overview to enteric G- bacteria Flashcards
what are the Enterobacteriaceae?
A family of gram-negative bacteria that includes Klebsiella, E. coli, Enterobacter, Salmonella, Shigella, and other species. Members possess intrinsic resistance against bile salts, which allows the bacteria to proliferate in the gastrointestinal tract.
in alcoholics and patients with DM, Enterobacteriaceae have a tendency to colonize??
Oropharyngeal colonization in alcoholics & patients with diabetes mellitus
how Enterobacteriaceae are classified?
1) Selective Media: All Enterobacteriaceae usually grow well on MacConkey Agar which inhibits the growth of gram-positive bacteria
2) Lactose Fermentation: Enterobacteriaceae are often sub-classified by their capacity to ferment lactose which can be visualized rapidly on EMB medium by the development of pigmented colonies when fermentation is positive. Consequently, organisms can be categorized as lactose fermenters and lactose non-fermenters
3) Indole Production: Enterobacteriaceae are often sub-classified by their capacity to produce indole from tryptophan leading to categorization as indole positive and indole negative organisms.
what are the most notable organisms in Enterobacteriaceae?
Escherichia coli Klebsiella pneumoniae Proteus mirabilis Enterobacter Serratia Salmonella Shigella
how Enterobacteriaceae proliferate in the GI tract?
Possess an intrinsic resistance against bile salts, which allows the bacteria to proliferate in the gastrointestinal tract
what is the O-antigen (also called a somatic antigen)
it is the exposed part of Lipopolysaccharide, which contributes to the variation of the Gram-negative bacterial cell wall.
what is the H-antigen?
any of various antigens associated with the flagella of motile bacteria and used in serological identification of various bacteria
— called also flagellar antigen
what is the bacterial K antigen?
The K antigen repeat units form a high molecular weight structure called ‘capsule’.
which is external K or O antigen?
K, capsular antigen
what is the bacterial capsule?
an envelope that surrounds some bacterial cells. Usually composed of polysaccharide. B. anthracis has a polypeptide capsule. Acts as a virulence factor that facilitates adherence to host cells and protection against phagocytosis, lysozymes, reactive oxygen species, and complement-mediated lysis.
what important bacteria produce tick capsule and appear with mucoid colonies on MacConkey agar?
Klebsiella pneumonia
what are the virulence factors of Enterobacteriaceae?
- -Adhesins – aid in binding to host cells, e.g. fimbriae
- -Lipopolysaccharide – potent inducer of host immune response via endotoxin release (lipid A)
- -Capsules – help avoid phagocytosis but poor immunogens
- -Toxins – e.g. hemolysins of E. coli
- -Antimicrobial resistance – e.g. via plasmid exchange
what are the virulence factors that allow colonization? (overall, not only for Enterobacteriaceae)
1)Lipoteichoic acid: primarily in gram-positive organisms
Bacterial adhesins: colonizing factors
–Pertussis toxin
–Hemagglutinins
2)Biofilms: adherence to foreign material (e.g., Staphylococcus epidermidis, Staphylococcus mutans, Pseudomonas aeruginosa)
3)Flagella: filamentous organelles that aid in the movement of bacteria
–Peritrichous flagella: flagella around the bacterium (e.g., Escherichia coli)
–Lophotrichous flagella: several flagella at one pole (e.g., Pseudomonas)
–Polar flagella: one flagellum at one of the bacterial poles (e.g., Vibrio cholerae)
what are the virulence factors that allow avoidance of the immune system? (overall, not only for Enterobacteriaceae)
1) Capsule
- -Streptococcus pyogenes (M protein)
- -Neisseria gonorrhoeae (pili)
- -Staphylococcus aureus (protein A)
2) IgA protease: cleaves mucosal IgA
- -Neisseria spp.
- -Haemophilus influenzae
- -Streptococcus pneumonia
3) Protein A: binds to Fc region of IgG (e.g., Staphylococcus aureus)
how Enterobacteriaceae are laboratory diagnosed?
• Gram-negative bacilli • Grow on non-selective & selective media – 35-37OC, aerobic/ anaerobic, air/CO2 – MacConkey selective agar …..lactose versus non-lactose fermenters
• Further identification:
– Biochemical testing or
– Mass Spectrometry: MALDI-TOF
– Antimicrobial susceptibility testing
what is the selective agar for Enterobacteriaceae?
MacConkey
A growth medium containing a neutral red pH indicator that turns pink when culturing bacteria that can ferment the lactose (e.g., Klebsiella pneumoniae, Enterobacter, Serratia), which results in the production of acid.
Enterobacteriaceae are anaerobe or aerobe?
Facultative anaerobe
Bacterial species that are capable of aerobic respiration but can switch to anaerobic respiration if no oxygen is available.
what is the clinical significance of Enterobacteriaceae?
