Indian Journal of Urology
: 2001  |  Volume : 17  |  Issue : 2  |  Page : 111--117

Bacteriology and chemical composition of renal calculi accompanying urinary tract infection

Seema Golechha, Aruna Solanki 
 Department of Microbiology, Dr S.N. Medical College, Jodhpur, India

Correspondence Address:
Aruna Solanki
18, Amarnath Building, Opposite M.G. Hospital, Jodhpur- (Rajasthan) - 342 001


Bacteriological study of pre-operative urine and stone along with chemical analysis of stones have been perforned in 100 cases of urolithiasis. Although the rate of infection accompanying stone formation is more in female (50%) in comparison to male (27.9%) but over­all incidence of stone formation is more in male (86%). The crushed stone core culture was positive in 31 cases (31 %) and out of these cases, 23 cases (74.19%) showed positive urine culture. 15 cases (48.38%) of stone positive culture showed same organism which were also isolated from pre-operative urine culture whereas 8 (25.80%) cases of culture positive stones showed dif­ferent micro-organisms than pre-operative urine cul­ture. Chemical analysis revealed increased incidence of mixed stone composed of calcium oxalate and cal­cium phosphate (51 %). The occurence of pure triple phosphate stone was only 13%. The commonest pathogen recovered from pre-operative urine culture and stone culture was E.coli (32.25% and 21.73%)followed by Pseudomonas (22.58% and 17.39%) from mixed stones composed of calcium oxalate with cal­cium phosphate and triple phosphate. Out of 31 infection stones, 13 stones which were composed mainly of triple phosphate showed highest incidence of infection (84.62%).

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Golechha S, Solanki A. Bacteriology and chemical composition of renal calculi accompanying urinary tract infection.Indian J Urol 2001;17:111-117

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Golechha S, Solanki A. Bacteriology and chemical composition of renal calculi accompanying urinary tract infection. Indian J Urol [serial online] 2001 [cited 2022 Jan 21 ];17:111-117
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A progressive increase in the prevalence of urolithi­asis in western zone of Rajasthan has been witnessed in last few decades in one of the studies from western Raj asthan. [1]

Numerous risk factors responsible for or contribut­ing to stone formation have been identified including environmental, metabolic, dietary, racial, sex, obstruc­tive uropathy and infection of urinary tract. The last is an important risk factor and at least in females, urinary tract infection is one of the most common causes of urolithiasis. [2]

There is controversy regarding role of the urea splitting organisms in formation of renal stones. [3],[4]

Therefore the present study was undertaken to evaluate chemical composition and bacteriological spectrum of re­nal stones and culture of their pre-operative urines.

 Material and Methods

The present study was conducted on 100 patients of urolithi­asis admitted in Urology and Surgical departments of Dr. S.N. Medical College, Jodhpur for management of renal stones.

Bacteriological study was conducted on pre-operative urine and operated renal stones. Pre-operative urine sam­ples were collected aseptically for macroscopic and micro­scopic examination. Both pre-operative urine and operated renal stones were processed for bacteriological culture.

Processing of stones for bacteriological culture was done as described by Ohkawa et al. [5] The renal stones were thor­oughly rinsed in sterile physiological saline and then crushed with sterile hack-saw. The crushed stone core was cultured in 5m1 thioglycollate broth which was incubated at 37°C for 18-24 hours and then subcultures were made on blood agar and MacConkey's agar plate for isolation of aetiological agents. The isolated organisms were identified by standard techniques. [6]

Chemical analysis of renal stones for oxalate calcium magnesium, ammonium and phosphate were performed as described by Bradley and Schurnann. [7]

 Observations and Results

The incidence of renal stone was more in male (86%) as compared with female (14%) i.e., in the ratio of 6.1:1 but the incidence of infection stone was more in females as compared to males, i.e., 1:1. 8. The incidence of sterile kidney stones [Figure 1] was 82.97% whereas the percentage of infection stones was more both in vesical [Figure 2] (48.57%) and ureteric stones, (33.33%). Out of 100 cases of renal stone 31 cases were culture positive, i.e., infection stones (31 %) whereas 69 cases proved culture negative [Table 1].

The incidence of sterile renal stones composed of cal­cium oxalate and calcium phosphate (84.31 %) was more in comparison to infection stone (15.69%) of same com­position. By contrast the incidence of infection stones was more in stones composed of triple phosphate (84.62%) and triple phosphate along with calcium oxalate (61.54%) [Table 2].

The comparison of micro-organisms isolated from crushed stones (31%) and pre-operative urine (23%), showed that E. coli was the predominant micro-organism isolated from preoperative urine as well as from crushed stone core culture (21.73% and 32.25%) [Table 3].

The E. coli (32.25%) was the predominant micro-or­ganism cultured from about one-third of crushed stones followed by Pseudomonas (22.58%). Staph aureus, Co­agulase negative Staphylococci, Strept. faecalis and Can­dida albicans were recovered in least number of cases. E. coli was isolated in maximum number from stones com­posed of calcium oxalate and calcium phosphate (50%), triple phosphate (27.27%) and triple phosphate and cal­cium oxalate (37.50%). Out of 8 stones of calcium oxalate and calcium phosphate, isolation rate of Pseudomonas was 50% and in case of triple phosphate stone Pseu­domonas was isolated in 27.27% cases [Table 4].

