Flashcards in Microbiology Deck (102):
Which enveloped viruses acquire the envelope from nuclear membrane of the host cell?
Herpesviruses (CMV, etc)
Infection that can cause achalasia. Common background of the patient. Mechanism.
- Trypanosoma cruzi ▶️ neurotoxin ▶️ destroy myenteric plexus ▶️ intramural, parasympathetic denervation of smooth muscle
- Patient come from central or South America
Coccus gram positive that can synthesize dextran from sucrose. What allow this property to do?
Streptococcus viridans (mutans, sangini)
Adhere to tooth enamel ▶️ dental caries
Adhere to fibrin-platelet of damaged heart valves ▶️ endocarditis
What component allows to some bacteria be acid-fast? Examples
Mycolic acid in its cell wall
Mycobacterium, Nocardia (weak)
Most common organism in a cat or dog bite. Why do the wound have a characteristic odor?. Antibiotic treatment.
- Pasteurella multocida
- Mouse-like odor→indole positive (Trp ▶️ (Tryptophanase) ▶️ indole)
Sequence of replication of Hepatitis B virus. What polymerase does it use?
- DNA double stranded→+RNA template→DNA double stranded progeny
- Polymerase reverse transcriptase
Transmission pathway of Neisseria meningitidis. Once stablished a contact how can you prevent secondary cases? Which drugs do you use?
- Direct contact with contaminated respiratory secretions or aerosolized droplets.
- Antibiotic Chemoprophylaxis for close or intimate contacts preferably within 24 hours ▶️ Rifampin, Ciprofloxacin, intramuscular Ceftriaxone.
Gram-negative encapsulated bacteria, lactose fermenting positive, causing pneumonia in elderly patient. Hallmark of presentation and organism.
- Klebsiella pneumoniae
- Currant-jelly sputum, upper lobe pneumonia, lung tissue necrosis, early abscess formation
- Immunocompromised ▶️ infants, elderley and specially alcoholics
Which is the protein that is part of peptidoglycan cell wall of a clusters of gram (+) cocci? Function.
Staphylococcus aureus ▶️ Protein A (virulence factor) ▶️ bind Fc portion of IgG ▶️ ❌ Complement activation ▶️ ⬇️ C3b ▶️ ❌ opsonization and phagocytosis.
What is the mechanism of resistance to vancomycin?, example of microorganism.
- Substitution of D-lactate in place of D-alanine in the synthesis of peptidoglycan cell wall [D-ala-D-lac] (Normally binds to D-alanyl-D-alanine terminal of the cell wall peptide precursors ▶️ ❌ formation of peptidoglycan)
- Vancomycin Resistant Enterococcus (VRE), VRSA (Staph)
How can occur Penicilin resistance?
- Beta-lactamase (penicilinase)
- Modify penicilin binding protein in cell wall ▶️ mechanism of MRSA ▶️ resistant to even penicilinase resistance antibiotics
Penicilinase resistant beta-lactam antibiotics
Cephalosporins, carbapenems, nafcilin, methicillin.
Mechanism of resistance to Tetracyclines
- Efflux of drug from bacteria via active-efflux pump
- ⬆️ Protein that allow translation
Mechanism of resistance of aminoglycosides
- Inactivation by aminoglycosides-modifying enzymes ▶️ acetylation, phosphorylation, etc.
- Pseudomonas ▶️ ⬇️ antibiotic entry
In which disease or presentation you should differentiate aspergillus fumigatus vs rhizopus species? How do you differentiate them?
- Fungal rhinosinusitis
- Light Microscopy (LM):
🔵Aspergillus ▶️ narrow hyphae branching in acute angles (V-shaped) with septations
🔴Rhizopus ▶️ broad, ribbon-shaped, non-septate hyphae with branch at wide angles
Why Haemophilus influenzae cannot grow in a 5% sheep blood agar? Why does it need staphylococcus aureus to grow? How is called that phenomenom?
Haemophilus ("blood lover") requires X factor (hematin), V factor (NAD+)
- Sheep blood agar not has enough nutrients and factors
- S. aureus cross-streaks in blood agar ▶️ secrete V factor; facilitates release release X factor from B-hemolysis ⏩ "Satellite phenomenon"
What confers to Hepatitis B virus the oncogenic feature? Which neoplasia associated?
