IntroductionPyelonephritis is generally the result of an ascending infection of the urinary tract (reflux is seen in 30- 50% of affected children) most common organism is Escherichia coli (Heiberger R.E., 2006). The bacteria that are most likely to cause pyelonephritis are those that normally occur in the feces. Pathogens isolated from patients with pyelonephritis include both gram positive and gram negative bacteria. R.E.Neiberger reported that of gram negative bacteria E.coli, Klebsielle, Enterobacter, Proteus, Pseudomonas and of gram positive bacteria Enterococcus, Staphylococcus saphrophiticus, group B.Streptococcus were prevalent in children with pyelonephritis. In another study conducted at the Pennsylvania University, USA, 70-95% of causes were related with E.coli, Proteus, Klebsiella, Pseudomonas, Staphylococcus saphrophiticus and Еnterobacter (Sammuel Baron, 2004). In the Indian study E.coli accounted for 88.1%, Pseudomonas aeruginosa for 7.1% and Klebsiella was in 4.8% of cases (Namalwar B.R., Vijayakumar M., Janani Sankar., Ramnath B and Prahlad N., 2004). Serotypes 01; 02; 04; 06; 07 were considered as most prevalent among E.coli causes of UTI (Sammuel Baron, 2004). Escherichia coli causes about 85% of acute bladder and kidney infections in patient with no obstruction or history of surgical procedures. Proteus, Klebsiella, Enterobacter or Pseudomonas are other common causes of infection(Namalwar B.R., Vijayakumar M., Janani Sankar., Ramnath B and Prahlad N., 2004). Once these organisms enter the urinary tract, they cling to the tissues that line the tract and multiply in them (Parveen J Kumar Michael L Clark Clinical medicine. London, 2003). Pyelonephritis is characterized by tubulo-interstitial inflammation, hyperaemia and oedema. Affected patients present with the abrupt onset of fever and chills, constant dull flank pain, and symptoms of cystitis (dysuria, frequency, urgency). Urinalysis usually procedures microabscess. Urine cultures will frequency be negative in the setting of haematogenousinfection (Namalwar B.R., Vijayakumar M., Janani Sankar., Ramnath B and Prahlad N., 2004). Asymptomatic infections of the urinary tract or Asymptomatic bactreuria are common. In childgood, about 1 percent of girls have asymptomatic bacteruria (Namalwar B.R., Vijayakumar M., Janani Sankar., Ramnath B and Prahlad N., 2004). In Mongolia females aged between 20-40 years old accounted for 60.3% of all patients with chronic pyelonephritis. In cases of bacteriuria E.Coli was 74.05%, with highest sensitivity to claforan (91.25%) and ciprofloxacin (90.65%) (B.Selengee, 2003). Last 5 years (2004-2008) 3709 children were treated in Nephrological department of Mathernal and Children’s Scientific Center, but between them 741(19.97%) children were illned by pyelonephritis. However no study was conducted on bacterial causes of pyelonephritis in children in Mongolia. Purpose:The main goal of study was to indicate the etiological and clinical specialaty of children’s pyelonephritis. Especially, to indicate the prevalently occurred type and the etiological bacterial groups also the clinical specialaty of children’s pyelonephritis. To study microbiological spectrum of pathogens causing pyelonephritis in Mongolian children, sensitivity of them to antimicrobial agent, mechanisms of their resistance and to identify genes related with microbial pathogenity.Materials and Мethods:My study covered 254 children wich illned by pyelonephritis, these were treated in Nephrological department of Mathernal and Children’s Scientific Center in last 5 years (2004-2008). From patient’s history we also used the clinical laboratorial analysis results such as biochemical, blood count and urine analysis. We used retrospective and prospective statistical methods for study on pathient’s history of children wich sickned by pyelonephritis and bacteriological method for indicating groups of bacteria. We collected information about patients by questionary chart. During study we also used electro-sonography(echo), Xray, radio-isotope, computer-tomography and reno-vascular angiography methods. Antibiotic susceptibility testing covered total 212 bacterial species to 19 kind of antibiotics by disk diffusion(DD) and minimium inhibitory concentration(MIC) methods. Strains were identified by API tests strip (BioMerieux, France) and antibiotic susceptibility was determined by disk diffusion method according to the ELSI recommendations. Types of the beta lactamase were determined by PCR using the blaTEM, blaSHV and blaCTX-M specific primer. 