MicROBIOLOGY UNIT EXAM 3 Pt. 2 Flashcards
Normal Flora
Discuss the amount of bacteria, the ratio of types, whether they are harmful/not?
Microorganisms found on or within healthy people
Mostly bacteria & fungi - 10^2-10^3:1 anaerobes to aerobes
Healthy human body has 10 - 100 X more bacterial cells than human cells
Some found only in association with the body; others can be free-living
Majority are commensals (coexist without harm), but some are transient
Some found in a fraction of the human population
Numbers of Bacteria:
Where are the largest, average, small number of bacteria found?
Large numbers: gingival pockets, feces
(10^11 organisms/gm)
Small numbers: skin, mouth, vagina
(10^6-10^7/ml or gm)
- skin is dry and salty
even smaller numbers: stomach
(10^3-10^5/gm)
What Body Parts Are Sterile
Sterile: presence of microbes suggestive of disease/infection. Very small transient presence may be ok. • Blood • CSF • Body fluids • Deep tissues
Nearly sterile: Presence of microbes fairly normal. Transiently maybe not so bad. • Bronchi, alveloli • Esophagus • Urinary bladder • Uterus
Note: often where issues arises when bacteria get to places that are sterile –> may be suggestive of disease / infection
Roles of Normal Flora (5)
- Human nutrition and metabolism (malnourished individuals affected more by these two roles)
Vitamin K, biotin, short chain fatty acids, folate, iron absorption
Deconjugation of hormones
Breakdown of complex carbohydrates
- Protection
Previous occupancy (competition for receptors)
Competition for nutrients
Production of antimicrobial factors (bactericins, lactic acid)
- Priming of immune system
Induce secretion of IgA
Influence development of humoral immune system
Modulate local T-cell responses and cytokine profiles
Low antibody titers to normal flora are beneficial
- Destruction or formation of carcinogens
Metabolize dietary carcinogens
Can produce carcinogens via bacterial enzymes
e.g cyclamate cyclohexamuine
- Opportunistic infections - normal flora can get to the wrong place, over grow –> creates a problem now.
Periodontitis - overgrowth in gingival crevices
Aspiration pneumonia- lowered resp. defenses
poor cough reflex due to a stroke
smoking-induced paralysis of ciliary clearance mechanisms
fibronectin/Gram positives
Anaerobic abscesses - colon, pelvis, brain
Growth on catheters and stents - S. epidermidis
Urinary tract infections - E. coli
What parameters are set to studying normal flora : conditions and characteristics of those organisms that are studied.
- Conditions
Sterile animals, breeder colonies
Germ-free living conditions
- Characteristics of Germ-free animals (e.g. may be more susceptible to infection due to lack of normal flora)
Vitamins required Faster weight gain than normal animals Decreased immunoglobulins Altered histology of intestine absence of low level inflammation observed in normal animals
What Happens When the Balance of Normal Flora is Shifted? Discuss the shifted balance of Clostridium difficile and the consequences to host, and what does it produce.
Clostridium difficile: A Shifting Balance
- Clostridium difficile (strict anaerobe found in GI, and is a bacillus), Gram +, anaerobe, bacillus
- We only know 10% of the normal flora of large intestine
- Outgrowth when competition is eliminated by broad spectrum antibiotic use. A decrease of % of several bacteria but if not doing well health wise the C. difficile can outgrow other bacteria types.
- Symptoms include: fever, diarrhea, and abdominal pain → pseudomembranous colitis
- Bacterium produces 2 toxins, toxins are only toxigenic if they reach a large amount.
Pathogenesis of Colitis Polymicrobial colonization via antibiotic treatment
Polymicrobial colonization of gut (normal flora) is treated with antibiotic and leads to the overgrowth of Overgrowth of Clostridium difficile. C. difficile INCREASES the production a toxin kills epithelial lining and produces a pseudomembrane resulting in colitis
Note: C. difficile is a Gram-positive OBLIGATE anaerobe that is ~3-10% of the normal flora of the large intestine in some individuals
Define what makes up the pseudomembrane.
How can Clostridium difficile spread via consumption? How does the uprising of Clostridium occur once in the GI tract?
Pseudomembrane - essentially just dead and dieing epithelial cells, bacterial, WBCs
Clostridium difficile is spread via the fecal-oral
route. The organism is ingested as hardy spores, which can
survive for long periods in the environment and
can traverse the acidic stomach.
In the small intestine, spores germinate into the vegetative form.
In the large intestine, C difficile-associated disease can arise if the normal flora has been disrupted by antibiotic therapy
C difficile reproduces in the intestinal crypts, releasing toxins A and B, causing severe inflammation. Mucous and cellular debris are expelled, leading to the formation of pseudomembranes.
Discuss the advent of nosocomial infections and hand washing.
Discuss the environment of the skin, how should hands be washed, and 3 examples of bacteria found on skin.
5% of people admitted (1.8 million) to hospital will pick up an infection; 20,000 will die
Vigorous soaping (10-15 sec), thorough rinse
Skin is dry, and slightly acid; relatively hostile environment (not a hospitable environment)
- Staphylococcus epidermidi
- Staphylococcus aureus
- Corynebacteriae sp
Key concepts of normal flora:
Microorganisms frequently found on or within the healthy human body
- Skin, respiratory, digestive, urinary and genital tracts contain large numbers of microorganisms
- Sterile sites include blood, CSF, synovial fluid and deep tissues; the urinary bladder and uterus can be transiently occupied
- They are a common source of infection, provide immune stimulation, keep out invaders, play a role in human nutrition and metabolism, and may be a source of carcinogens
- Alterations in the balance of normal flora can have serious consequences on human health
Informational
List the different types of oxygen growth conditions for bacteria. Periodontal pocket, dental plaque, colon,
crushing injuries that lead to impaired blood supply drops does what to the oxygen supply and its affect on certain bacteria
Growth Conditions for Anaerobes Oxygen concentration in air •obligate aerobes 20% •facultative anaerobes 20% to 0% (can use or not use oxygen for growth) •aerotolerant - prefer
Why can’t obligate anaerobes grow in oxygen?
Lack enzymes that protect against oxygen toxicity
- superoxide and H2O2 are toxic:
superoxide dismutase (superoxide to hydrogen peroxide) and catalase (hydrogen peroxide to water and oxygen)
- Inability to regenerate essential sulfhydryls in enzymes
Anaerobic Metabolism: how is ATP produced
Glycolysis, Fermentation, and Kreb cycle
ATP is produced largely by anaerobic respiration
Reduced coenzymes produced are oxidized by reactions that produce H2, methane, and organic acids (butyrate, propionate, lactate). MOST anaerobe infections are fowl smelling gas.
Note: Polymicrobial environment; strict anaerobe can be helped by a facultative anaerobe e.g. by using up oxygen.
Anaerobic Infections
Characteristics
Predisposing Conditions
Characteristics
- Caused by NORMAL FLORA, which invade normally sterile regions of the body
- Characterized by mixture of species: “polymicrobial”
- Species present reflect source of infection
- Result from trauma, disease, isolated events
- Frequently are abscesses
Predisposing Conditions
• Any condition that lowers redox potential of tissues
–Growth of facultative or aerobic bacteria
–Tissue necrosis
–Impaired blood supply
Classes of Anaerobes: Rods (Bacilli) (2)
Clostridium
Bacteroides
Discuss Inta-abdominal Sepsis. What needs to be initiated and what are the causes? What cavity is prone to contamination and the acute inflammation can lead to ____?
What is the most pathogenic anaerobe. Discuss the characteristics making this guy so BAD! and where is it found?
