Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus outbreak among healthcare workers in a long-term care facility.

BACKGROUND: We investigated an outbreak of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections that occurred among healthcare workers (HCWs) but not among residents of a long-term care facility (LTCF). METHODS: Cases of S. aureus infection were sought by reviewing the medical records of residents and HCWs. In order to identify risk factors for the development of an S. aureus infection, an unmatched case-control study was conducted. Cases were all HCWs with a clinically compatible S. aureus infection; controls were HCWs with no history of a clinically compatible S. aureus infection. Cases and controls were interviewed and anterior nasal swabs were collected. RESULTS: Over a period of 14 months, a total of eight cases were identified among practice nurses, giving an attack rate of 10% for this category of profession. All isolates were identified as MRSA Panton-Valentine leukocidin (PVL)-producing SCCmec type IV. By multivariate analysis, working in a specific zone and being a practice nurse were found to be statistically significant risk factors for infection. CONCLUSIONS: The current outbreak indicates that HCWs may serve as vehicles for the entry of PVL-positive MRSA strains from the community into LTCFs, and that deficient hygiene practices and unrecognized carriage may facilitate spread. Given the increasing prevalence of PVL-positive MRSA infections worldwide, guidelines for the eradication of PVL-positive MRSA carriage within closed communities should be established and efforts to obtain cultures from compatible infections should be made.

The mechanism of metals precipitation by biologically generated alkalinity in biofilm reactors.

Microbial strains, characterized by increased tolerance and ability to grow in metal bearing wastewaters as well as by effective metal sequestering capability by both active (bioaccumulative) and passive (biosorptive) processes, were tested as inoculum for metal laden wastewater treatment systems. Their capacity to grow in metal bearing wastewater, using an easily available and inexpensive carbon source such as acetate, was studied in batch experiments. Two principal conclusions were drawn: (1). Growth was observed for all the strains examined suggesting that the strains can be acclimated to metals bearing wastewaters. (2). Solution pH increased from neutral to alkaline values during growth (pH(initial)=7, pH(final)=10). The later was observed systematically for all strains. Metal precipitation, due to the metabolically generated alkalinity is expected as a result.Supporting evidence for this hypothesis was provided during the operation of two pilot moving bed sand filters treating two different metal bearing wastewaters. Acetate was used as carbon source to support the growth and maintenance of microbial biomass on the sand grains of the filters. The characteristics of the sludge produced from the operation of the pilot plants were subsequently studied in the laboratory. Both sludges were significantly loaded with large amounts of metals.A mechanism of metal precipitation induced by the metabolically generated alkalinity, when acetate is used as carbon source, could be proposed as the main process responsible for the metals sequestering inside the moving bed sandfilter reactor.

Mechanism of aluminum interference on uranium biosorption by Rhizopus arrhizus.

Uranium competitive uptake experiments by Rhizopus arrhizus were carried out at three different solution pH levels and in the presence of different concentrations of competing aluminum ions in order to examine the competing ion effect. The coion effect became more pronounced as the coion concentration in solution and pH level increased. A preliminary examination of the effect of aluminum on the rate of uranium uptake was also completed. Results showed that the presence of aluminum does not interfere with the kinetics of uranium uptake by R. arrhizus. Electron microscopic and energy dispersive X-ray analyses were also performed on samples of the biomass. The combination of spectral data and the information from the equilibrium studies and the kinetic studies suggested that aluminum interferes with the uranium biosorptive uptake capacity of R. arrhizus by the precipitation of a metastable amorphous hydroxy polymeric precipitate through a mechanism we refer to as steric competition.