8 - Bacterial Causes of UTIs

Staphylococcus saprophyticus

*Causes 5-15% of community acquired UTI's in newly sexually active women ("honeymoon cystitis")* Infection usually symptomatic *Always nitrate negative* on urine dipsticks, low CFU's on culture, sensitive to antibiotics

Klebsiella pneumoniae - culture

*Copious capsule*, Urease (+), Lactose (+), Indole (-)

Serratia marcescens - culture

*GNB, some strains red pigmented (prodigiosin)*, lactose (-), Indole (-)

Providencia and Morganella spp. - virulence

*Urease (+)* - Biofilm formation, catheter encrustation, bladder and renal stones - Highly resistant to antibiotics

Enterococcus faecalis & E. faecium - virulence

*intrinsic resistance to antibiotics (VRE)*

*Uncomplicated UTI - definition*

Acute cystitis or pyelonephritis in non-pregnant outpatient *woman* without abnormality or instrumentation of the urinary tract

Klebsiella pneumoniae - abx resistance

Antibiotic resistance a problem (MDR, ESBL, carbapenemases)

Pseudomonas aeruginosa - abx resistance

Antibiotic resistance a problem. *Treat as a complicated infection. Remove obstruction to prevent relapse.*

Asymptomatic Bacteriuria (ABU)

Bacteria present in the urine without signs and symptoms attributable to UTI. Bacteria usually characterized by a *low prevalence of virulence factors (E. coli, Enterococcus, Coagulase negative-Staphylococci)*

IBC: Intracellular Bacterial Colonies

Biofilm-like communities inside superficial bladder cells may be associated with persistence of E. coli (and other uropathogens) in the bladder → recurrent infections

Proteus mirabilis - virulence

Biofilms and encrustations on catheters *urease*→ ↑ pH → renal calculi, catheter obstruction Urine with *pH > 7* → culture for Proteus, check for *calculi (urolithiasis) *

Acinetobacter baumannii

Commonly isolated from hospital environments and patients. Infections uncommon. Infections usually involve organs with a high fluid content (e.g. urinary tract) Causes catheter-associated UTI's Is a Gram (-) bacillus with low virulence that is* multi-drug resistant.*

Culturing

Culture and antibiotic sensitivity testing important for complicated infections to be sure of eradication

S. epidermidis - virulence

Forms protective biofilm on devices

Klebsiella pneumoniae - UTIs

GI tract of humans 1-2% of community acquired UTI's, 5-17% of complicated UTI's

Proteus mirabilis - UTIs

GI tract of mammals Urinary tract most common site of infection. Infections in community, hospitals and LTCF *Most common in patients with structural abnormalities and catheters& esp. long term indwelling catheters*

Enterococcus faecalis & E. faecium - culture

Gram (+) cocci, catalase (-) Grows in 6.5% NaCl and at 45°C Grows in the presence of 40% bile salts and hydrolyzes esculin and N-pyrrolidonyl-2-naphthylamide (PYR)

Proteus: General Characteristics

Gram (-) rod, lactose (-), Indole (-), H2S (+), oxidase (-) *Urease (6-10X's more potent as that produced by other bacteria)* *swarming mobility*

Providencia and Morganella spp.- culture

Gram (-) rods, Urease (+), Indole (+) , motile, H2S (-)

Enterobacter cloacae and E. aerogenes - culture

Gram (-) rods, lactose (+), indole (-)

Pseudomonas aeruginosa - culture

Gram (-), motile, oxidase (+), urease (+), lactose (-), produces a capsule

Diagnosis: Establishment of bacteriuria

Gram stain of un-centrifuged urine Urine Nitrite Sticks test for reduction of nitrate to nitrite (Note: Detects GNB, but not all uropathogens can do this (ex. S. saprophyticus and Enterococcus)

S. aureus - UTIs

Healthy adults (30%) colonized in anterior nares, transiently on skin, perineal colonization common Associated with ~2.2 % of CAUTI's Presence of S. aureus in urine should prompt evaluation for bacteremia Antibiotic resistance a problem (MRSA)

Citrobacter

Healthy humans rarely colonized. Urinary tract accounts for 40-50% of Citrobacter infections Colonization and infection common in immune compromised and patients w/ co-morbid disease in LTCF and hospital Possesses plasmid encoded resistance genes

Enterobacter cloacae and E. aerogenes - UTIs

Healthy rarely colonized Source: hospital equipment, foods Causes particularly catheter-related UTI's

Serratia marcescens

Healthy rarely colonized; causes mostly hospital associated infections Found in moist environments and liquid products -Food, blood products, IV soln., milk, lotions.. Antibiotic resistance, not currently a major problem.

Diagnosis and Treatment: tailored to

Host (history) Nature & site of infection Local patterns of antimicrobial susceptibility

Recurrent UTI's

Infections that recur after antibiotic therapy - Relapse - Re-infection

Urinary Tract

Lower tract - Urethra (Urethritis) - Bladder (Cystitis) Upper tract - Kidney (pyelonephritis) - Prostate (prostatitis) *Devoid of normal flora*

Pathogenesis of UTI's - ascending infection

Majority of bacteria from the gut establish infection by ascending from the urethra to the bladder. e. coli, proteus, klebsiella

Urinary Tract Infection - dx

Microorganisms (usually bacteria) detected in urine or urinary tract including the prostate gland 102-105 CFU/ml in urine sample from CCMS, catheter, or suprapubic aspiration

S. epidermidis - UTIs

Most abundant species on skin, also in nasopharynx and vagina Common cause of catheter-associated UTI's

Escherichia coli - cause of UTI

Most common agent of all UTI's Predominate species of GNB in the colonic flora

Enterococcus faecalis & E. faecium - UTIs

Normal flora of GI tract Nosocomial pathogen, *esp. those treated with broad spectrum antibiotics* Significant % of UTI's asymptomatic; cause of chronic prostatitis

*If urine is consistently alkaline - consider:*

PROTEUS

Candida albicans...

