Microbiological Evaluation of Diabetic Foot Osteomyelitis

Diabetic foot infection - diagnosis and treatment

Diabetic foot (DF) is one of the most serious complications of diabetes, leading to high morbidity and mortality in patients with diabetes, significantly affecting their quality of life and placing a huge burden on the healthcare system. Diabetic foot infection (DFI) is a major factor in the non-healing of diabetic ulcerations of the lower limbs, increases the number of hospital admissions, prolongs their duration and is a frequent cause of increased number of amputations. The most serious form of foot infection is osteomyelitis. Management of infection in SDN includes proper diagnosis, including obtaining appropriate specimens for culture, indication of rational antimicrobial therapy or early surgical intervention, and provision of all other necessary wound care and overall patient care to prevent recurrence of DFI.

Infectious Diseases Management in Wound Care Settings: Common Causative Organisms and Frequently Prescribed Antibiotics

GENERAL PURPOSE

To provide information about the management of infected wounds in wound care settings.

TARGET AUDIENCE

This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and nurses with an interest in skin and wound care.

LEARNING OBJECTIVES/OUTCOMES

After participating in this educational activity, the participant will:1. Identify a host factor that may predispose a patient to a wound infection as well as characteristics of each stage of wound infection.2. Distinguish a common organism that causes early, acute wound infections and explain the preferred method for obtaining a wound specimen for culture.3. Apply knowledge of commonly prescribed antibiotics in wound care settings.

Analysis of the Composition and Functions of the Microbiome in Diabetic Foot Osteomyelitis Based on 16S rRNA and Metagenome Sequencing Technology

Metagenome sequencing has not been used in infected bone specimens. This prospective observational study explored the microbiome and its function in patients with diabetic foot osteomyelitis (DFO) and posttraumatic foot osteomyelitis (PFO) based on 16S rRNA sequencing and metagenome sequencing technologies. Spearman analysis was used to explore the correlation between dominant species and clinical indicators of patients with DFO. High-throughput sequencing showed that all the specimens were polymicrobial. The microbial diversity was significantly higher in the DFO group than in the PFO group. Firmicutes, Prevotellaceae, and Prevotella were the most abundant microbes in the DFO group. The most abundant microbes in the PFO group were Proteobacteria, Halomonadaceae, and Halomonas Prevotella denticola, Prevotella jejuni, and Prevotella fusca had positive correlation with the duration of diabetic foot infection (DFI_d). Proteus vulgaris was positively correlated with the infection index, while Bacteroides fragilis was negatively correlated. The microbial functional genes were more abundant in the DFO group than in the PFO group. Metagenome sequencing is feasible for the analysis of the microbiome in infected bone specimens. Gram-negative bacteria and anaerobes are dominant in DFO.

Admission Time Deep Swab Specimens Compared With Surgical Bone Sampling in Hospitalized Individuals With Diabetic Foot Osteomyelitis and Soft Tissue Infection

Whether deep swab cultures taken at admission reliably identify pathogens compared to surgical bone specimens in hospitalized individuals with diabetic foot osteomyelitis and soft tissue infection is unclear. Comparison of microbiological isolates between a deep wound swab (DWS) taken at the time of admission through the actively infected, discharging ulcer probing to the bone and the subsequent surgical bone sample (SBS) taken during surgical debridement was made. A total of 63 subjects (age 60.8 ± 13.5 years, 75% male, 80% Type 2 diabetes, HbA1C 8.9%±2.2%) were included. The proportion of Gram-positive (DWS 49% v SBS 52%) and Gram-negative (DWS 60% v SBS 60%) isolates was similar between the techniques. However, the overall concordance of isolates between the two techniques was only fair (κ=0.302). The best concordance was observed for Staphylococcus aureus (κ=0.571) and MRSA (κ=0.644). There was a correlation between number of isolates in SBS with prior antibiotic therapy of any duration (r= -0.358, p=0.005) and with the duration of ulceration (r=0.296, p=0.045); no clinical correlations were found for DWS. Prior antibiotic therapy (p=0.03) and duration of ulceration <8 weeks (p=0.025) were predictive of negative growth on SBS. In conclusion, we found only a fair concordance between deep wound swabs acquired at admission and surgical bone specimens in those presenting with a severe diabetic foot infection and features of osteomyelitis. Ensuring early surgical debridement of all infected tissue and obtaining bone specimens should be considered a clinical priority, which may also reduce the likelihood of negative growth on SBS.

