Microbiology Quiz on Viruses and Pathogens

Normal Microbiota

• Sites previously known to harbor normal microbiota: skin and adjacent mucous membranes, upper respiratory tract, gastrointestinal tract (including mouth), and outer portion of urethra.
• Additional sites now thought to harbor normal microbiota (or their DNA): lungs (lower respiratory tract), bladder (and urine), breast milk, amniotic fluid, and fetus.
• Sites where DNA from microbiota has been detected: brain, bloodstream.

Bacterial and Streptococcal Infections

• Beta-hemolytic staphylococci & streptococci examples: Streptococcus pyogenes, Streptococcus agalactiae, Staphylococcus aureus.
• These pathogens produce beta-hemolyse, causing erythrocyte hemolysis.
• Diagnosis of strep infection: Rapid test for the presence of Streptolysin O, Antistreptolysin O titer (ASO). Positive titer >200 IU/mL.
• ASO titer rises to a peak at 4-6 weeks post-infection and may remain elevated for 1 year.
• ASO test is positive in streptococcal infections (eg., upper airway infections, scarlet fever), post-streptococcal infection complications (eg., glomerulonephritis and rheumatic fever).
• ASO test can be falsely positive in some bacterial infections.
• Streptococcus infection may cause pharyngitis, which can lead to glomerulonephritis (kidney) or rheumatic fever (heart) if left untreated.

Viruses: Naked and Enveloped

• Viruses are classified as naked or enveloped.
• Naked viruses have a nucleocapsid, which consists of a capsid and nucleic acid.
• Enveloped viruses have a similar nucleocapsid but are also enclosed in an outer envelope.

Prions

• Prion characteristics: proteinaceous infectious agents made by all mammals.
• Normal prion PrP has α-helices.
• Disease-causing prion PrP has β-pleated sheets.
• Prion PrP causes cellular PrP to refold into prion PrP.
• Illustrations of normal brain tissue and spongiform encephalopathy brain are provided.

Skin Infections

• Fungi are decomposers/saprophytes that gain nutrition from dead and decaying tissues.
• Skin's superficial layer, stratum corneum, is composed of dead skin cells, making it a frequent site for fungal infections.
• Pityriasis versicolor (tinea versicolor) is caused by Malassezia furfur fungus.
• It's characterized by more or less pigmentation of skin (hyperpigmented or hypopigmented).

Gastrointestinal Tract Infections

• Norovirus and rotavirus cause stomach problems: nausea, vomiting, and diarrhea.
• Norovirus is more common in adults.
• Rotavirus primarily affects infants and young children.
• A vaccine is available for rotavirus, but not for norovirus.

Food Poisoning

• Causative agents of food poisoning: Bacillus cereus, E.coli 0157-H7, and other bacteria.
• Bacillus cereus causes emetic or diarrheal food poisoning.
• Emetic type is associated with cooked rice or starches left at room temperature for prolonged periods.
• Diarrheal type results from improperly stored meat and prepared meals.
• Escherichia coli 0157-H7 is characterized by bloody diarrhea.
• Shiga toxin produced by E. coli 0157-H7 causes damage to the intestine and systemic effects.
• Shiga toxin inhibits protein synthesis within target cells similar to ricin.

Stomach Ulcers & Cancer

• Helicobacter pylori causes stomach ulcers and cancer.
• H. pylori bacteria invade gastric mucus and attach to gastric epithelial cells.
• H. pylori, toxins, and inflammation cause the layer of gastric mucus to become thin.
• Gastric acid damages the epithelial cells and underlying tissue.

Cardiovascular and Lymphatic Infections

• Septicemia occurs when organisms multiply in the blood.
• Many bacteria and viruses can cause septicemia, with MRSA being a common cause.
• Fungal infections account for around 10% of cases.
• Common symptoms include fever, altered mental state, shaking, chills, gastrointestinal symptoms, increased breathing rate (with respiratory alkalosis), and low blood pressure.

Systemic Blood Infections

• Systemic blood infections caused by Streptococcus mutans and Staphylococcus aureus can progress to endocarditis.
• Post-streptococcal glomerulonephritis (PSGN) is a complication of pharyngitis or skin infections caused by Streptococcus pyogenes.

Chagas Disease

• Chagas disease is caused by Trypanosoma cruzi (protozoan).
• Symptoms include swelling at the infection site, fever, fatigue, malaise, body aches, headache, and loss of appetite.
• In the South-East of the US, infected people might develop fatal congestive heart failure 10-20 years after initial symptoms.

HIV Infection and AIDS

• A spectrum of clinical signs and symptoms associated with HIV.
• Symptoms tied to virus levels in the blood and T-cell levels.
• Initial symptoms include fatigue, diarrhea, weight loss, and neurological changes.
• Opportunistic infections or cancers can also develop.
• HIV is a retrovirus in the Lentivirus genus.
• Retroviruses have the potential to cause cancer and modify host DNA.
• Retroviruses contain reverse transcriptase (RT), which catalyzes the replication of DNA from single-stranded RNA.
• Viral genes integrate into the host genome, passed on to progeny cells.

Respiratory System Infections

• Influenza A, B, and C viruses (Orthomyxoviridae) are causative agents.
• Possess a lipoprotein envelope, glycoprotein spikes (hemagglutinin (H) and neuraminidase (N)) and ion channels; ssRNA genome.
• 10 genes on 8 RNA strands, contributing to variations.
• Influenza virus binds to ciliated cells of the respiratory mucosa, leading to severe inflammation and "cytokine storm".
• Hemagglutinin (H) binds to host cell receptors.
• Neuraminidase (N) aids in viral budding and release, affecting respiratory tract mucous.
• 2009 H1N1 (Swine flu) variants demonstrate efficient binding to lower respiratory tract, causing cytokine storm, with differing manifestations.

Bacterial Diseases of the Lower Respiratory System

• Tuberculosis (TB) is a leading global killer, with declining incidence in developed nations.
• TB is caused by Mycobacterium tuberculosis.
• The presence of mycolic acid is a crucial characteristic, contributing to features like slow growth, resistance to macrophages, and antimicrobial drugs.
• Mycoplasma pneumoniae is a very small bacterium without a cell wall; the causative agent of walking pneumonia, often mimicking ventilator-associated pneumonia.

Genitourinary System Infections

• Urinary tract infections (UTIs) can be acquired in healthcare facilities or outside.
• 95% of UTIs originate from normal gastrointestinal tract biota, with Escherichia coli accounting for 80%.
• Other causative agents include Staphylococcus saprophyticus and Enterococcus.

Syphilis

• Treponema pallidum is the causative agent; a spirochete with thin, coiled structure.
• Gram-negative, requiring cultivation in living host cells.
• Marked by primary, secondary, and tertiary stages, along with varying latent periods.
• Spirochetes are present in lesions and blood cultures during primary and secondary stages and are transmissible at these times, including the early latency period.
• Transmission is largely absent during the "late latent" and tertiary stages.

Infectious Diseases (Match-Up)

• Various matching questions are presented and information is included for disease, animal, symptom, organism type matching.