Bacteriological Profile of Diabetic Foot Ulcers and Detection of Methicillin-Resistant Staphylococcus aureus and Extended-Spectrum β-Lactamase Producers in a Tertiary Care Hospital

Abstract

Introduction Diabetic foot infection is the most dreaded complication of diabetes mellitus and the commonest cause of hospitalization and limb amputation. Identification of the causative agent responsible for diabetic foot infection and the earliest initiation of appropriate antimicrobial therapy are vital for the control and prevention of the complication of diabetic foot ulcers. Therefore, we conducted this study to determine the bacteriological profile of diabetic foot ulcers and to detect methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum β-lactamase (ESBL) producers in our institute. Methodology During the study period, samples were collected from the foot ulcers of 100 patients at the Diabetic Outpatient Department. The samples were processed according to the standard laboratory protocol, and bacterial isolates were identified. Antibiotic susceptibility testing was performed using the modified Kirby-Bauer disk diffusion technique, and results were interpreted according to the Clinical and Laboratory Standards Institute guidelines (CLSI 2016). A phenotypic test for MRSA detection was performed using cefoxitin (30 μg) disk. Results The highest incidence of diabetic foot ulcers was observed in patients aged 41-50 years. There were 83 men and 17 women, with a male to female ratio of 4.882. Of the 100 collected samples, 73 were positive for microbial growth, and 27 samples showed no growth. Of the 73 positive cultures, monomicrobial infection was found in 48 patients, and polymicrobial infection was found in 25 patients. Gram-positive pathogens were isolated from 34 patients, and gram-negative microbes were isolated from 64 patients. Among all collected isolates (n=100), Staphylococcus aureus was the most predominant organism and Acinetobacter species was the least common (only two isolates). Among the gram-negative bacteria, Pseudomonas aeruginosa was predominant. All the isolated gram-positive bacteria were susceptible to vancomycin. Gram-negative bacteria were highly susceptible to colistin with the exception of Proteus species which is intrinsically resistant to colistin and it is not reported for Proteus species. ESBL producers were primarily found among Klebsiella species isolates (22.22%). Among 29 S. aureus isolates, 8 (27.5%) were found to be MRSA producers. Conclusion Based on the bacteriological profile of diabetic foot ulcers, S. aureus among the gram-positive isolates and P. aeruginosa among the gram-negative isolates were the predominant pathogens. Infections caused by multidrug-resistant bacteria such as MRSA and ESBL producers have been reported with increasing frequency. According to the antibiotic susceptibility pattern, treatment can be initiated, continued, or altered, thereby reducing morbidity in patients with diabetic foot ulcers.

Keywords: antimicrobial therapy; diabetic foot infection; esbl; mrsa; phenotypic test.

Figure 1. Sex-wise distribution (n=100)