Comparison of Microbiological Results of Superficial Swab versus Deep Tissue Biopsy in Diabetic Foot Infections: A Prospective Observational Study from North India

Original Research

J Fam Med 2023; 10(1): 1322

Comparison of Microbiological Results of Superficial Swab versus Deep Tissue Biopsy in Diabetic Foot Infections: A Prospective Observational Study from North India

Rajesh Kumar, Jatinder K Mokta, Bilal A Mir*, Kiran Mokta, Tahir Majeed

Indira Gandhi Medical College, Shimla, India.

*Corresponding author: Bilal A Mir Department of gastroenterology, IGMC, Shimla, Himachal Pradesh, India.

Received: November 30, 2022; Accepted: January 02, 2023; Published: January 08, 2023


Introduction: Diabetes mellitus is the leading cause of nontraumatic lower extremity amputation worldwide. Risk of developing a foot ulcer in diabetic patients has increased to 12-25% during their lifetime. Inappropriate sampling technique leading to contaminated samples is a well-known threat among patients of diabetic foot. In this study we compared two microbiological sampling techniques, superficial swabbing and deep tissue biopsy for identification of pathogens.

Material and Methods: It was a prospective observational cross-sectional study. Diabetic foot was defined as per standard guidelines. Careful and meticulous examination of diabetic foot ulcer was done. Two specimens were collected from each wound. The first specimen was a wound swab collected by using Levine technique; another was taken via punch biopsy from the ulcer base. It was a deep tissue sample of 4 mm size.

Results: A total of 120 diabetic patients with diabetic foot infection were included in this study. In swab culture 80.83% patients had mono microbial growth, 15% had polymicrobial and 4.10% had no growth. In deep tissue culture 87.50% had mono microbial growth, 2.50% had poly microbial and 10% were sterile. Staphylococcus aureus was most common isolate followed by E. coli. It was observed that though monomicrobial growth was most common in both the types of samples but was higher in deep tissue biopsy than in superficial swab samples.

Conclusion: The isolation of microorganism via deep tissue sampling in diabetic foot ulcer patients is more reliable compared to superficial swab samples and a better guide to antibiotic therapy.

Keywords: DFU- diabetic foot ulcers; T2DM-Type 2 diabetes mellitus; IWGDF- International Working Group on Diabetic Foot; FBS- fasting blood sugar; PPBS- Post prandial blood sugar; BMIBody mass index


Globally, Type 2 Diabetes Mellitus (T2DM) has been associated with increased risk of developing cardiovascular morbidity and mortality. In India 69 million people are suffering from diabetes, which accounts for the second largest diabetic population of the world and this figure is expected to rise to 110 million by 2030 (>90% T2DM) [1]. Diabetes patients have a 12-25% risk of developing a foot ulcer during their lifetime [2]. Diabetes mellitus is the leading cause of non-traumatic lower extremity amputation in the United States. Foot ulcers and infections are also a major source of morbidity in individuals with diabetes mellitus. Risk factors for foot ulcers or amputation include male sex, diabetes for >10 years, peripheral neuropathy, abnormal structure of foot (bony abnormalities, callus, thickened nails), PAD, smoking, history of previous ulcer or amputation, visual impairment and poor glycaemic control [3]. Despite all preventive measures, it is well known that patients with Diabetes Mellitus (DM) complicating with foot ulcerations and infections create potentially a serious problem. Mostly infection in a diabetic foot ulcer are diagnosed clinically, by the presence of wound purulence or at least two classical signs or symptoms of inflammation (erythema, warmth, tenderness, pain, induration). However, some favour quantitative microbiologic assessment and define infection by the growth of ≥105 organisms per gram of tissue [4]. Therefore, it is very important to isolate the causative microorganism for appropriate treatment of the infected Diabetic Foot Ulcers (DFU). In our present study, we compared the superficial swab sample with deep tissue biopsy sample prospectively, for identification of microorganism and antimicrobial sensitivity testing.

Materials and methods

It is a prospective observational cross-sectional study which was conducted in tertiary care hospital from north India. This study was approved by the Institutional ethical committee, and was conducted according to the guidelines in the Helsinki Declaration. Written informed consent was obtained from all patients.


All known cases of diabetes Meletus of either sex of age> 18 years with history of diabetic foot were included. Cases of nondiabetic neuropathic foot, PVD, and traumatic foot ulcer were excluded. Diabetic foot with dry ulcer and dry gangrene were also excluded. Patients were excluded if they had antibiotic exposure (systemic or local) during preceding 4 weeks, if they were with known immunocompromised state or were on immunosuppressive drugs, if they have history of active malignancy. Patients not willing to participate in the study were also excluded.


After applying necessary inclusion and exclusion criteria, patient’s demographic, anthropometric and clinical variables were recorded according to standard methods. A detailed personal and family history along with assessment of metabolic risk factor profile was done. Diabetic status including disease duration, treatment type and complication status was recorded. Diabetic foot was defined as per standard guidelines by world health organization and International Working Group on the Diabetic Foot. Careful and meticulous examination of diabetic foot ulcer was done.

Specimen collection and microbiological culturing

Specimens were collected from each wound after the wound had been cleansed (using sterile saline and gauze) and debrided (removal of necrotic tissue, foreign material, calluses, and undermined wound edges) [24]. No antimicrobial agent (e.g., alcohol or iodine) or antiseptic was introduced into the wound before specimen collection. Each wound was swabbed using the Levine technique, involving rotation of a wound swab over a 1 cm2area of the wound for 5 seconds, using sufficient pressure to extract fluid from the inner part of the wound [25]. A deep tissue specimen of approximate 4mm in diameter was obtained from the base of the ulcer via punch biopsy [26].The specimens were placed into sterile transport containers and sent to the microbiology laboratory for aerobic culturing within 20 minutes. Anaerobic culturing was not performed in this study. Cultures were processed following the same standard procedures for the swab and tissue samples.


We prospective analysed data of 120 diabetic patients admitted with diabetic foot. The mean age of study population was 56.9 ± 15.61 years with 2/3rd of patients being males. The mean BMI of patients was 24.86 ± 3.2kg/m² with 17.50%being normal, 22.50% were overweight and 60% were obese. The baseline characteristics of study cohort is given in table 1. More than ½ of patients had diabetes for <10years with a mean HBA1c of 9.94 ± 2.8.Among the microvascular complication, neuropathy was most common and present in 100% of patients followed by nephropathy (30%) and retinopathy (25%) whereas PAD was most common macrovascular complication present in 2/3rd of patients followed by CAD and CVA with frequency of 18.3% and 7.5% respectively. As per Wagner’s grading of DFU done at the time sample collection 47(39.17%) patients had grade 2 ulcer, 39(32.50%) patient had grade 3 ulcer, 32(26.67%) patient had grade 4 ulcer and 2(1.67%) patients had grade 5 ulcer. The males were affected more than females by DFU with a male to female ratio of 1.72, and majority of deep and infected ulcers were seen in males compared to females and between the group difference was statistically significant (p<0.05).