- Viral DNA integration into the host genome
- Hepatocellular carcinoma
Which are the components or regions of endotoxin? What is the toxic compound? How is it secreted?
- Endotoxin=Lipopolysaccharide (LPS) ▶️ O antigen, core polysaccharide, Lipid A (toxic properties) ▶️ Sepsis
- LPS released during division or bacteriolysis (NOT actively secreted)
Gram (+) cocci catalase negative, able to grow in hypertonic saline (6.5%) and bile. What is the organism, diseases and risk factors associated to the transmission? What is the other laboratory identification useful for it organism?
- Enterococci (Enterococcus faecalis - 80-90%, Enterococcus faecium - 10-15%)
- Enterococcal Endocarditis (30% of nosocomial endocarditis), UTI, wound infection
- Genitourinary tract manipulation (cystoscopy, catheterization, instrumentation); GI tract manipulation (colonoscopy); obstetric procedures; Elderly.
- PYR (+)
What is the microorganism that can cause subacute endocarditis following a dental work and its laboratory features?
- Streptococcus viridans
- Gram (+), catalase (-), optochin resistant, bile insoluble
Function of virulence factor at the capsule of Haemophilus influenzae type b and its importance.
- Polyribosil ribitol phosphate (PRP) ▶️ evasion of mucosal immunity and inhibit complement mediated killing and phagocytosis
- Vaccine against type b PRP capsule
How can you identify and differentially diagnose botulism? Mechanism of action of neurotoxin.
- History of eat canned food
- 3 D´s→diplopia, dysphagia (nicotinic block), dysphonia. Also dry mouth (muscarinic block)
- Electrodiagnostic→↓compound of muscle action potential (CMAP), continous stimulus→↑CMAP►Facilitation
- (-) Ach release from presynaptic
Which gram negative rod is the most common cause malignant Otitis externa (swimmer's ear)? Association with which patients. Other features of the organism
- Pseudomonas aeruginosa
- Elderly patients
- Motile, aerobic Non-lactose fermenting, oxidase positive, grape-like fruity odor, exotoxin A (inactivates EF-2), phospholipase C (degrades cell membranes), pyocyanin (blue-green pigment, reactive O2 species), endotoxin
What mutation render to HIV resistance to HAART (both either PI's and NTRI, NNTRI)?
Pol gene mutations ▶️ protease variants and structural changes in reverse transcriptase
Which mutation allows to the HIV evades the humoral response?
Env gene ▶️ structural glycoproteins (neutralizing Ab's are directed against the epitopes of folded viral envelope glycoproteins)
Empiric treatment for a prosthetic valve endocarditis due to coccus gram positive catalase (+), coagulase (-). Why?
- CoN Staphylococcus ▶️ slime producer ▶️ nosocomial infection and in indwelling catheter (peritoneal catheter), implantated foreign body (vascular graft), posthetic valve endocarditis
- Vancomycin ▶️ >80% of CoN Staph are methicillin-resistant
Atypical pneumonia in homeless patient with CD4=188, IV drug abuse, what type of fungus do you suspect and which stain do you use to Dx?
- Pneumocystis jirovecii
- Extracellular atypical fungus
- Methamine silver staining ▶️ cysts in frothy alveolar exudates
How do you identify disseminated MAC infection in a HIV+ patient? keys to differentiare from extrapulmonary tuberculosis infection. What is the prophylaxis?
- MAC infection (in common - fever, weakness, weight loss, diarrhea)→anemia, hepatosplenomegaly, ↑phosphatase alkaline, ↑LDH (widespread involvement of reticuloendothelial system), MAC growth at 41°C.
- Prophylaxis at CD4+<50 cells/uL - Azithromycin
*Tx: Clarithromycin or Azithromycin + Rifabutin or Ethambutol
Microorganisms associated with facial nerve palsy
- Borrelia burgdorferi (Lyme disease)
Which organism that is one of the most common causes of gastroenteritis in adults and children can be transmitted by domestic animals? What others sources of transmission?
- Campylobacter jejuni (most common cause of acute gastroenteritis in children and adults in industrialized countries) ▶️ fecal-oral transmission
- Domestic animals ▶️ cattle, dogs, chicken, sheep (common in farm and laboratory workers); Contaminated food ▶️ undercooked poultry, unpasteurized milk
What is a gumma and in which stage of syphilis of you expect to find it? What others features do you find in this stage?
