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Questions and Answers
Which agar medium is selective for Burkholderia species?
Which agar medium is selective for Burkholderia species?
What is the primary mode of transmission for Vibrio cholerae?
What is the primary mode of transmission for Vibrio cholerae?
What is the appearance of colonies on OFPBL Agar?
What is the appearance of colonies on OFPBL Agar?
Which of the following describes a key feature of the cholera toxin?
Which of the following describes a key feature of the cholera toxin?
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What is the main causative pathogen of melioidosis?
What is the main causative pathogen of melioidosis?
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Which characteristic best describes Vibrio species?
Which characteristic best describes Vibrio species?
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What treatment is essential for reducing mortality in severe cholera cases?
What treatment is essential for reducing mortality in severe cholera cases?
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What is the recommended preventive measure against cholera before traveling to endemic areas?
What is the recommended preventive measure against cholera before traveling to endemic areas?
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What is the preferred treatment of Burkholderia infections?
What is the preferred treatment of Burkholderia infections?
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Which population is considered at highest risk for severe Vibrio vulnificus infection?
Which population is considered at highest risk for severe Vibrio vulnificus infection?
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What is the recommended age for the booster dose of the Hib vaccine?
What is the recommended age for the booster dose of the Hib vaccine?
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What is primarily responsible for the majority of Campylobacter infections in the US?
What is primarily responsible for the majority of Campylobacter infections in the US?
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What is the impact of H.pylori on the stomach's acid production?
What is the impact of H.pylori on the stomach's acid production?
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What method is NOT typically used for the diagnosis of H.pylori?
What method is NOT typically used for the diagnosis of H.pylori?
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Which disease is associated with infection by Campylobacter?
Which disease is associated with infection by Campylobacter?
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What is one of the key virulence factors of Neisseria species?
What is one of the key virulence factors of Neisseria species?
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What type of environment do Helicobacter species prefer for growth?
What type of environment do Helicobacter species prefer for growth?
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What is a treatment option recommended for symptomatic patients infected with H.pylori?
What is a treatment option recommended for symptomatic patients infected with H.pylori?
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What is a common method of transmission for Vibrio parahaemolyticus infections?
What is a common method of transmission for Vibrio parahaemolyticus infections?
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Which of the following describes a common symptom associated with primary bacteremia from contaminated oysters?
Which of the following describes a common symptom associated with primary bacteremia from contaminated oysters?
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Which bacterium is classified by the presence of an antiphagocytic polysaccharide capsule?
Which bacterium is classified by the presence of an antiphagocytic polysaccharide capsule?
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Which type of agar is essential for the growth of Haemophilus species?
Which type of agar is essential for the growth of Haemophilus species?
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What clinical syndromes are commonly associated with Haemophilus influenzae infections?
What clinical syndromes are commonly associated with Haemophilus influenzae infections?
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Which treatment is commonly recommended for Haemophilus influenzae infections?
Which treatment is commonly recommended for Haemophilus influenzae infections?
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What role do antibodies against the capsule of Haemophilus influenzae play?
What role do antibodies against the capsule of Haemophilus influenzae play?
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How do marine bacteria typically cause infections in humans?
How do marine bacteria typically cause infections in humans?
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What is the primary cause of gonorrhea?
What is the primary cause of gonorrhea?
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Which of the following proteins helps Neisseria gonorrhoeae bind to epithelial and phagocytic cells?
Which of the following proteins helps Neisseria gonorrhoeae bind to epithelial and phagocytic cells?
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What is a common complication of gonorrhea in males?
What is a common complication of gonorrhea in males?
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What diagnostic method is superior for detecting Neisseria gonorrhoeae infections?
What diagnostic method is superior for detecting Neisseria gonorrhoeae infections?
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Which of the following is a method of transmission for Neisseria meningitidis?
Which of the following is a method of transmission for Neisseria meningitidis?
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Which is a common symptom of meningitis caused by Neisseria meningitidis?
