The Microbiological Profile Of Diabetic Foot Infections

1. Department of Microbiology, Vinayaka Missions Hospital, Salem, Tamil Nadu, India.

Abstract

Background: Diabetic foot infections are a common cause of morbidity and mortality. This study was conducted in diabetic patients with foot ulcers to determine the bacterial profile and their anti-microbial pattern. Of the 68 patients, 44 were males and 24 were females. The presence of diabetic neuropathy was observed in 43(63.2%) patients. The swabs from 56 patients showed a positive culture and 12 patients did not grow any organisms. A total of 92 organisms were isolated from 56 patients with growth. 12(17.6%) patients had polymicrobial infections. S.aureus (26.1%) was the predominant pathogen which was isolated, followed by E.coli (18.4%).

Methods: This study was conducted on clinical specimens which were taken from 68 patients with diabetic foot infections, over a 1 year period. The clinical specimens were processed by using the standard aerobic microbiological techniques. The anti-microbial susceptibility pattern was studied by the Kirby-Bauer disc diffusion method.

Result: S.aureus was the most common isolate which was recovered from 26.1% of the cases. Other organisms which were isolated were E.coli (18.4%),,Klebsiella (9.7%), Proteus spp (6.5%), NFGNB(14.1%),,Pseudomonas aeruginosa (13%) and Enterococcus spp (4.3%).

Conclusion: The anti-microbial susceptibility data from our study suggests that piperacillin/tazobactum or cefeperazone /sulbactum would be appropriate for antibiotic coverage.

Diabetic foot, S.aureus, Multi-drug resistant organisms

Introduction
Diabetic foot ulcerations and infections are one of the leading causes of mortality and morbidity, especially in the developing countries (1). Diabetic patients were found to have a lifetime risk of as high as 25% for developing foot ulceration and the risk of lower leg amputation was found to increase by 15-46 times in diabetics than in persons who did not have diabetes mellitus (2). The major factor which predisposed to the foot ulceration which led to the infection was usually related to peripheral neuropathy and an impaired circulation which limited the access of the phagocytes (3),(4), (5). E.coli, Proteus, Pseudomonas spp, S.aureus, and Enterococcus spp are the most frequent pathogens which are cultured from diabetic foot ulcers (4),(5),(6). The infections in the diabetic foot are usually polymicrobial due to aerobic bacteria, anaerobes and Candida spp. The severe infections usually yield polymicrobial isolates, whereas the milder infections are generally monomicrobial (3),(5),(6),(7). In recent years, there has been an increase in the incidence of multidrug resistant organisms, which could increase the duration of the hospital stay, the cost, and the morbidity and the mortality (8). Sometimes the initial management comprises of empirical anti-microbial treatment which is based on the susceptibility data (9), but the proper management of these infections requires an appropriate antibiotic selection which is based on the culture and the antimicrobial susceptibility testing (10),(11). Therefore, this study was undertaken to determine the common aetiological agents of the diabetic foot infections in a tertiary care hospital and their invitro susceptibility pattern to the routinely used antibiotics.

Material and Methods

This was a prospective study in which 68 consecutive samples from diabetic patients who were admitted to a tertiary care hospital over a period of one year were included, after getting the informed consent from the study group. Pus or discharges from the ulcer and debrided necrotic tissue were obtained at the Microbiology Laboratory and the specimens were processed without any delay. The specimens were subjected to gram staining and they were inoculated onto Blood agar and Mac Conkey’s agar for the isolation of aerobic bacteria. The isolates were identified by the standard biochemical tests. Anti-microbial susceptibility testing was performed by the Kirby-Bauer disc diffusion method according to the CLSI guidelines (12).The antibiotic panel for the gram negative bacilli were cefuroxime, ceftazidime, cefepime, cefeperazone/sulbactum, piperacillin/tazobactum, gentamicin, amikacin, ciprofloxacin, levofloxacin, amoxycilin/clavulanic acid and imipenem. The antibiotics which were tested for S.aureus were oxacillin, erythromycin, gentamycin, clindamycin, ciprofloxacin, amoxicillin/clavulanic acid, cotrimaxazole and vancomycin. Penicillin, ampicillin, erythromycin, high level gentamycin, cotrimaxazole and ciprofloxacin were used for the Enterococcus spp and penicillin, erythromycin, ciprofloxacin, gentamicin, cotrimaxzole and amoxicillin/clavulanic acid were used for S.pyogenes.

