Microbiology Quiz: Antibiotic Effectiveness and Staining

Antibiotics and Microorganisms

• Aminoglycoside antibiotics are ineffective against anaerobes, Trypanosomes, and Plasmodium because they require oxygen to enter the bacterial cell.
• Silver stain is used to diagnose Helicobacter pylori, Legionella, Bartonella henselae, and fungi (e.g., Coccidioides, Pneumocystis jirovecii, Aspergillus fumigatus).
• Periodic acid Schiff stain is used to stain glycogen, mucopolysaccharides, and is used to diagnose Whipple disease (Tropheryma whipplei).

Anaerobes and Facultative Anaerobes

• Anaerobes can't breathe fresh air, and examples include Clostridium, Bacteroides, Fusobacterium, and Actinomyces.
• Mnemonic: Anaerobes Cant Breath Fresh Air.
• Facultative anaerobes utilize oxygen if it is present, but can use fermentation in its absence.
• Examples of facultative anaerobes include Clostridium/Clostridioides perfringens, which is a gas-forming bacterium.

Clostridium and Corynebacterium

• Clostridium tetani has a tennis racket, drumstick, or lollipop shape.
• Clostridium/Clostridioides perfringens causes gas gangrene.
• Corynebacterium diphtheria has a Chinese character, curved, non-motile shape.
• Corynebacterium diphtheria causes diphtheria, an important cause of serious healthcare-associated and community-acquired infections.

Staphylococcus and Streptococcus

• Staphylococcus aureus is a facultative anaerobe, catalase positive, and coagulase positive.
• Staphylococcus aureus has a reservoir in anterior nares and skin, and is transmitted through direct contact and fomites, contaminated food.
• Staphylococcus aureus has virulence factors, including coagulase, leukocidin, catalase, penicillinase, hyaluronidase, and protein A.
• Staphylococcus epidermidis is a facultative anaerobe, catalase positive, and coagulase negative.
• Staphylococcus epidermidis has a reservoir in skin, and is transmitted through direct contact, and autoinfection.

Helicobacter and Legionella

• Helicobacter pylori is a curved, non-motile bacterium.
• Helicobacter pylori is diagnosed using a silver stain.
• Legionella pneumophila grows in chocolate yeast extract agar, and requires L-cysteine and iron.
• Legionella pneumophila is transmitted through airconditioning systems, and has no person-to-person transmission.

Escherichia and Shigella

• Escherichia coli is a gram-negative rod, and is catalase positive.
• Escherichia coli has a capsule, fimbriae, pili, and flagella, which are used for attachment, causing cystitis and pyelonephritis.
• Escherichia coli has toxins, including endotoxin, entero toxins, and siderophores, which obtain iron from human transferrin or lactoferrin.
• Shigella spp. has a comma-shaped with single polar flagellum, and grows as flat yellow colonies on TCBS agar.
• Shigella spp. causes diarrhea, and has a characteristic sign, Washing Woman's Hands Sign, due to dehydration.

Aerotolerant Anaerobes

• Exclusively anaerobic but insensitive to the presence of oxygen
• Cryptococcus neoformans can be stained with India ink (mucicarmine can also be used)

Gram Positive vs. Gram Negative Bacteria Cell Walls

• Gram positive bacteria:
  • Thicker, multilayer peptidoglycan
  • Teichoic acid present
  • Lipopolysaccharide absent
  • Periplasmic space absent
• Gram negative bacteria:
  • Thinner peptidoglycan
  • Teichoic acid absent
  • Lipopolysaccharide present
  • Periplasmic space present

Exotoxins and Endotoxins

• Not mentioned in the provided text

Gram Positive Cocci

• In clusters: Staphylococci
  • Staphylococcus aureus: catalase positive, coagulase positive
  • Staphylococcus epidermidis: catalase positive, coagulase negative, novobiocin sensitive
  • Staphylococcus saprophyticus: catalase positive, coagulase negative, novobiocin resistant
• In chains: Streptococci
  • Streptococcus pneumoniae: catalase negative, alpha hemolytic, bile optochin sensitive
  • Viridans streptococci: catalase negative, alpha hemolytic, bile optochin resistant
  • Streptococcus pyogenes (Group A Beta-Hemolytic Streptococci): catalase negative, beta hemolytic, bacitracin sensitive
  • Streptococcus agalactiae (Group B Beta-Hemolytic Streptococci): catalase negative, beta hemolytic, bacitracin resistant

