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V23-15
[#permalink]
07 Jan 2024, 15:38
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50% (01:22) correct
Listeria monocytogenes (Lm) is a foodborne bacterial zoonotic pathogen that can cause listeriosis, a severe infection with a high case fatality rate in immunocompromised individuals. Molecular studies have shown the clonal population structure of Lm and the worldwide distribution of clonal complex 1 (Lm-CC1, initially called epidemic clone ECI), a cosmopolitan clonal group defined by multilocus sequence typing (MLST), which was first isolated from an Italian soldier with meningitis during the first world war (WWI). Notably, Lm-CC1 is the most prevalent clinical clonal complex in several countries and actually corresponds to 20% of all of Lm clinical isolates deposited at the National Center for Biotechnology Information (NCBI) . Lm-CC1 belongs to Lm major lineage I and evolved from a subgroup of serotype 4b ancestry.
While there is no proven interhuman horizontal transmission of listeriosis, it was only in 1983 that the foodborne transmission of human listeriosis was formally established. Since then, Lm-CC1 has been reported in different food matrices, including dairy products, which can be heavily contaminated and constitute a major source of human listeriosis. Previous studies have also demonstrated the hypervirulence of Lm-CC1, and its higher efficiency in gut colonization and fecal shedding, compared to hypovirulent Lm clones. Moreover, increasing evidence shows that bovines, which are frequent Lm asymptomatic carriers and contribute to Lm enrichment in soils, are the main source of disease and constitute a reservoir for Lm-CC1. In addition to Lm subclinical infections that may contaminate milk, the long-term persistence of Lm in cattle manure–amended soils also poses serious risks of transmission to fresh produce.
Understanding the global evolution of Lm-CC1, which is now spread over all continents, as well as its emergence and dissemination across different spatial levels is critical to understand Lm population dynamics and to develop better control strategies, particularly in countries with aging and/or immunosuppressed populations who are most at risk for severe infection. However, the complex movement of livestock and food products associated with asymptomatic intestinal colonization complicates traditional epidemiological investigations aiming at deciphering Lm epidemiology by linking isolates in space and time. Here, we took a population biology approach to fill this knowledge gap and conducted the largest genomic Lm-CC1 study to date, combining genomic and evolutionary approaches to decipher its evolutionary history and pattern of emergence and spread.
Which of the following most accurately describes the function of the first paragraph?
A. To provide a historical background on the discovery of Lm-CC1 during World War I.
B. To introduce the reader to the molecular characteristics of Lm-CC1.
C. To highlight the global prevalence of Lm-CC1 and its significance in clinical cases.
D. To discuss the lineage and ancestry of Lm-CC1.
E. To explain the methods of multilocus sequence typing (MLST).
While there is no proven interhuman horizontal transmission of listeriosis, it was only in 1983 that the foodborne transmission of human listeriosis was formally established. Since then, Lm-CC1 has been reported in different food matrices, including dairy products, which can be heavily contaminated and constitute a major source of human listeriosis. Previous studies have also demonstrated the hypervirulence of Lm-CC1, and its higher efficiency in gut colonization and fecal shedding, compared to hypovirulent Lm clones. Moreover, increasing evidence shows that bovines, which are frequent Lm asymptomatic carriers and contribute to Lm enrichment in soils, are the main source of disease and constitute a reservoir for Lm-CC1. In addition to Lm subclinical infections that may contaminate milk, the long-term persistence of Lm in cattle manure–amended soils also poses serious risks of transmission to fresh produce.
Understanding the global evolution of Lm-CC1, which is now spread over all continents, as well as its emergence and dissemination across different spatial levels is critical to understand Lm population dynamics and to develop better control strategies, particularly in countries with aging and/or immunosuppressed populations who are most at risk for severe infection. However, the complex movement of livestock and food products associated with asymptomatic intestinal colonization complicates traditional epidemiological investigations aiming at deciphering Lm epidemiology by linking isolates in space and time. Here, we took a population biology approach to fill this knowledge gap and conducted the largest genomic Lm-CC1 study to date, combining genomic and evolutionary approaches to decipher its evolutionary history and pattern of emergence and spread.
