Microbiology of Urinary Tract Infections Flashcards
What is a UTI?
An infection that affects part of the urinary tract
What are UTIs like?
Asymptomatic (subclinical infections)
Symptomatic (disease)
What are different examples of UTIs? What are they?
Asymptomatic bacteriuria (ASB)
Cystitis (inflammation of the bladder)
Prostatitis (inflammation of the prostate)
Pyelonephritis (symptomatic infections of the kidneys)
What typically causes cystitis?
A bacterial infection: bacteria enter the urethra and the bladder, and they begin to multiply
What are the different types of prostatitis?
Acute bacterial prostatitis: caused by sudden bacterial infection
Chronic bacterial prostatitis: characterized by recurrent bacterial infections of the prostate gland
How does prostatitis arise?
Bacteria enter the urethra, prostate and bladder
What is acute pyelonephritis a result of ?
Bacterial invasion of the renal parenchyma
What is acute pyelonephritis?
It is a potential organ and/or life-threatening infection that often leads to renal scarring
What usually causes pyelonephritis?
In most cases; ascending cystitis infection combined with anatomical defects
What kind of anatomical defects can lead to pyelonephritis? (3) Who do they mostly present in?
- Defective vesicoureteral junction (50% of children with UTIs have reflux)
- Bladder outlet obstruction (older males due to prostatic hypertrophy)
- Hematogenous infection <2% of UTIs (usually occurs in clinical settings of substantial bacteremia, like sepsis)
What are the symptoms of cystitis? (5)
- Dysuria: Pain or burning sensation during urination
- Hematuria: blood in the urine
- Urgency & Frequency
- Pain in the lower abdomen: lower back and suprapubic pain
- Pyuria: urine looks turbid/cloudy because of presence of pus
What are the symptoms of pyelonephritis? (3)
- Pain on either side of the lower back
- Fever and chills
- Nausea and vomiting
What population are UTIs most common in?
Women because of the anatomy of the urethra compared to men
What is the most common example of UTI?
Cystitis
When do men start being affected by UTIs and why?
After the age of 50, men start to get affected as well, more commonly because of the obstruction from prostatic hypertrophy
What is the prevalence of ABS among women?
5% among women between ages 20 and 40 and 40 to 50% among elderly women
During the neonatal period which gender is more commonly affected by UTIs and why?
Slightly higher among males because more likely to have congenial urinary tract anomalies
What determines whether or not the bacteria can establish an infection?
Bacteria can enter the bladder, but whether or not they can establish an infection depends on the interplay between the host, pathogen, and environment
Why is urine a good environment for bacteria to grow and multiply?
It has a lot of waste products that bacteria can feed on
What are the factors relating to the organism that determine infection, colonization, or elimination?
Type of organism
Presence of virulence factors
Expression of virulence factors
What are the factors relating to the host that determine infection, colonization, or elimination?
Genetic background
Behavioral factors
Underlying disease
Tissue-specific receptors
What are the factors relating to the environment that determine infection, colonization, or elimination?
Vaginal ecology
Anatomy/urinary retention
Medical devices
What is the pathogenesis of UTIs? (11)
They ascend from the urethra to the kidneys:
Contamination of the periurethral area
Colonization: occurs in the urethra
Uroepithelium penetration: occurs in the bladder
Neutrophil infiltration
Bacterial multiplication and immune system subversion
Biofilm formation
Epithelial damage due to toxins and proteases
Ascension: occurs in the ureters
Pyelonephritis: occurs in the kidneys
It can even lead to acute kidney injury
Bacteremia
What is the colonization of UTIs like?
Pathogen colonizes the periurethral area and ascends through the urethra towards the bladder
What is the uroepithelium penetration like in UTIs?
Fimbria allow the bladder epithelial cells to attach and penetrate
Following penetration, bacteria continue to replicate and may form biofilms
What is the ascension process like in UTIs?
Once sufficient bacterial colonization occurs, bacteria may ascend on the ureter towards the kidney
Fimbria may aid in the ascension process
Bacterial toxins may also play a role by inhibiting peristalsis
What are the different kinds of UTIs?
- Community-acquired UTIs
- Healthcare-associated CAUTI
- Catheter-acquired UTIs
What are the etiologic agents in uncomplicated UTI?
Mostly Gram-negative rods from the Enterobacteriaceae family
What percentage does E.coli account for, UTI?
75 to 90% of isolates
What are different members of the Enterobacterieae family?
- E.coli
- Klebsiella
- Proteus
- Citrobacter species
What is the colour of gram-negative bacteria?
Pink
What other microorganisms can be etiologies of uncomplicated UTIs?