Intra-abdominal Sepsis:
Colon wall breached via blunt trauma, ruptured bowel, penetrating wound or abdominal surgery
–Peritoneal cavity-prone to contamination
–Acute inflammation leads to localized abscesses
Bactericides fragilis: Most common pathogenic anaerobe!
- most common cause of anaerobic abdominal infections
- found below the diaphragm- resident in colon
- capsule: major virulence factor, inhibits phagocytosis
- resistant to beta-lactam antibiotics
- always mixed with other bacteria
- Gram-negative rod
Brain Abscesses: what type of bacteria are the most common perpetrators? The abscesses can arise from complications of what (4)? What are the symptoms (9)
Brain Abscesses Most are due to anaerobes Complications of – otitis media (middle ear) – sinusitis – sepsis from tooth extraction – endocarditis
Symptoms
low grade fever, headaches, drowsiness, confusion, nausea and vomiting, motor, sensory or speech disorders
Note: the area that normally contained the bacteria was not dangerous but once it gets access to sterile sites e.g. the blood of CNS (game over). Formation of abscesses helps to barricade these guys from oxygen.
Anaerobic Infections: Head, Neck, Mouth
Discuss Acute necrotizing ulcerating gingivitis (ANUG). What occurs?
Acute necrotizing ulcerating gingivitis (ANUG): E.g. by improper brushing
- Normal flora in gingival sulcus, tonsillar pouches, dental plaque can progress to Vincent’s angina: ulcerative infection of oral and throat mucosa. Fusobacteria and spirochetes in necrotic lesions; may spread to the deep tissues and cause tissue destruction.
- Fusobacterium spp., Gram-negative rod, Spindle shaped (fusoform)
- Treponema denticola, Gram-negative, spirochete
**Other Examples of Anaerobic Infections: The anaerobes can be gram +/- ***
- Cutaneous: 1. Necrotizing fasciitis (gas producing anaerobe vs non gas producing aerobe/fac. anaerobe), 2. Post-surgical cellulitis. 3. Infections of prosthetic devices (heart valves, artificial joints, catheters, shunts)
- Pulmonary: Mixed infection from pleural empyema (pus forming): both Gram + and - bacteria. Death of the lung- cell lining can lead to the anaerobic infection. Causes: malignancy in lung or elsewhere, oral disease or tooth extraction, altered consciousness (from alcoholism, anesthesia, narcotics, etc.), foreign body in the lung, immunosuppressive therapy.
Note: pulmonary infections of anaerobes are largely overlooked because of difficulty in obtaining diagnostic specimens-sputum is not suitable and blood cultures are rarely positive.
Diagnosis of Anaerobic Infections
Clinical Findings (6)
Lab Findings (4)
Clinical Findings –Foul-smelling discharge –Necrotic tissue –Gas in tissue –Infection associated with malignancy –Black discoloration of exudates –Predisposing conditions (e.g., septic abortion, G.I. surgery)
Lab Findings –Unique morphology on Gram stain –Failure to grow aerobically –Growth in anaerobic zone of liquid medium –Gas, foul odor in specimen on culture
Treatment of Anaerobic Infections
Discuss options (2).
- Surgical drainage often important
- Antibiotics
–Penicillin G is good for control of anaerobes other than Bacteroides—infections below the waist almost always involve Bacteroides
–Clindamycin is drug of choice, but does not cross blood-brain barrier
–Chloramphenicol crosses barrier, but is toxic
–Metronidazole (flagyl) also good for anaerobes
Key Concepts-Anaerobes
- Most pathogenic anaerobes are in the genera Bacteroides
- Obligate anaerobes lack superoxide dismutase and catalase and are sensitive to the presence of hydrogen peroxide and superoxide
- Anaerobes use compounds other than oxygen as final electron acceptors
- Anaerobic infections are usually caused by mixed infections of facultative and strict anaerobes that are part of the normal flora and gain access to tissue sites that are normally sterile
- Specimen collection and transport are critical for accurate diagnosis and treatment
Informational
Tetracycline prevent _______. Is derived from ______. Comment of structure and as a result has certain physical/chemical qualities. MOA. What contributes to its partial selective toxicity and has a greater affinity for host or non-host; why can we infer this?
prevent access of new amino acyl tRNA to mRNA-ribosome complex.
Derived from Streptomycin aureofaciens
•Composed of 4 fused six-membered unsaturated rings
- amphipathic, have color and respond to UV light
Mechanism of Action
- Inhibit protein synthesis by binding to 30s subunit and blocking access of the amino acyl-t-RNA to mRNA-ribosome complex at the acceptor site
- Active uptake mechanisms by susceptible organisms imparts some selective toxicity
- Greater affinity of non-host ribosomes since intracellular rickettsiae and chlamydiae are treatable.
Note: Rickettsia is a genus of nonmotile, Gram-negative, nonspore-forming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long), or thread-like (10 μm long).
Tetracycline Spectrum
Similar spectrum to what? Type of agent. Treatment can be for (7) examples.
- Broad spectrum because both bacteria and Rickettsia are susceptible
- Bacteriostatic
- Similar spectrum to erythromycin particularly intracellular organisms such as Mycoplasma pneumoniae, Chlamydia spp, Legionella spp, Ureaplasma, Rickettsiae
- Treatment of acne vulgaris and rosacea. Chlamydial infections, mycoplasma pneumonia, lyme disease, rocky mountain spotted fever (Rickettsiae), cholera.
Note: Tetracycline is rather limited and many strains are now resistant.
Tetracycline Resistance: What is the most important means of resistance, discuss the spread of resistance, and two other means of resistance.
- Resistance is widespread, transposable and commonly permanent because exists as multi-drug resistance gene cassettes
- Most important is active efflux
- Enzymatic inactivation
- Decreased affinity of target
Pharmacokinetics of Tetracycline
Bioavailability range, route, avoid, binds to tissues undergoing ____, penetrates _____ well,
•Orally active: range from 30% bioavailability for chlortetracycline to 95% for doxycycline.
- Dairy products, Mg++, Ca++and Al+++ions chelate tetracyclines and produce a non-absorbable complex
- Bound to tissues undergoing calcification (teeth and bones
- Penetrate tissues well –high concentrations in liver and kidney
- Cross the placenta
- Minocycline has high concentration in tears & saliva and can be used to treat meningococcal carrier state (not active)
Note: Effect of milk on tetracycline absorption is more inhibitory than Al(OH3) “antacid”
Host elimination of Tetracycline
How is it eliminated, what modification does it undergo, and what Rx plays an exception to elimination of Tetracyclines?
- Metabolized to varying extents, especially glucuronide formation which is very polar and ends up in kidney and biliary excretion.
- All undergo enterohepatic circulation except for doxycycline glucuronide
- Renal excretion is important for all except doxycycline which is excreted in the feces
Adverse Effects of Tetracycline
- Irritation of gastric mucosa –GI distress
- Deposition in bone and primary dentition (permanent teeth) during calcification (contraindicated in children sunburn
- Vestibular disturbance with minocycline
- Azotemia, Fanconi-like syndrome with outdated preparations
Drug Interactions of Tetracycline (3)
- Antacids
- Increased digoxin toxicity in 10% of patients
- Increased warfarin activity due in part to decreased intestinal flora which produce vitamin K
Note: TETRACYCLINE limits the growth of normal flora (organisms) that normally metabolize digoxin. Thus need to change the dose of digoxin e.g. decrease the dose b/c more digoxin will be absorbed than normally.
Avoid use of Chloramphenicols because of increased risk of toxicities due to what functional group?
- Antibacterial action
- Resistance (2)
- Spectrum (4)
- greater risk of toxicities with nitro group on a benzene ring.
