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Bacterial Agents of Disease
Gram-Positive Group
• Traditionally, this group was based on Gram stain
procedure
• Now the grouping is based on Genetic similarity
• Group is divided into two taxa based on GC content
– High GC Gram positives (>50%)
– Low GC Gram positives (<50%)
• Acid fast species such as the Mycobacterium spp. are in
this group even though they do not always stain positive
with Gram stain
• Mycoplasmas are included in this group even though
they lack a cell wall structure
Staphylococcus aureus
Diseases
• Folliculitis, Abscesses, Furuncles (boils), sty
• Pneumonia, meningitis, empyema, endocarditis, sepsis
• Scalded skin syndrome-exfoliative exotoxin-producing
strain
• Toxic shock syndrome
• Food poisoning by enterotoxin production in food
Transmitted by contact and airborne routes
Notes
• MRSA-Methecillin Resistant Staphylococcus aureus
Other Staph. species
• S. epidermidis
– Normal flora of skin, opportunistic pathogen
– Sepsis
– UTI
• S. saprophyticus
– Normal flora of skin and genitourinary mucosa
– UTI
Streptococci
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Classified by group-specific antisera
Important groups include
A -S. pyogenes, produce many toxins and enzymes
B -S. algalactiae
D –S. bovis, Enterococcus spp.(now a separate genus)
Streptococcus pyogenes
• Beta hemolytic, many other virulence factors
Diseases
• Wound infections
• Impetigo
• Necrotizing fasciitis ‘flesh-eating’
• Strep throat,
• Scarlet fever caused only by streps infected with
temperate phage
• pneumonia, meningitis, endocarditis
• Puerperal (childbed fever), rheumatic fever
S. pneumoniae
• Alpha hemolytic
Diseases
• Bronchitis
• Classic Pneumonia
• Streptococcal Meningitis
• Conjunctivitis (Pink eye)
• Otitis
Other streptococcal infections
• S. algalactiae -Group B strep disease
• S. mutans -Dental caries
Enterococcus spp.
• Enterococcus faecalis, and E. faecium
• Virulence factors not well understood
• Indicators of fecal pollution
Diseases
• Cholicystitis
• Endocarditis
• Septicemia
• UTI
• some strains are resistant to vancomycin (VRE)
Bacillus spp.
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Rod-shaped often in chains
Many species, most are found naturally in soil
Endospore formers resistant to environmental extremes
Non-hemolytic forms are generally more dangerous
Produce a variety of toxins
Bacillus cereus
– Heat-stable exotoxin can result in food poisoning
giving rise to vomiting w/in hours after ingesting
– Enterotoxin can cause diarrhea 10-12 hrs after
ingestion
Bacillus anthracis
• Anthrax can be:
– Pulmonary -Usually only ca. 5% of cases but most
severe form
– Skin/cutaneous
– Gastrointestinal
• Toxin producer
• Zoonosis, primarily affecting ungulates and occasionally
predators
• Vaccine widely used in livestock but not humans
Clostridium spp.
• Anaerobic, endospore-forming rods
• Found in soil, water and animals
• Clostridium perfringens
– Gas gangrene, tissue destruction by toxin and
enzymes
– Food poisoning through ingestion of toxins
• C. difficile
– Produces enterotoxin
– causes pseudomembranous colitis
– Causes antibiotic associated diarrhea
Clostridium tetani
• Causes tetanus, spastic paralysis
• Infections result when endospores enter host through
wounds (or umbilical stump in neonates) and germinate
under anaerobic conditions
• Produces toxin called tetanospasmin
• Toxin blocks release of inhibitory mediators (GABA and
Glycine) from vesicles in spinal and sympathetic NS
synapses causing spasms
• Life cycle includes periods in intestines of animals and
soil
• Vaccine commonly administered in U.S.
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Clostridium botulinum
• Causes food poisoning, flaccid paralysis, Infant botulism
• One of the most potent toxins known
• Endospores germinate under anaerobic conditions,
especially in improperly-packaged foods of humans or
animals
• Produces botulinum toxin (BT, Botox) which inhibits the
release of acetylcholine at neuromuscular junction
resulting in flaccid paralysis
Mycobacterium spp.
