Five to ten female and the same number of infected, unfed male Hyalomma ticks have been used for infection of cattle. The results of the efficacy test depends on factors such us immunological characteristics of the T. Research studies (35) show that calves vaccinated with schizont vaccine may exhibit an apparently near total protection or show a low level parasitaemia, accompanied by mild fever and insignificant alteration of the remaining parameters from their prevaccination values following a potentially lethal homologous challenge. A lesser degree of protection has been exhibited when cattle vaccinated with schizont vaccine were challenged with tick-derived parasites from a geographically remote area. In contrast, in most of the trials the non vaccinated control calves have exhibited a high level of parasitaemia and pancytopenia accompanied by severe clinical manifestations. In the absence of specific medication, the majority of the control animals have succumbed to the infection (35). Controversial results about the length of immunity engendered by vaccination with the cell culture vaccine have been obtained. Periods of from more than 48 months (39) to less than 13 months (32) have been reported. Field observations have also been used for evaluation of the efficacy of anti-theilerial vaccines (34, 39). Susceptible indigenous cattle as well as high-grade exotic breeds were protected against clinical theileriosis and death in pastures on which nonvaccinated cattle succumbed to theileriosis. As completely attenuated schizont vaccine does not yield piroplasms, the presence of this theilerial stage in vaccinated cattle showing no clinical signs is considered to be the result of unapparent tick-induced infection. Frozen vaccine remains stable during the storage period, even for long periods, but some loss of viability occurs during the freezing and thawing processes. Viability should be tested under conditions as similar as possible to those obtained when the vaccine is used in the field. For this reason, vaccine should be thawed and the diluted suspension of schizont-infected cells should be left at ambient temperature for 60 minutes before performing the viability tests. A simple test for evaluating viability of the infected cells is nigrosin dye exclusion counting (40). Viability of the schizonts is also reflected by the plating efficiency of the schizont-infected cells (40), as only cells containing viable schizonts multiply in culture. For this purpose, the thawed, diluted vaccine is transferred from the bottle to a centrifuge tube. A sample for counting is taken and the suspension is centrifuged for 15 minutes at 600 g. Meanwhile, the total number of cells (live and dead) is determined in order to ascertain that the frozen vaccine had the necessary initial concentration of cells. After centrifugation, the supernatant is discarded and the cells are resuspended to the original volume using complete culture medium. The number of wells theoretically containing 1 cell each in which growth is observed is counted. Field centres for storage and supply of vaccine can be set up in theileriosis-enzootic areas. Application of the frozen vaccine to field cattle begins by donning the face shield and temperature-resistant gloves. The required numbers of vials are withdrawn with the forceps from the canister of the liquid nitrogen refrigerator. When withdrawing the vials, the canister should be kept as deep as possible in the neck of the refrigerator to avoid quick warming of the remaining vials. Each withdrawn vial should be checked in order to ascertain that liquid nitrogen has not leaked inside.