Antimicrobial susceptibility pattern of aerobes in diabetic foot ulcers in a South-Indian tertiary care hospital

PURPOSE

Diabetic foot infections (DFIs) are major public health concerns. In the view of the ever increasing burden of multidrug-resistant (MDR) organisms, improving the use of antimicrobial agents (AMAs) is a national priority. Objective of the study was to determine antimicrobial susceptibility (AMS) pattern of aerobes in DFIs.

METHODS

A cross-sectional study was conducted for a period of 3 years at Department of Surgery, Kasturba hospital, Manipal, India during which, 260 diabetic foot ulcer (DFU) patients admitted in the general surgery wards were enrolled for the study. These patients' culture specimens were observed as Gram-stained smears and cultured aerobically on blood agar and MacConkey agar plates. AMS test was performed by disc diffusion technique according to Clinical and Laboratory Standards Institute (CLSI) guidelines.

RESULTS

A total of 354 microbes were isolated from the ulcer wounds of 213 diabetic foot patients, with an average of 1.7 organisms per lesion. Monomicrobial infections were less common (n=81; 31.2%) than polymicrobial infections (n=132; 50.7%). Gram-negative bacteria were the most common among the isolates (n=192; 54.2%). Aerobic Gram-positive Cocci accounted for 162 (45.8%) of all isolates. On the other hand, Staphylococcus aureus was the most frequently isolated aerobe (n=106; 29.9%) followed by Pseudomonas aeruginosa (n=91; 25.7%).

CONCLUSION

AMS data from our study recommends that doxycycline would be the appropriate choice as single drug for empirical coverage for Gram-positive organisms. The most appropriate antibiotic for Gram-negative organisms is meropenem. One of the critical observations is the presence of Acinetobacter, an MDR isolated from DFIs, which is either relatively or totally resistant to all the AMAs tested.

Understanding the microbiome of diabetic foot osteomyelitis: insights from molecular and microscopic approaches

OBJECTIVES

Rigorous visual evidence on whether or not biofilms are involved in diabetic foot osteomyelitis (DFO) is lacking. We employed a suite of molecular and microscopic approaches to investigate the microbiome, and phenotypic state of microorganisms involved in DFO.

METHODS

In 20 consecutive subjects with suspected DFO, we collected intraoperative bone specimens. To explore the microbial diversity present in infected bone we performed next generation DNA sequencing. We used scanning electron microscopy (SEM) and peptide nucleic acid fluorescent in situ hybridization (PNA-FISH) with confocal microscopy to visualize and confirm the presence of biofilms.

RESULTS

In 19 of 20 (95%) studied patients presenting with DFO, it was associated with an infected diabetic foot ulcer. By DNA sequencing of infected bone, Corynebacterium sp. was the most commonly identified microorganism, followed by Finegoldia sp., Staphylococcus sp., Streptococcus sp., Porphyromonas sp., and Anaerococcus sp. Six of 20 bone samples (30%) contained only one or two pathogens, while the remaining 14 (70%) had polymicrobial communities. Using a combination of SEM and PNA-FISH, we identified microbial aggregates in biofilms in 16 (80%) bone specimens and found that they were typically coccoid or rod-shaped aggregates.

CONCLUSIONS

The presence of biofilms in DFO may explain why non-surgical treatment of DFO, relying on systemic antibiotic therapy, may not resolve some chronic infections caused by biofilm-producing strains.

