Antibiotic Resistance Resultinq from Conjugative Transfer of a
Plasmid between Various Strains of Escherichia coli

Kerry Epps
School of Science and Natural Resources
Lake Superior State University

Abstract

	Over the past three decades, the synthesis of large numbers
of antibiotics has caused complacency about the threat of
bacterial resistance.  Resistance to antimicrobial agents by
bacteria may have resulted due to chromosomal changes or by the
exchange of genetic material via plasmids or transposons.
Plasmids are extrachromosomal genetic elements which appear as
cyclic, double-stranded DNA molecules capable of independent
replication and are distinct from the cellular chromosome.
Resistance plasmids, or R plasmids carry genes that ultimately
code for antibiotic resistance.  Conjugation is one mechanism
used by bacteria to transfer R plasmids.  The objective of my
experiment was to induce a state of antibiotic resistance in a
strain of Escherichia coli(E. coli) via the process of
conjugation over a period of time.  Three strains of bacteria
were used: E.coli with plasmid pBR322 which contained two genes
conferring resistance to ampicillin and tetracycline,
E.coli HT-99 which contained a plasmid carrying a chloramphenicol
resistance gene and E.coli J-53R which contained a chromosomal
gene for rifampin resistance.  All three strains of bacteria were
tested to verify growth or no growth on various antibiotic
mediums.  A ratio of 1/9 was used in the conjugation procedures
between the donor and the recipient.  The two donor strains used
were E.coli with pBR322 and E.coli HT-99 while E.coli J-53R was
the recipient strain.  A plasmid transfer takes approximately 20
minutes to occur; therefore, a time period of 20-200 minutes was
observed with the time interval being set at 20 minutes.
Theoretically, as time progressed, genetically new bacteria would
have resulted from the process of conjugation between the donor
and recipient strains.  Only the recipients that successfully
obtained the desired plasmid would grow and as a result would now
be considered 'genetically new bacteria1.


Selected References

Atlas,Ronald M. Principles of Microbiology. New York: Mosby-Year
Book Inc. 1995 p.261-271 p.366-371

Cohen, Mitchell L. Epidemiology of Drug Resistance:Implications
for a Post-Antimicrobial Era. Science 21 August 1992 : 1050-1055

Neu, Harold C. The Crisis in Antibiotic Resistance.  Science 21
August 1992 : 1064-1071