Microbiology Flashcards
Viral drugs that requires only cellular kinases for activation (ie don’t need to be phosphorylated.dot require intracellular activation)
o Cidofovir (VZV) o Foscarnet (CMV)
Drug of choice for lung abscesses?
Clindamycin – covers anaerobic oral flora (bacceroides, prevotella, fusobacterium, peptostrepto) and aerobic bacteria.
Bacterial or viral?
CSF: Inc opening pressure, inc neutrophils, dec glucose, elevated protein
Bacterial
Bacterial or viral?
CSF: nl opening pressure, nl glucose, elevated protein
Viral
Biopsy of caseous necrosis in Tb shows necrotic areas with large cells with abundant pale cytoplasm. What surface marker is most specific for those cells?
CD14
Fever, HA, severe myalgias, joint pain after travel to Mexico suggest what? Describe how secondary infections occur?
Dengue Fever
Primary - asymp or self-limited
Secondary - infection with DIFFERENT viral serotype and cause more severe illness
Alpha-hemolytic gram positive coccus, catalase negative that can cause infective endocarditis. Commonly found in the throat, nasopharynx, and mouth
Streptococcus mitis
How does giving abx in salmonella enterica prolong course?
Prolonged fecal excretion of the organism: when you damage the salmonella by abx you will release its content to blood and GI and cause more sx (salmonella can cause disease only in large amount 10 power 7 - acid labile)
chef with furuncle on face cooks meatloaf and people who eat it get sick in 4 hours. Cause?
pre-formed exotoxin (likely staph) causes vomiting (food poisoning) in this short time period
HSV encephalitis in neonates typically involves the ____ lobes. The MC means of infection is how?
- temporal
2. passage through the birth canal of a mother with active infection
MCC of ring-enhancing brain lesion in HIV positive patient?
Toxoplasmosis (crescentic microorganisms and necrosis on histo)
In hep B, what will most likely change in serology during the window period?
Patient will become HBsAg negative
How does hep B contribute to HCC?
integration of viral DNA into host genome –> triggers neoplastic change.
Insulin-like GF I can stim cell prolif
All gram negatives have LPS. What is the toxic component of LPS?
Lipid A
What causes meningoencephalitis in HIV+ patients? How can you test for it?
Cryptococcus - the latex agglutination test detects the polysaccharide capsule antigen; india ink stain shows round or oval budding yeast
What organisms are resistant to cephalosporins? Why?
listeria, MRSA, enterococci - resistant penicillin-binding proteins
atypicals (mycoplasma, chlamydia) - no cell wall
patients with CF (recurrent sinopulm infx and congenital absence of vas deferens) commonly get what bacterial infection?
pseudomonas or burkholderia cepacia
Non lactose fermenting gram neg rod.
Course of Hep B infection
Asymp: 4-26 weeks (typically 6-8).
During asymp period HBcAg, HBeAg, and HBsAg would be found.
HBsAg is typically the first to appear.
If you suspect EBV mono in a child and Monospot test is negative, what other test can be done to confirm the diagnosis?
EBV virus titers - younger kids have poor ab response to infection, so traditional diagnosis via monospot (heterophile) tests may fail.
Patient with EBV infection would have significant increase in B or T lymphocytes in the blood?
T lymphocytes - mount the immune response
Note: B lymphocytes are the cells infected with the virus and proliferate wildly due to viral stimulation. They are found in the LN, not the peripheral blood.
Atypical pneumonia due to mycoplasma pneumoniae. What is unique about the organism?
Lacks a cell wall. Requires cholesterol, purines and pyrimidines to grow.
Athletes foot is usually caused by what type of Trichophyton?
Trichophyton mentagrophytes - tinea pedis
Note:
trichophyton tonsurans and violaceum - tinea capitis
Pseudomonas is able to produce alginate. What is this?
Alginate is an exopolysaccharide capsule of P aeruginosa. Inhibits ciliary clearance in the tracheobronchial tree, allowing adhesion of bacteria to each other and prevents phagocytosis
MCC of septic shock?
Endotoxin from gram neg bacteria inducing the inflam cascade (E coli, Klebsiella, Proteus, pseudomonas, serratia, bacteroides)
What’s the best way to disinfect Norovirus?
Sodium hypochlorite (active ingredient in bleach) Good for naked capsid viruses. Destroys the capsid.
What is the best way to disinfect enveloped viruses?
alcohol and phenol. Destroys cell memb
How do you sterilize fomites that cannot be autoclaved?
