Keywords
Intensive Care Unit, anti-biotic susceptibility, gram-negative, cephalosporins, Extended Spectrum Beta Lactamase
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This article is included in the Genomics and Genetics gateway.
Bacterial infections in the Intensive Care Units are a threat to the lives of critically ill patients. Their vulnerable immunity predisposes them to developing bacteria-associated sepsis, deteriorating their already fragile health. In the face of increasing antibiotics resistance, the problem of bacterial infection in ICU is worsening. Surveillance of bacterial infections in ICUs and drug resistance will help to understand the magnitude of the problem it poses and inform response strategies. We assessed bacterial infections in ICU setting by identifying prevalent Gram-negative bacterial species and characterized their antibiotic susceptibility patterns.
Cross-sectional samples collected from Kenyatta National Hospital ICU between January and June 2021 were cultured and phenotypic identification of culture-positive samples performed using VITEK 2. Antibiotic susceptibility patterns were determined based on Antimicrobial Susceptibility Testing (AST) results. Cephalosporin-resistant Gram-negative bacteria were assessed by PCR to detect the presence of ESBL genes including ( bla CTX-M, bla SHV, bla TEM, bla OXA)
Out of the 168 Gram-negative isolates, Acinetobacter baumanii was the most abundant (35%). Other isolates that were present at frequencies more than 15% are Klebsiella pneumoniae and Escherichia. coli. A. baumaniii is known to be a notorious bacterium in ICU due to its multidrug resistance nature. Indeed, A. baumanii isolates from Kenyatta National Hospital showed significantly high level of phenotypic resistance. Concordant with the high level of phenotypic resistance, we found high carriage of the ESBL genes among the isolates analysed in this study. Moreover, majority of isolates harboured all the four ESBL genes.
A high rate of phenotypic and genetic resistance was detected among the tested isolates. Resistance to cephalosporins was primarily driven by acquisition of the ESBL genes. The high prevalence rate of ESBL genes in ICU bacterial isolates shown in this study has a important implication for ICU patient management and general antibiotics use.
Intensive Care Unit, anti-biotic susceptibility, gram-negative, cephalosporins, Extended Spectrum Beta Lactamase
This version of the manuscript has gone through a rigorous review, addressing the first and second reviewer comments. However, methods used, and data generated remains essentially the same. We have added the significance of the study in the background section of the abstract and corrected the names of the genes tested in our study. We have done minor edits throughout the background section. We have also made minor edits in the methods section; the subtitle "AST and phenotypic detection" has been revised to "Antimicrobial Susceptibility Testing (AST) and phenotypic detection of ESBL producers". We have also performed a Chi-Square analysis to assess the association between different patient parameters and ESBL production. We have also endeavoured to compare our findings to those reported before.
See the authors' detailed response to the review by Upendo O Kibwana
See the authors' detailed response to the review by Tajudeen Oladunni GANIYU
The intensive care unit (ICU) is a hotspot of nosocomial infections primarily because of the extremely vulnerable population of critically ill patients, usage of invasive procedures such as catheters and ventilators1,2 and immunosuppressive medication.3 These infections significantly increase the burden of bacterial associated morbidity, mortality, and healthcare costs. ICU acquired infections (ICU-AI) contribute 20-25% of all nosocomial infections globally.4 Recent studies have reported high risk of bloodstream infections caused by Gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae among COVID-19 patients admitted in ICU.5,6
Antimicrobial resistance (AMR) is a major contributor to the problem of ICU acquired infections. AMR reduces the effectiveness of antibiotics and other antimicrobial drugs in treating these infections. Emergence of AMR leads to a higher risk of treatment failure, longer hospital stays, and increased mortality rates, as well as greater healthcare costs and resource utilization.7 Drug resistant bacterial pathogens emerge and spread in the ICU environment as a result of acquisition of mutations, and selection of resistant strains, driven mostly by indiscriminate use of antibiotics.8 Additionally, Gram-negative bacteria have evolved an intrinsic mechanism involving the production of extended spectrum beta lactamases (ESBLs) that breakdown the beta lactam antibiotics.9 Resistance to antibiotics can be considered multidrug resistance (MDR) when the target organism develops resistance against more than one antimicrobial agent.10 The outbreak and spread of COVID-19 also contributed to spread of drug resistant bacterial infections in ICU due to the increased number of patients requiring ICU admission. A high prevalence of bacterial pneumonia, 44% (n= 716) among covid 19 patients admitted in ICU has been reported.11
