LEARN Flashcards
What are the general characteristics of Enterobacteriaceae?
Gram (-) bacilli or coccobacilli, non-spore formers, facultative anaerobes, catalase (+), ferment glucose, reduce nitrates to nitrites, cytochrome oxidase (-), motile except Klebsiella, Shigella, Yersinia, and some strains of E. coli
Motility in Enterobacteriaceae is typically peritrichous if the organism is motile.
Which genera are considered true pathogens among Enterobacteriaceae?
Salmonella, Shigella, Yersinia
These are not part of the normal intestinal flora.
What is the pathogenic classification of Escherichia coli?
Somewhere between overt pathogens and opportunistic pathogens
What are the virulence factors of Enterobacteriaceae?
- Ability to colonize, adhere and invade tissues
- Production of toxins
- Presence of plasmids that mediate resistance to antimicrobials
- Somatic Ag (O Ag)
- Flagellar Ag (H Ag)
- Capsular Ag (K Ag)
O Ag is located in the cell wall and is heat stable, while H Ag and K Ag are heat labile.
What is the primary plating medium used to isolate Salmonella and Shigella?
Xylose Lysine Desoxycholate Agar (XLD)
What are the cultural characteristics of Enterobacter species on Mac Conkey Agar (MCA)?
Mucoid colonies, lactose fermenters (LF) are pink
Non-lactose fermenters (NLF) appear colorless.
Fill in the blank: Citrobacter freundii is commonly associated with infectious diseases acquired in _______.
[hospital settings]
What infections are associated with Citrobacter freundii?
- UTI
- Pneumonia
- Intra-abdominal abscess
- Endocarditis
- Septicemia
- Meningitis
- Brain abscess
- Neurologic complications
True or False: Citrobacter diversus is associated with nursery outbreaks of neonatal meningitis.
True
What is the clinical significance of Enterobacter cloacae?
Associated with infections from contaminated medical devices
What is the primary virulence factor associated with Salmonella?
Fimbriae for adherence
What are the biochemical reactions of Edwardsiella tarda?
K/AG + H S, IMVC: + + - -, Urease (-)
What infections is Klebsiella pneumonia associated with?
- Liver abscess
- Pneumonia
- Septicemia
- UTI
What distinguishes Klebsiella species from other Enterobacteriaceae?
Absence of motility
What are the cultural characteristics of Serratia marcescens?
Produces a non-water soluble red pigment known as PRODIGIOSIN
What is the infective dose of Salmonella for gastroenteritis?
10,000,000 bacteria
What are the clinical features of typhoid fever caused by Salmonella typhi?
- Prolonged fever
- Bacteremia
- Involvement of RES (liver, spleen, intestines)
- Dissemination to multiple organs
Fill in the blank: Enterobacter species may harbor plasmids that encode multiple _______ resistance genes.
[antibiotic]
What is the detection method for lactose fermenters on Mac Conkey Agar?
Pink or red colonies
What is the significance of the Vi antigen in Salmonella?
Helps evade phagocytosis
What organs are primarily affected by the organism discussed?
Liver, spleen, intestines, and mesentery
How long does it take for the disease to develop after ingestion of the organism?
Approximately 9 – 14 days
What occurs during the first week of disease?
Organisms penetrate the intestinal mucosa and enter the lymphatic system
What happens to the organisms after they reach the bloodstream?
They are spread to the liver, spleen, and bone marrow, where they are engulfed by mononuclear phagocytes
What symptoms are experienced during the second to third week of disease?
Sustained fever with prolonged bacteremia
What are ‘rose spots’?
Blanching, rose-colored papules around the periumbilical region
What indicates the presence of the organism in large numbers?
Isolation from the stool
What is the focus of long-term carriage of the organism?
The gall bladder
What laboratory specimen is used for diagnosis in the first week?
Blood culture
What laboratory specimens are used for diagnosis in the second and subsequent weeks?
Stool and urine culture
What type of test is performed in the third and subsequent weeks?
Antibody testing (IgM), Fluorescent Antibody Test
What is the characteristic biochemical reaction for the organism?
K/A, H S (small amount only), IMVC: - + - -
What are the serovars included in other enteric fever?
S. paratyphi serovar A, S. paratyphi serovar B, S. paratyphi serovar C
What is the primary characteristic of bacteremia caused by non-typhoidal Salmonella?
Prolonged fever and intermittent bacteremia
What is the carrier state of Salmonella?
Individuals who recover may harbor the organisms in the gall bladder
What is the classification of Shigella based on Ewing’s Classification?
