Introduction
Bacteremia or bloodstream infection is defined as the presence of bacteria in the blood and is a major risk factor for the development of sepsis and septic shock (associated in up to 95%) and contributes to substantial morbidity and mortality1,2.
In these cases, the key to initial treatment is rapid restoration of blood perfusion and adequate antibiotic administration. The empirical choice of antibiotic is based on local prevalence and resistance patterns, and its administration is preferable within the 1st hour once the diagnosis is established3.
Sepsis is an infection associated with organ injury distant from the site of infection. Septic shock is established when a patient with sepsis presents with hypotension refractory to fluid resuscitation and requires vasopressors, and the risk of death increases substantially4,5.
In high-income countries, up to 31.5 million cases of sepsis are reported, of which 19.4 million are severe sepsis, causing approximately 5.3 million deaths annually. Information on the incidence and mortality of sepsis in middle- and low-income countries is scarce and varies across regions depending on factors such as population, etiological agents, and socioeconomic level4.
The case series differs greatly depending on the primary site of infection, specific populations, pathogens, antibiotic resistance, and geographic region. Escherichia coli is the most frequent causative microorganism of sepsis worldwide, while in South Korea, Staphylococcus aureus and Klebsiella pneumoniae are more common. This highlights the importance of having local epidemiological studies6.
Blood culture is the study of choice for diagnosing bacteremia and septicemia, as it allows the identification of the etiology, which is vital for optimizing therapy7,8.
A good collection technique that yields excellent sample quality is vital for obtaining reliable results. Inappropriate antibiotic therapy is associated with higher mortality. When implemented appropriately and early, it reduces mortality, days of hospitalization, and hospital costs, and avoids the inappropriate use of antibiotics even in severe bacterial infections. Therefore, emergency broad-spectrum empirical antibiotic therapy should be confirmed or rectified when microbiological data are available1,
The objective of this study was to describe the isolated microorganisms and their sensitivity and resistance patterns in patients from a tertiary care hospital of Instituto Mexicano del Seguro Social in Puebla, Mexico.
Material and methods
We conducted a descriptive, cross-sectional, retrospective study of patients with blood culture records from July 2020 through June 2023 in a tertiary care center of Instituto Mexicano del Seguro Social in Puebla, Mexico.
At the study hospital, the personnel who obtain blood culture samples are trained previously and periodically on the collection technique including the use of protective equipment (gloves and masks), aseptic and antiseptic technique of the collection area and the blood culture bottle cap, collection of the required blood volume, and incubation of the sample.
The records of the microbiology laboratory management computer system “R.E.A.L.” were consulted. The following were evaluated: number of blood culture samples per patient, isolated microorganisms, bacterial susceptibility or resistance, and the medical area in which the patients were hospitalized. For the antimicrobial resistance analysis, blood cultures belonging to the ESKAPE group and coagulase-negative Staphylococcus spp. (CNS) were considered. Once the data segmentation was performed, an analysis was carried out using the WHONET platform considering one isolate per patient; and generating a report of the percentage of antibiotic resistance with the division of relevant antibiotics for Gram-positive and Gram-negative microorganisms. Descriptive statistics were used for the rest of the analysis.
Results
A total of 974 blood culture studies with microorganism isolation were identified during the study period; 512 (52.56%) from male patients and 462 (47.44%) from female patients.
Regarding the hospital areas where the samples were taken, 4 areas were recorded: 582 (59.75%) studies from the medical area (internal medicine, pediatrics, hematology, etc.), 177 (18.17%) from the surgical area (general surgery, oncological surgery, neurosurgery, etc.), 166 (17.04%) patients from the critical care area (ICU, ED, COVID area), and 49 (5.04%) from other or unspecified services. A total of 704 (72.27%) blood cultures whose isolated germs corresponded to the ESKAPE group and with isolations of more than 15 microorganisms were recorded; these microorganisms were considered of epidemiological importance for the unit (importance group). The details of the results are shown in Table 1.