Phenotypic resistance to the third generation cephalosporins (cefotaxime, ceftazidime and ceftriaxone) is increasing, posing a significant public health threat.12,13 Cephalosporins are valuable agents used in the management of a wide range of Gram-negative infections including meningitis, Lyme disease, pseudomonas pneumonia, Gram-negative sepsis, streptococcal endocarditis, melioidosis, penicillinase-producing Neisseria gonorrhoea, and Gram-negative osteomyelitis.14 The use of molecular tools to profile the ESBLs producing Gram-negative bacteria have confirmed the presence of multiple ESBL genes (blaCTX-M, blaSHV, blaTEM, blaOXA) in isolates of Klebsiella pneumonia, Escherichia coli, and Proteus species, corresponding to high-level resistance to third generation cephalosporins.15
The current study sought to profile phenotypic and genetic resistance to cephalosporin in bacteria isolated from ICU patients’ samples. Identification of bacterial species and phenotypic susceptibility patterns were conducted using VITEK 2 (bioMérieux). Phenotypically resistant isolates were confirmed by PCR genotyping.
This was a cross sectional study carried out between January to June 2021 at Kenyatta National Hospital (KNH). KNH is the largest public referral and teaching hospital in Kenya with a bed capacity of approximately 1800. The hospital serves patients from the capital city with a population of over three million people. The hospital’s critical care unit department is composed of the main ICU and several other specialised units including Neurosurgery-CCU, Medical wards-CCU, Surgical ward-CCU, Neonatal-ICU, and the Casualty CCU. In this study, “ICU” to refers to both main ICU and other specialized CCUs.
This study was approved by the Kenyatta National Hospital (KNH)-University of Nairobi (UON) Ethics and research committee under the study number: P632/11/2020. Additionally, informed consent/assent were sought from participants or kin of the patient in cases of minors or unconscious patients. Written consent was obtained from next of kin for all participants but two. The two cases involved consent obtained from treating ICU physician, where the patients were incapacitated and their next of kin were unavailable to give consent. This decision was made based on the deferred consent principle backed by the following reasons
1. The research involves minimum harm to the participant
2. The deferment of consent procedure did not adversely affect the rights and welfare of the patient since the genomic testing (PCR) was carried out on the leftover bacterial isolates and not on the human DNA. These bacterial isolates are regarded as residual laboratory samples material
Patient confidentiality and data privacy was ensured by assigning unique study code to each participant. Participant metadata was collected using password protected excel data collection tool.
Study participants included all patients admitted to various ICUs in KNH suspected to have bacterial infection during their entire period of admission. Inclusion criteria included having a Gram-negative culture positive specimen. Patients with only Gram-positive cultures were excluded. Sample size was determined using the Cochrane’s and Finite population correction for proportions formula.16
Sample quality and quantity were reviewed prior to labelling for bacteriology assessment. Degraded samples or those with inadequate volume were excluded. Samples that passed the inclusion criteria were processed for organism identification and antimicrobial susceptibility of culture positive Gram-negative isolates using the Vitek®2 (Biomérieux, Marcy l’Etoile, France) with Minimum Inhibitory Concentration (MIC) breakpoints set according to CLSI 2020 guidelines. Prior to loading isolates into the VITEK® 2, bacterial suspensions were prepared by emulsifying the isolates in 0.5% saline and standardizing turbidity to 0.5 McFarland’s using a densitometer. The suspension was used for species identification, AST and phenotypic detection of ESBL producing organisms in the VITEK® 2 using Gram-negative cards (GN83). Vitek®2 Advanced Expert System (AES) was used. A commercially acquired Gram negative isolates as positive control was loaded for each run on Vitek. For negative controls we used bacterial suspension media (saline). Antimicrobial susceptibility profiles for Cefotaxime, ceftazidime and ceftriaxone were also recorded. The Minimum Inhibitory Concentrations (MICs) were set according to CLSI 2020 guidelines. For specimens identified phenotypically as ESBL producers, another inoculum was picked from residual specimen and stored in skimmed milk-tryptone-glucose-glycerol broth at -80°C to minimize risk of mutations during batching, awaiting PCR.
