General Pathology 300 (Defense mechanisms and types of infections) Flashcards
Patterns of infections
different ways to damage
different ways to damage (different mechanisms of infections)
1) The invasive organism produces local damage (e.g., warts)
2) The invasive organism is toxic (poisonous) to the host (e.g. botulism)
3) The invasive organism produces little local damage but has widespread effects (e.g., HIV)
spread of infection within host – 3 types
1) Directly - some pathogens produce enzymes that damage cell membranes, enabling them to move rapidly from cell to cell
2) Via natural channels such as membranes (meninges, pleura, peritoneum) and vessels (lymphatic, blood)
3) Through nerves or through phagocytes (e.g., herpes virus)
Mode of action (infection)
Mode of action of a pathogen refers to how the organism produces a pathologic process.
Great variation exists.
E.g.
1) Some intracellular pathogens, like viruses, invade cells and interfere with cellular metabolism, growth and replication.
2) Other organisms cause cell death.
Factors affecting occurrence and spread of infection
1) Pathogenic factors
2) Host factors
1) PATHOGEN FACTORS
- Virulence – the relative power and degree of pathogenicity
“the severity or harmfulness of a disease or poison.” - Dose – increased numbers are more effective
- Site of infection – some sites are more easily infected
E.g.
Mucous membranes - Synergism between different pathogens (i.e. one organism can impair external defenses and permit another to enter).
mucous membranes – infection
“The mucosal surfaces of the body are highly vulnerable to infection and possess a complex array of innate and adaptive mechanisms of immunity”
Pathogen factors, simplified
strength
= virulence
numbers
= dose
location of attack
= site
teamwork
= synergism
2) HOST FACTORS
Resistance to infection
Immune competency
Leukocyte count
Necrosis and ischemia of a tissue (e.g., anaerobic bacteria)
E.g.
via factors like age (older people, very young people, immunocomprimised people, etc.)
Diagnosis
- Direct visualization of organism
- Detection of microbial antigen
- Search for clues produced by the host immune response to specific micro-organisms
- Isolation of organism in culture
- Detection of specific microbial nucleotide sequences
Opportunistic infections
An opportunistic infection is any infection that results from a defective immune system that cannot defend against pathogens normally found in the environment. These infections are usually seen in patients with impaired defenses against disease.
I.e.
people with optimal immune system function will generally not be getting these, or not getting them as frequently (?)
Opportunistic infections (life threatening infectious diseases)
Life threatening infectious disease occurs when immunity is weak or suppressed
(e.g. transplant patients, AIDS patients, old age, newborns, malnourished, burn victims, etc).
why is immune system comprimised in severe burn patients?
“After the burn, the ability of neutrophils’ oxidative burst decreases, which in turn weakens phagocytosis [10,29]; there is a decrease in the speed of motility during chemotaxis [30,31] and decreased bactericidal capacity [14], which ultimately reduce innate immune function.”
Bacterial Infection types
Staphylococci
Streptococci
Pneumococci
Meningococci
cocci
spherical
STAPHYLOCOCCAL INFECTIONS
“Staph”
Among the most common bacteria normally residing on the skin
Over 30 subtypes
Cause a multitude of disease ranging from mild / asymptomatic to severe / fatal
Leading cause of nosocomial and community acquired infections
STAPHYLOCOCCI
most common type (Staphylococcus)
Most common - Staphylococcus aureus (S. aureus)
S. AUREUS
Extremely virulent
Nonmotile and facultative aerobic
motile vs nonmotile
(of cells, gametes, and single-celled organisms) capable of motion.
Bacterial motility is the ability of bacteria to move independently using metabolic energy.
facultative aerobic define
These are bacteria that, under normal circumstances, breathe anaerobically but can breathe aerobically when oxygen is available.
anaerobic respiration define
“Anaerobic respiration is respiration using electron acceptors other than molecular oxygen. Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.”
respiration, special define
BIOLOGY
“a process in living organisms involving the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.”
how well can S. AUREUS survive
Hardy; able to survive on inanimate objects for an extended period
what can S. AUREUS infect
Can infect the blood, skin, lungs, soft tissue, joints, bones
Risk factors for S. Aureus infection
Diabetes, chronic illness
HIV positive
Elderly, newborns, malnourished
Surgical/burn patients
Prosthetics
Etc.
prosthetics vs infection (???)
“Amputations can be the result of sepsis. Alternately, if you have an amputation, you could develop a pressure injury from a prosthetic or adaptive/assistive device and this could result in an infection that could cause sepsis.”
infectious diseases caused by STAPHYLOCOCCUS AUREUS
Osteomyelitis
Respiratory tract infections
Infectious (septic) arthritis
Septicemia
Endocarditis
Toxic shock syndrome
Food poisoning
Skin infections (cellulitis, mastitis)
management (when infected by S. AUREUS??)
