BIOL 251 - Ch. 4 Study Points

Understand the abundance and diversity of prokaryotes in the environment, and their
roles/contributions/importance

Ubiquitous and abundant

Estimated 1 million prokaryotic species

6,000 described

Many different environments including human body and other living things

Live in mixed cultures in the environment

Oxygen production, breakdown of organic matter, soil formation, carbon/nitrogen fixation, degradation of toxic compounds

Mutualism

Both benefit

Amesnalism

One is harmed

Other is unaffected

Commensalism

One benefits

Other is unaffected

Neutralism

Both are unaffected

Parasitism

One benefits

Other is harmed

Human microbiome

All microbes associated with humans

10:1 ratio

Resident or transient

Varies from site to site, can change over time

Rhizobium

Nitrogen-fixing bacteria

Live in the roots of legume plants such as clover, alfalfa, and peas

Produce ammonia which is then used by plants

Mycobaterium tuberculosis

Slow-growing colonies - grow after 8 day

Mycolic acid coat - waxy coat protects bacteria from some antibiotics, prevents them from drying out and blocks penetration by Gram stain

Special acid-fast staining procedure is used to visualize these bacteria

Widespread in nature, saprophytes, disease casuing

Rods (variable), mycolic coat, acid-fast

Hard to kill with antibiotics and disinfectants

Causes tuberculosis - impacts lungs

Multiple drug-resistant strains

Mycobacterium leprae

Causes leprosy (Hansen’s disease)

Found in peripheral body regions - cooler areas

Corynebacterium

Found in soil, water, plant surfaces, human skin and mucous membranes

Often harmless - unless produces toxins

Gram-positive

Rods forming a ‘V’ (palisades)

Corynebacterium diphtheriae

Gram-positive

Rods forming a ‘V’ (palisades)

Causes diphtheria

Produces toxin

Clostridium botulinum

Gram-positive

Rods

Endospore former

Obligate anaerobe

Found in anaerobic habitats - soil

Produces botulinum toxin - causes food poisoning

May infect infants - colonization of GI tract after spore ingestion (honey, improper canning)

Clostridium perfringens

Gram-positive

Rods

Endospore former

Obligate anaerobe

Found in anaerobic habitats - wounds

Causes gas gangrene (myonecrosis), food poisoning, and wound infections

Clostridium tetani

Gram-positive

Rods

Endospore former

Obligate anaerobe

Found in anaerobic habitats - soil, deep wounds

Produces tetanospasmin - causes tetanus

Clostridium difficile

Gram-positive

Rods

Endospore former

Obligate anaerobe

Found in anaerobic habitats

Causes severe forms of colitis - most severe cases often deadly

Streptococcus

Obligate fermenters - lactic acid bacteria

Gram-positive

Cocci

Grow in chains

Usually classified by serotypes called Lancefield groups and by ability to lyse RBCs when grown on blood agar

Streptococcus pyogenes

Obligate fermenters

Gram-positive

Cocci

Grow in chains

Beta-hemolytic group A

Pyogenic pathogen - pus production

Occasionally normal flora - <15% of upper respiratory tract population

Common cause of Strep throat - bacterial pharyngitis

Also causes skin infections, lesions (impetigo), necrotizing fasciitis (flesh eating)

Streptococcus pneumoniae

Obligate fermenters

Gram-positive

Cocci in pairs

Causes bacterial pneumonia

Virulent strains have capsule - protection from immune system

Nonvirulent - no capsule

Also causes meningitis, septicemia, osteomyelitis, and endocarditis (especially in newborns, the elderly, and patients with immunodeficiency)

Lactobacillus

Lactic acid is major byproduct of fermentation

Part of normal microbiota - GI tract, vagina (contribute to acidity of vaginal environment, inhibit growth of pathogenic yeasts)

Antibiotics can disrupt normal microbiota - can increase risk of secondary infections

Bacillus

Gram positive

Rods

Form endospores

100s of named species

Source of some antibiotics

Bacillus anthracis

Gram positive

Rods

Form endospores

Causes anthrax - disease that affects wild and domestic animals

In humans - charcoal-black ulcers on the skin, severe enterocolitis, pneumonia, and brain damage due to swelling

Fatal if untreated

Bacillus cereus

Gram positive

Rods in chains

Form endospores

Common soil bacterium - often found in milk

Pathogen that may cause food poisoning

Colonies appear milky white with irregular shapes when cultured on blood agar

Staphylococcus aureus

Coccus

Halophilic

Nonmotile

Various locales - nasal membranes

Pathogenic - skin infections that produce boils, carbuncles, cellulitis, or impetigo

Some strains produce enterotoxin - Staph food poisoning

Some strains produce toxin that causes toxic shock syndrome - cardiovascular collapse and death, cause of nosocomial (hospital-acquired) infection

Antibiotic resistant strains - MRSA and VRSA

Staphylococcus epidermidis

Coccus

Halophilic

Nonmotile

Main habitat is human skin

Rarely pathogenic - except for immunocompromised; skin wounds, artificial joints, intravenous catheters

Infections associated with intravenous catheters

Pseudomonas

Found widespread in soil and water

Motile, polar flagella

Form biofilms and pigments

Causes diverse infections in many body locations

Pseudomonas aeruginosa

Found widespread in soil and water

Motile, polar flagella

Form biofilms and pigments

Causes diverse infections in many body locations

Antibiotic resistant

Vibrio cholerae

Gram negative

Curved rods

Aquatic environment, more alkaline

O1 or O139 - produce a toxin that causes cholera, widespread epidemics

Profuse watery diarrhea and dehydration - hypersecretion of electrolytes and water in the large intestine

Transmission - water contact, ingestion of contaminated water or contaminated food (especially seafood)

Not common in US - people who travel are at risk

Legionella pneumophila

Gram negative

Aquatic environment - air conditioning units of large buildings

Often reside in protozoa

Causes Legionnaires disease - respiratory disease

Difficult to culture - charcoal-containing media

Escherichia coli

Gram negative

Rod

Lives in intestinal tract of humans and animals - most strains are mutualistic

Often used as indicator for fecal contamination

Some strains are highly pathogenic - O157:H7, foodborne infections, intestinal tract infections, urinary tract infections

Shiga toxin - potent toxin

Salmonella

Many species - lots of serotypes, identify using antisera

Causes salmonellosis - inflammation of intestine, fever, vomiting, diarrhea

Also causes - food poisoning and gastroenteritis

Salmonella enterobacterica serovar typhi

Causes typhoid fever

What is hemolysis?

Breaking of RBCs

What bacteria exhibits hemolysis?

Streptococcus

How are blood agar plates used?

Used to differentiate non-hemolytic and hemolytic cells

Coliforms

Ferment lactose completely

Non-coliforms

Can’t ferment lactose