Results

Demographic Characteristics 68 patients were included in the study. 44(64.7%) were males and 24 (35.2%) were females. The mean age of the patients was 55.12+/-12.08. 32(47%) were on oral antidiabetics and 25(36.7%) were on insulin, while 11 (16.17%) were on both insulin and oral antidiabetic drugs. 27(39.7%) had hypertension, and 8(11.7%) suffered from cardiovascular disease. 43(63.2%) had neuropathy, 17(25%) had nephropathy and 11(16%) had retinopathy. The demographic characteristics have been summarized in (Table/Fig 1).

MICROBIOLOGY
A total of 92 bacteria were isolated from these 68 patients. A statistically significant correlation was found between the bacterialgrowth and the deep ulcers. The different bacteria and the number of positive isolates which were isolated from the diabetic foot infections have been summarized in (Table/Fig 2) and (Table/Fig 3) . In 12(17.6%) patients, no growth was obtained from the specimen. 56 (82.3%) patients showed growth from one organism and two organisms were isolated from 23(33.8%) specimens, while 12(17.6%) patients showed growth from three organisms. Gram negative bacteria accounted for 62% (n=57) and gram positive bacteria accounted for 38.04% of the growth.(n=35) In our study, we found that cefeperazone/sulbactum, piperacillin/tazobactum and imipenem were the anti-microbial agents which were the most effective against gram negative bacilli, while vancomycin, erythromycin and ciprofloxacin were effective against the gram positive microorganisms . The resistance pattern of the gram negative bacilli and the gram positive coccal isolates are summarised in (Table/Fig 4) and (Table/Fig 5) respectively.

Discussion

Foot ulcers are a significant complication of diabetes and they often precede lower extremity amputation (2),(4).A wide range of bacteria can cause infection in these patients. While the foot infections with diabetes are initially treated empirically, the therapy which is directed at the known causative organisms may improve the outcome (6),(7),(9).This study presents a comprehensive microbiological survey of infected diabetic foot ulcers in our hospitalized patients. Foot ulcers account for 4% of all the diabetic hospitalizations (13) and the prevalence of diabetic foot ulceration was found to be 65% in males and 35% in females. The most common risk factors for diabetic foot ulceration include neuropathy, poor glycaemic control, ischaemia and infection.

Diabetic neuropathy was seen in 63.2% of our patients with diabetic ulcers. The detection of neuropathy before the development of its complications is the best way to prevent diabetic foot infections. In our study, S.aureus (26.1%) was the predominant pathogen which was isolated, followed by E.coli (18.4%), which was in accordance with the findings of the study which was conducted by Diane et al and Sharma et al [6,9]. But various other studies have demonstrated gram negative bacteria as the predominant pathogens (1),(2),(3),(4),(5),(7),(8). These discrepancies could be partly due to the differences in the causative organisms which occurred overtime and the geographical variation or the types and the severity of the infections which were included in the studies.

Poly-microbial infections were observed in 17.6% of the patients and mono-microbial infections were observed in 82.3% of the patients. The present study confirmed the fact that multidrug resistant organisms (MDRO) were common in hospitalized patients with diabetic foot ulcers (4),(7),(9),(11),(14). 54.2% of the S.aureus strains were oxacillin resistant and 50% of the isolated Enterococcus strains were resistant to vancomycin. Imipenem, piperacillin/tazobactum and cefeperazone / sulbactum were the agents which were most effective against gram negative organisms, while vancomycin was effective against the gram positive organisms. The increasing resistance to various anti-microbial agents could be due to the fact that ours was a tertiary care hospital with the widespread usage of broad spectrum antibiotics, leading to the survival advantage of the pathogens. Infection with these organisms may limit the choice of the antibiotic treatment and lead to worse outcomes.

To conclude, since there is an increasing rate of multidrug resistant organisms, there is a need for continuous surveillance to provide the basis of the empirical therapy and to reduce the risk of the complications. The inadvertent use of broad spectrum antibiotics should be discouraged. The selection of the antibiotic treatment should be based on the predominant organisms which are isolated and their antimicrobial susceptibility patterns. This will improve the overall antibiotic utilization and reduce the emergence of multidrug resistant organisms.

DOI and Others

DOI: JCDR/2012/4064:1991

DECLARATION ON COMPETING INTERESTS:
No competing Interests.


Date of Submission: Sep 27, 2011
Date of Peer Review: Jan 18, 2012
Date of Acceptance: Feb 09, 2012
Date of Publishing: May 01, 2012