Frequency of Blood Culture Isolates and their Antibiogram in a Teaching hospital

Introduction: Bloodstream infections are associated with significant patient morbidity and mortality. Antimicrobial susceptibility patterns should guide the choice of empiric antimicrobial regimens for patients with bacteremia. Methods: Blood sample received from the patient attending Nepal Medical College and Teaching Hospital from March, 2012 – August, 2012 were subjected to culture. Isolate identification and antimicrobial susceptibility testing was done by standard microbiological method. results: Out of the total 2,766 blood samples, 368 (13.3%) showed bacterial growth. The percentage of neonatal septicemia was 368 (13.3%). Staphylococcus aureus (28%) was the most common isolates followed by Salmonella enterica Serotype Typhi (22%), Coagulase negative Staphylococci (9.5%), Salmonella enterica Serotype Paratyphi ((7.6%) and Klebsiella pneumoniae (7.6%). 26.3% of the isolates of Staphylococcus aureus were oxacillin resistant. Most of the gram positive organisms were susceptible to amikacin and vancomycin and showed high level resistance to cefuroxime and cotrimoxazole. Out of 109 isolates of typhoid bacilli, 95.3% were resistant to nalidixic acid,79% to ciprofloxacin and 60.5% to ofloxacin. More than 50% of the isolates of Klebsiella pneumoniae and Escherichia coli showed resistance to cephalosporins and cotrimoxazole. Acinetobacter sp. showed high resistance (more than 60%) to ceftriaxone and ofloxacin. More than 20% of the isolates of Pseudomonas aeruginosa were resistant to ciprofloxacin and amikacin. conclusions: Ongoing surveillance for antimicrobial susceptibility remains essential, and will enhance efforts to identify resistance and attempt to limit its spread. _______________________________________________________________________________________


INtrODUctION
Blood stream infections remain one of the most important causes of morbidity and mortality worldwide. 1Despite important progresses in treatment and prevention of infectious diseases, they are considered as leading causes of death and disability and worsening life quality especially for millions of people in developing countries.
Bacteremia has an increasing trend in some regions of the world. 2 Bacteria isolated from bloodstream infections are numerous [3][4][5] and their associated diseases need urgent and invasive management with antimicrobial drugs.Rational and correct use of these agents requires understanding of common pathogens and drug resistance pattern in the region. 6Nowadays, bacterial drug resistance is an important problem, and due to wide variations in bacterial drug resistance, results of studies and reports vary from one region to another and in different periods of time. 3,6,7The surveillance of blood stream pathogens in a hospital is important in monitoring the spectrum of microorganisms that invade the blood stream and the types of organisms associated with a particular clinical discipline.Such data are often used to determine empiric antibiotic therapy and also to alert the clinicians to emerging pathogens that may pose a threat to the community. 8 there are limited published data on common etiological agents of blood culture isolates and their antibiogram in our set up, we attempt to determine the prevalence of bacteria causing bloodstream infections and their drug resistance in microbiology laboratory of Nepal Medical College and Teaching Hospital, Kathmandu.

MEtHODs
The study included all blood samples for culture obtained from the patients who presented to the Nepal Medical College and Teaching Hospital with a history of fever of variable duration from March 1 st , 2013 to August 31 st 2013.Blood samples were cultured in Brain Heart infusion (BHI) broth which supports the growth of all common pathogens causing bacteremia/septicemia.Collection of blood, aerobic incubation, and subculture(s) onto blood agar, MacConkey agar and identification of the organisms were done as per the standard microbiological method. 9The antimicrobial susceptibility testing was done by Kirby-Bauer disc diffusion technique that is recommended by Clinical Laboratory Standards Institute (CLSI) recommendations. 10