Which is a common symptom of meningitis caused by Neisseria meningitidis?
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What is the recommended treatment for gonorrhea?
What is the recommended treatment for gonorrhea?
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What role do Rmp proteins play in Neisseria gonorrhoeae?
What role do Rmp proteins play in Neisseria gonorrhoeae?
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What is the primary mode of transmission for Yersinia pestis during a Bubonic Plague outbreak?
What is the primary mode of transmission for Yersinia pestis during a Bubonic Plague outbreak?
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Which factor contributes to the higher mortality rate of Pneumonic Plague compared to Bubonic Plague?
Which factor contributes to the higher mortality rate of Pneumonic Plague compared to Bubonic Plague?
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What is the incubation period range for Yersinia enterocolitica infection?
What is the incubation period range for Yersinia enterocolitica infection?
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Which of the following characteristics is associated with Pseudomonas aeruginosa?
Which of the following characteristics is associated with Pseudomonas aeruginosa?
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Which virulence factor of Pseudomonas aeruginosa is responsible for endotoxin activity?
Which virulence factor of Pseudomonas aeruginosa is responsible for endotoxin activity?
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In which patient population is Pseudomonas aeruginosa most likely to be an opportunistic pathogen?
In which patient population is Pseudomonas aeruginosa most likely to be an opportunistic pathogen?
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What is a common clinical syndrome associated with Pseudomonas aeruginosa in hospitalized patients?
What is a common clinical syndrome associated with Pseudomonas aeruginosa in hospitalized patients?
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Which of the following syndromes is LEAST likely to be caused by Pseudomonas aeruginosa?
Which of the following syndromes is LEAST likely to be caused by Pseudomonas aeruginosa?
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What type of resistance is commonly seen with mucoid strains of Pseudomonas aeruginosa in cystic fibrosis patients?
What type of resistance is commonly seen with mucoid strains of Pseudomonas aeruginosa in cystic fibrosis patients?
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What characteristic differentiates Acinetobacter spp. from many other gram-negative bacteria?
What characteristic differentiates Acinetobacter spp. from many other gram-negative bacteria?
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Study Notes
Gram-Negative Aerobes: Antosz
- Gram-negative aerobic bacteria characteristics include morphology, growth characteristics, and classification
- Biochemical tests are used to identify gram-negative aerobic bacteria
- Clinically relevant species of gram-negative aerobic bacteria are listed
- Pathogenesis and clinical syndromes associated with each gram-negative aerobic bacteria are described
- Gram-negative bacteria resistance mechanisms against common antibiotic classes are recognized
Enterobacterales
- Enterobacterales are an order of gram-negative bacteria
- Enterobacterales share an enterobacterial common antigen
- Classified under the family Enterobacteriaceae
- Rod-shaped
- Facultative anaerobes (can survive with or without oxygen)
- Ferment glucose
- Reduce nitrate to nitrite
- Catalase positive
- Oxidase negative
- Some resistant to bile salts
Gram-Positive vs. Gram-Negative
- Gram-positive bacteria have a thick peptidoglycan layer in their cell wall and no lipopolysaccharide membrane; they produce exotoxins and stain purple
- Gram-negative bacteria have a thin peptidoglycan layer, a lipopolysaccharide membrane, produce endotoxins, and stain red/pink
Endotoxin
- Lipopolysaccharides in the outer membrane of gram-negative bacteria
- Capable of causing lethal shock to the cell
- Activates a complement system, leading to cytokines, leukocytosis, thrombocytopenia, fever, decreased peripheral circulation, and shock, death
Capsule
- Gram-negative bacteria encapsulated by hydrophilic capsular antigens
- Protected by phagocytosis by antigens binding to antibodies
- Protective role diminishes if specific anticapsular antibodies develop
Antimicrobial Resistance
- Extended-spectrum beta-lactamases (ESBLs)
- Mutations in DNA gyrase and topoisomerase
Common Enterobacterales
- Escherichia coli (Escherich; coli, of the colon)
How to Identify Organisms
- Sterile specimens: non-selective media (blood agar)
- Non-sterile specimens: selective media (MacConkey agar)
- Biochemical tests (automated systems, benchtop tests)
- Rapid diagnostic tests (spot indole, oxidase)
- Multiplex PCR
- MALDI-TOF MS
MacConkey Agar
- Selective and differential agar
Lactose-Fermenters
- Escherichia Coli
- Klebsiella spp.