Ethylene oxide sterilization gas
What is one of the only good agents to kill mycobacteria?
UV light
What viruses are able to act directly as mRNA using the host’s intracellular machinery for translation?
single stranded positive sense RNA
Negative sense definition?
nucleotide sequence complementary to mRNA that it encodes. Like DNA, this RNA cant be translated into protein directly. Must first be transcribed into a positive sense RNA that acts as an mRNA
MC organisms that cause septic abortions?
S aureus, E coli - due to seeding of uterine cavity during instrumentation
Norovirus and rotavirus present similarily. Which is more likely in a daycare setting?
Norovirus especially in developed countries, bc childhood vaccines have decreased incidence of rotavirus
How does HBV replicate in the liver?
DS DNA –> +RNA template –> DS DNA progeny
Note: 2 phases
- Proliferation phase- CD8-Tcells destroy hepatocytes–> injury
- Integration phase- Viral DNA integrated into genome of survived hepatocytes–> Hepatocellular ca
What is the eukaryotic equivalent of the prokaryotic Shine-Dalgarno sequence (UCCUCCA)
Kozak sequence (GCCGCCRCC)
How do non-pathogenic strains of C diphtheriae acquire pathogenicity?
Phage conversion permitting exotoxin production
What is staph epidermidis’ most important virulence mechanism?
Synthesis of an extracellular polysaccharide matrix –> biofilm
Biofilms can seed into the bloodstream and surrounding areas
In HIV, what protein becomes glycosylated before being proteolytically cleaved into 2 smaller proteins. What do those proteins do?
- Env –> gp120 and gp41
2. Virion attachment to the target cell
Retroviral gene therapy that codes for what enzyme is being considered in neonates who have low T lymphocyte count and severely decreased serum Ig levels
Adenosine deaminase - SCID tx
Note: adenosine deaminase is the 2nd MCC of SCID after x-link inheritance
Extended-spectrum beta-lactamase E coli inactivate extended spectrum penicillins, monobactams and cephalosporins. How did they acquire this ability?
Genes encoding the enzymes are located on plasmids that can be transferred between different species through CONJUGATION
Carbapenems are tx of choice for ESBL organisms
What is the most important host factor in preventing influenza infection in patients who have been vaccinated to influenza?
Antibodies against hemagglutinin
Note: ab to neuraminidase are NOT the main source of protection against reinfection
Host cell receptor and virion/virion protein binding specificities of HIV, EBV and parvovirus B19
HIV - CD4 w/gp120
EBV - CD21 w/gp350
Parvovirus B19 - erythrocyte P antigen w/parvovirus B19
3 ways to treat Cdiff. Which method inhibits RNA polymerase?
- oral metronidazole
- vancomycin
- FIDAXOMICIN - macrocyclic antibiotic that inhibits RNA pol (used primarily for recurrent CDI)
Changes in host range of viruses are most commonly caused by a mutation in what?
Viral-encoded surface GLYCOPROTEIN that mediates virion attachment to target host cell plasmalemma receptors.
Pain with hip extension fever, flank pain, inguinal mass, difficulty walking
psoas abscess
result of hematogenous or lymphatic seeding from distant site or by spread from an adjacent site
Patient with encephalitis, meningitis, or flaccid paralysis may be infected with what?
West Nile Virus - positive sense ss flavivirus from female mosquites in summer.
Most enveloped nucleocapsid viruses acquire their lipid bilayer envelope by budding through the PLASMA membrane of the host cell. What is the exception?
Herpesviruses (eg CMV) - bud through and acquire envelope from the host cell NUCLEAR membrane
HBV infection assists with HDV infection how?
Coating of viral particles - Hep B surface ag coats Hep D ag before it can infect hepatocytes and multiply
Intraerythrocytic ring inclusion organisms on peripheral blood smear indicate what? Organism can have incubation period of years
Babesiosis (Ixodes tick)
Note: aedes can also cause this but has incubation period of weeks
Congenital toxoplasmosis: hydrocephalus, intracranial calcifications, and chorioretinitis is acquired when?
In Utero (transplacental infection)
Meningitis secondary to E coli infection. What is the main VF causing this?
K1 capsular antigen
Note: LPS is the major VF that results in bacteremia and septic shock
What hepatitis can cause serum sickness-like syndrome with jt pain, lymphadenopathy, and pruritic urticarial rash?
