Antimicrobial Susceptibility Pattern in Diabetic Foot Ulcer: A Pilot Study

Abstract

Background:

Diabetic foot infections (DFIs) are major public health problems and knowledge of microbes that cause infections are helpful to determine proper antibiotic therapy.

Aims:

The aim was to investigate the antimicrobial susceptibility pattern of microbes in DFIs.

Subjects and Methods:

A cross-sectional study was conducted for a period of 6 months at the Department of General Surgery, KMC hospital, Manipal University, Manipal, India. During this period, 108 patients having DFIs admitted in the general surgery wards were tracked from the hospital data management system. These patients’ pus samples were examined as Gram-stained smear and cultured aerobically on blood agar and MacConkey agar plates. Antimicrobial susceptibility test was performed by disc diffusion techniques according to Clinical and Laboratory Standards Institute guidelines.

Results:

Of the 108 specimens of the diabetic foot lesions, culture showed polymicrobial growth in 44.4% (48/108). Prevalence of Gram-negative organisms (56%, 84/150) was found to be more than Gram-positive organisms (44%, 66/150). However, Staphylococcus aureus was the most frequent pathogen (28%, 42/150). All Gram-positive aerobes were sensitive to doxycycline. All Gram-negative isolates, including extended spectrum beta lactamase producing strains of Proteus mirabilis and Klebsiella oxytoca except Acinetobacter were highly sensitive to amikacin, cefoperazone/sulbactam, and meropenem. Acinetobacter was completely resistant to all the common antibiotics tested.

Conclusion:

Prevalence showed Gram-negative bacteria was slightly more than Gram-positive bacteria in diabetic foot ulcers. This study recommends doxycycline should be empirical treatment of choice for Gram-positive isolates and amikacin, cefoperazone/sulbactam, and meropenem should be considered for most of the Gram-negatives aerobes.

Introduction

Globally, diabetic foot ulcers are one of the major public health problems leading to socioeconomic burden to the suffering individuals.[1,2] Around 15% of all diabetic patients develop a foot ulcer that is highly vulnerable to infections, at some time in their life.[3] Foot ulcer infections usually spread rapidly on account of polymicrobial growth, predominantly consisting of aerobic, Gram-positive and Gram-negative organisms.[4,5] In recent years, the number of the incidents and complications-related to diabetic foot infections (DFIs) has drastically increased due to increased incidence of multidrug-resistant organisms.[6] Currently, there is a deficit of data on these causatives in diabetic foot, especially in this part of the world. Manipal is located in a region with high literacy, low infant mortality and better access to health care. In this context, data from this region is also likely to be different from data gathered in other parts of rural India.

Adequate management of these infections needs appropriate antibiotic selection on the basis of culture and susceptibility test reports.[7] Usually initial management often comprises empirical antimicrobial treatment based on local epidemiological data of antimicrobial susceptibility. Knowledge of microbes that cause infections is helpful in determining proper antibiotic therapy.[3] Hence, this pilot study was undertaken in order to investigate the antimicrobial susceptibility pattern of microbes isolated from diabetic foot ulcers.

Subjects and Methods

A cross-sectional study was conducted in the Department of General Surgery, KMC Hospital, Manipal for a period of 6 months (July 1, 2011–December 31, 2011). During this period, 2892 patients’ admission details in the general surgery wards were tracked from the hospital data management system, and identified newly diagnosed 108 diabetic foot ulcer patients. Informed consents were obtained from all the eligible subjects. These patients’ pus samples (for bacterial culture) were obtained at the time of admission before starting antibiotic therapy. Wound swabs or pus were collected (deep tissue specimens produce better results than superficial swabs, especially when osteomyelitis is suspected. However, deep tissue specimens are not always practical or available). These specimens were examined as Gram-stained smear and cultured aerobically on blood agar and MacConkey agar plates. Antimicrobial susceptibility test was performed by disc diffusion technique according to Clinical and Laboratory Standards Institute guidelines. Anaerobic culture was not done due to lack of resources for handling anaerobic samples. Hence, results were analyzed for aerobic flora only. Before beginning the study, ethical clearance was obtained from the Institutional Ethical Committee.

Results and Discussion

Baseline characteristics of the 108 diabetic foot ulcer patients taken for the study showed 72.2% (78/108) were males and 27.8% (30/108) were females [Table 1]. Increased male prevalence has been reported in other studies.[3,4] This may be due to higher levels of outdoor activity among males than females. The mean (SD) age of the subjects was 58.3 (7.4) years. The mean (SD) duration of diabetes and hospital stay was 5.6 (4.1) years and 11.6 (7.1) days, respectively. Ulcers were located on plantar digit 33.3% (36/108), plantar metatarsal 22.2% (24/108), dorsal digit 16.7% (18/108), heel 16.7% (18/108), and lateral metatarsal 11.1% (12/108). 22.2% (24/108) patients had a previous history of amputation. Of the 108 specimens from the diabetic foot lesions, culture showed polymicrobial growth in 44.4% (48/108), monomicrobial growth in 44.4% (48/108), and no growth in 11.1% (12/108). Polymicrobial nature of DFIs has been reported from several studies conducted both in this region and abroad.[4] Lipsky, et al. have reported the majority of DFIs are polymicrobial nature with aerobic Gram-positive cocci, and especially staphylococci, the most common causative agents.[5] Different result was found by Tiwari et al. study, in which monomicrobial infections cases (43.5%, 27/62) were more than polymicrobial infections (35.5%, 22/62).[8]

Table 1.

