[MICROBIO] Identification of Bacterial Species and Tests

Catalase-positive Gram-positive cocci?

Staphylococcus spp.

Coagulase-positive Staphylococcus?

Staphylococcus aureus

Novobiocin-resistant CoNS?

Staphylococcus saprophyticus

Alpha-hemolytic, optochin-sensitive, bile soluble?

Streptococcus pneumoniae

Beta-hemolytic, Bacitracin-sensitive GP cocci?

Streptococcus pyogenes

Gamma-hemolytic, grows in 6.5% NaCl?

Enterococcus faecalis

Gram-negative diplococci, oxidase-positive, ferments glucose only?

Neisseria gonorrhoeae

Gram-negative diplococci, ferments glucose & maltose?

Neisseria meningitidis

Organism growing on Thayer-Martin agar?

Neisseria spp.

Oxidase-positive, GN diplococcus, part of respiratory flora?

Moraxella catarrhalis

Spore-forming GP rod with bamboo like appearance causes anthrax?

Bacillus anthracis

Food poisoning from reheated rice (ingestion), lecithinase-positive?

Bacillus cereus

Selective media for Vibrio spp.?

TCBS agar

Comma-shaped GN rod, oxidase-positive, rice-water diarrhea?

Vibrio cholerae

Lactose fermenter, pink colonies on MacConkey?

E. coli

Non-lactose fermenter, swarming motility, H2S producer?

Proteus spp.

late lactose fermenter, red pigment, causes UTIs and wound infections?

Serratia marcescens

Non-motile, mucoid, encapsulated enteric pathogen?

Klebsiella pneumoniae

Cause of infantile diarrhea, Bundle pilus encoded by plasmid EPEC adherence factor (EAF), Chromosomal locus of enterocyte effacement (LEE)

EPEC (Enteropathogenic E. coli)

Traveller’s diarrhea, Heat-labile/stable toxins causing watery diarrhea?

ETEC (Enterotoxigenic E. coli)

Produces shiga-like toxin, associated with Hemolytic Uretic Syndrome?

EHEC/VTEC (Verocytotoxin-producing E. coli)

Negative lactose fermenter, non-H2S producer, causes dysentery?

Shigella spp.

Lactose fermenter, IMViC ++--?

E. coli

TSI: K/A

(Pa-Shy-Si Ante)

• Shigella

• Providencia

• Serratia

• Anaerogenic E. coli

TSI: A/A with gas?

E. coli, Klebsiella, Enetrbacter

TSI: K/A with no H2S?

Shigella

Catalase Test: +

Staphylococcus

Coagulase Test: (+)

Staphylococcus aureus

Oxidase Test: purple color indicates?

Positive result (e.g., Neisseria, Vibrio)

EMB agar: Green metallic sheen?

E. coli

XLD agar: Black-centered colonies?

Salmonella

Lecithinase activity on Egg Yolk Agar?

Positive in Bacillus cereus

TSI slant: All yellow?

A/A = Glucose and lactose/sucrose fermentation

TSI slant: Red/yellow with black?

K/A, H2S+

Eosin-Methyleene Blue (EMB) Agar

Selective for Gram-negative bacteria; inhibits Gram-positive bacteria

lactos fermenters

purple colonies in EMB

non-lactose fermenters

colorless colonies in EMB

green metallic sheen

E. coli in EMB

MacConkey agar

Selective for Gram-negative bacteria; differentiates lactose fermenters from non-lactose fermenters

pink/red colonies

LF in MacConkey Agar

colorless

NLF in MacConkey Agar

Hektoen enteric agar

• Selective for stool pathogens; inhibits normal flora

• Produces black-centered colonies for H2S producers

Salmonella

specie for black-centeered colonies for H2S in HEA

Xylose Lysine Deoxycholate (XLD) Agar

Isolation and differentiation of stool pathogens

yellow colonies

xylose fermentation in XLD Agar

red colonis

non-fermenters in XLD

Triple Sugar Iron (TSI) Agar

• Used to identify enterics based on carbohydrate fermentation and H2S production.

• Reactions indicate fermentation of glucose, lactose, and sucrose

Lysine Iron Agar (LIA)

• Determines lysine decarboxylation and H2S production.

Purple slant

indicates lysine decarboxylation in LIA

black ppt

indicates H2S production in LIA

Indole production test

Identifies organisms capable of producing indole from tryptophan.

red ring in indole production test

(+) result after adding Kovac’s reagent

Methyl Red Test

Tests for mixed acid fermentation

red color in the broth

(+) in Methyl Red test

Voges-Proskauer Test

Detects acetoin production

pink-red complex

(+) in Vogues-proskauer test after adding KOH and naphthol

Citrate Utilization Test

Determines if an organism can utilize citrate as the sole carbon source

prussian blue color in Simmon’s Citrate Agar

(+) in Citrate Utilization Test

Urease test

Identifies urease-producing organisms

pink color

(+) Urease test

Beef and yeast extracts, peptone

protei source that supports growth in TSI medium

Lactose, glucose, sucrose

carbohydrates that can be fermented by the bacteria in TSI

Phenol red

pH indicator in TSI

Ferrous sulfate and ferric ammonium citrate

indicators for H2SH2​S production in TSI

indicators for MacConkey Agar

bile salt, neutral red, crystal violet

Sulfide Indole Motility (SIM) test detects

tests for H2S production (black precipitate), indole production (red ring), and motility (diffuse growth from stab line)

tests for bacterial motility

By wet mount, hanging drop, or SIM medium. Motile organisms move in a definite direction or show diffuse growth away from inoculation line.