Part of mouth and gut flora Risks for cystitis→ diabetes mellitus, catheterization, use of broad spectrum antibiotics, prior surgical procedures Most common pathogen of nosocomial UTI's in patients on intensive care units Vast majority of patients are asymptomatic Unless UTI complicated, treatment not indicated

Enterobacter cloacae and E. aerogenes - abx resistance

Prominent nosocomial pathogen may be due to *significant resistance to antibiotics*

Catheter-associated UTI's

Source of bacteria: patients bowel (periurethral); hands of personnel, solutions, instruments (interluminal) Formation of a biofilm on catheter affects treatment and prevention strategies Note: bacteria in the biofilm may not be causing the UTI of patient or more than one bacterium may be causing the UTI Infecting strains more antibiotic resistant than community-acquired strains - tx: change catheter, culture urine

*Complicated UTI - definition*

Symptomatic cystitis or pyelonephritis in a man or woman with an anatomic predisposition to infection, a foreign body in UT, or factors that increase the risk of failing therapy (obstruction)

Pseudomonas aeruginosa - UTIs

Ubiquitous in the health-care environment Associated with foreign body in urinary tract

Etiology: Unusual pathogens

Ureaplasma urealyticum and Mycoplasma genitalium and M. hominus - roles not completely defined Adenovirus causes hemorrhagic cystitis in children and young adults Candida albicans commonly causes UTI in catheterized patients in ICU M. tuberculosis: Clinical setting → culture (-), pyuria, acidic urine, with abnormalities in UT

Escherichia coli: dipsticks

Urine dipsticks positive for nitrites, Gram (-) rod, lactose (+), indole (+), oxidase (-)

Providencia and Morganella spp. - UTIs

Used to belong to Proteus genus Common in catheterized LTCF patients (> 30 day catheterization)

UTI: pathogens (how many?)

Usually due to a single pathogen (uncomplicated) Polymicrobial infections -institutionalized elderly (ie LTCF) -obstruction, catheter associated UTI's

*Escherichia coli: virulence*

Virulence of Uropathogenic Strains (UPEC) - Type 1 fimbriae (cystitis), P fimbriae (pyelonephritis) - hemolysins, aerobactin (siderophore) - Resistance to serum killing, capsule, IBC formation - Antibiotic resistance a problem (MDR GNB; ESBL)

Diagnosis: Establishment of pyuria

Wet mount of spun urine Look for→ 8 WBC's per mm3 Urine Leukocyte Esterase Sticks

A 25 year old woman presents with a 48-hour history of dysuria, frequency and hematuria. She had similar symptoms about 8 months ago. She is currently in a monogamous relationship and uses condoms and spermicide.

What is the most likely diagnosis? *UTI* What factors have put the patient at risk? *female, spermacide, sex* What organism is most likely causing the infection and what characteristic virulence factors does it possess? *E. coli, staph saprophyticus* What is the source of the pathogen? *GU tract* How would you select antimicrobial therapy to treat this infection? *impirically*

An 83 year old female resident of a nursing home is transferred to the hospital with a fever. She is bed bound with an indwelling Foley catheter. The catheter is encrusted and is draining cloudy urine that has an alkaline pH.

What organisms could possibly be causing this patients infection? *proteus, E. coli, epidermydis* What is the source of the pathogen(s)? *exogenous, skin* What bacterial factor(s) is causing the pH of her urine to be alkaline and contributing to the encrustation of the catheter? *urease* Should you obtain a urine specimen for culture? *yes* How would you treat this infection? *remove catheter, culture, abx*

A 40 year old male that has been a paraplegic for 10 years, manages his bladder emptying by condom drainage. He complains of increased bladder spasms which he attributes to a urinary tract infection, because he has had two similar episodes in the past. Culture of a specimen of his urine grows K. pneumoniae of greater than 105 CFU/ml that exhibited resistance to fluoroquinolones and aminoglycosides.

Why is the patient experiencing a UTI? *condom drainage, problem voiding* Why is the isolate resistant to some antimicrobials? *because he has been tx before, resistance developing* How would you select therapy to treat this infection? *culture & abc susceptibility*

Enterobacter cloacae and E. aerogenes: risk factors

antibiotic treatment, co-morbid disease, treatment in ICU

Enterococcus faecalis & E. faecium - risks

catheterization, UT instrument., anatomic abnormality.

S. epidermidis - culture

novobiocin sensitive, antibiotic resistance a problem

Recurrent UTI's - Relapse

occurs within 2 weeks after therapy unresolved infection of kidney or prostate gland???

Recurrent UTI's - Re-infection

occurs within 6 months of an acute infection new bug isolated or initial strain persisting in fecal flora??? caused by *quiescent intracellular reservoirs (QIR)*? (bacteria viable in bladder inside cells although absent in the urine)

Always do Abx sensitivity test for

psuedomonas

*Etiology of Acute Cystitis & Pyelonephritis* - uncomplicated vs. complicated

women - usually uncomplicated - E. coli complicated - lot of opportunistic infections