Ultrastructure alterations of Staphylococcus aureus exposed to RP59500

Combining Quinupristin/Dalfopristin with Other Agents for Resistant Infections

OBJECTIVE

To review the resistance mechanisms of Enterococcus and Staphylococcus spp. and summarize quinupristin/dalfopristin's (QD's) effects on these resistant organisms when combined with other antibiotics via review of the literature and unpublished data.

DATA SOURCES

Data were identified by a PubMed search (1996—May 2003) using the search terms quinupristin/dalfopristin, synergy, in vitro, in vivo, vancomycin-resistant Enterococcus faecium (VREF), methicillin-resistant Staphylococcus aureus (MRSA), and individual antibiotic names. Bibliographies of the resultant PubMed searches were reviewed and included if applicable.

STUDY SELECTION AND DATA EXTRACTION

All studies reviewed were analyzed; specific drug data were included only if clinically pertinent. In vitro data from studies with adequate design were discussed, whereas all case reports and clinical trials were utilized.

DATA SYNTHESIS

In the treatment of VREF, available information seems conflicting, although some clear differences have become apparent. QD—ampicillin and QD—doxycycline combinations have demonstrated beneficial activity, usually displaying synergistic or additive effects even in macrolide-, lincosamine-, and streptogramin-resistant (MLSB) isolates. Vancomycin and chloramphenicol have shown some efficacy, but antagonistic or null results also have been observed. Regarding MRSA, results from many studies of QD combinations have been ambiguous. More common combinations displayed synergy or additive effects against MRSA, but only QD—rifampin showed consistent beneficial activity against MRSA and MLSB isolates. Most other combinations displayed antagonism when tested in vitro.

CONCLUSIONS

Data supporting the use of various QD—antibiotic combinations against VREF and MRSA are increasing, but further in vitro and in vivo data are needed to confirm the findings.

Efficacies of quinupristin-dalfopristin combined with vancomycin in vitro and in experimental endocarditis due to methicillin-resistant Staphylococcus aureus in relation to cross-resistance to macrolides, lincosamides, and streptogramin B- type antibiotics

A beneficial effect of the combination of quinupristin-dalfopristin and vancomycin was observed against two methicillin-resistant strains of Staphylococcus aureus harboring or not harboring the ermC gene, which codes for constitutive macrolide, lincosamide, and streptogramin B resistance. The beneficial effect was observed in time-kill studies, in which the drugs were used at inhibitory concentrations, and in a rabbit model of endocarditis, in which the combination was highly bactericidal and more active than monotherapies.

Quinupristin-dalfopristin combined with beta-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolide-lincosamide-streptogramin B antibiotics

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin active against most gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). In experimental endocarditis, however, Q-D was less efficacious against MRSA isolates constitutively resistant to macrolide-lincosamide-streptogram B (C-MLS(B)) than against MLS(B)-susceptible isolates. To circumvent this problem, we used the checkerboard method to screen drug combinations that would increase the efficacy of Q-D against such bacteria. beta-Lactams consistently exhibited additive or synergistic activity with Q-D. Glycopeptides, quinolones, and aminoglycosides were indifferent. No drugs were antagonistic. The positive Q-D-beta-lactam interaction was independent of MLS(B) or beta-lactam resistance. Moreover, addition of Q-D at one-fourth the MIC to flucloxacillin-containing plates decreased the flucloxacillin MIC for MRSA from 500 to 1,000 mg/liter to 30 to 60 mg/liter. Yet, Q-D-beta-lactam combinations were not synergistic in bactericidal tests. Rats with aortic vegetations were infected with two C-MLS(B)-resistant MRSA isolates (isolates AW7 and P8) and were treated for 3 or 5 days with drug dosages simulating the following treatments in humans: (i) Q-D at 7 mg/kg two times a day (b.i.d.) (a relatively low dosage purposely used to help detect positive drug interactions), (ii) cefamandole at constant levels in serum of 30 mg/liter, (iii) cefepime at 2 g b.i.d., (iv) Q-D combined with either cefamandole or cefepime. Any of the drugs used alone resulted in treatment failure. In contrast, Q-D plus either cefamandole or cefepime significantly decreased valve infection compared to the levels of infection for both untreated controls and those that received monotherapy (P < 0.05). Importantly, Q-D prevented the growth of highly beta-lactam-resistant MRSA in vivo. The mechanism of this beneficial drug interaction is unknown. However, Q-D-beta-lactam combinations might be useful for the treatment of complicated infections caused by multiple organisms, including MRSA.

Disorganization of cell division of methicillin-resistant Staphylococcus aureus by a component of tea (Camellia sinensis): a study by electron microscopy

A component of aqueous extracts of green tea (Camellia sinensis), known to reverse methicillin-resistance in staphylococci, causes extensive morphological changes in methicillin-resistant but not in methicillin-sensitive Staphylococcus aureus. Clumps of partly divided cocci, consisting of up to 14 individuals, with thickened internal but normal external cell walls were seen by electron microscopy in cultures of methicillin-resistant S. aureus grown in the presence of the active principle. The morphological changes observed were consistent with selective inhibition of penicillin-binding proteins.