- Antibacterial action: Binds to 50s to a site very similar to
to macrolides and clindamycin- interfering with both peptidyl transferase (make peptide bond) and translocation. - Resistance:
–Enzymatic conversion to an inactive product by bacteria (acetyl CoA transferase)
–Decreased affinity
3. Spectrum –H. influenzae –Acute typhoid fever –Rickettsial infections (Rocky Mountain Spotted fever) –Anaerobic infections
Chloramphenicol Pharmacokinetics
route distribution specialty penetration metabolism excretion
Chloramphenicol Blood Levels in Two Different Age-groups of Children- compare rate of excretion
Chloramphenicol Pharmacokinetics:
- Orally active; parenteral preparations also
- Well distributed; even enters CNS in absence of inflammation
- Crosses placenta
- Extensive metabolism by host. Ultimate product is a glucuronide
- Excreted in urine
Chloramphenicol Blood Levels in Two Different Age-groups of Children:
3-5 days old vs 1-5 year olds: Older children have a much higher rate of excretion.
Define glucuronide. Like it to the jaundice of neonates.
A glucuronide, also known as glucuronoside, is any substance produced by linking glucuronic acid to another substance via a glycosidic bond.
This links back to the competition aspect of HbF bursting and heme is now competing to get glucuronosylated.
Adverse Effects of Chloramphenicol (3)
What are the cautions when giving the Rx?
•Hematological
–Hemolytic anemia in G-6-P DH deficiency
–Reversible anemia, leukopenia and thrombocytopenia –dose related; occurs during therapy
–Idiosyncratic (dependent on the number of COURSES of CHLORAMPHENICOL Rx Treatments!!!) aplastic anemia –probably allergic in origin
•Gray baby syndrome - at high enough doses will affect host mitochondria of these growing infants and thus cannot use oxygen —> gray color. Fail to thrive.
Adjust dose to weight as opposed to surface area.
•Drug interactions because of CYP 450 inhibition: caution in patients on warfarin, phenytoin, etc.
Note of caution: Easier to reverse adverse effects of penicilin compared to chloramphenicol –> aplastic anemia. Thus more cautious when administer this Rx.
Therapeutic Uses of Chloramphenicol (4)
- Anaerobic infections due to Bacteroides fragilis
- Typhoid fever and H. influenzaemeningitis when first line therapy fails or cannot be employed
- Pneumococcal or meningococcal meningitis in penicillin-allergic patients
- Rickettsial diseases as a substitute for tetracycline( Sensitivity, ESRD, pregnancy, particularly children
MOA of Aminoglycosides and downstream effects of that. What type of agent and effective against what bacteria? How does it get into bacterial cell and why?
Rx is effective against Gram negative aerobes and are bacteriocidal.
- Binding to 30s subunit prevents initiation of protein synthesis
- Blocks further translation & causes premature termination
- Causes misreading of mRNA codon by binding to the 3rd codon.
- Entry across bacterial cell membrane occurs via an active transport system that REQUIRES OXYGEN because Rx is polar.
Note: Aminglycosides are bacteriocidal as opposed to most of the protein synthesis inhibitors that are bacteriostatic.
Mechanisms of Resistance of Aminoglycosides (3)
- Absence of the oxygen-dependent transport system (ACTIVE TRANSPORT TO GET AMINOGLYCOSIDE INSIDE) –obligatory anaerobes are resistant
- Decreased affinity at the 30s subunit binding site
- Plasmid associated inactivating enzymes that can acetylate, adenylate or phosphorylate the aminoglycoside
Comparison of Resistance Enzyme Activity on Kanamycin vs. Amikacin
AC = acetylation AD = adenylation P = phosphorylation Bar = bacterial plasmid enzymes will be likely to alter the fxnal group and render it ineffective.
Natural Resistance!
Amikacin - Most of the fxnal groups are resistant to the modification by the bacterial plasmid enzymes as opposed to Kanamycin- more sensitive to modification.
Amikacin due to the resistance of being modified by plasmid enzymes DOES NOT lend itself to cross resistance by all members of the bacterial class. CROSS RESISTANCE DOES NOT OCCUR!
E.g. gave a pt Kanamycin and they became resistant during Tx. The bacteria will not have a cross resistance to Amikacin thus it will be effective.
Spectrum of Activity of Aminoglycoside
Streptomycin
Gentamicin, Tobramycin, Amikacin
What is a frequent combination with Aminogylcosides?
•Streptomycin –Mycobacterium tuberculosis
•Gentamicin, tobramycin, amikacin
–Gram negative aerobic bacteria Pseudomonas aeruginosa
•NOTE: aminoglycosides are frequently combined with ß-lactams to treat serious, life-threatening infections because of synergy between the groups.
Aminoglycoside spectrum of action
Tularemia
Infections due to Enterococci
Infections due to Pseudomonas Aeruginosa
Pharmacokinetics of Aminoglycoside
Route Dosing interval Distribution Specialty penetration What organs does it get concentrated in? Elimination What else is required when administering this drug over a week or so?
- Must be given parenterally
- Once a day dosing because exhibit dose-dependent killing
•Distribution -extracellular fluid; do not enter CSF
- Dissolve well but don’t cross membranes well. Are highly polar
- Cross the placenta
- Concentrated in renal cortex and endolymph (vestibular and cochlear apparatus.)
- Dependent on glomerular filtration (as opposed to beta-lactams which are also actively secreted into kidney tubules) for elimination
- Therapeutic monitoring (because have a narrow therapeutic range thus have to routinely monitored esp. when getting infusion over a week or so.)
Aminoglycoside
Once a day vs 3 times a day dosing
Done 3 times a day why?
Killing of bacteria vs adverse effects (dose dependent/time dependent)
What are the advantages of one over the other?
3 times a day because of the dependency of glomerular filtration rate.
Once a day give the same of cumulative dose with the 3 times a day. We get 50 % of the time (12 hrs) exposed to concentrations of adverse effects. With 3 times a day (18 hrs) exposed to concentration of adverse effects.
Killing of bacteria - dose dependent (more the dose the more the killing)
Adverse effects - longer the time exposed to drug the increase in severity of adverse effects.
Note: concentrations of adverse effects are above the threshold - - - -. No sig difference between the adverse effects of once a day vs 3 times a day and clinical difference not really apparent. Cheaper and less likely to miss a dose with once a day administration.
Patient factors affecting dosing of aminoglycosides (5)
Measurement of plasma creatinine is a quick way to measure GFR.
Patient factors affecting dosing of aminoglycosides
- Age - increase in age proportional to decrease of GFR. Starting at age 50 every decade decrease of about 15% GFR
- Obesity - Not as much fluid in higher fat content thus will end up with higher [ ] in extracellular fluid
- Renal function - This goes for any antibiotic…. best way is to change length of time between time if there is impaired GFR.
- Pregnancy
- Hepatic function- this factor does not have a significant role for amino glycoside administration
- If there is muscle wasting (as in the elderly) you have normal creatinine levels but decreased GFR
Toxicity (4) related to Aminoglycosides
- Ototoxicity - Either vestibular or cochlear function. Cause loss of hearing or be dizzy.
- Fetal auditory toxicity - reason why it is not given during pregnancy.
- Nephrotoxicity
- Neuromuscular paralysis
Establishment of Infection (7)
Encounter
Entry
Spread - Agent spreads from site of entry; this step doesn’t always have to occur. Can remain localized.
Multiplication/Colonization
Damage - Agent or host response causes damage
Outcome - Agent wins, host wins, coexistence
Note: Defenses at each step!!!
