Urinary Tract Infections (UTI): Types and Factors

In this article we will discuss about Urinary Tract Infections (UTI):- 1. Meaning of Urinary Tract Infections (UTI) 2. Types of UTI 3. Clinical Features 4. Predisposing Factors 5. Causal Organisms 6. Pathogenesis and Source 7. Laboratory Diagnosis 8. Transport 9. Laboratory Methods 10. Hospital Urinary Infection 11. Source 12. Tuberculosis of Kidney and Urinary Tract.

Contents:

1. Meaning of Urinary Tract Infections (UTI)
2. Types of UTI
3. Clinical Features of Urinary Tract Infections (UTI)
4. Predisposing Factors of Urinary Tract Infections (UTI)
5. Causal Organisms of Urinary Tract Infections (UTI)
6. Pathogenesis and Source of Urinary Tract Infections (UTI)
7. Laboratory Diagnosis of Urinary Tract Infections (UTI)
8. Transport of Urinary Tract Infections (UTI)
9. Laboratory Methods of Urinary Tract Infections (UTI)
10. Hospital Urinary Infection
11. Source of Urinary Tract Infections (UTI)
12. Tuberculosis of Kidney and Urinary Tract

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1. Meaning of Urinary Tract Infections (UTI):

Infection of urinary tract (UTI-Urinary tract infection) is defined as bacteriuria, i.e. the multiplication of the organisms in urinary tract and the presence of more than a hundred thousand (10⁵) organisms per ml in the midstream sample of urine (MSU).

Pyuria means the presence of pus cells in urine and it occurs after the urinary tract infection. Normally, urinary tract (renal tissue, ureters, bladder and proximal urethra) is sterile, in distal urethra, many species of bacteria are encountered as transient flora, they are derived from the faecal flora.

2. Types of UTI:

UTI is divided into two categories:

A. Lower tract infection:

(1) Urethritis;

(2) Cystitis;

(3) Prostatitis.

B. Upper tract infection:

(1) Acute pyelitis-infection of pelvis of kidney;

(2) Acute pyelonephritis-infection of parenchyma of kidney.

Factors Limiting Multiplication of Organism:

Certain factor normally play an important role in limiting the bacteria multiplication as the urine is a good culture medium:

1. A high rate of urine flow.

2. Regular complete bladder emptying.

3. Constant dilution of residual urine in the bladder by inflow from kidney.

4. Mucosal defences act by rapid clearing of bacteria from the mucosa.

5. Local antibody, complement and lysozyme may also give protection.

6. Secretions of prostate and periurethral glands possess antibacterial activity.

Factors Favouring Multiplication of Organism:

The ability of urine to support the growth of bacteria depends on pH, osmolality and chemical constituents:

i. pH 6.0-7.0 favours bacterial growth.

ii. Osmolality. Lowered osmolality of urine encourages bacteriurial multiplication and decreases with the return of increasing concentrating ability.

iii. Glucose provides source of energy for bacterial growth.

iv. Obstruction-to urine flow.

3. Clinical Features of Urinary Tract Infections (UTI):

1. Asymptomatic:

Symptomless urinary tract infection or “Covert bacteriuria” is common. Adult women (5%), girls (1-3%), and boys (0.3%) have covert bacteriuria that can be detected only by urine culture.

2. Symptomatic:

Symptoms are dysuria, frequency, suprapubic pain along with loin pain and tenderness. There may be fever and rigors. Fever is associated with pyelonephritis. UTI is more frequent in women than men. Almost 50% women suffer from UTI during their adult lives. In males, incidence is much less and, in persons over 60, UTI due to enlarged prostate is common.

4. Predisposing Factors of Urinary Tract Infections (UTI):

I. Gender and Sexual Activity:

a. Females are more frequently affected by UTI (particularly cystitis) due to following reasons:

b. Female urethra is prone to colonisation of Gram-negative bacilli because it is close to anus.

c. Short length of urethra favours the introduction of bacteria into the bladder.

II. Pregnancy:

Pregnancy predisposes the upper urinary tract due to:

a. Dilatation of ureters and renal pelvis.

b. Stasis in ureter up to the brim of pelvis. Dilatation and stasis are partially caused by pressure of the enlarged pregnant uterus on the ureter of the brim of pelvis.

c. Temporary incompetence of vesicourethral valves.

III. Other Factors:

a. Obstruction to flow the urine (tumour, stone, stricture, prostatic hypertrophy)

b. Neurogenic bladder dysfunction (spinal cord, injury, multiple sclerosis).

c. Vesicoureteral reflux (reflux of urine from bladder into ureters and sometimes in the renal pelvis).

d. Bacterial virulence.

