Gram-Positive Bacilli Part One

Gram-Positive BacilliGram-Positive BacilliPart OnePart One

MLAB 2434: MicrobiologyKeri Brophy-Martinez

General Characteristics: General Characteristics: BacillusBacillus

Habitat◦Thermal springs, fresh and salt water,

soil, on plantsAerobicSpore-formers

◦Resistant to radiation, heat, disinfections, and desiccation

Mostly contaminants in clinical specimens◦EXCEPTION: Bacillus anthracis

More on SporesMore on SporesProduced when the bacteria gets stressed

◦ Drying◦ Temperature extremes

Aid in organism’s survival

Heat shock induces spores◦ Temperature raised to 56o

Gram stain◦ Appear as clear areas within the bacterial cell

SignificantSignificant Bacillus Bacillus Species SpeciesBacillus anthracis

◦ Agent of anthrax, a disease in livestock◦ Humans acquire infection by contamination of

wound or ingestion or inhalation of sporesBacillus cereus

◦ Causes food poisoning◦ An opportunist

Bacillus subtilis◦ Common laboratory contaminant◦ Used in sterility testing

Bacillus anthracisBacillus anthracisCutaneous anthrax

◦ “Malignant pustule” (also called “black escher”)◦ Woolsorter’s disease/ Rag-pickers disease◦ Organisms gain access through cuts; localized

infection◦ Majority of cases in the world are cutaneous

Inhalation anthrax◦ Acquired through inhalation of spores◦ May result in respiratory distress and death

Gastrointestinal◦ Acquired by ingestion of contaminated raw meat◦ Usually fatal

Bacillus anthracisBacillus anthracis: : Clinical Infections in Humans Clinical Infections in HumansCutaneous anthrax

Laboratory DiagnosisLaboratory DiagnosisMedia

◦Most species grow well on SBA Most species beta-hemolytic, except B.

anthracis

◦No growth on MacConkey◦Fast growers◦Colony characteristics vary

Catalase positive

Laboratory DiagnosisLaboratory Diagnosis

Goal in identification is to RULE OUT B. anthracis

If B. anthracis is suspect, MUST work under safety hood

Other Bacillus, identified to genus level ONLY

Identification Identification of Bacillus of Bacillus anthracisanthracis

Microscopic morphology◦ Large, square-

ended gram-positive rods

◦ Bamboo appearance

◦ Spores may be absent in patient smears

Identification Identification of Bacillus of Bacillus anthracisanthracis

Colony Morphology◦ Nonhemolytic on blood

agar; raised, large, grayish white, irregular, fingerlike edges

◦ “Medusa head” or “beaten egg whites”

Bacillus cereusBacillus cereusFood poisoning

◦ Diarrheal syndrome Associated with meat, poultry, and soups Incubation period of 8 to16 hours Fever uncommon Resolves within 24 hours

◦ Emetic form Associated with fried rice Abdominal cramps and vomiting Incubation period of 1 to 5 hours Resolves in 9 hours

Bacillus cereusBacillus cereusLocal infections

◦ Postsurgical/traumatic wounds◦ Burns◦ Eye infections

Rare conditions◦ Meningitis◦ Bacteremia◦ Endocarditis◦ Osteomyelitis

Bacillus subtilisBacillus subtilis

Found in the environmentCommon laboratory and hospital contaminantUsed as a QC agent for sterilization procedures

Key Characteristics of Key Characteristics of Bacillus SpeciesBacillus Species

Characteristic B. Anthracis B. Cereus Other Bacillus

Beta-hemolysis Negative Positive, Large zones

variable

Motility Negative Positive Positive

Pencillin Sensitive Resistant Variable

ReferencesReferences http://www.atsu.edu/faculty/chamberlain/golden2000/

case5.htm http://chesschumpion.blogspot.com/2007/03/time-to-put-on-

your-thinking-caps.html http://en.wikipedia.org/wiki/File:Bacillus_subtilis_Gram.jpg https://labs.uhstx.com/clinical_int/dols/appb.htmlhttp://

www.iccb.state.il.us/pt3/mod/science/mod_bio111/mod10/p4.html

http://www.flickr.com/photos/microbeworld/sets/72157625392265538/detail/http://www.uaz.edu.mx/histo/pathology/ed/ch_9b/c9b_clue.htm

Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.

Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.