilli were the predominant organisms isolated from the 'clean contaminated', 'contaminated' and 'dirty' type of surgery.

Escherichia coli was isolated from cases of laparotomy (9), tracheal resection (2), APR for Ca rectum (3), cholecystectomy (1). There was a total of four isolates of Pseudomonas aeruginosa, from cases of laparotomy (3) and Trendelenburg operation (1). Enterobacter was isolated from cases of triple anastomosis (1), hernia repair (1). Klebsiella oxytoca (1) was isolated from a case of laparotomy. Acinetobacter baumannii was isolated from one case of Trendelenburg operation and Serratia marcescens from one 'clean' case of lipoma excision (Table 1b). Repeat swabs were collected after 3-4 days in all culture-positive cases. Same results were obtained except in one case of paraumbilical hernia with appendicular abscess where first swab grew Coagulase-negative staphylococci and repeat swab yielded growth of Staphylococcus aureus (MRSA).

Mixed bacterial infection was observed in five cases. These were three cases of laparotomy, one case of APR for Ca rectum and one case of Trendelenburg operation. Infection with Escherichia coli and Staphylococcus aureus occurred in one case of APR for Ca rectum, and in two cases of laparotomy. Pseudomonas aeruginosa and E. coli mixed infection was seen in one case of laparotomy. Infection with Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus occurred in one case of Trendelenburg operation. (Table 1c).

Analysis of the antibiotic sensitivity pattern of the isolates: There were eighteen isolates of Staphylococcus aureus. None of the isolates were sensitive to penicillin and erythromycin. 100% sensitivity was shown towards vancomycin. There were fifteen isolates of MRSA (Methicillin-resistant Staphylococcus aureus). Cloxacillin had 28% sensitivity. Only three isolates of staphylococcus aureus were Cloxacillin sensitive. 22% of the isolates were sensitive to gentamicin. Among the isolates of Gram-negative bacilli, none were sensitive to Ampicillin. There were total twenty-four Gram-negative bacterial isolates, twenty-two were multidrug resistant (92%). Of the Gram-negative isolates, fifteen were Escherichia coli. All the strains were resistant to ampicillin, cefazolin, ceftriaxone, ciprofloxacin. Amikacin had a sensitivity of 73.3%. Ten isolates of E. coli were sensitive only to amikacin, two isolates were sensitive to both gentamicin and amikacin.

Enterobacter isolates showed 50% sensitivity towards ciprofloxacin. Only one out of the four isolates of Pseudomonas was sensitive to cephalosporins & aminoglycosides. The single isolate of Acinetobacter baumannii showed 100% sensitivity towards amikacin, gentamicin, ciprofloxacin and ceftriaxone. The single isolate of Serratia marcescens was resistant towards the first line antibiotics (ampicillin, gentamicin) and second line antibiotics (amikacin, 3rd generation cephalosporins and ciprofloxacin) that are routinely used for Gram-negative bacilli. All Gram-negative isolates were sensitive to imipenem (100%). ESBL was not detected due to limited resources.

DISCUSSION

The incidence and pattern of wound infection varies from centre to centre. In the present study, the incidence of postoperative wound infection is 5.36% of the one hundred and two clinically suspected cases of post-operative wound infection studied. Prevalence of infection in the study group is 35%.

The prevalence of postoperative wound infection among 'clean' cases was 18.5%, 'clean-contaminated' 37.5%, 'contaminated' 38.5% and 'dirty' 47%.

While the global estimates of SSI have varied from 0.5-15%, studies in India have consistently shown higher rates ranging from 23-38%.1112 In a prospective study of surgical site infections in a teaching hospital in Goa, the overall SSI rate was estimated to be 30.7%. 5.4% for clean, 35.5% clean-contaminated and 78.8% for contaminated operations. [13] Antibiotic sensitivity pattern of the isolates: Penicillin resistance was seen in eighteen of the isolates of Staphylococcus aureus in this study. Erythromycin resistance was also eighteen. Fifteen of the isolates were resistant to Cloxacillin.

