ENTEROBACTERIACEAE

ENTEROBACTERIACEAE

Morphology & Identification • Gram-negative non-spore forming rods, catalase +ve, Oxidase -ve. • Primarily normal flora of gastrointestinal tract. • transient colonizers of skin, water streams. • Facultative anaerobes: mixed acid fermentation. • All ferment glucose; all reduce nitrates to nitrites. • Lactose fermentation: usually normal flora positive and pathogens negative. • Primary isolation media include eosin-methylene-blue (EMB) and MacConkey agar. • Differential selective media for specific organisms include: Salmonella-Shigella (SS) medium, bismuth sulfite media, Hektoen enteric agar, XLD, deoxycholate-citrate agar.

Antigenic Structure • Most are motile by peritrichous flagella --H antigens. • Capsule – Kantigen (Vifor Salmonella). • LPS (endotoxin) –O antigen. • various outer membrane proteins. • Pili - various antigen types, some encoded by plasmids • O (lipopolysaccharide) • H (flagellar) • K (capsular) • OKH (e.g., E. coli O55:K5:H21)

Opportunistic diseases -Enterobacteriaceae • septicemia, • pneumonia, • meningitis • urinary tract infections e.g., CitrobacterEnterobacter Escherichia Hafnia Morganella Providencia Serratia

Enterobacteriaceae:Foodborne infections • Escherichia coli • Salmonellae • Shigellae • Yersinia entercolitica

Reiter's syndrome • Associated with histocompatibility antigen (HLA) B27 • Most common in young males. most common form of arthritis affecting men between 20-40 years old • Symptoms • Arthritis (pain, swelling, stiffness, redness) • Conjunctivitis • iritis/uveitis (rare but requires immediate treatment) • Urinary tract infection (dysuria) may include reproductive organs • Skin rash • Heart problems in 10% of cases. • Causes: • NotEnterobacteriaceae • Campylobacter • Chlamydia • Enterobacteriaceae • Salmonella • Shigella • Yersinia

community acquired • otherwise healthy people • Klebsiella pneumoniae • respiratory diseases • prominent capsule • urinary tract infection • fecal contamination • E. coli • Proteus • urease (degrades urea) • alkaline urine .. Cause stones

Escherichia coli

Escherichia coli • Toxins: two types of enterotoxin; Shiga-type toxin; ST toxin; Hemolysins; Endotoxin, LT toxin • Adhesions: colonization factors; both pili or fimbriae ;non-fimbrial factors involved in attachment. There are at least 21 different types of adhesions. • Virulence factors that protect the bacteria from host defenses: Capsule/Iron capturing ability Outer membrane proteins

E.coli urinary tract infection Is the leading cause of urinary tract infections which can lead to acute cystitis (bladder infection) and pyelonephritis (kidney infection).Polyuria, dysuria, hematouria, pyuria, flank pain..Can cause bacteremia. Typically uropathogenic E. coli produce hemolysins

E.coli-Meningitis and Sepsis • Neonatal meningitis – is a leading cause of neonatal meningitis and septicemia with a high mortality rate. Usually caused by strains with the K1 capsular antigen.

Enteropathogenic E. coli • infantdiarrhea • fever • vomiting • nausea • non-bloody stools • Destruction of surface microvilli • This is a problem mainly in hospitalized infants and in day care centers.

Enterotoxigenic E. coli • A watery diarrhea, nausea, abdominal cramps and low-grade fever for 1-5 days. • Traveller’s diarrhea • diarrhea in children in developing countries • Transmission is via contaminated food or water.

Enterotoxigenic E. coli • Causes diarrhea like cholera but milder • caused by LT, ST, or LT/ST and colonization factors

Enterotoxigenic E. coli • Heat labile toxin • Adenylcyclase activation • cyclic AMP • secretion water/ions • Heat stable toxin • Guanylatecyclase activation • cyclic GMP • uptake water/ions

E.coli-Enteroinvasive (EIEC) • The organism attaches to the intestinal mucosa via pili • Outermembrane proteins are involved in direct penetration, invasion of the intestinal cells, and destruction of the intestinal mucosa. • There is lateral movement of the organism from one cell to adjacent cells. • Symptoms include fever, severe abdominal cramps, and watery diarrhea followed by bloody diarrhea (+ mucous, and pus). • resembles shigellosis

Enteroinvasive E. coli (EIEC) • Dysentery • resembles shigellosis • The EIEC are like Shigella: non-motile and non-lactose fermenter.