Isolates that showed phenotypic resistance to Cefotaxime, ceftazidime and ceftriaxone were selected and used for subsequent PCR genotyping. The Isolate II Genomic DNA kit (Bioline London, UK) was used for total DNA extraction. The kit applies affinity columns to extract genomic DNA. Proteinase K, together with cell lysis buffers containing chaotropic salt ions are used to lyse cells releasing gDNA, which is captured by the affinity resins (silica gel membrane). DNA extraction was followed according to manufacturer’s instructions and eluted in a final volume of 40 ul PCR amplification was then performed using MyTaq™ PCR mix (Bioline, London, UK) in a final volume of 20μl, comprising a master-mix, 0.4 μM of each forward and reverse primers and 3 μl of DNA template. Primers specific to ESBL encoding genes (blaTEM, blaSHV, blaCTX-M and blaOXA) were used as described by.17,18 These ESBL genes were chosen for PCR genotyping since they were most frequently detected based on phenotypic resistance detection.
Briefly, amplicons were analysed by gel electrophoresis run in 1% agarose gel, 1×TAE buffer and SYBR™ Safe (Invitrogen, Carlsbad, CA, USA) and a 1KB ladder at 70 volts for 30 minutes. The amplified products were visualized under Ultraviolet trans-illumination using the UVTEC Gel Documentation Systems (Cleaver Scientific, United Kingdom,) to identify presence of ESBL genes. The commercial E.coli KEN063 isolate was used as a positive control, while E.coli 25922 negative control. The primer sequences and thermocycling conditions used in this study are provided in the Supplementary table 1 and Supplementary table 2 in the Data Availability section (DOI: 10.6084/m9.figshare.22369975).
Statistical analyses were performed in MS. Excel 2010 and GraphPad Prism (version 8.0.4). Shapiro-Wilk test was used to assess data normality prior to analyses. Descriptive statistics including means and frequencies were used for data summary. Mean comparisons among three or more groups was performed using one-way ANOVA with Tukey’s post-hoc. Associations between variables were determined using Chi-Square test. Descriptive data was presented as mean ± SD and data considered statistically significant at p value <0.05.
The highest number of bacteria were isolated from tracheal aspirate (TA) (99/168) followed by urine (38/168) and blood (19/168) while ascitic tap, CVC tip and sputum had one isolates each. Table 2 T/A harboured all the isolated tested, with a total of 99 isolates. The distribution of species in T/A showed that A. baumanii were the highest in TA (38/99). Urine specimen had the second highest number of species (38/168). Out of the 8 species identified, urine had 5 species, with K. pneumoniae being the most frequent, identified 13 times (Table 1).
A total of 168-Gram-negative isolates were phenotypically identified from ICU patients’ samples. The isolates comprised of 8 Gram-negative bacteria species, with A. baumanii being the most abundant (35%) followed by K. pneumoniae (24%), and E. coli, 18% while the remaining species were present at frequencies ≤10% ( Figure 1).
Phenotypic susceptibility analysis revealed high level of resistance among the bacterial isolates identified. Overall, 101/168 (60.1%) isolates were ESBL producers while 67/168 (39.9%) were ESBL non-producers. blaTEM was the most abundant ESBL, occurring in 99/168 followed by shv (88/168), blaCTX-M (81/168), and blaOXA (54/168) ( Table 2). blaOXA was produced by most of the organisms, but there were no statistically significant difference when compared to other ESBLs ( Table 2).
Majority of patients 76% were males and the highest number of bacterial isolates were from patients aged between 21 to 40 years 75/168 and 50 out of the 75 isolates were phenotypically resistant to at one cephalosporin. Conversely, few isolates (3/168) were isolated from patients aged >80 years; all the isolates were phenotypically susceptible to all tested cephalosporins ( Table 3).
P values were obtained by performing chi-square analysis.