First Encounters of bacteria
Prebirth
Birth
Types of Encounter
Define colonization, carrier, and resolution of colonization
Prebirth - uterine environment normally sterile, but congenital infections possible (transplacental)
- E.g. rubella, syphilis, HIV, cytomegalovirus
Birth - microorganisms in vaginal canal (mother’s antibodies sometimes protect); skin contact
Types of Encounter:
- Exogenous- some pathogens never establish normal flora
agents in the environment - food, insect bites, etc.
exchange of bodily fluids - sneezing, sex
- Endogenous
agents in or on the body
normal flora in the wrong place
Colonization- implies that the patient has a sufficiently high concentration of organisms at a site that they can be detected, yet the organism is causing no signs or symptoms.
A carrier is a person who is colonized with an organism and may transmit the organism to other people. Colonization can persist for days to years, with resolution influenced by the immune response to the organism, competition at the site from other organisms and, sometimes, use of antimicrobials.
Establishment of Infection
Entry (4)
Without crossing epithelial barriers • Inhalation via aerosol droplets, dust • Ingestion of food or water • No entry or penetration into tissues - toxins (cholera, whooping cough, cystitis)
Crossing epithelial barriers
• Pass through epithelia directly - bind to receptors
• Insect bite or break in skin
• Burrowing worms
Organ transplants
• Kidney transplants (CMV)
Blood transfusions
• HIV, Hepatitis B Virus
Note: with infants and children a normal floral lacks thus a colonization that normally would not be an infection to adults may be so along with the toxification.
Spread & Multiplication with the establishment of an Infection
Spread - Ways to spread (3)
Factors influencing Multiplication
Spread
- Lateral propagation (to contiguous tissues)- may be done so by enzymes that can break down muscle, tissue and lead to dissemination
- Dissemination to distant sites
- Microbial motility- e.g. vibrio cholera, bacteria in liquid areas.
**Enzyme action • hydrolases, elastases • collagenases, proteases • hyaluronidases, DNases • keratinases
Multiplication
Depends on environment
Incubation period
- Early defenses, Growth
Nutrition
Antimicrobial substances
Iron limitation
Temperature optimum
pH
- Stomach acid
Population density
- quorum sensing: colony will get a sense of their density and with the favorable conditions decide how much more to grow. can occur within a single bacterial species as well as between disparate species, and can regulate a host of different processes, essentially serving as a simple communication network.
Adherence
Possible Damage from the point of Infection (4)
Mechanical obstruction- rare for bacteria, more common for parasites to do this. E.g the parasite that cause elephantiasis. Hookworms or helminths are large enough to block normal function
Cell death
- cytolytic toxins, activation of cell-killing WBCs
Toxins botulinum, tetanus
Inflammation and immunoprotective mechanisms
Ag-Ab complexes (glomerulonephritis)
Cell-mediated immunity-activation of macrophages (TB)
Possible Outcome due to Infection (3)
Depends on complicated interplay between human host and microbe
Agent wins and host dies
Host wins and disease is cleared
Coexistence as with the normal flora
Steps in Ingestion and Killing by Phagocytes
Opsonization of bacteria
engulfment by PMN/macrophage
phagosome fuses with lysosomes ==> phagolysosome
Exocytosis of bacterial fragments
What are ways to avoid phagocytosis and can an example of a bacterium that does so?
- Capsule: Streptococcus pneumonia
- Important Surface Components: protein A performs an extremely tight interaction to IgG thus blocks the Fc portion and now not available for Fc receptor to bind.
- Staphylococcus aureus: protein A binds Fc portion of IgG molecules; prevents opsonization
- Streptococcus pyogenes: M protein protects from phagocytosis - Killing Phagocytes
Bacterial enzymes that lyse phagocytes
Streptococcus pyogenes—> Streptolysin Clostridium perfringens —> Alpha-toxin
During phagocytosis how can bacteria avoid from being killed (3)
- Escape the phagosome before fusion of lysosome
Rickettsia Trypanosoma Shigella Listeria Francisella
- Tolerance of being inside phagolysosome- a. Catalase, superoxide dismutase detoxify oxygen intermediates
b. Some cell walls are refractory to destruction by lysosomal proteases
Coxiella Ehrlichia Leishmania Mycobacterium leprae Salmonella typhi
- Avoidance can remain in phagosome for a period of time. Can block the fusion with lysosome and may continue to divide although slowly.
Chlamydia
Mycobacterium tb
Legionella Brucella
Toxoplasma
Intracellular Growth: what does that allow the bacteria to do?
Intracellular Growth- permits bacteria to use the cell as a place to grow and hide from the immune responses. Intracellular replication gives cells a place to grow and protects from antibodies of the immune system.
Mycobacterium sp. Rickettsiae Francisellae Brucellae Chlamydiae Listeria monocytogenes Salmonella typhi Shigella dysenteriae Yersinia pestis Legionella pneumophila
Antigenic variation: How does this play a role with the immune response. Give two examples.
Immune response must elicit new attack upon antigenic variation. E.g when the bacteria count is low as a result of an effective immune response the bacteria can undergo antigenic variation
Neisseria gonorrheae pilin protein
Trypanosoma surface glycoproteins
Borrelia (Lyme disease), Neisseria (gonorrhea), Plasmodia (malaria)Polysaccharide capsule buries C3b component of complement and prevents opsonization
List virulence factors (8)
Capsules/slime layers Pili/Adhesins Biofilm formation Invasins Type III secretion systems sIgA proteases Fe binding proteins Toxins
Capsules: List its varied functions (4)
Capsules: Most common bacterial mechanism to avoid phagocytosis
- Prevent phagocytosis – prevent binding of opsonins to bacteria AND interaction between opsonins and their phagocyte receptors on Adhesion of phagocytes and binding of opsonins
- Complement-mediated bacterial cell lysis
- Enhance adhesion to the host cell
- Prevent bacterial desiccation - e.g. coughing up a bacterium onto a surface it may survive longer.
Adherence Factors
Adhesins are advantageous for what reason? Give some examples (3).
Adhesins:
- Protein or carbohydrate molecules bind tightly to sugars on target tissue
- Prevent washing away - bladder, intestine, blood vessels
1. Pili
2. Afimbrial adhesins- Afimbrial adhesins refer to proteins that serve as adherence factors, but do not form the long, polymeric fimbrial structure. Afimbrial adhesins generally mediate more intimate contact with the host cell that occurs over a shorter range than with fimbriae.
3. Techoic acids from the gram positive bacteria
Biofilms: what are its advantages?
Bacterial adaptation that facilitates colonization
•a sticky web of polysaccharides (slime) anchors cells
e.g. dental plaque, indwelling catheters, valves
•protects from host defenses and antibiotics
Invasion Factors
Define invasins. Discuss which bacteria have invasins and the mechanism of action. How are invasions present within the genome of bacteria? How are invasions regulated?
Invasins - Proteins that help bacteria cross mucosal membranes
Shigella, Salmonella, Yersinia - invasin protein allows binding of bacteria to M cells of colon and encourage uptake, or go from one cell to another
Genes for invasion machinery encoded on a Pathogenicity Island
PAI - very large, unstable chromosomal regions
Sets of genes encoding numerous virulence factors
- Regulated by a single stimulus
Mobile genetic element transferrable as a unit to other bacteria (TGEs)
Type III Secretion Systems - what is the advantage to this?
Type III Secretion Systems- more effective to get enzymes/toxins directly into a host cell via connection than just secreting enzymes/toxins extracellularly.
Export system - delivers proteins through both inner and outer membranes of Gram negative pathogens
Secretory IgA Proteases: Describe this defense mechanism and what is it against.
Mucin: proteoglycan mucin protects mucosal cells, contains secretory IgA
Host defense - sIgA binds to glycoprotein in mucin layer and traps bacteria; prevents bacteria from reaching mucosa
Bacterial offense - sIgA protease -cleaves hinge region (much more likely to cause bacterial infection in mucosal regions) of sIgA, releasing bacteria
Iron Acquisition
What’s so important about Iron and how does host respond in defense and how does bacteria counteract the host response?
