Intro - Microbial Pathogens
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- Non-cellular infectious proteins
- These proteins cause the mis-folding of normal human cellular proteins into additional prions.
Def: PrPc and PrPsc
- PrPc - normal human cellular proteins that are folded into prion-like proteins
- PrPsc - New prions synthesized by the mis-folding of normal human proteins
What is transmissible subacute spongiform encephalopathy?
A fancy name for a Prion disease. Named because these diseases are transmissible and create sppongiform pathological changes in teh brain resulting fron encephalopathy.
Common subacute spongiform encephalopathies
- Creutzfelt-Jakob disease
- Mad Cow disease
- Kuru ("shivering")
Characteristics of prions
- Long incubation time
- No host immune response
- Non-inflammatory process in teh brain
- Gradual increase in severity leading to death within months of onset.
Common characteristics of viruses:
- Obligate intracellular organisms
- DNA or RNA, not both
- May have an envelope
- Attachment proteins on capsid or envelope determine specificity of infection.
- Some antivirals, but not many
What is safranin, and how is it used to determine if a bacteria is Gram + or Gram -?
safranin is a counter-stain (red dye) used in the last step of the staining process. Gram + cells will take up the crystal violet (blue) dye, gram - cells will not. However, the gram - cells will absorb the red dye.
What is the function of transpeptidase in the formation of a bacterial cell wall?
Transpeptidase is used to form a stable cross-link between amino acids on neighboring disaccharides.
Where is the enzyme transpeptidase located in a bacterial cell?
The inner cytoplasmic membrane
What enzyme does penicillin inhibit?
What is another name for penicillin binding protein?
Describe the thickness of both the Gram - and Gram + cell walls
- Gram - has a thin cell wall with simple cross-linking.
- Gram + has a very thick cell wall with extensive cross linking.
What components of an animal cytoplasmic membrane are missing from the bacterial cell cytoplasmic membrane?
Sterols and cholesterol
What are the main components of the gram + peptidoglycan cell wall layer?
- Cross-linked peptidoglycan
- Teichoic acid
What is the function of teichoic acid?
Acts as an antigenic determinant, so it is important for serologic identification of many gram-positive species.
How is the gram- cell envelope different from the gram+ in terms of different layers?
The gram negative cell envelope also contains an outer membrane (outside of the thin peptidoglycan wall).
What type of substances are located in the periplasmic space?
Proteins and enzymes
What are the components of the gram - peptidoglycan layer?
- Murein lipoprotein
- Does not have teichoic acid
Function of Murein lipoprotein
Originiates from the peptidoglycan
Common pathogen for neonatal meningitis
- Streptococcus agalactiae
- catalse -
- Facultative anaerobe
Common pathogen for child/adult meningitis (not neonatal)
- Streptococcus pneumoniae
- Catalase -
- Facultative anaerobe
The most common pathogen that causes otitis media in all age groups
- Streptococcus pneumoniae
- Catalase -
- Facultative anaerobe
Second most common pathogen that causes otitis media
- Haemophilus influenzae
- Only reservoir is man (obligate human parasite)
- Transmitted via respiratory route
Group A streptococci pyogenes is identified by the presence of:
- Sensitive to bacitracin on blood agar plates
What is the only beta-hemolytic streptococcus which is sensitive to Bacitracin?
Group A Streptococci pyogenes
Normal throat flora exhibits what type of hemolysis?
Alpha or gamma, NOT beta
What is the beta-hemolysis pattern?
Clear halos around bacterial colonies
What is the alpha hemolysis pattern?
Incomplete/partial hemolysis, with yellowish/greenish/brownish discoloration around the colony.
What is the gamma hemolysis pattern?
No hemolysis, so there is no change to the color of the medium.
Why do gram-negative bacteria appear red?
They cannot hold onto the crystal violet dye after successive washes with water, and will retain the counterstain (safranin or fuchsine).
Why can Gram-positive bacterial hold onto the crystal violet dye?
They lack the outer membrane that is found in Gram-negative bacteria.
How can you differentiate between staphylococci and streptococci on the basis of shape/arrangement?
- Both are round/spherical
- Staph - in clusters; division occurs in various directions
- Strep - in chains; division occurs in one linear direction
What is the main criterion for differentiation between Staphylococcus and Streptococcus?
- Catalase test
- Staph - catalase+
- Strep - catalase-
What is catalase?
An enzyme used by bacteria to reduce hydrogen peroxide to water and oxygen.
Which has greater pathogenicity for humans - staph aureus or staph epidermidis?
