Antibiotic Resistance in the Neonatal Intensive Care Unit

Antimicrobial Stewardship: A Correct Management to Reduce Sepsis in NICU Settings

The discovery of antimicrobial drugs has led to a significant increase in survival from infections; however, they are very often prescribed and administered, even when their use is not necessary and appropriate. Newborns are particularly exposed to infections due to the poor effectiveness and the immaturity of their immune systems. For this reason, in Neonatal Intensive Care Units (NICUs), the use of antimicrobial drugs is often decisive and life-saving, and it must be started promptly to ensure its effectiveness in consideration of the possible rapid evolution of the infection towards sepsis. Nevertheless, the misuse of antibiotics in the neonatal period leads not only to an increase in the development and wide spreading of antimicrobial resistance (AMR) but it is also associated with various short-term (e.g., alterations of the microbiota) and long-term (e.g., increased risk of allergic disease and obesity) effects. It appears fundamental to use antibiotics only when strictly necessary; specific decision-making algorithms and electronic calculators can help limit the use of unnecessary antibiotic drugs. The aim of this narrative review is to summarize the right balance between the risks and benefits of antimicrobial therapy in NICUs; for this purpose, specific Antimicrobial Stewardship Programs (ASPs) in neonatal care and the creation of a specific antimicrobial stewardship team are requested.

Baseline azithromycin resistance in the gut microbiota of preterm born infants

BACKGROUND

Macrolides, including azithromycin, are increasingly used in preterm-born infants to treat Ureaplasma infections. The baseline carriage of macrolide resistance genes in the preterm stool microbiota is unknown.

OBJECTIVES

Identify carriage of azithromycin resistant bacteria and the incidence of macrolide resistant genes.

METHODS

Azithromycin resistant bacteria were isolated from serial stool samples obtained from preterm infants (≤32 weeks' gestation) by culturing aerobically/anaerobically, in the presence/absence of azithromycin. Using quantitative PCR, we targeted 6 common macrolide resistance genes (erm(A), erm(B), erm(C), erm(F), mef(A/E), msr(A)) in DNA extracted from selected bacteria resistant to azithromycin.

RESULTS

From 89 stool samples from 37 preterm-born infants, 93.3% showed bacterial growth in aerobic or anaerobic conditions. From the 280 azithromycin resistant isolates that were identified, Staphylococcus (75%) and Enterococcus (15%) species dominated. Macrolide resistance genes were identified in 91% of resistant isolates: commonest were erm(C) (46% of isolates) and msr(A) (40%). Multiple macrolide resistance genes were identified in 18% of isolates.

CONCLUSION

Macrolide resistance is common in the gut microbiota of preterm-born infants early in life, most likely acquired from exposure to the maternal microbiota. It will be important to assess modulation of macrolide resistance, if macrolide treatment becomes routine in the management of preterm infants.

IMPACT STATEMENT

Azithromycin resistance is present in the stool microbiota in the first month of life in preterm infants 91% of azithromycin resistant bacteria carried at least one of 6 common macrolide resistant genes Increasing use of macrolides in the preterm population makes this an important area of study.

Antimicrobial Resistance Pattern and Empirical Antibiotic Treatments in Neonatal Sepsis: A Retrospective, Single-Center, 12-Year Study

Neonatal sepsis is an important cause of morbidity and mortality in neonatal intensive care units (NICUs). Continuous evaluation of antimicrobial resistance (AMR) profiles is advised to implement antimicrobial stewardship (AMS) programs and establish effective empiric antibiotic protocols. AMS may reduce AMR in NICUs and improve sepsis outcomes. In this retrospective observational study, we report data on culture-positive neonatal sepsis, assessing differences after the implementation of an AMS program (2011-2016 vs. 2017-2022). A total of 215 positive bacterial cultures from 169 infants were retrieved, with 79 early-onset (36.7%) and 136 late-onset (63.3%) sepsis episodes. Frequent causative agents for early-onset sepsis were S. agalactiae and E. coli, all susceptible to empiric treatment. Late-onset sepsis was mainly caused by Enterobacterales and S. aureus. Aminoglycosides, cefotaxime, and piperacillin-tazobactam resistance among Enterobacterales was substantially low; S. aureus was mostly susceptible to oxacillin and vancomycin. There were no differences in mortality and multidrug-resistant pathogens rates between the two study periods. There were five episodes of fungal late-onset sepsis, mostly due to C. albicans, of which one was fatal. The microbial distribution pattern and AMR profiles overlapped with other European studies. Because susceptibility patterns are rapidly changing worldwide, with the emerging threat of Methicillin-resistant S. aureus and extended-spectrum beta-lactamases producers, infection prevention and control practices and AMS strategies require continuous optimization to limit selection pressure and AMR escalation.

