INTRODUCTION

Bloodstream infections are quite common in the pediatric age group and are a significant cause of morbidity and mortality, particularly in neonates and children. These infections pose a life-threatening risk, especially in immunocompromised patients admitted to intensive care units (ICUs).¹ Globally, bloodstream infections affect approximately 30 million people annually, resulting in 6 million deaths.² Every year, 3 million neonates and 1.2 million children suffer from sepsis, leading to serious health issues.³

In ICUs, Gram-positive microorganisms are most frequently isolated from blood cultures. Among them, coagulase-negative staphylococci (CoNS) are the most common, followed by Staphylococcus aureus (S. aureus) and Enterococcus species.^4,5 Gram-negative bacteria, such as Acinetobacter species, Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Klebsiella pneumoniae (K. pneumoniae), and Haemophilus influenzae (H. influenzae), are also frequently isolated.^1,5

The identification of bloodborne pathogens and the determination of their antibiotic susceptibility are urgent medical priorities.⁶ However, since bacteriological cultures and susceptibility testing take several days, empirical antimicrobial treatment is typically initiated before blood culture results are available in nearly all cases.⁷ A major issue associated with empirical therapy is the emergence of antibiotic resistance.⁸ The increasing antimicrobial resistance in bloodstream infections, particularly in developing countries, is a growing concern, and studies conducted in these regions have reported a rise in antibiotic resistance.^9-12 Rational and appropriate use of antibiotics requires knowledge of the most commonly isolated bacteria from blood cultures and their antibiotic susceptibility patterns.¹³ Early detection of antimicrobial susceptibility patterns has been shown to reduce morbidity and mortality associated with bloodstream infections.¹⁴

The aim of this study is to determine the bacterial profile and antibiotic resistance status of pathogens isolated from blood cultures of children admitted to neonatal and pediatric intensive care units of a university hospital in Türkiye over a five-year period.

MATERIAL AND METHODS

Study design

This study is a retrospective evaluation of approximately 1,197 blood cultures sent from neonatal and pediatric ICUs to the Medical Microbiology Laboratory of a university-affiliated Health Application and Research Hospital.

Study population and sample

The study includes blood culture results from patients admitted to neonatal and pediatric intensive care units between January 1, 2018, and December 31, 2022. The hospital where the study is conducted has a 39-bed neonatal intensive care unit (5 at level 1, 17 at level 2, and 17 at level 3) and a 15-bed pediatric intensive care unit (5 at level 2 and 10 at level 3). These units serve as a center with a high volume of cases involving anomalies, chronic diseases, and post-surgical patients. Patients without blood culture data were excluded from the study.

Data collection tools

The data regarding blood culture results were obtained through a retrospective review of patient records. Microorganisms were identified using conventional methods and the Phoenix automated system (Becton Dickinson, Sparks, Maryland, USA). Antibiotic susceptibility results were evaluated according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria.¹⁵

This study was approved by the Kahramanmaraş Sütçü İmam University Medical Research Ethics Committee (approval date 12.09.2023, number 2023/13-03).

Statistical analysis

Statistical analyses were performed using the SPSS software version 22 (IBM Corp. Released 2010. IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp.). Categorical data were presented with n and %.

RESULTS

Over the course of five years, 6,291 blood cultures were collected from neonatal and pediatric intensive care units, with microbial growth detected in 1,197 samples (19.02%). Of the microorganisms isolated, 621 (51.88%) were from male and 576 (48.12%) from female patients. Among the 1,197 cultures with growth, 776 (64.82%) were obtained from neonatal ICUs, while 421 (35.18%) were from pediatric ICUs.

Among the 1,197 microorganisms isolated, 868 (72.51%) were identified as Gram-positive bacteria, 259 (21.63%) as Gram-negative bacteria, and 70 (5.84%) as Candida species. The most frequently isolated microorganism was CoNS (62.40%), followed by K. pneumoniae (6.59%), A. baumannii (6.26%), Candida parapsilosis (C. parapsilosis) (3.17%), and Enterococcus faecalis (E. faecalis) (2.08%). The distribution of microorganisms isolated from blood cultures is shown in Table 1.

