Automatic Microplot Localization Using UAV Images and a Hierarchical Image-Based Optimization Method.

To develop new crop varieties and monitor plant growth, health, and traits, automated analysis of aerial crop images is an attractive alternative to time-consuming manual inspection. To perform per-microplot phenotypic analysis, localizing and detecting individual microplots in an orthomosaic image of a field are major steps. Our algorithm uses an automatic initialization of the known field layout over the orthomosaic images in roughly the right position. Since the orthomosaic images are stitched from a large number of smaller images, there can be distortion causing microplot rows not to be entirely straight and the automatic initialization to not correctly position every microplot. To overcome this, we have developed a three-level hierarchical optimization method. First, the initial bounding box position is optimized using an objective function that maximizes the level of vegetation inside the area. Then, columns of microplots are repositioned, constrained by their expected spacing. Finally, the position of microplots is adjusted individually using an objective function that simultaneously maximizes the area of the microplot overlapping vegetation, minimizes spacing variance between microplots, and maximizes each microplot's alignment relative to other microplots in the same row and column. The orthomosaics used in this study were obtained from multiple dates of canola and wheat breeding trials. The algorithm was able to detect 99.7% of microplots for canola and 99% for wheat. The automatically segmented microplots were compared to ground truth segmentations, resulting in an average DSC of 91.2% and 89.6% across all microplots and orthomosaics in the canola and wheat datasets.

Allelic variation of the streptokinase gene in beta-hemolytic streptococci group C and G isolates of human origin.

Genetic diversity of the streptokinase gene (sk) from 36 strains of S. equisimilis and 54 strains of group G streptococci was examined. The strains were isolated from patients with various streptococcal disease manifestations and healthy carriers. The region of the gene that corresponds to amino acid residues 174-244, was PCR amplified. The amplified product was subjected to MluI, PvuII, DraI and DdeI digestion. Based on the restriction enzyme digestion patterns nine sk alleles were recognized. There was no correlation between the various sk gene alleles and streptococcal disease manifestations. Three of the nine sk gene alleles, sk4, sk7, and sk8, were detected earlier among group A streptococci. The other six alleles were unique to S. equisimilis and group G streptococci. The most common alleles were sk5, found in 21/90 (23%) and sk10 detected in 43/90 (47%) of the strains. Alleles sk1 and sk2, the most frequent among group A streptococci, were not found among the strains in the present investigation. Thus, it appears that the sk gene has been evolving in line with other species distinguishing features of the streptococci.

Streptokinase activity among group A streptococci in relation to streptokinase genotype, plasminogen binding, and disease manifestations.

Certain genotypic variants of streptokinase (ska) of beta-hemolytic streptococci group A have been associated with acute post-streptococcal glomerulonephritis (APSGN). In our earlier studies on strains isolated from Ethiopian children with various streptococcal disease manifestation, we reported an even distribution of streptokinase genotypes with no association to disease patterns. Considering the possibility that strains could differ in their ability to secrete the protein, levels of streptokinase activity in culture supernatants of these strains were determined by a plasminogen activation assay using a synthetic tripeptide, H-D-valyl-leucyl-lysin-p-nitroaniline, as a substrate. Of the 53 streptococcal group A strains, ten (19%), which belonged to genotype ska4 and ska8, did not activate human plasminogen. These strains did not activate bovine, sheep, horse, rabbit or porcine plasminogens either. They represented at least five M protein and non-typeable serotypes, and were characterized by high human plasminogen binding activity. Six of the 53 strains (11%) harbouring genotype ska3 and ska7 showed low levels of human plasminogen activation. Strains of ska1 and ska2, 37/53, activated human plasminogen at a higher level (p < 0.005). Levels of plasminogen activation were not significantly different among the ska1 and ska2 strains associated with various streptococcal disease manifestations. Antibody levels against streptokinase were higher (p < 0.05) in convalescent sera from acute rheumatic fever and APSGN patients in comparison with sera from other patient categories and healthy controls. Streptokinase genotype and in vitro streptokinase production do not correlate directly to streptococcal disease manifestation, indicating a probable significance of additional streptococcal and/or host factors in the initiation of APSGN.

Streptokinase gene polymorphism in group A streptococci isolated from Ethiopian children with various disease manifestations.

Certain variants of streptokinase from group A streptococci have been associated with acute post-streptococcal glomerulonephritis (APSGN). The streptokinase gene (ska) has previously been grouped into nine different polymorphic genotypes of which ska1, ska2, ska6, and ska9 were identified in group A streptococci associated with clinical and experimental APSGN. A total of 53 group A streptococci isolated from Ethiopian children: five from acute rheumatic fever, 18 from APSGN, ten each from tonsillitis, impetigo and healthy carriers, were analyzed for ska gene polymorphism using polymerase chain reaction (PCR) and restriction enzyme analysis. The frequency of the nephritis-associated streptokinase genotypes was 83% among the APSGN isolates and 74% in the non-ASPGN isolates. ska2 was the most commonly found genotype with a frequency of 64% among all isolates, 66% among the APSGN isolates, and 63% among the non-APSGN isolates. ska1 was identified in 13% among all isolates and 17% among the APSGN isolates. Seventeen non-APSGN isolates from Scandinavian countries were studied for comparison and all carried either ska1 or ska2. The other nephritis-associated ska6 and ska9 were not detected among the 53 Ethiopian isolates. ska1 was exclusively associated with serum opacity reaction (SOR) producers. ska2 was evenly distributed among SOR-positive and SOR-negative isolates. The other genotypes were detected only among SOR-negative strains. The findings of the present study showed an even distribution of the nephritis-associated streptokinase gene among group A streptococcal isolates with no correlation to disease pattern. Thus additional factors must also be operative in the pathogenesis of APSGN.

