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 key11. Serra-Freire NM, Mello RP. Entomologia e Acarologia na Medicina Veterinária. 1st ed. Rio de Janeiro: LFLivros; 2006. 200p.(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.
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 Tn154622. Mlynarczyk A, Mlynarczyk G, Luczak M. Conjugative transfer of glycopeptide and macrolide resistant genes among Enterococci and from Enterococcus faecalis to Staphylococcus aureus. Med Dosw Mikrobiol. 2002;54(1):21-8.,33. McGuinness WA, Malachowa N, DeLeo FR. Vancomycin Resistance in Staphylococcus aureus. Yale J Biol Med. 2017;90(2):269-81.. 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.
1Serra-Freire NM, Mello RP. Entomologia e Acarologia na Medicina Veterinária. 1st ed. Rio de Janeiro: LFLivros; 2006. 200p.
2Mlynarczyk A, Mlynarczyk G, Luczak M. Conjugative transfer of glycopeptide and macrolide resistant genes among Enterococci and from Enterococcus faecalis to Staphylococcus aureus Med Dosw Mikrobiol. 2002;54(1):21-8.
3McGuinness WA, Malachowa N, DeLeo FR. Vancomycin Resistance in Staphylococcus aureus Yale J Biol Med. 2017;90(2):269-81.
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08 May 2018