Establishment of infection
Bacterial Classification
Bacterial Growth
Bacterial Classification
Bacterial Growth
What are the six steps for a bacterial encounter?
Encounter(agent meets host)
Entry (agent gets in)
Spread (from the entry site)
Multiplication (in the host)
Damage (caused by the agent, the host response, or both)
Outcome (host wins, agent wins, or they coexist)
What are the 3 ways genes move between bacterial cells and what broad term do they all fall under?
Genes move between bacterial cells by three distinct mechanisms: conjugation, transduction, and transformation which are all forms of horizontal gene transfer
Which pathogen's only environmental reservoir is colonized humans?
The natural home of Streptococcus pneumoniae (the pneumococcus) is the mucosal surface of the human nasopharynx. The organism's only environmental reservoir is colonized humans, not animals or the inanimate environment, and it shows a marked (still unexplained) tropism for the human respiratory tract.
What pathogen is the major cause of hospital-acquired diarrhea?
Clostridioides difficile (C.diff)
Where does Legionella thrive and give an example?
Warm man-made water sources
Hot water tanks and tap water distribution systems.
Evaporative cooling towers (institutional central air-conditioning systems).
Whirlpool spas, hot tubs, decorative fountains, and showers.
Respiratory therapy equipment and ice machines.
A 24-year-old male presents with acute fever and systemic symptoms from a bacterial infection. He is prescribed penicillin. Penicillin is most effective against bacteria in which phase of the bacterial growth curve?
Log Phase: Many antibiotics Penicillin included act on biosynthetic pathways which occur primarily during Log phase
What is the most pyogenic bacterium in human disease and where can it form focal abscesses?
S aureus is the most common pyogenic ("pus-forming") and can produce focal abscesses at almost any site
Name 3 symptoms of an Clostridium tetani infection
Infection by which bacteria results in spastic paralysis: trismus (lockjaw), risus sardonicus (Fixed sneer or smile), exaggerated reflexes, opisthotonos(rigid backward arching of the head, neck and spine) , and respiratory failure, with high mortality.
How does H. influenzae hold onto the mucosa?
IgA protease: It cleaves IgA1 into two fragments Fab and Fc, disabling the Fc portion prevents the host immune system from neutralizing the bacteria and in lots of cases the bacteria retains the Fab portion to hide
A 65-year-old male with a history of heavy smoking presents with a high fever, non-productive cough, severe watery diarrhea, and progressive lethargy and confusion. Laboratory testing reveals a low serum sodium level (hyponatremia). Which diagnosis best unifies these clinical and laboratory findings?
Legionnaires' disease: presents as a severe atypical pneumonia characterized by high fever, cough, and dyspnea, classically accompanied by extrapulmonary features such as watery diarrhea, neurological symptoms (confusion, lethargy), and hyponatremia
Cigarette smoking and age >50>50 are prominent risk factors
A 34-year-old male presents with a painful, fluctuant soft tissue abscess following a cutaneous streptococcal infection. Aspiration yields thick, highly viscous pus. Which bacterial extracellular enzyme directly thins this purulent fluid to facilitate tissue spread?
Deoxyribonuclease: Streptococcal deoxyribonuclease hydrolyzes DNA released from dead leukocytes, thinning viscous pus and enabling local bacterial dissemination
A microbiology laboratory isolates a resistant strain of Escherichia coli. Genetic analysis demonstrates that the resistance determinants are organized within transposons that move between plasmids and the chromosome. Which class of resistance enzymes is organized on transposons?
Aminoglycoside-modifying enzymes: Plasmid mediated Beta-lactamases, tetracycline resistance genes, and aminoglycoside-modifying enzymes are organized within transposons
A 68-year-old hospitalized patient with an indwelling urinary catheter develops a urinary tract infection. Lab analysis identifies a Gram-positive organism that reacts with group D antisera and is distinguished from streptococci by its ability to resist bile and high salt concentrations. What is the primary route of transmission for this organism in hospital settings?
Enterococcus: Hands of health care workers
A 35-year-old construction worker recovers from generalized tetanus after receiving intensive supportive care and human tetanus immune globulin. Prior to discharge, his physician administers a dose of active tetanus toxoid vaccine (Tdap). What is the primary rationale for actively immunizing a patient who has just survived clinical tetanus?
The amount of tetanospasmin required to cause severe clinical disease is too small to be immunogenic so immunization with the toxoid is still necessary
A medical researcher studies the spatial distribution of the human microbiome across various anatomical biomes. Which anatomical site harbors the highest overall microbial density in the human body, dominated primarily by strict anaerobes such as Bacteroides species?
The large intestine (colon) possesses the highest microbial density in the human body, which is predominantly populated by strict anaerobes such as Bacteroides species and Escherichia coli.
A 42-year-old field worker in rural South America presents with fever, lymphadenopathy, and a swollen bite lesion on his face. He reports being bitten by a triatomine bug at night and rubbing the area. What mechanism permitted Trypanosoma cruzi entry?
