High Resistance Potential Research Articles

Strategies to control antibiotic resistance.

Antibiotic resistance is becoming a worldwide concern. Antibiotic resistance may be caused by sporadic mutations, which are not important unless spread clonally. Clonal resistance may disseminate a highly resistant clone to widespread geographic areas. The most effective interventions to limit the clonal spread of resistant organisms are effective infection control measures. Hospital antibiotic formulary restriction is the only control measure with proven effectiveness to control resistance related to antibiotic use. Hospital formularies should eliminate or restrict antibiotics with a high-resistance potential (eg, ceftazidime, ciprofloxacin, and imipenem), and should be replaced with equivalent antibiotics with a low-resistance potential (eg, cefe-pime, levofloxacin, and meropenem). Such low-resistance-potential antibiotics can either prevent or eliminate resistance problems associated with Klebsiella pneumoniae, Enterobacter species, or Pseudomonas aeruginosa. High-resistance-potential antibiotics, particularly ciprofloxacin and ceftazidime, also may indirectly increase the prevalence of highly resistant organisms (eg, methicillin-resistant Staphylococcus aureus [MRSA], vancomycin-resistant enterococci [VRE]). Vancomycin use should be restricted, not because it increases enterococcal resistance per se, but because it selects out naturally resistant enterococcal strains (eg, Enterococcus faecium that are vancomycin resistant). Linezolid does not increase the prevalence of VRE. Clinicians in the outpatient setting should also preferentially use oral antibiotics with a low-resistance potential (eg, clindamycin, metronidazole, doxycycline, minocycline, fluoroquinolones except ciprofloxacin, linezolid, and oral cephalosporins) in preference to their high-resistance-potential counterparts. For antibiotic resistance control interventions to be effective, they must be applied simultaneously to all antibiotics with activity against the specific resistance pathogen at the hospital formulary level. Multiple antibiotic substitutions are usually necessary to eradicate resistance problems caused by a particular pathogen. Multiple drugs of the same spectrum and low-resistance potential are necessary to eliminate resistance problems; single antibiotic substitutions are not effective.

Pseudomonas aeruginosa: resistance and therapy.

Pseudomonas aeruginosa resistance to antimicrobials is an important therapeutic consideration. Antibiotic resistance to P. aeruginosa may be chromosomally or plasmid mediated. Resistance to P. aeruginosa may also be affected by changes in the cellular membrane or intracellular environment. P. aeruginosa is primarily a nosocomial organism that most commonly colonizes respiratory secretions and urine. The selection of an antipseudomonal antibiotic depends on its inherent in vitro activity and its resistance potential. Anti-P. aeruginosa antibiotics with a high-resistance potential include gentamicin, tobramycin, ciprofloxacin, ceftazidime, and imipenem. Anti-P. aeruginosa antibiotics with a low-resistance potential include amikacin, piperacillin, cefoperazone, cefepime, meropenem, and polymyxin B.

NOSOCOMIAL PNEUMONIA: Diagnostic and Therapeutic Considerations

Many patients with presumed nosocomial pneumonia probably have infiltrates on the chest radiograph, fever, and leukocytosis resulting from noninfectious causes. Because of the high mortality and morbidity associated with nosocomial pneumonias, however, most clinicians treat such patients with a 2-week empiric trial of antibiotics. Before therapy is initiated, the clinician should rule out other causes of pulmonary infiltrates, fever, and leukocytosis that mimic a nosocomial pneumonia (e.g., pre-existing interstitial lung disease, primary or metastatic lung carcinomas, pulmonary emboli, pulmonary drug reactions, pulmonary hemorrhage, collagen vascular disease affecting the lungs, or congestive heart failure). If these disorders can be eliminated from diagnostic consideration, a 2-week trial of empiric monotherapy is indicated. The clinician should treat cases of presumed nosocomial pneumonia as if P. aeruginosa were the pathogen. Although P. aeruginosa is not the most common cause of nosocomial pneumonia, it is the most virulent pulmonary pathogen associated with nosocomial pneumonia. Coverage directed against P. aeruginosa is effective against all other aerobic gram-negative bacillary pathogens causing hospital-acquired pneumonia. The clinician should select an antibiotic for empiric monotherapy that is highly effective against P. aeruginosa, has a good side-effect profile, has a low resistance potential, and is relatively inexpensive in terms of its cost to the institution. The preferred agents for empiric monotherapy for nosocomial pneumonia are cefepime, meropenem, and piperacillin. Single organisms are responsible for nosocomial pneumonia, not multiple pathogens. S. aureus rarely, if ever, causes nosocomial pneumonia but is mentioned frequently in studies based on cultures of respiratory tract secretions. S. aureus, unless accompanied by a necrotizing pneumonia with rapid cavitation within 72 hours, in the sputum indicates colonization rather than infection and should not be addressed therapeutically. Antibiotics associated with a high resistance potential should not be used as monotherapy or included in combination therapy regimens (i.e., ceftazidime, ciprofloxacin, imipenem, or gentamicin). Combination therapy is more expensive than monotherapy and is indicated only when P. aeruginosa is extremely likely, based on its characteristic clinical presentation, or is proved by tissue biopsy. Therapy should not be based on respiratory secretion cultures regardless of technique. Optimal combination regimens include cefepime or meropenem plus levofloxacin or piperacillin or aztreonam or amikacin. Nosocomial pneumonias usually are treated for 14 days. Lack of radiographic or clinical response to appropriate empiric nosocomial pneumonia monotherapy after 14 days suggests an alternate diagnosis. In these patients, a tissue biopsy specimen should be obtained to determine the cause of the persistence of pulmonary infiltrates unresponsive to appropriate antimicrobial therapy.