- Staph aureus is the most pathogenic
- Staph epidermidis is part of the normal flora
What is the only Staphylococci to have a positive coagulase test?
What is coagulase?
An enzyme used by S. aureus to induce coagulation and convert soluble fibrinogen into fibrin which will protect bacteria from the immune system.
What streptococci fall into the "beta-hemolytic" category?
- Group A - strep pyogenes
- Group B - strep agalactiae
What streptococci fall into the alpha or gamma hemolytic groups?
- Strep pneumoniae
- Viridans group
What does a high IgG titer mean in terms of timing of an infection?
Current or remote infection
Name the pathogen: Gram stain of pustular exudate, gram(+), cluster-forming coccus non-motile, non spore-forming, facultative anaerobe
If a chest x-ray shows a pulmonary consolidation with central cavitation, what is the likely pathogen?
Staphylococcus aureus - central cavitation is the key
What are the biological properties that directly contribute to a necrotizing pneumonia?
- Hyaluronidase to break down connective tissue and coagulase (forms fibrin around the bacteria).
- Remember, staph aureus is the only staphylococci to be coagulase+.
Where is staphylococcus aureus normally found?
It is normal flora of the nasal passages, skin and mucous membranes.
What pathogen causes folliculitis and carbuncles around hair follicles?
How does staphylococcus pneumonia normally become pathogenic?
Secondary to a viral infection (commonly influenza).
What is the hallmark of a staph. aureus infection?
Describe the protein A:IgG interaction of staphylococcus aureus
Protein A binds to the Fc site of IgG, and helps protect the organism against opsonization and phagocytosis.
How does a capsule help streptococcus pneumoniae avoid phagocytosis?
During invasion, the capsule is an essential determinant of virulence-interferes with phagocytosis by preventing complement C3b opsonization of the bacterial cells.
In the lungs, do localized infiltrates or diffuse infiltrates lead toward a diagnosis of a bacterial infection?
- Localization of infiltrates to a single lobe leads towards a bacterial infection.
- Viruses have diffuse infiltrates.
Typical pneumoniae is due to what pathogen(s)?
- Streptococcus pneumoniae - community acquired
- Staphylococcus aureus (secondary, post-viral)
What are the symptoms of typical pneumonia?
Sudden onset, chills, fever, dyspnea, productive cough with purulent sputum, rales
What pathogens cause atypical pneumonia?
Viral, uncommon in adults; mycoplasma, chlamydia, legionella
What are the symptoms associated with atypical pneumonia?
Gradual onset, nonproductive cough, headache, sore throat
What pathogen causes pneumonia in neonates?
Group B streptococcus - strep. agalactiae
What pathogen causes pneumonia in adults/elderly?
What pathogen causes hospital acquired pneumonia (nosocomial)?
Gram negative rods
What pathogen causes pneumonia in alcoholics?
- S. pneumoniae
- Klebsiella pneumoniae
What pathogen causes pneumonia in IV drug users?
What is impetigo, and what pathogen causes it?
- Impetigo - isolated pustules that rupture and become crusted.
- S. pyogenes
What streptococci pathogen causes severe and rapid tissue destruction?
Rheumatic fever occurs as a delayed antibody mediated response to what infection?
Streptococcal throat infection
How do you differentiate spit from sputum in a histological slide?
- Spit - numerous epithelial cells, few neutrophils
- Sputum - large number of neutrophils, few (if any) epithelial cells.
Which type of Nisseria affects the nervous system?
What type of Nisseria causes gonorrhea?
What are the virulence factors associated wtih Neisseria Meningitis?
- Capsule - polysaccharide capsule surrounding the bacterium, is antiphagocytic as long as there are no opsonins.
- Endotoxin - LPS, causes blood vessel destruction and sepsis (bv destruction causes petechiae).
- IgA1 protease - cleaves IgA in half
- Extracts iron from transferrin
- Pili - allows attachment to human nasopharyngeal cells and undergoes antigenic variation to avoid attack by the immune system.
Who are the high-risk groups susceptible to the pathogen Neisseria meningitdis?
- Infants aged 6 months to 2 years old
- College freshmen
- Army recruits
What causes the petechial rash associated with meningococcal disease?
The release of endotoxin from the meningococcus, causing vascular necrosis, an inflammatory reaction, and hemorrhage into the surrounding skin.
What is Fulminant meningococcemia?
Septic shock. DIC and coma may develop. Death can occur rapidly (6-8 hours)
What bacteria can cause meningitis within the first 3 months of life?
