A 63-year-old man with uncontrolled insulin-dependent diabetes mellitus was admitted with fever, mental confusion, signs of peripheral artery disease, and deep wounds filled with myiasis larvae and emitting a fetid odor (Figures A, B). Eight larvae of Cochliomyia hominivorax (Coquerel, 1858), which feed on living tissues, were isolated from the lesion and identified based on a taxonomic key1(Figures C, D). Biopsy samples confirmed osteomyelitis (Figures E, F). Bone culture detected vancomycin-resistant strains of Pseudomonas aeruginosa, Enterococcus gallinarum, and Enterococcus faecalis; an erythromycin-resistant (MIC >8 µg/mL) and vancomycin-susceptible (MIC >2 µg/mL) Staphylococcus aureus strain was also detected (Figures G, H, I, J). Previously, lesion cultures have only detected methicillin-resistant S. aureus strains with MICs of 0.5-1µg/mL. Despite the use of piperacillin/tazobactam and carbapenem regimens, ischemia was irreversible; Syme’s amputation was performed successfully.
FIGURES (A, B): Diabetic foot with multiple infected wounds showing exposed part of the extensor digitorum longus tendon, typical erysipelas (wine-colored) with epidermis peeling, and necrotic areas. (C): A C. hominivorax larva in the third instar of development with anterior respiratory spiracles and dark tracheal trunks. (D): A C. hominivorax larva showing characteristic thorn-like spines. (E, F): Bone phalange biopsy exhibiting typical bone architecture disorganization, with dead bone areas (sequestrum), chronic inflammatory infiltrate, fibrosis, and suppurative exudates in the medullary region; hematoxylin-eosinstaining, 40x magnification. (G): Enterococci culture on sheep blood-containing agar. (H): Gram-positive diplococci, 40x magnification. (I): S. aureus culture on agar-containing petri plate. (J): Gram positive S. aureus, 40x magnification.
S. aureus and P. aeruginosa are virulent bacteria that are frequently resistant to common antibiotics. However, vancomycin-, tigecycline-, and linezolid-resistant S. aureus strains are rare. Various studies have identified a link between vancomycin- (MIC ≥16 µg/mL) and erythromycin-resistant S. aureus and enterococci, mediated by the acquisition of the transposon Tn15462,3. Antibiotic abuse is most likely responsible for increased resistance; this article highlights the potential of gene exchange between enterococci and S. aureus in clinical scenarios during their co-existence in chronic wounds for long time periods.
