Introduction to Enterobacteriaceae

Introduction to Enterobacteriaceae

• This family of bacteria is a large group
• Most are non-pathogenic, normal flora
• Some are opportunistic pathogens associated with human diseases
• Members are commonly found in soil and water, as well as in the intestinal tracts of animals and humans.
• They are Gram-negative bacilli
• They have similar gram stain characteristics
• They are associated with various human diseases, like GIT infection, UTI, wound infections, and respiratory tract infections.

Family Members

• Escherichia coli (E.coli) is the most commonly isolated member.
• Other members include Klebsiella, Enterobacter, Citrobacter, Serratia, Pantoea, Salmonella, Shigella, Proteus, Morganella morganii, Providencia, and Yersinia.
• Some are lactose fermenting, others are non-lactose fermenting

E.coli Species

• E.coli is a motile, non-spore-forming, non-capsulated bacterium
• E.coli is commonly found in the gastrointestinal tracts of humans and animals.
• Different E.coli serotypes can cause various infections, each requiring different diagnostic methods.
• E. coli species are distinguished by their specific antigens

Identification-Culture and Colony Characters

• E.coli is aerobic and facultative anaerobic
• Optimum temperature range is 10-40°C (1-37°C)
• Can grow on nutrient agar
• Nutrient agar colonies are typically large, 2-3mm, circular, opaque, gray, or white.
• Blood agar and MacConkey's agar are used for identifying E.coli's traits
• Gram's stain, Beta-haemolytic traits identified on Blood agar, MacConkey's Pink flat-due to L.F
• Biochemical tests are used for more specific identification.

Identification-Biochemical Reactions

• Various biochemical tests are used, including IMViC, Voges-Proskauer, Methyl Red, Citrate, Triple Sugar Iron, and Urease tests
• E.coli's tests give: Indole (I)-Positive, Methyl red (MR)-Positive, Voges-Proskauer (VP)-Negative, and Citrate (C)-Negative.

Antigenic Diversity

• E.coli has various antigens, including H antigens (flagellar), O antigens (somatic), and K antigens (capsular).
• Different antigens and their variations are used to differentiate the serotypes of the bacteria
• O Antigen, commonly used in conjunction with K antigen serotyping, aid in epidemiological studies.
• K-Ag and F-Ag are associated with Urinary Tract Infections (UTIs)

Serotype and Typing Method

• Over 700 serotypes of E.coli have been identified
• Serotyping is based on O and H antigens
• Various typing methods are used to identify E.coli serotypes

Factors of Pathogenicity and Virulence

• Surface antigens (including LPS, envelope/K-Ag, fimbriae) play a role in infection
• Toxins (enterotoxins, e.g., LT, ST, VT and verocytotoxins/shiga-like toxins, and hemolysins) affect pathogenicity
• Specific characteristics of the various E.coli toxins lead to symptoms like watery diarrhea, intestinal infections, and urinary tract infections

Heat Labile Toxin (LT)

• LT is heat-labile
• Binds to specific GM1 gangliosides receptors on small intestine epithelial cells
• Stimulates cAMP production, leading to Cl secretion
• Resulting in secretory diarrhea

Heat Stable Toxin (ST)

• ST is heat-stable
• Activates guanylate cyclase, leading to cGMP production
• cGMP inhibits sodium chloride co-transport.
• Resulting in diarrhea

Pathogenicity/Clinical Infections

• E.coli is associated with various infections, including diarrhea, urinary tract infections (UTIs), wound infections, and septicemia

Urinary Tract Infections (UTIs)

• E.coli is a leading cause of UTIs.
• Predisposing Factors include female gender, pregnancy, sexual activity, urinary tract abnormalities, and catheters.
• Symptoms include frequent urination, pain, and cloudy/bloody urine.
• Pathogenesis involves colonization, multiplication, and immune response in the urinary tract.

Symptoms of UTI

• Pain, burning sensation, or frequent urination, cloudy urine, strong smelling urine, pelvic pain
• Additional symptoms relating to kidney involvement (high fever, nausea, vomiting, shaking, chills).

Pathogenesis of UTIs

• E.coli infections often arise from contamination of the periurethral areas (e.g., fecal matter or poor hygiene).
• The bacteria then adhere to and penetrate the bladder wall, increasing in numbers and leading to the symptoms associated with UTIs

Diarrheal and Dysentery Pathotypes

• Some E.coli infections come from different classifications like EPEC, ETEC, EIEC, EHEC, and EAEC
• The specific variations of each lead to different symptoms like diarrhea

EPEC-Enteropathogenic E.coli

• Usually associated with diarrhea in infants and children
• Attaches to small intestinal mucosa, damaging the brush border of microvilli

ETEC-Enterotoxigenic E.coli

• Endemic in tropical regions of developing countries
• Causes mild diarrhea to cholera, traveller's diarrhea
• Produces enterotoxins (LT and ST) which cause diarrhea

EIEC-Enteroinvasive E.coli

• Invasive diseases are similar to Shigellosis (Dysentery)
• Causes diseases like Shigellosis-dysentery (non-motile and non-lactose fermenters).

