Amoxicillin-tolerant Pasteurella multocida strain isolated from chronic dermohypodermitis after suboptimal exposure to amoxicillin is not associated with reduced growth rate

Pasteurella multocida is rarely observed in human chronic infections. A Pasteurella multocida strain was isolated from a skin biopsy of chronic dermohypodermitis in a 21-year-old woman without an immunocompromised state. As this strain was viable one month after a cat scratch despite treatment by amoxicillin-clavulanic acid, we compared this strain's growth rate, amoxicillin Minimal Inhibitory and Bactericidal Concentrations (MIC and MBC), resistance to serum and ability to activate neutrophil granulocytes with those of control strains isolated during acute infections in humans without previous antibiotics exposure. This particular strain was not more resistant to serum and did not induce a lower phagocytic activity than control strains. It did not grow more slowly than control strains even after suboptimal exposure to amoxicillin. This particular strain was tolerant to amoxicillin but tolerance did not appear sufficient alone for the induction of a chronic infection in a host without an immunocompromised state.

[Skin pigmentation induced by meropenem and levofloxacin]

BACKGROUND

Various cutaneous side-effects, including, exanthema, pruritus, urticaria and Lyell or Stevens-Johnson syndrome, have been reported with meropenem (carbapenem), a rarely-prescribed antibiotic. Levofloxacin (fluoroquinolone), a more frequently prescribed antibiotic, has similar cutaneous side-effects, as well as photosensitivity. We report a case of cutaneous hyperpigmentation induced by meropenem and levofloxacin.

PATIENTS AND METHODS

A 67-year-old male was treated with meropenem (1g×4 daily), levofloxacin (500mg twice daily) and amikacin (500mg daily) for 2 weeks, followed by meropenem, levofloxacin and rifampicin (600mg twice daily) for 4 weeks for osteitis of the fifth metatarsal. Three weeks after initiation of antibiotic therapy, dark hyperpigmentation appeared on the lower limbs, predominantly on the anterior aspects of the legs. Histology revealed dark, perivascular and interstitial deposits throughout the dermis, which stained with both Fontana-Masson and Perls stains. Infrared microspectroscopy revealed meropenem in the dermis of involved skin. After withdrawal of the antibiotics, the pigmentation subsided slowly.

DISCUSSION

Similar cases of cutaneous hyperpigmentation have been reported after use of minocycline. In these cases, histological examination also showed iron and/or melanin deposits within the dermis, but the nature of the causative pigment remains unclear. In our case, infrared spectroscopy enabled us to identify meropenem in the dermis. Two cases of cutaneous hyperpigmentation have been reported following use of levofloxacin, and the results of histological examination were similar. This is the first case of cutaneous hyperpigmentation induced by meropenem.