Gram negative bacteria (Facultative Anaerobic Gram-Negative Rods) 1st part

Family Enterobacteriaceae

A large family of Gram-negative, facultative anaerobic, non-spore-forming rods commonly found in the

gastrointestinal tract of humans and animals.

Fimbriae (Pili)

Many members possess — that aid in attachment to host mucosal surfaces, which is crucial for colonization and infection.

Sex Pili

Some strains have —, specialized structures that facilitate bacterial conjugation — a process where plasmid DNA, often containing antibiotic resistance genes (R plasmids), is transferred from one bacterium to another.

Family Enterobacteriaceae

Known for their antigenic diversity (e.g., O, H, K antigens) and ability to cause opportunistic and nosocomial infections.

Family Enterobacteriaceae

Includes both pathogenic (e.g., Salmonella, Shigella, Escherichia coli, Yersinia) and commensal organisms (e.g., Enterobacter, Klebsiella, Proteus).

Lives in the intestinal tract of humans and warm-blooded animals.

common habitat for Escherichia coli

Produces acid and gas, used in laboratory diagnostics and water contamination testing.

General Characteristics of Escherichia coli (Ferments Lactose)

O antigen, H antigen, K antigen

Antigenic structure of Escherichia Coli:

O antigen

Lipopolysaccharide (cell wall).

H antigen

Flagellar

K antigen

Capsular polysaccharide.

fimbriae, toxins, conjugation (sex pili)

virulence factors of Escherichia coli

Fimbriae

Attachment to host epithelial cells.

Toxins

Depending on strain, may produce enterotoxins or Shiga-like —.

Conjugation (Sex Pili)

DNA exchange—can spread antibiotic resistance

Urinary Tract Infection (UTI), Traveler’s Diarrhea, E. coli O157:H7 Infection (Enterohemorrhagic E. coli)

diseases of Escherichia Coli:

Escherichia Coli

common pathology to humans

Escherichia Coli

causes UTI

Dysuria, urgency, frequency, cloudy or bloody urine; severe cases may lead to bacteremia.

symptoms of UTI

Dysuria

inability to urinate

Polyuria

cloudy or bloody urine

Mild cases may self-resolve; Common antibiotics (Ciprofloxacin, Trimethoprim-Sulfamethoxazole (TMP-SMX), Nitrofurantoin); Based on urine culture and sensitivity testing.

Treatments of UTI:

Ciprofloxacin, Trimethoprim-Sulfamethoxazole (TMP-SMX), Nitrofurantoin

Antibiotics for UTI:

Traveler’s Diarrhea

Often caused by Enterotoxigenic E. coli (ETEC).

Enterotoxigenic E. coli (ETEC)

Travelers Diarrhea is caused by —

Fecal-oral route; ingestion of contaminated food or water.

Transmission of travelers disease

Nausea, vomiting, watery diarrhea, abdominal cramps (1–3 days).

Symptoms of Travelers Disease

Streptomycin

drug for travelers disease

Streptomycin

Effective against ETEC and other enteric pathogens.

Streptomycin, Primary treatment includes fluid and electrolyte replacement, Avoid dairy products during illness.

Treatment of Travelers disease:

Shiga toxins (Stx1, Stx2)

Toxin of E. coli O157:H7 Infection (Enterohemorrhagic E. coli)

Bloody diarrhea, Hemorrhagic colitis, Hemolytic Uremic Syndrome (HUS) – triad: hemolytic anemia, thrombocytopenia, acute renal failure

Symptoms of E. coli O157:H7 (Enterohemorrhagic E. coli)

hemolytic anemia, thrombocytopenia, acute renal failure

Hemolytic Uremic Syndrome (HUS) – triad:

No antibiotics or antidiarrheals, Supportive therapy: fluid/electrolyte replacement.

Treatment for E.coli O157:H7 (Enterohemorrhagic E.coli):

ETEC (Enterotoxigenic), EPEC (Enteropathogenic), EIEC (Enteroinvasive), EHEC (Enterohemorrhagic

/ VTEC), EAEC (Enteroaggregative), DAEC (Diffusely Adherent)

Pathogenic Groups of E. coli:

Heat-labile (LT) and Heat-stable (ST) toxins

Virulence Factors of ETEC (Enterotoxigenic):

Attaching and effacing lesions

Virulence Factors of EPEC (Enteropathogenic)

Invasion of epithelial cells

Virulence Factors of EIEC (Enteroinvasive)

Shiga toxins (Stx1, Stx2)

Virulence Factors of EHEC (Enterohemorrhagic/ VTEC)

Biofilm formation, toxins

Virulence Factors of EAEC (Enteroaggregative)

Diffuse adherence to cells

Virulence Factors of DAEC (Diffusely Adherent)

Traveler's diarrhea

Disease of ETEC (Enterotoxigenic)

Infantile diarrhea

Disease of EPEC (Enteropathogenic)

Dysentery-like illness

Disease of EIEC (Enteroinvasive)

Hemorrhagic colitis, HUS

Disease of EHEC (Enterohemorrhagic / VTEC)

Persistent diarrhea

Disease of EAEC (Enteroaggregative)

Diarrhea

Disease of DAEC (Diffusely Adherent)

Watery diarrhea, nausea, cramps

Clinical Features of ETEC (Enterotoxigenic) (Traveler's diarrhea)

Watery diarrhea, mucus, dehydration

Clinical Features of EPEC (Enteropathogenic) (Infantile diarrhea)

Bloody diarrhea, fever, pain

Clinical Features of EIEC (Enteroinvasive) (Dysentery-like illness)

