Microbiological Profile and Antibiogram of Blood Stream Isolatesata Referral Hospital in North Delhi: A One Year Study

Introduction: Blood culture is the gold standard for diagnosis of bacteremia. It identifies the pathogen and allows susceptibility testing. Objective: To identify Blood stream infections (BSI) which are critical and may prove fatal if not treated promptly. Material and Methods: This was a retrospective study done at our institution to identify the prevalent microbial agents causing infections in hospitalized patients. A total of 1521 blood cultures were processed. Antimicrobial susceptibility was performed for clinically significant isolates. Results: Of total cultures, 16.1% were positive for bacterial growth and 3.1%for fungal growth. Conclusion: Local microbiological profile with antibiogram of frequently isolated organisms should be known to limit the severity of disease and initiate empiric treatment for blood stream infections.


1.Introduction
Bloodstream infections (BSIs) occur due to the failure of our immune system to restrict infection at a focal site; leading to widespread disease. It is a major cause of morbidity and mortality. The occurrence of these infections, their epidemiology, and the invading pathogens have altered in parallel with the evolution in medical care, particularly with emergence of increasingly ill and immunocompromised population of hospitalized patients who are often heavily reliant on medical support and indwelling devices. [1] The responsible bacteria are usually human pathogens. In contrast, many cases of severe sepsis that occur currently are associated with bacterial or fungal microbes that are members of the patient's own microbial flora. [2] These commensal microbes include Coagulase negative Staphylococci (CoNS), enteric gramnegative bacilli, Enterococcus, Candida species, and other pathogens infrequently cause disease in humans who have normal innate immune defenses. Individuals who develop serious disease due to commensal bacteria generally have a significant immune defect, most often breach in the epithelium barrier or immunosuppression. [2]Prompt diagnosis of BSI and antibiotic susceptibility results helps the clinician for further management. [3] This aids in reducing complications and hospital stay, resulting in major financial saving for the institution as well as improved care of the patient. [4] Current study reports about the prevalence and antimicrobial susceptibility profile of blood culture isolates over a span of one year.

Results
A total of 343isolates were recovered out of 1521 blood culture received in our laboratory over a period of one year, culture positivity 22.5%.Out of these 247clinically significant blood stream infections were identified, showing a positivity of 16.2%during the study period. Out of these, 56.6% were from admitted patients and 43.3% from Intensive Care Units. Overall frequencies of isolation was 137(39%) gram positive cocci, 109(31%) gram negative bacilli and 8(3.1%)Candida spp.

Discussion
Blood culture results provide useful information about the incriminating bacteria and their susceptibility patterns. Besides helping in treatment of the patient, profile of the isolated organisms provides useful adjuncts to choice of empiric therapy in a given set up. Comparison of the etiological profile of our blood cultures with various studies has been done in Table 1 [1,[7][8][9][10][11][12][13][14][15][16][17][18][19][20]. We observed in our study, maximum number of isolates was Coagulase negative Staphylococcus (40.5%).Similar findings have been reported by other authors -41.2% by Lu et al [7], 42% by Karlosky et al [8]and 54.3% by Bharmare et al [13]. CoNS have been considered the most common blood culture contaminant but multiple positive cultures from the same patient are considered significant [21]. According to Souvenir et al, clinical significance of CoNS was defined as at least two blood cultures positive for CoNS within 5 days or one positive blood culture plus clinical evidence of infection, which includes abnormal leucocyte count and temperature or blood pressure [9]. Incidence of nosocomial bacteremia due to CoNS is increasing due to frequent use of vascular access devices.Coagulase negative Staphylococcusis the third most common cause of BSI [22] and the most common cause of nosocomial BSI [23]. Methicillin resistance rate was higher in CoNS as compared with S. aureus, which is similar to study by Mathur et al [16], Mir et al [24]. The methicillin resistance for CoNSwas less in our study (25%) in comparison to study by Mathur et al [16]and Mir et al [23].CoNS and Staphylococcus aureus isolates displayed maximum resistance to ampicillin, similar to study by Mathur et al [16] while all isolates were sensitive to vancomycin. Among gram negative bacteria, imipenem was the most effective agent against Acinetobacter spp. and Klebsiella spp. Maximum resistance was demonstrated by these bacteria to ciprofloxacin. The number of isolates of Salmonella Typhi in our study is in concordance with Duggal et al [15]. SalmonellaTyphi displayed zero resistance to ceftriaxone,similar to study by Madhulika et al [25], but highest resistance was observed for nalidixic acid (89%) followed by ciprofloxacin (42%). Multidrug resistance (MDR, ACCo resistance) was seen only in a single isolate of S. Typhi which is different from study by Jain et al [26]. According to WHO, the percentage of MDR(ACCo) resistance in India was 7% and nalidixic acid resistance was 57%. [27]The details of antimicrobial susceptibility of isolates are shown in figures 1-4.
The overall contamination rate in our blood cultures was 5.8%, which is higher than the published benchmark standards [28]. Contamination rate reported by other authors was 12.6%by Chraiti et al [29] and 18% by Malik et al [30]. In our study, contamination rate of blood cultures was higher than the permitted level (≤3%). We intend to take measures for reducing contamination. A method known as ISDT (Initial specimen diversion technique) can be implemented for the reduction of blood culture contamination as described by Binkhamis et al [21].
Even though a small number of patients receive care in intensive care units, majority of the nosocomial BSIs are reported from these units.An active infection prevention team can help in reducing nosocomial blood stream infections. The tracking and reporting of blood stream infection rates are both important activities that rely heavily on the accurate differentiation of contamination from true bacteremia. [28]

Conclusion
Blood culture remains the gold standard for the detection of bacteremia despite the limitations. The correct interpretation of blood culture including the clinical scenario will go a long way in the implementation of active control measures.Patterns of species distribution and drug susceptibilities in local patient populations, can guide empirical therapy of BSIs.

Declaration
The manuscript is original and is not published or communicated for publication elsewhere either in part or full.