Characterisation of membrane surface proteins of Mycoplasma agalactiae during natural infection. Experimental vaccination of against Mycoplasma agalactiae using different inactivated vaccine. Post-mortem examination reveals fibrinous pleuropneumonia with massive lung hepatisation and pleurisy, accompanied by accumulation of straw-coloured pleural fluid. The disease has been shown recently to affect wild ruminants such as the wild goats (Capra aegagru), Nubian Ibex (Capra ibex Nubian) and Laristan Mouflon (Ovis orientalis laristanica) and Gerenuk (Litocranius walleri). Clinical disease and seropositivity have been reported in sheep in contact with affected goats, but the role of sheep as reservoirs of infection is unclear. Identification of the agent: Definitive diagnosis requires culture of the causative organism from lung tissue samples and/or pleural fluid taken at post-mortem. After cloning and purification, isolates can be identified by several biochemical, immunological and molecular tests. Recently polymerase chain reaction based tests have been described and shown to be specific, sensitive and can be applied directly to clinical material, such as lung and pleural fluid. Such tests are best used on a herd basis rather than for diagnosis in individual animals. A specific competitive enzyme-linked immunosorbent assay has been developed, but is not widely available. As with the other serological tests, it does not detect all reactors, but its specificity and suitability for large-scale testing make it an appropriate test for epidemiological investigations. Mccp has also been isolated from healthy sheep (21) and the role of sheep as a reservoir for the disease has to be considered. The disease affected wild goats (Capra aegagrus), Nubian Ibex (Capra ibex nubiana), Laristan mouflon (Ovis orientalis laristanica) and Gerenuk (Litocranius walleri) with significant morbidity and mortality in these species (2). It must be differentiated from other similar clinico-pathological syndromes such as: peste des petits ruminants, to which sheep are also susceptible; pasteurellosis, which can be differentiated on the basis of distribution of gross lung lesions; and what has been called `mastitis, arthritis, keratitis, pneumonia and septicaemia syndrome or more often as contagious agalactia syndrome (47). As the longer name implies, the pneumonia is accompanied by prominent lesions in other organs. The disease caused by Mccp is readily contagious and fatal to susceptible goats of all ages and both sexes, rarely affects sheep and does not affect cattle. It shows a branching filamentous morphology in vivo that can be observed by dark-field microscopy in exudates or tissue suspensions from lesions or pleural fluid. The other caprine mycoplasmas show a short filamentous or coccobacillary morphology. All mycoplasmas of the mycoides cluster can be assigned a precise phylogenetic position by using a multilocus sequence typing approach which may be used for identification purposes (30). During transport, samples should always be kept as cool as possible, as mycoplasma viability diminishes rapidly with increasing temperature. Tissue samples are best minced using scissors, and then shaken vigorously, or pulverised in medium 1 using 1 g of tissue to 9 ml of medium. The suspension is usually prepared with a mycoplasma medium, but if parallel bacteriological examination is to be carried out, a high quality bacteriological medium, such as nutrient broth, may be used to provide a suspension suitable for both forms of examination.
Symptomatic patients with stage 3 disease may require resection and immediate reconstruction with a reconstruction plate or an obturator. The potential for failure of the reconstruction plate because of the generalized effects of the bisphosphonate exposure needs to be recognized by the clinician and patient. Case reports with small sample sizes describe successful immediate reconstruction with vascularized bone. The extraction of symptomatic teeth within exposed, necrotic bone should be considered since it is unlikely that the extraction will exacerbate the established necrotic process. A thorough histologic analysis is indicated for all resected bone specimens (especially for patients with a history a malignant disease) since metastatic cancer has been reported in such specimens. Regardless of the disease stage, mobile segments of bony sequestrum should be removed without exposing uninvolved bone. These studies are responsible for many of the new data and information that was presented in this paper. The position paper is based on a review of the existing literature and the clinical observations of a Special Committee composed of oral and maxillofacial surgeons, oral pathologists, and oncologists experienced in the diagnosis, surgical and adjunctive treatment of diseases, injuries and defects involving both the