Distribution of presumptive pathogenicity factors among beta-hemolytic streptococci isolated from Ethiopia.

Beta-hemolytic streptococci are known to bind several mammalian proteins, which are presumed to be important in pathogenicity. The distribution of such binding structures was examined for mouse albumin, human serum IgA, human IgG, human fibrinogen, and human plasminogen. A total of 218 group A beta-hemolytic streptococci (GAS) were studied: 5 isolates from children with acute rheumatic fever (ARF), 18 from acute post-streptococcal glomerulonephritis (APSGN), 57 from tonsillitis, 52 from skin infections, and 86 from healthy carriers. Sixty-eight Streptococcus equisimilis and 20 group G streptococci were also included. Most of the S. equisimilis (60/68) and group G (14/20) were obtained from apparently healthy carriers. The results were evaluated with respect to T type, serum opacity reaction (SOR), site of isolation, and disease type. No direct correlation was detected between the protein-binding structures studied. There was no apparent correlation between any particular protein-binding structure and specific T type. Albumin-binding and IgA-binding activities were inversely correlated among skin and nephritis GAS isolates. A strong correlation was demonstrated between IgA-binding activity and SOR production, while albumin-binding activity correlated with SOR-negative strains. Albumin-binding levels in isolates from ARF, APSGN and tonsillitis were significantly higher than in isolates from healthy carriers (P < 0.001). A higher albumin-binding capacity was shown in skin isolates from APSGN than in isolates from impetigo (P < 0.001).

A one-year study of streptococcal infections and their complications among Ethiopian children.

Post-streptococcal complications are known to be common among Ethiopian children. Little is known, however, about the epidemiology of beta-haemolytic streptococci in Ethiopia. A total of 816 children were studied during a one-year period: 24 cases of acute rheumatic fever (ARF), 44 chronic rheumatic heart disease (CRHD), 44 acute post streptococcal glomerulonephritis (APSGN), 143 tonsillitis, 55 impetigo, and 506 were apparently healthy children. Both ARF and APSGN occurred throughout the year with two peaks during the rainy and cold seasons. The female:male ratio among ARF patients was 1.4:1 and 1:1.9 among APSGN. The monthly carrier rate of beta-haemolytic streptococci group A varied from 7.5-39%, average being 17%. T type 2 was the most frequent serotype. Marked seasonal fluctuations were noted in the distribution of serogroups among apparently healthy children. Beta-haemolytic streptococci group A dominated during the hot and humid months of February-May. Strains were susceptible to commonly used antibiotics, except for tetracycline.

Receptors for human plasminogen on the biological response modifier OK-432.

The biological response modifier OK-432, constituting cell wall fragments from a group A Streptococcus strain and used in anticancer therapy trials, was tested for its ability to interact with different plasma proteins. The uptake of 125I-labelled protein was measured using a panel of six different plasma proteins all known to react with receptors on a majority of streptococcal strains. Of the proteins tested, plasminogen demonstrated the most substantial uptake, with uptake values ranging from 70 to 79%. A slight interaction with fibrinogen was also detected whereas no significant interaction was found with either human immunoglobulin (Ig)A, IgG, serum albumin, or mouse albumin. The results with plasminogen suggest the possibility of a new explanation of the antitumor activity described for OK-432.

Nasal carrier rates and antibiotic resistance of Staphylococcus aureus isolates from hospital and non-hospital populations, Addis Ababa.

Surgical staff of five different hospitals and university biology students were screened for nasal carriage of Staphylococcus aureus: 32.4% of the surgical staff and 21.6% of the students were carriers. The rate for the hospital staff was significantly higher (chi 2 = 9.2, P less than 0.01). The carrier rates among the surgical staff varied between 59.1% for surgeons and 22.7% for other surgical staff. 195 S. aureus strains were isolated: 109 from surgical staff and 86 from students. All were tested for their resistance to antibiotics. Resistance to penicillin was 86.2% and 74.4%, respectively, for hospital and non-hospital isolates. Resistance to erythromycin, gentamicin, kanamycin or co-trimoxazole was not detected among the non-hospital isolates. All isolates were sensitive to vancomycin, cephalothin and clindamycin. Over 96% and 88% of hospital and non-hospital isolates, respectively, were resistant to at least one antibiotic. About 45% of the hospital isolates and 2.3% of the non-hospital isolates showed multiple resistance. The rate of multiple resistance among the hospital staff isolates was considered high and indicative of still higher rates among clinical isolates. Further studies are suggested in order to take appropriate measures against bacterial resistance to antibiotics.