Ch. 19 - Aerobic Gram-Positive Rods

UNT Biol 3381

Bacillus General characteristics

• Most facultative anaerobes; some are obligate aerobes

• Optimum temperature is 35-37 degree C

• Large Gram-positive straight edged rod

• Capsule may be present. Capsule made of protein

• Pathogenic strains produce anthrax toxins

Bacillus Biochemical tests

• Motility

• Phenylethyl alcohol agar (PEA) selective media for Gram positive

• Lecithinase test, hydrolyzes lecithin

• Mannitol salt agar (MSA)

  • Growth in presence of 7.5% NaCl

  • Mannitol fermentation

• Penicillin susceptibility

Bacillus anthracis (B. anthracis) Micro morph ID

• Large GPR that resemble “bamboo plants”

• Often rectangular, with square ends, and long chains

• May appear gram-negative if old, starving or exposed to antibiotics

• Spores are oval, central to subterminal spores; cell is not swollen

B. anthracis Colony Morph ID

SBA (Sheep Blood Agar):

• Large (2 to 5 mm), flat, slightly convex, colony

• Irregular border, ground glass appearance

• Medusa Head”

• Nonhemolytic

• Stands up like “Beaten egg” when teased with a loop

B. anthracis main tests to diff against Bacillus species

Hemolysis: Neg.

Catalase: pos

Motility: Nonmotile

B. anthracis Virulence Factors

• Capsule

• Exotoxin

• Sporulation

B. anthracis Pathogenesis

• breaks in the skin, inhalation, or ingestion.

• Germination of spores produce vegetative cells

• Vegetative cells produce exotoxin resulting in necrosis

  and edema

• Death due to septicemia, toxemia, or pulmonary

  complications occur 1-7 days after exposure

B. anthracis Disease

• only causes anthrax

• 3 manifestations

  • Gastrointestinal anthrax

    • Rare in humans

    • usually occurs after eating contaminated meat.

    • infective dose (ID50): 10-50

  • Inhalation anthrax

    • Rare in humans

    • handling products with the spores

    • Inhalation of airborne endospores

    • High mortality rate

    • infective dose (ID50): 10k-20k

  • Cutaneous anthrax

    • Produces ulcer called an “eschar” or lesion

    • Fatal in 20% of untreated patients

    • infective dose (ID50): 250K-1 mil

B. anthracis Diagnosis

Large, nonmotile, Gram-positive bacilli in lung or skin

samples

B. anthracis Treatment

Many antimicrobials are effective against B. anthracis

B. anthracis Prevention

• Control of disease in animals

• Effective vaccine available

  • Requires multiple doses and boosters

• burn and deeply bury animal carcasses w/ anthrax cause of endospores

Non-endospore forming Rods

Non-spore-forming, gram-positive rods which have two parallel sides with

rounded ends

Useful biochemical tests for Non-endospore forming Rods

Useful biochemical tests

• Motility

• Incubate at room temperature (25 C) and 35-37 C

• Listeria monocytogenes is positive at 25 C but negative at 35-37 C

• Bile Esculin test

• CAMP Test

• Positive (umbrella) motility reaction

Listeria monocytogenes General characteristics

• Non-endospore-forming bacillus

• Found in soil, water, and animals

• Facultative anaerobe

• Grows in high concentrations of salt and cold environments

• Catalase + and oxidase —

  ▪ Resembles Group B streptococcus.

L. monocytogenes Micro Morph ID

• Gram + rods

• No spores

• Regular shaped or coccobacillary

• Arranged in singles, chains, or palisades

L. monocytogenes Colony Morph

• Small, grayish-white colony

• Narrow zone of beta-hemolysis

L. monocytogenes Pathogenesis

• intracellular pathogen

  • Ingested via contaminated food. Once ingested the microbe

    enters the bloodstream from the alimentary tract to cause a

    systemic illness

  • Grows in phagocytes often in the gallbladder

L. monocytogenes Virulence Factors

• Listeriolysin S helps Listeria avoid digestion by the host cell

• Virulence directly related to Listeria's ability to live within cells

L. monocytogenes Disease

• Listeriosis, a type of food poisoning resulting in mild to severe gastroenteritis may occur.

• Can cause meningitis in certain at-risk groups

• Pregnant women exhibit “flu-like” symptoms which usually are not severe enough to warrant a visit to a physician.

  • If the pregnant female becomes septic, the organism can cross the placenta, endangering the fetus. Infection may result in premature birth, spontaneous abortion, or stillbirth.

• The newborn may acquire this organism and develop sepsis and meningitis.

L. monocytogenes Diagnosis

• Presence of bacteria in the cerebrospinal fluid of individuals with meningitis

• Rarely seen in Gram-stained preparations

L. monocytogenes Treatment

• Ampicillin

• Other antibiotics used for patients allergic to penicillin

L. monocytogenes Prevention

At-risk individuals should avoid certain foods

Lactobacillus General characteristics

• Can be obligate aerobes or facultative anaerobes

• Grow on enriched media and media selective for gram-positive bacteria

Lactobacillus Micro Morph ID

• Gram +

• Non spore forming

• Long and filamentous

• Also, coccobacillary in chains and palisades and pleomorphic GP

Lactobacillus Colony Morph ID

• Aerobic lactobacilli can be tiny, pin-point, alpha-hemolytic to large, rough, gray colonies

• May require 48 hours for growth

Lactobacillus biochem tests

• Most labs use Gram stain to identify to genus

• Negative reactions for catalase, H2S, motility

Lactobacillus Clinical significance

• Lactobacilli are commensal or normal flora in the oral cavity, gastrointestinal tract, and female genital tract.

• They play a significant role in maintaining the acidic environment needed for healthy vagina flora.