• Staphylococcus aureus• - Boils: Walled off from body with fibrin• - Can produce toxic shock superantigen• - MRSA: Methicillin-resistant S. aureus• - Major cause of nosocomial infections (in

hospitals)• - Some strains make exfoliative toxin (scalded skin

syndrome).

Skin and Soft-Tissue Infections

Figure 26.2

• Streptococcus pyogenes• - Best known for causing sore throats and

immunological sequelae, such as rheumatic fever • - Also necrotizing fasciitis (“flesh-eating” disease)• - Many prophages carry virulence factors.

Skin and Soft-Tissue Infections

Figure 26.3

Impetigo S. pyogenes or Staph aureus

• Viruses cause a maculopapular skin rash.• - Usually infects through respiratory tract• - Paramyxovirus: Rubeola (“measles”)• - Herpes virus: Chickenpox, shingles• - Togavirus: Rubella (“German measles”)

Skin and Soft-Tissue Infections

Figure 26.4

measles

Chicken pox

Respiratory tract infections

Figure 26.5

S. pneumoniae

Scarlet fever

normal TB show tubercules

diphtheria

Gastrointestinal tract infections

Salmonellosis in the US

norovirus

Genitourinary tract infections

Sexually Transmitted Diseases• Syphilis• - Caused by the spirochete Treponema pallidum• - Primary syphilis: Chancre at site of infection• - Secondary syphilis: Generalized rash• - Tertiary syphilis: Effects on heart and CNS

Figure 26.11

Sexually Transmitted Diseases

• Chlamydia• - Most frequently

reported STD in U.S. • - Caused by unusual

Gram-negative bacteria - Chlamydia trachomatis

• - Chlamydia pneumoniae

• - Obligate intracellular pathogens

• - Both cause STDs, as well as pneumonia and trachoma of the eye.

Figure 26.12

Figure 18.45

Chlamydia on fallopian tube tissue

Sexually Transmitted Diseases• Gonorrhea• - Caused by the Gram-negative diplococcus

Neisseria gonorrhoeae• - Most infected men exhibit symptoms, while

most women are asymptomatic.• - Binds to CD4+ T cells, inhibiting T-cell activation

Figure 26.13

• Meningitis– - Infection of membrane surrounding brain– - Some bacteria cross blood-brain barrier.

• - Streptococcus pneumoniae• - Haemophilus influenzae• - Neisseria meningitidis

Central Nervous System Infections

- Has thick capsule and type IV pili- Dangerous if gets into bloodstream- Crosses from capillary into cerebrospinal fluid- Once in meninges, very difficult to treat- Effective vaccine to capsule components

Figure 26.16D Figure 26.16B

West Nile virus

Figure 26.18 Figure 26.19

• Animation: Retrograde Movement of Tetanus Toxin to an Inhibitory Neuron

Click box to launch animation

Central Nervous System Infections

• Prions• - Proteinaceous infectious particles• - Cause spongiform encephalopathies• - Improperly folded proteins form

aggregates that damage the brain.• - Most mammals suffer from these

diseases.Figure 26.20

Systemic infections

Figure 26.23

Figure 26.24

Lyme disease

Lyme disease

Figure 26.25

Lyme disease

deer ticks

Deer tick eating

Lyme disease rash

Lyme Disease• Borrelia burgdorferi• Spirochete• Obligate Intracellular pathogen

Borrelia burgdorferi

• 1.5Mbp• Strange genomic layout

– Linear chromosome (900 kb)– Has over 20 circular AND linear plasmids

• Genome decay in obligate intracellular bacteria

• Loses many biosynthesis pathways (why make it if you can get it from the host)

Rocky Mt. spotted fever

Vaccine LYMErix• Recombinant Outer surface

protein A (OspA)– Your body doesn’t make

antibodies to OspA normally– OspA only expressed in unfed

ticks, not in fed ticks or host

• Temperature is the trigger to stop OspA and start making OspC – other triggers for making

virulence proteins are pH and Fe starvation

How the vaccine works

• Bacterial migration from midgut to salivary glands is inhibited when ticks feed on OspA (and also in OspC) immunized mice

• So immune serum appears to kill the bugs in the tick or prevent migration

Rocky mountain spotted fever

Rickettsia inside cells (arrows)

leprosy