Pattern of Bacterial Pathogens and Their Antimicrobial Susceptibility from Blood Culture Specimens in a Tertiary Care Setting

The objective of this paper is to find out the pattern of bacterial pathogens and their antimicrobial susceptibility from blood culture specimens received from a tertiary care referral setting. This cross-sectional observational study was carried out at the Department of Microbiology, Armed Forces Institute of Pathology, from July 2011 through June 2012. Blood culture specimens were dealt with brain heart infusion broth based manual method and automated BACTEC system. The specimens yielding positive growth were further analyzed and antimicrobial susceptibility carried out as per CLSI recommendations. Out of 2921 blood culture specimens, 465 (16%) yielded growth. Out of these, 245 (53%) isolates were Gram positive, 209 (45%) Gram negatives while 11 (2%) were yeast. Among Gram positive isolates, 208 (85%) were Staphylococcus spp. and among these 158 (76%) were methicillin resistant. Amongst Gram negative group, 115 (55%) isolates were members of enterobacteriaceae family and E. coli was the leading pathogen, while 94 (45%) were non-fermenters (NF). Among these, Acinetobacter spp. and Pseudomonas aeruginosa were common pathogens. In vitro antimicrobial susceptibility of staphylococci revealed that 100% isolates were susceptible to vancomycin and linezolid. The organisms of family enterobacteriaceae revealed better susceptibility to amikacin (68.7%) and imipenem (64.3%). The NF group showed better in vitro susceptibility to tazobactam/piperacillin (65%). Gram positive organisms were predominantly causing blood stream infections. Vancomycin and linezolid in case of Gram positive and amikacin and tazobactam/piperacillin against Gram negative organisms revealed better in vitro efficacy.


Introduction
Blood stream infections (BSIs) are a potentially life-threatening condition with a case fatality rate of 20-50% and among the most common health-care associated infections reported by Gupta et al. (2010) and Khawaja et al. (2013).Changing epidemiology and antimicrobial susceptibility among blood stream pathogens is a significant problem worldwide with severe consequences including increased cost of care, morbidity and mortality highlighted by Gupta et al. (2010) and Pourakbari et al. (2012).BSIs are affecting over 200,000 individuals annually with a mortality rate of 32% in the United States alone reported by Pourakbari et al. (2012).Antimicrobial resistance among blood stream pathogens is a significant problem around the globe.This is especially true in countries like Pakistan, where antibiotics are widely used and considerable resistance has been reported from all over the country (Akhtar, 2010 andKhawaja et al., 2013).The increasing resistance to many antibiotic compounds results in a reduction in therapeutic options suggested by Pourakbari et al. (2012).Hence detection of BSIs must be a priority in all clinical settings.The blood culture remains a gold standard in the diagnosis of BSIs.
Selecting appropriate antimicrobial for treating BSI is multifaceted; including possible cause and source of infection, in vitro activity of the drug according to microbiological susceptibility testing results, pharmacokinetics and adverse effects of the drug.However, before considering these aspects, the choice of antibiotic mainly relies on knowledge of the pathogen likely to be involved.For the benefit of patient, empirical therapy often has to be initiated without exact knowledge of the causative organism and its antimicrobial susceptibility profile, confirmed by Assadian et al. (2009).Monitoring and analyzing the antimicrobial susceptibility patterns of most frequently isolated microorganisms according to local epidemiology helps clinicians to choose effective empirical therapies and develop rational prescription policy for antibiotics.Therefore, analysis of occurrence of pathogens and their cumulative susceptibility profiles is widely used in hospital settings as suggested by Assadian et al. and Barati et al. (2009).A study conducted by Paul et al. (2010) highlighted that mortality was significantly higher among patients receiving inappropriate empirical therapy.
Different studies have been published regarding frequency and pattern of nosocomial infections in tertiary care settings but limited work has been reported regarding bacterial pathogens causing BSIs in our country in the last decade (Mumtaz et al. andShaikh et al., 2008 andLatif et al., 2009).The objective of this study was to determine the pattern of pathogens and their antimicrobial susceptibility from blood culture specimens in a tertiary care setting to facilitate the formulation of antibiotic policy for empirical treatment.

Materials and Methods
This study was carried out at the Department of Microbiology, Armed Forces Institute of Pathology (AFIP) Rawalpindi, Pakistan.Permission from Institutional Ethical Committee & Institutional Review Board was taken.Sampling technique was non probability consecutive; all admitted patients with unexplained/undiagnosed fever, whose blood cultures specimens were sent to AFIP were included in the study.Contaminated, duplicate and repeat specimens from same patient were excluded from the study.Blood sample was collected aseptically from each patient before the start of antimicrobial therapy; in adults 8ml blood was added to each of brain heart infusion (BHI) broth (Oxoid, UK) and automated BACTEC 9050 (BD Diagnostics) culture bottles; and in children 3ml.Blood culture specimens from patients admitted in different wards and intensive care units of two 1000-bedded tertiary care referral hospitals at Rawalpindi, Urology and Bone marrow Transplant institutes were dealt with during the study.Manual and automated BACTEC 9050 (BD Diagnostics) blood culture systems were used for blood culture.For the manual method, BHI bottles were incubated at 37 o C after shaking and sub-cultured as per standard protocol on blood and MacConkey's agar (Oxoid, UK).Gram staining was performed on smears from the broth of positive culture bottles.  ) showed that there has been an increase in Gram positive organisms especially coagulase negative CoNS) and Staphylococcus as causative agents in causing BSI.Most of the isolates in our study were either from immune-compromised patients or serious patients in ICUs.Most of them fit in the category of hospital acquired infections.This also highlights the importance of prevailing organisms and their sensitivity pattern.

Enterobacteriaceae
The rapid emergence of antibiotic resistance and its implications on empirical therapy point towards all clinical settings that they should have active ongoing microbiological surveillance.Such effort of monitoring the antibiotic-resistant pathogens would definitely benefit the current antimicrobial regimens especially in a resource poor country like ours.One of the factors for low yield of blood culture was over advice for blood cultures as these hospitals are providing free healthcare services.The observation in this study has been communicated to the concerned authorities for proper advice.The data on bacterial pathogens and antibiotic susceptibility, we believe, are an important pillar in our efforts at improving infection control practices by formulating policy for empirical treatment.We will continue the surveillance in future that will definitely improve novelty and robustness of data regarding the changing profile, if any, of pathogens and their susceptibility.

Conclusion
Gram positive organisms were predominant causing BSIs in our setup.Resistance to methicillin among Staphylococcus spp.& ceftriaxone resistance in Gram negative organisms are on the rise.Amikacin and tigecycline showed better in vitro efficacy against Gram positive as compared to Gram negative isolates, while susceptibility of carbapenems has decreased in both lactose fermenters as well as non fermenters.Vancomycin and linezolid yielded excellent in vitro activity against Gram positive organisms.

Table . Break Down of Patients from Different Wards and Outcome after Antibiotic Therapy Following Culture Report
Fayyaz, Irfan Ali Mirza, Shahid Ahmad Abbasi, Aamer Ikram, Aamir Hussain and Inam Ullah Journal of Virology & Microbiology, DOI: 10.5171/2015.621269Figure 2.

Susceptibility Pattern of Negative Isolates (N=209) % Age Sensitivity
f Patients