3.1 Bacteria, Viruses, Fungi & Parasites

Why Microbiology Anchors the Exam

Microbiology is the study of microorganisms — living things so small they can only be seen with a microscope. Also called microbes or germs, these organisms are the reason the entire infection-control curriculum exists. On the PSI cosmetology theory exam, the Safety and Infection Control domain is the largest-weighted science area, and nearly every sanitation and safety question traces back to the material in this section. If you can classify an organism, name its shape, and explain how it spreads, you can answer the majority of science questions on the test.

The exam expects you to know four broad groups of microbes: bacteria, viruses, fungi, and external parasites. Each behaves differently, spreads differently, and requires a different control strategy in the salon.

Bacteria

Bacteria are one-celled microorganisms that exist nearly everywhere — on skin, in water, in the air, and on every surface in a salon. The single most-tested fact about bacteria is that most of them are not dangerous.

• Nonpathogenic bacteria are harmless, and many are actually beneficial. The great majority of bacteria fall into this category. Nonpathogenic bacteria help digest food, protect the skin's surface, and are used to make products like yogurt and cheese. Many nonpathogenic bacteria are saprophytes, meaning they live on dead or decaying organic matter.
• Pathogenic bacteria are the disease-causing minority. These are the organisms infection-control procedures are designed to destroy.

The Three Bacterial Shapes

Exam questions constantly ask you to identify bacteria by shape and arrangement. Memorize this chart:

Cocci are round cells that appear alone or in groups:

• Staphylococci are pus-forming bacteria that grow in clusters, like bunches of grapes. They are among the most common human pathogens and cause abscesses, pustules, and boils. A dangerous antibiotic-resistant form, MRSA, belongs to this group.
• Streptococci are pus-forming bacteria that grow in chains, like a string of beads. They cause strep throat and serious blood infections.
• Diplococci grow in pairs and are the cause of diseases such as pneumonia.

Bacilli are rod-shaped bacteria and are the most common bacterial shape overall. Many bacilli are motile, moving themselves with whip-like projections called flagella. Cocci, by contrast, rarely move on their own.

Spirilla are spiral or corkscrew-shaped cells that are also motile, rotating through fluids like a screw.

How Bacteria Grow and Survive

Bacteria live in two distinct stages, and the exam will test both:

1. Active (vegetative) stage — Bacteria grow and reproduce. They thrive in dark, damp, dirty conditions with food available, which is exactly why a dirty salon is dangerous. Bacteria multiply by binary fission, splitting one cell into two, and under ideal conditions they can double their population rapidly.
2. Inactive (spore-forming) stage — When conditions turn unfavorable (heat, dryness, lack of food), certain bacteria coat themselves in a tough, waxy outer shell and become spores. Spores are dormant and extremely resistant — ordinary disinfectants and even boiling may not destroy them. When favorable conditions return, the spore reactivates and the bacterium resumes growing. Spore-forming capability is a major reason salons rely on hospital-level disinfectants and strict procedures rather than casual cleaning.

Viruses

A virus is a submicroscopic infectious particle, far smaller than a bacterium, that can only multiply by invading a living host cell. A virus takes over the cell's machinery and forces it to produce copies of the virus, often destroying the host cell in the process.

Two exam-critical facts separate viruses from bacteria:

• Viruses require a living host to reproduce. Outside the body they cannot multiply, though some can survive on surfaces for limited periods.
• Antibiotics do not work against viruses. Antibiotics kill bacteria only. This is why viral illnesses like the common cold and influenza cannot be cured with antibiotics, and why vaccination is the main medical defense against many viral diseases.

Salon-relevant viruses include the common cold, influenza, hepatitis (a liver disease, with types A, B, and C), HIV (the virus that causes AIDS), herpes simplex (cold sores and fever blisters, which a cosmetologist may see around a client's mouth), and HPV (human papillomavirus), which causes warts on hands and feet. Because viruses are generally harder to kill than bacteria, salon disinfectants must carry an EPA-registered virucidal label claim to be trusted against them.

External Parasites

Parasites are organisms that live on or inside another living organism, called the host, and draw nourishment from it. The two external parasites every cosmetology student must know:

• Pediculosis capitis (head lice) — Tiny insects that infest the scalp and hair, feeding on blood and laying eggs (nits) attached to hair shafts. Lice spread through direct head-to-head contact and through shared combs, brushes, headrests, and towels — which is why a salon can never service a client with lice. All tools must be removed from service and disinfected, and the client must be referred for treatment.
• Scabies (itch mite) — A microscopic mite that burrows beneath the skin, causing intense itching and a pimple-like rash. Scabies is highly contagious through skin contact and is another absolute reason to refuse service.

Fungi

Fungi include molds and yeasts. Some fungi are harmless (mildew on a damp shower curtain), but others cause contagious disease. Fungi that infect humans typically feed on keratin, the protein in hair, skin, and nails, which makes salons a natural transmission site. The fungal infections you must know all belong to the ringworm family, called tinea:

• Tinea capitis — ringworm of the scalp, showing as scaly, round patches with broken hair
• Tinea corporis — ringworm of the body, the classic red ring-shaped rash
• Tinea pedis — athlete's foot, with itching and peeling between the toes
• Tinea unguium (onychomycosis) — fungal infection of the nail, causing thick, discolored, crumbly nails

Despite the name, ringworm is not a worm at all — it is a fungus, and the exam loves that trick question.

Biofilms

A biofilm is a colony of microorganisms that sticks to a surface and to each other, then wraps itself in a slimy protective coating. Biofilms form in water lines, drains, and — famously — in the pipes and jets of whirlpool foot spas. The coating shields the microbes inside, making the colony far more resistant to disinfectants than free-floating germs. The practical exam takeaway: biofilms must be physically broken up by scrubbing before disinfection can work, and foot spas must be cleaned and disinfected after every client exactly according to manufacturer instructions.

Comparing the Four Groups

Keep this table in mind as the organizing framework for the rest of the chapter: each group spreads differently, so each demands its own control strategy.