functional and esthetic aspects of the hard and soft tissues of the oral and maxillofacial regions, epidemiologists, and basic researchers. The position paper is informational in nature and is not intended to set any standards of care. Primary Indication Osteoporosis Osteoporosis Osteoporosis Nitrogen Containing Yes Yes Yes Dose 10 mg/day 70 mg/week 5 mg/day 35 mg/week 2. Therefore further controlled, prospective studies will be required to more fully characterize the risk of jaw necrosis associated with these agents. Major P, Lortholary A, Hon J, et al: Zoledronic acid is superior to pamidronate in the treatment of hypercalcemia of malignancy: a pooled analysis of two randomized, controlled clinical trials. Fizazi K, Carducci M, Smith M, et al: Denosumab versus zoledronic acid for treatment of bone metastases in men with castration-resistant prostate cancer: a randomised, double-blind study. Landesberg R, Woo V, Cremers S, et al: Potential pathophysiological mechanisms in osteonecrosis of the jaw. Bamias A, Kastritis E, Bamia C, et al: Osteonecrosis of the jaw in cancer after treatment with bisphosphonates: incidence and risk factors. Bi Y, Gao Y, Ehirchiou D, et al: Bisphosphonates cause osteonecrosis of the jaw-like disease in mice. Mortensen M, Lawson W, Montazem A: Osteonecrosis of the jaw associated with bisphosphonate use: Presentation of seven cases and literature review. Mehrotra B, Ruggiero S: Bisphosphonate complications including osteonecrosis of the jaw. Wood J, Bonjean K, Ruetz S, et al: Novel antiangiogenic effects of the bisphosphonate compound zoledronic acid. Sinningen K, Tsourdi E, Rauner M, et al: Skeletal and extraskeletal actions of denosumab. Marx R: Oral and Intravenous Bisphosphonate Induced Osteonecrosis of the Jaws: History, etiology, prevention, and treatment. Ficarra G, Beninati F, Rubino I, et al: Osteonecrosis of the jaws in periodontal patients with a history of bisphosphonates treatment. Kang B, Cheong S, Chaichanasakul T, et al: Periapical disease and bisphosphonates induce osteonecrosis of the jaws in mice. Mawardi H, Treister N, Richardson P, et al: Sinus tracts-an early sign of bisphosphonate-associated osteonecrosis of the jaws? Lopez-Jornet P, Camacho-Alonso F, Martinez-Canovas A, et al: Perioperative antibiotic regimen in rats treated with pamidronate plus dexamethasone and subjected to dental extraction: a study of the changes in the jaws. Hansen T, Kunkel M, Weber A, et al: Osteonecrosis of the jaws in patients treated with bisphosphonates - histomorphologic analysis in comparison with infected osteoradionecrosis. Kos M, Junka A, Smutnicka D, et al: Pamidronate enhances bacterial adhesion to bone hydroxyapatite. Another puzzle in the pathology of bisphosphonate-related osteonecrosis of the jaw? Bezzi M, Hasmim M, Bieler G, et al: Zoledronate sensitizes endothelial cells to tumor necrosis factor-induced programmed cell death: evidence for the suppression of sustained activation of focal adhesion kinase and protein kinase B/Akt.
Kikuchi is a professor and chairman, pedodontics, Nippon Dental University; and Dr. Beierle is an associate professor, basic science, University of Southern California. Beierle J, Mallen E, Schaeffer D, Berson R: A cell-to-cell adhesion assay for oral bacteria. Berson R, Schaeffer D, Beierle J: the effect of fluoride preparations on oral microbial adherence in vitro. Treasure P: Effects of fluoride lithium and strontium on extracellular polysaccharide production by Streptococcus mutans and Actinomyces viscosus. Review the importance of bright-blood imaging for assessment of vascular structures in the body. The nail matrix, the nail bed, the proximal nail fold and the hyponychium compose the different units of the nail plate. The periungual zone consists in the proximal fold, the lateral folds and the distal fold. In psoriasis there is thickening of the nail bed, increasing vascularity, hyperechoic foci in the ventral plate with acoustic shadow and deformation of the nail plates. Each case has a audio discussion and a series of "pearls" or vignettes are also presented with each case. In each category between 20 and 50 cases are available and a set of 2 images with 4 possible answers are provided. For each case a 30-60 second audio is provided discussing the case and the possible answers. Head to toe, complete organ system case-based review highlighting the imaging and clinical findings, treatment options, and indications. Once spread is outside the defined regional nodes, the disease is upstaged to M-stage disease thereby affecting patient treatment options. To formulate an effective search strategy for evaluation of cross-sectional imaging studies, it is important to be aware of potential sites of regional nodal metastasis, and to be familiar with N-stage classification for pelvic tumors. Depict regional nodal spread for carcinomas of the vulva, vagina, cervix uteri, corpus uteri, fallopian tube, ovary, testis, penis, prostate, urethra, and bladder using a simplified illustrated reference. Correlate regional nodal spread with N-stage classification according to the 2012 Cancer Staging Atlas from the American Joint Committee on Cancer. Pictorial review of regional nodal spread with N-stage classification for carcinomas of the vulva, vagina, cervix uteri, corpus uteri, fallopian tube, ovary, testis, penis, prostate, urethra, and bladder. Melquiades, Rio de Janeiro, Brazil (Abstract Co-Author) Nothing to Disclose Rachel F. Provide practical algorithms and decision trees for the most common reporting systems. Discuss the available clinical evidence and applicability of each reporting system in daily practice. Algorithms and decision trees for each reporting system Table of comparison between each reposting system. Clinical evidence, knowledge gaps, challenges and future oportunities for each data system. The stringent criteria for malignancy are round shape and absence of echogenic hilum. Benign nodes have sharp margins and malignant nodes usually have blurred/irregular margins due to extracapsular spread. Necrosis, calcifications, focal cortical nodes, reticulation and matting are common indicators of malignancy. Benign lymph nodes have central or hilar vascularity while malignant lymph nodes have peripheral /capsular flow or mixed hilar and peripheral flow pattern. Benign nodes portray a single vascular pedicle in contrast to malignant nodes which show multiple vascular pedicles with chaotic flow. No single feature distinguishes benign from malignant ln but a constellation of ultrasonographic signs aid in their differentiation. Illustrate the sonographic features of benign and malignant lymph nodes including size, shape, echogenicity, margins, structural changes and Dopler criteria.
High concentrations of electrolyte are required to maintain the structural integrity of. The organisms are chemoorganotrophs which use amino acids and/or carbohydrates as principal sources of carbon, and which typically grow aerobically; metabolism is respiratory (oxidative). The cells are lophotrichously flagellated (or non-motile) frequently pleomorphic rods or filaments, or discs; they often contain gas vacuoles (which are plasmid-encoded in at least some strains), and they lyse in dilute solutions. Motile, typically rod-shaped cells which grow aerobically or (strains with a purple membrane) anaerobically in the light. Amino acids are used for carbon and energy, although growth may be stimulated by carbohydrates (without acid formation). Mainly discoid or cup-shaped cells which are (apparently) non-flagellated but which are sometimes capable of a rotatory movement. The organisms are much more resistant than are Halobacterium spp to hypotonic solutions. Halomonas A genus (incertae sedis) of aerobic, facultatively anaerobic, chemoorganotrophic, halotolerant, Gram-negative halonitrosoureas bacteria which occur. Cells: non-pigmented or yellow-pigmented, polarly or laterally flagellated rods, 0. Metabolism may be respiratory (oxidative), with O2 or nitrate (anaerobic respiration) as terminal electron acceptor, or fermentative; anaerobic growth, without nitrate, can occur with glucose but not with other carbohydrates. Carbon sources include a wide range of alcohols, amino acids, organic acids and sugars. On illumination, halorhodopsin undergoes cyclical changes in its absorption characteristics with a periodicity of ca. Halorhodopsin undergoes bleaching when illuminated in the presence of hydroxylamine. The causal agent is usually coxsackievirus A16, but A4, A5, A9, A10, B2 and B5 have also been implicated. The whole is then inverted, so that the drop hangs freely beneath the cover-glass, and can be examined under the microscope. Most species can ferment glucose, some can also ferment other sugars, and some. Species have been isolated from tree exudates, soil, insect larvae and frass, etc. The spores are operculate and characteristically bear filamentous extensions which arise from the outer spore coat and are typically coiled around the spore. A hapten may be artificially bound to a protein in order to increase the immunological specificity of that protein. Autocoupling haptens bind spontaneously to tissue carriers in vivo, thus becoming antigenic. Symptoms: yellowing and falling of leaves and blackening of inflorescences; unripe, internally blackened coconuts fall prematurely. A haustorium may be spherical, club-shaped or elongated (branched or unbranched) according to the species of fungus which forms it. Thus, termination of packaging is determined only by the length of the nucleic acid packaged, and not by a specific sequence in the nucleic acid. The heat-shock regulon is under the control of a positive transcriptional activator encoded by gene rpoH (previously called htpR).