Iron is critical for humans and most pathogens - required for cytochromes, cofactor for enzymes, etc
- Iron limitation restricts bacterial growth
- Low free [Fe] in humans
***To compete with lactoferrin/transferrin for iron, bacteria contain Siderophores- Fe chelators
Define Toxins.
What cell envelope components may be toxic? Describe the effects on the host.
Define exotoxins. Describe their effects on the host and what it targets.
Toxins are bacterial products that directly harm tissue or trigger destructive biologic activities
Cell envelope components: Endotoxin, teichoic acid, etc.
Alarm signals to immune system –>
release acute phase cytokines, fever, vasodilation, shock!
Exotoxins: cytolytic enzymes/hemolysins or receptor binding proteins
- Damage cell membranes (phospholipases or lecithinases)
- Pore forming proteins
- Targets: ribosomes, transport mechanisms, intracellular signaling
Note : Exotoxins are more limited to certain species or even only certain subspecies (strains)
Range of Choices
Different genera/species/subspecies of bacteria can have a different range of attacks.
Discuss Corynebacterium diphtheria, Staphylococcus aureus, Escherichia coli
Corynebacterium diphtheria- non invasive, toxin does the damage.
- Single virulence factor: Diphtheria toxin
Staphylococcus aureus
- Many virulence factors: adhesins, degradative enzymes, toxins, catalase, coagulase
Escherichia coli
- Different strains of one species have different virulence factors: urinary tract infections v. diarrhea v. meningitis
Define symbiotic and commensal relationship. Microbe causing disease is dependent on two factors
Cooperation between microorganisms and humans is the rule, disease is the exception. The majority of these relationships are symbiotic (mutual benefit)
Commensal (co-existence, no harm).
1) the virulence of the microorganism
2) the response of the host.
Infection in the microbiologic sense is not synonymous with infectious disease in the clinical sense.
What is defining of an infectious disease?
Infectious disease occurs when there is tissue injury (leading to inflammation) or altered host physiology.
Typically, most bacterial diseases are acute clinical diseases which are characterized by an acute inflammatory reaction regardless of the organ involved
Discuss the reactions and what molecules are involved.
What are some exceptions?
Acute inflammation: redness, swelling, increase of temperature
- Polymorphonuclear leukocytes (aka PMNs, neutrophils) (e.g., acute pneumococcal or Klebsiella pneumonitis, acute bacterial colitis, acute staphylococcal osteomyelitis, Acute laryngotracheitis).
a. Pyogenic (suppuration) when there is significant necrosis —> abscesses (pyogenic cocci, some gram (-) bacilli) —————> furuncles (Staph.) or —-> cellulitis (Strep.) or necrotizing pneumonia
b. Adhesins, fimbriae, bacterial peptides/proteins, lipopolysaccharides (LPS), cytokines, C5a. - Exceptions: clinically acute disease (e.g.Typhoid fever, S. typhosa) but with a mononuclear cell response associated with reactive hyperplasia of the intestinal and systemic lymphoid cell population; Bordetella pertussis.
Granulomatous: certain bacteria (many slow-growing organisms) elicit a chronic inflammatory, cell-mediated immune response, usually associated with a clinically chronic disease that is granulomatous in character and includes: (4)
-Generality about a certain bacteria (location) that causes chronic inflammatory (immune reactions)
Chronic- lymphocytes, neutrophiles, monocytes
- Tuberculosis: necrotizing (caseating) granulomata
- Brucellosis and tuberculoid type Leprosy: non-necrotizing granulomata
- Plasma cell infiltrates and granulomata: Treponema pallidum (syphilis)
- Chronic, non-granulomatous but with aggregation of macrophages: Mycobacterium avium intracellulare (MAC), lepromatoid Leprosy.
C. As a generality, intracellular bacteria induce chronic inflammatory (immune) reactions.
Note: Mixed acute and chronic inflammation can exist, and Cytologic changes +/- inflammation (viruses are responsible for this one)
Pyogenic cocci
Which is the main perpetrator type and give 3 examples that fall under this type and their associated host harm.
mainly Gram + cocci that evoke a neutrophilic exudation and account for most of the suppurative lesions in medical practice including:
- Staphylococcus aureus- furuncle/carbuncle, bronchopneumonia, impetigo, osteomyelitis, toxic shock
- Streptococcus pyogenes and pneumoniae: pharyngitis,URTI, lobar and bronchopneumonia; scarlet fever, cellulitis, necrotizing fasciitis, glomerulonephritis, rheumatic fever
- Neisseria (Gram -) -meningitis, gonorrhea, arthritis
Pyogenic bacilli
Which is the main perpetrator type and give 3 examples that fall under this type and their associated host harm.
mainly Gram-negative bacilli
- E.coli (UTI, Hemolytic-Uremic Syndrome, severe colitis/peritonitis), pyelonephritis.
- Klebsiella pneumoniae (bronchopneumonia with abscess and pleural involvement)
- Pseudomonas aeruginosa (burns): bronchopneumonia.
Childhood infections
Give 3 examples of prevalent childhood infections
- Hemophilus influenzae type B: encapsulated, particularly young children affected, (meningitis, bronchiolitis, epiglottis)
- Bordetella pertussis (whooping cough)
- Cornyebacterium diphtheriae: (exotoxin local necrosis- e.g. laryngeal pseudomembrane formation - and systemic effects - e.g. myocardial necrosis)
Enteropathogenic bacteria cause (3) and examples of the species.
Enteropathogenic bacteria- cause GI disturbances by toxins (Vibrio cholerae, Clostridium difficile, E.coli O157:H7), invasion (Salmonella typhi), or both (dysentery-Shigella sp.)
Gram pos rods (toxin producers)
Discuss two manner of which host is exposed to toxins and their ultimate effects on host.
Gram pos rods (toxin producers)
- Clostridium tetani and C. perfringens (spore contamination of wounds —> toxin)
- C. botulinum (ingest preformed toxin), Septic clostridial infection. Cause rapid and severe tissue damage, sometimes without inflammation, that frequently —> death.
Spirochetes
- Treponema pallidum: Syphilis: primary (chancre most commonly on either penis or vulva), secondary (rash, condyloma lata), tertiary (gumma, CNS, CV, congenital). Plasma cells are characteristic and distinctive inflammatory cell reaction. Occasionally also granulomas in secondary and tertiary stages.
- Borrelia burgdorferi-Lyme Disease-primary, secondary, tertiary. Chronic inflammatory reactions, may lead to fibrosis and tissue destruction.
Chlamydia (C. trachomatis and psittaci)
- Intracellular bacteria
- More common than Neisseria as a sexually transmitted disease organism causing cervicitis, pelvic inflammatory disease, urethritis, epididymitis. In impoverished countries a leading cause of blindness (trachoma). Chronic inflammatory reactions, sometimes with immunoblast clusters. C. psittaci: pneumonia.
- More recently are being implicated in pathogenesis of atherosclerosis! (persistent low grade intravascular infections mild inflammation fibrosis)
Rickettsia (transmitted by arthropod vectors) (includes Ehrlichiosis)
Where can it be found, what kind of host reaction does it cause, and what may it be associated with?
- Intracellular bacteria
- Cause chronic inflammatory reactions
- Some rickettsia are associated with vasculitis due to injury to endothelial cells.
Mycoplasma (atypical pneumonia)
Briefly list where it can be found and what type of host response does it cause?
- Free-living bacteria
2. Cause inflammatory reactions
What’s the Tx against some bacteria have a large influential tropism (peculiar affinity for certain tissue types).