Transmission electron micrograph Enterohemorrhagic E. coli Also called Shiga toxin producing E. coli (STEC) • Usually O157:H7

E.coliEnterohemorrhagic (EHEC) • Hemorrhagic colitis • bloody, copious diarrhea • few leukocytes • afebrile • hemolytic-uremic syndrome • hemolytic anemia • thrombocytopenia (low platelets) • kidney failure

Enterohemorrhagic E. coliO157:H7 Diagnosis • Usually sorbitol –ve • MUG –ve • Can be also identified by serology (for shiga toxin) • Testing using Vero cells • PCR

Enteroaggregative E. coli • a cause of persistent, watery diarrhea with vomiting and dehydration in infants. • the bacteria adheres to the intestinal mucosa and elaborates enterotoxins (heat-stable toxin (ST)). • The result is mucosal damage, secretion of large amounts of mucus, and a secretory diarrhea.

Sanitary significance • Total bacterial number: number of bacteria contained per ml or gm of the sample; the standard of drinking water is less than 100. • Coliform bacteria index: the number of coliform bacteria detected out per 1000 ml sample; the standard of drinking water is less than 3

Escherichia coli • Genetically E. coli and Shigella are genetically highly closely related. For practical reasons (primarily to avoid confusion) they are not placed in the same genus. Not surprisingly there is a lot of overlap between diseases caused by the two organisms. • 1) Enteropathogenic E. coli (EPEC). Certain serotypes are commonly found associated with infant diarrhea. The use of gene probes has confirmed these strains as different from other groups listed below. There is a characteristic morphological lesion with destruction of microvilli without invasion of the organism that suggests adhesion is important. Clinically one observes fever, diarrhea, vomiting and nausea usually with non-bloody stools. • 2) Enterotoxigenic E. coli (ETEC) produce diarrhea resembling cholera but much milder in degree. Also cause "traveler’s diarrhea". Two types of plasmid-encoded toxins are produced. a) Heat labile toxins which are similar to choleragen (see cholera section below). Adenyl cyclase is activated with production of cyclic AMP and increased secretion of water and ions. b) Heat stable toxins; guanylate cyclase is activated which inhibits ionic and water uptake from the gut lumen. Watery diarrhea, fever and nausea result in both cases. • 3) Enteroinvasive E. coli (EIEC) produce dysentery (indistinguishable clinically from shigellosis, see bacillary dysentery below). • 4) Enterohemorrhagic E. coli (EHEC). These are usually serotype O157: H7. These organisms can produce a hemorrhagic colitis (characterized by bloody and copious diarrhea with few leukocytes in afebrile patients). Outbreaks are often caused by contaminated hamburger meat. The organisms can disseminate into the bloodstream producing systemic hemolytic-uremic syndrome (hemolytic anemia, thrombocytopenia and kidney failure). Production of Vero toxin (biochemically similar to shiga toxin thus also known as "shiga-like") is highly associated with this group of organisms; encoded by a phage. Hemolysins (plasmid encoded) are also important in pathogenesis. • As noted above, there are at least 4 etiologically distinct diseases. However, in the diagnostic laboratory generally the groups are not differentiated and treatment would be on symptomatology. Generally fluid replacement is the primary treatment. Antibiotics are generally not used except in severe disease or disease that has progressed to a systemic stage (e.g.hemolytic-uremia syndrome). Two major classes of pili are produced by E. coli : mannose sensitive and mannose resistant pili. The former bind to mannose containing glyocoproteins and the latter to cerebrosides on the host epithelium allowing attachment. This aids in colonization by E. coli.

Shigella

Shigella • S. flexneri, S. boydii, S. sonnei, S. dysenteriae • bacillary dysentery • shigellosis • bloody feces • intestinal pain • pus

Genral features • Contain pili. • Most strains can not ferment lactose; S. sonnei can slowly_ ferment lactose. • According to O antigen, 4 serogroups. • Easily acquiring drug-resistance.

