A microbiological study of patients with diabetic foot at tertiary care centre

 

 

Abstract               Background: Diabetic foot is one of the most feared complications of diabetes and is the leading cause of hospitalization in diabetic patients. It is important to know the common pathogens isolated and their antibiogram to select appropriate antibiotics for the proper management of these infections. Aim: To determine the common pathogens isolated from diabetic foot in a tertiary hospital and their susceptibility to routinely used antibiotics.Material and Methods: This prospective study included a total of 70 patients with diabetic foot infections. The bacterial agents were isolated and their antibiotic susceptibility pattern was determined. Members of Enterobacteriaceae were tested for extended spectrum β-lactamase (ESBL) production and Staphylococcal isolates were tested MRSA production. Results: In 32 (45.7%) patients only one pathogen was isolated, while in 34 (48.6%) patients more than one pathogen was isolated. Gram-negative bacteria accounted for 76 (74.5%), while gram-positive bacteria accounted for 26 (25.5%). Of the 76 gram negative bacteria, majority were E. coli 42 (55.3%) followed by K. pneumoniae 14 (18.4%) and Pseudomonas aeruginosa 12 (15.8%). Majority of isolates of Escherichia coli and Klebsiella pneumoniae were susceptible to amikacin and imipenem. Conclusion: Diabetic foot infections are mostly polymicrobial and caused by gram negative bacteria. There is a need for continuous surveillance of resistant bacteria to provide the basis for empirical therapy.

Key Word: Diabetic foot, polymicrobial, gram negative bacteria, susceptibility pattern

 

 

INTRODUCTION

Diabetes mellitus (DM) is a major global cause of morbidity and mortality. Diabetic patients have a lifetime risk as high as 25% for developing foot ulceration.¹ Diabetic ulcers have 15 to 46 times higher risk of limb amputation than foot ulcers due to other causes.² Every year more than a million diabetic patients require limb amputation.³ Diabetic foot is a complex and costly complications of DM. It is one of the most feared complications of diabetes and is the leading cause of hospitalization in diabetic patients. It is characterized by several pathological complications such as neuropathy, peripheral vascular disease, foot ulceration and infection with or without osteomyelitis, leading to development of gangrene and even necessitating limb amputation.^1,4 Diabetic foot infections are often polymicrobial.5,6 It has been shown that Escherichia coli, Proteus spp., Pseudomonas spp., Staphylococcus aureus and Enterococcus spp. are the most frequent pathogens isolated from diabetic foot infections.4,5 Methicillin-resistant Staphylococcus aureus (MRSA) has been commonly isolated from 10-40% of the diabetic wounds.^7,8It is important to know the common pathogens isolated and their antibiogram to select appropriate antibiotics for the proper management of these infections. So, this study was performed to determine the common pathogens isolated from diabetic foot in a tertiary hospital and their in vitro susceptibility to routinely used antibiotics.

 

 

MATERIAL AND METHODS

 

This prospective study included a total of 70 patients with diabetic foot infections visited tertiary care teaching hospital over a period of two years.Processing of specimens Pus or discharges from the ulcer base and debrided necrotic tissue were obtained. The specimens were taken immediately to the microbiology laboratory and processed without any delay. The specimens were subjected to Gram staining and were simultaneously inoculated on blood agar and MacConkey agar for isolation of aerobic bacteria. After 24 hours incubation at 37(C, the bacterial isolates were identified based on standard bacteriological methods. The isolates were identified based on colony characters on Blood agar and MacConkey agar by standard biochemical tests.⁹ Antibiotic susceptibility testing Antibiotic susceptibility testing was performed by Kirby Bauer’s disc diffusion method according to Clinical Laboratory Standards Institute (CLSI) guidelines.10 The discs used were ciprofloxacin (5µg), ofloxacin (5µg), amikacin (30 µg), co-trimoxazole (1.25/23.75µg), ceftazidime (30µg), cefepime (30µg), imipenem (10µg), piperacillin+tazobactam combination (100µg+10µg) and colistin (10µg) disc was used. Penicillin, amoxicillin-clavulanic acid, cefoxitin, erythromycin, trimethoprim-sulfamethoxazole, ciprofloxacin, gentamicin, linezolide and vancomycin were tested for Staphylococcus species. Staphylococcus aureus isolates were screened for methicillin resistance using cefoxitin according to CLSI guidelines.¹⁰ Combination disc method using both cefotaxime and ceftazidime, alone and in combination with clavulanic acid was performed for detection of extended spectrum β-lactamase (ESBL) among the members of Enterobacteriaceae. Five mm or more increase in zone of inhibition for either cefotaxime-clavulanic acid or ceftazidime- clavulanic acid disc was taken as confirmatory evidence of ESBL production.

 

RESULTS

Of the 70 patients with diabetic foot, 52 (74.3%) were male and 18 (25.7%) were female. The age ranged from 32 to 73 years with mean age being 46±8 years. A total of 102 bacteria were isolated from these 70 patients. In 32 (45.7%) patients only one pathogen was isolated, while in 34 (48.6%) patients more than one pathogen was isolated. In 4 (5.71%) samples, no pathogen was isolated. Gram-negative bacteria accounted for 76 (74.5%), while gram-positive bacteria accounted for 26 (25.5%). Of the 76 gram negative bacteria, majority were E. coli 42 (55.3%) followed by K. pneumoniae 14 (18.4%) and Pseudomonas aeruginosa 12 (15.8%).

Majority of isolates of Escherichia coli and Klebsiella pneumoniae were susceptible to amikacin and imipenem, but resistant to other antibiotics tested. Similarly, most of Proteus spp. were susceptible to ciprofloxacin, ofloxacin, amikacin, piperacillin-tazobactam and imipenem, while being less susceptible to trimethoprim-sulfamethoxazole and cefuroxime. Citrobacter spp. were susceptible to piperacillin-tazobactam, amikacin and imipenem, but resistant to other antibiotics tested. Colistin resistance was not detected in our study. Most of the Pseudomonas aeruginosa were susceptible to piperacillin-tazobactam and imipenem, while they were showing varying susceptibility to ciprofloxacin and amikacin. Similarly, majority of Acinetobacter spp. were susceptible to piperacillin-tazobactam, imipenem and trimethoprim-sulfamethoxazole, while being less susceptible to amikacin, ciprofloxacin and ceftazidime.

 

Table 1: Antibiogram of gram negative bacteria isolated from diabetic footBacteria isolated Sensitivity pattern

Staphylococcus aureus were most often susceptible to amikacin, linezolide and vancomycin, but were relatively less susceptible to erythromycin, clindamycin, amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole, ciprofloxacin. None of the Staphylococcus aureus were susceptible to penicillin G.

 

Table 2: Antibiogram of gram positive bacteria isolated from diabetic foot Bacteria isolated Sensitivity pattern

Out of the 18 Staphylococcus aureus isolates 14 (77.8%) were resistant to cefoxitin and were therefore considered as methicillin resistant Staphylococcus aureus (MRSA). ESBL production was detected in 19 of the 56 (33.9%) isolates belonging to Enterobacteriaceae.