Scratching vector feces into the bite wound: Reduviid bugs defecate as they bite/feed and host scratching introduces the parasites to enter into the bite wound
A newborn infant develops severe neonatal sepsis shortly after birth. Maternal history reveals consumption of unpasteurized soft cheese during the third trimester. The causative pathogen is a Gram-positive rod. Which other patient populations are highlighted as particularly susceptible to serious infections from this organism?
Listeria monocytogenes is a Gram-positive rod that causes serious, life-threatening infections primarily in infants, pregnant women, and immunocompromised adults.
A 62-year-old male with lobar pneumonia develops high fever, shaking chills, splinting pleuritic chest pain, and rust-colored sputum. Shortly after receiving his first dose of bactericidal antibiotic therapy, his inflammatory symptoms temporarily worsen. Which bacterial structure is primarily responsible for inducing this intense host inflammatory response?
Released cell wall fragments
An intubated patient in the intensive care unit develops ventilator-associated pneumonia caused by a gram-negative rod. Culture confirms the presence of an organism that does not require Factors X(Heme) or V(NAD) and has no available vaccine or contact prophylaxis. What is the habitat and human colonization of this organism?
The organism causing ventilator-associated pneumonia in this setting is Acinetobacter baumannii. It lives in environmental water and also colonizes human skin and the upper respiratory tract.
A microbiology technician prepares Thayer-Martin selective agar to isolate Neisseria species from a non-sterile mucosal swab. Name 3 of the specific combination of antimicrobial agents is incorporated into Thayer-Martin agar to suppress Gram-positive bacteria, Gram-negative bacteria, fungi, and Proteus species.
Thayer-Martin agar is a selective chocolate agar base used for isolating Neisseria species from non-sterile sites. It contains Vancomycin (inhibits Gram-positives), Colistin (inhibits Gram-negatives), Nystatin (inhibits fungi), and Trimethoprim (inhibits swarming Proteus)
A bedridden, elderly patient hospitalized in the intensive care unit develops hospital-acquired pneumonia caused by Pseudomonas aeruginosa. What alteration in mucosal surface biochemistry predisposed the patient to oropharyngeal colonization by Gram-negative bacilli?
Loss of surface fibronectin protein: Fibronectin normally coats mucosal epithelium and favors Gram-positive colonization; loss of it combined with poor health lets gram-negative bacilli displace gram-positives
Four hours after consuming potato salad at an outdoor picnic, a 30-year-old man experiences a sudden onset of severe nausea, intense abdominal cramping, and profuse vomiting. He remains afebrile, and several other attendees report identical acute symptoms. Which property of staphylococcal enterotoxins explains why disease occurs rapidly without requiring active bacterial replication inside the host?
Enterotoxins are heat-stable, protease-resistant preformed toxins that act on the brain vomiting center
Four hours after eating fried rice at a restaurant buffet where cooked rice had been kept warm for several hours, three patrons experience an abrupt onset of severe nausea and vomiting. The causative aerobic, spore-forming gram-positive rod produced an enterotoxin responsible for this short-incubation emetic presentation. The action of which specific emetic toxin resembles this response?
Bacillus cereus spores on grains such as rice survive steaming and rapid frying, germinating when rice is kept warm for hours. B. cereus produces two distinct enterotoxins:
A short-incubation (~4 h) emetic toxin causing nausea and vomiting, which acts like staphylococcal enterotoxin
A long-incubation (~18 h) diarrheal toxin causing watery diarrhea, which acts like cholera toxin (ADP-ribosylates G protein →→ ↑↑cAMP)
A laboratory scientist attempts to isolate Bordetella pertussis from a nasopharyngeal swab collected from an infant during the early catarrhal stage of whooping cough. The standard agar media used for growing common Gram-negative rods fails to support growth. The addition of which component to specialized growth media (such as Regan-Lowe or Bordet-Gengou agar) is essential to neutralize fatty acids and toxic metabolites that inhibit B. pertussis?
Charcoal and Potato Starch: Bordetella pertussis is a fastidious organism that is extremely sensitive to fatty acids, heavy metals, peroxides, and sulfur compounds present in standard media.
Specialized media, such as Bordet-Gengou (potato-glycerol-blood) or Regan-Lowe (charcoal-horse blood agar), utilize blood for nutritional demands, while charcoal or potato starch acts to neutralize inhibitory fatty acids and toxic compounds.
A 19-year-old college student presents with fatigue, low-grade fever, and a persistent dry, hacking cough ("walking pneumonia"). Sputum testing confirms Mycoplasma pneumoniae. Based on its structural characteristics, why are beta-lactam antibiotics completely ineffective against this organism?
Mycoplasma species completely lack a peptidoglycan cell wall, being bounded only by a single plasma membrane containing sterols. Because beta-lactam antibiotics act specifically by inhibiting peptidoglycan synthesis, Mycoplasma species are inherently resistant to all beta-lactam agents