Among CoNS isolates, the highest resistance was observed against ampicillin (99.63%), oxacillin (93.44%), and erythromycin (88.88%). The lowest resistance was found against vancomycin (0.80%), linezolid (2.14%), and daptomycin (2.14%). In S. aureus isolates, the highest resistance was noted against oxacillin (54.54%), erythromycin (43.47%), and clindamycin (40.90%). No resistance to vancomycin was detected in S. aureus isolates, while the lowest resistance was observed against linezolid (4.34%) and daptomycin (4.54%). Enterococcus species showed 100% resistance to trimethoprim/sulfamethoxazole, with no resistance detected to linezolid. Among Streptococcus species, the highest resistance was observed against erythromycin (75%), while no resistance was detected to vancomycin, teicoplanin, linezolid, levofloxacin, or daptomycin. Antibiotic resistance rates for Gram-positive bacteria are presented in Table 2.

Among Gram-negative bacteria, Klebsiella species, Serratia marcescens (S. marcescens), and Enterobacter cloacae (E. cloacae) isolates demonstrated the highest resistance to ampicillin, with a 100% resistance rate. The ampicillin resistance rate for E. coli was 85.71%. A. baumannii was identified as the most resistant bacterium, with resistance rates exceeding 90% for most antibiotics tested, except trimethoprim/sulfamethoxazole. The second-highest resistance rates were found in Klebsiella species, while the lowest resistance rates were observed in S. marcescens and E. cloacae isolates. The highest carbapenem resistance was found in A. baumannii, followed by Klebsiella species, Pseudomonas, and E. cloacae. Antibiotic resistance rates for Gram-negative bacteria are shown in Table 3.

In Candida albicans (C. albicans) isolates the highest antifungal resistance was observed against voriconazole (85.00%). In contrast, in C. parapsilosis isolates, the highest resistance was observed against fluconazole (24.24%). No resistance to caspofungin was detected in either Candida species. Antifungal resistance rates for Candida species are presented in Table 4.

DISCUSSION

The 19.02% culture positivity rate observed in this study is consistent with findings from previous research on the subject. For instance, Deku et al.¹⁶ reported a culture positivity rate of 13.1% in Ghana, Gupta et al.¹⁷ found 16.5% in North India, and Oyekale et al.¹⁸ reported 19.2% in Nigeria. However, some studies have reported lower rates, including Khanal et al.,¹⁹ Gohel et al.,²⁰ and Gülmez et al.²¹ who documented culture positivity rates of 10.3%, 9.2%, and 7.7%, respectively, in bloodstream infection cases.

Gram-positive bacteria were the most frequently isolated strains from blood cultures, followed by gram-negative bacteria and candida.²² In this study, gram-positive bacteria were found to be the predominant strains (72.51%) (Table 1). This finding aligns with prior studies, which have also reported Gram-positive bacteria as the dominant isolates in bloodstream infection cases.^16,23 However, some research has highlighted Gram-negative bacteria as the most frequently isolated pathogens in bloodstream infections.^17,18

Although the importance and role of CoNS as etiological agents of neonatal sepsis have been proven in many studies, determining whether CoNS isolates are true pathogens or contaminants remains problematic.²⁴ In this study, CoNS was the most frequently isolated microorganism (62.40%), followed by Enterococcus spp. (4.09%). This result is consistent with the findings of Ergül et al.²² The high isolation rate of CoNS may be attributed to the frequent invasive procedures performed on patients.

The prevalence of S. aureus in blood cultures varies across different studies. For example, S. aureus rates of 42.39% in Pakistan²⁵, 40.72% in India²⁶, 11.95% in Afghanistan²⁷, and 8.87% in Iran⁷ have been reported, while lower rates (0.9-12.8%) have been observed in Türkiye.^21,22,28,29 The isolation rate of S. aureus in our study (1.92%) is consistent with the rates reported in Türkiye.