- Enterobacter spp.
- Citrobacter spp. (except C. koseri)
Nonlactose-Fermenters
- Salmonella spp.
- Shigella spp.
- Serratia spp.
- Proteus spp.
Spot Indole Test
- Detects bacteria ability to metabolize tryptophan to produce indole
- Drop indole reagent on filter paper
- Observe color change within 20 seconds
- Indole (+): Escherichia coli; Klebisella oxytoca
- Indole (-): Enterobacter cloacae; Klebsiella aerogenes
Oxidase Test
- Identify bacteria that produce cytochrome c oxidase.
- Drop reagent (tetramethyl-p-phenylenediamine) onto filter paper
- Observe color change within 10 seconds.
- Oxidase (+): Pseudomonas spp.; Vibrio spp.
- Oxidase (-): Salmonella spp., Acinetobacter spp.
Escherichia Coli
- Most common and clinically significant Enterobacterales
- Part of normal GI tract flora; can colonize lower urethra/vagina
- Associated with urinary tract infections (UTI), gastroenteritis, meningitis (neonatal), and sepsis
E. Coli Morphology
- Circular, smooth, flat, nonviscous colonies with distinct edges
- Hemolysis on blood agar
- Metallic sheen on different agars
- Lactose fermenter
- Indole positive
Clinical Syndromes: UTI
- Treatment for UTI involves using antimicrobials that achieve concentrations in urine (fosfomycin, nitrofurantoin, bactrium, fluoroquinolones).
Salmonella
- Transmission: Contaminated food or water
- Symptoms: N/V, non-bloody diarrhea, fever, cramps, myalgias, headaches
- Onset: 2-7 days, most common: Salmonella Typhi, Salmonella Paratyphi, and Salmonella choleraesuis
Clinical Syndromes: Bacteremia/Sepsis
- Typically from urinary or GI tract infections
- 40-60 % of all bloodstream infections caused by gram-negative bacteria
- High mortality rate
Escherichia Coli: Resistance
- Beta-lactamases
Klebsiella Spp.
- Non-motile, large polysaccharide capsules (mucoid)
- Wet, heaped, viscous colonies
- Most common species: K. pneumoniae, K. oxytoca, K. aerogenes
- Lactose fermenter, Indole (-): K. pneumoniae, K. aerogenes/ Indole (+): K. oxytoca
- Associated with Pneumonia, UTIs (cystitis, pyelonephritis), and wound/soft tissue infections
Resistance mechanism
- Similar to E. coli
- blaKPC gene encodes carbapenemase enzyme
Enterobacter Spp.
- Raised colonies, no sheen, motile, somewhat mucoid
- Most common: E. Cloacae
- Lactose fermenting
- Indole negative
- Associated with hospital-acquired infections
Serratia Spp.
- Small, rounded colonies, some pink-pigmented
- Slow lactose fermenter (often negative)
- Oxidase negative
- Associated with pneumonia, bacteremia, and endocarditis.
Citrobacter Spp.
- Motile, Citrate (+)
- Most common clinical species are C. freundii and C. koseri
- C. freundii is lactose-fermenting
- Associated with hospital-acquired infections (UTIs, wounds).
Enterobacter, Citrobacter, Serratia Resistance
- AmpC: beta-lactamase aka “cephalosporinases.”
- Confer resistance to penicillin, monobactams, ß-lactamase inhibitors, and cephalosporins
- Level of enzyme expression determines resistance degree.