ANTIBIOTIC RESISTANCE

Widespread resistance problems exist today in a global sense because of the incorporation of antibiotics with a high resistance potential into animal feeds and because of the uncontrolled use of antibiotics with a high resistance potential in the clinical setting. The only proven method of controlling nonoutbreak resistance problems in hospitals is to limit the hospital formulary to antibiotics with little or no resistance potential. The control of multiresistant organisms in outbreaks occurring in hospitals is best contained using appropriate infection control containment measures. Physicians treating infections in the community, with all other factors being equal, should preferentially select antibiotics with a low resistance potential. The titles and headings of much of the resistance literature are misleading. Articles should not contain fluoroquinolone resistant in the title when ciprofloxacin-resistant organisms are described. Many articles concerning penicillin-resistant pneumococci are entitled fluoroquinolone-resistant S. pneumoniae. These articles describe ciprofloxacin-resistant S. pneumoniae and not resistance to other fluoroquinolones. The same error is perpetuated in describing third-generation cephalosporins and carbapenems. Virtually all of the resistance problems associated with third-generation cephalosporins and carbapenems are due to ceftazidime or imipenem. More precise titling in the literature would remind physicians that antibiotic resistance is related to a specific agent and not class phenomena.

Antibiotic Resistance: A Historical Perspective

Antibiotic resistance is an increasing problem worldwide. Much of the antibiotic resistance occurs among community-acquired and nosocomial pulmonary pathogens. Antibiotic resistance may be classified as relative or absolute, which has important therapeutic implications. Considerable misunderstanding exists with regard to the factors that are responsible for antibiotic resistance. Misuse and overuse of antibiotics should be avoided; however, high volume of antibiotic use alone does not result in resistance. Antimicrobial resistance is agent specific and not related to antibiotic class. The antibiotics associated with a high resistance potential include ampicillin, cefamandole, ceftazidime, imipenem, ciprofloxacin, and vancomycin. The use of these antibiotics should be restricted to prevent generalized resistance problems. The substitution on the formulary of ;;vacuum cleaner'' antibiotics, along with effective infection control measures, can eliminate resistance problems in institutions. The key to controlling antibiotic resistance is to selectively use antibiotics with a low resistance potential and restrict those with a high resistance potential.

Hydrophilic Polymer Amendment in Field Soil to Improve Establishment of Perennial Wildflowers at Transplanting

Perennial wildflowers, once established, are a low-maintenance alternative in a flowerbed. However, water stress and poor root development in field soil can be detrimental to young plants at the time of transplanting. A fully expanded hydrogel, HydroSource, was incorporated to replace 0% (control), 7.5%, 15% (recommended rate), and 30% of the volume of a clayey field soil to determine its effect on plant water status. Addition of hydrogel reduced water stress in Asclepias incarnata and Gaillardia grandiflora plants. Plants growing in hydrogel amended soil had: 1) significantly lower stomatal resistance (P < 0.01); and 2) significantly higher leaf water potential (P < 0.01). Gaillardia grandiflora control plants showed considerable wilting (reflected in high stomatal resistance and low water potential readings) on the 3rd day of the drought period while those with 15% and 30% hydrogel were turgid even on the 5th day. Hydrogel-amended soil appeared less compacted, and root growth in Asclepias incarnata increased with the increasing rate of hydrogel added to the soil.

Antibiotic resistance.

Antibiotic resistance is an increasing problem in many parts of the world. Antibiotic resistance has been associated with the use of some antibiotics but not with others. Due to the overuse of antibiotics with a high resistance potential, there has been an increase of resistance with certain bacteria, e.g., Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pneumoniae. This article discusses the antibiotics associated with a high resistance potential and those that are safe to use with a low resistance potential. Strategies for minimizing antibiotic resistance are discussed.