Tx: adhesin molecules against the surface molecules of bacteria that interact with host surface.
Define Abscess.
area of millions of neutrophils and liquefied tissue debris. The lysosome connects and secretes into not completely closed phagosome. Now all these enzymes get into host tissues —> abscess.
Burn victim are prone to what type of infection?
Pseudomonas infection which leads to pus (BLUE/GREEN). This leaves behind a cavity from the suppurative inflammation.
Necrotizing Bronchopneumonia
Septicemic abscesses in kidney. What is the hallmark of septicemia?
Pus has destroyed the wall of the bronchiole and thus the acute inflammatory because to spread to peribronchial tissue.
Septicemic abscesses in kidney break down tissue, disseminate –> metastatic abscesses.
- multiple foci of infection in an organ is indicative of septicemia
Acute endocarditis
Bacteria disseminate and leads to acute cardiac insufficiency where pus formed in the valve and left a huge gaping hole.
spreading infections (cellulitis) look for what as culprit?
Seeing a spreading inflammatory process will see diffuse swelling “Cellulitis” —> most likely Streptococcal
Bordetella pneumonia leads to what type of inflammatory state?
Bordetella pneumonia (mononuclear and interstitial) : intracellular in nature —> chronic inflammatory
Mononuclear cells respond to the intracellular bacteria.
TB describe how granulomas are formed? What’s a Ghon complex?
A necrotizing granuloma with giant cells. Survive phagocyte, outlive phagocyte, induction of CMI. CMI doesn’t kill TB thus becomes granuloma.
Ghon complex (Primary Tuberculosis)
Secondary Tuberculosis (cavitary)
Occurs in upper apical lobe.
Mycobacterial infections - immunodeficiency pt exposed to microbe. Similar to how lepromatous leprosy looks like.
Informational
Intracellular organism to cause non-necrotizing granulomas
Brucella hepatitis (non-necrotizing granulomas)
influx of B cells that mature into plasma cells : a distinct mononuclear response.
Plasmacellular inflammation (Syphilis)
Food poisoning is usually caused how and by what bacteria genus?
Staphylococcal infections
- usually caused by the ingestion of the toxin present in the food
Types of Exotoxins
Discuss the three types
Three basic types:
1.A-B Type (A is enzymatic, B is binding) - B brings the A subunit to the cell.
•Simple (A & B subunits, connected by S-S)
•Complex (A & 5B subunits)
2.Membrane disrupting
•Passive channel - membrane complex protein that may erupt holes into the membrane.
•Phospholipase - cleaves the phosphate head groups off the outer leaflet of the membrane
- Superantigens (mimic MHC ClassII/CD4+TH interaction)
- much more likely to produce the various cytokines.
Describe the cascade of AB-type extoxins produced by bacterium
Bacterium adheres to mucosal surface. Bacterium synthesizes toxinogen. Cleavage –> active toxin. AB subunits held together by disulfide bonds. Toxin moves to target cell. B binds to cell surface receptor. Subunit A enters by: 1. Endocytosis, or 2. Translocation. Inside subunit A catalyzes enzymatic activity and exert toxic effects.
Note: bacterium does not get into cell, the toxin produced is what transverses the cell and get into blood. In most cases the bacterium does not even cross the epithelial layer.
A Subunit of A-B Type Exotoxins
Discuss two features of A subunit.
- Some (not all) have NADase activity
- NADase effects:
a. stimulate adenylate cyclase (Increase cAMP)
b. inactivate elongation factor 2 (block translation) ADP ribosylation
Note: NADase an enzyme that catalyes hydrolysis of NAD+ to nicotinamide and adenosine diphosphoribose.
How does an exotoxin accomplish membrane disruption (2) and what is the result?
The exotoxin creates a non selective pore. H20 rushes in and cell swell and lysis
The exotoxin is a phospholipase cleaving the phospho groups of the outer leaflet —-> unstable membrane
Compare the effects of antigen and super antigen. Give ratios of activation.
Antigen presenting cell with antigen stimulates T cells receptors 1 in 10^4 resulting in IL-2, T cell proliferation, T- B interaction, B cell proliferation, and Antibody production
Superantigens:
- Many (1 in 5) T-cells stimulated!
- Excess IL-1, IL-2, IL-6, TNF-a, IFN-g —> SHOCK!
Corynebacterium diphtheria. It is common in the US?
Provide describing features, where it colonizes, clinical effects, how it’s selected for in culture, and particular effect with children.
Not common because of vaccine.
K+ Tellurite selection- Potassium tellurite (K2TeO3) is used together with agar as part of a selective medium for growth of some bacteria (Clauberg medium). Corynebacteria and some other species reduce TeO32− to elemental Te, which stains the bacteria black. (SMALL, BLACK COLONIES)
- Gm pos, clubbed ends, pleomorphic bacillus
- Aerobic
- Colonizes throat & nasopharynx, non invasive, thick, grey mucoid coat (pseudomembrane) that leaves bloody patches when removed
- Clinical effects - heart and peripheral nerves
Note : pseudomembrane formation particularly in the young covers the throat —-> suffocation (Death)
Diphtheria ExoToxin (top):
How is toxin expression regulate? What are it’s effects, what does it bind to, and what kind of toxin is it?
- Iron regulated (low iron = high tox expression); DtxR repressor
- Binds to heparin-binding EGF precursor (most cells of body)
- ADP-ribosylates Elongation Factor-2 (EF2)
- Simple A-B
Note: Toxin is phage encoded; transcription is repressed by iron + DtxR repressor
Treatment and Prevention of Corynebacterium diphtheriae (2). What causes the deaths of one of the Txs?
- Antitoxin & antibiotics (Penicillin or erythromycin)
- “D” of DPT vaccine (toxin)
2004 - 5,000 deaths worldwide, largely due to incomplete vaccination
Bordetella pertussis
- type of bacteria
- growth
- disease characteristics
- Can it be eradicated?
- Small, Gm negative coccobacillus
- Fastidious, slow growing
- Colonizes region between airway and lungs
- Disease:
- cold symptoms, with paroxysmal coughing interrupted by whooping
- extremely contagious, significant cause of morbidity worldwide (39,000,000 cases & 300,000 deaths!)
- low incidence in USA (vaccination – P of DPT)
- no known other carrier. Thus it is possible to eradicate. Vaccine is against the protein extract of pertussis. Long term death due to pneumonia. It can be invasive –> becomes intracellular (e.g. in macrophages)
Note: may produce a fever but difficult to differentiate from a cold.
Bordetella pertussis
Virulence factors (3)
Virulence factors
- Adhesins: attach to ciliated cells
(esp. FHA = filamentous hemagglutinin) - Adenylate cyclase toxin: bacterial AC (which has no host intracellular regulation) translocates to cytoplasm of mammalian cell and increases intracellular cAMP.
- Pertussis toxin: complex A/B toxin, stimulates host AC by inhibiting Gi via ADP ribosylation thus Gs is left unbalanced and increasing intracellular cAMP production
Note: the high increase of cAMP is ultimately the cause of death –> e.g. leading to fluid in alveolar space (pneumonia)
Bordetella pertussis Tx. Discuss the effects of time when giving Rx Tx. What other Tx is used and what prevention is used?
Treatment
1. Antibiotics – (changes course only if early, but blocks spread)
- Adequate oxygen support
Prevention
1. Vaccine – P of DPT
Note : Bordetella pertussis is a disease more likely to result in death in children 5 yo or less.
Pseudomonas aeruginosa
Type
Color/smell characteristics
nutritional requirement
virulence effectiveness
Pathogenesis
- what population
- where in the body
- gives names for the sites of infections and areas.
