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Saudi Journal of Kidney Diseases and Transplantation
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Year : 2013  |  Volume : 24  |  Issue : 2  |  Page : 418-423
Bacteriological study and structural composition of staghorn stones removed by the anatrophic nephrolithotomic procedure

1 Department of Urology, Shaheed Beheshti Hospital, Babol, Iran
2 Department of Microbiology, Rouhani Hospital, Babol University of Medical Sciences, Babol, Iran
3 Department of Medicine, Rouhani Hospital, Babol University of Medical Sciences, Babol, Iran

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Date of Web Publication26-Mar-2013


This study was conducted to determine the composition of staghorn stones and to assess the proportion of infected stones as well as the correlation between infection in the stones and bacteria grown in urine. Samples of 45 consecutive stones removed through anatrophic nephrolithotomic procedures were taken from the operation site and samples of urine were obtained by simultaneous bladder catheterization. The frequency of infection in the stones and correlation between infection of stone and urine samples were determined with respect to the composition of the stones. Twenty-two males and 23 females, with respective mean ages of 48.3 ± 15.6 years and 51 ± 7.4 years, were studied. The stone and urine cultures yielded positive results in ten and 16 patients, respectively, of a total of 45 patients (22.2% and 35.5%, respectively). Calcium oxalate was the main constituent of staghorn stones, seen in 31 patients (68.8%), uric acid in 12 patients (26.6%) and struvite and/or calcium phosphate in 11 patients (24.4%). In seven of ten stones with bacterial growth, bacteria were isolated from urine cultures as well, which accounted for a concordance rate of 70%. The bacteria grown in the stone were the cause of urinary tract infection (UTI) in 43.5% of the cases. Stone infection was significantly associated with UTI (OR = 6.47; 95% CI 1.43-31.7, P = 0.021) and presence of phosphate in the stones (OR = 18, 95% CI 3.28-99.6, P = 0.0006). E. coli was the most common bacteria grown from the stones, and was isolated in 50% of the cases; Ureaplasma urealyticum was the most common organism causing UTI, grown in 62.5% of the urine samples. There was a high concordance rate between bacteria in the stones and urine. These findings indicate that the urine culture can provide information for selection of an appropriate anti-microbial agent for stone sterilization. In addition, preventing re-growth or recurrence of stones and treatment of post-surgical infections would be facilitated based on the results of the urine culture.

How to cite this article:
Shafi H, Shahandeh Z, Heidari B, Sedigiani F, Ramaji AA, Pasha YY, Kassaeian AA, Pasha AA, Mir MA. Bacteriological study and structural composition of staghorn stones removed by the anatrophic nephrolithotomic procedure. Saudi J Kidney Dis Transpl 2013;24:418-23

How to cite this URL:
Shafi H, Shahandeh Z, Heidari B, Sedigiani F, Ramaji AA, Pasha YY, Kassaeian AA, Pasha AA, Mir MA. Bacteriological study and structural composition of staghorn stones removed by the anatrophic nephrolithotomic procedure. Saudi J Kidney Dis Transpl [serial online] 2013 [cited 2022 May 20];24:418-23. Available from: https://www.sjkdt.org/text.asp?2013/24/2/418/109623

   Introduction Top

Staghorn calculi are a major threat to health due to recurrent urinary tract infections (UTI) and subsequent deterioration of renal function. [1],[2],[3] Deleterious effects of these stones are a source of concern even after surgical removal. Most staghorn calculi are infection-related stones composed of struvite and/or carbonate apatite. [4],[5],[6] Sometimes, calcium oxalate, cystine and uric acid are also present in these calculi. [7],[8],[9] The clinical problems, such as sepsis and renal damage, which the struvite stones can create are greater than those caused by any other stone type. [9],[10],[11] For these reasons, even after successful removal of these stones, careful medical follow-up of the affected patients is required. [1],[10]

There is a significant association between UTI caused by urease-producing organisms such as Proteus, Staphylococcus aureus, Klebsiella, Providencia, Pseudomonas and Urea-plasma urealyticum and stone formation. [1],[2],[12],[13],[14],[15] These bacteria live within the interstices of the urinary stones where antimicrobial agents do not penetrate; thus, persistent infection results in rapid growth of stones and filling of all, or part of, the renal pelvis over a period of weeks or months. [15]

Until recently, only struvite stones were considered to be derived from bacterial infection. However, other types of stones such as calcium-based stones might also become secondarily infected with urease-splitting organisms and result in secondary struvite stone formation. These stones may contain a mixture of struvite and other materials. [12],[16]

At present, anatrophic nephrolithotomy is the preferred choice for removing staghorn stones. [17] Any procedure used for the removal of stones may be associated with infectious complications and subsequent recurrence or re-growth of stones requiring long-term antibiotic therapy. [12],[18] Identification of bacteria in the stone and sterilization of the urinary system with appropriate antimicrobial agents can prevent re-growth of residual stones after initial removal. [12],[18] Currently, selection of antibiotic agents is based on bacteria isolated from urine culture. However, the efficacy of treatment of stone bacteria cannot be ascertained due to uncertainty in similarity of stone and urine bacteria.