Which of the following most accurately describes the function of the first paragraph?
A. To provide a historical background on the discovery of Lm-CC1 during World War I.
B. To introduce the reader to the molecular characteristics of Lm-CC1.
C. To highlight the global prevalence of Lm-CC1 and its significance in clinical cases.
D. To discuss the lineage and ancestry of Lm-CC1.
E. To explain the methods of multilocus sequence typing (MLST).
Re V23-15
[#permalink]
07 Jan 2024, 15:38
Expert Reply
Official Solution:
Listeria monocytogenes (Lm) is a foodborne bacterial zoonotic pathogen that can cause listeriosis, a severe infection with a high case fatality rate in immunocompromised individuals. Molecular studies have shown the clonal population structure of Lm and the worldwide distribution of clonal complex 1 (Lm-CC1, initially called epidemic clone ECI), a cosmopolitan clonal group defined by multilocus sequence typing (MLST), which was first isolated from an Italian soldier with meningitis during the first world war (WWI). Notably, Lm-CC1 is the most prevalent clinical clonal complex in several countries and actually corresponds to 20% of all of Lm clinical isolates deposited at the National Center for Biotechnology Information (NCBI) . Lm-CC1 belongs to Lm major lineage I and evolved from a subgroup of serotype 4b ancestry.
While there is no proven interhuman horizontal transmission of listeriosis, it was only in 1983 that the foodborne transmission of human listeriosis was formally established. Since then, Lm-CC1 has been reported in different food matrices, including dairy products, which can be heavily contaminated and constitute a major source of human listeriosis. Previous studies have also demonstrated the hypervirulence of Lm-CC1, and its higher efficiency in gut colonization and fecal shedding, compared to hypovirulent Lm clones. Moreover, increasing evidence shows that bovines, which are frequent Lm asymptomatic carriers and contribute to Lm enrichment in soils, are the main source of disease and constitute a reservoir for Lm-CC1. In addition to Lm subclinical infections that may contaminate milk, the long-term persistence of Lm in cattle manure–amended soils also poses serious risks of transmission to fresh produce.
Understanding the global evolution of Lm-CC1, which is now spread over all continents, as well as its emergence and dissemination across different spatial levels is critical to understand Lm population dynamics and to develop better control strategies, particularly in countries with aging and/or immunosuppressed populations who are most at risk for severe infection. However, the complex movement of livestock and food products associated with asymptomatic intestinal colonization complicates traditional epidemiological investigations aiming at deciphering Lm epidemiology by linking isolates in space and time. Here, we took a population biology approach to fill this knowledge gap and conducted the largest genomic Lm-CC1 study to date, combining genomic and evolutionary approaches to decipher its evolutionary history and pattern of emergence and spread.
Which of the following most accurately describes the function of the first paragraph?
A. To provide a historical background on the discovery of Lm-CC1 during World War I.
B. To introduce the reader to the molecular characteristics of Lm-CC1.
C. To highlight the global prevalence of Lm-CC1 and its significance in clinical cases.
D. To discuss the lineage and ancestry of Lm-CC1.
E. To explain the methods of multilocus sequence typing (MLST).
The first paragraph focuses on the prevalence of Lm-CC1, noting its widespread distribution and its status as the most prevalent clinical clonal complex in several countries. This aligns with choice C, which accurately captures the paragraph's emphasis on the global prevalence and clinical significance of Lm-CC1.
Choice B can be eliminated by 2 indicators/aspects:
1. Choice B is too narrow in scope. While B mentions molecular characteristics in passing, It does not just introduces the reader to the molecular characteristics of Lm-CC1 (it goes way beyond it before and after that segment)
2. Choice B also does not really do a good job of introducing the molecular characteristics of Lm-CC1. The first paragraph text lacks any details of molecular characteristics... I would have assumed that would entail some long scientific text.
Can we rework choice B to make it work?
Yes, we can. Choice B would be more spot on if it said "Introduce reader to the Lm-CC1" - I think that would be a better description than with the phrase "molecular characteristics". Because it does not do that.