Gram Positive Bacilli

• Spore-formers: living
• Parts of a Bacteria
  • Cytoplasmic membrane: lipoprotein bilayer without sterols, site of oxidative and transport enzymes
  • Ribosome: RNA and protein in 50s and 30s subunits, protein synthesis
  • Nucleoid: DNA, genetic material
  • Mesosome: invagination of plasma membrane, participates in cell division and secretion
  • Periplasm: space between plasma membrane and outer membrane, contains many hydrolytic enzymes
  • Capsule: polysaccharide, protects against phagocytosis
  • Pillus or Fimbria: glycoprotein, for attachment and conjugation
  • Glycocalyx: polysaccharide, mediates adherence to surfaces
  • Flagellum: protein, for motility
  • Spore: keratin-like coat, dipicolinic acid, resistant to heat and chemicals
  • Plasmid: glycogen, lipids, polyphosphates, genes for antibiotic resistance and toxins
  • Granule: glycogen, lipids, polyphosphates, site of nutrients in cytoplasm

Mechanism of Resistance: Beta-Lactamase

• Not mentioned in the provided text

Intracellular Organisms

• Obligate intracellular organisms: rely on host's ATP
  • Genus Rickettsia, Chlamydia, Coxiella
• Facultative intracellular organisms:
  • Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis

Antimicrobial Drugs

• Not mentioned in the provided text

Bacterial Metabolism

• Aerobic metabolism:
  • Obligate aerobes: completely dependent on oxygen for ATP generation
  • Microaerophiles: use fermentation but can tolerate low amounts of oxygen
• Anaerobic metabolism:
  • Obligate anaerobes:
    • Genus Clostridium, Bacteroides, Fusobacterium, Actinomyces
    • Lack catalase and/or superoxide dismutase and are susceptible to oxidative damage
    • Generally foul-smelling (short-chain fatty acids)
    • Difficult to culture
    • Produce gas in tissue (CO2 and H2)

Staining Techniques

• Gram staining: single most important initial test in bacteriology
• Giemsa stain: for certain bacteria that do not take up the Gram stain well

Other Microorganisms

• Streptococcus agalactiae (GBS):

  • Metabolism: catalase negative, bacitracin resistant
  • Transmission: vagina, transvaginal and transplacental
  • Clinical syndromes: UTI in pregnant women, neonatal pneumonia, sepsis, and meningitis

• Causative Agents of Neonatal Meningitis:

  • Group B strep, E. coli, Listeria

• Group D Streptococci:

  • Metabolism: catalase negative, bile optochin resistant
  • Transmission: reservoir: human, urethra and female genitalia may be colonized
  • Clinical syndromes: UTI due to indwelling urinary catheter and instrumentation, biliary tract infections### Clostridium difficile

• Caused by Clindamycin, ampicillin, 2nd-3rd gen cephalosporins

• Nonbloody diarrhea associated with pseudomembranes

• Toxic megacolon

• Diagnosis: anaerobic condition, thioglycolate agar, patient's serum injection to mice causing death

• Treatment: antitoxin, human botulism Ig, metronidazole or penicillin, supportive Tx, Botox

Clostridium perfringens

• Transmission: endospores, contamination of wound with soil or feces, food poisoning
• Toxins: alpha toxin (lecinthase), splits lecithin, cleaves cell membranes
• Clinical syndromes: gas gangrene, d/t alpha toxin, gas by anaerobic metabolism, pain
• Diagnosis: culture under anaerobic conditions, double hemolysis on blood agar, growth on egg yolk agar
• Treatment: wound care, penicillin, radical surgery, supportive

Clostridium botulinum

• Wound botulism: similar to food botulism but without GI symptoms
• Diagnosis: anaerobic condition, thioglycolate agar, patient's serum injection to mice causing death
• Treatment: antitoxin, human botulism Ig, metronidazole or penicillin, supportive Tx

Corynebacterium diphtheriae

• Metabolism: facultative anaerobe, catalase positive
• Transmission: reservoir - throat, transmitted by respiratory droplets
• Virulence Factors: pseudomembrane, exotoxin (from a temperate bacteriophage)
• Clinical syndromes: diphtheria, mild sore throat with fever initially, pseudomembranes forms on the pharynx
• Diagnosis: club/comma-shaped rods arranged in V or L, culture: potassium tellurite, modified Elek Test
• Treatment and Prevention: antitoxin, penicillin or Erythromycin, vaccine DPT is a formalin inactivated exotoxin

Listeria monocytogenes

• Transmission: ingestion of contaminated raw milk or cheese from infected cows
• Toxins: listeriolysin O (allows escape from phagolysosomes), actin rockets (propels through bacteria through one membrane to another)
• Clinical syndromes: early onset neonatal listeriosis, granulomatosis infanseptica, late onset neonatal listeriosis, meningitis, meningoencephalitis, adult listeriosis
• Diagnosis: rods arranged in V or L shapes, tumbling motility, culture can grow at cold enrichment to isolate from normal flora
• Treatment and prevention: ampicillin + Gentamicin, TMP + SMX, NOT Cephalosporins

Neisseria meningitidis

• Metabolism: ferments both maltose and glucose, oxidase Positive on chocolate agar, grows best in high CO2
• Transmission: URT droplets, high carriage in close quarters, dormitories, camps
• Virulence Factors: capsule (13 serotypes), endotoxin LPS (causes blood vessel destruction and sepsis), pili (allow attachment to human Nasopharynx and undergo antigenic variation to avoid attack by immune system)

Helicobacter Pylori

• Damages goblet cells
• Facultative gram-negative with peritrichous flagella
• Swarming pattern
• Urease positive
• Causes peptic ulcer disease

Pseudomonas aeruginosa

• Metabolism: non-lactose fermenter, oxidase positive
• Virulence factors: motile, elastase, protease, pyocyanin
• Toxins: endotoxin, exotoxin A (similar to diphtheria toxin)
• Clinical syndromes: burn and wound infections, hot tub folliculitis, skin graft loss, bone and cartilage infections, ear infections, pneumonia, gastrointestinal infections, ecthyma gangrenosum
• Treatment and prevention: antipseudomonal penicillins, cephalosporins, carbapenems, fluoroquinolones

Chlamydia trachomatis

• Metabolism: obligate intracellular parasite
• Transmission: sexual, passage through birth canal, hand-to-eye contact
• Virulence factors: resistant to lysozyme
• Clinical syndromes: trachoma, genital tract infection, neonatal pneumonia, lymphogranuloma venereum
• Diagnosis: cytoplasmic inclusions, PCR, NAAT
• Treatment and prevention: doxycycline, erythromycin, azithromycin, ceftriaxone

Mycobacterium tuberculosis

• Metabolism: slow grower, obligate aerobe, acid-fast organism
• Transmission: inhalation of respiratory droplet nuclei
• Virulence factors: mycolic acid, cord factor, sulfatides, wax D
• Clinical syndromes: exudative and granulomatous lesions, primary complex, Ghon complex, reactivation tuberculosis
• Diagnosis: acid-fast stain, PCR, NAAT
• Treatment and prevention: antituberculous medications, vaccination

Bacteroides fragilis

• Metabolism: anaerobe, capsule, pili
• Transmission: predominant anaerobe of human colon
• Virulence factors: lipopolysaccharide, capsule
• Clinical syndromes: abdominal abscess, peritonitis, pericarditis, endocarditis, cerebral abscess
• Diagnosis: anaerobic gram-negative
• Treatment and prevention: metronidazole, chloramphenicol

Mycobacterium leprae

• Transmission: prolonged exposure to nasal secretions with lepromatous form
• Clinical syndromes: leprosy, Hansen disease
• Diagnosis: PCR, biopsy
• Treatment and prevention: antileprotic medications, vaccination

Neisseria meningitidis

• Resistant to colistin, most saprophytic species of Neisseria susceptible

Bordetella pertussis

• Transmission: via respiratory droplets
• Virulence Factors:
  • Capsule
  • Beta lactamase
  • Filamentous hemagglutinin mediates attachment
• Toxins:
  • Pertussis Toxin: ADP ribosylation activates G proteins
  • Extracytoplasmic adenylate cyclase: inhibits phagocytosis
  • Tracheal cytotoxin: kills epithelial cells and paralyzes cilia
• Clinical syndromes: whooping cough, paroxysmal pattern of hacking coughs
• Diagnosis:
  • Nutritionally fastidious
  • Pleomorphic
  • Poorly gram-negative rods
• Treatment and Prevention:
  • Azithromycin
  • Levofloxacin
  • Doxycycline
  • Reducing cigarette and alcohol consumption
  • High temperatures and hyperchlorination in hospital water supply

Escherichia coli

• Metabolism:
  • Indole Positive
  • Lactose fermenter on EMB and MacConkey agar
  • Green metallic sheen on EMB
  • Triple Sugar Iron Agar shows acid with gas and no H2S production
• No H2S production

Shigella

• Biochemically inert enterobacteriaceae
• Transmission: infection
• Shigella is usually non-chalant since gastrectomy or use of antacids lowers infectious dose significantly
• Symptoms: N/V, abdominal pain, and nonbloody diarrhea
• Reactive arthritis (Reiter syndrome): triad of Uveitis, Urethritis, Arthritis
• Diagnosis: comma-shaped or S-shaped with single polar flagellum
• Treatment and Prevention: symptomatic treatment, Erythromycin for severe cases

Campylobacter jejuni

• Necrotizing Pneumonia
• Usually nosocomial with thick bloody sputum
• UTI
• Sepsis

Haemophilus influenzae

• Facultative with large polysaccharide capsule
• Currant jelly sputum
• Treatment and Prevention: culture-guided treatment, Cephalosporins +/- Aminoglycosides

Proteus mirabilis

• Metabolism:
  • Urease positive
  • Indole negative
  • Non-lactose fermenter
• Virulence Factors:
  • Motile
  • Fimbriae for adherence
  • LPS
  • Urease production
• Clinical syndromes:
  • Complicated UTI associated with nephrolithiasis
  • Sepsis

Helicobacter pylori

• Metabolism:
  • Microaerophilic
  • Oxidase positive
  • Catalase positive
  • Urease positive
  • Triple positive
• Transmission: ingestion, habitat: human stomach
• Virulence Factors:
  • Urease produces ammonia makes the environment alkaline

Neisseria meningitidis

• Resistant to colistin, most saprophytic species of Neisseria susceptible

Bordetella pertussis

• Transmission: via respiratory droplets
• Virulence Factors:
  • Capsule
  • Beta lactamase
  • Filamentous hemagglutinin mediates attachment
• Toxins:
  • Pertussis Toxin: ADP ribosylation activates G proteins
  • Extracytoplasmic adenylate cyclase: inhibits phagocytosis
  • Tracheal cytotoxin: kills epithelial cells and paralyzes cilia
• Clinical syndromes: whooping cough, paroxysmal pattern of hacking coughs
• Diagnosis:
  • Nutritionally fastidious
  • Pleomorphic
  • Poorly gram-negative rods
• Treatment and Prevention:
  • Azithromycin
  • Levofloxacin
  • Doxycycline
  • Reducing cigarette and alcohol consumption
  • High temperatures and hyperchlorination in hospital water supply

Escherichia coli

• Metabolism:
  • Indole Positive
  • Lactose fermenter on EMB and MacConkey agar
  • Green metallic sheen on EMB
  • Triple Sugar Iron Agar shows acid with gas and no H2S production
• No H2S production

Shigella

• Biochemically inert enterobacteriaceae
• Transmission: infection
• Shigella is usually non-chalant since gastrectomy or use of antacids lowers infectious dose significantly
• Symptoms: N/V, abdominal pain, and nonbloody diarrhea
• Reactive arthritis (Reiter syndrome): triad of Uveitis, Urethritis, Arthritis
• Diagnosis: comma-shaped or S-shaped with single polar flagellum
• Treatment and Prevention: symptomatic treatment, Erythromycin for severe cases

Campylobacter jejuni

• Necrotizing Pneumonia
• Usually nosocomial with thick bloody sputum
• UTI
• Sepsis

Haemophilus influenzae

• Facultative with large polysaccharide capsule
• Currant jelly sputum
• Treatment and Prevention: culture-guided treatment, Cephalosporins +/- Aminoglycosides

Proteus mirabilis

• Metabolism:
  • Urease positive
  • Indole negative
  • Non-lactose fermenter
• Virulence Factors:
  • Motile
  • Fimbriae for adherence
  • LPS
  • Urease production
• Clinical syndromes:
  • Complicated UTI associated with nephrolithiasis
  • Sepsis

Helicobacter pylori

• Metabolism:
  • Microaerophilic
  • Oxidase positive
  • Catalase positive
  • Urease positive
  • Triple positive
• Transmission: ingestion, habitat: human stomach
• Virulence Factors:
  • Urease produces ammonia makes the environment alkaline