Microbiology and Antimicrobial Therapy for Diabetic Foot Infections

In addition to being the prime factor associated with amputation, diabetic foot infections (DFIs) are associated with major morbidity, increasing mortality, and reduced quality of life. The choice of appropriate antibiotics is very important in order to reduce treatment failure, antimicrobial resistance, adverse events, and costs. We reviewed articles on microbiology and antimicrobial therapy and discuss antibiotic selection in Korean patients with DFIs. Similar to Western countries, Staphylococcus aureus is the most common pathogen, with Streptococcus, Enterococcus, Enterobacteriaceae and Pseudomonas also prevalent in Korea. It is recommended that antibiotics are not prescribed for clinically uninfected wounds and that empirical antibiotics be selected based on the clinical features, disease severity, and local antimicrobial resistance patterns. Narrow-spectrum oral antibiotics can be administered for mild infections and broad-spectrum parenteral antibiotics should be administered for some moderate and severe infections. In cases with risk factors for methicillin-resistant S. aureus or Pseudomonas, empirical antibiotics to cover each pathogen should be considered. The Health Insurance Review and Assessment Service standards should also be considered when choosing empirical antibiotics. In Korea, nationwide studies need to be conducted and DFI guidelines should be developed.

Isolation and Antibiotic Susceptibility of the Microorganisms Isolated from Diabetic Foot Infections in Nemazee Hospital, Southern Iran

Background. Diabetic foot infections (DFIs) are a major public health issue and identification of the microorganisms causing such polymicrobial infections is useful to find out appropriate antibiotic therapy. Meanwhile, many reports have shown antibiotic resistance rising dramatically. In the present study, we sought to determine the prevalence of microorganisms detected on culture in complicated DFIs in hospitalized patients and their antibiotic sensitivity profiles. Methods. A cross-sectional study was conducted for a period of 24 months from 2012 to 2014 in Nemazee Hospital, Shiraz, Iran. The demographic and clinical features of the patients were obtained. Antimicrobial susceptibility testing to different agents was carried out using the disc diffusion method. Results. During this period, 122 aerobic microorganisms were isolated from DFIs. Among Gram-positive and Gram-negative bacteria, Staphylococcus spp. and E. coli were the most frequent organisms isolated, respectively. Of the isolates, 91% were multidrug while 78% of S. aureus isolates were methicillin resistant. 53% of Gram-negative bacteria were positive for extended-spectrum β-lactamase. Conclusion. Given the involvement of different microorganisms and emergence of multidrug resistant strains, clinicians are advised to consider culture before initiation of empirical therapy.

Management of hospitalized patients with diabetic foot infections

Diabetic foot infections (DFIs), which present with a variety of clinical manifestations, are commonly encountered by clinicians. They are associated with a high morbidity, a high amputation rate, a high mortality, and increased health care costs. An effective management of DFIs requires a multidisciplinary approach with a strong collaboration among all involved health care providers as well as patient involvement. Diagnosing DFIs appropriately requires consideration of the clinical symptoms and signs of infection in addition to supplementary laboratory testing such as inflammatory markers and imaging studies. The comprehensive patient assessment should include the predisposing risk factors for infection; the type, severity, and extent of the infection; and the assessment of neurologic and vascular status, comorbid conditions, and psychosocial factors. The comprehensive management of DFIs include not only effective antibiotic therapy but also surgical debridement, pressure offloading, wound care and moisture, maintaining good vascular perfusion, control of edema and pain, correction of metabolic abnormalities such as hyperglycemia, and addressing psychosocial and nutritional issues. Discharge planning that addresses full medical and social needs along with suitable follow-up, patient education and counseling, and clear communication with outpatient providers are critical for ensuring a safe and successful transition to outpatient management of hospitalized patients with DFIs.

Diagnosis and management of infection in the diabetic foot

Foot infections are common in persons with diabetes mellitus. Most diabetic foot infections occur in a foot ulcer, which serves as a point of entry for pathogens. Unchecked, infection can spread contiguously to involve underlying tissues, including bone. A diabetic foot infection is often the pivotal event leading to lower extremity amputation, which account for about 60% of all amputations in developed countries. Given the crucial role infections play in the cascade toward amputation, all clinicians who see diabetic patients should have at least a basic understanding of how to diagnose and treat this problem.

Clinical significance of the isolation of Staphylococcus epidermidis from bone biopsy in diabetic foot osteomyelitis

Introduction

Coagulase-negative staphylococci are considered as microorganisms with little virulence and usually as contaminants. In order to establish the role of Staphylococcus epidermidis as a pathogen in diabetic foot osteomyelitis, in addition to the isolation of the sole bacterium from the bone it will be necessary to demonstrate the histopathological changes caused by the infection.

