Genotypic and phenotypic variations in methicillin-resistant Staphylococcus aureus isolates from outpatient, inpatient and nursing homes.

PURPOSE: The epidemiological shift in MRSA distribution from healthcare-related facilities to the general population is distressing and requires continuous monitoring to manage and control the rate of incidences. METHOD: The retrospective relationship between genetic and phenotypic variability of methicillin-resistant Staphylococcus aureus (MRSA) isolates was determined in respect to the specimen source, patient location, sex and age. A total of 521 MRSA isolates were classified based on SCCmec, mec, agr, pvl and spa genetic markers using three different multiplex PCRs. RESULTS: Based on the genetic variability, the isolates were divided into 97 profiles, of which 59% belonged to only two profiles (P17 and P33). P17 was the predominate profile, harbouring SCCmecIVa, ccr2, mecB, agr1, spa413 and pvl markers. P17 was more prevalent among the younger population (average 33.9 years) from outpatient (77%) locations and wound (88%) sources. The second largest profile was P33, harbouring SCCmecII, ccr2+ccr3, mecA, agr2, spa413 and no PVL. P33 was more prevalent in the older population (average 70.7 years) and more common in females (62%) than males (38%). With respect to antibiotic resistance, P33 exhibited a high rate of resistance to penicillins, cephalosporins, fluoroquinolones and macrolides, and P17 had a lower resistance to fluoroquinolones. CONCLUSION: This report contributes to the existing understanding of evolutionary epidemiology of antibiotic resistance in MRSA. The diversity of MRSA isolates and unique environmental preferences for each profile highlights the importance of epidemiological knowledge of MRSA distribution to determine the best treatment for patients in both community and hospital settings.

Patient age as a factor of antibiotic resistance in methicillin-resistant Staphylococcus aureus.

PURPOSE: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the leading causes of nosocomial infections. A thorough understanding of the epidemiology and distribution of MRSA allows the development of better preventive measures and helps to control or reduce the rate of infection among the general population. METHODOLOGY: A retrospective survey was performed on 511 cases of MRSA infections from inpatient, outpatient and nursing home populations over a 12-month period. To study the relationships between two continuous quantitative variables (patient age vs resistance percentage), a simple linear regression was calculated for each antibiotic to predict the antibiotic resistance percentage with respect to patient age.Results/Key findings. The pattern of antibiotic resistance with respect to the age of patients depended on the antibiotic mode of action. Antibiotics that target DNA synthesis (i.e. fluoroquinolones) display a direct correlation with the age of patients, with higher rates of resistance among the older population, while antibiotics that target ribosomal functions (i.e. aminoglycosides) or cell wall synthesis (i.e. cephalosporin) do not display an age-dependent pattern and have a consistent degree of resistance across all age classes. CONCLUSION: Antibiotics that target DNA synthesis result in a progressively higher number of resistant isolates among the older population. The results emphasize the importance of patient age on antibiotic selection as a preventive measure to reduce the rate of resistant infections in each susceptible population. This pattern suggests that physicians should take into consideration patient age as another factor in determining the best antibiotic regiment with the aim of curtailing the emergence of newer resistant phenotypes in the future.

Epidemiology and susceptibilities of methicillin-resistant Staphylococcus aureus in Northeastern Ohio.

A retrospective survey was performed on all staphylococcal infections diagnosed by the Ashtabula County Medical Center (Ashtabula, OH) during 2006 and 2007. Of the 1,612 Staphylococcus aureus isolates evaluated for their antibiotic resistances, 947 were methicillin-resistant S aureus (MRSA). In 2007, MRSA infections reached 589 cases per 100,000 inhabitants, a 77% increase compared with 2006. The increase in MRSA infections was noticeable among youth (6-25 years old), middle-aged people (45-50 years old), and elderly people (86-90 years old). MRSA infections increased among inpatients by 58%, among outpatients by 43%, and among nursing home residents by 183%. More than 66% of MRSA infections were found among healthy people in the community with no apparent risk factors. More than 88.7% of the infections belong to only 9 profiles of antibiotic resistance indiscriminately distributed among inpatients, outpatients, and nursing home residents. This report sheds further light on the rapid spread of MRSA across Northeastern Ohio, stressing the need for better education in preventive measures and infection control at the level of community and health care settings.

N-methyl-D-aspartate receptor antagonists have variable affect in 3-nitropropionic acid toxicity.