Genetic factors (genetically determined receptors on uroepithelial cells).

5. Causal Organisms of Urinary Tract Infections (UTI):

A. Gram-Negative Bacilli:

They are the most infecting agents:

1. Escherichia coli is the commonest cause of UTI in acute infection (60-90%) in general population without urologic abnormalities or calculi and 50% of hospital acquired infection.

Sero groups (02, 04, 06, 07, 08, 075) of E. coli are well adapted to enter the urinary tract and form majority of isolates of UTI. Factors associated with virulence of E. coli are:

(a) K. antigens that inhibit phagocytosis and bactericidal effects of complement.

(b) Bacterial adhesion to receptors on uroepithelium by specialised fimbriae.

2. Klebsiella sp.

3. Proteus sp. specially P. mirabilis.

4. Enterobactor, Ps. aeruginosa, serratia.

Though Klebsiella, Proteus, Pseudomonas, Enterobacter, and Serratia are responsible for a small number of uncomplicated infections. They gain importance in hospital acquired infection and infections associated with urologic manipulation, calculi or obstruction.

Proteus sp. due to production of urease and Klebsiella sp. through the production of extracellular lime and polysaccharide predispose to formation of stone and are more frequently associated with UTI with Calculi.

B. Gram-Positive Cocci:

They are not much associated with UTI:

1. Enterococci are normal flora of the intestine. They are common in urine as contaminants. Sometime they cause urinary tract infection after invasive procedure.

2. Staph, saprophyticus is a true primary pathogen of urinary tract and causes urethritis and cystitis (2-3%) in sexually active or healthy young females. Staph, epidermidis and micrococci are common contaminants of urine.

Staph, aureus and Enterococci cause urinary infection in individuals with renal calculi or after instrumentation. Isolation of Staph, aureus in urine is suggestive of localised lesions of the kidney or is secondary to prostatectomy or catheterisation.

Acute uncomplicated urinary infection is caused by one predominant organism (E.coli). Chronic complicated infection is often associated with more than one type of organisms.

6. Pathogenesis and Source of Urinary Tract Infections (UTI):

1. Ascending Route:

In most of the cases, urinary infection is ascending from the perineum; aided in females by short distance between urethra and anus, interposition of the vaginal introitus and the shortness of urethra. The distal urethra and vaginal introitus are normally colonised by lactobacilli, streptococci, diphtheria and staphylococci but not by enteric bacilli that are normally responsible for urinary tract infection.

Factors predisposing to periurethral colonisation by enteric bacilli:

(a) Alteration of the normal perineal flora by antibiotics or by contraceptives, especially diaphragm and spermicide.

(b) Faecal incontinence in infants.

(c) Entrance of periurethral bacteria inside bladder during intercourse.

(d) Poor hygienic habits in adults.

2. Haematogenous Route:

In the aetiology of UTI, haematogenous spread is rare. It may play an important role in renal infection of the newborn. In many infections, bacteriaemia occurs. Bacteriaemia may lead to abscess formation in renal parenchyma or mere excretion of the organism in the urine.

7. Laboratory Diagnosis of Urinary Tract Infections (UTI):

Before treatment, culture of urine is of great necessity for identification of the organism, antimicrobial susceptibility test and assessment of the result of treatment.

Specimen:

Specimen of urine should be in sufficient quantity, and it should be free from urethra and genital tract contamination.

1. Mid-Stream Specimen of Urine (MSSU/MSU):

Before collecting a sample of urine, the women should be instructed to swab the vulva and men to retract the foreskin and clean the glans penis. The patient begins to pass urine in toilet or bedpan.

The first portion is allowed to pass, then without interruption of the urine flow, midstream of the urine is collected in sterile wide-mouthed container or test tube and the terminal portion of urine stream is passed into the toilet or bed pan. The first portion of urine flushes out the normal flora. MSU is most ideal for culture for diagnosing bacterial cystitis and quantitative examination for presence of significant bacteria.

2. Catheter Specimen (CSU):

In catheterized patients, urine should be collected directly from the catheter which should not touch the container.

3. Urine Specimen from Infants:

A clean catch specimen obtained carefully produces excellent result, the catheterisation should not be advocated because of the risk of introducing infection.

8. Transport of Urinary Tract Infections (UTI):

It there will be delay in transporting within 2 hours to the laboratory, the specimen should be preserved as:

(a) Refrigeration at 4°C.

(b) Dip slide coated on both sides, with culture medium is inoculated by dipping into freshly passed urine and keeping in a sterile container for transport and growth can be observed after incubating.