Tip:
You should always check the first and the last sentences of a paragraph on the GMAT. They will always have more importance than the middle sentences and that can give you a feel for where the paragraph is leaning when you have a few choices that look appealing and you can't make up your mind.
Answer: C
Listeria monocytogenes (Lm) is a foodborne bacterial zoonotic pathogen that can cause listeriosis, a severe infection with a high case fatality rate in immunocompromised individuals. Molecular studies have shown the clonal population structure of Lm and the worldwide distribution of clonal complex 1 (Lm-CC1, initially called epidemic clone ECI), a cosmopolitan clonal group defined by multilocus sequence typing (MLST), which was first isolated from an Italian soldier with meningitis during the first world war (WWI). Notably, Lm-CC1 is the most prevalent clinical clonal complex in several countries and actually corresponds to 20% of all of Lm clinical isolates deposited at the National Center for Biotechnology Information (NCBI) . Lm-CC1 belongs to Lm major lineage I and evolved from a subgroup of serotype 4b ancestry.
While there is no proven interhuman horizontal transmission of listeriosis, it was only in 1983 that the foodborne transmission of human listeriosis was formally established. Since then, Lm-CC1 has been reported in different food matrices, including dairy products, which can be heavily contaminated and constitute a major source of human listeriosis. Previous studies have also demonstrated the hypervirulence of Lm-CC1, and its higher efficiency in gut colonization and fecal shedding, compared to hypovirulent Lm clones. Moreover, increasing evidence shows that bovines, which are frequent Lm asymptomatic carriers and contribute to Lm enrichment in soils, are the main source of disease and constitute a reservoir for Lm-CC1. In addition to Lm subclinical infections that may contaminate milk, the long-term persistence of Lm in cattle manure–amended soils also poses serious risks of transmission to fresh produce.
Understanding the global evolution of Lm-CC1, which is now spread over all continents, as well as its emergence and dissemination across different spatial levels is critical to understand Lm population dynamics and to develop better control strategies, particularly in countries with aging and/or immunosuppressed populations who are most at risk for severe infection. However, the complex movement of livestock and food products associated with asymptomatic intestinal colonization complicates traditional epidemiological investigations aiming at deciphering Lm epidemiology by linking isolates in space and time. Here, we took a population biology approach to fill this knowledge gap and conducted the largest genomic Lm-CC1 study to date, combining genomic and evolutionary approaches to decipher its evolutionary history and pattern of emergence and spread.
Which of the following most accurately describes the function of the first paragraph?
A. To provide a historical background on the discovery of Lm-CC1 during World War I.
B. To introduce the reader to the molecular characteristics of Lm-CC1.
C. To highlight the global prevalence of Lm-CC1 and its significance in clinical cases.
D. To discuss the lineage and ancestry of Lm-CC1.
E. To explain the methods of multilocus sequence typing (MLST).
The first paragraph focuses on the prevalence of Lm-CC1, noting its widespread distribution and its status as the most prevalent clinical clonal complex in several countries. This aligns with choice C, which accurately captures the paragraph's emphasis on the global prevalence and clinical significance of Lm-CC1.
Choice B can be eliminated by 2 indicators/aspects:
1. Choice B is too narrow in scope. While B mentions molecular characteristics in passing, It does not just introduces the reader to the molecular characteristics of Lm-CC1 (it goes way beyond it before and after that segment)
2. Choice B also does not really do a good job of introducing the molecular characteristics of Lm-CC1. The first paragraph text lacks any details of molecular characteristics... I would have assumed that would entail some long scientific text.
Can we rework choice B to make it work?
Yes, we can. Choice B would be more spot on if it said "Introduce reader to the Lm-CC1" - I think that would be a better description than with the phrase "molecular characteristics". Because it does not do that.
Tip:
You should always check the first and the last sentences of a paragraph on the GMAT. They will always have more importance than the middle sentences and that can give you a feel for where the paragraph is leaning when you have a few choices that look appealing and you can't make up your mind.
Answer: C