#FEMSmicroBlog: Exploring bacterial cooperation in diabetic wound infections


Diabetes is a group of metabolic diseases affecting over 500 million individuals globally. Many affected people develop wounds on their feet or lower legs. These wounds often become chronic due to the presence of bacterial pathogens and an impaired immune response. The study “Virulence characteristics of Gram-positive bacteria isolated from diabetic foot ulcers” in FEMS Microbes explores the bacterial composition of diabetic wounds to find better treatment options, as explained by Rebecca Keogh in this #FEMSmicroBlog. #FascinatingMicrobes


Chronic wounds due to diabetes

As a hallmark of diabetes, chronic hyperglycemia, or elevated blood sugar, can lead to long-term complications. Poor circulation, nerve damage, and an impaired immune response lead to a high susceptibility to microbial infections and poor wound healing.

These conditions leave diabetic individuals prone to tissue damage. One in four people with diabetes will develop a wound on their feet or lower legs during their lifetime. As about 25% of these wounds will become chronic, it results in approximately 1.6 million amputations a year.

Chronic wound infections are difficult to treat since many infections are of polymicrobial nature with more than one species present. Additionally, microbes residing in chronic wounds often carry intrinsic antibiotic resistances or tolerances, while many live in biofilms protected from antibiotic penetration by physical barriers.


Investigating bacteria in diabetic wounds

To find better treatment options and improve the quality of life of diabetic individuals, understanding the bacterial species in wounds and their virulence potential is necessary. The study “Virulence Characteristics of Gram-positive Bacteria Isolated from Diabetic Foot Ulcers” in FEMS Microbes aims to unravel which microbes survive and cause infections in diabetic wounds.

For this, discarded debridement tissue from individuals with diabetic wounds was collected. Across all samples, hundreds of microbes from ~100 individuals were identified and isolated for future testing in the lab.

Isolating bacteria from debridement tissue from diabetic wounds
Isolating bacteria from debridement tissue. By Rebecca Keogh.

The most commonly identified species were Staphylococcus aureus, Enterococcus faecalis, Staphylococcus epidermidis and Streptococcus agalactiae. These results support previous 16S and metagenomic studies which also found numerous Gram-positive species residing in diabetic wound infections.

Most of the plated discarded tissue samples contained more than one species. Hence, it seems that different bacterial species may cooperate in diabetic wound infections to promote each other’s growth and survival.


Virulence characteristics of bacteria in diabetic wounds

To determine how these bacteria survive in diabetic wound environments, the study tested their abilities to adapt to antibiotic treatment and grow within biofilm communities.

Furthermore, the study focused on how these species cooperate in infection settings. Antibiotics are often the first strategy to treat wound infections. However, since many bacterial pathogens carry antibiotic resistances or tolerances, antibiotics may fail to kill entirely bacterial species. The study also showed high levels of resistance to antibiotics for many of the identified bacteria, including penicillin-resistant S. aureus and clindamycin-resistant S. agalactiae.

Focusing on the biofilm-forming abilities of the identified strains, S. aureus was found to be the most efficient biofilm-forming species. This species was also the most prevalent in chronic wound sites, and most frequently co-isolated with E. faecalis and S. agalactiae. Therefore, it is possible that by forming biofilms, S. aureus protects other microbes against antibiotic penetration.

To show this, the study tested whether these species cooperated in diabetic wounds. When S. aureus was present, E. faecalis and S. agalactiae survived better in wound infections than when either species grew by itself. This phenomenon could be mediated by biofilms formed by S. aureus. Mixed biofilms might protect all included species from attacks by antibiotics or the immune system.

This work successfully sheds light on bacterial species residing in diabetic wounds, giving a greater understanding of the virulence characteristics of isolates present in diabetic infection. It explores how biofilm formation and antibiotic resistance help pathogens survive and maintain polymicrobial infection in infection settings. Based on these results, better treatment options for affected people may be on the horizon to hopefully reduce future amputations and improve the quality of life of affected people.


About the author of this blog

Rebecca Keogh is a postdoctoral fellow at the University of Colorado Anschutz. She works in the labs of Drs. Kelly Doran and Alex Horswill where she studies bacterial infections in the diabetic wound environment. Her current research focuses on the bacterium Streptococcus agalactiae and its mechanisms of bacterial survival to immune cell inflammation. In addition to scientific research, Rebecca has a passion for mentorship and scientific outreach to the greater community.


About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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