β-Lactam Resistance Mechanisms of Methicillin-Resistant Staphylococcus aureus

In vitro and in vivo activity of amoxicillin and penicillin G alone or combined with a penicillinase inhibitor (clavulanate) were tested against five isogenic pairs of methicillin-resistant Staphylococcus aureus (MRSA) producing or not producing penicillinase. Loss of the penicillinase plasmid caused an eight times or greater reduction in the MICs of amoxicillin and penicillin G (from ⩾64 to 8 µg/ml), but not of the penicillinase-resistant drugs methicillin and cloxacillin (⩾64 µg/ml). This difference in antibacterial effectiveness correlated with a more than 10 times greater penicillin-binding protein 2a affinity of amoxicillin and penicillin G than of methicillin and a ⩾90% successful amoxicillin treatment of experimental endocarditis due to penicillinasenegative MRSA compared with cloxacillin, which was totally ineffective (P < .001). Amoxicillin was also effective against penicillinase-producing parent MRSA, provided it was combined with clavulanate. Penicillinase-sensitive β-lactam antibiotics plus penicillinase inhibitors might offer a rational alternative treatment for MRSA infection

Coxiella burnetii vascular graft infection

BACKGROUND: Coxiella burnetii, the causative agent of Q fever, may cause culture-negative vascular graft infections. Very few cases of C. burnetii infection of a vascular graft have been reported. All were diagnosed by serology. CASE PRESENTATION: We report the first case of Coxiella burnetii vascular graft infection diagnosed by broad-range PCR and discuss the diagnostic approaches and treatment strategies of chronic C. burnetii infection. CONCLUSION: C. burnetii should be considered as etiological agent in patients with a vascular graft and fever, abdominal pain, and laboratory signs of inflammation, with or without exposure history. Broad-range PCR should be performed on culture-negative surgical samples in patients with suspected infection of vascular graft