- Common mechanism of acquisition is chromosomal AmpC gene.
Proteus Spp., Morganella Spp., Providencia Spp.
- Motile, slow/non-lactose fermenters
- Proteus species can swarm on media due to motility.
- Proteus and Morganella: urease (+) - generates CO2 and ammonia (distinctive ammonia smell)
- Increases urine pH, causing precipitation of Mg and Ca, leading to kidney stones.
- Providencia: urease (-)
- Associated with UTIs, pneumonia, bacteremia
Salmonella Spp.
- Motile
- Ferments glucose and mannose
- Resistant to bile salts
- Produces H2S
- Non-lactose/non-sucrose fermenter
- Transmission: fecal-oral.
- Associated with gastroenteritis, bacteremia, enteric fever, and asymptomatic colonization.
Hekaton Enteric Agar
- Selective and differential media
- Divides Salmonella, Shigella, and other species
- Selective ingredients: bile salts, lactose, sucrose, salicin, peptone; Differential ingredients: lactose, sucrose, and salicin fermentation decreases pH; vibrant yellow-orange color.
- Black colonies: H2S (+).
- Green colonies: H2S (-).
- Yellow-orange: H2S (-) Sugar Fermentation (+).
Salmonella Classification
- Most common form of salmonellosis
- Transmission: contaminated food/water
- Highest incidence in summer/fall
- Common sources: poultry, eggs, dairy, contaminated cutting boards
- Symptoms: N/V, non-bloody diarrhea, fever, cramps, myalgias, headaches
- Onset: 6-48 hours, Duration 2-7 days
Salmonella: Bacteremia
- Most common species are Salmonella Typhi, Salmonella Paratyphi, and Salmonella choleraesuis
- Higher risk in peds and immunocompromised
- Clinical presentation similar to other gram-negative infections. Localized suppurative infections (osteomyelitis, endocarditis, arthritis) can occur.
Salmonella: Enteric Fever (Typhoid Fever)
- Severe systemic illness, caused by Salmonella Typhi or Salmonella Paratyphi
- Less frequent in developed countries
- Reservoir: humans, transmission: contaminated food or water
Symptoms:
- Persistent water diarrhea, vomiting, dehydration, low-grade fever
Pathogenesis:
- Autoagglutination: adherence of rods ("stacked bricks") over epithelium of small intestine → cytokine release, shortening of microvilli, hemorrhage, decreased fluid absorption
Shiga Toxin-Producing Escherichia Coli (STEC)
- Consumption of undercooked ground beef/meat products, water, and unpasteurized milk/fruit juices.
- Fewer than 100 bacteria can produce the disease.
- Signs and symptoms include bloody diarrhea (hemorrhagic colitis) and abdominal cramps, which might lead to hemolytic uremic syndrome (HUS).
- Transmission: Person-to-person spread occurs
- Pathogenesis: evolved from EPEC, defined by the presence of Shiga toxin 1 or 2 which disrupts protein synthesis
Enteroinvasive Escherichia Coli (EIEC)
- Rare
- Pathogenic strains are restricted to a few serotypes (0124, 0143, 0164)
- Similar to Shigella
- Symptoms: watery diarrhea; minority progress to dysenteric form (fever, cramps, blood in stool)
- Transmission: fecal-oral
- Pathogenesis: plasmid-mediated invasion and destruction of colonic epithelial cells
Pseudomonas Aeruginosa Epidemiology
- Not part of normal human flora
- Opportunistic pathogens
- After antibiotic exposure; typically restricted to patients receiving broad-spectrum antibiotics that suppress normal intestinal bacterial population.