Baseline characteristics of the study group (n=108)

Organisms isolated from the DFIs are presented in Table 2. Microbiological evaluation of diabetic foot ulcer infections showed that the prevalence of Gram-negative organisms (56%, 84/150) were found to be more than Gram-positive organisms (44%, 66/150) which is in accordance with earlier studies.[1] However, Staphylococcus aureus was the most frequent pathogen (28%, 42/150), followed by Pseudomonas aeruginosa (24%, 36/150). Almost similar results were obtained by two Indian studies.[3,4] Zubair et al. study conducted in North India also found Gram-negative aerobes were most frequent organisms (63.8%, 65/102) and Gram-positive aerobes (36.1%, 37/102).[9] Al Benwan, et al. also reported Gram-negatives were more prevalent, but predominant organisms isolated were members of the Enterobacteriaceae.[10] This study revealed that multidrug-resistant (MDR) organisms are very common in hospitalized patients with diabetic foot ulcers. This is in line with the report of Gadepalli, et al. study.[3] Zubair et al. noticed 45% (46/102) of diabetic foot ulcers were present MDR organisms.[9]

Table 2.

Bacteria isolated from diabetic foot infections of 96 patients

The antimicrobial susceptibility pattern of the Gram-positive and Gram-negative organisms are shown in Table 3. S. aureus isolates were 100% (48/48) sensitive to cotrimoxazole and totally resistant to ciprofloxacin. However, some previous studies reported sensitivity to ciprofloxacin.[4] The rate of Methicillin Resistant S. aureus (MRSA) in this study was found to be much lower than the studies conducted by Gadepalli, et al. and Bansal, et al.[3,4] MRSA was resistant to all the antibiotics except linezolid, doxycycline, and cotrimoxazole. Other Gram-positive cocci like Enterococci and Beta hemolytic streptococci isolates were 100% (12/12, 6/6, respectively) susceptible to chloramphenicol, gentamicin, and doxycycline. All Gram-positive aerobes except Enterococci were 100% (54/54) sensitive to cotrimoxazole. Except MRSA, all other Gram-positive aerobes were susceptible to gentamicin. All Gram-positive aerobes were sensitive to doxycycline. Al Benwan et al., study showed vancomycin was the most effective antibiotics for Gram-positive bacteria.[10]

Table 3.

Antimicrobial susceptibility (%) pattern of microbes in diabetic foot infections (n=96)

Most of studies have reported varying resistance patterns of P. aeruginosa toward commonly used antibiotics, but our studies showed a different pattern of susceptibility.[4] Extended spectrum beta lactamase (ESBL) producing Escherichia coli was resistant to most of the antibiotics except cefoperazone/sulbactam, meropenem, piperacillin/tazobactam, and ticarcillin/clavulanic acid. Similarly, Gadepalli, et al. study also observed ESBL producing E. coli.[3] All Gram-negative isolates (but not Acinetobacter) including ESBL-producing strains of Proteus mirabilis and Klebsiella oxytoca were highly sensitive to amikacin, cefoperazone/sulbactam and meropenem. Similarly, Al Benwan et al. have reported imipenem, piperacillin-tazobactam and amikacin were the most effective antibiotics for Gram-negative bacteria.[10] Acinetobacter was totally resistant to all the common antibiotics tested. This was in accordance with multidrug-resistant Acinetobacter isolates from Bansal, et al. study.[4] The main limitations of our study are a small sample size and the specimen used for the culture that is wound swab and pus.

Conclusion

This study showed most common organisms present in the diabetic foot ulcer were Gram-negative aerobes. However, S. aureus was the most predominant organism isolated from the lesions. There were equal proportions of monomicrobial and polymicrobial cultures noticed in the DFIs. Presence of MDR organisms was alarmingly high in the diabetic foot ulcers. These observations are important, especially for patient management and the development of antibiotic treatment guidelines. Moreover, increasing prevalence of MDR organisms raises serious concerns because MDR infections limit the choice of antibiotic therapy and may lead to poor prognosis. Findings of this study propose that large prospective studies are essential to assess the suitable empirical antibiotic regimen in diabetic foot ulcer infections. This study also directed us toward proper treatment strategies for the management of diabetic foot ulcers with appropriate antibiotics such as doxycycline and gentamicin for Gram-positive cocci and amikacin, cefoperazone/sulbactam and meropenem for Gram-negative bacilli. Clinical guidelines must be implemented to cut the incidence of MDR bacteria in this population and for better patient's outcomes. Simultaneously, we have to seek effective agents for microbes such as MDR Acinetobacter.