University Archives

Escherichia coli is a gram-negative bacillus that can cause urinary tract infections, digestive issues, blood infections, and meningitis. The purpose of this investigation was to isolate spontaneous lipopolysaccharide (LPS) mutants of E. coli. It grows well on many types of laboratory media. The LPS is a major molecular component of the cell membrane and can act as an endotoxin in the blood stream. Selection of mutants was performed with a bacterial virus (phage) in a routine test dilution (RTD) assay. Infection of host cells with this particular phage appeared to be associated with LPS. Samples of dilutions of phage were delivered on a lawn of bacteria inoculated on the surface of brain heart infusion (BHI) agar. The highest phage dilution to make a complete zone of lysis (RTD) was about 10 to the power of negative 6. Distinct resistant colonies grew in the lytic zones made by the phage. Cells from potential mutant colonies were extracted with a needle, purified by serial streak plate culture and tested to confirm phage resistance by the agar cross streak method. The antibiotic sensitivity disc technique demonstrated that mutants exhibited significantly increased growth inhibition zone diameters for some antibiotics. The Enterotube/Enteropluri multiple biochemical test device confirmed that mutant strains isolated were E. coli. The mutants may be useful for evaluating characteristics of agents used to control microorganisms.