In our study, in addition to CoNS, Klebsiella, Acinetobacter, S. aureus, Enterobacter, E. coli, Pseudomonas, Streptococcus, Serratia, and candida species were isolated (Table 1). These findings are consistent with previous studies^22,27,30 and it has been reported that infections caused by these bacteria pose a significant threat to the lives of children.²⁷

In our study, the methicillin resistance rate in CoNS was found to be significantly higher compared to S. aureus (CoNS 93.44%, S. aureus 54.54%) (Table 2). Similar findings have also been reported in several studies conducted in Türkiye.^22,28 In this study, which evaluated five years of data, no vancomycin resistance was detected in S. aureus. In contrast, vancomycin resistance rates in CoNS and enterococci were found to be 0.80% and 24.44%, respectively. The resistance rates for teicoplanin were determined to be 8.69%, 12.32%, and 22.22%, while linezolid resistance was 4.34% in S. aureus and 2.14% in CoNS (Table 2). Previous studies have reported higher susceptibility to vancomycin, teicoplanin, and linezolid.^26,31

In our study, the most frequently isolated gram-negative bacteria were Klebsiella spp. (7.35%), followed by Acinetobacter spp. (6.51%) (Table 3). This finding contrasts with reports from a study in Western India, where Acinetobacter spp. was the most frequently isolated bacterium, followed by Klebsiella spp.³¹ Additionally, similar studies have shown variability in bacterial ranking.^6,22,25,27 Klebsiella spp isolated in our study showed high levels of resistance to most of the tested antibiotics. Specifically, the antibiotics to which Klebsiella spp. showed the highest resistance were ampicillin (100%), cefuroxime (85.54%), cefepime (84.33%), and ceftriaxone (83.52%) (Table 3). These results are consistent with other studies.^6,22 Our study suggests that the high aminoglycoside and cephalosporin resistance observed in Klebsiella strains may be due to the inappropriate use of these antibiotics in empirical treatment.

Acinetobacter spp. has shown high levels of resistance to all tested antibiotics (Table 3). Consistent with our findings, Shehab El-Din et al.²⁴ reported even higher resistance rates. Moradi et al.¹¹ also found results similar to ours, although they reported still high antibiotic resistance. In contrast, Maham et al.⁷ presented lower antibiotic resistance rates for A. baumannii than our study. The high resistance observed in Acinetobacter species to various antibiotics has led to colistin and tigecycline becoming important treatment options.²²

In this study, among the bacteria isolated from blood cultures, S. marcescens, which was isolated at a rate of 1.50%, was identified as the bacterium with the highest sensitivity rate to the tested antibiotics (excluding ampicillin) (Table 3). However, Shehab El-Din et al.²⁴ reported higher resistance rates for S. marcescens than our findings. This discrepancy may be attributed to Shehab El-Din et al.²⁴ isolating S. marcescens more frequently (7.17%) from blood cultures, which suggests that they may have used antibiotics more often in treating infections caused by this pathogen.

P. aeruginosa was isolated at a rate of 1.50%, and the most resistant antibiotic was imipenem, with a resistance rate of 72.22%, followed by levofloxacin, with a resistance rate of 53.84%. The most sensitive antibiotic was amikacin, with a resistance rate of 11.11%, followed by gentamicin, with a resistance rate of 12.50% (Table 3). Our study is consistent with the study of Akman et al.,²⁹ in which they found the resistance rates of amikacin (14.8%) and gentamicin (24.1%) to be lower than the resistance rate of imipenem (66.6%). However, Maham et al.⁷ reported resistance rates (amikacin 37.1%, gentamicin 69.0%, imipenem 21.6%), contrary to our study. In this study, high carbapenem (66.6%) and quinolone resistance (53.84%) observed in P. aeruginosa strains may be related to inappropriate antibiotic use in empirical treatment. According to our results, aminoglycosides and ciprofloxacin may be preferred before carbapenems and quinolones in empirical treatment in patients with suspected Pseudomonas infection.

In our study, 1.25% of E. coli was isolated from blood cultures (Table 3). Khan et al.²⁵ isolated E. coli strains from blood cultures at a rate similar to our study (1.09%). However, in a study conducted by Fox-Lewis et al.³², the percentage of E. coli was reported to be 47.2%, while a study conducted in Pakistan reported this percentage as 5%.³³ In our study, E. coli strains showed resistance rates of 85.71% to ampicillin, 64.28% to cefuroxime, and 20% to gentamicin; resistance rates for other tested antibiotics remained below 10%. The literature reports varying resistance rates for E. coli; for instance, Khan et al.²⁵ indicated that E. coli strains were susceptible to amikacin but highly resistant to imipenem and cefepime. Fox-Lewis et al.³² did not detect carbapenem resistance, but they found gentamicin resistance to be approximately 45% and ampicillin resistance to be over 90%. Er et al.³⁴ reported low resistance rates for imipenem, meropenem, and amikacin while noting high resistance to cephalosporins and quinolone antibiotics. These differences may be related to the diversity of microorganisms that are frequently isolated in the hospitals where the studies were conducted and the frequency of treatment practices associated with them.

In this study, E. cloacae, which was isolated at a rate of 0.66% and has the highest antibiotic susceptibility after S. marcescens (excluding ampicillin), shows antibiotic resistance rates generally around 25% and slightly above (Table 3). However, various resistance rates have been reported in studies conducted in different countries and geographical regions.^24,29

In recent years, there has been a significant increase in the isolation of Candida species in blood cultures due to the rise in occurrences of neutropenia, preterm birth, surgical procedures, and the use of intravascular catheters.²¹ In this research, 5.84% of positive blood cultures were identified as Candida (Table 4). Different Candida rates have been reported in studies: Khan et al.²⁵ 2.17%, Tariq et al.²⁷ 3.41%, Mokaddas et al.⁸ 7%, Gülmez et al.²¹ 10.8%, Kumar et al.³⁵ 21%. In our study, C. parapsilosis (3.17%) was the most frequently isolated fungal species (Table 4). These findings contradict reports indicating that C. albicans is the most commonly isolated fungal pathogen in neonatal ICUs.^22,28,35

Limitations of the study

The fact that the broth microdilution method used to determine colistin sensitivity was not tested in our hospital during the periods when the data were collected is among the limitations of our study.

CONCLUSION

In conclusion, this study identified gram-positive bacteria isolated from blood cultures as the dominant strains, with CoNS being the most frequently isolated bacteria. Antibiotic resistance was observed at the highest rate in A. baumannii, while resistance rates vary according to bacterial species. Studies in the literature reveal that the types of microorganisms isolated from blood cultures and antibacterial resistance rates vary significantly among hospitals in different countries. The main factors contributing to the increase in antimicrobial-resistant bacteria include poor infection control practices and inappropriate antibiotic use. Restriction of unnecessary antibiotic use, promotion of rational use, and specific antibiotic use strategies such as combination antibiotic therapy may help control the development of resistance. In addition, it would be useful to update the bacteriological profile and antibiotic susceptibility pattern in blood cultures at regular intervals to ensure correct empirical treatment.

Ethical approval

This study has been approved by the Kahramanmaraş Sütçü İmam University Medical Research Ethics Committee (approval date 12.09.2023, number 2023/13-03).

Author contribution

Study conception and design: MeA, AK, ZO; data collection: BK, ÖK; analysis and interpretation of results: MuA, ÖK; draft manuscript preparation: ZO, AK. All authors reviewed the results and approved the final version of the article.

Source of funding

The authors declare the study received no funding.

Conflict of interest

The authors declare that there is no conflict of interest.