Board 088 - OLIGOPEPTIDE TRANSPORTERS OF STREPTOCOCCUS PNEUMONIAE INCREASE RESISTANCE TO Β-LACTAM ANTIBIOTICS THROUGH ALTERED CELL WALL STRUCUTRE (ID 573)
Abstract
Background
Genetic exchange, mutations, and non-genetic mechanisms all contribute to antibiotic resistance in Streptococcus pneumoniae. Changes in gene expression can alter the cell wall composition and decrease sensitivity to antibiotics. It has previously been shown that pneumococcal oligopeptide transporters alter gene expression. We hypothesize that pneumococcal oligopeptide transporters increase expression of clpL and reduce sensitivity to β-lactam antibiotics.
Methods
Antibiotic susceptibility was tested through growth curve analysis of wildtype and mutant pneumococcal strains. Inducible expression vectors of clpL were also used along with luciferase reporters for monitoring expression levels. Microscopy was performed to determine alterations in the cell wall structure in various mutants.
Results
Deletion of the oligopeptide transporters aliC and aliD increased susceptibility to cefdinir, amoxicillin, ampicillin, but not vancomycin. We found that overexpression of clpL decreased antibiotic susceptibility. Also, deletion of oligopeptide transporters reduced clpL expression and increased susceptibility[LM1] . Along with this we observed that changes in growth conditions altered clpL expression. Incorporation of the fluorescent label HADA was increased in wildtype strains compared to oligopeptide transporter mutants, this indicates reduction of cell wall cross linking in the mutants. Increased expression of clpL also showed an increase in cell wall cross linking.
Conclusions
Determination of minimum inhibitory concentration values for clinical intervention may be inaccurate due to the growth media used during testing. Oligopeptide transporters can alter gene expression and increase cell wall cross linking reducing efficacy of cell wall targeting antibiotics. Therefore, increased study on these resistance mechanisms are required to more accurately determine antibiotic susceptibility.