Acute hep B
Sickle cell
- MC VIRAL cause of aplastic crisis in sickle cell patients?
- Functionally asplenic –> inc risk of infection with what?
- MCC of osteomyelitis
- Parvovirus
- encapsulated org (strep pneumo, H influenza)
- Salmonella (S aureus, and Ecoli next MC)
How does M pneumoniae cause anemia?
Shares antigens with human erythrocytes. When the body mounts a response against these antigens, it also lyses RBCs (cold agglutinins)
Note: has no peptidoglycan cell wall, only a phospholipid bilayer cell memb
Acid-fast staining carried out by applying aniline dye (eg carbolfuchsin) to a smear and then decolorizing with acid alcohol tests for presence of what cell wall component?
Mycolic acid
Will not decolorize if mycolic acids are present
What molecule is in the cell wall of gram positive bacteria but not gram negative?
Teichoic acid
Common lab finding in patients with Legionella pneumonia
hyponatremia
Note: present with high fever, bradycardia, neuro sx, diarrhea
What STI causes a painless ulcer that later progresses to painful inguinal lymphadenopathy and ulceration?
Chlamydia trachomatis L1-L3
Painless ulcer = lymphogranuloma venereum
Painful lymphadenopathy = buboes
Histo: chlamydia inclusion bodies in host cell cytoplasm
Asplenic patients are prone to infections caused by encapsulated orgs (eg S pneumoniae, H influenzae, N meningitidis). Impairment of what mechanism contributes to severity of infection with these orgs?
Systemic bacterial clearance
Spleen filters blood and removes circulating pathogens (major site of opsonizing ab synthesis)
MC organisms involved in intraabdominal infections
Polymicrobial (B fragilis, Ecoli MC)
Neutropenic patients are at high risk for what fungal infections? Which is more common in lungs?
Candida and Aspergillus
Aspergillus is more common in the lungs (can colonize and form a fungus ball within a preexisting lung cavity). Can also cause lung HSR in allergic bronchopulm aspergillosis in indiv w/asthma
Deficiency in what results in recurrent infections by Neisseria?
C5b-C9 –> cant form membrane attack complex
How do penicillins and cephalosporins function?
How is resistance to cephalosporins acquired?
IRREVERSIBLY bind to penicilin-binding proteins such as TRANSPEPTIDASES (fcn to cross-link peptidoglycan in the bacterial cell wall).
Resistance to cephalosporin - can be d/t change in structure of penicillin-binding proteins
What is the most concerning feature of hep E?
High mortality rate in pregnant women.
Unenveloped ssRNA spread fecal-orally.
Typically self-limited and not assoc with chronic liver disease or carrier state.
Cholera and eneterotoxigenic E coli cause purely toxin-mediated WATERY diarrhea. Stool micro shows what?
Mucus and some sloughed epithelial cells
No fecal leukocytes or red cells bc the toxins modify electrolyte handling by enterocytes and do not cause cell death
What fungus shows organisms within macrophages on light microscopy of bone marrow aspirate?
Histoplasma - oval or round yeasts in macrophages
Grows hyphae on Sabouraud agar (dimorphic)
PAS+ stain of small bowel mucosa in the setting of abd discomfort, loose stool and recent weight loss indicates what disease?
Tropheryma whippelii / Whipple disease.
PAS stains glycoprotein in cell walls of T whippelii and is diastase-resistant
Patients with chronic granulomatous disease have a defect in NADPH oxidase. They develop recurrent bacterial and fungal infections caused by what organisms?
Catalase positive organisms: S aureus Burkholderia cepacia Serratia marcescens Nocardia Aspergillus
In additional to Tzanck smear, HSV can be tested for how?
PCR
Ruptured ectopic pregnancy is assoc with prior infection with what organism?
Neisseria gonorrhea
Chlamydia trachomatis
Signs: abd pain, bloody vaginal d/c, orthostatic hypotension, positive preg test
What process is most important in eliminating listeria from the body?
Cell-mediated immunity
Intracellular bacteria (chlamydia, legionella, mycobacterium, N meningitidis, Nocardia, rickettsia, salmonella) are protected against circulating immune factors such as abs and complement
Pregnant women, elderly, immunocomp, have compromised cell-mediated immunity
What are the cellular receptors associated with the following virions: CMV EBV HIV Rabies Rhinovirus
CMV - cellular integrins EBV - CD21 (CR2) HIV - CD4 and CXCR4/CCR5 Rabies - nicotinic ach receptor Rhinovirus - ICAM1 (CD54)
Note: CCR5 is a chemokine - C chemokine receptor type 5
Tropheryma whippelii is a G+ actinomycete –> Whipple disease. It involves the small intestine, joints, and CNS. histo?
small intestine mucosa with enlarged FOAMY macrophages with rod-shaped bacilli and PAS-positive, diastase-resistant granules
Systemic symptoms (fever, hypotension, confusion) due to staph aureus are caused by what?
