Which organisms are antibiotics ineffective against?

Antibiotics are specifically designed to combat bacterial infections by targeting structures and functions unique to bacteria, such as cell wall synthesis, protein synthesis, and specific metabolic pathways. However, their effectiveness is limited to bacteria and does not extend to other types of organisms.

Viruses, for instance, do not have cell walls or the metabolic machinery that antibiotics target. Instead, viruses rely on host cells to replicate, making them inherently resistant to antibiotics. Similarly, protozoans are a different type of organism that antibiotics are not tailored to address, as they belong to the kingdom Protista and have complex life cycles and cellular structures. Parasitic helminthes, which are worms and complex multicellular organisms, also differ significantly from bacteria in terms of biology and metabolism.

Thus, while antibiotics can effectively treat infections caused by bacteria, they do not work against viruses, protozoans, or parasitic helminthes, underscoring their specificity. Therefore, among the choices provided, the statement that antibiotics are ineffective against parasitic helminthes is correct, as this group is complex and requires different treatment approaches, such as antiparasitic medications, rather than antibiotics.