There is accumulating evidence that excitotoxicity and oxidative stress resulting from excessive activation of glutamate (N-methyl-D-aspartate) NMDA receptors are major participants in striatal degeneration associated with 3-nitropropionic acid (3NP) administration. Although excitotoxic and oxidative mechanisms are implicated in 3NP toxicity, there are conflicting reports as to whether NMDA receptor antagonists attenuate or exacerbate the 3NP-induced neurodegeneration. In the present study, we investigated the involvement of NMDA receptors in striatal degeneration, protein oxidation and motor impairment following systemic 3NP administration. We examined whether NMDA receptor antagonists, memantine and ifenprodil, influence the neurotoxicity of 3NP. The development of striatal lesion and protein oxidation following 3NP administration is delayed by memantine but not affected by ifenprodil. However, in behavioral experiments, memantine failed to improve and ifenprodil exacerbated the motor deficits associated with 3NP toxicity. Together, these findings suggest caution in the application of NMDA receptor antagonists as a neuroprotective agent in neurodegenerative disorders associated with metabolic impairment.

Mitochondrial imaging in dorsal root ganglion neurons following the application of inducible adenoviral vector expressing two fluorescent proteins.

Mitochondrial morphology and dynamics are known to vary considerably depending on the cell type and organism studied. The objective of this study was to assess the potential application of adenoviral-fluorescent protein constructs for long-term tracking of mitochondria in neurons. An adenoviral vector containing two fluorescent proteins, the enhanced green fluorescent protein (eGFP) targeted to the cytoplasm to highlight the neuronal processes, and the red fluorescent protein (RFP) directed to mitochondria under the control of an inducible promoter, facilitated an efficient and accurate method to study mitochondrial dynamics in long-term studies. Dorsal root ganglion neurons from rat embryos were cultured and infected. The infected neurons exhibited green fluorescence after 24h, while 16 h following induction with doxycycline, red fluorescence protein began to localize within mitochondria. The red fluorescent protein was transported into mitochondria at the cell body followed by distribution within processes. As the neurons aged, the expression of red fluorescent protein was confined to cytoplasmic vacuoles and not mitochondria. Further analysis suggested that the cytoplasmic vacuoles were likely of lysosomal origin. Taken together, the current study presents novel strategies to study the life history of cellular organelles such as mitochondria in long-term studies.

Influence of cytosolic and mitochondrial Ca2+, ATP, mitochondrial membrane potential, and calpain activity on the mechanism of neuron death induced by 3-nitropropionic acid.

3-Nitropropionic acid (3NP), an irreversible inhibitor of succinate dehydrogenase, induces both rapid necrotic and slow apoptotic death in rat hippocampal neurons. Low levels of extracellular glutamate (10 microM) shift the 3NP-induced cell death mechanism to necrosis, while NMDA receptor blockade results in predominantly apoptotic death. In this study, we examined the 3NP-induced alterations in free cytosolic and mitochondrial calcium levels, ATP levels, mitochondrial membrane potential, and calpain and caspase activity, under conditions resulting in the activation of apoptotic and necrotic pathways. In the presence of 10 microM glutamate, 3NP administration resulted in a massive elevation in [Ca(2+)](c) and [Ca(2+)](m), decreased ATP, rapid mitochondrial membrane depolarization, and a rapid activation of calpain but not caspase activity. In the presence of the NMDA receptor antagonist MK-801, 3NP did not induce a significant elevation of [Ca(2+)](c) within the 24h time period examined, nor increase [Ca(2+)](m) within 1h. ATP was maintained at control levels during the first hour of treatment, but declined 64% by 16h. Calpain and caspase activity were first evident at 24h following 3NP administration. 3NP treatment alone resulted in a more rapid decline in ATP, more rapid calpain activation (within 8h), and elevated [Ca(2+)](m) as compared to the results obtained with added MK-801. Together, the results demonstrate that 3NP-induced necrotic neuron death is associated with a massive calcium influx through NMDA receptors, resulting in mitochondrial depolarization and calpain activation; while 3NP-induced apoptotic neuron death is not associated with significant elevations in [Ca(2+)](c), nor with early changes in [Ca(2+)](m), mitochondrial membrane potential, ATP levels, or calpain activity.

Calpain activates caspase-3 during UV-induced neuronal death but only calpain is necessary for death.

While caspases have been strongly implicated in delayed neuronal death in a variety of experimental paradigms, other proteases such as calpain can also contribute to neuronal death. To evaluate the relative roles of caspase and calpain, we used a model system wherein UV treatment induced moderate or severe delayed cortical neuronal death, as quantified by propidium iodide and calcein AM. UV treatment led to increases in both caspase and calpain activation. Calpain inhibitor III (MDL-28170) reduced caspase activation, suggesting that caspase activation was mediated by calpain. Calpain contributed to neuronal death, as indicated by strong neuroprotection provided by calpain inhibitor III, calpeptin, or Ca2+-free medium. In contrast, caspase inhibitors were not neuroprotective. These results suggest that UV neurotoxicity is mediated by a loss of Ca2+ homeostasis which leads to a calpain-dependent, caspase-independent cell death. That calpain, but not caspase, may mediate death in instances involving the activation of both proteases may have relevance to other neuronal death models.