Impact of the bacteriology of diabetic foot ulcers in limb loss

Toward non-invasive collection methods for sampling the microbiome of diabetic foot ulcers

Identifying the microbiome within chronic diabetic foot ulcers is essential if effective antimicrobial therapies are to be administered. Using culture and 16S rRNA gene sequencing, the aim of this study was to compare the microbiome of paired tissue scraping samples with swab samples, collected from participants during attendance at a high-risk foot clinic. The mean richness of cultured swab and tissue scraping samples was consistent, with anaerobes infrequently isolated from both sample types. Comparing percentage frequencies of detection of selected genera of known and potential pathogens namely Staphylococcus, Streptococcus, Enterococcus, Corynebacterium, Enterobacteriaceae and Pseudomonas from cultured and sequenced swab and tissue scrapings indicated that both collection methods captured varying percentages of all the selected genera. The mean abundance of sequenced samples was not significantly different between swabs and tissue scrapings. The mean richness or number of distinct operational taxonomic units (OTUs) and Shannon's H diversity index were not significantly different between the two collection methods. The mean relative abundance of the selected genera of known and potential pathogens, including anaerobes Anaerococcus and Finegoldia, was higher in swabs compared with tissue scrapings and significantly so in Staphylococcus and Pseudomonas genera. Multivariate analyses confirmed no significant differences between the bacterial community compositions of the paired samples. These results suggest that tissue scrapings and swabs can effectively capture the microbiome of chronic DFUs using culture and 16S rRNA gene sequencing.

Polymicrobial Foot Infection Patterns Are Common and Associated With Treatment Failure

BACKGROUND

That foot infections are predominately polymicrobial has long been recognized, but it is not clear if the various species co-occur randomly or in patterns. We sought nonrandom species co-occurrence patterns that might help better predict prognosis or guide antimicrobial selection.

METHODS

We analyzed tissue (bone, skin, and other soft tissue), fluid, and swab specimens collected from initial foot infection episodes during a 10-year period using a hospital registry. Nonrandom co-occurrence of microbial species was identified using simple pairwise co-occurrence rates adjusted for multiple comparisons, Markov and conditional random fields, and factor analysis. A historical cohort was used to validate pattern occurrence and identify clinical significance.

RESULTS

In total, 156 unique species were identified among the 727 specimens obtained from initial foot infection episodes in 694 patients. Multiple analyses suggested that Staphylococcus aureus is negatively associated with other staphylococci. Another pattern noted was the co-occurrence of alpha-hemolytic Streptococcus, Enterococcus fecalis, Klebsiella, Proteus, Enterobacter, or Escherichia coli, and absence of both Bacteroides and Corynebacterium. Patients in a historical cohort with this latter pattern had significantly higher risk-adjusted rates of treatment failure.

CONCLUSIONS

Several nonrandom microbial co-occurrence patterns are frequently seen in foot infection specimens. One particular pattern with many Proteobacteria species may denote a higher risk for treatment failure. Staphylococcus aureus rarely co-occurs with other staphylococci.

The association between bacteria and outcome and the influence of sampling method, in people with a diabetic foot infection

Purpose

Different bacteria lead to divers diabetic foot infections (DFIs), and some bacteria probably lead to higher amputation and mortality risks. We assessed mortality and amputation risk in relation to bacterial profiles in people DFI and investigated the role of sampling method.

Methods

We included people (> 18 years) with DFI in this retrospective study (2011–2020) at a Dutch tertiary care hospital. We retrieved cultures according to best sampling method: (1) bone biopsy; (2) ulcer bed biopsy; and (3) swab. We aggregated data into a composite determinant, consisting of unrepeated bacteria of one episode of infection, clustered into 5 profiles: (1) Streptococcus and Staphylococcus aureus; (2) coagulase-negative Staphylococcus, Cutibacterium, Corynebacterium and Enterococcus; (3) gram-negative; (4) Anaerobic; and (5) less common gram-positive bacteria. We calculated Hazard Ratio’s (HR’s) using time-dependent-Cox regression for the analyses and investigated effect modification by sampling method.

Results

We included 139 people, with 447 person-years follow-up and 459 episodes of infection. Sampling method modified the association between bacterial profiles and amputation for profile 2. HR’s (95% CI’s) for amputation for bacterial profiles 1–5: 0.7 (0.39–1.1); stratified analysis for profile 2: bone biopsy 0.84 (0.26–2.7), ulcer bed biopsy 0.89 (0.34–2.3), swab 5.9*(2.9–11.8); 1.3 (0.78–2.1); 1.6 (0.91–2.6); 1.6 (0.58–4.5). HR’s (95% CI’s) for mortality for bacterial profiles 1–5: 0.89 (0.49–1.6); 0.73 (0.38–1.4); 2.6*(1.4–4.8); 1.1(0.58–2.2); 0.80(0.19–3.3).

