The role of salivary antimicrobial peptides in shaping Streptococcus mutans ecology

180 Pages·2017·9.59 MB·English

University of Iowa
Iowa Research Online
Theses and Dissertations
Summer 2010
The role of salivary antimicrobial peptides in
shaping Streptococcus mutans ecology
Ekarat Phattarataratip
University of Iowa
Copyright 2010 Ekarat Phattarataratip
This dissertation is available at Iowa Research Online: https://ir.uiowa.edu/etd/724
Recommended Citation
Phattarataratip, Ekarat. "The role of salivary antimicrobial peptides in shaping Streptococcus mutans ecology." PhD (Doctor of
Philosophy) thesis, University of Iowa, 2010.
https://doi.org/10.17077/etd.1pjhbf54.
Follow this and additional works at:https://ir.uiowa.edu/etd
Part of theOral Biology and Oral Pathology Commons
THE ROLE OF SALIVARY ANTIMICROBIAL PEPTIDES IN SHAPING
STREPTOCOCCUS MUTANS ECOLOGY
by
Ekarat Phattarataratip
An Abstract
Of a thesis submitted in partial fulfillment
of the requirements for the Doctor of
Philosophy degree in Oral Science
in the Graduate College of
The University of Iowa
July 2010
Thesis Supervisor: Professor Jeffrey A. Banas
1
ABSTRACT
Antimicrobial peptides are among the repertoire of host innate immune defenses.
In mucosal immunity, the health-disease balance can be greatly modulated by the
interplay between host immune factors and colonized microflora. Microbial ecology
within dental plaque is constantly shaped by environmental factors present within the oral
cavity. Several antimicrobial peptides are detected in saliva and their bactericidal
activities against oral bacteria, including Streptococcus mutans, the primary etiologic
agent of dental caries, have been clearly demonstrated. However, the role of these
antimicrobial peptides in S .mutans ecology and host caries experience is not well-
defined. We hypothesized that various strains of S. mutans possess different inherent
susceptibility/resistance profiles to host salivary antimicrobial peptides and that host-
specific quantities of these peptides may influence plaque colonization by particular S.
mutans strains.
S. mutans strains from subjects with variable caries experience were tested for
susceptibility to a panel of antimicrobial peptides, including HNP-1-3, HBD-2-3 and LL-
37, revealing that the susceptibilities of S. mutans to these peptides were strain-specific.
S. mutans strains from high caries subjects showed greater resistance to these peptides at
varying concentrations than those from caries-free subjects. In addition, when
combinations of these peptides were tested, they showed either additive or synergistic
interaction against S. mutans.
Determinations of the salivary levels of these peptides showed that their
concentrations were highly variable among subjects with no correlation to host caries
experience. However, positive relationships between the salivary concentrations of HNP-
2
1-3 and MS in dental plaque were found. Additionally, the levels of a number of these
peptides in saliva appeared to be positively correlated within an individual. An analysis
of the salivary peptide concentrations and the susceptibility profiles of S. mutans strains
showed that S. mutans strains obtained from subjects with higher concentrations of HNP-
1-3 in saliva appeared to be more resistant to HNP-1.
Collectively, our findings showed that salivary antimicrobial peptides affect S.
mutans ecology by restricting the overall growth of this bacterium within the oral cavity
and that their activity may help select resistant strains of S. mutans to colonize within
dental plaque. The relative ability of S. mutans to resist host salivary antimicrobial
peptides may be considered a potential virulence factor for this species.

