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list the main microorganisms responsible from UTI explain the importance of significant bacteriuria and quantitative culture method List the main advantages and disadvantages of each type ofsample for the laboratory diagnosis List the laboratory tests for UTI Urinary tract infections are common, especially among women 20-30% of women have recurrent urinary tract infections (UTI) at some time in their life. UTIs in men are less common and primarily occur after 50 years of age. Although the majority of infections are acute short-lived they contribute to a significant amount of morbidity in the population. Severe infections result in a loss of renal function and serious long-term sequelae. In females, a distinction is made between cystitis, urethritis and vaginitis, but the genitourinary tract is a continuum and the symptoms often overlap. Coagulase negative staphylococci Viridans nonhemolytic streptococci Lactobacilli ♀ Diphtheroids Non pathogenic Neisseria species Commensal Mycobacterium species Yeasts Bacterial infection : usually acquired by the ascending route from the urethra to the bladder The infection may then proceed to the kidney. Occasionally, bacteria infecting the urinary tract invade the bloodstream to cause septicemia. Bacterial infection : Less commonly, infection may result from hematogenous spread of an organism to the kidney with the renal tissue being the first part of the tract to be infected. From an epidemiological viewpoint, UTIs occur in two general settings: 1-community-acquired and 2-hospital (nosocomially) acquired, most often being associated with catheterization. Hospital-acquired UTIs, while less common than community acquired, contribute significantly to overall nosocomial infection rates. The Gram-negative rods: Escherichia coli (the commonest cause of ascending UTI ) Other members of the Enterobacteriaceae: -Proteus mirabilis -Klebsiella, Enterobacter, Serratia spp. and Pseudomonas aeruginosa The Gram-negative rods: Enterobacteriaceae: -Proteus mirabilis: associated with urinary stones (calculi), probably because this organism produces a potent urease, which acts on urea to produce ammonia, rendering the urine alkaline. The Gram-negative rods: Enterobacteriaceae: -Klebsiella, Enterobacter, Serratia spp. and Pseudomonas aeruginosa : are more frequently found in hospitalacquired UTI because their resistance to antibiotics favors their selection in hospital patients Gram-positive species Staphylococcus saprophyticus : ◦ especially in young sexually active women. Staphylococcus epidermidis and Enterococcus species are more often associated with UTI in hospitalized patients (especially those with AIDS), where multiple antibiotic resistance can cause treatment difficulties. Gram-positive species corynebacteria and lactobacilli Obligate anaerobes: very rarely Hematogenous spread to the urinary tract: other species may be found: Salmonella typhi, Staphylococcus aureus Mycobacterium tuberculosis (renal tuberculosis). Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier rare hemorrhagic cystitis and other renal syndromes may be recovered from the urine in the absence of urinary tract The human polyomaviruses, JC and BK cytomegalovirus (CMV) and rubella Adenovirus:hemorrhagic cystitis The rodent-borne hantavirus mumps and HIV Candida spp. and Histoplasma capsulatum The protozoan: Trichomonas vaginalis Schistosoma haematobium : hematuria. A variety of mechanical factors predispose to UTI Pregnancy, prostatic hypertrophy, renal calculi, tumors and strictures are the main causes of obstruction to complete bladder emptying Catheterization is a major predisposing factor for UTI A variety of virulence factors are present in the causative organisms The healthy urinary tract is resistant to bacterial colonization A key feature is the detection of significant bacteriuria. Infection can be distinguished from contamination by quantitative culture methods the urinary tract is sterile, the distal region of the urethra is colonized with commensal organisms, which may include periurethral and fecal organisms. As urine specimens are usually collected by voiding a specimen into a sterile container, they become contaminated with the periurethral flora during collection. Infection can be distinguished from contamination by quantitative culture methods. the urinary tract is sterile, the distal region of the urethra is colonized with commensal organisms, which may include periurethral and fecal organisms. As urine specimens are usually collected by voiding a specimen into a sterile container, they become contaminated with the periurethral flora during collection. Midstream urine (MSU) Infection can be distinguished from contamination by quantitative culture methods. is defined as 'significant' when a properly collected midstream urine (MSU) specimen is shown to contain over 105 organisms/ml. Infected urine usually contains only a single bacterial species. Contaminated urine usually has <104 organisms/ml and often contains more than one bacterial species Distinguishing infection from contamination when counts are 104-105 organisms/ml can be difficult. Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier urine specimens collected from: Catheters nephrostomy tubes suprapubic aspiration directly from the bladder: any number of organisms may be significant because the specimen is not contaminated by periurethral flora. Infection of sites in the urinary tract below the bladder by organisms that are not members of the normal fecal flora: may not lead to the presence of significant numbers in the urine. Difficult 'Bag urine' may be collected by sticking a plastic bag to the perineum in girls or to the penis in boys such specimens are frequently heavily contaminated with fecal organisms. with minimum delay because urine is a good growth medium for many bacteria and multiplication of organisms in the specimen between collection and culture will distort the results should be collected before antimicrobial therapy is started. If the patient is receiving, or has received, therapy within the previous 48 h, this should be stated clearly on the request form. a catheter specimen of urine is used Patients should not be catheterized simply to obtain a urine sample. Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier M. tuberculosis Schistosoma haematobium M. tuberculosis three early morning urine samples on consecutive days S. haematobium the last few ml of a late morning urine sample collected after exercise Microscopic examination of urine allows a rapid preliminary report Bacteria may be seen on microscopy when present in the specimen in large numbers. However, they are not necessarily indicative of infection, but may indicate that the specimen has been poorly collected or left at room temperature for a prolonged period of time. Microscopic examination of urine The presence of red and white blood cells, although abnormal, is not necessarily indicative of UTI. infection of the urinary tract and elsewhere (e.g. bacterial endocarditis) renal trauma calculi urinary tract carcinomas clotting disorders thrombocytopenia Occasionally, red blood cells may contaminate urine specimens of menstruating women. White blood cells are present in the urine in very small numbers (e.g. <10/ml) in health a count of over 10/ml is considered abnormal, but is not always associated with bacteriuria. Sterile pyuria is an important finding and may reflect: concurrent antibiotic therapy other diseases such as neoplasms or urinary calculi infection with organisms not detected by routine urine culture methods. Renal tubular cells, seen in the urine of aspirin-misusers, may be confused with white blood cells. Urinary casts are also indicative of renal tubular damage. A laboratory diagnosis of significant bacteriuria requires quantification of the bacteria Conventional culture methods produce results within 18-24 h, but rapid methods (e.g. based on bioluminescence, turbidimetry, leukocyte esterase/nitrate reductase test, etc.) are also available. storage - the urine must be cultured within 1 h of collection or held at 4°C for not more than 18 h before culture antibiotic treatment - in a patient receiving antibiotics, smaller numbers of organisms may be significant and may represent an emerging resistant population; simple laboratory methods are available to detect antibacterial substances fluid intake - the patient may be taking more or less fluid than usual, and this will clearly influence the quantitative result the specimen - the quantitative guidelines are valid for MSU specimens; they do not apply to catheter specimens, suprapubic aspirates or nephrostomy samples. 1. Microscopy 2. Quantitative culture 3. Susceptibility testing Gram staining→ presence of leukocytes and microorganisms microscopic examination: Presence of significant number of bacteria in uncentrifuged urine sample–high magnifaction power in immersion field; x1000- with Gram stain): ≥ 1 bacterium or bacteria/high power field. conventionally accepted to correspond ≥105 CFU/mL) Culture: Presence of significant number of bacteria inuncentrifuged urine sample (quantitative culture result): ≥ 103 to ≥105 CFU/mL Bacteria/ no.of coloni In asemptomatic patients 105 cfu/ml (male 104): identification and antibiotic susceptibility test (AST) 104- 105 cfu/ml : contact with clinician if >2 bacteria is seen 102 cfu/ml : significant if it is taken from catheter 10 cfu/ml: significant if its suprapubic aspiration Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier E. coli (%50-90) Other Enterobacteriaceae S. saphrophyticus (♀) P. aeruginosa Enterococcus spp. Other CNS