Relationship between temperature optima and secreted protease activities of three Pythium species and pathogenicity toward plant and animal hosts.

The in vitro physiological characteristics of three species of Pythium (oomycetes) that utilize different food sources were compared with their ecological activities: P. insidiosum is a pathogen of mammals (including humans), P. graminicola infects the roots of graminaceous hosts, and P. grandisporangium is an enigmatic water mold isolated from mangrove leaves and marine algae. P. insidiosum and P. graminicola showed peak growth rates at 37 degrees C before complete inhibition of growth at 40 degrees C; P. grandisporangium grew fastest at 22 degrees C. Differences between the invasive pressures exerted by the hyphae of these microorganisms were not considered significant in relation to the substrates colonized by these water molds. All three species showed substantial secreted protease activity, producing three or more serine proteases with weights ranging from 24-38 kDa. Fastest growth rates were supported when collagen was supplied as the sole carbon source, and none of the species were able to grow on purified plant cell wall polysaccharides. The growth and nutritional characteristics of P. graminicola and P. grandisporangium bear little obvious relationship to the ecological niches that they inhabit. This highlights the caution necessary in extrapolating from laboratory analyses to the natural environment, and points to the potential importance of ecological opportunity in determining the host range and food source of certain microorganisms.

Biomechanics of stipe elongation in the basidiomycete Coprinopsis cinerea.

Stipe elongation in fruit bodies of Coprinopsis cinerea (syn. Coprinus cinereus) was examined from a biomechanical perspective. Two strains were studied: the self-compatible Amut Bmut homokaryon that produces normal fruit bodies with relatively short stipes, and mutant B1918 that produces abnormally elongated stipes. Measurements of the pressure exerted by developing mushrooms were made using strain gauges, and these data were compared with measurements of the pressures exerted by vegetative hyphae of the same strains. The experiments demonstrate that AmutBmut hyphae elongating within stipe tissue push with the same pressure (approx. 0.5 atmosphere) as vegetative hyphae growing through their food sources. In purely biomechanical terms, the fruit body may therefore be viewed as a relatively uncomplicated sum of its parts. Analysis of the mutant strain B1918 demonstrated that hyperelongation of the stipe is not associated with any difference in the pressure exerted by the fruit body. The fault in the mechanism of stipe extension in B1918 may be reflected in the increased fluidity of the cell wall of vegetative hyphae of this strain, but further work is necessary to resolve this.

Biomechanical evidence for convergent evolution of the invasive growth process among fungi and oomycete water molds.

Diverse microorganisms traditionally called fungi are recognized as members of two kingdoms: mushroom-forming species and their relatives in the Fungi, and oomycete water molds in the Stramenopila. Phylogenetic analysis suggests that these kingdoms diverged early in the evolution of eukaryotes. The phylogenetic detachment of the fungi and oomycetes is reflected in radical differences in their biochemistry, cell structure, and development. In terms of their biological activities, however, they show great similarity, because both groups form colonies of filamentous hyphae that invade and decompose solid food sources. Here we present biomechanical evidence of the convergent evolution of the invasive growth process in these microorganisms. Using miniature strain gauges to measure the forces exerted by single hyphae, we show that the hyphae of species in both kingdoms exert up to 2 atmospheres of hydrostatic pressure as they extend at their tips. No other eukaryotes have adopted this process for meeting their nutritional needs.

Molecular epidemiology of oxacillin-resistant Staphylococcus aureus in Brooklyn, New York.

Although oxacillin-resistant Staphylococcus aureus (ORSA) are well-established pathogens in many hospitals, the impact of infection control measures on the clonal distribution of ORSA is poorly defined. A citywide surveillance study of Staphylococcus aureus in Brooklyn, New York revealed that 36% of isolates were ORSA. Molecular typing showed that one strain (Cluster A) accounted for more than half of the isolates and was present in all 15 hospitals. In one hospital, a distinct strain (Cluster B) accounted for 20% of ORSA isolates. Infection control measures in this hospital significantly decreased the percentage of clinical isolates that belonged to Cluster B, but did not have an effect on the strain endemic to the city (Cluster A). Regional infection control strategies may need to be developed to limit the spread of the ORSA clone endemic to this area.

