Mycobacterium avium-intracellulare was considered relatively harmless until the late 20th century, when it became common in certain infections. Explain how this bacterium’s pathogenicity changed.

The bacterium causing pseudomembranous colitis is

a. Clostridium difficile

b. Streptococcus pyogenes

c. Mycobacterium avium-intracellulare

d. Corynebacterium diphtheriae

Which of the following is not characteristic of mycoplasmas?

a. Cytochromes

b. Sterols in cytoplasmic membranes

c. Use of UGA codon for tryptophan

d. rRNA nucleotide sequences similar to those of Gram-positive bacteria

For each of the following diseases or conditions, indicate the genus (or genera) of bacterium that causes it.

___ Scalded skin syndrome

___ Osteomyelitis

___ Pharyngitis

___ Scarlet fever

___ Pyoderma

___ Rheumatic fever

___ Glomerulonephritis

___ Sinusitis

___ Otitis media

___ Anthrax

___ Myonecrosis

___ Diphtheria

___ Leprosy

___ Dental caries

___ Acne

A. Staphylococcus

B. Streptococcus

C. Mycobacterium

D. Listeria

E. Propionibacterium

F. Corynebacterium

G. Bacillus

H. Clostridium

I. Actinomyces

Why are mycoplasmas able to survive a relatively wide range of osmotic conditions, even though these bacteria lack cell walls?

Explain why Staphylococcus epidermidis is rarely pathogenic while the similar S. aureus is more commonly virulent.

Why is mycolic acid a virulence factor for mycobacteria?

Compare and contrast mycoplasmas and viruses.

Match the genera of pathogens to their appearance in stained smears: Actinomyces, Bacillus, Clostridium, Mycobacterium, Staphylococcus, Streptococcus.

(a) Methenamine silver <IMAGE>

(b) Gram <IMAGE>

(c) Gram <IMAGE>

(d) Acid fast <IMAGE>

(e) Gram <IMAGE>

(f) Gram <IMAGE>