Out of 100 cases 46 cases showed infection in pre-op­erative urine and/or stone core culture while rest of 54 cases were sterile for both pre-operative urine and crushed stone core culture. Pre-operative urine culture was posi­tive in 38% cases while the stone core culture was posi­tive in 31 % cases. Out of 31 % positive stone core culture, the pre-operative urine culture in these cases were posi­tive in 23% cases. 15 cases (48.38%) of stone positive culture showed same organisms which were also isolated from pre-operative urine culture. 8 (25.8%) cases of cul­ture positive stone showed different micro-organisms than pre-operative urine culture. 8 (25.80%) cases of culture positive stones showed sterile pre-operative urine cul­ture. 15 cases (39.47%) showed positive urine culture whereas their stones were sterile for culture [Table 5].


The study was conducted on 100 patients of urolithiasis which include identification of causative micro-or­ganisms from pre-operative urine, crushed stone core cul­ture and chemical analysis of stones. The higher incidence of renal stones in males in comparison to females may be due to increased serum testosterone level which favours increased endogenous oxalate production by liver which in turn predisposes to oxalate stone formation. Moreover, increased urinary citrate concentration in females may help in protection against calcium urolithiasis. [8]

Contrary to overall increased incidence of renal stones in males, the preponderance of infection stone is more in females (1:1.8) which is in conformity with the study of Simon et al. [3]

The increased incidence of infection stone in females, may be due to increased incidence of recurrent urinary tract infection in them which is due to close proximity of urethra to anus and sexual activity additionally serves to increase chance of bacterial contamination of female ure­thra. The pregnancy causes anatomical and hormonal changes that favour development of urinary tract infec­tion. A change in genitourinary tract mucosa due to meno­pause may play a role in colonization of the introitus by coliforms, a major background factor for recurrent blad­der infection in females. [9]

Urolithiasis was mainly observed in kidney (47%) and urinary bladder (35%) as compared to stones lodged in ureter (18%). Moreover 82.97% kidney stones were found to be sterile on culture whereas in urinary bladder, infec­tion stones were more frequent (48.57%). This could be that kidney acts as a first barrier filter for crystals thereby damaging tubular epithelium which acts as a nidus for ster­ile stone formation. Recurrent urinary tract infection pre­disposes to infected renal stone formation in urinary bladder due to proximity of bladder to urethra. [9]

In this study the increased incidence of mixed stones composed of calcium oxalate and calcium phosphate (51 %) is in conformity with the observation made by Sutor and Wooley et al and Sharma et al. [10],[11],[12] The occurrence of pure triple phosphate stone was only 13% similar to the study made by Sharma et al. [12] The observed variation in chemical composition may be due to geographical varia­tion and dietary habits which have some contributory in­fluence in the incidence of urinary tract calculi and type of calculi which occur within a given area. [13] The present study showed the lowest frequency of associated infec­tion oxalate stones and mixed stones composed of cal­cium oxalate and calcium phosphate and highest in triple phosphate and mixed stones composed of triple phosphate and calcium oxalate, consistent with the findings of Holmgren et al. [14]

The bacteriological study of urine and stone samples revealed that commonest pathogen were E. coli, Pseu­domonas, Enterobacter and Proteus. E. coli is not a urease producing organism and is not considered to be a stone producing micro-organism. [15] However the present study revealed that E. coli was the predominant micro-organ­ism recovered from mixed stones (calcium oxalate, triple phosphate and calcium phosphate). The present finding is consistent with the study of Dajani and Shahabi Bratell et al. [4],[16]

The recovery of E. coli from mixed stones indicates that non-urease producing organisms probably also contribute in the calculus formation at some stage of their development.There was recovery of Candida albicans from one case of renal stone in present study as well as in another study of Jackson et al and Ohkawa et al. [5],[17] Although Candida albicans is found to be the causative organism of urinary tract infection in a small number of cases [18] but its aetiological role in stone formation needs further elucidation.

While correlating the result of concurrent bacteriologi­cal analysis of stones and urine culture it is evident that same organisms from urine culture and stone culture were isolated in 15 (48.38%) cases but different organisms in 8 (25.80%) cases. Thus it appears that voided urine does not always reflect the bacteriology of urinary tract stones which is in aggrement with the results of previous stud­ies. [19],[20] The findings might be due to intermittent release of small number of micro-organisms from the stone which may or may not be isolated from urine. The explanation for presence of bacteria within the calculi may be due to insignificant intermittent bacteremia from where the bac­teria are excreted in renal pelvis and may act as a nidus for deposition of crystals either by damaging the mucous coat or perhaps also by acting as a nidus for crystalliza­tion of salts. [10]

An alternative explaination for the presence of bacteria within stone and urine is that of secondary ascending in­fection from the bladder urine. Penetration of bacteria in the stone will prevent complete eradication of urinary tract infection by conventional antibiotic therapy and thus al­low the development of resistant organisms with inter­mittent shedding in urine. Thus a vicious cycle starts, infection bringing about stone formation and stone formation causing infection. [21],[22]


The present study thus revealed that urolithiasis is pre­dominant in males. Of these, kidney stones are found to be commonest followed by bladder stones. Bacteriological analysis indicates that only in few stones micro-organisms were identified. The infection stones were recovered more in females. The mixed stones composed of calcium oxalate and calcium phosphate are more common but bacterial iso­lation in these stones are least. Although triple phosphate stones are less common but micro-organisms in these stones are frequently isolated.

E. coli was the predominant micro-organism recovered from mixed stones composed of calcium oxalate, triple phosphate and calcium phosphates.

So it is concluded from present study that the micro­organism can influence the stone forming process in many different ways. According to this view stone formation is a multifactorial and dynamic process.


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