Microscopic Morphology MBLB4500 Flashcards
Streptococcus pyogenes
Gram-positive cocci in chains Group A Beta-hemolytic (SBA) Catalase - Bacitracin sensitive (.04 units) Latex agglutination PYR’ase + (pyroglutamyl aminopeptidase)
Virulence factors
- M protein
- Hyaluronidase
- Streptokinase
- Streptolysin O
Infections
- Pharyngitis, tonsillitis
- Otitis media
- Scarlet fever
- Impetigo
- Cellulitis
Post-streptococcal sequelae
- Rheumatic fever
- Acute glomerulonephritis
Streptococcus agalactiae
Gram-positive cocci in chains Group B Beta-hemolytic (weakly) Catalase - CAMP test + Bacitracin resistant Hippurate hydrolysis + Latex agglutination
Virulence factors
- Produces polysaccharide capsules
- 5 major antigen types
Infections
- Colonizer of female genital tract (10-30%)
- Leading cause of meningitis, septicemia, pneumonia in neonate
(a) Mortality rate 10-15%
(b) Recommendation is to screen all women in 3rd trimester - Urinary tract infections and bacteremia in elderly and immunocompromised 4. Post-surgical gynecologic infection
Streptococcus bovis
Gram-positive cocci
alpha hemolytic/nonhemalytic
Group D
Members of the former “S. bovis group” which are infectious for humans include S. gallolyticus and S. infantarius.
Catalase negative Bile
esculin positive
6.5% NaCl negative (no growth)
Infections - associated with colon cancer and other GI diseases
Streptococcus pneumoniae
Gram-positive diplocci (elongated in shape/Lancet-shaped)
Alpha hemolytic
Catalase -
Optochin susceptible
Bile soluble
Capsule polysaccharide typing (Quellung reaction)
Virulence factors
1. Polysaccharide capsule prevents phagocytosis
2. Pneumolysin that is toxic to pulmonary endothelial cells and may allow spread to
bloodstream
Infections- virulent strains are encapsulated
- Most frequent cause of otitis media in children -Community acquired bacterial pneumonia
- Meningitis
- Sinusitis
Can be normal flora of upper respiratory tract
Enterococcus fecalis
Gram-positive cocci Group D Weakly alpha or non-hemolytic (usually) Catalase negative (or weakly positive) Bile esculin positive Grows in 6.5% NaCl PYR positive
Infections
- Normal flora of intestinal tract
- UTI
- Endocarditis
- Wound infections
Enterococcus faecium
Gram-positive cocci Group D Weakly alpha or non-hemolytic (usually) Catalase negative (or weakly positive) Bile esculin positive Grows in 6.5% NaCl PYR positive
Infections
- Normal flora of intestinal tract
- UTI
- Endocarditis
- Wound infections
Staphylococcus aureus
Gram-positive cocci in clusters
Catalase positive
Coagulase positive
Facultative anaerobe
Non-motile
Non-spore forming
Tolerates increased salt concentrations
Beta-hemolytic (golden pigment on sheep)
Mannitol fermentation (yellow colonies on MSA)
Found on the skin, in the nose, axillae and groin.
Survives for long periods in the environment.
Virulence Factors
- Coagulase
- Leukocidin
- Entertoxins (6 types)
- Lipases
- Hyaluronidase
- Protein A
- Hemolysins
- Skin Infections -
a. Pimples, folliculitis, impetigo, furuncles or boils, carbuncles, abscesses (referred to as pyoderma)
b. Scalded skin syndrome - Food Poisoning
- Toxic Shock Syndrome
- Pneumonia
- Osteomyelitis
- Gastroenteritis
Staphylococcus epidermidis
Gram-positive cocci in clusters Catalase positive Coagulase negative Facultative anaerobe Non-motile Non-spore forming No Mannitol fermentation Tolerates increased salt concentrations
Inhabits skin of most people and is of low virulence.
Diseases
- Endocarditis - heart valves infected
- Prosthetic infections - slime layer of organism inhibits phagocytosis 3. IV site infections - sepsis
Staphylococcus saprophyticus
Gram-positive cocci in clusters Catalase positive Coagulase negative Facultative anaerobe Non-motile Non-spore forming Tolerates increased salt concentrations Resistant to novobiocin
A. Associated with urinary tract infections in young, sexually active women
B. Unique binding property to epithelium of urethra or bladder
Peptostreptococcus sp.
