Diabetic foot ulcers with myiasis: a potential route for resistance gene dissemination for enterococci?

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 Tn1546^2,3. 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.

REFERENCES

• ¹ Serra-Freire NM, Mello RP. Entomologia e Acarologia na Medicina Veterinária. 1st ed. Rio de Janeiro: LFLivros; 2006. 200p.
• ² 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.
• ³ McGuinness WA, Malachowa N, DeLeo FR. Vancomycin Resistance in Staphylococcus aureus Yale J Biol Med. 2017;90(2):269-81.

Publication Dates

• Publication in this collection
  Nov-Dec 2018

History

• Received
  13 Nov 2017
• Accepted
  08 May 2018