Effects of antibiotics on bacterial structure and their pathogenicity.

Subinhibitory concentrations of beta-lactam antibiotics as well as some other antibacterial agents alter the ultrastructure of bacteria. The separation of replicated genomes of Gram positive cocci is inhibited, and results in clusters of as many as 30 organisms held together by thick cross walls. The separation of the replicated genomes of Gram negative bacilli is also inhibited and results in the formation filaments. These altered forms of bacteria usually exhibit lower pathogenicity than their respective normal counterparts such as; decreased adherence to epithelial cells, higher susceptibility to phagocytosis and decreased output of bacterial enzymes. Contrary to common belief, subinhibitory concentrations do not generate a significant increase in bacterial resistance to the respective drug.