- Chronic necrotizing granuloma ▶️ painless, may ulcerate ▶️ skin, mucosas, subcutaneous tissue, bones and within organs
- Tertiary syphilis
- Cardiovascular syphilis ▶️ ascendent aortic aneurysms (with calcifications), aortic insufficiency (diastolic murmur, high-pitched tambour S2)
*Neurosiphylis (meningoencephalitis, tabes dorsalis, etc) classically occur in tertiary but can be present in any stage.
How do you differentiate with laboratory tests the both B-hemolytic streptococci?
- S. Pyogenes (group A) ▶️ Bacitracin sensitive, pyrrolidonyl arylamidase (PYR) (+)
- S. Agalactiae (group B) ▶️ Bacitracin resistant, CAMP (+), PYR (-), Hippurate test (+)
Which streptococcus is PYR(+) and also can grow in hypertonic salt (NaCl 6,5%) and bile? What culture medium use the former properties to isolate the organism?
- Enterococcus faecalis and faecium→gamma-hemolytic (variable)
- Bile esculin agar
Unique characteristic of coccidoides immitis. Where is the endemic area?
- Mold (hyphae) at 25-30 grades C (environment), thick-walled spherules containing endospores at body temperature.
- Southwestern US ▶️ California, Arizona, New Mexico, some regions of central ans south america.
*Also Dx→Sabouraud agar, serology
To what antibiotic is resistant Listeria monocytogenes, and then which antibiotic you should use as empiric therapy when suspect meningitis?
- 3rd generation cephalosporins resistant (altered penicillin-binding proteins)
- Ampicilin sensible
What type of immunity is required to clear Listeria monocytogenes and why?
- Cell-mediated immunity→facultative intracellular gram (+) rod with "rocket-tails"→pass cell to cell, move intracellularly→avoid antibodies and phagocytosis
- Susceptible group→deficient CMI►infants, chemotherapy patients, HIV(+)
Antimalarial drug for plasmodium falciparum erythrocytic forms contracted from africa, why?
Cloroquine resistant, give mefloquine
Treatment for chagas disease
Diagnose of Legionella penumophila. Distinctive laboratory abnormality. Diseases.
- Legionella Urine antigen test
- Culture of organism in BCYE (Buffered charcoal yeast extract)
- Pontiac fever (flu-like, self-limited) or Legionaries disease (exposed contaminated water, pneumonia)
*Gram stain→many neutrophils but few or no organism
Gram negative rod, oxidase positive, green pigment producer (pyocyanin), that growth in moist environment. What is the microorganism and what diseases cause in that enviroment? Others features of the organism.
- Pseudomonas aeruginosa
- Swuimmer's ear, hot tub folliculitis, burn wound
- non-lactose fermenting, motile
*Hot tub folliculitis acquired in public or hotel swimming pool or hot tubs.
Stainings that can be useful to identify Cryptococcus neoformans
- Methenamine silver stain→in tissue→round cells with narrow-based buds
- India Ink→polysaccharide capsule (unique pathogenic fungus) clear, unstained zone
- Mucicarmine→polysaccharide capsule red (bronchoalveolar washings, tissue samples, etc)
Mechanism of production of tetanus disease. Against what is directed the vaccination?
- Tetanospasmin (exotoxin of C. tetani)→heavy chain bins to ganglioside of neuronal receptor, light chain→↓release glycine and GABA from inhibitory neurons
- Tetanus toxoid vaccination→elicitis humoral immunity specific for tetanus toxin
Enveloped, partial double-stranded circular DNA, with a RNA-dependent DNA-polymerase
Hepatitis B virus
Icosahedral core, enveloped, double-stranded linear DNA. How do these organisms acquire their envelopes?
- The only viruses that acquire their envelopes by budding from the nuclear membrane
What features make most probably causative organism CMV when you have a infectious mononucleosis like syndrome? what others organism associate with that presentation?
- Heterophiles antibodies negative (make twice to confirm)
- Lack of sore throat and lymphadenopathy (suggest EBV), immunocompetents
- HHV-6, HIV, toxoplasmosis
What strains of HPV are oncogenic and how can they cause malignancy?