DIscUssION
Patients with bacteremia have remained a challenge to treat.Knowledge of the hospital epidemiology and antimicrobial resistance pattern of blood isolates helps physicians to effectively manage bloodstream infections. 11In the present study, 13.3% of the total sample comprised the culture positivity, which is very close to the finding of study done in Kuala Lumpurl. 8owever, different studies have reported variable results (10.23% -45.9%) [9][10][11][12] which can be due to reasons like different methods of blood culture, administration of prior antibiotics, and infection with anaerobes or effective control in spread of nosocomial infection.
In the present study, gram negative bacilli (55.2%) represents the majority of the isolates causing blood steam infection.However, Staphylococcus aureus (28%) was the most frequent organism isolated.This can be comparable to the study where 60% of the infections were by gram negative bacilli and Staphylococcus aureus (21.3%) was the most frequent pathogen.3][14] The present study isolated 9.5% of the CoNS.The clinical significance of CoNS when isolated from blood cultures should always be evaluated.Some studies have reported that upto 85% of CoNS represent contamination rather than true bacteremia. 15,16However, in recent years, CoNS have become an important nosocomial pathogen partly because of the increasing use of medical devices such as long term indwelling catheters, vascular grafts, and prosthetic heart valves and joints. 17,18teric fever is one of the common public health problems in Nepal.The present study reported high prevalence of Salmonella Typhi (22%) and Salmonella Paratyphi (7.6%).Findings of present study indicated the endemicity of enteric fever in the peri-urban area of Kathmandu Valley.The overall growth positive rate for Salmonella spp was relatively low (5.4%) in a previous study done in the same institution and in other studies(5.1%,][21] Amongst the Enterobacteriaceae, Klebsiella pneumoniae (7.6%) were the most frequent isolates followed by 4.9% Escherichia coli, 1.3% each spp of Proteus and Enterobacter sp. and 1.2% Citrobacter sp.High percentage of isolation of Escherichia coli (21.1%) and Klebsiella pneumoniae (8.3%) are reported in study done by Arora et al. 22 The isolation of nonlactose fermenters like Acinetobacter sp.(7.1%) and Pseudomonas aeruginosa(1.3%)revealed in the current study, though low, is of concern.Both of these bacteria are associated with a high degree of resistance to antibiotics.High occurrence of these bacteria in blood stream infections is reported by study done in South India. 22 the present study, all staphylococcal isolates and Enterococci spp were susceptible to vancomycin and amikacin.Oxacillin resistance is reported in 26.3% of the S aureus which is comparable to the study done by Rina et al. 8 However, James et al, reported high percentage of Oxacillin resistant Staphylococci (49.3%). 23Greater than 30% of Enterococci sp. were resistant to Cotrimoxazole.
6][27] These observations may have important clinical significance, given that with the emergence of multidrug resistant Salmonella Typhi, quinolone particularly Fluoroquinolones has been widely used and recommended as an alternative drug for typhoid fever,and their resistance may be due to irrational use without prescription and misuse of antibiotics even for milder cases is common in Nepal.More than 90% of the typhoid bacilli were susceptible to Aminoglycosides, Cephalosporins and Cotrimoxazolein the present study.
Among the gram negative bacteria in the current study, Klebsiella pneumoniae, Escherichia coli, and Acinetobacter sp. were highly resistant to cephalosporins in the present study.A study done in Pakistan had showed similar rate of resistance to cephalosporins by gram negative bacilli. 12More than 85% of the isolates of Pseudomonas aeruginosa were susceptible to tobramycin and piperacillin/tazobacatam.However, Babak et al, had reported high level of resistance of Pseudomonas aeruginosa to almost all the antibiotics tested. 13In the present report, none of the antimicrobial agents tested were sufficiently effective against Escherichia coli isolates in vitro.Therefore, physicians and hospital formulary groups need to search for other effective antimicrobial agents against infections caused by these drug resistant bacteria.

cONcLUsION
Data derived from this study shows that, with a few exceptions (vancomycin susceptible to gram positive cocci and cephalosporin susceptible to typhoid bacilli), resistance to most antimicrobial agents for a number of species implicated in bacteremia has reached worrisome levels.High resistance to recommended drugs like cephalosporins, aminoglycosides and fluroroqinolones are of major concern and aware the clinicians and the health care workers to seek for alternative antimicrobial agents.Our data underscore the need for periodic survey of etiological agents and their resistance surveillance reports which can provide valuable insight into resistance trends to assist in guidance in the appropriate choice of empiric therapy.