Table2 shows the relationship between aerobactin genotype and other metrics. For
ID: 178783 • Letter: T
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Table2 shows the relationship between aerobactin genotype and other metrics. For example: 11 of 13 (85%) of E.coli strains that did not have aerobactin genes were found in compromised patients, while 36 of 45 (80%) of E. coli strains that had aerobactin genes were found in these patients. Therefore, aeorbactin genes do not influence whether E. coli is a problem for compromised patients. On the other hand, of the 45 strains that had the genes, 12 of 12 (100%) that had plasmid-encoded genes were found in compromised patients, but only 24 of 33 (73%) that had chromosome-encoded genes were found in compromised patients. Therefore, plasmid-encoded aerobactin is associated with infections of compromised patients.
What does this table suggest about the locations (plasmid vs chromosomal) for antibiotic resistance, and the genes for virulence factors P fimbriae and hemolysin? Does this make sense? Why?
TABLE 2. Comparison of aerobactin genotype with other bacterial and host characteristics No. of strains positive for characteristic tin determinants in total DNA Location of aerobactin determinants Characteristic Plasmid Chromosome Absent Present P value P value (n 45) (n 12) (n 33) (n 13) 23 (51) 11 (92) Resistance to 21 antimicrobial agent 7 (54) NS 0.001 Antimicrobial-agent resistance score 4.5 0.0001 NS 34 (6) 28 (85) 0.004 P fimbriae NS 6 (50) 19 (42) 19 (58) 0.0004 Hemolysin" 0 (00 6 (46) NS 11 (85) 36 (80) 24 (3) Compromising medical or urological condition NS 12 (100) 0.09 Based on Southern blot analysis of total DNA with probe for aerobactin, Pfimbriae, or hemolysin. P values were calculated by using the chi-square statistic or Fisher's exact test for comparisons between the two groups, NS, Not significant. Total DNA positive but plasmid-DNA negative with aerobactin probe. Median number of antimicrobial agents (of 12 tested) to which the strains were resistant.Explanation / Answer
Aerobactin is a bacterial iron sequestration and transport system which enables E. coli to grow in iron- poor environments such as dilute urine. Iron is a vital trace element for bacterial growth, the functions of iron in the cells are to activate the electron transport systems and enzymes like ribonucleotide reductase, catalase, oxidases, superoxide dismutase. Due to this aerobactin is considered to be a virulence factor in various urinary tract infections.Considering the table, it shows that the plasmid located aerobactin ecoli has more antibiotic resistance (92%) as opposed to the chromosome mediated (36%). This shows that the plasmid located ones might also be having some factor to garnish anti microbial resistance as shown by the score also which is really high for the plasmid located aerobactin.
Next, P fimbrae and hemolysin factors are seen very less when the gene is on the plasmid as opposed to on the chromosome. When plasmid present, P fimbrae is seen only on the 50% strains and there are no strains showing hemolysin as opposed to 85% and 58% respectively strains showing presence of these factors on chromosome mediated genes.
Antimicrobial resistance is higher in compromised hosts because of the greater exposure of antimicrobials for treatment.We can conclude that urologically impaired hosts, characteristically lack P fimbrial and hemolysin determinants, and often carry a plasmid-encoded aerobactin system (possibly on multiple antimicrobial resistance plasmids), whereas B2 strains more commonly invade noncompromised hosts, express P fimbriae and hemolysin, carry chromosomal aerobactin determinants, and lack antimicrobial resistance. The connection between them is unclear so it is not making perfect sense as if the incidence of disease is more then more virulence factors should be there.
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