Methods

A consecutive series of 222 diabetic patients with foot osteomyelitis treated surgically in the Diabetic Foot Unit at La Paloma Hospital (Las Palmas de Gran Canaria, Canary Islands, Spain) between 1 October 2002 and 31 October 2008. From the entire series including 213 bone cultures with 241 isolated organisms, we have analyzed only the 139 cases where Staphylococci were found. We analyzed several variables between the two groups: Staphylococcus aureus versus Staphylococcus epidermidis.

Results

Of the 134 patients included in this study, Staphlylococcus epidermidis was found as the sole bacterium isolated in 11 cases and accompanied by other bacteria in 12 cases. Staphlylococcus aureus was found as the sole bacterium isolated in 72 cases and accompanied by other bacteria in 39 cases. Histopathological changes were found in the cases of osteomyelitis where Staphylococcus epidermidis was the sole bacterium isolated. Acute osteomyelitis was found to a lesser extent when Staphylococcus epidermidis was the sole bacterium isolated but without significant differences with the cases where Staphylococcus aureus was the sole bacterium isolated.

Conclusion

Staphylococcus epidermidis should be considered as a real pathogen, not only a contaminant, in diabetic patients with foot osteomyelitis when the bacterium is isolated from the bone. No differences in the outcomes of surgical treatment have been found with cases which Staphlylococcus aureus was isolated.

Diabetic foot osteomyelitis: a progress report on diagnosis and a systematic review of treatment

The International Working Group on the Diabetic Foot appointed an expert panel to provide evidence-based guidance on the management of osteomyelitis in the diabetic foot. Initially, the panel formulated a consensus scheme for the diagnosis of diabetic foot osteomyelitis (DFO) for research purposes, and undertook a systematic review of the evidence relating to treatment. The consensus diagnostic scheme was based on expert opinion; the systematic review was based on a search for reports of the effectiveness of treatment for DFO published prior to December 2006. The panel reached consensus on a proposed scheme that assesses the probability of DFO, based on clinical findings and the results of imaging and laboratory investigations. The literature review identified 1168 papers, 19 of which fulfilled criteria for detailed data extraction. No significant differences in outcome were associated with any particular treatment strategy. There was no evidence that surgical debridement of the infected bone is routinely necessary. Culture and sensitivity of isolates from bone biopsy may assist in selecting properly targeted antibiotic regimens, but empirical regimens should include agents active against staphylococci, administered either intravenously or orally (with a highly bioavailable agent). There are no data to support the superiority of any particular route of delivery of systemic antibiotics or to inform the optimal duration of antibiotic therapy. No available evidence supports the use of any adjunctive therapies, such as hyperbaric oxygen, granulocyte-colony stimulating factor or larvae. We have proposed a scheme for diagnosing DFO for research purposes. Data to inform treatment choices in DFO are limited, and further research is urgently needed.

Bacteriology of moderate-to-severe diabetic foot infections and in vitro activity of antimicrobial agents

As part of a United States-based multicenter clinical trial, conducted from 2001 to 2004, that compared ertapenem to piperacillin-tazobactam for the treatment of moderate-to-severe diabetic foot infections (DFIs), we obtained 454 pretreatment specimens from 433 patients. After debridement, the investigators collected wound specimens, mostly by curettage or biopsy, and sent them to the R. M. Alden Research Laboratory for aerobic and anaerobic culture. Among the 427 positive cultures, 83.8% were polymicrobial, 48% grew only aerobes, 43.7% had both aerobes and anaerobes, and 1.3% had only anaerobes. Cultures yielded a total of 1,145 aerobic strains and 462 anaerobic strains, with an average of 2.7 organisms per culture (range, 1 to 8) for aerobes and 2.3 organisms per culture (range, 1 to 9) for anaerobes. The predominant aerobic organisms were oxacillin-susceptible Staphylococcus aureus (14.3%), oxacillin-resistant Staphylococcus aureus (4.4%), coagulase-negative Staphylococcus species (15.3%), Streptococcus species (15.5%), Enterococcus species (13.5%), Corynebacterium species (10.1%), members of the family Enterobacteriaceae (12.8%), and Pseudomonas aeruginosa (3.5%). The predominant anaerobes were gram-positive cocci (45.2%), Prevotella species (13.6%), Porphyromonas species (11.3%), and the Bacteroides fragilis group (10.2%). Pure cultures were noted for 20% of oxacillin-resistant Staphylococcus aureus cultures, 9.2% of Staphylococcus epidermidis cultures, and 2.5% of P. aeruginosa cultures. Two or more species of Staphylococcus were present in 13.1% of the patients. Ertapenem and piperacillin-tazobactam were each active against >98% of the enteric gram-negative rods, methicillin-sensitive S. aureus, and anaerobes. Among the fluoroquinolones, 24% of anaerobes, especially the gram-positive cocci, were resistant to moxifloxacin; 27% of the gram-positive aerobes but only 6% of the members of the family Enterobacteriaceae were resistant to levofloxacin. Moderate-to-severe DFIs are typically polymicrobial, and almost half include anaerobes. Our antibiotic susceptibility results can help to inform therapeutic choices.