- Group A: Shigella dysenteriae
- Group B: Shigella flexneri
- Group C: Shigella boydii
- Group D: Shigella sonnei
What are the general characteristics of Shigella?
- Non-motile
- Lysine decarboxylase (-)
- H S (-)
- Non-Lactose Fermenters
- Non-encapsulated
What is dysentery characterized by?
Presence of blood, mucus, and pus in the stool
How is Shigella transmitted?
Direct person-to-person contact via fecal-oral route
What is the infective dose required for Shigella to cause disease?
Fewer than 200 bacilli
What is a key feature of Shigella dysenteriae?
Most virulent species with significant morbidity and high mortality
What is the mortality rate associated with Shigella dysenteriae?
5 – 10%
What is Yersinia pestis known for?
Causative agent of plague
What type of staining is characteristic of Yersinia pestis?
Bipolar staining
What are the three forms of plague?
- Bubonic plague
- Pneumonic plague
- Septicemic plague
What is the primary clinical manifestation of Yersinia enterocolitica infection?
Acute Enteritis
What medium is used for the selective isolation of Yersinia enterocolitica?
CIN Agar
What are the clinical manifestations of Yersinia pseudotuberculosis infection?
Septicemia accompanied by mesenteric lymphadenitis
What is the major characteristic of diarrheagenic E. coli?
Five major types including EPEC, ETEC, EIEC, EHEC
What is the main virulence factor of Enteropathogenic E. coli (EPEC)?
Intimin
What symptom is associated with Enterotoxigenic E. coli (ETEC)?
Non-bloody, profuse, watery stool
What is the significance of serotyping in Shigella species?
Based on Somatic LPS O Antigen
What is the role of DNA probes in laboratory diagnosis?
Used for stool samples
What are the symptoms of diarrhea that may indicate an infection?
Diarrhea with fever, malaise, severe abdominal cramps
What type of diarrhea is characterized by watery stool followed by scanty stool with pus, mucus, and blood?
Watery diarrhea followed by scanty stool with pus, mucus, and blood
What is the definitive identification test for certain E. coli infections?
Sereny Test – bioassay with a positive result of Keratoconjunctivitis in guinea pig
What cell cultures are used for identification of certain E. coli strains?
Monolayer cell cultures with Hep-2 cells
What type of E. coli is also known as Verotoxin Producing E. coli (VTEC)?
ENTERHEMORRHAGIC E. COLI (EHEC)
What toxin is produced by EHEC that is similar to a toxin produced by Shigella dysenteriae?
Toxin similar to shiga toxin
What is the most well-known serotype of EHEC?
Serotype 0157:H7
What conditions can be caused by EHEC infection?
- Hemorrhagic diarrhea
- Colitis
- Hemolytic uremic syndrome (HUS)
What foods are associated with EHEC infections?
- Processed meat
- Unpasteurized milk
- Apple cider
What are the two verotoxins produced by EHEC?
- Verotoxin I
- Verotoxin II
What is a distinguishing feature of EHEC stool compared to EIEC and Shigella dysentery?
Stool does not have pus cells
What fermentation characteristic helps differentiate EHEC from other E. coli?
(-) Sorbitol Fermentation using Sorbitol-McConkey
What symptoms are associated with ENTEROAGGREGATIVE/ENTEROADHERENT E. COLI (EAEC)?
- Watery diarrhea
- Vomiting
- Dehydration
- Occasionally abdominal pain
What is the major cause of E. coli associated urinary tract infections?
UROPATHOGENIC E. COLI (UPEC)
What are some virulence factors of UPEC?
- Adhesions
- Hemolysins
- Aerobactin
What does Meningitis/Sepsis Associated E. coli (MNEC) cause?
Neonatal meningitis resulting in high morbidity and mortality
What percentage of MNEC strains are positive for K1 antigen?
80%
What is a common cause of bacteremia in adults?
GIT infections
What is a characteristic of Escherichia fergusonii?
Multiple abscesses following a gunshot to the abdomen
What is the significance of Escherichia hermannii?
Has been isolated from spinal fluid, wound, and blood
What are the antimicrobial susceptibility testing groups for the genus Escherichia?
- Group A
- Group B
- Group C
- Group O
- Group U
What antibiotic is a surrogate test for uncomplicated UTI in Group U?
Cefazolin
Fill in the blank: EHEC is also known as _______.
Verotoxin Producing E. coli (VTEC)
True or False: EHEC can be detected using vero cell culture.
True