None of the Gram-negative bacilli isolated in this study was sensitive to Ampicillin. All the Escherichia coli isolated from wound infection showed multiple resistance. Amikacin sensitivity was 73.3% for E. coli. One isolate of Escherichia coli, was resistant to all routine antibiotics & was sensitive to imipenem only. Table 2 explains the ABST of the isolates. In a prospective study of surgical site infections in a teaching hospital in Goa, 79% of isolates were Gram-negative and almost 64% demonstrated polyantimicrobial resistance. [13] Data from the NNIS CDC 2007 shows that multidrug resistant Klebsiella, E. coli, Acinetobacter, Pseudomonas, etc. are now the major hospital pathogen. [1,14]

Escherichia coli were the most resistant organisms causing wound infection among the Gram-negative bacilli in the present study. Patients in this study belonged to 18 to 83 years of age group. Maximum number of cases were between 15-25 years of age (20 cases) and 46-55 years of age (20 cases). Maximum infection rate was observed in old age, particularly between 76-85 years of age (67%). Four out of the six cases in this group got infected.

Sex

Out of the one hundred and two cases, thirty-two patients were female and seventy patients were male. A slightly higher infection rate of 36% (25/70) was observed in the males compared to 34.3% (11/32) in females. Diabetes, hypertension and anaemia were not observed in majority of the cases. So its influence on wound infection could not be studied in detail.

CONCLUSION

Postoperative wound infection (surgical site infection) is an important aspect of nosocomial infections which is a serious problem in hospital practice. The study was selected to find out the pattern of postoperative wound infection and the role of antibiotics in these patients which is responsible for much morbidity and mortality to patients. One hundred and two cases of postoperative wounds were studied in detail during the one year period from July 2007 to June 2008 at Calicut medical college. The prevalence rate of post-operative wound infection among study group was 35%. The most important isolate in the study was Staphylococcus aureus in clean surgeries. In clean-contaminated, contaminated and dirty surgery cases, multidrug resistant E. coli and Staphylococcus aureus (MRSA) were the main pathogens followed by Pseudomonas, Enterobacter, Acinetobacter and Klebsiella. The incidence of post-operative wound infection was 5.36%. Even the clean category surgery patients received antibiotic prophylaxis which may be the reason for the low incidence of post-operative wound infection. Antibiotics have a definite role in the treatment of established infections. Development of a suitable antibiotic policy along with proper surveillance programme is essential for our hospital to reduce the postoperative wound infection rates.

Financial or Other, Competing Interest: None.

Submission 27-12-2016, Peer Review 08-01-2017, Acceptance 12-01-2017, Published 19-01-2017.

Corresponding Author:

Prasanna Gupta, Associate Professor, Department of Microbiology, F.H. Medical College Tundla, Firozabad, Uttar Pradesh.

E-mail: pramin1414@yahoo.co.in

DOI: 10.14260/jemds/2017/98

REFERENCES

[1] Bai RJT. Hospital infection-present scenario. Proceedings of the fourth triennial conference of the academy of clinical Microbiologists and pre-conference seminar on changing trends in hospital infections 2008:18-23.

[2] Ayton M. Wound care: wounds that won't heal. Nurs Times 1985;81(46):16-9.

[3] Falanga V, Grinnell F, Gilchrest B, et al. Workshop on the pathogenesis of chronic wounds. J Invest Dermatol 1994;102(1):125-7.

[4] Kingsley A. A proactive approach to wound infection. Nurs stand 2001;15(30):50-4, 56, 58.

[5] Collier M. Understanding wound inflammation. Nurs Times 2003;99(25):63-4.

[6] Cutting KF, Harding KG. Criteria for identifying wound infection. J wound care 1994;3(4):198-201.

[7] Martone WJ, Nichols RL. Recognition, prevention, surveillance, and management of surgical site infections: introduction to the problem and symposium overview. Clin Infect Dis 2001;33(Suppl 2):S67-8.

[8] Howe CW. Postoperative wound infections due to staphylococcus aureus. N Engl J Med 1954;251(11):4117.

[9] Pulaski EJ. Discriminate antibiotic prophylaxis in elective surgery. Surg Gynecol Obstet 1959;108(4):385-8.

[10] McKittrick LS, Wheelock FC. The routine use of antibiotics in elective abdominal surgery. Surg Gyn Obstet 1954;99(3):376-7.

[11] Ganguly PS, Khan Y, Malik A. Nosocomial infections & hospital procedures. Indian J Commun Med 2000;25:990-1014.

[12] Subramanian KA, Prakash A, Shrinivas, et al. Postoperative wound infection. Ind J Surg 1973:57-64.