Clinical validation of the molecular BD GeneOhm StaphSR assay for direct detection of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus in positive blood cultures

The rapid detection of Staphylococcus aureus bacteremia and a swift determination of methicillin susceptibility has serious clinical implications affecting patient mortality. This study evaluated the StaphSR assay (BD GeneOhm, San Diego, CA), a real-time PCR assay, for the identification and differentiation of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) from 300 positive blood cultures. The BD GeneOhm StaphSR assay was performed and interpreted according to the manufacturer's recommendations. Positive blood cultures (containing predominantly gram-positive cocci in clusters) were subcultured on 5% sheep blood agar plates. After 18 to 24 h of incubation, isolates morphologically consistent with S. aureus were presumptively identified by latex agglutination (Staphaurex Plus; Remel, Lenexa, KS). Susceptibility testing was initially performed with the Phoenix automated microbiology system (BD Diagnostics, Sparks, MD). Additional susceptibility testing of samples with discrepant results was done using BBL oxacillin screen agar (BD Diagnostics, Sparks, MD), oxacillin and cefoxitin Etests (AB Biodisk, Solna, Sweden) on Mueller-Hinton agar, an immunoassay for penicillin binding protein 2' (Denka Seiken Co., Tokyo, Japan), and mecA PCR. The sensitivity, specificity, and positive and negative predictive values of the BD GeneOhm StaphSR assay for MSSA detection were 98.9, 96.7, 93.6, and 99.5%, respectively. For the detection of MRSA, the BD GeneOhm StaphSR assay was 100% sensitive and 98.4% specific; positive and negative predictive values for MRSA detection were 92.6 and 100%, respectively. Inhibition was seen with only one sample, and the issue was resolved upon retesting. The BD GeneOhm StaphSR assay appears to be a valuable diagnostic tool for quickly differentiating bacteremia caused by MSSA and MRSA from that caused by other gram-positive cocci.

Probe-to-bone test for diagnosing diabetic foot osteomyelitis: reliable or relic?

OBJECTIVE

We sought to assess the accuracy of the probe-to-bone (PTB) test in diagnosing foot osteomyelitis in a cohort of diabetic patients with bone culture proven disease.

RESEARCH DESIGN AND METHODS

In this 2-year longitudinal cohort study, we enrolled 1,666 consecutive diabetic individuals who underwent an initial standardized detailed foot assessment, followed by examinations at regular intervals. Patients were instructed to immediately come to the foot clinic if they developed a lower-extremity complication. For all patients with a lower-extremity wound, we compared the results of the PTB test with those of a culture of the affected bone. We called PTB positive if the bone or joint was palpable and defined osteomyelitis as a positive bone culture.

RESULTS

Over a mean of 27.2 months of follow-up, 247 patients developed a foot wound and 151 developed 199 foot infections. Osteomyelitis was found in 30 patients: 12% of those with a foot wound and 20% in those with a foot infection. When all wounds were considered, the PTB test was highly sensitive (0.87) and specific (0.91); the positive predictive value was only 0.57, but the negative predictive value was 0.98.

CONCLUSIONS

The PTB test, when used in a population of diabetic patients with a foot wound among whom the prevalence of osteomyelitis was 12%, had a relatively low positive predictive value, but a negative test may exclude the diagnosis.