Conclusions

In people with DFI, there was no association between bacterial profiles in ulcer bed and bone biopsies and amputation. Only in swab cultures, low-pathogenic bacteria (profile 2), were associated with a higher amputation risk. Infection with gram-negative bacteria was associated with a higher mortality risk. This study underlined the possible negative outcome of DFI treatment based on swabs cultures.

Examining the effect of wound cleansing on the microbiome of venous stasis ulcers

Common treatment for venous leg wounds includes topical wound dressings with compression. At each dressing change, wounds are debrided and washed; however, the effect of the washing procedure on the wound microbiome has not been studied. We hypothesized that wound washing may alter the wound microbiome. To characterize microbiome changes with respect to wound washing, swabs from 11 patients with chronic wounds were sampled before and after washing, and patient microbiomes were characterized using 16S rRNA sequencing and culturing. Microbiomes across patient samples prior to washing were typically polymicrobial but varied in the number and type of bacterial genera present. Proteus and Pseudomonas were the dominant genera in the study. We found that washing does not consistently change microbiome diversity but does cause consistent changes in microbiome composition. Specifically, washing caused a decrease in the relative abundance of the most highly represented genera in each patient cluster. The finding that venous leg ulcer wound washing, a standard of care therapy, can induce changes in the wound microbiome is novel and could be potentially informative for future guided therapy strategies.

Interplay between ESKAPE Pathogens and Immunity in Skin Infections: An Overview of the Major Determinants of Virulence and Antibiotic Resistance

The skin is the largest organ in the human body, acting as a physical and immunological barrier against pathogenic microorganisms. The cutaneous lesions constitute a gateway for microbial contamination that can lead to chronic wounds and other invasive infections. Chronic wounds are considered as serious public health problems due the related social, psychological and economic consequences. The group of bacteria known as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter sp.) are among the most prevalent bacteria in cutaneous infections. These pathogens have a high level of incidence in hospital environments and several strains present phenotypes of multidrug resistance. In this review, we discuss some important aspects of skin immunology and the involvement of ESKAPE in wound infections. First, we introduce some fundamental aspects of skin physiology and immunology related to cutaneous infections. Following this, the major virulence factors involved in colonization and tissue damage are highlighted, as well as the most frequently detected antimicrobial resistance genes. ESKAPE pathogens express several virulence determinants that overcome the skin's physical and immunological barriers, enabling them to cause severe wound infections. The high ability these bacteria to acquire resistance is alarming, particularly in the hospital settings where immunocompromised individuals are exposed to these pathogens. Knowledge about the virulence and resistance markers of these species is important in order to develop new strategies to detect and treat their associated infections.

Antimicrobial Susceptibility Testing and Phenotypic Detection of MRSA Isolated from Diabetic Foot Infection

Background

Diabetic foot infection (DFI) is a common and costly complication of diabetes that may be caused by various bacteria with multi-resistant genes. The aim of this study is to evaluate the efficacy of phenotypic methods for identification of methicillin-resistant Staphylococcus aureus (MRSA) with genotypic detection of MRSA-related genes.

Methods

In this cross-sectional study, swab samples were collected from patients with DFI from hospitals in Sulaimani/Iraq in April–July 2019. All the samples were processed for microbiological assessment and further MRSA phenotypic and genotypic testing.

Results

A total of 46 swab samples were collected from diabetic foot ulcers of 29 males and 17 females. Most samples (93.5%) showed positive growth, with higher proportions of monomicrobial (23; 53.5%) than mixed-bacterial infections (20; 46.5%) and S. aureus as the predominant pathogen. Conventional methods of MRSA detection, such as cefoxitin disc diffusion, can predict methicillin resistance in 45.8% of the cases. Real-time/conventional PCR showed that 41.6% of Staphylococcus aureus were positive for the mecA gene, while none of the isolates was positive for PVL.

Conclusion

Staphylococcus aureus was the predominant pathogen in DFI. Although cefoxitin and oxacillin disc diffusion methods can help in the prediction of MRSA, real-time PCR is a reliable method for MRSA detection and confirmation.

Human myiasis in patients with diabetic foot: 18 cases

BACKGROUND

Myiasis complication of diabetic foot ulcer has only been presented in a few case reports. Therefore, there is a need for additional data on this infestation.

OBJECTIVE

Evaluate clinical characteristics of human myiasis in patients with diabetic foot.

DESIGN

Case series.

SETTINGS

A tertiary referral healthcare institution and a diabetic foot center.

PATIENTS AND METHODS

Patients with diabetic foot infection com.plicated by myiasis who were admitted between June 2012 and July 2017.

MAIN OUTCOME MEASURES

Bacterial infection rate, accompanying bacterial agents, amputation (morbidity) and mortality rate.

SAMPLE SIZE

18.