..
diagnosis
Diagnosis - culture
treatment
Treatment - antibiotics
S. Aureus infection – PROGNOSIS
Prognosis is generally good although some strains of S. aureus are particularly difficult to treat
E.g. MRSA
MRSA
Methicillin-resistant Staphylococcus aureus
Methicillin = antibiotic
“Methicillin-resistant Staphylococcus aureus is a group of gram-positive bacteria that are genetically distinct from other strains of Staphylococcus aureus.”
“MRSA is responsible for several difficult-to-treat infections in humans.”
how do S. Aureus strains adapt to antibiotics
“Intrinsic Antibiotic Resistance. The resistance rates of S. aureus infection and multidrug resistant strains are increasing, making the clinical anti-infective treatment more difficult.”
“Staphylococcus aureus is notorious for its ability to become resistant to antibiotics.”
“Staphylococcus aureus is capable of becoming resistant to all classes of antibiotics clinically available and resistance can develop through de novo mutations in chromosomal genes or through acquisition of horizontally transferred resistance determinants.”
de novo mutation
“A de novo mutation is any mutation or alteration in the genome of an individual organism that was not inherited from its parents. This type of mutation spontaneously occurs during the process of DNA replication during cell division.”
STREPTOCOCCAL INFECTIONS
Group A – Streptococcus pyogenes (S. pyogenes)
Group B – Streptococcus agalactiae (S. agalactiae)
Streptococcus pyogenes
One of the most common bacterial pathogens of human of any age
Causes many diverse diseases of many diverse organs and systems
Steptococcus pyogenes – pus vs no pus
Can cause suppurative and non-suppurative disease
S. pyogenes – transmission
Transmission – contact, droplets, foodborne (vehicle)
Diseases caused by STREPTOCOCCUS PYOGENES
Streptococcal pharyngitis (strep throat) – very common cause of sore throat occurring mostly in children
Scarlet fever – usually follows untreated strep throat and but more severe
Impetigo – skin infection that occurs in children, particularly in hot weather
Cellulitis – acute skin infection
Necrotizing fasciitis – very serious and potentially fatal infection that spreads quickly along fascial planes
Streptococcus AGALACTIAE
..
S Agalactiae – can cause
Leading cause of neonatal pneumonia, meningitis, sepsis
Infrequent cause of pyogenic disease in adults
—> Referring to pus (??)
or referring to infections that S Pyogenes causes (??)
pyogenic deifne
adjective: pyogenic
involving or relating to the production of pus.
pyogenic
“Pyogenic is a term describing bacteria capable of causing local purulent inflammation or generalized infection, and Streptococcus pyogenes is aptly named after this characteristic.”
“Streptococcus pyogenes (GAS) is known to cause pyogenic infections of the pharynx and skin.”
Streptococcus agalactiae – Treatment
Rapid administration of antibiotics is essential
S. Agalactiae (group B strep) and pregnancy
(GROUP B strep in pregnancy)
Pregnant women are routinely screened
“Group B Streptococcus (GBS) is a gram-positive bacteria that colonizes the gastrointestinal and genitourinary tract. It is known to cause both early onset and late onset infections in neonates.”
“In women, GBS most often is found in the vagina and rectum. This means that GBS can pass from you to your fetus during labor. This is rare.”
“While GBS may not be harmful to you, it can be very harmful to your baby. If you’re pregnant, you can pass it to your baby during labor and childbirth.”
GBS and strep
Group B Streptococcus (group B strep, GBS) is a type of bacteria often found in the urinary tract, digestive system, and reproductive tracts. The bacteria come and go from our bodies, so most people who have it don’t know that they do. GBS usually doesn’t cause health problems.
“Health problems from GBS are not common. But it can cause illness in some people, such as the elderly and those with some medical conditions.”
“some babies can become very sick from GBS. Premature babies are more likely to be infected with GBS than full-term babies because their bodies and immune systems are less developed.”
PNEUMOCOCCAL INFECTIONS
Pneumococcus or Streptococcus pneumonia (S. pneumonia)
Can cause pneumonia, sepsis, otitis media, meningitis
MOST COMMON CAUSE OF COMMUNITY ACQUIRED PENUMONIA
Pneumococcus – AKA Streptococcus pneumonia (S. pneumonia)
most common cause of nosokomial pneumonia
Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus [MRSA])
Pneumococcal infections –> who is susceptible?
Very young and very old particularly susceptible
Pneumococcus
Often follows influenza, viral respiratory infections
Risk factors include chronic disease and alcohol abuse, immunosuppression, etc.