- Wide range of infections in the community & in healthcare facilities, affecting normal & immunocompromised patients
- Isolated in microbiology laboratories from urine, blood, abdominal specimens, respiratory tract
- Resistance to multiple antibiotics - an increasing problem
describe the general features of E. coli
• Part of the normal flora especially in the colon (‘coliforms’)
• Most strains nonpathogenic in the GIT but some cause intestinal infection & infection elsewhere
• Pathogenic strains usually produce common virulence factors
- Adhesins – various pili
- Exotoxins – e.g. Shiga toxin, heat-labile toxin
what is the bacterial pilus?
A bacterial appendage found on the surface of gram-negative bacteria. Facilitates adhesion of bacteria to specific surfaces. Sex pili are used to exchange genes with other bacteria during conjugation.
what is the labile toxin?
A virulence factor that is destroyed at high temperatures and produced by certain bacteria, including enterotoxigenic E. coli (ETEC), Clostridium perfringens, and Bacillus cereus. Heat-labile enterotoxin over-activates adenylate cyclase, increasing the production of cyclic adenosine monophosphate (cAMP). This causes increased secretion of chloride and water efflux into the intestinal lumen, which results in watery diarrhea.
what infections commonly cause E. Coli
- Urinary tract infection (UTI)
- Intra-abdominal infections – cholecystitis, peritonitis, cholangitis
- Neonatal meningitis
- Bloodstream infection (BSI)
- Gastroenteritis
what is the most common cause of UTI?
E. Coli
why does E. Coli cause more UTI in females than males?
1)Shorter in females hence why UTI more common)
2)Originates from the perianal area & travels along the urethra to the bladder
3)Strains often have pili/fimbriae that aid attachment to epithelial cells – Type 1 fimbriae
4)Certain serotypes more commonly
associated with UTI - 01, 02, 04
what are the symptoms of UTI?
- Suprapubic pain (cystitis – inflamed bladder)
- Flank pain (pyelonephritis – inflamed kidney)
- Dysuria = pain when passing urine
- Frequency* = passing urine every 1-2 hours
- Urgency* = The urge to pass urine, must pass urine NOW!
- Nocturia* = passing of urine during the night which is out of usual habit
what are the P fimbriae?
virulence factor of uropathogenic E. coli that promotes adherence to urothelial cells via cellular projections composed of glycoproteins. Involved in the pathogenesis of cystitis and pyelonephritis.
what intra-abdominal infections can be caused by E. Coli?
– appendicitis – acute cholecystitis – peritonitis – sub-phrenic abscess – liver abscess
E. Coli can cause meningitis. True/False
True
– Neonate – early after delivery, acquired during birth
– Post-traumatic/post-operative, e.g. major road traffic accident
what age group is particularly at risk of meningitis caused by E. Coli
neonates
what are the common sources of E. Coli sepsis?
- intra-abdominal pathology
- urinary tract sepsis
- neonatal meningitis
list the serotypes of E.Coli that cause gastroenteritis?
A. Enterotoxigenic E. coli (ETEC) B. Enterohaemmorhagic (EHEC) C. Enteropathogenic E.coli (EPEC) D. EnteroinvasiveE. coli (EIEC) E. Enteroaggregative E. coli (EAEC)
which bacteria is the most common cause of Traveller’s diarrhea?
ETEC
what is the traveler’s diarrhea?
Infectious diarrhea caused by a variety of bacterial, viral, and parasitic organisms. Typically acquired during travel to resource-limited regions, most commonly through the ingestion of contaminated food or water. Causative pathogens include enterotoxigenic E. coli (most common), enterohemorrhagic E. coli, Campylobacter, Salmonella, Entamoeba histolytica, Norovirus, and Rotavirus.
ETEC prodduce diarrhea by ivasion into intestinal wall. True/False
False
It is non-invasive (vs shigella, salmonella, EHEC). Diarrhea is due to enterotoxins
how toxins produced by ETEC cause diarrhea?
1) Heat-labile enterotoxin (AB toxin; two-component protein, similar to cholera toxin): activation of adenylate cyclase → ↑ cAMP-level → increased chloride secretion → water efflux into the intestinal lumen (secretory diarrhea)
2) Heat-stable enterotoxin: activation of guanylate cyclase → ↑ cGMP-level → decreased NaCl reabsorption → water efflux into the intestinal lumen (secretory diarrhea)
what are the clinical features of the traveler’s diarrhea?
- -Watery diarrhea
- -Abdominal cramping
- -Nausea and possibly vomiting
- -Fever
- -Decreased appetite
ETEC causes bloody diarrhea. True/False
False
Secretory not inflammatory
