Unknown Gram-Negative Bacteria Assignment Week 6 by Joseph DeFinis

Lactose Fermenter Test

josephdefinis7 — 2025-10-05 03:34:54 UTC

(+) LF

josephdefinis7 — 2025-10-05 03:35:15 UTC

The following organisms listed in the textbook are lactose fermenting (LF):

Citrobacter amalonaticus
Citrobacter braakii
Citrobacter farmeri
Citrobacter freundii
Citrobacter koseri
Citrobacter spp.
Cronobacter dubliniensis (previously Enterobacter sakazakii)
Cronobacter malonaticus (previously Enterobacter sakazakii)
Cronobacter muytjensii (previously Enterobacter sakazakii)
Cronobacter sakazakii (previously Enterobacter sakazakii)
Cronobacter turicensis (previously Enterobacter sakazakii)
Cronobacter universalis
Enterobacter asburiae
Enterobacter bugandensis
Enterobacter cancerogenus
Enterobacter cloacae subsp. cloacae
Enterobacter hormaechei subsp. hormaechei
Enterobacter kobei
Enterobacter ludwigii
Enterobacter massiliensis
Escherichia coli (including extraintestinal and diarrheagenic pathotypes)
Escherichia spp.
Hafnia alvei
Hafnia paralvei
Klebsiella aerogenes
Klebsiella granulomatis
Klebsiella ozaenae
Klebsiella pneumoniae subsp. pneumoniae
Klebsiella pneumoniae subsp. ozaenae
Klebsiella pneumoniae subsp. rhinoscleromatis
Klebsiella oxytoca
Klebsiella quasipneumoniae
Klebsiella variicola
Kosakonia cowanii (previously Enterobacter)
Pantoea agglomerans (previously Enterobacter agglomerans)
Pantoea ananatis
Pantoea spp.
Plesiomonas shigelloides
Pluralibacter gergoviae (previously Enterobacter gergoviae and Enterobacter pyrinus)
Raoultella spp.
Serratia marcescens subsp. marcescens (slow LF)
Serratia marcescens subsp. marcescens biogroup 1
Serratia liquefaciens complex (Serratia liquefaciens sensu stricto, Serratia proteamaculans, and Serratia grimesii; slow LF)
Serratia rubidaea
Serratia odorifera biogroups 1 and 2 (slow LF)

(-) LF

josephdefinis7 — 2025-10-05 03:35:26 UTC

non-LF Salmonella spp., Shigella spp., Proteus spp., Morganella morganii, Providencia spp., Edwardsiella tarda, and pathogenic Yersinia spp., as they appear colorless on MAC and red and black on HE/XLD.

Hydrogen Sulfide Test

josephdefinis7 — 2025-10-05 03:36:48 UTC

(+) H2S

josephdefinis7 — 2025-10-05 03:37:19 UTC

Remaining suspected organisms: All the other Enterobacterales are H2S-/variable, but majority negative. E. coli, K. pneumoniae, K. oxytoca, E. cloacae, S. marcescens

(-) H2S

josephdefinis7 — 2025-10-05 03:37:34 UTC

Removed by Hydrogen Sulfide (H2S) Negative Test Result (Include All Possible in Family)

Hydrogen sulfide producers are cut (black precipitate on TSI/LIA or black centers on HE/XLD).

The chapter's list is typically Salmonella and among others with H2S+.

Organisms that would be cut out:

Citrobacter freundii (variable, but many strains H2S+)
Edwardsiella tarda
Proteus mirabilis
Proteus vulgaris (variable H2S+)
Proteus penneri (variable)
Salmonella, all serotypes (most H2S+; e.g., Salmonella serotype Typhi variable but often weak+)

Motility test at 37 degrees C.

josephdefinis7 — 2025-10-05 03:41:14 UTC

Motile

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E. coli, E. cloacae, S. marcescens

Non-Motile

josephdefinis7 — 2025-10-05 03:42:08 UTC

Motility testing at 37°C (i.e. flagella; observed by wet mount or MIU), removes non-motile species at body temperature. Most Enterobacterales are motile. Some are non-motile or show reduced motility at 37°C.

Removed organisms:

Klebsiella aerogenes
Klebsiella granulomatis
Klebsiella ozaenae
Klebsiella pneumoniae subsp. pneumoniae
Klebsiella pneumoniae subsp. ozaenae
Klebsiella pneumoniae subsp. rhinoscleromatis
Klebsiella oxytoca
Klebsiella quasipneumoniae
Klebsiella variicola
Shigella dysenteriae (group A)
Shigella flexneri (group B)
Shigella boydii (group C)
Shigella sonnei (group D)
Yersinia pestis (non-motile at 37°C; motile at 22°C)
Yersinia enterocolitica subsp. enterocolitica (reduced motility at 37°C)
Yersinia pseudotuberculosis (reduced motility at 37°C)

Voges-Proskauer (VP) Testing

josephdefinis7 — 2025-10-05 03:43:00 UTC

Positive result would indicate acetoin production (i.e. red ring after alpha-naphthol/KOH).

(+) VP

josephdefinis7 — 2025-10-05 03:44:12 UTC

Remaining Suspected Organisms: Enterobacter cloacae, Serratia marcescens

(-) VP

josephdefinis7 — 2025-10-05 03:44:26 UTC

Removed organisms:

Citrobacter amalonaticus
Citrobacter braakii
Citrobacter farmeri
Citrobacter freundii
Citrobacter koseri
Citrobacter spp.
Cronobacter dubliniensis
Cronobacter malonaticus
Cronobacter muytjensii
Cronobacter sakazakii
Cronobacter turicensis
Cronobacter universalis
Edwardsiella tarda
Escherichia coli (all pathotypes)
Escherichia spp.
Morganella morganii subsp. morganii
Morganella morganii subsp. sibonii
Proteus mirabilis
Proteus penneri
Proteus vulgaris
Providencia alcalifaciens
Providencia rettgeri
Providencia stuartii
Salmonella, all serotypes
Shigella dysenteriae (group A)
Shigella flexneri (group B)
Shigella boydii (group C)
Shigella sonnei (group D)
Yersinia pestis
Yersinia enterocolitica subsp. enterocolitica
Yersinia pseudotuberculosis

Indole Testing

josephdefinis7 — 2025-10-05 03:46:03 UTC

Indole(-) would mean no observed red ring on Kovac's reagent after tryptone broth. This would remove indole(+) species.

(+) Indole

josephdefinis7 — 2025-10-05 03:46:29 UTC

Removed organisms:

Escherichia coli (all pathotypes)
Escherichia spp.
Morganella morganii subsp. morganii
Morganella morganii subsp. sibonii
Proteus vulgaris
Providencia rettgeri

(-) Indole

josephdefinis7 — 2025-10-05 03:46:38 UTC

Remaining Suspected Organisms: Enterobacter cloacae, Serratia marcescens, Shigella sonnei

ONPG Testing

josephdefinis7 — 2025-10-05 03:48:41 UTC

o-Nitrophenyl-β-D-galactopyranoside (ONPG) results in a positive (i.e. yellow color; indicates β-galactosidase for lactose hydrolysis) and removes any ONPG-negative species because most LF are +, late/slow fermenters may also be – at first.

ONPG(+)

josephdefinis7 — 2025-10-05 03:49:00 UTC

Enterobacter cloacae, Serratia marcescens

ONPG(-)

josephdefinis7 — 2025-10-05 03:49:07 UTC

Removed organisms:

Shigella sonnei (group D) early strains ONPG-, but later +.