This retrospective study was conducted in the Department of Microbiology, Central Laboratory, School of Medical Sciences and Research, Sharda Hospital, Greater Noida, Uttar Pradesh, India. This study was conducted for a period of six months from May 2019 to October 2019. Institutional Ethics Committee provided approval for this study (Ref no. - SU/SMS&R/76-A/2019/35). All the isolates from blood culture positive samples collected over period of six months were included in the study. All the blood samples received in bacteriological laboratory for culture were used for study. Automated method i.e., (BACT-ALERT system) was used to culture the bottles received in the bacteriology laboratory. The bottles were put inside the automated machine, when there was a signal the bottles were removed and the blood from the positive blood culture bottles was subjected to subculture on 5% sheep blood agar and MacConkey agar. The growth on culture plates was identified on the basis of colony morphology, Gram stain and various biochemical tests. Blood cultures were repeated for confirmation of results. Antimicrobial susceptibility testing was performed for all blood cultures isolated on Muller Hinton agar by Kirby-Bauer disc diffusion method as recommended in the CLSI (Clinical and Laboratory Standards Institute guidelines) 2019. Commercially, available antibiotics disks (Himedia) were used for antimicrobial susceptibility testing [Table/Fig-1]. The antibiotics used for Gram positive bacteria were levofloxacin (5 ug), clindamycin (2 ug), ciprofloxacin (5 ug), linezolid (30 ug), penicillin (10 units), erythromycin (15 ug), gentamicin (10 ug), vancomycin, cefotaxime (30 ug) and the antibiotics used for gram negative bacteria were cefotaxime (30 ug), cefepime (30 ug), cefuroxime (30 ug), levofloxacin (5 ug), ampicillin (10 ug), gentamicin (10 ug), imipenem (10 ug), meropenem (10 ug), amoxiclav (30 ug), ceftriaxone (30 ug).

[Table/Fig-1]:

Antibiotic susceptibility test (disk diffusion method).

Simple descriptive analysis of the distribution of sample, age, gender, and antimicrobial susceptibility data were done, and the results were obtained and presented as frequencies and percentages.

A total of 1367 blood samples were received in the bacteriology lab for culture, out of which 274 samples showed culture positivity. Out of 274 positive samples obtained, 156 were male patients and 118 were females. The maximum number of samples was obtained from patients between age group 0-10 years followed by the age group 40-50 and 60-70 years [Table/Fig-2].

CoNS constituted maximum proportion of isolates followed by Pseudomonas species and E. coli. [Table/Fig-3]. Most of the cases were positive for coagulase negative organisms and amongst all the antibiotics, vancomycin (100%) emerged as most sensitive drug against CoNS followed by linezolid (90%), and clindamycin (55%). Strains of CoNS showed high resistance for erythromycin (76.2%) followed by penicillin (65.7%) and ciprofloxacin (59.6%) [Table/Fig-4].

Amongst all the antibiotics, linezolid and vancomycin emerged as most sensitive drug against Staphylococcus spp. Strains of Staphylococcus spp. showed high resistance for Penicillin. Linezolid was found most sensitive drug against Enterococcus spp. Strains Enterococcus spp. showed high resistance for ampicillin and penicillin. E.coli was found most susceptible to gentamicin, imipenem, cotrimoxazol and meropenem. Strains of Escherichia coli showed high resistance for cefuroxime and ceftriaxone [Table/Fig-5].

Imipenem (89%) and meropenem (77%) emerged as most sensitive drug against Klebsiella spp. Strains of Klebsiella spp. showed high resistance for cefepime (89%), ceftrioxone and ampicillin (78%). Ampicillin and gentamicin were found most effective against Citrobacter spp. Strains of Citrobacter spp. showed high resistance for cefepime. Piperacillin+Tazobactum and Levofloxacin were most efficient against Pseudomonas spp.

Strains of Pseudomonas spp. showed high resistance for Aztreonam [Table/Fig-6]. Gentamicin and Levofloxacin were observed most sensitive drug against Acinetobacter spp. Strains of Acinetobacter spp. showed high resistance for tetracycline and ceftriaxone.

MDR was observed in approximately 32 positive culture isolates which constituted 11.6% of total positive cultures. Gram negative bacilli constituted higher percentage (27, 10%) than gram positive organism (5, 1.8%) among MDR isolates. Among gram negative organisms Pseudomonas spp. were most common isolates to demonstrate MDR [Table/Fig-7].

In this study, gram positive bacteria were more common isolates than gram negative organism. Gram positive bacteria accounted for 71% of the isolates. This was also observed by Prabhu K et al., who found 64% of isolates were gram positive organisms [9]. Among gram positive bacteria CoNS was isolated in most samples (92%) than Staphylococcus aureus (4%). Jamal WY et al., found that most common isolate in BSI was CoNS (46%) [10]. In a similar study done by Valles J et al., CoNS accounted for 49.8% of the isolates [11]. Wattal C et al., reported CoNS as the most common isolate causing BSIs in ICU patients [12]. It has been demonstrated by some studies upto 85% of CoNS represent contamination rather than true bacteremia [13]. In order to avoid this repeat blood cultures were done for confirmation. In the present study, gram negative bacilli accounted for 28.1 of BSIs, similar observations were done by Prabhu K et al., who observed 35% of the culture isolates were gram negative bacilli [9]. Pseudomonas spp. are most common and accounted for 42.6% among gram negative organisms.

In this study, males were more commonly involved accounting for 56.9% of total number of positive cases and females account for approximately 43% of total number of positive cases. The result was consistent with the study done by Kaur A and Singh V who reported high culture positivity in men 65.2% [14]. Hussein A et al., reported 66.6% positivity in men and 33.3% in women [15]. Zenebe T et al., found that women (59.8%) were effected more than men (40.2%) [16].

From amongst the bacteria isolated in present study, CoNS showed 100% sensitivity to vancomycin and 90% sensitivity to linezolid. Vancomycin and Linezolid were sensitive to all species of CoNS in the study by Asangi SY et al., and Singh L et al., [17,18]. The organisms were found highly resistant to erythromycin (76%) followed by penicillin (65%). The second common isolate among gram positive bacteria was Staphylococcus spp. which showed 100% sensitivity to linezolid and vancomycin, followed by clindamycin (75%). The organisms were found highly resistant to penicillin (87%) followed by erythromycin (75%) and cefoxitin (62%). The antimicrobial susceptibility testing revealed that resistance to penicillin was frequent in Staphylococcus spp. (87%) and CoNS (65%) this was consistent with the study of Roy I et al., who observed 89% of Staphylococcus isolated were resistant to pencillin and none of isolates were resistant to vancomycin [19]. Among gram negative organisms, Pseudomonas spp. was the most common isolate in which Piperacillin+Tazobactum (87%) emerged as most sensitive drug followed by piperacillin (75%), meropenem (75%) and ciprofloxacin (75%). Patel PH et al., observed 100% susceptibility to imipenem of Pseudomonas spp. [20]. However, Pourakbari B et al., had reported resistance to most of antibiotics by Pseudomonas spp. Imipenem (89%) emerged as most sensitive drug against Klebsiella spp. followed by meropenem (77%) and cotrimoxazole (67%). Strains of Klebsiella showed high resistance for cefepime (89%) followed by ceftriaxone (78%), ampicillin (78%) and amoxyclav (55%). Citrobacter spp. was highly sensitive to imipenem (75%) and appear resistant to ampicillin (62%) [21]. Sphingomonas paucimobilis was detected in 2 samples. It was highly sensitive to imipenem (100%) which was consistant with study of Bayram N et al., [22]. Carbapenems were the most effective therapy. Burkholderia cepacia was found in single culture constituting a mere 0.36% of total number of isolates. Gautam V et al., isolated 39 isolates of Burkholderia cepacia from various specimens which accounted for 0.35% of total number of isolates [23]. It showed sensitivity to co-trimoxazole, imipenem, levofloxacin and appeared resistant to cephalosporins, ampicillin and gentamicin. In this study, 32 isolates showed MDR which constitute 11.6% of total number of positive cultures with gram negative organisms most commonly involved. Among gram negative organisms Pseudomonas spp. mainly show MDR. Tam VH et al., observed that in P. aeruginosa bloodstream isolates approximately 10-17% showed MDR [24]. The number of isolates obtained in this study has been compared with other previous studies [Table/Fig-8] [25-30].

Thus, the present study clearly indicates that most common isolates from BSIs were CoNS which appeared highly sensitive to vancomycin and linezolid whereas, among gram negative organisms, Escherichia coli were commonly isolated. MDR isolates also constituted a significant number and were commonly found among gram negative organisms.

This study was conducted for shorter period of time that is six months and thus chances for identifying risk factors for mortality were reduced. Another limitation of this study was its retrospective analysis which may be prone to selection bias which was omitted by selecting all samples in present study.

This study formed a useful reference for clinical microbiologists, physicians and others attempting to monitor the prevalence of BSIs and for the treatment of patients with such infections. Utilising various methods for reduction of development of antibiotic resistance is utmost requirement which can be established by adopting specific antibiotic utilisation strategies e.g., reducing antibiotic usage, developing combination therapy, using antibiotics only after standard antimicrobial susceptibility testing and recycling of antibiotics. Using methods for proper infection control and proper channelization of antibiotic programs are most important and are of prime requirement.