For this reason, the present study was designed to identify the type of bacteria living within staghorn stones and to determine the proportion of infected stones among stoneforming patients. In addition, the concordance between urine and stone bacteria and the capability of urine culture in identification of stone bacteria were examined by matching the results of the stone and urine cultures.

   Patients and Methods Top

The subjects of this study consisted of all 45 patients who underwent anatrophic nephrolithotomy procedures for removal of staghorn stones in a teaching hospital at Babol over a period of 18 months, from December 2007 through June 2009. Samples of stones were taken from the removed staghorn stones at the time of operation and samples of urine were obtained through simultaneous bladder catheterization. After washing the stone several times with normal saline and softening the stone fragments, a homogenous dilution of the softened stone was prepared in saline. Samples from these prepared specimens were sent for bacteriological examination and chemical analysis of stone contents. Both stone and urine specimens were placed in appropriate culture media for identification of urease-producing bacteria as well as common gram positive and gram negative bacteria. The results of stone and urine cultures were considered positive if growth of ≥100.000 organisms/mL was observed after 24 h. The negative cultures were re-examined after an additional 24 h for confirmation.

The proportion of infected stones and UTI were determined in the data analysis. In addition, the association between stone infection and UTI was assessed with respect to gender and chemical content of the stones. Furthermore, the isolated species of bacteria from the stones were compared with those isolated from urine culture to determine the correlation between stone and urine infections by the same bacteria.

   Results Top

Twenty-two males with mean age of 48.3 ± 15.6 years and 23 females with mean age of 51 ± 7.4 years were studied. The prevalence rates of stone infection and UTI are shown in [Table 1]. Seven of ten bacteria isolated from the stones were detected in urine cultures, which indicates a concordance rate of 70% between stone and urine bacteria [Table 2]. Stone bacteria were the cause of UTI in 43.5% of the cases. Infection of the stone was significantly associated with phosphate-containing stone compared with non-phosphate-containing stones, [OR = 18.95 (95% CI 3.28-99.6, P = 0.0006)] [Table 3].
Table 1: Frequency of infection-related stones and urinary tract infections according to stone composition in patients with staghorn stones who underwent anatrophic nephrolithotomic procedures.

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Table 2: Concordance between microorganisms isolated from 10 infection-related staghorn stones and bladder urine in patients who underwent anatrophic nephrolithtomic procedures in Northern Iran.

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Table 3: Association between infection-related stones and phosphate-containing staghorn stones removed by anatrophic nephrolithotomy by odds ratio with 95% confidence interval (95% CI).

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E. coli was the most common bacteria, and was isolated from five stones and four urine samples. Simultaneous infection of both stone and urine samples with E. coli was observed in three patients. Staphylococcus (aureus, cohini, cepra) species were isolated from three stone samples and three urine samples with concurrent Staphylococcus infection of both stone and urine in two of them. Enterobacter alone was isolated from one stone and Enterobacter together with E. coli in another case. Urea-plasma urealyticum was the most common cause of urine infection, seen in ten of 16 patients (62.5%). Simultaneous infection of both stone and urine with Ureaplasma urealyticum was observed in only one patient.

UTI was detected in 16 of the 45 patients studied (35.5%). It was significantly more frequent in women than in men (52.1% vs. 18.1%, P = 0.03). The prevalence of UTI in patients with phosphate-containing stones was higher compared with that in patients with non-phosphate-containing stones, but the difference was not significant (45.5% vs. 32.3%, P = 0.4). There was a positive association between UTI and stone infection [OR = 6.4 (95% CI 1.4-31.7, P = 0.021)]. In sub-group analysis according to gender, the association of UTI and stone infection was positive only in males [OR = 32 (95% CI 2.2-447, P = 0.007)] as compared with females (P = 0.63) [Table 4]. There was no association between UTI and stone composition or age of patients. The results of bacteriological analysis of infected stones according to composition are presented in [Table 1].
Table 4: Association between urinary tract infection and stone infection according to gender in patients who underwent the anatrophic nephrolothotomy procedure for removal of staghorn stones.

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Structural analysis of stones demonstrated that pure calcium oxalate was the most common constituent of staghorn stones, seen in 46.6%, followed by pure uric acid, seen in 17.8% of the cases. Struvite, as pure, was the constituent of only 6.7% of the stones. Overall, calcium oxalate as pure or mixed with other chemicals was the main component of stag-horn stones matrix, seen in 31 patients (68.8%); uric acid as pure or mixed with other chemicals was seen in 12 patients (26.6%) and struvite and calcium phosphate was seen in 11 patients (24.4%).