Biomechanical interaction between hyphae of two Pythium species (Oomycota) and host tissues.

Forces exerted by hyphae of the phytopathogen Pythium graminicola and mammalian pathogen Pythium insidiosum were compared with the mechanical resistance of their hosts' tissues. Hyphal apices of both species exerted a mean force of 2 microN, corresponding to mean pressures of 0.19 microN microm(-2) (or MPa) for P. graminicola, and 0.14 microN microm(-2) for P. insidiosum. Experiments with glass microprobes showed that the epidermis of grass roots resisted penetration until the pressure applied at the probe tip reached 1-12 microN microm(-2). Previously published data show that mammalian skin offers even greater resistance (10-47 microN microm(-2)). Clearly, tissue strength exceeds the pressures exerted by hyphae of these pathogens, verifying that secreted enzymes must play a critical role in reducing the resistance of plant and animal tissues. It is presumed that hyphae are sufficiently powerful to bore through any obstacles remaining after enzyme action.

Mechanics of solid tissue invasion by the mammalian pathogen Pythium insidiosum.

The relative significance of mechanical penetration versus the action of substrate-degrading enzymes during solid tissue invasion has not been established for any fungal disease. Pythium insidiosum is an oomycete fungus (or stramenopile) that causes a rare, but potentially lethal infection in humans and other mammalian hosts. Experiments with miniature strain gauges showed that single hyphal apices of this pathogen exert forces of up to 6.9 microN, corresponding to maximum pressures of 0.3 microN microm(-2) or MPa. Samples of cutaneous and subcutaneous tissue from fresh human cadavers displayed a mean strength (resistance to needle puncture) of 24 microN microm(-2), and a mean pressure of 30 microN microm(-2) was necessary to penetrate skin strips from slaughtered horses. These experiments demonstrate that P. insidiosum does not exert sufficient pressure to penetrate undamaged skin by mechanics alone, but must effect a decisive reduction in tissue strength by proteinase secretion.

Comparison of automated ribotyping to pulsed-field gel electrophoresis for genetic fingerprinting of Streptococcus pneumoniae.

Fifty-two isolates of Streptococcus pneumoniae were characterized by pulsed-field gel electrophoresis (PFGE) and automated ribotyping by using HindIII and PvuII. HindIII ribotypes correlated well with PFGE. PvuII produced fewer bands and was less discriminatory. Automated ribotyping with HindIII is an accurate method for genetic fingerprinting of S. pneumoniae and can complement PFGE.

Current and future treatment of Lyme disease.

Lyme borreliosis, a tick-transmitted spirochetal disease, may begin with a characteristic expanding skin lesion at the site of the tick bite. Within several days to weeks, the infection can spread haematogenously to involve the heart, nervous system or the joints. After months to years, the spirochete may persist in these organs causing a chronic form of illness. All stages of this disease can be treatable with antimicrobial agents.

Laboratory testing of UV transmission through fabrics may underestimate protection.

Laboratory testing of the ultraviolet protection factor (UPF) provided by fabrics normally utilizes a collimated source of UV radiation and either a broadband sensor or spectroradiometer to detect the radiation, both unattenuated and after passing through the fabric sample held in a flat tensionless state. We report the results of an in vivo study of UV transmission through various T-shirts at several sites on the trunk and arms of a life-size mannequin irradiated with diffuse radiation and using UV sensitive polymer films as the sensor. We found a variation in UPF by a factor of two or more at different anatomical sites for a given T-shirt, with lower UPFs seen at sites where the fabric is stretched; and found that at every site and for each T-shirt this in vivo UPF was higher than the conventional in vitro UPF determined using collimated radiation.