Abstract Approved: ____________________________________
Thesis Supervisor
____________________________________
Title and Department
____________________________________
Date
THE ROLE OF SALIVARY ANTIMICROBIAL PEPTIDES IN SHAPING
STREPTOCOCCUS MUTANS ECOLOGY
by
Ekarat Phattarataratip
A thesis submitted in partial fulfillment
of the requirements for the Doctor of
Philosophy degree in Oral Science
in the Graduate College of
The University of Iowa
July 2010
Thesis Supervisor: Professor Jeffrey A. Banas
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
PH.D. THESIS
_______________
This is to certify that the Ph.D. thesis of
Ekarat Phattarataratip
has been approved by the Examining Committee
for the thesis requirement for the Doctor of Philosophy
degree in Oral Science at the July 2010 graduation.
Thesis Committee: ___________________________________
Jeffrey A. Banas, Thesis Supervisor
___________________________________
Kim A. Brogden
___________________________________
David R. Drake
___________________________________
John W. Hellstein
___________________________________
Timothy D. Starner
___________________________________
Fang Qian
To Mom and Dad
ii
ACKNOWLEDGMENTS
This thesis would not have been completed without many people who have helped
and supported me in every way over the years. I am grateful to have Dr. Jeff Banas as my
thesis supervisor, for the opportunities he has given me, and for his guidance, support and
understanding throughout my study. I would like to thank my thesis committee members,
Drs. Kim Brogden, David Drake, John Hellstein, Fang Qian and Timothy Starner. Their
questions, comments and suggestions are invaluable and greatly help my research
progress forward in a timely manner. I would also like to thank Dr. Steven Levy for
kindly allowing me to use the samples in this study, as well as Barbara Broffitt who
promptly provided me the subject information and is always there to answer my
questions.
I am fortunate to have worked with many great people in Dows, including Min
Zhu, David Lynch, Yuan Liu, Bonny Olson, and Deepa Gadre who have become good
friends and are very helpful in discussing problems and ideas in my project. I also owe
my deepest gratitude to former and current faculty and staff members of OPRM
department, as well as my fellow residents, who always provide me great support
throughout the course of five years in Iowa. Special thanks to Dr. Zoya Kurago, who has
taught me from the very beginning and always believes in me.
I also feel extremely lucky to know and share my time here in Iowa with a lot of
good friends, Ohm, Dew, Oi, Kaew, Jib, Ore, Ron, Moovan, Ball, Fon, Ik, Bow, Todd,
Kim-E, and many other Thai students in Iowa. I can’t thank them enough for their nicest
companionships. Special thanks to Ohm who has been an incredible support and
iii
encouragement. I am also grateful for kind hospitality and generosity of Dr. Ronald
Ettinger and his wife, Sonia, who always provide the warmest support for us, Thai
students. Importantly, I would like to thank my mom, dad, sisters, brother and friends in
Thailand, including Ann, Oat, Antt and Earth, who have been there for me throughout
this long process. I could not have done this without them. Last but not least, I would like
to thank the Royal Thai Government Scholarship for providing me the financial support
for my graduate study and giving me the opportunity to study here in Iowa.
iv
ABSTRACT
Antimicrobial peptides are among the repertoire of host innate immune defenses.
In mucosal immunity, the health-disease balance can be greatly modulated by the
interplay between host immune factors and colonized microflora. Microbial ecology
within dental plaque is constantly shaped by environmental factors present within the oral
cavity. Several antimicrobial peptides are detected in saliva and their bactericidal
activities against oral bacteria, including Streptococcus mutans, the primary etiologic
agent of dental caries, have been clearly demonstrated. However, the role of these
antimicrobial peptides in S .mutans ecology and host caries experience is not well-
defined. We hypothesized that various strains of S. mutans possess different inherent
susceptibility/resistance profiles to host salivary antimicrobial peptides and that host-
specific quantities of these peptides may influence plaque colonization by particular S.
mutans strains.
S. mutans strains from subjects with variable caries experience were tested for
susceptibility to a panel of antimicrobial peptides, including HNP-1-3, HBD-2-3 and LL-
37, revealing that the susceptibilities of S. mutans to these peptides were strain-specific.
S. mutans strains from high caries subjects showed greater resistance to these peptides at
varying concentrations than those from caries-free subjects. In addition, when
combinations of these peptides were tested, they showed either additive or synergistic
interaction against S. mutans.
Determinations of the salivary levels of these peptides showed that their
concentrations were highly variable among subjects with no correlation to host caries
experience. However, positive relationships between the salivary concentrations of HNP-
v