In our study, E. coli was the predominant pathogen, followed by E. cloacae, S. aureus, P. aeruginosa, A. baumannii (9.6%), similar to several previous findings [15, 16]. However, a cross-sectional descriptive study found that P. aeruginosa was the predominant microorganism (36.17%) causing nosocomial infections in orthopedics, whereas E. coli was only the fourth most prominent (6.38%); E. cloacae and S. aureus were even rarer [17]. This apparent discrepancy is likely due to the different procedures and tissue samples. Sarker et al. [17] only surveyed pathogens isolated from incisional secretions, but here we surveyed pathogens isolated from a much larger variety of samples. For example, E. coli and S. aureus were frequently found in non-incisional secretions, such as urine [18]. Another reason for the difference may be that the two hospitals have dissimilar disease entities. Third of the orthopedics patients in the hospital we investigated were in the trauma division, and a study carried in Sichuan province, China, found that Gram-negative bacilli were the most common isolates and that S. aureus was the most common Gram-positive bacterium in trauma patients [19]. Finally, social, economic, and environmental variations may also account for between-study differences.
Among the most widespread bacteria worldwide, E. coli is a known cause of urinary tract and bloodstream infections [18, 20]. The antibiotic-resistance patterns of E. coli in this study corresponded to those in previous reports [16, 21, 22]. Taken together, the findings suggest that we should reduce the usage of antibiotics to which E. coli is highly resistant, such as ampicillin. Additionally, we also recommend restricted usage of third-generation cephalosporin, despite observing low resistance. Our study identified a high percentage of ESBL-producing E. coli, and third-generation cephalosporins are the main factors leading to the emergence and spread of these strains [23].
In the event of E. coli infection, we recommend cautious use of antibiotics to which the bacterium is less resistant (e.g., amikacin). Currently, many doctors use empirical antibiotics without waiting for sensitivity reports [24, 25]. Fortunately, an antibiotic with a rate of accumulated bacterial resistance below 15% should be safe for use in empiric therapy [26]. Nevertheless, during the course of our 6-year study, we observed a clear increase in resistance to imipenem and piperacillin-tazobactam. This outcome serves as a warning against excessive antibiotic prescription, even if the target bacteria are initially less resistant.
Staphylococcus aureus was the dominant Gram-positive bacteria causing nosocomial infections in our study, in line with previous reports [27, 28, 29]. Specifically, we found high proportions of MRSA. Previous studies have similarly identified penicillin-resistant S. aureus [30], and indeed, our study identified only two S. aureus strains that were sensitive to penicillin. Furthermore, all strains were resistant to ampicillin. Together, these results indicate the real danger of MDR S. aureus. We therefore strongly advise against the empiric use of both penicillins and ampicillins. In contrast, S. aureus was not resistant to nitrofurantoin, linezolid, or vancomycin, suggesting that they can be safely used in clinics. However, a vancomycin-resistant S. aureus isolate was reported in 2002, and subsequently, 14 isolates have been found in the United States [31]. Therefore, the three antibiotics should only be used in severe infections that cannot be controlled by other antibiotics. Fluoroquinolones and cotrimoxazole may be preferable, as our data show that S. aureus strains are not resistant to them. If neither are available, tetracycline can be a viable alternative based on the observed sensitivity of S. aureus to this drug.
Importantly, our findings clearly demonstrated a major problem with antimicrobial resistance in the study hospital, corroborating worldwide trends. Given that MDR bacteria are now recognized as a major cause of nosocomial infections [32], hospitals must work to control their incidence rate. Here, 43.3% and 74.2% of the strains were MRSA isolates and ESBL-positive E. coli, respectively, similar to a previous study in China [22]. The similarity suggests that some demographic and clinical characteristics could increase the risks of MDR bacterial infections. Indeed, we showed that patients with open fractures are more susceptible to MRSA infections, consequently contributing to multiple complications [33]. Regular attempts by surgeons to control infection via antibiotics likely explains the increased MDR in bacteria.
We observed a significant link between ESBL-producing E coli infections and degenerative diseases, which mainly affect elderly patients. Previous studies have indicated that elderly patients are at high risk of nosocomial infections, especially from MDR bacteria [22, 34]. This age-related risk was somewhat supported in our study, although we did not identify a significant relationship between elderly patients and MDR bacterial infections. Finally, other potential risk factors like biological sex, recreational drug use, diabetes, and hypertension did not increase the likelihood of multidrug-resistant bacterial infections.
However, our research had some limitations. First, we only analyzed the drug-resistance of the major bacteria, and thus, our findings may not be fully representative of the drug-resistance of the whole department. Second, we did not analyze the bacterial spectrum and drug-resistance in different disease entities. Further studies are therefore required to address these issues.