1080 bp, 400 bp and 570 bp PCR product were interpreted as positive for blaTEM, blaSHV and blaCTX-M genes. WHONET5.1 programm was used for the analysis of susceptibility testing according to the WHO recommendation. Pathogens from 1 month consequent urine culture of patients treated at the pediatric nephrology, urology units and outpatient clinic at the MCHRC and patients from nephrology and urology departments at the CCH were isolated using disk diffusion test and minimum inhibitory concentration. Bacterial resistance and pathogenity related genes were identified using PCR method.Results:There were the girls prevalently sicked by pyelonephritis (n=181 or 71.25%) than boys (n=73 or 28.74%) and the primary (n=155 or 61.02%) and secondary chronic pyelonephritis (n=99 or 38.97%) also was prevalently occurred. During pyelonephritis are occurring following clinical symptoms these are high temperature, edema eyelid, loss of appetite, sludged urinate, skin dryness, womiting and nicthuria. By our study the main clinical symptoms of children’s pyelonephritis are high temperature (58.55%), back pain (51.0%), edema of eyelid (34.42%) and polyuria (25.79%). Also the main influencing factors for inducing children’s pyelonephritis are hyphoplasia (33.3%), hydronephrosis (19.23%), single kidney (15.38%) and vesico-uretheral reflux (6.41%). Study was conducted on 110 positive cultures (E.coli-52, Citrobacter spp.-8, E.cloacae-10, Proteus spp.-7, K.pneumoniae-7, P.aeruginosae-22 ба A.baumennii-2, S.aureus-1, Enterococci-1). The bacterial sensitivity and resistance to antimicrobial agents differed between various pathogens. From Gram negative oxydase negative Enterobacteriaceae by PCR testing, 19 isolates contained blaTEM types, 11 strains contained blaSHV types and 16 strains contained blaCTX-M type genes. On the study of PCR the virulence gene “aer” were determined 50% of E.coli strains. blaTEM type resistance can divided to 5 groups, from them 2 groups had the resistance to single beta-lactamic antibiotics, but 3 groups had to both beta-lactamic and aminoglycoside antibiotics.blaSHV type resistance had 2 groups antibiotics, these were beta-lactamic and aminoglycoside antibiotics. blaCTX-M type resistance had 2 groups, these were beta-lactamic and aminoglycoside antibiotics. Both the blaTEM and blaSHV type co-resistance had 2 groups, these were CEP and CXA antibiotics. blaTEM and CTX-M type resistance can divided to 4 groups, from them 1 group had the resistance to single beta-lactamic antibiotics, other 3 groups had to aminoglycoside antibiotics. Both the blaSHV and CTX-M type co-resistance had 2 groups, these were lactamic and aminoglycoside antibiotics. blaTEM, SHV and CTX-M type co-resistance can divided to 3 groups, these were also beta-lactamic and aminoglycoside antibiotics. On the study of PCR the virulence “aer (aerobacterin) gene” expression was identified in 50% of E.coli strains.Conclusion:There were the girls (181 cases or 71.25%) prevalently sick by pyelonephritis than boys(73 cases or 28.74%) was prevalently occurred.In Mongllia the primary pyelonephritis(155 cases or 61.02%) was occurred prevalently than secondary chronic pyelonephritis( 99 cases or 38.97%). The gasteroenterological and toxic symptoms prevalently occurred in clinical symptoms, but later kidney and urinary tract symptoms noticed.In Mongolia the main influencing factors for inducing children’s pyelonephritis are hyphoplasia (33.3%), hydronephrosis (19.23%), single kidney (15.38%) and vesico-uretheral reflux (6.41%).The prevalent pathogen causing pyelonephritis in Mongolia is E.coli. Other causes include Enterobacter spp., Klebsilla spp., Proteus spp., P.aeruginosa, Aceinobacter baumenii and S.aureus. The virulence gene “aer” were determined 50% of E.coli strains. The most prevalent resistance was resistance to beta-lactam, aminoglycoside, tetracycline and trimethoprim sulfometohoxazole. Resistance to beta-lactamic antibiotics was related with blaSHV, blaTEM, blaCTX-M gene experessions in 25-40% of cases. blaTEM, blaSHV and bla CTX-M type of the beta-lactamase were determined 25-40% of Gram negative oxidase negativebacilli. Pathogenic “aer” gene was identified in 50% of E.coli in Mongolia.