Gram-positive cocci
Micrococcus sp.
Gram-positive cocci Aerobic Catalase + Coagulase - Fermentation of glucose anaerobically - Bacitracin (.04 units) susceptibility: S Furozolidone (100 μg) susceptibility: R Normal flora on skin and in mucous membranes; found in soil and water
Identification: on sheep blood agar, colonies are slow growers (48 hrs) and are often yellow pigmented.

Infection: Rare cause of endocarditis
Neisseria meningitidis
Gram-negative cocci (diplococci; kidney shaped)
Catalase +
Oxidase +
Pili: aid attachment of bacteria to human cells
Aerobic
Capnophilic
Optimal growth at 35-37°C in moist environment
Nonmotile
Non-spore-former
Affinity for mucous membranes
FASTIDIOUS (sensitive to drying and temperature; survives poorly in environment)
Capsules present
Normal nasopharyngeal flora (10%) only reservoir.
Neisseria gonorrhoeae
Gram-negative cocci (diplococci; kidney shaped)
Catalase +
Oxidase +
Pili: aid attachment of bacteria to human cells
Aerobic
Capnophilic
Optimal growth at 35-37°C in moist environment
Nonmotile
Non-spore-former
Affinity for mucous membranes
FASTIDIOUS (sensitive to drying and temperature; survives poorly in environment)
More fastidious than N. meningitidis
Not encapsulated
Veillonella sp.
Gram-negative cocci
Moraxella catarrhalis
Gram-negative cocci Normal flora of upper respiratory tract Not fastidious as N. gonorrhoeae and N. meningitidis (a) grows well on sheep blood agar (b) not sensitive to drying or temperature (c) “push” positive 4. Oxidase + 5. CTA sugars negative
Infections
- otitis media
- sinusitis
- In immunocompromised and elderly
(a) pneumonia
(b) bronchitis
Listeria monocytogenes
Gram-positive rod
Non-spore-former
- Facultative anaerobe
- Beta hemolysis on Sheep Blood Agar
(zone is narrow and colony looks like Strep agalactiae) - Catalase +
- Bile esculin +
- Tumbling motility at 25° C
- Cold enrichment - the organism grows well at 4°C
In humans, significant infections in neonates, pregnant women, and immunocompromised persons
Corynebacterium sp. (“diphtheroids”)
Gram-positive bacilli- pleomorphic rods that palisade or resemble “Chinese characters”
Non-spore-former
Most are catalase +
Corynebacterium diphtheria
Gram-positive bacilli Non-spore-former -Methylene blue stain - shows metachromatic granules -Media/isolation: 1. Loeffler agar slant 2. Sheep blood agar 3. Tellurite or Tinsdale -Toxin production using an Elek plate - this is to determine if the isolate produces diphtheria toxin. Infection – diphtheria
Corynebacterium jeikeium
Gram-positive bacilli
Non-spore-former
1. Normal flora of skin
2. Causes infection mostly in immunocompromised
(a). prosthetic heart valve (b). septicemia
(c). skin infections
3. Often resistant to multiple antibiotics
Nocardia asteroides
Gram-positive bacilli (branching)
Non-spore-former
1. Produces aerial hyphae
2. Always considered a pathogen; pulmonary infections, brain abscesses
3. Colonies are heaped and folded and are often orange or salmon in color
4. Partially acid-fast using the modified Kinyoun stain
Erysipelothrix rhusiopathiae
Gram-positive rod
Erysipelothrix rhusiopathiae
Gram-positive bacilli
Non-spore-former
- One species only
- Facultative anaerobe
- Catalase negative
- Non-motile
- Grows in 8.5% NaCl
- Grows well on SBA, CNA, and Chocolate
- Produces hydrogen sulfide on Triple Sugar Iron
- Disease in humans associated with animals
- Localized infection on skin, particularly fingers and hands
Bacillus sp.
Gram-positive bacilli (large, box car shaped rods that may stain gram variable)
Spore-former
- Generally considered low virulence saprophytes found in the soil, water, dust, and animal products.
- Common contaminants in the laboratory.
