Biology
Bacteria and Fungi
The three common pathogens are Bacteria, Fungi and Viruses. When these pathogens enter the body, infections occur. They are parasitic, taking energy from hosts. Any living organism can be affected by pathogens. Bacteria and Fungi are facultative pathogens while viruses are obligate pathogens. Obligate pathogens need host for their life cycle.
Bacteria are one cell organisms. They belong to prokaryotic group which lack organelles and an organized nucleus. A gram of soil contains about 40 million bacterial cells. The structure of the bacteria is that it contains a cell wall which gives it its shape, plasma membrane inside cell wall that transports chemicals, cytoplasm inside plasma membrane that contains genetic material and ribosomes, DNA inside cytoplasm that contains genetic instructions, flagellum used for movement and pill that is used to stick to surfaces.
Classification of Bacteria based on shape
• Cocci (spherical shaped) – e.g. streptococcus group which causes strep throat
• Bacilli (rod shaped) – e.g. Salmonella typhi which causes typhoid
• Spirilla (spiral shaped) – e.g. Helicobacter pylori
• Vibrios (comma shaped) – e.g. Vibrio cholerae which causes cholera
• Spirochaetes (corkscrew) – e.g. Borrelia burgdorferi which causes lyme disease
Gram-positive bacteria
• cell walls are made of a thick layer of peptidoglycan
• cell walls don’t have outer membrane
• the thick, peptidoglycan layer in their cell walls will retain the dye and they will stain violet
Gram-negative bacteria
• cell walls are made of a thin layer of peptidoglycan
• cell walls have an outer membrane
• the dye will leak out of the thin peptidoglycan layer, and the bacteria will stain red
Aerobic bacteria
• They need oxygen to survive
• Important for biological decomposition
• They do not require energy input to proceed with any activity
• Found in soil, water etc.
• Examples are lactobacillus, E.Coli, Salmonella
Anaerobic bacteria
• Cannot survive in the presence of oxygen
• Useful for fermentation etc.
• They require energy input to proceed
• Substances like nitrate, methane etc. are produced
• Examples are clostridium, bacteroides etc.
Heterotrophic bacteria
• They depend on dead organic matter for food
• They are abundant in nature
• They may be parasites, saprophytes or symbionts
• Parasites obtain food from other organisms. e.g. salmonella typhi which causes typhoid
• Saprophytes obtain food from dead organic matter by fermentation, putrefaction and decay
• Symbionts live in symbiotic association with other plants. e.g. Rhizobium present in root nodules of legumes and E.coli in human intestine
Autotrophic bacteria
• They synthesize their own food
• They make use of light and chemical energy
Symptoms of Bacterial infections
• Fever
• Headache
• Chills
• Fatigue
Fungi
They are members of the group of eukaryotic organisms. They can be either single-celled(yeast) or multicellular. They have a nucleus and organelles. They are heterotrophs. They grow in moist and warm places. Mostly they have filamentous structure. They study of fungi is known as mycology.