BACTERIA MORPHOLOGY
INVESTIGATION LAB
Bacillus cereus is an endemic, soil-dwelling, Gram-positive, rod-shaped,
beta hemolytic bacterium. Some strains are harmful to humans and cause
foodborne illness, while other strains can be beneficial as probiotics for
animals.[1] It is the cause of "Fried Rice Syndrome," as the bacteria is
classically contracted from fried rice dishes that have been sitting at room
temperature for hours (such as at a buffet). B. cereus bacteria are facultative
anaerobes, and like other members of the genus Bacillus can produce
protective endospores. B. cereus competes with other microorganisms such
as Salmonella and Campylobacter in the gut, so its presence reduces the
numbers of those microorganisms. In food animals such as chickens, rabbits
and pigs, some harmless strains of B. cereus are used as a probiotic feed additive to reduce Salmonella in the
intestines and cecum. This improves the animals' growth as well as food safety for humans who eat their meat.
Kingdom:
Bacteria
Phylum:
Firmicutes
Class:
Bacilli
Order:
Bacillales
Family:
Bacillaceae
Genus:
Bacillus
Species:
B. cereus
Micrococcus luteus is a Gram-positive, spherical, saprotrophic bacterium that belongs to the family
Micrococcaceae. An obligate aerobe, M. luteus is found in soil, dust, water and air, and as part of the normal flora
of the mammalian skin. The bacterium also colonizes the human mouth,
mucosae, oropharynx and upper respiratory tract.
Considered a contaminant in sick patients.M. luteus is resistant to reduced
water potential and can tolerate drying and high salt concentrations without
forming spores, probably by slowing of major metabolic processes and
induction of unique genes. It was discovered by Sir Alexander Fleming
before he discovered Penicillin in 1928.
M. luteus is coagulase negative, bacitracin susceptible, and forms bright yellow colonies on nutrient agar. To
confirm it is not Staphylococcus aureus, a bacitracin susceptibility test can be performed.
Kingdom:
Bacteria
Phylum:
Actinobacteria
Order:
Actinomycetales
Family:
Micrococcaceae
Genus:
Micrococcus
Species:
M. luteus
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive
bacterium.[3] A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough,
protective endospore, allowing the organism to tolerate extreme environmental conditions. Unlike several other
well-known species, B. subtilis has historically been classified as an obligate aerobe, though recent research has
demonstrated that this is not strictly correct.[4]
Although this species is commonly found in soil, more evidence suggests that B. subtilis is a normal gut commensal
in humans. A 2009 study compared the density of spores found in soil (~10 6 spores per gram) to that found in
human feces (~104 spores per gram). The number of spores found in the human gut is too high to be attributed solely
to consumption through food contamination. Soil simply serves as a reservoir,
suggesting that B. subtilis inhabits the gut and should be considered as a normal
gut commensal.
B. subtilis can divide symmetrically to make two daughter cells (binary fission),
or asymmetrically, producing a single endospore that can remain viable for
decades and is resistant to unfavourable environmental conditions such as
drought, salinity, extreme pH, radiation and solvents. The endospore is formed
at times of nutritional stress, allowing the organism to persist in the
environment until conditions become favourable. Prior to the process of
sporulation the cells might become motile by producing flagella, take up DNA from the environment, or produce
antibiotics. These responses are viewed as attempts to seek out nutrients by seeking a more favourable environment,
enabling the cell to make use of new beneficial genetic material or simply by killing of competition.
Domain:
Bacteria
Phylum:
Firmicutes
Class:
Bacilli
Order:
Bacillales
Family:
Bacillaceae
Genus:
Bacillus
Species:
B. subtilis
Sarcina is a genus of Gram-positive cocci bacteria in the family
Clostridiaceae. A synthesizer of microbial cellulose, they have a cuboidal
cell arrangement. Various members of the genus are human flora and
may be found in the skin and large intestine. Sarcina lutea is a Grampositive, spherical bacterium, found in soil, dust, water and air, and as part
of the normal flora of mammalian skin. It also colonizes the human mouth,
mucous membranes, oropharynx and upper respiratory tract. S. lutea can
grow well in environments with little water or high salt concentrations.
They grow optimally at 37°C.
Kingdom:
Bacteria
Phylum:
Firmicutes
Class:
Clostridia
Order:
Clostridiales
Family:
Clostridiaceae
Genus:
Sarcina
Serratia marcescens is a species of Gram-negative, rod-shaped bacterium in the family Enterobacteriaceae. A
human pathogen, S. marcescens is involved in nosocomial infections, particularly catheter-associated bacteremia,
urinary tract infections and wound infections, and is responsible for 1.4% of nosocomial bacteremia cases in the
United States. It is commonly found in the respiratory and urinary tracts of hospitalized adults and in the
gastrointestinal system of children. Serratia may be correctly pronounced Ser-ra-shia (common) or Ser-rah-tee-a.
Due to its ubiquitous presence in the environment, and its preference for damp conditions, S. marcescens is
commonly found growing in bathrooms (especially on tile grout, shower corners, toilet water line, and basin), where
it manifests as a pink discoloration and slimy film feeding off phosphoruscontaining materials or fatty substances such as soap and shampoo residue.
Once established, complete eradication of the organism is often difficult, but
can be accomplished by application of a bleach-based disinfectant. Rinsing and
drying surfaces after use can also prevent the establishment of the bacterium by
removing its food source and making the environment less hospitable.
S. marcescens may also be found in environments such as dirt, supposedly
"sterile" places, and the subgingival biofilm of teeth. Due to this, and the fact
that S. marcescens produces a reddish-orange tripyrrole pigment called prodigiosin, S. marcescens may cause
extrinsic staining of the teeth.
Kingdom: Bacteria
Phylum:
Proteobacteria
Class:
Gamma Proteobacteria
Order:
Enterobacteriales
Family:
Enterobacteriaceae
Genus:
Serratia
Species:
S. marcescens