The microbiology of diabetic foot infections: a Ghanaian perspective

Diabetic foot ulcer (DFU), a major complication of both types 1 and 2 diabetes, develops in about 15–25% of people living with the disease. In Ghana, DFUs contribute to most hospital admissions (53%) among diabetics with high rates of amputation (33.3%) and death (8.8%). Diabetic foot ulcers are predisposed to infections from bacteria in the environment which normally colonise these wounds as multicellular communities called biofilms. Biofilms have been found to have increased resistance to antimicrobial agents probably due to the presence of an extracellular matrix that retards or prevents the entry of antimicrobial agents into the bacterial community, antibiotic resistance genes and/or the presence of persister cells that are unresponsive to antimicrobial agents.

The work presented here studied the role of 2 multidrug resistant DFU isolates, Klebsiella pneumoniae and Proteus mirabilis in maintaining the chronicity of diabetic foot ulcers. Using 3 in vitro biofilm models; the conventional microtitre plate and Minimum Biofilm Eradication Concentration (MBEC™) High-Throughput assays and the Quasi–Vivo® continuous flow system, K. pneumoniae and P. mirabilis were found to be positive for acyl–homoserine lactone production, biofilm and persister cell producers and could resist and/or tolerate antibiotics such as ceftazidime and levofloxacin up to 1280 times their minimum inhibitory concentration. K. pneumoniae and P. mirabilis were also found to express the interspecies AI–2 quorum sensing molecules which significantly increased biofilm formation and fold induction of bioluminescence in a luxS mutant V. harveyi reference strain.

Quorum sensing (QS) inhibition assays using baicalin hydrate, cinnamaldehyde and 2(5H)–furanone showed considerable inhibition of K. pneumoniae and P. mirabilis biofilm formation but failed to completely inhibit their growth. The combinatorial effects of antibiotics and QS inhibitors/antimicrobial peptides such as polymyxin B and polymyxin B nonapeptide determined as fractional inhibitory concentration (FIC) index suggests that, additive and synergistic effects produced by the combination of two antimicrobial agents have the potential to eradicate biofilms. Data from the FIC indices determined from the combination assays can provide the basis for the formulation of topical treatment for DFUs.