Staphylococcus saprophyticus (5 to 15%)
Enterococcus
Which population does Staphylococcus saprophyticus usually affect?
Younger women during the child-bearing period
What are recurrent UTIs considered as?
Complicated UTIs
What are the different etiologies of complicated UTIs & CAUTIs?
Gram-negative rods: mostly from Enterobacteriaceae
Gram-positive bacteria
Yeasts
What are examples of gram-negative rods that can cause complicated UTIs and CAUTIs? (7)
- E.coli
- Psudomonal aeruginosa
- Klabsiella
- Proteus
- Citrobacter
- Aceinetobacter
- Morgenella species
What are examples of gram-positive bacteria that can cause complicated UTIs and CAUTI? (2)
Enterococci
Staphylococcus aureus
Which population is usually affected by yeasts (complicated UTIs)?
Commonly seen in immunosuppressed patients: diabetes, pregnant, etc.
What are the kind of bacteria in the Enterobacteriaceae family?
Gram-negative facultative anaerobic bacilli (rods) or coccobacilli
What are the Enterobacteriaceae micro-organisms further classified into?
Lactose fermenters
Non-lactose fermenters
What are examples of lactose fermenters (Enterobacteriaceae)? (4)
E.coli
Citrobacter
Klebsiella
Enterobacter
What are examples of non-lactose fermenters (Enterobacteriaceae)? (4)
Proteus
Salmonella
Shigella
Yersinia
What is the mechanism of bacterial pathogenesis?
Pathogenic bacteria harbor virulence factors that facilitate infectiona nd contribute to disease progression and manifestation
What are exaples of bacterial virulence factors?
Adherence
Invasion
Byproducts of growth
Toxins
Degradative enzymes
Cytotoxic proteins
Endotoxins
Superantigen
Induction of excess inflammation Evasion of phagocytic and immune clearance
Capsule
Resistance to antibiotics
Intracellular growth
What is the importance of the capsule virulence factor?
Protect bacteria from complement system and phagocytosis
What is the importance of endotoxin or LPS virulence factors?
Bind to TLR4 and induce potent inflammatory responses
What is TLR4?
A sensor of PAMPs like LPS, expressed in WBC, mainly macrophages
What is the pathophysiology of uropathogenic E. coli (UPEC) infection in the bladder?
Attachment to the urothelium, invasion through p fimbriae or type 1 Pilli, replication –> proliferate to the extent that the cell can no longer tolerate and it undergoes apoptosis, exfoliation of epithelial cells
What is the importance of exfoliation of the epithelial cells in the pathophysiology of UPEC?
Identification way of realizing that there is a pathogen in the the body
Wha is the most common cause of UTIs?
Uropathogenic E. coli
What are the virulence factors of UPEC that help with colonization? (6)
- Fimbrial adhesins
- Non-fimbrial adhesins
- Siderophores
- Secreted toxins
- Cytotoxic necrotizing factor 1
- Capsule-forming polysaccharides
What is the function of adhesins (both fimbrial and non-fimbrial)?
Adhesion
What is the function of siderophores?
Iron-acquisition systems
What is the function of secreted toxins?
Hemolysin
What is the function of the cytotoxic necrotizing factor 1 virulence factor?
Acts on epithelial or endothelial cells or monocyte macrophages via activation of GTP-binding proteins
What is the function of the capsule-forming polysaccharides?
Immune evasion
What is Proteus?
A motile gram-negative rods bacteria that can swarm
Which species of Proteus are commonly isolated from complicated UTIs and CAUTI?
Proteus mirabilis and Proteus vulgaris
WHich bacterium has the unique characteristic of being really fast and what is its effect?
Proteus species travel and move very fast beacuse of their multiple flagella, they form a swarming pattern upon culture
What are the main virulence factors of Proteus?
Urase
Flagella
Secretory enzymes
Exotoxins
What can proteus mirabilis cause? How?
Kidney stones (struvite)
Proteus mirabilis produces urease, which alkalinizes urine, leading to the precipitation of calcium and magnesium salts, which then leads to stone formation and renal epithelium damage
What kind of bacterium is Klabsiella?
Gram-negative rods encapsulated bacteria that produce mucoid colonies
What are examples of Klebsiella virulence factors?
Capsule
Adhesins
Iron capturing ability
Which types of Klebsiella species are responsible for nosocomial infections?
Klebsiella pneumoniae
Klebsiella oxytoca
Can cause: hospital-acquired pneumonia, UTIs, sepsis and meningitis
What do Klebsiella species carry and spread and how?
Antibiotic resistance (AMR)
They produce ESBL (extended-spectrum beta-lactamase) therefore, nosocomial infections with high morbidity and mortality rates –> secondary and tertiary generation drugs do not work on them
What is CAUTI?
