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After diagnosing Barbara with pneumonia, the PA writes her a prescription for amoxicillin, a commonly-prescribed type of penicillin derivative. More than a week later, despite taking the full course as directed, Barbara still feels weak and is not fully recovered, although she is still able to get through her daily activities. She returns to the health center for a follow-up visit.
Many types of bacteria, fungi, and viruses can cause pneumonia. Amoxicillin targets the peptidoglycan of bacterial cell walls. Since the amoxicillin has not resolved Barbara’s symptoms, the PA concludes that the causative agent probably lacks peptidoglycan, meaning that the pathogen could be a virus, a fungus, or a bacterium that lacks peptidoglycan. Another possibility is that the pathogen is a bacterium containing peptidoglycan but has developed resistance to amoxicillin.
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Many bacterial cells have protein appendages embedded within their cell envelopes that extend outward, allowing interaction with the environment. These appendages can attach to other surfaces, transfer DNA, or provide movement. Filamentous appendages include fimbriae, pili, and flagella.
Fimbriae and pili are structurally similar and, because differentiation between the two is problematic, these terms are often used interchangeably. J.A. Garnetta et al. “Structural Insights Into the Biogenesis and Biofilm Formation by the Escherichia coli Common Pilus.” Proceedings of the National Academy of Sciences of the United States of America 109 no. 10 (2012):3950–3955. T. Proft, E.N. Baker. “Pili in Gram-Negative and Gram-Positive Bacteria—Structure, Assembly and Their Role in Disease.” Cellular and Molecular Life Sciences 66 (2009):613. The term fimbriae commonly refers to short bristle-like proteins projecting from the cell surface by the hundreds. Fimbriae enable a cell to attach to surfaces and to other cells. For pathogenic bacteria, adherence to host cells is important for colonization, infectivity, and virulence. Adherence to surfaces is also important in biofilm formation.
The term pili (singular: pilus) commonly refers to longer, less numerous protein appendages that aid in attachment to surfaces ( [link] ). A specific type of pilus, called the F pilus or sex pilus , is important in the transfer of DNA between bacterial cells, which occurs between members of the same generation when two cells physically transfer or exchange parts of their respective genomes (see How Asexual Prokaryotes Achieve Genetic Diversity ).
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