Sweethearts (Clivers). Mebendazole.
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Medical records were reviewed to identify the first-listed diagnosis for the current hospitalization and to determine whether participants were hospitalized for any reason within one year of the current admission. Five participants reported a home address that could not be geocoded; however, the address listed in their medical records was different and could be assigned coordinates. For these 5 participants, coordinates were assigned according to the address in the medical record. Human and swine population densities and rural area classifications Topically integrated geographic encoding and referencing shapefiles from the 2010 United States Census [21] were used to identify the census block group of each home or work address, and to classify home addresses as being in rural areas; in urban clusters, which contain at least 2,500 people; or in urbanized areas, which contain 50,000 or more people [22]. Densities of total, farrowing, and non-farrowing permitted swine in each census block group (number of swine/square miles in the block group) were calculated using a publicly available database from the North Carolina Division of Water Quality, which lists the type and address of livestock facilities in North Carolina that hold non-discharge wastewater permits, as well the number of permitted animals at each. In addition, 2010 census data was used to assign human population densities to each block group (number of people/square miles in the block group). Block groups are subdivisions of census tracts; in North Carolina, they contain an average of 1,549 residents [21]. The data for each sample consisted of a dendogram, a virtual gel image (banding pattern), a graph of fluorescence corresponding to each banding pattern, and a similarity matrix. Isolates that did not match any samples in the library according to the above criteria were classified as non-matches. Quality of the assembly was determined by the N50 parameter as well as by mapping that reads back to the assembly [25]. Sequence similarity matches of genes were determined using thresholds of 100% nucleotide identity and 100% coverage of the query sequence length. Isolates in the clade nearest to this bifurcation point were used to root subsequent trees. Statistical analysis For a number of reasons, not all eligible patients were available to be interviewed- they were discharged from the hospital, unconscious, sleeping, or receiving medical treatments at the time of interviewer contact, for example. Therefore, after data collection was complete, some participants did not have a matching case or control. To avoid double loss of information in analysis, case and control matched sets were pooled; the gender and age matching case or control who was admitted to the hospital within the shortest amount of time of unmatched participants was selected for the pooled set. Using the same control for more than one case has been described as a valid approach that should not bias measures of association [30,31]. Any participant who worked > 0 hours per week within 2 weeks of their hospital admission was considered employed. Coding decisions were based on variable distributions and comparison of Akaike information criterion statistics. Except variables representing human and swine population density, all exposures were coded as binary terms. Variables representing densities of total, farrowing, and non-farrowing swine were categorical (0 swine/square-mile, referent vs. Zero was the median and mode of the distribution of total swine density and 149 was the 25th percentile of the distribution of observations with non-zero total swine density values. Because of small numbers within categories of non-farrowing and farrowing swine density, these variables were also categorized according to their own distributions (0 swine/squaremile vs. The cut-points 77 and 616 were the median of the distribution of non-zero values for farrowing and non-farrowing densities, respectively. All participants provided written informed consent and signed Health Information Portability and Accountability Act authorization forms. Results From July - December 2011, 164 cases and 190 controls were invited to participate, and 121 (73. Four cases and three controls who reported zip codes outside the eligible areas were subsequently excluded, leaving 117 cases and 119 controls. Table 1 Characteristics of methicillin resistant Staphylococcus aureus nasal carriers and matched controls hospitalized at Vidant Medical Center in eastern North Carolina, 2011 Characteristics Female Age, years 18-29 29 24. Participants lived in 152 block groups in eastern North Carolina or the most eastern part of central North Carolina.