9. Laboratory Methods of Urinary Tract Infections (UTI):

After sending a portion of urine sample to the laboratory for cultural test the rest is examined immediately under microscope.

A. Microscopy:

(i) Direct examination of deposit bacteria, pus cells, epithelial cells can be detected by microscopic examination of centrifuged deposit of urine. Pyuria is associated with most of the clinical infections but may be absent in symptomless bacteriuria.

Pus cells with RBCs are usually found in haemorrhagic cystitis. Pyuria without bacteriuria may indicate renal tuberculosis. Microscopical examination of deposit also reveals urinary casts, red cells, tubular epithelial cells or atypical cells that will indicate non-infective renal lesion such as glomerulonephritis or tumour.

(ii) Gram stained smear of deposit may show white cells and bacteria that may have come from genital or urinary tract.

B. Culture:

I. Media:

(i) Blood agar;

(ii) MacConkey’s agar n. Semi-quantative culture . Most laboratories use this technique by standard loop. Dip slide technique is useful while examining large quantity of urine specimens.

Standard Loop Technique:

A standard calibrated loop is used for transferring a fixed volume of undiluted urine to- culture medium and incubated overnight. Next day the number of colonies obtained is counted. Say, the fixed volume loop used can hold 0.04 ml. The total viable bacterial count per ml sample = Number of colonies x 250. When number of colonies formed in plate, say 400 — i.e. 100, 000 or 10⁵ organisms per ml. of unspun urine sample.

Dip Slide:

Commercially available plastic slides coated with Cysteine lactose electrolyte deficient (CLED) agar on one side and MacConkey’s agar on the other side is dipped into the freshly voided urine and replaced in a sterile container and incubated.

Viable count is obtained by comparing the growth on the media with the manufacturer’s charts. Though this technique is costly, it avoids the problems of transport of specimen to the laboratory and is useful in screening for significant bacteriuria in busy out-patient department (e.g. antenatal clinic).

Interpretation of Results:

(a) More than 100,000 (10⁵) viable bacteria of a single species per ml: Significant growth, sensitive test is to be done.

(b) Between 10,000 to 100,000 bacteria per ml: of doubtful significance, further specimens are to be cultured.

(c) Less than 10,000 bacteria per ml: no significant growth regarded as contaminants.

III. Identification of the organism is performed by biochemical and/or serological tests.

Bacteriuria of Pregnancy:

The prevalence of significant bacteriuria in pregnancy is 5% in first trimester rising to 10% at term. About 25% of these women with symptomless bacteriuria eventually develop clinical episodes during pregnancy. These women require antimicrobial treatment. If these infections persist and become chronic, they may progress to cause hypertension and ultimate renal failure.

If the bacteriuria responds to treatment during pregnancy, the risk of pyelonephritis is prevented; but if the patients have not received treatment or did not respond to treatment, acute pyelonephritis develops in 30% bacteriuric women with pregnancy.

10. Hospital Urinary Infection:

About 75% hospital acquired urinary tract infections occur after urethral catheterization or instrumentation.

11. Source of Urinary Tract Infections (UTI):

1. Endogenous:

Contamination of individual’s urethra and perineum by his own intestinal flora.

2. Exogenous:

Cross-infection with bacteria from urinary tract of another patient through instrument (Cystoscope, Catheter) or hands of nurses and doctors.

12. Tuberculosis of Kidney and Urinary Tract:

Tuberculosis of kidney is a blood-borne infection. Early lesions occur in blood vessel surrounding the glomeruli. Then these microscopic foci expand and erode into pelvis and spread downwards to bladder. In many cases, epididymis and seminal vesicles are infected.

The patients present with increased frequency and painless hematuria and urine shows numerous pus cells and RBCs but routine culture does not show any urinary pathogen. Tuberculosis can be considered in cases of pyuria without bacteriuria.

Specimen:

Tubercle bacilli are excreted from kidney intermittently, so MSU is not useful. Early morning urine should be collected in sterile container on three consecutive days which are to be preserved in the refrigerator till examined.

Laboratory methods :

Preparation of concentrate (Petroff’s method):

Urine is decontaminated by treatment with 4% sodium hydroxide for 15-30 minutes. After centrifugation the deposit is neutralized with N/10 or 8% hydrochloric acid in presence of an indicator (e.g. phenol red):

1. Ziehl-Neelsen film:

Smear made from decontaminated deposit may reveal acid-alcohol fast bacilli which have to be excluded from saprophytic mycobacteria (e.g. M. smegmatis) that may be present in normal urine.

2. Culture:

Lowenstein-Jensen medium is inoculated with the uncontaminated urine deposit and incubated for 6-8 weeks.