Bloody diarrhea, abdominal cramps

Clinical Features of EHEC (Enterohemorrhagic/ VTEC) (Hemorrhagic colitis, HUS)

Especially in children and immunocompromised

Clinical Features of EAEC (Enteroaggregative) (Persistent diarrhea)

Mostly in children

Clinical Features of DAEC (Diffusely Adherent) (Diarrhea)

Lactose fermentation, IMViC tests, Serotyping

Laboratory Diagnosis of E.coli O157:H7 (Enterohemorrhagic E.coli)

Lactose fermentation

Positive (MacConkey agar – pink colonies)

IMViC tests

Indole (+), Methyl Red (+), Voges-Proskauer (-), Citrate (-)

Serotyping

Used for identification of pathogenic strains (e.g., O157:H7)

Azithromycin

drug of choice of travelers diarrhea

BRAT (Banana, Rice, Apple, Toasted bread)

travelers diarrhe treatment (food)

Inhabit the gastrointestinal tract (GIT) of animals and can be transmitted to humans through contaminated food and water.

Common Habitat of Salmonella

S. typhi, S. paratyphi

2 kinds Salmonella:

Typhoid Fever, Salmonellosis

diseases of Salmonella:

Salmonella enterica serotypes

Causative Agents of Typhoid Fever

Ingestion of contaminated food or water

Portal of Entry of Salmonella:

Prolonged fever; Headache, muscle pain, malaise; Rose-colored spots on the abdomen

Symptoms of Typhoid fever:

Chloramphenicol, Ampicillin, Ciprofloxacin

Treatment of Salmonella:

Various Salmonella enterica serotypes (e.g., S. Enteritidis, S. Typhimurium)

Causative Agents for Salmonellosis:

Ingestion of undercooked or contaminated meat, eggs, dairy; Contact with infected animals or environment

Portal of Entry of Salmonellosis:

Non-bloody diarrhea, Vomiting, Fever, Headache

Symptoms of Salmonellosis:

Supportive care (oral rehydration, electrolyte replacement), Antibiotics for severe or complicated cases (Ciprofloxacin)

Treatment for salmonellosis:

Ciprofloxacin

Antibiotic for Salmonellosis

Shigella

Gram-negative, non-motile, non-lactose fermenting, facultative anaerobes

Shigella

Reservoir: Humans only (no animal reservoir)

Shigella

Causes shigellosis (bacillary dysentery), a form of inflammatory diarrhea

shigellosis (bacillary dysentery)

Shigella causes — a form of inflammatory diarrhea

Shigella dysenteriae, Shigella flexneri, Shigella boydii, Shigella sonnei

Causative Agents (Species of Shigella)

Shigella dysenteriae

Most severe form; produces Shiga toxin; can cause epidemics and HUS

Shigella flexneri

Most common in developing countries; causes moderate to severe disease

Shigella boydii

Less common; mostly found in South Asia

Shigella sonnei

Most common in developed countries; causes milder disease

Fecal-oral route, Highly contagious, Common in overcrowded areas with poor sanitation

Transmission of Shigella:

Gastrointestinal tract via contaminated hands, food, water

portal of entry of Shigella:

Invades and multiplies in colonic epithelial cells, Induces inflammatory response → tissue damage, Some strains (especially S. dysenteriae) produce Shiga toxin, which:

o Inhibits protein synthesis

o Causes cell death

o May lead to hemolytic uremic syndrome (HUS)

pathogenisis of Shigella:

Shigella dysenteriae

produce Shiga toxin, which:

o Inhibits protein synthesis

o Causes cell death

o May lead to hemolytic uremic syndrome (HUS)

Purulent, bloody diarrhea, Crampy abdominal or rectal pain, Tenesmus, Fever, Nausea and vomiting

Symptoms of Shigellosis:

Severe dehydration, Febrile seizures (especially in children), Hemolytic Uremic Syndrome (HUS) – particularly with S. dysenteriae, Toxic megacolon or intestinal perforation (rare but serious)

Complications of Shigella:

Mild cases may resolve on their own with supportive care, Moderate to severe cases or outbreaks require antibiotics, Antibiotic Options (based on susceptibility testing):

• Ciprofloxacin

• Azithromycin

• Rifaximin (not for invasive strains)

• Ceftriaxone (especially in severe pediatric cases)

Treatment for Shigella

Ciprofloxacin, Azithromycin, Rifaximin, Ceftriaxone

Antibiotics for Shigella:

Proper hand hygiene, Safe food and water practices, Sanitation and public health education, No widely used vaccine yet (under development)

Prevention of Shigella:

Klebsiella

Gram-negative, nonmotile, capsulated, facultative anaerobes

Klebsiella

Known for causing opportunistic and healthcare-associated (nosocomial) infections

Nonmotile, Capsule Production: Prominent polysaccharide capsule

general characteristics of Klebsiella:

Nonmotile

Does not possess flagella for movement.

Capsule Production: Prominent polysaccharide capsule:

o Inhibits phagocytosis

o Enhances virulence

o Gives colonies a mucoid appearance on agar

Urinary Tract Infections (UTIs); Respiratory Tract Infections; Wound Infections; Bloodstream Infections; Liver abscess, meningitis

Pathogenic Capabilities Common Infections of Klebsiella:

purulent

puss and mucus

tenesmus

strain/ painful strain during bowel movement

Klebsiella pneumoniae

immune compromised

Lobar pneumonia

other name for Klebsiella pneumoniae

Inhalation of aerosolized droplets containing the bacterium; Often affects individuals with weakened immune systems, alcoholics, diabetics, or those with chronic lung disease

Portal of Entry of Klebsiella pneumoniae: