Effects of Noise Bandwidth and Amplitude Modulation on Masking in Frog Auditory Midbrain Neurons

Natural auditory scenes such as frog choruses consist of multiple sound sources (i.e., individual vocalizing males) producing sounds that overlap extensively in time and spectrum, often in the presence of other biotic and abiotic background noise. Detection of a signal in such environments is challenging, but it is facilitated when the noise shares common amplitude modulations across a wide frequency range, due to a phenomenon called comodulation masking release (CMR). Here, we examined how properties of the background noise, such as its bandwidth and amplitude modulation, influence the detection threshold of a target sound (pulsed amplitude modulated tones) by single neurons in the frog auditory midbrain. We found that for both modulated and unmodulated masking noise, masking was generally stronger with increasing bandwidth, but it was weakened for the widest bandwidths. Masking was less for modulated noise than for unmodulated noise for all bandwidths. However, responses were heterogeneous, and only for a subpopulation of neurons the detection of the probe was facilitated when the bandwidth of the modulated masker was increased beyond a certain bandwidth – such neurons might contribute to CMR. We observed evidence that suggests that the dips in the noise amplitude are exploited by TS neurons, and observed strong responses to target signals occurring during such dips. However, the interactions between the probe and masker responses were nonlinear, and other mechanisms, e.g., selective suppression of the response to the noise, may also be involved in the masking release

Epidemiology of non-multiresistant methicillin-resistant Staphylococcus aureus infection in Queensland, Australia: Associations with indigenous populations and Panton-Valentine leukocidin

The purpose of this study was to determine the extent of the spread of epidemic clones of non-multiresistant methicillin-resistant Staphylococcus aureus (nmMRSA) and the epidemiology of resultant infections throughout the state of Queensland. We collected a sample of clinical isolates of nmMRSA from laboratories serving public hospitals and clinics throughout the state. Three hundred isolates were typed and tested for the presence of Panton-Valentine leukocidin (PVL) genes and demographic and clinical data were collected from associated cases. Fifteen percent of S. aureus isolates were nmMRSA and 69% of these belonged to PVL-positive clones, predominantly ST93 and CC30. Low numbers of USA300- and USA400-like isolates were also present. Infections due to PVL-positive strains were much less frequently acquired in hospital (3.4%) than those due to PVL-negative nmMRSA (23.7%). Thirty-seven percent of cases were in indigenous people who make up only 3.6% of the general population. The proportion of cases with PVL-positive, but non-negative isolates decreased progressively with age, suggesting that immunity to PVL might be an important determinant of protection. nmMRSA strains are present throughout Queensland and cause infections in both community and healthcare settings

Methicillin-susceptible, non-multiresistant methicillin-resistant and multiresistant methicillin-resistant Staphylococcus aureus infections: a clinical, epidemiological and microbiological comparative study

Abstract Non-multiresistant methicillin-resistant Staphylococcus\ud aureus (nmMRSA) infections are emerging worldwide\ud and are often community-associated. This prospective\ud case–cohort study compares features of 96 nmMRSA\ud clinical isolates with 96 matched multiresistant MRSA\ud (mMRSA) and 192 matched methicillin-susceptible S.\ud aureus (MSSA) clinical isolates. Seventy-four percent of\ud nmMRSA infections were healthcare-associated. nmMRSA\ud infections were much more likely to involve skin and soft\ud tissue (skin and soft tissue infections; SSTIs) and were\ud much less likely to be treated appropriately with antibiotics\ud than MSSA or mMRSA infections. Panton-Valentine\ud leukocidin (PVL) genes were detected in 55% of\ud nmMRSA, 16% of MSSA and 2% of mMRSA isolates.\ud Independent of the methicillin-resistance phenotype, 59%\ud of PVL-positive SSTIs presented as furunculosis compared\ud to only 10% of PVL-negative SSTIs. Patients with PVLpositive\ud infections were much younger than patients with\ud PVL-negative infections. The proportion of PVL-positive\ud infections peaked in the 10–29 years old age group,\ud followed by a linear decline