EHEC-Enterohemorrhagic E.coli

• Symptoms range from mild diarrhea to severe hemolytic uremic syndrome (HUS).
• Produces verocytotoxins (VT) which can cause serious health complications

EAEC-Enteroaggregative E.coli

• Associated with persistent diarrhea in developing countries
• Forms aggregates on HEp2 cells, causing the stacked-brick form.

Pyogenic infection and Septicemia

• E.coli causes various infections like wound infections, peritonitis, biliary tract infections, and meningitis (newborns).
• Sepsis caused by E.coli can lead to serious conditions like septic shock and systemic inflammatory response syndrome (SIRS).

Summary

• E. coli is a significant pathogen, causing a wide range of infections.
• UTIs, Diarrhea, and septicemia are commonly linked to E.coli.
• Specific strains show various virulence factors leading to different symptoms.
• Prevention of cross contamination is crucial.

Klebsiella

• Klebsiella species are gram-negative, non-motile, non-spore-forming rods.
• They are encapsulated, often causing mucoid colonies.
• They are opportunistic pathogens.

Clinical Significant Species of Klebsiella

• K.pneumoniae (important species), K.oxytoca, K.planticola, K.ornithinolytica, K.ozaenae, K.pneumoniae, K.rhinoscleromatis, K.aerogens

Morphological Features of Klebsiella

• Gram-negative, non-motile, non-sporing bacilli
• Often capsulated, producing mucoid colonies
• Size range from 1 to 2um in length and 0.5 to 0.8um in width
• Visible Capsule staining (Quelling Reaction)

Cultural and Biochemical Characteristics of Klebsiella

• Optimum temperature 37°C, pH 7–2 - 7–.4

Infections Caused by Klebsiella

• Respiratory infections may occur
• Urinary tract infections (UTIs), wounds commonly associated infections
• Atrophic Rhinitis, ozaena, Rhinoscleroma
• Meningitis and pyogenic infections.

Other Enterobacteriaceae genera

• Various other genera often associated with E.coli infections or opportunistic pathogenic infections include Enterobacter, Serratia, Edwardsiella tarda, Citrobacter, Hafnia, and Erwinia

Proteus

• Proteus is a gram-negative species
• Pleomorphic and actively motile
• Possesses Peritrichous flagella
• Nonsporing and non-capsulated

Proteus Morphological Features

• Gram-Negative coccobacilli
• Pleomorphic
• Size- 1-3μ X 0.6μ
• Long filaments up to 80µ
• Active motile-peritrichous flagella

Proteus Cultural characteristics

• Growth can occur in aerobic or facultative anaerobic environments
• Often has a seminal or fishy odour
• Colonies sometimes appear as a swarm on agar
• Swarming is a result of chemotaxis (migration of bacteria towards a chemoattractant).

Proteus Biochemical Reactions

• L-Negative, G-Positive, M-Negative, S-Negative, I-Variable
• Motility positive, VP-Negative, Citrate-Variable, Urease-Positive, TSI-alkaline with H2S

Proteus Pathogenesis

• Causes UTIs, more serious infections compared to E.coli.
• Causes wound infections and other pyogenic infections.
• Causes bacterial ammonia production and precipitation of phosphates leading to calcium formation in the urinary tract, resulting in calculus formation.

Shigella

• Shigella is a genus of bacteria causing bacterial dysentery
• These are gram-negative bacilli, non-motile, non-spore forming; nonspecific shape.
• Four species of Shigella: dysenteriae, flexneri, boydii, sonnei
• Shigellae are relatively small and are only 2-4um × 0.6um in size

Shigella Morphological Features

• Gram-negative
• Small, rod-shaped bacteria
• Nonmotile and non-spore-forming
• Non-capsulated
• Specific stains showing fimbriae (pili)

Shigella Cultural Characteristics

• Aerobic and facultative anaerobic bacteria that grow well at their optimal pH and temperature.

Shigella Biochemical Reactions

• Oxidase-Negative
• Indole-Variable for Shigella dysenteriae types 1 -
• Methyl Red-Positive
• VP-negative
• Urease-negative
• Mannitol-fermented by all, except Sh.dysenteriae

Shigella Serotypes

• Sh.dysenteriae (Serogroup A, 1-12), Sh.flexneri (Serogroup B, 1-6 with 15 subtypes), Sh.boydii (Serogroup C, 1-18) and Sh.sonnei (Serogroup D,1)

Shigella Pathogenesis and Virulent Factors

• Infection occurs through ingestion
• Bacteria invade colon mucosa cells
• Infections result in inflammation and dysentery with abdominal cramps, fever, bloody diarrhea (dysentery with bloody diarrhea), and in extreme cases, hemolytic uremic syndrome (HUS).

Shigella Mode of Transmission

• Transmission primarily through the fecal-oral route (e.g., contaminated food/water or person-to-person contact)
• Vectors like flies can contribute to transmission.

Shigella Prevention and Control

• Shigella prevention centers around hygiene practices: proper hand washing, waste disposal, and access to safe drinking water.
• Vaccines may become available, but careful monitoring and control of susceptible populations is crucial