- HPV 16, 18, 31
- Integrate into human genome→overexpression of viral oncogenes:
*E7→binds to RB1 gene and displaces transcription factors normally bound►inhibits RB1 suppressor gene→↓pRB [tumor supressor protein]
What measure can avoid the recurrence of episodes of genital HSV-2 infection?
Supressive therapy→oral valacyclovir (preferred as dosed once daily, good bioavailability), acyclovir or famciclovir
*Reactivation of latent HSV-2 infection within S2, S3, S4 dorsal root (sensory) ganglia
Most specific marker of acute for diagnosis acute Hepatitis B and why?
IgM anti-HBc (core)→acute phase→window period►HBsAg cleared and anti-HBs is not yet detectable
*IgG anti-HBc→recovery from disease
What type of hematologic disturbance can occur in a mycoplasma pneumoniae infection? how can you diagnose it?
- Intravascular hemolytic anemia→complement mediated→similarity between antigens in the cell membrane of mycoplasma and RBC (I-antigen)
- "Cold agglutinins"→↑cross reacting IgM antibodies→Dx mycoplasma infection
- Positive coombs test, ↑reticulocyte count, ↑LDH
Extrapulmonary manifestations of mycoplasma pneumoniae
Steven-johnson syndrome, joint pains, encephalitis, cardiac rythm disturbances, bullous myringitis, intravascular hemolytic anemia
E. coli virulence factor associated to meningitis? In what group of age?
- K1 capsular antigens▶️prevents phagocytosis and complement-mediated lysis
- Neonatal meningitis
Tropism of HPV 6 and 11
Squamous stratified epithelium: anus, vagina, cervix, true vocal cords
*Infants can acquired respiratory papillomatosis via passage through and HPV-infected birth canal
Diseases caused by Bartonella henselae infection and factors associated
- Cat-scratch fever→veterinarian, cat scratches or bites→tender regional lymphadenopathy (axillary extremely common)
- Bacillary angiomatosis→immunocompromise→vascular proliferations also found in viscera (falta if left untreated)
- Culture-negative endocarditis
Organism that cause respiratorory infections outbreaks, dry, nagging cough, chest x-ray findings worst than clinical status, needs cholesterol to grow in culture
Pathognomonic finding of pulmonary CMV infection. Most commonly affected patients.
- Prominent intranuclear inclusions sorrounded by a clear halo
- Transplant patients
Which organism have IgA protease?
Neisseria meningitidis, gonorrhoeae; Streptococcus pneumoniae, Haemophilus influenzae
Virulent factor of staphylococcus aureus that can inhibit complement fixation
Staphylococcal protein A→binds to Fc portion of IgG→impair complement-mediated cell lysis
Distinctive laboratory features of enterohemorrhagic E. coli (EHEC) O157:H7
- Doesn't ferment sorbitol→sorbitol-containing MacConkey agar to isolate
- Doesn't produce glucuronidase
Which is the exotoxin of EHEC O157:H7 and its function?
Shiga-like toxin→inactivate 60s ribosomal subunit→stop protein synthesis►cell death
Best test to confirm vaginitis by trichomonas vaginalis (trichomoniasis)
Saline microscopy (wet mount) of the discharge
What mean that a virus exposed to a ether or other organic solvent loss its infectivity?
*Solvent induce disruption or dissolution of envelope (outer lipid bilayer coat). Nonenveloped viruses resistant to ether.
Source and mechanism of damage of tetrodotoxin
- Puffer fish poisoning
- Bind to voltage-gate Na channels▶️🚫Na influx▶️🚫depolarization
Most common agent causing peumonitis in postransplanted recipient. Classification of microorganism and histopathology finding. Prophylaxis.
- CMV→enveloped double-stranded DNA
- Enlarged cells with intranuclear and intracytoplasmic inclusions (viral particles) with surrounding halo (owl's eye)
Most common exposure factor implicated in anthrax infection. Laboratory findings in Bacillus antrachis culture.
- Handling animal products▶️goat hair, infected animal hides, hide-based clothes, wool
- Large gram (+) rod, "medusa head" or serpentine colonies at standard media (microscopy)
What distinctive pathogenicity factor do bacillus antrachis use?