- Immunocompromised Patients
- Hospitalized Patients
Clinical Syndromes: Pulmonary Disease
- Tracheobronchitis, pneumonia, especially hospital-acquired and ventilator-associated; pulmonary exacerbations in cystic fibrosis
- Asymptomatic colonization → severe necrotizing bronchopneumonia
- Colonization is common in cystic fibrosis patients, chronic lung diseases, and neutropenia
- Mucoid strains are commonly isolated and difficult to eradicate
- Associated with an increase in acquired antibiotic resistance and expression of adaptive responses
Clinical Syndromes: Skin and Soft Tissue
- Most commonly seen with diabetic foot infections and burn wounds
- Colonization of wounds can lead to localized vascular damage, tissue necrosis, and bacteremia.
- Immersion in contaminated water (hot tubs, pools)
Other Clinical Syndromes
- UTIs
- Catheter-related
- Outer ear infections (Swimmer's ear)
- Eye infections
- Bacteremia
- Resistance to Pseudomonas is increasing; combination of antimicrobials may be indicated in serious infections
Acinetobacter Spp.
- Strictly aerobic
- Gram variable: can appear gram-negative or gram-positive
- Ubiquitous saprophytes (found in moist and dry surfaces; rare for gram-neg)
- Most common species is A. baumannii
- Non-lactose fermenter, Oxidase (-)
Associated with
- Part of normal human flora in some humans
- Hospital-acquired infections; especially after antibiotic exposure—Pulmonary infections—Wound infections—UTIs—Bacteremia
Resistance similar to Pseudomonas
- B-lactamases (ESBLs, AmpC, carbapenemases), porin mutations, efflux pumps, aminoglycoside (AGs) modifying enzymes and quinolone (FQs) gyrA and parC mutations
Stenotrophomonas Spp.
- Small, motile, polar flagella
- Ubiquitous in water, soil, plants
- Moist prosthetic surfaces (catheters, ventilators)
- Most common species is S. maltophilia
- Non-lactose fermenter, Oxidase (-), Catalase (+)
- Low pathogenicity, rarely infectious.
Moraxella Spp.
- Short, non-motile gram-negative coccobacilli (except M. catarrhalis, which is diplococci)
- Most common species is M. catarrhalis.
- Non-lactose fermenter
- Oxidase (+), Catalase (+)
- Associated with sinusitis, otitis, bronchitis, pneumonia, and resistant to penicillin
Burkholderia Spp.
- Obligate gram-negative aerobe, motile with flagella
- Most common species are B. cepacia complex (9 species), and B. pseudomallei.
- B. mallei is found in animals
- Everywhere in the environment and moist surfaces
- Non-lactose fermenter
- Most are oxidase (+) and Catalase (+)
- Burkholderia cepacia complex is an opportunistic pathogen with low virulence except in pulmonary infections
- Increased risk in patients with cystic fibrosis and chronic granulomatous disease
- Colonization contraindicated in lung transplant patients with CF.
Burkholderia pseudomallei
- Gram stain: bipolar staining "safety pin" appearance.
- Ashdown's media: crystal violet, gentamicin, neutral red
- Cornflower head-like, metallic colonies, earthy odor
- Causative pathogen in melioidosis
- Endemic in Southeast Asia, Africa, and Australia
- Transmission- inhalation, ingestion, direct contamination of wounds
- Symptoms: skin lesions, fever, malaise, bronchitis/pneumonia → sepsis
- Used in biological weapons
Vibrio Spp.
- Short, curved, motile gram-negative rods
- Facultative anaerobes
- Salt-loving (halophilic; require NaCl for growth)
- Most common species: V. cholerae, V. parahaemolyticus, and V. vulnificus
- All are non-lactose fermenters
Vibrio cholerae
- Causative pathogen of cholera
- 01 and 0139 produce cholera toxin: epidemics
- Common in African and South American regions
- Transmission: consumption of fecally contaminated water; ingestion of shellfish that has not been adequately cooked
- Symptoms: watery diarrhea (“rice-water stools”), vomiting, and electrolyte imbalances
- Cholera toxin is a complex A-B toxin; ring of 5B subunits internalize and interact with G proteins that control adenylate cyclase. This results in the catabolic conversion of ATP to cAMP, leading to hypersecretion of water and electrolytes (able to adhere to mucosal cell layer.)