[13] Kamat US, Fereirra AMA, Kulkarni MS, et al. A prospective study of surgical site infections in a teaching hospital in Goa. Indian J Surg 2008;70(3):1204.

[14] National nosocomial infections surveillance system. Centers for disease control and prevention (CDC). Health care associated infection (HCAI) updated 2007.

Prasanna Gupta (1), Atul Agrawal (2)

(1) Associate Professor, Department of Microbiology, F. H. Medical College, Tundla, Uttar Pradesh.

(2) Associate Professor, Department of Psychiatry, G. R. Medical College, Gwalior, Madhya Pradesh.
Table 1a. Organisms Isolated from Infected Wounds

Organisms                  No. of Isolates   % of Isolation

Staphylococcus aureus             18                43
Escherichia Coli                  15                36
Pseudomonas aeruginosa            4                 9.5
Klebsiella oxytoca                1                 2.3
Enterobacter kobei                1                 2.3
Enterobacter intermedius          1                 2.3
Acinetobacter baumannii           1                 2.3
Serratia marcescens               1                 2.3
Total                             42                100

Table 1b. Relationship between the Type of Surgery and
Organisms in 31 cases which were Infected with Single
Organism

Type of             Infected No.           Organisms           No. of
Surgery               of Cases             Isolated           Isolates

Laparotomy               17            Escherichia Coli           7
                                     Staphylococcus aureus        6
                                    Pseudomonas aeruginosa        2
                                      Klebsiella oxytoca          1
                                   Enterobacter intermedius       1
Hernia repair             1           Enterobacter kobei          1
Mastectomy                4          Staphylococcus aureus        4
Appendicectomy            2          Staphylococcus aureus        2
APR for Ca rectum         2         Staphylococcus aureus,        1
                                       Escherichia Coli           1
Abscess I & D             1          Staphylococcus aureus        1
Cholecystectomy           1            Escherichia Coli           1
Tracheal resection        2            Escherichia Coli           2
Lipoma excision           1           Serratia marcescens         1

Table 1c. Infection with Multiple Organisms

Type of Surgery            No.    Organisms Isolated

APR for Ca rectum           1     Escherichia coli, Staphylococcus
                                  aureus

Laparotomy                  2     Escherichia Coli, Staphylococcus
                                  aureus

                            1     Pseudomonas aeruginosa,
                                  Escherichia Coli

Trendelenburg operation     1     Acinetobacter baumannii,
                                  Pseudomonas aeruginosa,
                                  Staphylococcus aureus

Table 2. ABST Pattern of the Isolates in (%)

Antibiotic       S. aureus    E. Coli    Enterobacter    Pyo    Kleb
                     18          15            2          4       1

Penicillin          Nil          NT           NT          NT     NT
Erythromycin        Nil          NT           NT          NT     NT
Gentamicin          22.2        13.3          Nil         25     100
Ampicillin           NT         Nil           Nil         NT     Nil
Vancomycin          100          NT           NT          NT     NT
Cefazolin           22.2        Nil           Nil        Nil     Nil
Ceftazidime          NT          NT           NT          25     NT
Oxacillin           27.7         NT           NT          NT     NT
Piperacillin         NT          NT           NT          25     NT
Amikacin             NT         73.3          100         25     100
Ciprofloxacin        NT         Nil           50          25     Nil
Ceftriaxone          NT         Nil           Nil         NT     Nil

Antibiotic       Serratia    Acineto
                     1          1

Penicillin          NT          NT
Erythromycin        NT          NT
Gentamicin          Nil        100
Ampicillin          Nil        Nil
Vancomycin          NT          NT
Cefazolin           Nil        100
Ceftazidime         NT          NT
Oxacillin           NT          NT
Piperacillin        NT          NT
Amikacin            Nil        100
Ciprofloxacin       Nil        100
Ceftriaxone         Nil        100

NT--Not tested

Fig. 1: Prevalence of postoperative wound
infection in the study group

Infection      35%
No Infection   65%

Note: Table made from pie chart.
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Title Annotation:Original Research Article
Author:Gupta, Prasanna; Agrawal, Atul
Publication:Journal of Evolution of Medical and Dental Sciences
Article Type:Report
Date:Jan 19, 2017
Words:2852
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