- E.coli (gram - rods)
- Group B Streptococcus (gram + cocci)
- Listeria monocytogenes (gram + rods)
What bacteria cause meningitis later in life after the maternal antibodies passively given to the fetus wane?
- Nisseria meningitidis
- Haemophilus influenzae (not as common anymore due to vaccination)
What media do Nisseria grow best on?
- Specifically, Thayer-Martin VCN media (chocolate agar with antibiotics to kill competing bacteria).
- V: vancomycin, kills gram + organisms
- C: colistin (polymyxin), kills all gram - organisms (except nisseria)
- N: Nystatin, eliminates fungi
How do you differentiate between the Nisseria species in the lab?
Neisseria meningitidis have teh ability to produce acid from maltose metabolism, while Neisseria gonorrhoeae cannot.
What antibiotic can be used to treat disseminated meningococcemia (septicemia)?
- Penicillin G or ceftriaxone
- Close contact with an infected person - treatment with rifampin or ciprofloxacin
What are the virulence factors for Neisseria Gonorrhoeae?
- Pili - Adheres to host cells. Antigenic variation protect the bacteria from our antibodies.
- Outer membrane pore porins - PorA and PorB, promote invasion into epithelial cells.
- Opa proteins - outer membrane proteins that promote adherence and invasion into epithelial cells; names as their expression results in opaque colonies.
Does chlamydia or gonorrhea infection result in a purulent urethral discharge?
Gonococcal infection of the cervix can progress to what disease?
PID ("pus in dere")
How often does gonococcal bacteremia occur in men and women?
Rarely. If this occurs, manifestations include fever, joint pains, and skin lesions.
Explain the relationship between gonococcal disease and septic arthritis.
- Acute onset of fever occurs along with pain and swelling of 1 or 2 joints. Examination of synovial fluid usually reveals increased WBCs. Gram stain and culture of the synovial fluid reveals gram - diplococci within the WBCs.
- Gonococcal arthritis is THE MOST common kind of septic arthritis in young, sexual active individuals.
Ophthalmia neonatorum results from what?
- The transmissio of Neisseria gonorrhoeae from an infected mother to a child during delivery.
- This eye infection usually occurs on the first or second day of life and can damage teh cornea, causing blindness.
- Erythromycin eye drops are given to all newborns.
What bacteria is associated with the following finding? - tiny doughnut-shaped diplocci within WBCs
What do Haemophilus influenzae, Bordetella pertussis and Legionella pneumophila have in common?
They are all acquired through the respiratory tract.
What does the word Haemophilus mean? How does this describe a property of Haemophilus influenzae?
- "Blood loving"
- Haemophilus influenzae requires a blood-containing medium for growth. Hematin found in blood is necessary for the bacterium's cytochrome system. Blood also contains NAD+ needed for metabolic activity.
True or False: Haemophilus influenzae is the etiologic agent of the flu
- Haemophilus influenzae was cultured from teh upper respiratory tracts of "flu" patients, though is not the etiologic cause of the "flu".
True or False: Haemophilus influenzae is a facultative human parasite
- This bacteria is an OBLIGATE human parasite
What type of capsule is assciated with invasive Haemophilus influenzae disease in children (meningitis, epiglottis, septic arthritis, etc.)?
Capsule b (remember, b = bad)
Explain the virulent invasiveness of nonencapsulated strains of Haemophilus influenzae.
- Non-encapsulated (nontypeable) strains lack the virulent invasiveness and can only cause local infection.
- Frequently cause otitis media in children.
Patients with COPD get frequent infections with what type of bacteria?
- Nontypeable H. influenzae
- Causes a worsening of the symptoms associated with COPD.
At what age can children develop their own antibodies to H. influenzae?
- It takes 3-5 years of H. influenzae colonization and infection for children to develop their own antibodies.
- Passively acquired antibodies are passed from the mother to child transplacentally and in breast milk, and last for about 6 months.
Haemophilus influenzae type b causes what serious infections in children?
- Meningitis - most serious infection caused by encapsulated H. influenzae type b (causes infection from 6 months - 3 yo)
- Acute epiglottitis - Rapid swelling of the epiglottis, which can obstruct the respiratory tract and esophagus.
- Septic arthritis - H. influenzae is the MOST COMMON cause of septic arthritis in infants.
What antibiotic can be used to treat diseases caused by H. influenzae?
- Cephalosporin for serious infections
- Ampicillin or amoxicillin - less serious infections (such as otitis media)
What bacteria is responsible for the STD "chancroid"?