• Closely related to Gram positive organisms but do not
always stain as such using Gram procedure due to the
lipid mycolic acid in cell wall
• Intracellular parasites that resist digestion within
phagosomes
• Several species can cause disease in humans and
animals
• Some species are found in the environment
Mycobacterium tuberculosis
• Causes tuberculosis (consumption)
• Infection leads to tissue necrosis and chronic
granulomas, mainly lungs but also other tissues
including bones
• Infection leads to hypersensitivity in host (positive
PPD), but not necessarily active disease
• Most cases in US are reactivation of initial infections
• Increasingly resistant to antibiotics
Mycobacterium leprae
• Hansen’s disease (leprosy)
• Mainly a human disease; however, armadillos are also
known to contract the disease
• Infection gives rise to lesions on the extremities
• Incubation is slow (2-10 yrs)
• Endemic to Asia and Africa
Mycobacterium ulcerans
• Causes Buruli Ulcer
• An emerging disease in Africa and other tropical
countries
• Results in necrotic lesion that can cause significant
disfigurement
Other diseases involving mycobacteria
• Mycobacterium (avium) ssp. paratuberculosis causes
Johnes disease in ungulates (hoofed animals), an
intestinal wasting disease
• Some evidence to implicate as a cofactor for Irritable
bowel syndrome or Crohne’s disease
Actinomyces isrealii
• Anaerobic, filamentous, branching rods
• Normal flora that can be opportunistic pathogen
• Causes hard lesions mostly around face, neck
abdominal lesions after surgery , and uterine infections
after IUD use
Corynebacterium diptheriae
• Cell structure similar to Mycobacterium
• Some strains cause Diptheria
• Tox gene which is needed to cause the disease is
introduced into genome by phage
• Diptheria toxin can damage to heart, kidneys and NS
• Can cause formation of pseudomembrane
Listeria monocytogenes
• Short rods or coccobacilli
• Listeriosis
• Food borne (processed meats, milk, soft cheeses, and
veggies)
• Threat to fetus of pregnant women
• Can grow in the refrigerator
Proprionibacterium acnes
• Cofactor/proximate cause for acne
• Clinical impact of treatment
– Antibiotic use may increase resistance
– Acutane (isotretinoin): strongly interferes with
developmental processes may have severe side
effects on tissues
Proteobacteria
Alphaproteobacteria
Brucella spp.
• Cause Brucellosis, Malta fever
• Several species that are genotypically similar, are
differentiated by the primary host and cell surface
antigens
– B. abortus (cows)
– B. melitensis (goat)
– B. suis (pig)
• they are highly infectious and considered to be potential
agents of biowarfare/bioterrorism
Rickettsial Pathogens
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Cat scratch fever- Bartonella henslae
Oroya fever/Verrugia Peruana- Bartonella bacilliformes
Trench fever- Rochalimaea (Bartonella) quintana
Epidemic typhus- Rickettsia prowazekii
RMSF- Rickettsia riskettsii
Scrub typhus- Rickettsia tsutsugamishi
Endemic typhus- Rickettsia typhi
Rickettsial pox- Rickettsia akari
HME- Ehrlichia chaffeensis
HGE-Anaplasma (Ehrlichia) phagocytophilum
Rickettsia spp.
Species
Rickettsia prowazekii
Disease
Epidemic
typhus
Rickettsia riskettsii
RMSF
Rickettsia tsutsugamishi Scrub
typhus
Rickettsia typhi
Rickettsia akari
Vectors
louse
Reservoir
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tick
mite
Dogs, rod.
rodents
Endemic flea
typhus
Rickettsial mite
pox
rodents
mice
Other rickettsial pathogens
Species
Bartonella henslae
Bartonella bacilliformes
Rochalimaea quintana
Ehrlichia chaffeensis
Anaplasma (Ehrlichia)
phagocytophilum
Disease
Cat scratch
fever
Verrugia
peruana
Trench fever
Vectors Reservoir
Fleas? cats
HME
HGE,
anaplasmosis
Ticks
Ticks
Sand
flies
Lice
?squirrels
mammals
rodents
Betaproteobacteria
• Neisseria
• Burkholderia
• Bordetella
Bordetella pertussis
• Whooping Cough (Pertussis)
• Gram (-) coccobacillus
• Non-invasive, toxin producing
Neisseria gonorrhoeae
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Gonorrhea (the clap)
Gram (-) diploccocci
Endotoxin damages mucosa
Can spread to other systems, PID
Pus-filled discharge
# 1 communicable disease
Neisseria menigitidis
• Meningococcal meningitis
• Waterhouse-Friderichsen syndrome (endotoxic shock)
Gammaproteobacteria
• Extremely diverse group
• Contains many of the Gram negative enteric organisms
Bacterial Enteritis
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Salmonellosis-Salmonella enteriditis
Enterocolitis- S. typhimurium
Typhoid fever- Salmonella typhi
Shigellosis- Shigella spp.