Variation in water potential components among half-sib families of shortleaf pine (Pinusechinata) in response to soil drought

To assess family differences in response to drought, various water potential components of seedlings from six half-sib families of shortleaf pine (Pinusechinata Mill.) were compared under control (well-watered) and drought conditions. Drought stress resulted in significant changes in water relations parameters of the seedlings between treatments and among families. Although both Montgomery (103) and Pope (322) families had a superior capacity to adjust osmotically to both treatments, Montgomery (103) family exhibited greater potential to adapt to droughty environments through having the lowest values of osmotic potential both at maximum turgor and at the turgor loss point and having the highest values of (i) mean volume of osmostic water at the turgor loss point per volume of symplasmic water, (ii) symplasmic water volume per total shoot water volume, (iii) maximum bulk elastic modules, and (iv) turgor potential. Families Polk (115) and Scott (202) showed intermediate responses to drought. Both Scott (219) and Yell (342) families showed the lowest ability for osmotic adjustment to both treatments, but Yell (342) family revealed even lower drought resistance responses. Results from this study may provide the means of screening families that have high drought resistance potential during the field establishment period.

Temperaturresistenz inneralpiner Trockenrasen

Heat and frost resistance of all organs of the steppe grasses Stipa capillata and Stipa eriocaulis , of a C 4 grass, Bothriochloa ischaemum , and of Carex humilis from semiarid grassland in a central alpine valley (the Vinschgau) were studied throughout the course of the year. The heat resistance increases from the lowest level during the growing phase in spring to a summer maximum, and remains fairly high also in autumn and winter. During periods of heat, in which the daily maxima of air temperature are between 30 and 35°C, the heat resistance (based on the temperature causing 50 % damage after 30 min) of Stipa spp. and of Carex humilis attains values of 60 (leaves) to 65°C (shoot bases). The C 4 grass Bothriochloa ischaemum has an even higher hardiness and can survive temperatures approaching 70°C. Despite this extraordinary resistance, the organs near to soil surface are protected by an only narrow margin of safety with respect to highest temperatures in the habitat: 60-65°c at soil surface are frequently measured, as well as extreme values of 70°C and above. The leaves heat up to 40-45°C under strong irradiation; when fully hardened, they are unlikely to suffer damage. However, for C 3 grasses, leaf temperatures of this magnitude fall within the range of heat inhibition of photosynthesis. The potential frost resistance , determined after cold conditioning at −5 and −10°C, is sufficient to enable Carex humilis and Stipa species to survive frost of −30 to −35°C without severe injury, whereby Stipa capillata is slightly hardier than Stipa eriocaulis . The shoot apex, the crown and the leaf sheats are the most resistant, the roots the most sensitive parts of the plants (see Table 2). The apical meristem of Carex humilis acquires unlimited frost tolerance and cannot even be killed by immersion in liquid nitrogen. The crown tissues, rhizomes and roots of Bothriochloa ischaemum also attain a remarkable degree of frost resistence (down to −25°C), the pronounced cold sensitivity typical for C 4 grasses being restricted to the permanently freezing-sensitive leaves, so that this species can only develop and retain its leaves during the frost-free period of the year. The low degree of cold stress to which the graminoids in the Vinschgau are exposed (annual minimum air temperature usually not below −10 to −16°C) induces only moderate hardening. Calculation of frost stress response indices (see page 128) reveals that under such mild winter conditions the hardiness capacity of Carex humilis is only exploited to about 1/3, that of Stipa spp: to 1/2, and that of Bothriochloa ischaemum to 2/3. Despite this, the Stipa population growing at the margins of its distribution range has not lost the high resistance potential that is a necessary attribute for surviving the severe winters of the Eurasian continental steppe regions. This means that in the central alpine valleys an ecotype differentiation with respect to frost resistance has apparently not taken place.

The Damascus Cow—An Unexplored Source of Dairy Germ Plasma

Summary Damascus cattle are an excellent indigenous breed, showing a high potential for milk production, longevity, heat tolerance, and disease resistance. All of these qualities make it highly desirable as a milk producer in areas with hot, arid, or subtropical climates. In spite of many desirable qualities some important defects have crept in and are being accentuated, namely: 1.Short lactation period in some strains. 2.Disproportionate body depth to height. 3.High-set sacro-eoccygeal articulation with the pelvis. 4.Narrow pelvic outlet. 5.Fine bone. None of these defects are characteristic of the breed and a large number of animals are free from such defects. Future development of breed will depend upon a planned and controlled breeding and selection program.