Diabetic foot ulcers are considered the most threatening and disabling complication of diabetes. An initial trivial lesion may progress to chronic, nonhealing wounds or gangrene that may need amputation of the toe, foot, or leg. Successful treatment of DFUs depends on a correct evaluation of the patient, isolation of pathogens, and identification of their antibiotic susceptibility patterns.
In the present study, the largest number of DFUs were observed in the age group of 61 to 70 years (32.14%) and the mean patient age was 59.72 ± 11.75 years. These findings are similar to previous studies.9-12 In developing countries, the majority of people with diabetes are in the age group of 45 to 64 years13; DFUs in this age group can be caused by the compounding effects of neuropathy, peripheral vascular disease, and atherosclerosis associated with diabetes.14 In the present study, men were more commonly affected (80%) than women (20%). This finding agrees with previous studies.10,12,15 The increased occurrence of DFUs in men may be attributed to smoking and outdoor activities.
In the present study, 89.29% of cases had a positive culture while 10.71% of cases were sterile on culture. These results are consistent with Mukkunath et al9 and Akhi et al,16 who also reported sterile culture rates of 10%, but are not in concordance with Umadevi et al15 (2.9%) and Tiwari et al (21%).17 In the present study, patients who had a BSL > 200 mg/dL showed a greater number of culture-positive samples (83, 94.32%) and had a greater number of isolates (100; 1.20 isolates/case). These findings are in agreement with Patil and Patil.18 The higher culture-positive rates in patients with a BSL > 200 mg/dL may be attributed to significant diminution in intracellular bactericidal activity of leukocytes in patients with poorly controlled diabetes.
In the present study, the majority of cases were Wagner grade 2 DFUs (45%), and the percentage of polymicrobial infections increased from grade 1 (0%) to grade 5 (27.2%). Similar patterns of infection have been reported in earlier studies.9,19,20 An increase in the DFU grade correlated with an increase in depth of ulcer and chronicity, leading to polymicrobial infections.
In the present study of 147 isolates, 27.21% were gram-positive cocci and 72.79% were gram-negative bacilli. These findings are consistent with earlier studies.15,17-20,21-24 The pattern of isolation of S aureus (21.09%) as the most predominant aerobic isolate followed by P aeruginosa (19.05%) is in agreement with Gadepalli et al,12 Sridhar et al,24 and Chopdekar et al.25 This may be attributed to the common occurrence of these organisms in the surrounding environment and as a part of normal skin flora.
In the present study, gram-positive aerobes showed 100% susceptibility to linezolid and 97.5% resistance to penicillin. Linezolid has been reported to be 100% effective against gram-positive isolates from DFUs in previous studies,16,22 showing that it currently is the most effective antimicrobial agent against gram-positive isolates because of its restricted use. Penicillin was an ineffective antimicrobial agent against gram-positive isolates, indicating that this antibiotic has lost its clinical efficacy in the treatment of infections caused by gram-positive cocci and should be omitted from the empirical treatment. Against gram-negative bacteria, imipenem (75.70%) was found to be an effective antimicrobial agent. However, other antimicrobial agents, including meropenem, ceftazidime, gentamicin, levofloxacin, and cotrimoxazole, were less effective against gram-negative isolates. These findings are in concordance with previous reports.5,11,15,16,19,22,26,27
The overall observation shows there is a predominance of S aureus in the present study, which contrasts studies from urban areas that show either Escherechia coli17or P aeruginosa28,29 as the predominant bacteria associated with DFUs. In the present study, both gram-positive and gram-negative isolates showed differential susceptibility patterns, which is different from the antibiotic susceptibility pattern of the isolates of earlier studies from urban areas.12,28 The majority of the isolates from the present study were found to be resistant to most of the antibiotics, usually prescribed on an empirical basis.