Most common cause of bacterial meningitis in adults, infants and toddlers
Streptococcus Pneumonia
MENINGOCOCCAL INFECTIONS
Meningococci cause meningitis and septicemia
Symptoms are usually severe and can include headache, nausea, vomiting, photophobia, lethargy, rash, multiple organ failure, shock, and disseminated intravascular coagulation (DIC)
ANAEROBIC BACTERIAL INFECTIONS
Anaerobic bacteria are intolerant of oxygen, replicating at sites of potentially low oxygen such as necrotic, devascularized tissues.
anaerobic bacteria vs pus
These infections are usually suppurative, causing abscess formation and tissue necrosis.
Anaerobic Infections – E.g.
Diphtheria
Plague (www.merck.com/mmpe)
Botulism (www.merck.com/mmpe)
Cholera
Diphtheria
An acute pharyngeal or cutaneous infection caused by Corynebacterium diphtheria (C. diphtheria)
Diphtheria caused by
Corynebacterium diphtheria (C. diphtheria)
who is vaccinated? (Diphtheria)
Children are routinely vaccinated
how does diphtheria spread?
The disease spreads by contact and secretions of nose, mouth and skin lesions
Diphtheria – SSx
Symptoms include nonspecific skin infections (inflammation and necrosis of local tissues)
or pseudomembranous pharyngitis followed by myocardial and neural tissue (heart, nerve, kidney) damage
Diphtheria – Tx
Tx – antibiotics; prognosis – good
Plague
Aka Bubonic Plague or Black Death
Plague caused by which bacteria
Caused by Yersinia pestis (Y. pestis)
Plague – Sx
Symptoms are either severe pneumonia or massive lymphadenopathy with high fever often progressing to septicemia
characteristic feature – pathognomonic feature (?)
Enlarged lymph nodes called buboes
Plague via
Wild rodents carry disease
Transmitted from rodent to human by the bite of a flea vector
Human-to-human transmission occurs by inhaling droplets from infected humans
Highly contagious
Massive human pandemics rare today due to antibiotics
Botulism
Neuromuscular poisoning caused by Clostridium botulinum
Botulism can be food-borne or wound-borne
Most frequently manifests as a severe form of food poisoning
Common sources include home-canned foods, vegetables, fish, fruits, condiments, meat, dairy
Botulism – pathogenesis
Bacteria produces toxin that can interfere with release of acetylcholine at peripheral nerve endings (NMJ)
Botulism – SSx
Symptoms include nausea, vomiting, abdominal cramps and diarrhea followed by weakness and paralysis
botulinum spores (?)
“Spores are common in the environment” (?)
“botulinum spores are often found on the surfaces of fruits and vegetables and in seafood. The organism grows best under low-oxygen conditions and produces spores and toxins. The toxin is most commonly formed when food is improperly processed (canned) at home.”
about spores (botulism)
Although the spores are heat resistant, cooking kills the toxins
A spore is a cell produced by spore-forming bacteria (bacillus) to withstand extreme conditions
“It can remain viable for decades”
spore define
MICROBIOLOGY
(in bacteria) a rounded resistant form adopted by a bacterial cell in adverse conditions.
(??)
C. botulinum spores
“Spores produced by the bacteria Clostridium botulinum are heat-resistant and exist widely in the environment, and in the absence of oxygen they germinate, grow and then excrete toxins. There are 7 distinct forms of botulinum toxin, types A–G. Four of these (types A, B, E and rarely F) cause human botulism.”
Cholera – including SSx
Acute infection of the small bowel by Vibrio cholerae
Secretes a toxin that produces copious watery diarrhea
Leads to dehydration, oliguria, and collapse (shock)
circulatory collapse (?)
collapse
In medicine, collapse can refer to various forms of transient loss of consciousness such as syncope, or loss of postural muscle tone without loss of consciousness. It can also refer to: Circulatory collapse.
cholera – how infected
Infection is typically through water or seafood that is contaminated with the excrement of infected people
Esp after natural disaster when plumbing structures are affected near ocean
Cholera – Tx
Treatment – rehydration with water and electrolytes; antibiotics
SPIROCHETTE INFECTIONS
A spirochete is a slender, spiral, motile bacteria that lives off dead and decaying matter in soil and water.
E.g. Lyme disease, syphillis
Lyme disease
An infectious multisystemic disorder
Caused by Borrelia burgdorferi
Vector-borne disease carried by a deer tick
Ticks carrying the bacteria can transmit it to mammals by injecting saliva into the host.
Lyme disease – Sx
Symptoms include skin lesions and a “bull’s eye” rash (erythema migrans). The bacteria reach other organs through the blood and cause nausea, vomiting, neurological and arthritis-like symptoms.
Lyme disease – when common?
most common tick-borne disease in the states (?)
Lyme disease – Tx
Treatment - antibiotics
