Beyond MRSA: VISA and VRSA: what will ward off these pathogens in health care facilities?

Melittin, a honeybee venom‑derived antimicrobial peptide, may target methicillin‑resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is difficult to treat using available antibiotic agents. Honeybee venom has been widely used as an oriental treatment for several inflammatory diseases and bacterial infections. The venom contains predominantly biologically active compounds, however, the therapeutic effects of such materials when used to treat MRSA infections have not been investigated extensively. The present study evaluated bee venom and its principal active component, melittin, in terms of their antibacterial activities and in vivo protection against MRSA infections. In vitro, bee venom and melittin exhibited comparable levels of antibacterial activity, which was more marked against MRSA strains, compared with other Gram-positive bacteria. When MRSA-infected mice were treated with bee venom or melittin, only the latter animals were successfully rescued from MRSA- induced bacteraemia or exhibited recovery from MRSA-infected skin wounds. Together, the data of the present study demonstrated for the first time, to the best of our knowledge, that melittin may be used as a promising antimicrobial agent to enhance the healing of MRSA-induced wounds.

A battle for iron: host sequestration and Staphylococcus aureus acquisition

The use of iron as an enzymatic cofactor is pervasive in biological systems. Consequently most living organisms, including pathogenic bacteria, require iron to survive and replicate. To combat infection vertebrates have evolved sophisticated iron sequestration systems against which, pathogenic bacteria have concomitantly evolved equally elaborate iron acquisition mechanisms.

Can methicillin-resistant Staphylococcus aureus be found in an ambulance fleet?

OBJECTIVE

To perform an initial screening study of methicillin-resistant Staphylococcus aureus (MRSA) contamination in an ambulance fleet.

METHODS

This was a cross-sectional study of MRSA contamination in an ambulance fleet operating in the western United States in June 2006. Five specific areas within each of 21 ambulances (n = 105) were tested for MRSA contamination using dacron swabs moistened with a 0.85% sterile saline solution. These samples were then plated onto a screening media of mannitol salt agar containing 6.5% NaCl and 4 mcg/mL oxacillin.

RESULTS

Thirteen samples isolated from 10 of the 21 ambulances (47.6%) in the sample group tested positive for MRSA.

CONCLUSIONS

The results of this preliminary study suggest that ambulances operating in the emergency medical services (EMS) system may have a significant degree of MRSA contamination and may represent an important reservoir in the transmission of potentially serious infections to patients.

Intracellular metalloporphyrin metabolism in Staphylococcus aureus

The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human morbidity and mortality, and the ability of S. aureus to cause disease is absolutely dependent on the acquisition of iron from the host. The most abundant iron source to invading staphylococci is in the form of the porphyrin heme. S. aureus is capable of acquiring nutrient iron from heme and hemoproteins via two heme-acquisition systems, the iron-regulated surface determinant system (Isd) and the heme transport system (Hts). Heme acquisition through these systems is involved in staphylococcal pathogenesis suggesting that the intracellular fate of heme plays a significant role in the infectious process. The valuable heme molecule presents a paradox to invading bacteria because although heme is an abundant source of nutrient iron, the extreme reactivity of heme makes it toxic at high concentrations. Therefore, bacteria must regulate the levels of intracellular heme to avoid toxicity. Although the molecular mechanisms responsible for staphylococcal heme acquisition are beginning to emerge, the mechanisms by which S. aureus regulate intracellular heme homeostasis are largely unknown. In this review we describe three potential fates of host-derived heme acquired by S. aureus during infection: (i) degradation for use as a nutrient iron source, (ii) incorporation into bacterial heme-binding proteins for use as an enzyme cofactor, or (iii) efflux through a dedicated ABC-type transport system. We hypothesize that the ultimate fate of exogenously acquired heme in S. aureus is dependent upon the intracellular and extracellular availability of both iron and heme.