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 foodTransmitted by contact and airborne routesNotes• 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

• 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 factorsDiseases• 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 hemolyticDiseases• 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 pollutionDiseases• Cholicystitis• Endocarditis• Septicemia• UTI• some strains are resistant to vancomycin (VRE)

Bacillus spp.

• 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.• .

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

• 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

Corynebacterium diptheriae

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• 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 Disease Vectors ReservoirRickettsia prowazekii Epidemic

typhuslouse ?

Rickettsia riskettsii RMSF tick Dogs, rod.Rickettsia tsutsugamishi Scrub

typhusmite rodents

Rickettsia typhi Endemic typhus

flea rodents

Rickettsia akari Rickettsial pox

mite mice

Other rickettsial pathogens

Species Disease Vectors ReservoirBartonella henslae Cat scratch

feverFleas? cats

Bartonella bacilliformes Verrugia peruana

Sand flies

Rochalimaea quintana Trench fever Lice ?squirrelsEhrlichia chaffeensis HME Ticks mammalsAnaplasma (Ehrlichia) phagocytophilum

HGE, anaplasmosis

Ticks rodents

Betaproteobacteria

• Neisseria• Burkholderia• Bordetella

Bordetella pertussis

• Whooping Cough (Pertussis)• Gram (-) coccobacillus• Non-invasive, toxin producing

Neisseria gonorrhoeae

• 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

• 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• 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

• 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

• 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