Vibrio Cholerae: Treatment
- Rehydration (IV replacement) is crucial; decreases mortality
- Severe dehydration: 10% of body weight replacement within 2-4 hours
- Antibiotics (doxycycline, z-pak, ciprofloxacin) may be needed for severe cases or hospitalization.
- Zinc therapy in children is helpful.
Vibrio Cholerae: Prevention
- Wash hands
- Boil it, cook it, peel it, or forget it
- Vaccine (single dose, live oral cholera vaccine): recommended for those traveling to areas of active cholera transmission, 10 days prior to travel.
Vibrio vulnificus
- Virulent species
Other Gram-Negative Bacteria
- Most clinically important: S. dysenteriae, S. sonnei, and S. flexneri
- Transmission: fecal-oral, low inoculum
- Pathogenesis: invade M cells in Peyer’s patches
- Symptoms: diarrhea, fever, abdominal pain, cramping (tenesmus)
Helicobacter Spp.
- Small, thin, motile, spiral-shaped gram-negative rods
- Rapid, corkscrew movement.
- Grow in microaerophilic atmosphere (low O2, high CO2)
- Unable to ferment or oxidize carbohydrates.
- H. pylori is the most common species.
H. Pylori Pathogenesis
- Can establish lifelong colonization in the stomach by blocking acid production, neutralizing acid (via urease), adhering to gastric epithelial cells, and evading immune systems.
- Causes damage through virulence factors.
H. Pylori Diagnosis
- Antibody detection (non-invasive)
- Tissue examination of gastric biopsy
- Urease testing (biopsy or breath test)
- Culture is challenging due to adherence to gastric mucosa.
Treatment
- Symptomatic patients receive combination therapy (e.g., clarithromycin, amoxicillin, PPI)
- Alternatives: bismuth subsalicylate, tetracycline, metronidazole, PPI
Neisseria Spp.
- Short, gram-negative diplococci
- Most common species are "N. gonorrhoea" and "N. meningitides”
- Oxidase (+) and Catalase (+).
N. Meningitides Virulence Factors
- Pili: Attachment to host cells, transfer of genetic material
- Porin proteins (PorA and PorB): form channels for nutrient and waste transport across membranes in bacterial cells.
- Opa proteins: mediate binding to epithelial and phagocytic cells and play a role in cell-to-cell signaling
- Rmp proteins: stimulate antibodies that interfere with serum bactericidal activity
- Protein receptors: transferrin and hemoglobin for iron scavenging.
- Immunoglobulin A1 protease: inactivates IgA1
- Polysaccharide capsule protects against antibody-mediated phagocytosis.
N. gonorrhoeae
- Causative pathogen of gonorrhea
- 2nd most common STD
- Reservoir: exclusively humans
- Transmission: sexual contact
- Females: cervix/vagina
- Males: Urethra/Penis
- Symptoms: symptomatic urethritis
Other Complication Associated with Neisseria Infections
- Epididymitis (most frequent)
- Anorectal infections
- Women: cervicitis, anorectal infections, pelvic inflammatory disease
- Dissemination (septic arthritis, endocarditis, dermatitis, meningitis)
N. meningitidis
- Common causative pathogen of meningitis or meningococcemia
- 6 serotypes: A, B, C, W135, X, Y
- Transmission: respiratory droplets
- Symptoms: fever, headache, vomiting, neck stiffness, myalgia, petechial skin lesions
- Prevention: close contacts receive chemoprophylaxis (rifampin, ciprofloxacin, ceftriaxone)
- Vaccines available.
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Description
Test your knowledge on various bacterial species and their associated diseases with this quiz. Questions cover topics such as transmission, treatment, and prevention of infections caused by Burkholderia, Vibrio, and H. pylori. Ideal for students studying microbiology or healthcare professionals.