Positive (n=101) | Negative (n=4) | p-value | ||
---|---|---|---|---|
HIV | YES | 2 | 0 | 1.000 |
NO | 100 | 4 | ||
HYPERTENSION | YES | 12 | 1 | 0.235 |
NO | 89 | 3 | ||
DIABETES | YES | 6 | 2 | 0.131 |
NO | 96 | 2 | ||
COVID-19 | YES | 7 | 0 | 1.000 |
NO | 95 | 4 |
The susceptibility pattern revealed high level of phenotypic resistance against three cephalosporins (Ceftazidime, Ceftriaxone, and Cefotaxime) ( Table 4).
The 101 isolates that were phenotypically resistant to cephalosporin were subjected to PCR genotyping and 97 (96%) isolates harboured at least one of the four gene tested while four isolates were negative for all the four genes. blaTEM was the most predominant gene at 96% (97/101), followed by SHV = 85.6% (86/101), CTX-M = 78.8% (80/101) and OXA= 52.9% (54/101). blaTEM/blaSHV/blaCTX-M/blaOXA and blaTEM/blaSHV/blaCTX-M gene combinations were present at 49% (n=49/101) and 25.7% (n=26/101) respectively. Other common gene combinations included blaTEM/SHV at 6.7% (n=7/101), blaTEM/CTX-M/OXA at 1.9% (n=2/101), blaTEM/SHV/OXA at 1.9% (n= 2/101), blaSHV/CTX-M at 1.9% (n= 2/101) ( Table 5)
Bacterial infection in the ICUs represent a major burden and safety concern for patients admitted to the ICU.19 Patients in ICU are often critically ill and require urgent care. As a result, they are prescribed antimicrobial therapy empirically to manage their condition while waiting for culture result.4 The World Health Organization (WHO) considers this irrational use of antimicrobial in ICU a major contributor to development of antimicrobial resistance.20 In light of the rampant use of antibiotics in ICU, this study was conducted to evaluate the level of bacterial colonization in various sample types drawn from ICU patients and the corresponding level of antibiotic resistant Gram-negative bacteria. Additionally, susceptibility to three classes of cephalosporins (Ceftazidime, Ceftriaxone and Cefotaxime) was assessed.
Acinetobacter baumanii, Klebsiela pneumoniae and E. coli were the most abundant organisms (35%, 24%, and 18% respectively). The current study corroborates with other studies reporting similar rates of Acinetobacter species (30.9%) and Klebsiella species (29.7%) followed by Pseudomonas aeruginosa (22.9%) in ICU environment.21 A study that sought to assess the prevalence of ESKAPE, a group of pathogens consisting of Enterococcus faecium, Staphylococcus aureus, Klebsiella neumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa showed that Enterobacter spp showed that Klebsiella pneumoniae, Acinetobacter baumanii and Pseudomonas aeruginosa were frequently isolated the in ICUs.22 In yet another study, Pseudomonas species was found to be high (29.1%) in ICU setting followed by Acinetobacter (27.5%).23 The trend in ICU bacterial colonization appears to be dominated by the three main organisms Acinetobacter species, Klebsiella species and Pseudomonas species, as demonstrated in previous studies22,23 and corroborated by our study. We also showed that Acinetobacter baumanii and Klebsiela pneumoniae ICU isolates were resistant to all tested cephalosporins. The resistance to multiple cephalosporins might partially explain the high prevalence of these bacteria in ICUs. Our findings were in agreement with Saxena and colleagues who reported multiple drug resistance in Acinetobacter and Klebsiella.4
Organism distribution varied significantly among different specimen types. Tracheal aspirate had the highest isolates (59%) followed by urine (23%) and blood (11%) while ascitic tap, CVC tip and sputum had (0.6%) each. These findings agreed with previous report of high prevalence (56%) of pulmonary colonization among ICU patients identified by tracheal aspirate culture.24 Tracheal aspirate culture has been evaluated as a non-invasive method for diagnosis of ventilator-associated pneumonia colonization.25 The ease of obtaining tracheal aspirate sample and availability of established protocol could explain why more tracheal aspirate samples were obtained and cultured successfully. Urine, blood and pus swabs yielded 23%, 11% and 5% of total organisms respectively. The lower proportion of culture positivity could be influenced by the small number of samples or the culture method used.