Table 1. Frequency of isolated microorganisms, Gram stain, and group
| Microorganism | Isolates | Gram stain | Group |
|---|---|---|---|
| Escherichia coli | 193 | Gram – | ESKAPE |
| Staphylococcus epidermidis | 184 | Gram + | Importance for the unit |
| Staphylococcus hominis | 98 | Gram + | Importance for the unit |
| Klebsiella pneumoniae | 67 | Gram – | ESKAPE |
| Staphylococcus haemolyticus | 54 | Gram + | Importance for the unit |
| Staphylococcus aureus | 39 | Gram + | ESKAPE |
| Pseudomonas aeruginosa | 37 | Gram – | ESKAPE |
| Acinetobacter baumannii | 17 | Gram – | ESKAPE |
| Enterococcus faecium | 15 | Gram + | ESKAPE |
| Total | 704 |
Gram -: Gram-negative; Gram +: Gram-positive.
The percentage of resistance by isolated microorganism of the Gram group is shown in Tables 2 and 3. In the case of the Gram-positive group, a higher percentage of resistance to erythromycin is observed; in the Gram-negative group, a higher percentage of resistance to ciprofloxacin is observed. The most frequently isolated microorganisms by the hospital area are presented in Table 4.
Table 2. Isolated Gram-positive microorganisms and percentage of antimicrobial resistance
| Microorganisms | Isolates | AMP %R | CLI %R | OXA %R | GEN %R | SXT %R | CIP %R | ERY %R | LVX %R | MFX %R | VAN %R | LNZ %R |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Staphylococcus epidermidis | 184 | 64 | 75 | 16 | 35 | 46 | 74 | 51 | 28 | 0 | 0 | |
| Staphylococcus hominis | 98 | – | 69 | 76 | 4 | 42 | 59 | 82 | 62 | 57 | 1 | 0 |
| Staphylococcus haemolyticus | 54 | – | 79 | 87 | 65 | 74 | 85 | 87 | 85 | 79 | 0 | 0 |
| Staphylococcus aureus | 39 | – | 40 | 33 | 4 | 6 | 16 | 34 | 17 | 17 | 6 | 0 |
| Enterococcus faecium | 15 | 100 | – | – | – | – | 91 | 100 | 91 | – | 82 | 0 |
| Total | 390 | 100 | 64 | 70 | 21 | 40 | 56 | 74 | 59 | 45 | 9 | 0 |
%R: percentage of resistance; AMP: ampicillin; CLI: clindamycin; OXA: oxacillin; GEN: gentamicin; SXT: trimethoprim/sulfamethoxazole; CIP: ciprofloxacin; ERY: erythromycin; LVX: levofloxacin; MFX: moxifloxacin; VAN: vancomycin; LNZ: linezolid.
Table 3. Isolated Gram-negative microorganisms and percentage of antimicrobial resistance
| Microorganism | Isolates | AMK %R | AMP %R | CAZ %R | FEP %R | CRO %R | IPM %R | MEM %R | CIP %R | SXT %R | TZP %R |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Escherichia coli | 193 | 16 | 92 | 74 | 74 | 74 | 8 | 7 | 72 | 81 | 25 |
| Klebsiella pneumoniae | 67 | 0 | 100 | 52 | 52 | 52 | 9 | 9 | 60 | 57 | 18 |
| Pseudomonas aeruginosa | 37 | 31 | – | 52 | 31 | 100 | 54 | 56 | 38 | – | 3 |
| Acinetobacter baumannii | 17 | – | 64 | 60 | 67 | 75 | 56 | 72 | 60 | 94 | – |
| Total | 325 | 14 | 94 | 63 | 58 | 70 | 25 | 24 | 63 | 73 | 28 |
%R: percentage of resistance; AMK: amikacin; AMP: ampicillin; CAZ: ceftazidime; FEP: cefepime; CRO: ceftriaxone; IPM: imipenem; MEM: meropenem; CIP: ciprofloxacin; SXT: trimethoprim/sulfamethoxazole; TZP: piperacillin/tazobactam.