Superantigen activation of T lymphocytes
Chlamydophila pneumoniae is an obligate intracellular infectious agent. What type of immunity is used against this type of agent?
Cell-mediated immunity
CD8 cytotoxic T cells
Praziquantel MOA?
Inc permeability of the cell membranes of schistosome cells towards CALCIUM –> paralysis, dislodgement and death of the parasite.
What is the most likely cause of increased susceptibility to recurrent yeast infection when there is a myeloperoxidase deficiency?
Inability to produce hydroxy-halid radicals
Halide (eg Cl).
MPO converts hydrogen peroxide to hypochlorite (antimicrobicidal) in the presence of Cl.
What causes resistance of pseudomonas to multiple appropriate antibiotics?
Biofilm formation of the lower resp tract.
Pseudomonas is known to form biofilms
What do you do if a patient is an undocumented immigrant diagnosed with Tb but doesnt want you to report bc he will be deported?
Report the case to the health department to ensure that family members and work site contacts are identified and evaluated
Tb is a reportable disease
E. coli can become multidrug-resistat by transfering between different bacterial strains determinants of antibiotic resistance on a plasmid. This process is what?
Bacterial conjugation - the transfer of genetic material between bacterial cells by DIRECT CELL-TO-CELL CONTACT or by a BRIDGE-like connection between two cells. It is a mechanism of horizontal gene transfer as are transformation and transduction although these two other mechanisms do not involve cell-to-cell contact
How can viruses such as CMV evade MHC class I molecule presentation?
Virus causes translocation of nascent class I MHC molecules from the RER into the cytosol where it gets degraded by proteasomes. The normal for the MHC 1 molecule is that its made in the RER and then transported to the Cell membrane. If it gets translocated to the cytosol, its likely to be degraded.
HIV positive male with MRI showing multiple enhancing lesions in the cerebral cortex most likely has what?
Lymphoma
The definitive diagnosis is arrived at from tissue, i.e. a biopsy. MRI or contrast enhanced CT classically shows multiple ring-enhancing lesions in the deep white matter. The major ddx (based on imaging) is cerebral toxoplasmosis, which is also prevalent in AIDS patients and also presents with a ring-enhanced lesion, although toxoplasmosis generally presents with more lesions and the contrast enhancement is typically more pronounced. imaging techniques cannot distinguish the two conditions with certainty, and cannot exclude other diagnoses. Thus, patients undergo a brain biopsy
Both live and killed polio vaccines (sabin and sulk respectively) are able to induce what immune response?
Neutralizing antibodies in the circulation (humoral)
Note:
- live vax: elicit both cell-med and humoral immunity
- killed vax: elicit humoral immunity
Poliovirus mRNA lacks 5’ m7G cap but is translated efficiently by cellular ribosomes. What additional feature of the mRNA is most likely allowing the virus to be translated in the absence of a cap?
INTERNAL RIBOSOME ENTRY SITE
Unlike the host cell’s mRNAs the 5’ end of poliovirus RNA is extremely long—over 700 nucleotides—and is highly structured. This region of the viral genome is called internal ribosome entry site (IRES) and it directs translation of the viral RNA.
What feature is characteristic of G- organisms that G+ organisms dont have
Outer membrane
Note: G- have thinner peptidoglycan layers than G+
Patient with positive HIV ELISA, HIV Western blot, and low CD4+ T count but low HIV-1 viral load is due to what?
infection with HIV-2
MCC of mastitis
S aureus
Virulence factor that causes Ecoli UTI
Fimbria (P pili)
PID d/t Neisseria gonorrhea causes infertility by primarily affecting what structure?
Inflammation and scarring of the fallopian tube
Neutropenia most commonly prediposes patients to what type of organisms?
Neutropenia most commonly predisposes to overwhelming BACTERIAL infection. It may also be worth noting that patients with neutropenic fever must be covered with an antibiotic that covers for pseudomonas (e.g. pip-tazo, ceftazadime, or cefepime).*