Cholera- Vibrio cholerae
Vibriosis- Vibrio parahemolyticus and Vibrio vulnificus
Campylobacter jejuni
Yersinia enterocolitica
Salmonella typhi
• Typhoid fever, nervous fever
• Transmitted by fecal contamination
• Several clinical stages last for weeks
Salmonella enterica
• Salmonellosis “food poisoning”
• Produce enterotoxins and cytotoxins
• One species is divided into several serovars- different
types that are distinguished only by antigens
• Serovars that commonly cause salmonellosis are
typhimurium and enteritidis
• May be found in intestines of many vertebrates including
birds, reptiles and mammals
Shigella spp
• Shigellosis, dysentery
• Endotoxin irritates bowel
• Endotoxin affects intestine and nervous system
Escherichia coli
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Most strains are non-pathogenic
Various genes increase virulence
Enteroinvasive E. coli
Enterotoxogenic E. coli
Enterohemorrhagic
– E. coli O157:H7 is the most notable EHEC strain
– produces Shiga toxin
– Cattle may be primary reservoir
Opportunistic infections
• Traveler's diarrhea
• Cholecystitis, cholangitis (infalmmation of gallbladder ,
bile ducts)
• Prostatitis, UTI, kidney infections, septicemia
Pseudomonas aeruginosa
• Burn infections
• Eye infections associated with contact lenses
Yersinia pestis
• Diseases: Bubonic, pneumonic and septicemic plague
• Transmitted to humans by fleas such as Xenopsylla
cheopis as well as through aerosolized fluids from
infected hosts
• Reservoirs: rodents
• Sporadic, isolated outbreaks occur around the world
Vibrio cholerae
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causes Cholera
Worldwide distribution, especially common in the tropics
Lives in environmental waters
Copepods and shellfish are reservoirs and can also be
considered as vectors if swallowing them results in the
disease
• Infectivity is enhanced when organisms pass through
human intestine
• Route of transmission is usually through food or water
contaminated with feces
• Serogroups 0139 and 01 are most capable of producing
epidemics
Other important Vibrio spp.
• Vibrio vulnificus- wound infection, septicemia,
endometritis, food “poisoning”
– Mortality rate of around 40%
– Acquired by eating raw oysters or swimming
in ocean where organism lives naturally
– Organisms invade through wounds, GI tract,
and give rise to septicemia
– 1 case report of endometritis
• Vibrio parahemolyticus- food “poisoning”
Haemophilus spp.
• Haemophilus ducreyi –Chancroid
• Haemophilus influenzae
– Found on mucous membrane of upper respiratory
tract infections
– Can cause meningitis in children
– Encapsulated forms resist phagocytosis
– Hib vaccine
Legionella pneumophila
•Pontiac Fever is mild form
•Legionnaire's Disease
•Several protozoan reservoirs
•Reside in phagocytes of human host
Others
• Francisella tularensis -Tuleremia (rabbit fever)
• Coxiella burnetii -Q fever
• Pasteurella multocida -animal bite infections
• Spirillum minor- rat bite fever
Epsilonproteobacteria
Helicobacter pylori
• Lives in gastric mucosa
• Produce urease and break down urea into ammonia to
neutralize stomach acids
• High infection prevalence, especially in developing
countries
• Cofactor for peptic ulcers and stomach cancer
• Route of transmission may be fecal-oral but details
unknown
• One of the most common bacteria in humans (50%
infection rate worldwide, some populations 100%)
Campylobacter jejuni
• Common cause of diarrhea
• Can cause septicemia
• Transmitted through food and water contaminated with
feces
Spirochaetes and other bacteria
Spirochetes
• Borrelia spp.
• Treponema pallidum
• Leptospira interrogans
Borrelia spp.
• Relapsing fever- Borrelia recurrentis
– Lice and argasid ticks are vectors
• Lyme disease- Borrelia burgdorferi (sensu lato)
– Worldwide in distribution
– Vectors include several species of Ixodes ticks
– Produces characteristic rash, erythema
chronicum migrans.
Lyme Borreliosis
• Several genospecies of B. burgdorferi are recognized
around the world and cause similar diseases
• Reservoirs: Rodents, and other wild mammals
• Dogs and Livestock may also become infected
• Severity of disease may vary by strain, higher genetic
variability of B. burgdorferi in Southern U.S.
• Primary vector: the black-legged tick (deer tick) Ixodes
scapularis (Eastern U.S.) Ixodes pacificus (Western
U.S.)
• Higher prevalence of infection in New England and
Upper Midwest
Leptospira interrogans
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Causes Leptospirosis
Zoonosis
Carried by many wild and domestic mammals
Acquired through contact with water/soil
Treponema pallidum
• Diseases: syphilis, yaws, bejel, pinta
• Lesions called chancre
• Disease consists of primary, secondary and tertiary
stages that increase in severity, sporadic symptoms after
latent periods
• Immunopathology can cause serious nervous
degeneration and insanity
• STD, also transmitted through saliva
• Congenital syphilis trans-placental transmission
• Recent (ca. last 10000 years) co-evolution with changing
human lifestyles
Chlamydia spp.
Chlamydia trachomatis
• Obligate intracellular parasites
• Nongonococcal urethritis in men
• PID in women
• Lymphogranuloma venereum (LGV) caused by a
particular strain
• Self-inoculation of eyes leading to conjunctivitis
• Trachoma, a leading cause of blindness
Chlamydia psittaci causes Psitticosis/Ornithosis, a
respiratory zoonosis