   Discussion Top

The findings of this study indicated a 22.2% prevalence of stone infection and a 35.5% prevalence of urine infection at the time of operation for staghorn stones. In this study, 70% of the microorganisms that were grown from the staghorn stones also caused UTI, which accounted for 43.5% of the UTI in this population. There was a positive association between UTI and stone infection in men, but this was not seen in women. There was also a significant association between stone infection and phosphate-containing stones.

The composition of staghorn stones has been investigated in a number of previously published studies. [4],[5],[6],[7],[8],[9],[19],[20] Almost any compound can form staghorn-shaped stones. Earlier studies demonstrated that calcium phosphate and struvite were the major constituents of staghorn stones. [4],[5],[6] The lower prevalence rate of struvite stones in this study compared with other reports may be attributed to the presence of different bacterial flora in our patients, including lack of urease-producing gram negative bacteria such as Proteus species. In addition, other factors, such as diet and genetic background, metabolic disorders and anatomic or functional abnormalities of the kidney, may be responsible for struvite stones formation. [4],[12],[19]

Staghorn stones with compositions similar to the present study were also reported in other studies. [8],[9] Calcium oxalate as the most common constituent of staghorn stones, seen in 98.8% of the patients, was reported in a study from North India. [7] In a study of 86 patients from Thailand, uric acid was the main component of staghorn stones. [20]

Data on the bacteriology of staghorn stones are few due to the small number of studies performed in this context. [19],[21],[22] A concordance rate of 70% between stone and urine bacteria in this study indicates that a significant proportion of stone bacteria can be identified by urine cultures. Concordance between micro-organisms living in the stones and those isolated from urine cultures has been investigated in a number of previous studies. The concordance rate varied from 25% to 92.8% and the proportion of stone infection ranged from 40% to 70%. [19],[21],[22] However, some of these studies did not have adequate power due to the small sample size.

In contrast to previous studies, [16],[23] none of the well known bacteria that contribute to formation of staghorn stones, such as Proteus or Providencia, were isolated from the urine or stone samples of our patients. E. coli and Staphylococcus were the most common bacteria isolated from stones and Ureaplasma urealyticum and E. coli were the most common isolates from bladder urine. Isolation of Staphylococcus from urine and stone cultures should not be attributed to contamination. This is because the method applied for isolation of bacteria and considering colony counts ≥100,000 bacteria as positive test results renders the probability of contamination of both urine and stones in the patients very unlikely. Furthermore, the role of Staphylococcus as a ureasepositive microorganism in association with struvite stones has been shown. [12],[24]

The potential of E. coli in the formation of staghorn-like structure and its contribution in the development of post-surgical infection, particularly among patients with phosphate-containing calculi, has been shown in previous studies. [19],[25] E. coli concurrent with other bacteria has been reported as a cause of UTI in stag-horn stones. [23],[25]

Our analysis is in confirmation with previous data that present new information on non-struvite infection stones and the role of common bacteria in the development of staghorn stones. Identification of stone-forming bacteria from stones at the time of anatrophic nephrolithotomic procedures and simultaneous culture of urine to confirm stone and urine bacteria has not been performed yet. Additionally, the sample size of this study was higher compared with that of similar previous studies. [19],[21],[22]

The limitation of this study should be considered. Because all patients with previously diagnosed UTI were treated with antibiotics before surgery, the actual prevalence rate of stone and urine infection may be higher than that observed in this study. Although the stone samples were washed several times before transferring to culture media, the possibility of trapping bacteria in the stones from co-existing UTI, or developing infection stones following UTI, cannot be excluded with certainty. [14] Lack of association between phosphate-containing stones and UTI in this study can be attributed to inadequate number of infection stones. On the other hand, the strength of this study is based on study design, particularly simultaneous sampling of stones and urine at the time of operation. Therefore, the isolated bacteria from either stone or urine cultures are expected to be exclusive to the same specimen, and the probability of secondary contamination can be ruled out.

In conclusion, this study demonstrated that in the geographic region in north of Iran, a significant proportion of staghorn stones are non-infection related or non-struvite types of stones. Infection-related stones are positively associated with UTI and phosphate content of the stone matrix. About 70% of the stone-forming bacteria can be identified through urine cultures. These data are helpful in selecting appropriate antimicrobial agents for sterilization of stones or preventing stone regrowth or stone recurrences. Further studies with larger samples may be needed to determine the association between species of micro-organisms and composition of stones.

   References Top

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Correspondence Address:
Behzad Heidari
Department of Medicine, Rouhani Hospital, Babol University of Medical Sciences, Babol
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1319-2442.109623

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  [Table 1], [Table 2], [Table 3], [Table 4]

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