Table 4. Medical areas and total isolates per microorganism
| Microorganism | Critical area | Medical area | Surgical area | Other | Overall total |
|---|---|---|---|---|---|
| Escherichia coli | 14 | 153 | 14 | 12 | 193 |
| Staphylococcus epidermidis | 46 | 101 | 31 | 6 | 184 |
| Staphylococcus hominis | 23 | 56 | 18 | 1 | 98 |
| Klebsiella pneumoniae | 7 | 40 | 15 | 5 | 67 |
| Staphylococcus haemolyticus | 17 | 25 | 8 | 4 | 54 |
| Staphylococcus aureus | 3 | 27 | 6 | 3 | 39 |
| Pseudomonas aeruginosa | 5 | 25 | 6 | 1 | 37 |
| Acinetobacter baumannii | 3 | 11 | 2 | 1 | 17 |
| Enterococcus faecium | 5 | 5 | 5 | – | 15 |
| Total | 123 | 443 | 105 | 33 | 704 |
Discussion
The diagnosis of bacteremia can be crucial when deciding the treatment of at-risk patients, and correct and timely management makes a difference in the patient’s outcome. Therefore, in patients who present with syndromes associated with a moderate probability of bacteremia, blood cultures are justified if there is no option for culture from the primary site of infection12.
The blood culture sample must be obtained correctly and before the start of any antibiotic in the patient. On the other hand, errors in the sample are usually: single sample (2-3 samples are recommended), insufficient volume, inadequate collection and processing method13,14. Greater contamination has been demonstrated if the collection site comes from catheters versus samples taken by peripheral venipuncture, with the exception of a sample from a newly inserted catheter15. At the hospital where this work was carried out, care is taken with the sample collection technique, with frequent and periodic training of those who take it (laboratory technicians, nurses, residents, etc.).
The lack of bacterial growth in blood culture studies is associated with problems in the sample collection technique (contamination, insufficient blood volume, etc.), and the fact that the patient has previously received some antimicrobial treatment12,16. In this work, the 35 blood cultures that did not show microorganism growth suggest one of these problems. The World Health Organization considers a list of antibiotic-resistant bacteria as a priority for the research of new drugs. This list is called “ESKAPE” for the acronym of the critically prioritized bacteria included (Acinetobacter baumannii, Pseudomonas aeruginosa, K. pneumoniae, and Enterobacter spp.) and highly prioritized bacteria (Enterococcus faecium and S. aureus)17. These microorganisms are responsible for approximately 40% of infections in hospital centers due to their mechanisms of evasion of treatments, and whose infections lead to high levels of mortality and costs in the health sector18. In this study, these bacteria were responsible for 52% of positive results in blood cultures, while the microorganisms considered important for the unit were responsible for 47%.
This epidemiological basis guides the initiation of empirical antibiotic therapy, such as in cases where it is not possible to wait for the blood culture result.
The percentage of unreported data in the clinical laboratory records in this work represents an opportunity for improvement in that process in the unit. Furthermore, the increase in the supervision of an adequate technique in sample collection involves clinical and paraclinical personnel. A limitation of this study was the lack of clinical correlation.
Conclusions
The most frequently identified microorganism in blood cultures with bacterial growth in this tertiary hospital in Puebla, Mexico was E. coli, followed by Staphylococcus epidermidis and Staphylococcus hominis. The hospital area with the highest number of isolates in its blood cultures was the medical area with 153 isolates out of 193 for Escherichia coli. It is necessary to maximize the optimization of the blood culture sampling technique to achieve a record that adequately guides the initiation of empirical antibiotic therapy.
Funding
The authors declare that they have not received funding.
Conflicts of interest
The authors declare no conflicts of interest.
Ethical considerations
Protection of humans and animals. The authors declare that no experiments involving humans or animals were conducted for this research.
Confidentiality, informed consent, and ethical approval. The authors have obtained approval from the Ethics Committee for the analysis of routinely obtained and anonymized clinical data, so informed consent was not necessary. Relevant guidelines were followed.
Declaration on the use of artificial intelligence. The authors declare that no generative artificial intelligence was used in the writing of this manuscript.