- Gm neg rod; found in soil, water, animals
- Colonies fruity odor and blue-green pigment
- Minimal nutritional requirements
- Obligate aerobe
Pathogenesis:
- Opportunistic infections (esp. immunocompromised and patients with catheters)
- Both localized (e.g. pneumonia) and systemic (e.g. gets into circulation –> sepsis) infections
- Infects lungs of CF patients, cancer, burns/wounds and catheter sites, ear (otitis externa – swimmer’s ear), eye (contact lenses are risk factor), pneumonia, endocarditis (esp. drug users)
Note : doesn’t require much thus we are exposed to it all the time but does not have very good virulence effectivness.
Pseudomonas aeruginosa
Virulence factors
- Alginate – thick gel, slime layer (antiphagocytic)
- Pili – required for initial colonization (replaced by
mucoid slime layer)
Pseudomonas aeruginosa Treatment and Prevention
Aggressive use of 2 antibiotics because:
- resistance mechanisms
- opportunistic infection
Prevention
Strict attention to control measures
Note: aggressive use because it’s a soil bacteria and will have resistance mechanisms. Especially in the case of immunocompromised patients. drug resistance common and P. aeruginosa is opportunistic
Clostridium species
- Type
- Three major clinical species
Gm positive, obligate anaerobes
Spore forming
Three major clinical species:
- Clostridium tetani - tetanus
- Clostridium botulinum - botulism
- Clostridium perfringens - gas gangrene
- Clostridium difficile
-obligate anaerobes but as spores can survive to exposure of oxygen. with favorable conditions will begin to grow vegitatively.
Clostridium tetani
- type
- found in nature
- infectious form
- affects physiology of host how
- death rate us vs worldwide
- comment on the infection
Clostridium tetani
A. Gm + slender rods, terminal spores
B. Feces and contaminated soil (high density)
C. Infectious form - spore in anaerobic environment
D. Tetanus - spastic paralysis
- localized (lock jaw)
E. 50 – 70 deaths/yr in USA,
almost 1 million worldwide
F. Diagnosis – clinical (infection is
often minor). Vaccinate against toxin. Little toxin is lethal!
Note: often introduced as a polymicrobial solution. Very little growth of bacteria because the toxin is so toxic. Vaccination is against the toxin
Clostridium tetani
Toxin type and effect.
Toxin:
1. Simple A-B type toxin
- A subunit – endopeptidase, blocks release of inhibitory neurotransmitters
- Results in the continuous stimulation → spastic paralysis
tetanus toxin go up motor neuron and passes transsynaptically to the inhibitory synapse. If we block the inhibitory synapse thus we can’t release the vesicles to inhibit the excitatory synapse vesicles.
Clostridium tetani Tx (3) and prevention (1)
Prevention discuss the time intervals of prevention.
Treatment:
- Isolation (decrease stimulii)
- Anti-tetanus Ig
- Debride wound & antibiotic
Prevention:
T of DPT (inactive toxin)
- inactive toxin every 10 years
- previous exposure not protective because little infection
Clostridium botulinum
Why called the "sausage" disease? how many cases a year discuss the three types of botulism type of toxin End result of toxin
A.botulus - “sausage” disease- the bacteria would grow in sausages and thus consumption would lead to infection.
B.40-80 cases/yr
C.Three types of botulism:
i. classic (food borne) – intoxication (the toxin is what gets ingested. No bacterial growth, no bacteria to treat.)
ii. wound – bacterial growth (rare). Spores in wound, bacteria grow, toxins produced
iii. infant – bacterial growth (HONEY!). Spores ingested, bacteria grow in GI, toxin produced
D.Simple A-B type toxin, cleaved in GI
E.flaccid paralysis: Initial slurred speech, difficulty swallowing, visual disturbance, progressive flaccid paralysis results in respiratory paralysis or cardiac arrest
Note: Honey can be home to the C. botulinum spores. Spores that are ingested exist in the intestine. Spores in the GI would not do well and eventually will be done away. Infants don’t have normal flora thus we don’t give honey because the spores can be in the honey.
Botulinum Toxin Action
Describe the cascade of action
Affect peripheral cholinergic synapses (NOT CNS), block release of acetylcholine and cause FLACCID paralysis
Botulinum toxin, subunit B binds to the gangliosides of motor end plate. Subunit A blocks the release of ACh at the motor end plate —> lack of excitation leads to flaccid paralysis
works on the motor neuron. Blocks the release of vesicles containing acetylcholine
Difference between Clostridium tetani/botulinum toxin
Symptoms reflect where toxin acts, which is thought to reflect action of B SUBUNIT!
Clostridium botulinum Tx (2) and prevention.
Treatment:
- Anti-botulinum Ig (it is an intoxication)
- Antibiotic for infant and wound botulism
Prevention:
Proper food handling
Clostridium perfringens
Type of bacteria
Location to be found
Pathogenicity: What can it cause?
Virulence (3)
A.Gram positive, stout, truncated, spores
B.Obligate anaerobe
C.Vertebrate GI, spores in soil
D.Pathogenicity
- gas gangrene (myonecrosis)
- food poisoning (7% USA) - self limiting
E. Virulence: - alpha Toxin (phospholipase) - enterotoxin - degradative enzymes (proteinases, DNAses, hyluronidase, collagenase)
Note: In GI can grow not well but if grows enough can make enough enterotoxin to be virulent.
Clostridium perfringens
Discuss alpha toxin and gas gangrene
Alpha-toxin
- Lecithinase C (phospholipase)
- Membrane disruption
Gas gangrene
- spores into severe, open wound with other bacteria
- germinate & grow rapidly in anaerobic condition
- rapid spread and necrosis, gas (CO2 & H2) formed from
fermentation of tissue carbohydrates, copious pus, foul smell
- uniformly fatal without intervention
Clostridium perfringens
Dx criteria (10) Tx (3)
Diagnosis
- clinical grounds
- disproportionate local pain; tachycardia; tachypnea; fever; delirium; skin becomes stretched, necrotic, blisters and then malodorous discharge (similar to nectrotizing fasciitis)
Treatment
- surgical debridement (from 100% to 30%)
- penicillin IV (another 5%)
- hyperbaric oxygen
A 2-year-old male child experienced an upper respiratory infection 2 weeks prior to hospital admission. Four days prior to admission, anorexia and lethargy were noted. The patient was seen in the emergency room 3 days prior to admission. At that time he had a fever of 39.9 oC. Physical examination revealed a clear chest, exudative pharyngitis, and bilaterally enlarged cervical lymph nodes. A throat culture was taken, and a course of penicillin was begun. The child’s course worsened, and he became increasingly lethargic; he developed respiratory distress on the day of admission. It was noted that the throat culture from 3 days prior top admission had not grown any group A streptococci. On examination, the patient was febrile to 38.9oC and had an exudate in the posterior pharynx that was described as a yellowish thick membrane that bled when scraped and removed. The patient’s medical history revealed that he had received no immunizations.
- The patient was admitted to the hospital and treatment was begun. Special cultures of the pharynx were requested that subsequently grew the suspected pathogen. What was the pathogen? Which types of media are used to isolate this pathogen?
- Does this organism invade the bloodstream? If not, how does it cause disease?
- How can this disease be prevented?
- How is this disease treated?
Answer
A 48-year-old man had a long history of alcoholism and was admitted to the intensive care unit with profound hypotension and gastrointestinal bleeding. He was intubated and given intravenous fluids and transfused with packed red blood cells. He remained intubated and ventilator dependent for several weeks. He developed fevers and was treated with broad-spectrum antibiotics. After further antibiotic therapy, Gram stain of his tracheal aspirate showed polymorphonuclear leukocytes and Gram-negative rods. Culture of the tracheal apsirate yielded a heavy growth of an oxidase-positive, Gram-negative, lactose non-fermenting rod that produced a greenish hue on the culture plates.