Concordant with phenotypic susceptibility findings, we reported high level of genetic resistance in A. baumanii, K. pneumoniae and E. coli. A. baumanii is an opportunistic nosocomial pathogen that is resistant to most antimicrobial.26 Resistance to multiple antibiotics could be responsible for the high prevalence in ICU settings. A previous study linked A. baumanii to ventilator-associated pneumonia.27 Carbapenem resistance in A. baumanii is mediated by class D β-lactamases belonging to blaOXA-type. In addition, A. baumanii possesses an intrinsic chromosomally encoded oxacillinase blaOXA-51, which may account for the high prevalence of blaOXA (48.8%) reflecting its ability to resist eradication.28 A study in hospital wards in neighbouring Uganda investigated carriage of blaCTX-M, blaTEM, and blaSHV genes and showed that 61 (59%) of all isolates carried ESBL-encoding genes, with blaCTX-M being the heighest (93%, 57/61).29 Also, a study in Tanzania by Kibwana and colleagues found that blaCTX-M-15 was the common EBSL gene among admitted febrile children.30 In study we report 57.6% of K. pneumoniae isolates possess blaOXA gene. Similar findings were recently reported demonstrating the involvement of blaOXA gene in mediating resistance to cephalosporins.31 The high prevalence cabapenem resistant bacteria in ICU setting has important implications for patient management in these critical care settings especially when patients are critically ill. Nosocomial infections are likely to be common in these settings resulting to high mortality in ICUs. During severe disease outbreaks requiring hospitalization and admission to ICUs, more people are exposed to these infections.
Analysis of blaCTMX, blaTEM, and blaSHV genes revealed a carriage of resistance gene in more than 50% of studied isolates. A study performed previously in an Indonesian hospital reported similar findings.32 Moreover, molecular surveillance of ESBL in neonates samples from Kenya and Nigeria revealed a high prevalence of ESBL producing bacteria.33 The high prevalence of ESBL producing bacteria in ICU underscore the need to heighten surveillance of antibiotic resistance to provide the much-needed information to tackle resistance. This study contributes to the understanding of the burden antibiotic resistant bacteria in ICU, which can inform antibiotic use policies to combat resistance. In conclusion, this study has revealed the growing challenge of prevalence of antibiotic resistant bacterial isolated in ICUs. Despite the fragile nature of ICU patients, it continues to be colonized by antibiotic resistant bacterial isolates as we have demonstrated. While there are no definitive measures to eradicate antibiotic resistant bacteria in ICUs, vaccines against these pathogens remain elusive and where available, they are unaffordable. Thus, prudent use of antibiotics in ICU to avoid widespread resistance is recommended. Additionally, the research for development of more potent antibiotics with genetic barrier to resistance should be supported if we are to win the battle against antibiotic resistance.
Figshare. Phenotypic and genetic Extended Spectrum Beta Lactamase cephalosporin resistance profiles of bacterial isolates from ICU in Tertiary Level Hospital in Kenya. DOI: https://doi.org/10.6084/m9.figshare.22369975.v2.34
This project contains the following data:
Extended Spectrum Beta Lactamase.xlsx: The data contain phenotypic antibiotic susceptibility values for bacterial isolates and genotypic resistance data assessed by detection of ESBL genes is also part of the data.
Raw DATA_VITEK Bacterial identification.xlsx: Bacterial identification readings from VITEK 2.
Supplementary Materials.docx: This file contains the PCR primer sequences and thermocycler conditions.
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).
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Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical Microbiology and Microbial Biotechnology
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Bacteriology, infectious diseases
Is the work clearly and accurately presented and does it cite the current literature?
Partly
Is the study design appropriate and is the work technically sound?
Yes
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical Microbiology and Microbial Biotechnology
Is the work clearly and accurately presented and does it cite the current literature?
Yes
Is the study design appropriate and is the work technically sound?
Yes
Are sufficient details of methods and analysis provided to allow replication by others?
Yes
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Bacteriology, infectious diseases
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Version 1 05 May 23 |
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