Evaluation of antibiotic susceptibility in wound infections: A pilot study from Bangladesh

Introduction

Wounds follow the loss of skin integrity, which provides a moist, warm and nutritive environment that is known to be conducive to microbial colonization and proliferation¹. Wound infections are considered a major complication of surgery, and can be classified into three types: incisional surgical wounds, deep incisional wounds, and organ-specific infections². Despite maintaining the high standards of preoperative preparation, antibiotic prophylaxis, and operative procedures, the appearance of postoperative wound infections remains a grave threat among the clinicians³. Some of the most frequent causative microorganisms are related to wound infections and include Staphylococcus aureus, Streptococcus pyogenes, Enterococci, Escherichia coli, Klebsiella pneumonia, Proteus species and Pseudomonas aeruginosa. However, the severity of complication is largely based on the virulence of the infecting pathogen and the site of infection⁴. The reporting trend of infection varies depending on the surgeon’s ability, operative area, surgical procedures, patient characteristics, etc. For instance, approximately 5,00,000 infections per year take place in the United States among an estimated 27 million surgical procedures⁵. The incidence of hospital-based postoperative infection varies from 10%–25% in India⁶. Nosocomial infection is becoming a serious problem affecting hospitalized patients both in developed and developing countries. According to a study conducted in Bangladesh, it was reported that among 38% of nosocomial infections, more than 50% were due to wound infection⁷. Moreover, wound infections were found to be higher (49%) among post-operative patients as compared to pre-operative patients (15.9%) in that study⁷. Post-operative wound infections have emerged as one of the important causes of morbidity among the hospitalized patients⁸. Emmerson et al. reported that surgical wound infections account for 12.3% of all hospital-acquired infections⁹. Wound infection is becoming a major concern among patients and healthcare practitioners for its increased toll on morbidity and financial loss. It also generates demand for attaining expensive management within the public health system⁵. Active and passive surveillance of surgical site infections in the hospital will help the surgeons and clinicians to know the antibiotic susceptibility pattern related to the surgical site, which can help reduce postoperative complications¹⁰.

The present study aimed to collect data on the bacteriological profiles of wound infections and their antibiotic susceptibility patterns in a teaching hospital in Bangladesh.

Methods

Results

Characteristics of study participants

The mean (±standard deviation) age of the study participants was 37 (±08) years, and 57.1% of participants were male. The rate of isolation of bacteria was 92.3%. Figure 1 shows the frequency of bacterial growth. Around 62.9% of culture positive plates turned out to be Gram-positive organisms, and 37.1% Gram-negative (n=97). Only 7.6% did not yield any growth in a culture plate.

Figure 1. Pattern of bacterial growth among total samples (N=105).

In this figure, red, magenta, and green portion indicates the Gram Positive, Gram Negative, No growth, respectively and indicates the percentage of bacterial growth.

Isolation of different types of bacteria

Staphylococcus aureus (n=54; 55.7%) was predominantly found to be isolated among all the presenting bacteria. The frequency of Escherichia coli and Pseudomonas species was 23.7% and 8.2%, respectively (Figure 2).

Figure 2. Rate of isolation of different bacteria (N=97).

Rate of isolation of different bacteria are mentioned here based on number and their corresponding percentage.

Discussion

Management of post-operative wound infection remains a significant concern for physicians globally¹³. The problem has magnified due to the rapidly spreading resistance to the available array of antimicrobial agents^14,15. We found that Gram-positive organisms accounted for 62.9% of isolates, compared to Gram-negative isolates that accounted for 37.1%. Staphylococcus aureus (55.7%) was the major microbial pathogen responsible for the wound infections. According to Centre for Disease Control and Prevention (CDC), Staphylococcus aureus is the most common organism associated with surgical wound infections. This study supports the results reported by Nwachukwu et al.¹⁶, where 42.3% of infections were found to be caused by Staphylococcus aureus. Among the Gram-negative organisms, Escherichia coli were frequently isolated (23.7%) in our study. This finding is in line with a previous study which identified Escherichia coli as the major pathogen in the wound infection, followed by Staphylococcus aureus in a different setup¹⁷. A previous survey conducted in Lahore supported our findings demonstrating that Staphylococcus aureus was the main causative organism of surgical infection¹⁸.