Antiphagocytic D-glutamate capsule (unique in that composition - instead polysaccharide)
Why can you find widened mediastinum in chest X ray during bacillus anthrax infection?
Spores inhaled▶️alveoli▶️machophage▶️germinate into vegetative cells▶️mediastinal lymph nodes▶️hemorrhagic mediastinitis⏩bloody pleural effusions, septic shock, death
What organism produces intracellular polyphosphate granules? How can you see them? Other culture for it.
- Corynebacterium diphteriae in loeffler medium and methylene blue staining
- Cysteine-tellurite agar→black, slightly iridescent colonies
How can you explain a finding of budding yeast that form germ tubes at 37 degrees at sputum culture?
Candida albicans (unique to form true hyphae) oral cavity colonization▶️usually doesn't cause lung disease (contamination of sputum sample, not indicate disease)
What define the tropism of enveloped virus?
Viral enveloped glycoprotein affinity to surface host cell surface glycoprotein
Causes of candida vaginitis, which of them is the most common?
- Antibiotic use (most common)▶️⬇️lactobacilli population▶️⬆️candida overgrowth
- Uncontrolled diabetes mellitus
- Systemic corticoid use
- Pregnancy▶️⬆️estrogen levels
Most common cause of endocarditis in patients with prosthetic valves and septic arthritis in patients with prosthetic joints.
Staphylococcus epidermidis▶️coagulase-negative, susceptible to novobiocin
An fungi that reduces the amount of ergosterol in its membrane, is most probably resistant to which antifungals?
Polyenes▶️amphotericin B (systemic: candida, hystoplasma, aspergillus, coccidioides, blastomyces, cryptococcus), nystatine (topical: oral candidiasis)
Congenital infection with Parvovirus B19
Hydrops fetalis▶️congestive heart failure, pleural effusion and secondary pulmonary hypoplasia, ascites, pericardial effusion, severe anemia
Which conditions would make a patient more susceptible for a vibrio cholerae gastroenteritis? Media where it can grow.
- Achlorydia▶️⬇️gastric acid production (vibrio cholerae is extremely acid-sensitive)
- Thiosulfate-citrate bile salt agar (TCBS)▶️highly alkaline selective media
Description of a virus that cause aplastic crisis in patients with sickle cell disease
Nonenveloped single stranded DNA virus
How can EBV enter to B lymphocytes (CD19+)? What others cells can infect with same mechanism?
- Viral envelope glycoprotein gp350 binds CD21 (CR2) [cellular receptor for C3d complement component]
- Nasopharyngeal epithelial cells
Diagnostic test of choice for Neisseria ghonorroeae and Chlamydia trachomatis
NAAT (nucleic acid amplification test) - urine, urethral, endocervical specimens
Evidence of strongyloides stercolaris infection in stool. What is the infectious form?
- Rhabditiform (noninfectious) larvae in the stool
- Filariform larvae (infectious)
Most important source of protection against influenza
Antibodies against hemagglutinin▶️🚫binding to the host cells
Bacteria producing dextran from sucrose may stick to what substrate? What is the organism
- Fibrin platelets aggregates→colonizing during bacteremia→pre-existing valvular lesion→endocarditis (risk is low follow dental procedure with mitral valve prolapse)
- Streptococcus viridans
What organism do you suspect as a cause of epiglotitis in a unvaccinated child? Radiographic finding.
- Haemophilus influenzae type b
- Thumprint sign
What is the most important mechanism of immune defense against giardia lamblia? Patients at high risk of chronic infection.
- CD4+ helper T lymphocytes and secretory IgA production
- IgA deficiency, X-linked agammaglobulinemia, common variable immune deficiency
What organism is strongly associated with ecthyma gangrenosum? What condition may have the patient to predispose to it?
- Pseudomonas aeruginosa bacteremia▶️perivascular invasion of of arteries and veins in dermis and subcutaneous tissue, release of exotoxins▶️exotoxin A (🚫protein synthesis), elastase (degrades elastin▶️blood vessels destruction), phospholipase C (cellular membrane destruction), pyocyanin (⬆️ROS)➡️insufficient blood flow▶️skin patches with necrosis and ulceration
- Febrile neutropenia (Neu<500/mm3)▶️⬆️susceptibility to infections by gram (-)
Conditions associated with pseudomonas aeruginosa infections
Major virulence factor of Streptococcus pyogenes and its function
- Protein M
- Inhibit phagocytosis and complement activation, mediates bacterial adherence, cytotoxic for neutrophils in the serum
- Antigenic→target of specific humoral immunity
*Lancefield Group A streotococci are divided into >80 serogroups based on M proteins
Similitude and difference between E. coli and Enterobacter cloacae
- Both fast lactose fermenter gram negative rods, UTI organisms.