Shigellosis • within 2-3 days • epithelial cell damage

Shiga toxin • enterotoxic • cytotoxic • inhibits protein synthesis • lysing 28S rRNA

Shigella attachment and penetration • Within 2-3 days • Epithelial cell damage

After the incubation period: fever, cramping, abdominal pain, and watery diarrhea (due to the toxin)for 1-3 days. • This may be followed by frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa). • It is rare for the organism to disseminate. • The severity of the disease depends upon the species. S. dysenteria is the most pathogenic followed by S. flexneri, S. sonnei and S. boydii.

Clinical significance • man only "reservoir” • Highly infectious 103 rather then 105-108 for salmonellae and vibrios. • Transmission via: • fecal to oral contact • Insects (flys..etc) • transmitted by adult food handlers • unwashed hands

Diagnosis of Shigella infection • Specimen: freshstool, mucus flecks, rectal swabs / or serum to demonstrate rise in titer of agglutination antibodies. • Primary media: MacConkey, EMB, • Selective media: Hektoen enteric agar, SS agar, XLD, Deoxycholate-citrate agar • Identification: TSI, Slide agglutination

Treating shigellosis • manage dehydration • patients respond to antibiotics , Problem of drug-resistance + dysentery vaccine.

Shigella • Shigella (4 species; S. flexneri, S. boydii, S. sonnei, S. dysenteriae) all cause bacillary dysentery or shigellosis, (bloody feces associated with intestinal pain). The organism invades the epithelial lining layer, but does not penetrate. Usually, within 2-3 days, dysentery results from bacteria damaging the epithelium lining layers of the intestine often with release of mucus and blood (found in the feces) and attraction of leukocytes (also found in the feces as "pus"). Shiga toxin (chromosomally encoded) is neurotoxic, enterotoxic and cytotoxic plays a role. The toxin inhibits protein synthesis (acting on the 80S ribosome and lysing 28S rRNA). This is primarily a fecal-oral disease and it can be transmitted by infected food handlers, contaminating food. The source in each case is unwashed hands. Man is the only "reservoir". • Patients with severe dysentery are usually be treated with antibiotics (e.g. ampicillin). In contrast to salmonellosis, patients respond to antibiotic therapy and disease duration is diminished.

Salmonella • Salmonellosis may present as one of several syndromes including gastroenteritis, enteric (typhoid) fever or septicemia.

Virulence factors • Endotoxin – may play a role in intracellular survival • Capsule (for S. typhi and some strains of S. paratyphi) • Adhesions – both fimbrial and non-fimbrial • Type III secretion systems and effector molecules – 2 different systems may be found: • One type is involved in promoting entry into intestinal epithelial cells • The other type is involved in the ability of Salmonella to survive inside macrophages • Outer membrane proteins - involved in the ability of Salmonella to survive inside macrophages • Flagella – help bacteria to move through intestinal mucous • Enterotoxin - may be involved in gastroenteritis • Iron capturing ability

Enteric or typhoid fever • Enteric or typhoid fever occurs when the bacteria leave the intestine and multiply within cells of the reticuloendothelial system. • The bacteria then re-enter the intestine, causing gastrointestinal symptoms. • Typhoid fever has a 10-14 day incubation period and may last for several weeks. • Salmonella typhi is the most common species isolated from this type salmonellosis. • Human reservoir: carrier state common • Contaminated food: water supply • Poor sanitary conditions

Typhoid • Septicemia • -occurs 10-14 days • lasts 7 days • gall bladder • shedding, weeks • acute phase, gastroenteritis gastrointenteritis

Typhoid -Therapy • Antibiotics • essential • Vaccines Vi (capsular) antigen :protective

Salmonella gastroenteritis • Salmonella gastroenteritis is the most common form of salmonellosis and generally requires an 8-48 hour incubation period and may last from 2-5 days. • Symptoms include nausea, vomiting and diarrhea (non-bloody stool). Salmonella enteritidis is the most common isolate. • Poultry, eggs. no human reservoir • self-limiting (2 - 5 days)

Salmonella septicemia • Salmonella septicemia (bacteremia) may be caused by any species but S. choleraesuis is the most common. This disease resembles other Gram-negative septicemias and is characterized by a high, remittent fever with little gastrointestinal involvement.

Immunity (S. typhi) • Vi (capsular) antigen • protective

ENTEROBACTERIACEAE