Catheter-associated UTI: a symptomatic or asymptomatic bacteremic UTI in a patient who has an indwelling urinary catheter at the time of or within 48 hours before the onset
What is the most common healthcare associated infection?
CAUTI
What is the pathogenesis of a CAUTI?
- Normally, urethral flora is flushed out
- With catheterisation, flushing mechanism circumvented
- Flora can pass up through catheter or from drainage bag
- Hands of personnel may contaminate the system during insertion or management
Which population is usually most prone to CAUTI?
Usually bed-ridden or hospitalised patients –> inability to move –> greater chance of infection
What are some examples of species that cause CAUTI?
E. coli (most common)
Candida spp
Enterococcus spp
P. aeruginosa
Klebsiella spp
What are organsims that cause CAUTI like?
They carry and spread antibiotic resistance, therefore preventing CAUTI is important in tackling the growing problem of antibiotic resistance in bacteria
What is the effect of biofilms of CAUTI?
They contribute to the pathogenesis of the species and also increase resistance to host defenses and antibiotic treatment
What are planktonic bacteria?
Bacteria that live alone, separate from one another
What is the progression of biofilms like?
Adhesion to surface
Formation of monolayer and production of “slime”
Microcolony formation, with multi-layering cells
Mature biofilm with characteristic “mushroom” formed of polysaccharide. Cells start to detach, reverting to planktonic cells and completing the cycle
What kind of bacterium is P. aeruginosa?
A gram-negative bacilli obligate aerobic bacteria and opportunistic pathogen
MDRO (multi-drug resistant organism)
Which population of patients does P. aeruginosa target?
Hospital infections in patients in Burns units, ICU, palliative care and CAUTI (immunosuppressed patients)
What are some virulence factors of P. aeruginosa?
Pyocyanin
Elastase
Exotoxins
Alkaline protease
What is the difference between pyocyanin and pyoverdine?
Pyocyanin is a blue-green pigment
Pyoverdine is a fluorescent green pigment
What kind of bacterium is Acinetobacter baumanii?
Gram-negative coccobacilli obligate aerobic bacterium that causes significant nosocomial infections
MDRO
Which population of people does Acinetobacter baumanii target?
Sick and vulnerable people
What are exampels of virulence factors of Acinetobacter baumanii?
Capsule
Fimbriae
Siderophores
What kind of infections does Acinetobacter baumanii cause?
Respiratory, urinary, wounds and septicemia
Where does Acinetobacter baumanii live?
Solid surfaces, soil, water & form biofilm in catheters and central lines
What % of E.coli isolates from CAUTI are resistant to fluoroquinolones?
25%
What % of P. aeruginosa isolates from CAUTI are resistant to fluoroquinolones?
1/3
What other medications are gram-negative pathogens isolated from CAUTI also resistant to?
Cephalosporins
Carbapenems
What kind of bacterium is Staphylococcus?
Gram-positive bacteria that cause infections in humans like pyelonephritis and uncomplicated UTI
Which species of Staph causes pyelonephritis?
S. aureus
Which species of Staph causes uncomplicated UTIs?
S. saprophyticus
What is S. saprophyticus?
The 2nd most common cause of UTIs in young women is coagulative negative and resistance to Novobiocin antibiotic
What are the virulence factors of Staph bacteria?
Capsule
Clumping factor
Coagulase & other enzymes
Hemolysin
Toxins (leukocidin, enterotoxin, TSST)
What are the different types of kidney stones?
- Calcium stones (most common –> 80%)
- Struvite stones (10%)
- Uric acid stones (9%)
- Cystine stones (1%)
- Xanthine stones
- Silica stones
What are calcium stones?
Formed due to an excess of a mineral called oxalate, commonly found in fruit, vegetables, nuts, and chocolate (food-related stone)
What are struvite stones?
Less common and caused by infection in the urinary tract, it can grow quickly and become quite large
What are uric acid stones?
Due to chronic dehydration, the risk increases in those with gout
What are cystine stones?
In people. with an inherited disorder that causes the kidneys to excrete an excess of certain amino acids
What are xanthine stones?
Caused by an enzyme deficiency that causes a build-up of xanthine deposits
What are silica stones?
Rare and caused by certain medications or herbal supplements
Why is the midstream urine collected for a urine analysis exam?
Flush all the normal flora and collect urine straight from the bladder
If nitrites are positive in dipstick analysis, what does that mean?
UTI
What does the dipstick test instantly screen for?
Infection (leukocytes)
Protein
Glucose
Ketones
What are the antibiotic resistance testing methods?
Disc diffusion method, zone of inhibition in mm
E-testing method, determine MC in μg/ml