In our study, we found imipenem as the most active antibiotic, with a susceptibility of 94.4% against Staphylococcus aureus. This study showed high sensitivity of Staphylococcus aureus against imipenem, vancomycin, and gentamycin. This finding corresponds to a previous study that also found that Staphylococcus aureus was susceptible to higher generation of antibiotics¹⁹. The high sensitivity to gentamycin has also been reported by other authors as well²⁰. We found that Staphylococcus aureus is usually resistant to various antibiotics and the infection might be acquired in the hospital.

Among the Gram-negative bacteria, Escherichia coli was found to be susceptible to ceftriaxone, cefotaxime, gentamycin, cefixime, ceftazidime, and cefuroxime. Furthermore, we found that Escherichia coli were less sensitive to cloxacillin with a frequency of 47.8%. Among three isolated Klebsiella spp., all organisms were resistant to cephradine, penicillin, cloxacillin, cefuroxime, tetracycline, and ciprofloxacin. Similarly, Okonko et al.²¹ had observed a high level of resistance by Klebsiella spp. to most antibiotics. However, they noticed that all three Klebsiella spp. Isolates were susceptible to gentamycin and ceftazidime. This high susceptibility pattern might support gentamycin as a suitable antibiotics to treat Klebsiella infection²². Among eight isolated Pseudomonas spp., all were resistant to cephradine, penicillin, cloxacillin, cefuroxime, amoxicillin, and cefotaxime in this study. We found that five Pseudomonas isolates were susceptible to ceftriaxone, four were susceptible to imipenem and gentamycin, and three were susceptible to tetracycline, ciprofloxacin, azithromycin, and ceftazidime. Only one Pseudomonas spp. isolate was susceptible to co-trimoxazole, cefixime, and nitrofurantoin.

The susceptibility pattern that we found indicates that most of the isolated strains were multi-drug resistant. Similarly, a study conducted in European setting reported a high resistance of Pseudomonas spp., mostly isolated from surgical wounds²³. Several previous studies carried out in different settings also support the multi-drug resistance pattern of Pseudomonas spp.^24–26. The mechanisms of intrinsic resistance of Pseudomonas spp. over most of the antimicrobial agents has emerged because of the low permeability of its outer membrane and the naturally occurring chromosomal Amp β-lactamase^27,28.

The control of wound infections is becoming difficult due to widespread bacterial resistance to antibiotics. Previous studies also notified an increased incidence of bacterial infections by methicillin-resistant Staphylococcus aureus, polymicrobial flora and different fungi²⁹. As wound infections are found to be common in this study, prior knowledge of the causative agents of can be a helpful tool in selecting the empiric antimicrobial therapy to control infection

In developing countries, physicians generally do not wait for the culture reports and sometimes, there may be a delay in conducting or reporting of a culture sensitivity test. Hence, with our study, we would like to urge the physicians to start an empirical therapy with a combination of either of the following as an empirical treatment regime:

1) Azithromycin/Imipenem and Ceftriaxone;

2) Gentamycin and Imipenem/Ceftriaxone

3) Ceftazidime and Imipenem.

After application of the above mentioned combination regime, culture sensitivity is advised to be performed in next step. Irrespective of the report, the entire course should be completed and if the condition still remains has not improved, urgent change of treatment plan according to the culture sensitivity report should be carried out.

We would discourage the use of penicillin and amoxicillin, since the resistance towards them has been on the rise. We would also urge physicians to not to prescribe the last resort drugs like vancomycin and linezolid, since they should be used as only in high resistance cases.

Conclusions

The most common isolate in wound infection was Staphylococcus aureus, followed by Escherichia coli, Pseudomonas spp., Klebsiella spp., and Streptococcus pyogenes. Gram-negative bacteria were sensitive to fewer than thirty percent of the commonly prescribed antibiotics, which can be a matter of great concern when treating wound infections. The judicious use of antibiotic prophylaxis and reporting can be the most effective means to reduce the wound infection rate.

Data availability

Dataset 1: Patient characteristics. Age, sex, residence, occupation, blood pressure, and diabetic mellitus status are given. DOI, 10.5256/f1000research.12887.d185740³⁰.

Dataset 2: Antibiotic susceptibility of bacterial cultures. Includes data on S. aureus, S. pyogenes, E. coli, Klebsiella spp, Pseudomonas, and Proteus. DOI, 10.5256/f1000research.12887.d185741³¹.