- H. ducreyi
- Symptoms are painful genital ulcers, may have swollen inguinal lymph nodes
Differential diagnosis for the STD chancroid
- Syphilis - painless, no pus
- Herpes - systemic infections such as fever (chancroid does not produce fever)
- Lymphogranuloma verereum - painless
Gram staining of H. ducreyi should reveal what morphology?
Gram negative coccobacilli
Treatment for H. ducreyi
"Pertussis" means what?
- "violent cough"
- Bortella pertussis causes Whooping cough
Virulence factors associated with Bordatella pertussis:
- Pertuss toxin: A-B toxin; A subunit activates cell membrane bound G-proteins, increase [cAMP], activates protein kinases and other intracellular messengers. B subunit binds to target cell receptors.
- Extra cytoplasmic adenylate cyclase - adenylate cyclase "grenades" are released from the bacteria, which are then ingested by the host cells - inhibits chemotaxis and impaired generation of H2O2 and superoxide. This weakens the host defense cells' ability to phagocytose and clear the bactera.
- Filamentous hemagluttinin (FHA): This is a pili rod that extends from the surface of the bacteria and binds to ciliated epithelial cells of teh bronchi. Exotosins are then released.
- Tracheal cytotoxin: Destroys the ciliated epithelial cells, resulting in impaired clearance of bacteria, mucus, and inflammatory exudate. This toxin is responsible for the violent cough.
What toxin is responsible for the violent cough associated with Bordatella pertussis?
What bacteria is a frequent cause of chronic unexplained cough in adolescents and adults?
Where is legionella pneumophila commonly found in the environment?
- Natural and man-made water environments (aerosolized contaminated water is inhaled, resulting in infection).
- Sources: AC systems, cooling towers, whirlpools
True or False: Legionella pneumophila is a facultative intracellular parasite
True - it settles in the lower respiratory tract
How does legionella pneumophilia avoid being destroyed, if it resides inside cells?
Once phagocytosed, it prevents phagosome-lysosome fusion. This allows them to survive and replicate intracellularly.
Which bacteria can enter a low metabolic state in the environment and survive in a biofilm?
- Legionella pneumophila
- Disruption of this biofilm can result in massive release of Legionella pneumophila into the water.
How is pseudomonas aeruginosa commonly acquired?
It is a hostpital-acquired infection. Healthy people do not get infected with this bactera. However, once inside a weakened patient, the story changes.
Why is Pseudomonas aeruginosa so dangerous?
- It colonizes and infects sick, immunocompromised hospitalized patients.
- Is resistant to almost every antibiotic.
What bacteria produces a sweet grape-like scent?
- Pseudomonas aeruginosa
- Wound dressings and agar plates are often sniffed for organism identification.
What exotoxin is associated with Pseudomonas aeruginosa?
- Exotoxin A
- Same mechanism of action as Diptheria toxin (stops protein synthesis), but is not antigenically identical.
Most cystic fibrosis patients have their lungs colonized with what bacteria?
Pseudomonas aeruginosa. These patients develop a chronic pneumonia which progressively destroys their lungs.
How is osteomyelitis related to Pseudomonas aeruginosa?
Ulcers affected with this bacteria can penetrate into the bone, resulting in osteomyelitis.
What two bacteria are frequent causes of right heart valve endocarditis in IV Drug abusers?
S. aureus and Pseudomonas aeruginosa
MNEMONIC for infections caused by P. aeruginosa
- BE PSEUDo!!!
- External malignant otitis media
- Diabetic osteomyelitis
What bacteria commonly causes pneumonia in alcoholics?
"Red current jelly" sputum is associated with what bacteria?
Case: 3 week old infant develops meningitis. The culture is gram negative rods, catalase(+), oxidase(-). What is the responsible bacteria?
E. coli, gram negative and responsible for meningitis early in life (first 3 months).
Case: 53 yo patient is in the burn unit with "sweet smelling wounds" on one arm, and "blue-green wounds" on the other arm. What is the responsible bacterial agent?
Pseudomonas aeruginosa - these are classic findings with this bactera
When cultured on a media containing pyoverdin (blue pigment), what bacteria produces pyocyanin (blue pus)?
What organism is responsible for producing painful ulcers that produce pus and bleed?
Haemophilus ducreyi - the associated disease is "Chancroid"
Gram(-) pleomorphic rod-shaped bacteria that causes vaginal infections?
Vaginal disease that manifests with an unpleasant odor and milky discharge? What bacteria causes this disease?
- Bacterial vaginosis
- Gardnerella vaginalis
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