- E. coli→convert tryptophan to indole►indole (+)
What type of virus can make reassortment? which are they and what allow that property?
- Segmented viruses
- Influenza virus, rotavirus, orthomyxoviruses, reoviruses, bunyaviruses, arenaviruses
- Exchange of entire genomic segments→ex, new strain in influenza virus►new epidemia or pandemia
Most common etiology agent of endocarditis in intravenous drug user. What maneuver during auscultation do you use to hear the most probably finding and why?
- Staphyloccus aureus→acute right-sided endocarditis►most probably tricuspid regurgitation results, septic embolization to lungs
- Inspiration→↑venous return to right heart
*Left-sided endocarditis→septic embolization to brain and systemic circulation
*Less common agents→candida, pseudomonas
What damages cause the clostridium difficile toxins at intestinal mucosal cells?
Toxin A (enterotoxin), Toxin B (cytotoxin)→inactivate Rho-regulatory proteins→ normally signal transduction and actin cytoskeletal structure maintenance►disruption of intercellular tight junctions→retraction, ↑intestinal fluid secretion
Causal agent of "traveler's" diarrhea, which toxin mediates it?
Enterotoxigenic E. coli (ETEC):
- LT (heat labile) enterotoxin [cholera-like toxin]►(+)Gs protein→(+) adenylate cyclase→↑cAMP.
- ST (heat stable)→(+) guanylate cyclase→↑cGMP
*↓reabsorption, ↑secretion of Na, H2O, electrolytes►watery diarrhea
Which streptococcus is CAMP test positive and why?
- Streptococcus agalactiae
- Produces CAMP factor→enlarges area of hemolysis formed by S aureus
Which bacterial toxins are encoded in a lysogenic phage?
- Group A strep erythrogenic toxin
- Botulinum toxin
- Cholera toxin
- Diphtheria toxin
- Shiga toxin
Laboratory diagnosis for chlamydia trachomatis infection.
- Cytoplasmic inclusions (reticulate bodies) on Iodine, Giemsa or ﬂuorescent antibody–stained smear
- Inside epithelial cells
How can be the human infected by schistosoma species? Organ target and diseases caused by the different species.
- Freshwater snails (incubate infectious larvae)
- Larve penetrate intact human skin→liver (maturation):
- Schistosoma japonicum→mesenteric venules►hepatic schistosomiasis
- Schistosoma mansoni→menseteric venules►intestinal schistosomiasis
- Schistosoma haematobium→urinary bladder plexus►urinary schistosomiasis
Major virulence factor among E. coli strains that cause neonatal meningitis
K1 capsular antigen (polysaccharide)→prevent recognition of bacterial antigens, complement deposition, phagocytosis►survival in the blood
*Immunogenic→anti-capsular antibodies are protective against repeat infection
Common description of the organism that cause thin, grayish-white, fishy odor discharge from vagina and clue cells from cytologic smear
Gardnerella vaginalis→anaerobic, gram-variable rod
What are the clue cells and in which setting you may see them?
Squamous epithelial cells covered with bacterial organisms→wet mount microscopy or cytology in Gardnerella vaginalis infection
Vaccine composition of Haemophilus influenzae type b
Capsular polysaccharide (polyribosylribitol - PRP) conjugated to diphteria toxin or other protein (carrier)→T cell dependent vaccine►(+) B cells to isotype switching
Organism that can cause food poisoning and soft tissue infections, wound infections and septicemia? Source of it.
- Vibrio vulnificus
- Contact contaminated water or shellfish, ingestion contaminated or raw seafood
Which are the RNA viruses that replicate in nucleus?
Influenza virus and Retroviruses
Mechanism of action of dyphteria toxin
AB exotoxin→ribosylation (inactivation) of EF-2→inhibit protein synthesis►cell death