- What is the likely agent of infection? Is this organism part of the normal oral flora? Where is it found in the hospital environment? Does it commonly cause pulmonary infections in healthy individuals?
- This organism produces an exotoxin that is similar to the exotoxin of which other bacteria? How do they act on cells?
- This organism was isolated after the patient received a prolonged course of broad-spectrum antibiotics. Is this organism normally sensitive or resistant to many of the commonly used antibiotics?
- Bacterial genes may code for a variety of proteins that inactivate antibiotics. In addition to the bacterial chromosome, where can these genes be found?
Answer
Pyogenic Gram + Bacteria
Two examples, where are they found, and structure of bacteria.
Staphylococci
- Gram + cocci
- clusters
- Nasopharynx, skin, GI
Streptococci
- Gram + cocci
- pairs/chains
- Nasopharynx, skin, GI
Differentiating Staph and Strep
What test do we run?
CATALASE TEST
Staphylococci; YES catalase
Streptococci; NO catalase
Staphylococcal Species Common Properties (5)
• Gm + cocci • Grow in high salt (7.5% NaCl) • Standard growth medium • Normal Flora • Resistant to drying/heat, many antibiotics MAJOR problem in hospitals (spread by nasal & skin carriage)
Note: doesn’t mean they like salt, and the drying and heat resistance not to the extent of spores.
Staphylococcal Species (3) and list their infections or harmful effects.
- Staphylococcus aureus (most common)
- skin infections, osteomyelitis, toxic shock syndrome,
food poisoning, large number types of infections. Including unrelated diseases due to the toxin carried in the bloodstream. - Staphylococcus epidermis
- septicemia and endocarditis (implanted device). can colonize catheters & indwelling shunts. - Staphylococcus saprophytic
- urinary tract infections, urinary tract infections. Can colonize catheters and shunts.
Differentiating Staphylococci
What test to use and which one is differentiating with a positive result?
Coagulase
Staphylococcus aureus + (causes clotting)
Staphylococcus epidermidis -
Staphylococcus saprophytic -
fibrinogen — coagulase binds to prothrombin —> fibrin (clot)
Staphylococcus aureus
Discuss the properties (colonies and pathogenic capacity) and a diagnostic tool used to detect them
Properties
• Pathogenic strains often b-hemolytic, yellow pigmented colonies
• Pathogenic capacity = surface molecules, extracellular factors + toxins
blood agar plate- bacteria are lysing the blood cells and we get a zone of clearing - beta-hemolysis. There are lysing that exists with other blood cells but we use this for diagnostic purposes.
Note: it has not been possible to develop a serologic assay.
Surface Components & Virulence of S. aureus (2.1)
• Fibronectin binding protein
- adhesion
• Clumping factor
– binds fibrinogen (aggregates Staph)
– prevent phagocytosis
• Protein A (only S. aureus)
– linked to peptidoglycan
– bind Fc of IgG1, IgG2, IgG4 –> no phagocytosis since phagocyte Fc receptor can’t bind
– prevent phagocytosis
Extracellular Factors & Virulence of Staphylococci (5)
- Catalase – counteract PMN’s
- Coagulase – clotting
(poor penetration by WBC’s) - Hemolysins
- a (“a toxin”): transmembrane channels; cytolytic exotoxins attack mammalian cell membranes —> hemolysis. transmembrane channel, dermatonecrosis, and lethality; 3 other hemolysins - may be cytotoxic for a variety of cells - b-lactamase – narrow spectrum (90% of strains)
- Leukocidin – K+ channel, products capable of killing granulocytes and macrophages
Note: With clotting have to debri the wound because the coagulse can form a “boil” and prevent WBCs from getting to the site
Exotoxins; Staph aureus exotoxins and Enterotoxins
Discuss them and precautions to take.
Exotoxins:
Staph exotoxins
- Exfoliative toxins – Scalded skin syndrome
– desmosomal protease: cleaves the proteins the hold parts of the epithelial layer together. In this manner the toxin can be spread throughout the body with the need for bacterial penetration.
Toxic shock syndrome
– superantigen (exotoxin)
– 20% S. aureus
Enterotoxins( no infection. The effect is the toxin being ingested) – Food poisoning
– superantigen (heating of food does not help. Have to make sure it is not present before ingestion. Unlike C. Botullium can be killed by heating food.
Staph Infections types (5). Just list.
Skin & soft tissue Musculoskeletal Endocarditis Genitourinary Toxin based
Staph Suppurative (formation of pus) Infections; Skin infections
Discuss the signs (5) and an assoc. to another bacteria.
Skin infections:
- Folicullitis- infection starts at break of at hair follicle
- Furuncles (boil) - often start at the break of hair follicle but can be in other areas; hot, tender, low fever
- Carbuncle
confluence of boils - Impetigo – epidermal lesion
- Thick yellowish crust (children)- easily transmittable and kids are gross, they wipe on anything
- Often mixed with S. pyogenes
Note: careful with fever because then Tx would be systemic antibiotics
Suppurative Infections of Staph
Discuss surgical/burn wound infections, pneumonia, and osteomyelitis
• Surgical/burn wound infections
- Bacteremia & endocarditis
• Pneumonia (1-5%)
- Sequela of influenza
- Fever, cough, purulent sputum
• Osteomyelitis (bone necrosis)
Note: Strep. pyogenes is the more common cause of pneumonia but Staph. aureus can cause pneumonia
Toxic Infections of Staph
Discuss Scalded Skin Syndrome
Who gets it, what toxin involved of MOA, what can rule that the skin is not infected, and diagnosis.
Scalded Skin Syndrome
- Children
Toxic Infections of Staph aureus
• Toxic shock syndrome
- toxin, chemokines, symptoms (7)
- Tx, mortality %, who is affected
• Toxic shock syndrome
- TSST-1 (20% S. aureus)
- Elevated IL-2 & TNF levels lead to shock
- Fever, macropapular rash, hypotension, vomiting, respiratory distress, irrational behaviour, multi-organ
- 3% mortality
- Supportative measures & antibiotics
- Women and men (originally associated with super absorbent tampons)
Note: Streph pyogenis 30% death - Toxic shock like syndrome toxin
Staph Food Poisoning
Common cause
properties of toxins
length of time to feel the effects - why?
Tx
Common cause
S. aureus is responsible for 5 to 25% of all reported cases of food poisoning.
Intoxication - Staphylococcal enterotoxin
- Enterotoxins are heat stable!
- 1- 6 hr post ingestion exhibit severe
vomiting and diarrhea (up to 48 hrs)
Toxins have superantigen activity and act directly on neural receptors that stimulate the vomiting center in the brain.
Diagnosis: Clinical presentation (no infection)
Treatment: - Hydration
- Monitor/correct electrolytes
Note: occurs pretty quickly because the toxins are preformed. Is self limiting because the toxin you ingested - that’s it. No ingestion of bacteria will not have increasing amounts of toxin produced.
Diagnosis of Staph for Localized & Systemic Infection (4)
- Culture from abscess, lesion, sputum, blood sample
- Growth on salt agar (7.5% NaCl)
- Coagulase, catalase tests
- Antibiotic sensitivity: esp. Methicillin Resistance! Methicillin resistance due to presence of a mutant PBP in a pathogenicity island
- Hospital Acquired Methicillin Resistant S. aureus (HA-MRSA) is associated with multi-drug resistance
- Community Acquired Methicillin Resistant S. aureus (CA-MRSA) is not associated with multi-drug resistance
** both were derived from different lineages.**
