Enterobacterales pt 4

Proteus species are common inhabitants of the gastrointestinal tract.
Characterized by a distinct odor often referred to as a "chocolate cake" or "burnt chocolate" smell, although some may not personally identify with this description.
This distinct odor is recognized as a hallmark for identification in examinations.

Commonly isolated species: Proteus mirabilis, more prevalent than Proteus vulgaris.
To differentiate between the two:
- **Indole Test:
- Proteus mirabilis:** Indole negative
- Proteus vulgaris:** Indole positive
Swarming Growth
- Proteus species exhibit a swarming growth pattern on agar, resembling ripples in water.
- Swarming is attributed to the organism's motility.
- Cultivation should be done on special plates to avoid interference with other organisms.

Key Features:
- Lactose negative
- Produce Hydrogen Sulfide (H2S)
- Urease positive
- Motile, but some strains lack swarming capability
Tests for identification:
- Indole Test (for species differentiation)
- Ornithine Decarboxylase Test (alternative speciation method, but takes longer)

Primary Species: Morganella morganii
Typical habitat: Normal microbiota of the gastrointestinal tract.
Associated conditions:
- Diarrheal diseases
- Skin and soft tissue infections
- Urinary tract infections, especially in cases of poor hygiene practices
- Identified as a cause of neonatal sepsis
- Possible contamination between amniotic fluid and fecal material during childbirth.
Biochemical traits:
- Non-lactose fermenter
- Positive for Phenylalanine Deaminase test (notable among three organisms, including Proteus and Providencia)

Key Pathogenic Species:
- Providencia rettgeri
- Providencia stuartii
Normal inhabitants of the environment and gastrointestinal tract, associated with:
- Urinary tract infections
- Diarrheal diseases in children
High resistance to antimicrobials, complicating treatment.
Providencia rettgeri: Urinary tract pathogen, occasionally seen in nosocomial infections.
Providencia stuartii: Associated with outbreaks in burn units, detectable in urine cultures, does not exhibit swarming.
All Providencia species are lactose negative and phenylalanine deaminase positive.

Primary pathogen from the Edwarsiella genus.
Typically associated with aquatic environments, transmitted through contaminated fish.
Higher susceptibility in immunocompromised individuals, with systemic infections possible in:
- Liver disease patients
- Those with iron overload conditions like hemochromatosis.
Biochemical Characteristics:
- Produces H2S
- Positive indole result
- No urease production
- Negative for citrate utilization.

Found in soil and aquatic environments, associated with:
- Gastroenteritis, presenting with symptoms like fever and vomiting.
- Usually self-limiting but can cause serious conditions like meningitis, septicemia, or shock in neonates.
Notable differences from other Enterobacteriaceae:
- Oxidase positive (an exception to the oxidase negative characteristic of Enterobacteriaceae).
- Facultative anaerobe, does not produce capsular material.
- Decarboxylation Reactions: Positive for all three amino acids: lysine, ornithine, and arginine.
- No gas production from glucose fermentation when inoculated in specific media like TSI or LIA.

Specimen Sources:
- Found in various clinical specimens including wounds, urinary tract infections, cerebrospinal fluid (CSF), and blood.
Analytical Considerations:
- Importance of considering specimen source when isolating organisms; contextual validity is crucial for accurate identification.
- Gram-negative rods appear similar microscopically, lacking distinct morphology.
- Evaluation of growth characteristics on agar is vital:
- Example: Growth on Salmonella or Shigella agar typically indicates one of these organisms.
Incubation Conditions:
- Most Enterobacteriaceae grow quickly and do not require unique growth conditions.
- Serological grouping may be necessary for epidemiological studies, particularly for Salmonella and Shigella.

Key Resistance Mechanisms:
- Extended Spectrum Beta Lactamases (ESBLs):
- Most commonly found in E. coli and Klebsiella species; capable of hydrolyzing extended spectrum cephalosporins.
- Carbapenem Resistant Enterobacteriaceae (CREs):
- Serious resistance concern, associated with carbapenemase production or loss of porins in conjunction with beta-lactamase activity.
- Limited treatment options increase mortality risk.
Molecular vs. Phenotypic Resistance Detection:
- Clinical labs rely on phenotypic methods even when resistance genes are identified molecularly.
Salmonella typhi:
- Notable for changing resistance patterns over time; multidrug-resistant strains are a public health concern, particularly the H58 lineage.