RESULTS

Eight (44.4%) of the patients were female. Sixteen (88.9%) had moderate-to-severe infections; 15 (83.3%) had necrotic tissue. Larval debridement therapy was performed on all patients at the bed.side in consecutive sessions. A third-stage larva of Calliphora was detected in one case (5.6%). Second- and third-stage larvae of Lucilia sericata were detected in 5 (27.8%) and 7 (38.9%) patients, respectively. All the patients had a bacterial infection with myiasis. Twelve (66.7%) patients underwent amputation. Three (16.7%) patients died. Myiasis was more frequent in the months of May, June and July.

CONCLUSION

To our knowledge, this is the largest reported series of cases of diabetic foot with myiasis. The most common parasitic agent was Lucilia sericata. Bacterial soft tissue infections were observed in all cases. Poor hygienic conditions were noteworthy and all patients were in need of radical surgery. Myiasis complication of diabetic foot is more frequently seen in the spring and summer.

LIMITATIONS

Insufficient follow-up time for analysis of possible confounding factors.

CONFLICT OF INTEREST

None.

Microbial Host Interactions and Impaired Wound Healing in Mice and Humans: Defining a Role for BD14 and NOD2

Chronic wounds cause significant patient morbidity and mortality. A key factor in their etiology is microbial infection, yet skin host-microbiota interactions during wound repair remain poorly understood. Microbiome profiles of noninfected human chronic wounds are associated with subsequent healing outcome. Furthermore, poor clinical healing outcome was associated with increased local expression of the pattern recognition receptor NOD2. To investigate NOD2 function in the context of cutaneous healing, we treated mice with the NOD2 ligand muramyl dipeptide and analyzed wound repair parameters and expression of antimicrobial peptides. Muramyl dipeptide treatment of littermate controls significantly delayed wound repair associated with reduced re-epithelialization, heightened inflammation, and up-regulation of murine β-defensins 1, 3, and particularly 14. We postulated that although murine β-defensin 14 might affect local skin microbial communities, it may further affect other healing parameters. Indeed, exogenously administered murine β-defensin 14 directly delayed mouse primary keratinocyte scratch wound closure in vitro. To further explore the role of murine β-defensin 14 in wound repair, we used Defb14^-/- mice and showed they had a global delay in healing in vivo, associated with alterations in wound microbiota. Taken together, these studies suggest a key role for NOD2-mediated regulation of local skin microbiota, which in turn affects chronic wound etiology.

Risk factors for amputation in patients with diabetic foot infection: a prospective study

There is a variety of diagnostic and therapeutic algorithms for diabetic foot infections (DFIs). Some of them are too difficult to be applied in routine clinical approach. In the routine clinical approach, it is necessary to find new risk factors and end up with a quick and easy assessment of DFIs. In this study, we aimed to evaluate the independent risk factors for osteomyelitis, amputation and major amputation in patients with DFI using standard scoring procedures. We prospectively studied 379 patients with DFI. The variables were analysed using logistic analysis. A total of 126 cases (33·2%) underwent amputation. The odds ratios in the amputation model were 3·09 for osteomyelitis (P < 0·001), 4·90 for arterial stenosis (AS) (P < 0·001), 3·67 for the history of DFI (P = 0·001), 2·47 for ulcer duration >60 days (P = 0·001), 3·10 for ulcer depth > 15 mm (P < 0·001) and 10·28 for fungal DFI (P = 0·015). In this study, the unusual result of well-known literature was fungal DFI as an independent risk factor for amputation in patients with DFI.

Bacterial Prevalence and Antibiotic Resistance in Clinical Isolates of Diabetic Foot Ulcers in the Northeast of Tamaulipas, Mexico

Diabetic foot ulcers (DFUs) are a serious and common problem in patients with diabetes mellitus and constitute one of the major causes of lower extremity amputation. The microbiological profile of DFUs depends on the acute or chronic character of the wound. Aerobic gram-positive cocci are the predominant organisms isolated from DFUs. Diabetic foot biopsies from patients admitted to the Angiology and Vascular Surgery Hospital of the Northeast, in Reynosa, Tamaulipas from December 2011 to April 2016 were analyzed. The samples were processed using standard microbiology techniques. Antimicrobial susceptibility testing was carried out according to the protocol established by the Clinical & Laboratory Standards Institute (CLSI). We obtained 246 bacterial isolates, based on the results of phenotypic resistance. The least effective antibiotics for gram-positive bacteria were penicillin and dicloxacillin; for gram-negative bacteria, cefalotin and penicillin were the least effective. Levofloxacin, cefalotin, and amikacin were the most effective antibiotics for gram-positive and negative bacteria, respectively. Enterobacter genus was significantly associated with muscle biopsies ( P = .011) and samples without growth were significantly associated with specimens of pyogenic origin ( P = .000). In 215 DFU samples, we found that Staphylococcus aureus was the most commonly isolated pathogen followed by Enterobacter sp. This is consistent with previous reports. Enterobacter species may play an important role in the colonization/infection of certain tissues; however, further studies are needed in this regard.