Syndromes
When two dilutions of antigen are suitable, the more concentrated antigen suspension must be chosen in order to avoid prozone occurrence. It must not produce anticomplementary effects at the working strength for the test. A control serum that gives a minimum positive reaction should be tested in each set of tests to verify the sensitivity of test conditions. The absence of anti-complementary activity is checked for each serum in the first row. Therefore positive reactions should be investigated using suitable confirmatory strategies. The negative serum and the buffer control should give reactions that are always less than the positive/negative threshold (97). The threshold should be established in the test population using appropriate validation techniques (see Chapter 1. Monoclonal, polyclonal antiglobulin or protein A/G enzyme conjugates may be used depending on availability and performance requirements. The test method described below is an example of a test that has been internationally validated and has been used extensively in internationally sponsored, technical cooperation and research collaboration projects world-wide. The brownish phenol in the bottom layer is removed with a long cannula and large cell debris may be removed by filtration (using a Whatman No. The precipitate is stirred with 80 ml of distilled water for 18 hours and centrifuged at 10,000 g for 10 minutes. The supernatant solution is recovered by centrifugation as above and pooled with the previously recovered supernatant. After stirring for 10 minutes, the precipitate is removed by centrifugation and the translucent supernatant solution is dialised against distilled water (two changes of at least 4000 ml each) and then freeze dried. The control wells containing the strong positive serum are considered to be 100% positive and all data are calculated from these absorbance readings (between 1. The test method described below is an example of a test, which has been internationally validated and has been used extensively in internationally sponsored, technical cooperation and research collaboration projects world-wide. Plates are incubated for 30 minutes at ambient temperature with shaking for at least the initial 3 minutes. It is a homogeneous assay in which analytes are not separated and it is therefore very rapid. If a molecule is labelled with a fluorochrome, the time of rotation through an angle of 68. This antigen is added to diluted serum or whole blood and a measure of the antibody content is obtained in about 2 minutes (for serum) or 15 seconds (for blood) after the addition of antigen using a fluorescence polarisation analyser (62, 66). Control sera of strong positive, weak positive and negative, as well as S19 vaccinate serum, should be included.
Nonetheless, Fred Eggan (1954) argued that anthropological methods are more insightful if more attention is devoted to regional comparisons. The experiment isolated the effect of the influence of industrial livestock stakeholder policy implementation on two counties (Pike and Adams) compared with the two counties (LaSalle and Peoria) that were controlled by not having that influence. The controlled comparison method attempts to find regularities, common denominators, and also differences. The exploratory nature of the research has the built-in weakness that it will lack replicability. I learned that these four counties each have their own agencies, stakeholders, and culture so any comparison would only be suggestive to the larger theme concerning the corporate takeover of municipalities, counties, states, and the nation. Ethnographic Methods Participant observation, field notes, semi-structured interviews, and archival work were used to triangulate data. The strength of participant observation is that the researcher becomes the conduit for data collection and analysis through their experiences (Salkind 2012). Participant observation is suitable for collecting data on behaviors that happen naturally in their normal contexts. It also allows for a natural understanding of the four county comparison to gain 22 confidence about the meaning of data. It extends the validity of what we learn from watching and participating with people. In a comfortable situation where rapport is established, researchers are likely to obtain insider perspectives. I believe the perspectives that people confided in me concerning intimidation and fear tactics within the county were done so because of the rapport that was established. As a participant observer, the researcher becomes less of a curiosity and less of a distraction (Bernard 2006, 452). While I participated and observed community activist gatherings, public information sessions, and county board governmental events as part of my fieldwork, I was able to partially blend in. When conducting participant observation, anthropologists should be cautious about their presence to not disrupt normal activity. Anthropologists should never be secretive or intentionally deceptive about their research project or their role in it. The participation of people in my research was only on a voluntary basis (Mack et al. Knowledge, beliefs, attitudes, rituals, behavior, or other impressions recorded in field notes helped point out aspects of cultural diversity. Preliminary notes from the field generally form an outline for when the researcher is ready to critically analyze their findings. Field notes serve the crucial role of connecting researchers and their subjects in 23 making inquiries, and should not be a neglected part of cultural anthropological research (Wolfinger 2002). A semi-structured interview is open-ended, but follows a general script and covers a list of topics. I started with grand tour questions and moved on to political questions later (see Appendix C). These open-ended questions set no limits on the range or length of responses, instead giving participants the opportunity to explain their position, feelings, or experiences. It demonstrates that the researcher has control of the subject matter, and leaves both anthropologist and interviewee free to follow new leads. The semi-structured interview shows that the researcher is prepared and competent, but that they are not trying to exercise excessive control (Salkind 2012). In the field I felt that it would be inappropriate to contact county board officials until after I contacted citizens. Given that citizens felt so intimidated, I tried to the best of my abilities, to placate their trepidation in doing an interview. After conducting the majority of interviews with citizens, I then contacted county board members and other local officials via email or phone, although very few consented to an interview. The process of mapping has practical, investigative, and explanatory purposes in scientific and political frameworks (Rocheleau 2008).