- Aerobic or facultative anaerobe
- Catalase +
Bacillus anthracis
Gram-positive bacilli
Spore-former
Causes the infection called anthrax. It is the most virulent human pathogen of the Bacillus species.
a. Animals
b. Humans
- Cutaneous, Pulmonary, GI
Bacillus cereus
Gram-positive bacilli
Spore-former
- Causes food poisoning associated with rice, and eye and wound infections
Bacillus subtilus
Gram-positive bacilli
Spore-former
- Laboratory contaminant
Clostridium perfringens
Gram-positive bacilli (large box car shaped rods)
Spore-former
Anaerobes
Catalase negative (usually)
a. Produces many exotoxins and enzymes that divide the organism into 7 types (A-G), with type A being the most important to humans.
b. Beta-hemolytic on sheep blood agar (double zone hemolysis)
c. Rapid Growth
d. Produces high amounts of gas
e. Lecithinase positive on egg yolk agar
Infection: Gas gangrene (Gas is produced when the muscle carbohydrates are fermented by the organisms.)
Food poisoning.
Clostridium tetani
Gram-positive bacilli
Spore-former
Anaerobes
Catalase negative (usually)
a. Ubiquitous in soil, dust, human and animal excreta.
b. Spores enter the body through wounds, then germinate to vegetative cells. c. Toxin is produced if conditions are right. The toxin goes to the CNS
via the blood stream or lymph nodes and neurally through the tissues.
Infection: Tetanus (Tetanus toxin blocks the relaxation, so both sets of muscle contract.)
Clostridium botulinum
Gram-positive bacilli (large rods)
Spore-former
Anaerobes
Catalase negative (usually)
a. spores in soil, water, and on surface of fresh vegetables.
Infections: Food botulism (The organism multiplies in storage and releases the toxin. The toxin is inactivated by sufficient cooking - heat 1000C for 10 min.) Wound botulism.
Toxin: acts on the peripheral nervous system blocking muscle contraction, resulting in paralysis.
Treatment:
High doses horse antitoxin Supportive measures Penicillin
Actinomyces sp.
Gram-positive rod
Clostridium difficile
Gram-positive bacilli (large rods)
Spore-former
Anaerobes
Catalase negative (usually)
a. Present in the bowel of healthy persons or acquired from an exogenous source.
b. Antibiotic therapy alters the normal flora of the bowel and allows C. difficile to overgrow.
c. Produces toxins; bloody diarrhea is a result and may develop a pseudomembrane - Pseudomembraneous colitis
- Identification is made by detecting the toxin in the stool b. CCFA agar (Cycloserine-Cefoxitin-egg Fructose agar)
- colonies are yellowish with ground glass appearance
- colonies smell like horse manure!
Propionibacterium acnes
Gram-positive rod
Mobiluncus sp.
Gram-positive rod
Escherichia coli
Gram-negative rod
-The major facultative anaerobe inhabitant of the large intestine
-The most commonly isolated opportunistic human pathogen causing urinary tract
and wound infections, pneumonia, meningitis and septicemia.
-Some serogroups and toxin-producing strains are highly virulent primary
pathogens.
-Primary cause of “Travelers’ Diarrhea.”
-There are at least 165 “O” antigens, 100 “K” antigens, and 50 “H” antigens
described for E. coli.
Escherichia coli
Gram-negative rod
-The major facultative anaerobe inhabitant of the large intestine
-The most commonly isolated opportunistic human pathogen causing urinary tract
and wound infections, pneumonia, meningitis and septicemia.
-Some serogroups and toxin-producing strains are highly virulent primary
pathogens.
-Produces heat-stable and a heat-labile enterotoxin.
-Primary cause of “Travelers’ Diarrhea.”
-There are at least 165 “O” antigens, 100 “K” antigens, and 50 “H” antigens
described for E. coli.
Klebsiella oxytoca
Gram-negative rod
Enterobacter cloacae
Gram-negative rod
Citrobacter freundii
Gram-negative rod
Citrobacter diversus
Gram-negative rod
Edwardsella tarda
Gram-negative rod
Serratia marcescens
Gram-negative rod
Proteus mirabilis
Gram-negative rod
Proteus vulgaris
Gram-negative rod
Proteus penneri
Gram-negative rod