Under optimal conditions, a bacterial cell infected with only one phage particle can produce hundreds of progeny in twenty minutes. Temperate phage A bacterium infected with a temperate phage can have the same fate as a bacterium infected with a virulent phage (lysis rapidly following infection). In this state (prophage), the expression of phage genes is repressed indefinitely by a protein (repressor) encoded within the phage genome. Lysogenic bacteria Lysogenic bacteria carry a prophage; the phenomenon is termed lysogeny, and the bacterial cell is said to be lysogenized. The acquisition by bacteria of properties due to the presence of a prophage is called lysogenic conversion. Conjugation Conjugation is the process by which bacteria transfer genes from one cell to another by cell-to-cell contact. Specifically, the process requires the presence on the donor cell of hairlike projections called sex pili that make contact with specific receptor sites on the surface of the recipient cell. Top view of agar plate Growth of uninfected bacteria creates an opaque lawn except at the location of the original infected cell, where there is a plaque (hole) containing millions of phage. There are two ways in which this can occur: generalized transduction and specialized transduction. In each case, the transducing phage is a temperate phage, so that the recipient cell survives the phage infection. Generalized transduction: In generalized transduction, a random 2 One strand of the plasmid is nicked. If this fragment becomes integrated into the recipient chromosome by recombination, the recipient cell will be stably transduced. The phage acquires the bacterial genes by a rare, abnormal excision from the bacterial chromosome. Transformation process: Studies of the transformation phe- 4 the single strand is cut after one complete circle is transferred. The remaining single strand invades the resident chromosome, seeking a region of sequence homology. If such a sequence is found, the invading strand replaces one of the two resident strands by a complex cut-and-paste process. Transformation probably has only a minor effect on gene flow in natural bacterial populations, but it is useful experimentally for introducing a cloned gene (for example, the human gene for insulin) into bacterial cells. Rare abnormal excision of prophage picks up the adjacent s+ gene (s+ = special bacterial gene). By one mechanism (A) any bacterial gene can be transferred; by a second mechanism (B) only certain genes can be transferred, namely those in close proximity to a prophage. Some mutations are unstable (that is, they frequently revert back to their original state), and others do not noticeably affect the organism. Mutations that come under study are usually those that are stable, and that cause some change in the characteristics of the organism. Transposon at this original site can jump to other sites, leaving behind a copy of itself. Antibiotic Resistance cba Left inverted repeat these two genes control the movement of the transposon. Transposons do not exist as segments free of the genome but only as segments within the genome. A nonreplicative transposon does not leave a copy of itself at the original location. If transposition inserts a transposon into a functional gene, the function of the gene is generally destroyed; this was the original basis by which transposons were discovered. The transposition process and the structure of a typical replicative transposon are shown in Figure 7. The transposase and resolvase genes code for enzymes involved in the transposition process, whereas the antibiotic resistance gene is a "passenger. These inverted repeats are the elements recognized by the transposase as it initiates the transposition. Mobile genetic elements are probably responsible for most of the genetic variability in natural bacterial populations, and for the spread of antibiotic resistance genes. Mechanisms of acquired antibiotic resistance Acquired antibiotic resistance requires a temporary or permanent gain or alteration of bacterial genetic information.
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