Surveillance of Multidrug-Resistant Pathogens in Neonatal Intensive Care Units of Palermo, Italy, during SARS-CoV-2 Pandemic

BACKGROUND

Antimicrobial resistance (AMR) is a topic of concern, especially in high-level care departments like neonatal intensive care units (NICUs). The systematic use of an "active" epidemiological surveillance system allows us to observe and analyze any changes in microbial distribution, limiting the risk of healthcare-associated infection (HAI) development.

METHODS

We have conducted a longitudinal observational study in the five NICUs of Palermo, comparing the "pre-pandemic period" (March 2014-February 2020) with the "pandemic" one (March 2020-February 2022). The primary aim of the study was to evaluate the cumulative prevalence of carriage from multi-drug resistant (MDR) bacteria in the cumulative NICUs (NICU C).

RESULTS

During the "pre-pandemic period", 9407 swabs were collected (4707 rectal, 4700 nasal); on the contrary, during the "pandemic period", a total of 2687 swabs were collected (1345 rectal, 1342 nasal). A statistically significant decrease in MDR-Gram-negative bacteria (GNB) carriage prevalence was detected during the pandemic. At the same time, there was a general worsening of the carriage of carbapenemase-forming MDR-GNB (CARBA-R+) and methicillin-resistant Staphylococcus aureus (MRSA) during the pandemic period. A significant reduction in methicillin-susceptible Staphylococcus aureus (MSSA) carriage was detected too.

CONCLUSIONS

The surveillance of MDRO carriage in NICUs is fundamental for limiting the social and economic burden of HAIs.

Early antibiotic exposure in very-low birth weight infants and infection risk at 3-7 days after birth

OBJECTIVE

To determine rates of late-onset infection (LOI) during postnatal days 3-7 among preterm infants, based on antibiotic exposure during days 0-2.

STUDY DESIGN

Retrospective cohort study of infants born <1500 grams and ≤30 weeks gestation, 2005-2018. We analyzed the incidence and microbiology of LOI at days 3-7 based on antibiotic exposure during postnatal days 0-2.

RESULTS

The cohort included 88,574 infants, of whom 85% were antibiotic-exposed. Fewer antibiotic-exposed compared to unexposed infants developed LOI (1.5% vs. 2.1%; adjusted hazard ratio, 0.28, 95% CI 0.24-0.33). Among antibiotic-exposed compared to unexposed infants, Gram-negative (38% vs. 28%, p = 0.002) and fungal (11% vs. 1%, p < 0.001) species were more commonly isolated, and gram-positive organisms (49% vs. 70%, p < 0.001) were less commonly isolated.

CONCLUSIONS

We observed low overall rates of LOI at days 3-7 after birth, but antibiotic exposure from birth was associated with lower rates, and with differing microbiology, compared to no exposure.

3-(Bromoacetyl) coumarin is a potential therapeutic agent against neonatal sepsis-associated Pseudomonas extremorientalis

Neonatal sepsis is a severe bacterial infection that can lead to life-threatening complications in newborns. Pseudomonas extremorientalis is a Gram-negative bacterium and these Gram-negative organisms have been identified as a major cause of neonatal sepsis. The virulence factors produced by this bacterium play a crucial role in its pathogenicity. Therefore, targeting these virulence factors could be a potential strategy to treat neonatal sepsis caused by P. extremorientalis. In this study, we investigated the efficacy of 3-(bromoacetyl) coumarin (3-BC) in reducing the virulence factors of P. extremorientalis strains isolated from neonatal sepsis. Our results showed that 3-BC effectively reduced the production of various virulence factors, including protease, elastase, siderophore, and exopolysaccharide in these strains. Furthermore, at a concentration of 125 µg/ml, 3-BC also inhibited the biofilm formation ability of these strains in combination with ciprofloxacin. It was discovered that 3-BC was functionally effective in protecting C. elegans against bacterial infection. Moreover, the in vitro and in vivo outcomes were strongly correlated with docking studies of various activator proteins. Overall, our findings suggest that 3-BC could be a potential therapeutic agent for the treatment of neonatal sepsis caused by P. extremorientalis. Further studies are needed to explore the mechanism of action of 3-BC and its potential use in clinical settings.

Antibiotic Resistance and Biofilm Infections in the NICUs and Methods to Combat It

Neonatal sepsis is an important cause of neonatal morbidity and mortality. A significant proportion of bacteria causing neonatal sepsis is resistant to multiple antibiotics, not only to the usual empirical first-line regimens, but also to second- and third-line antibiotics in many neonatal intensive care units (NICUs). NICUs have unique antimicrobial stewardship goals. Apart from antimicrobial resistance, NICUs have to deal with another problem, namely biofilm infections, since neonates often have central and peripheral lines, tracheal tubes and other foreign bodies for a prolonged duration. The aim of this review is to describe traditional and novel ways to fight antibiotic-resistant bacteria and biofilm infections in NICUs. The topics discussed will include prevention and control of the spread of infection in NICUs, as well as the wise use of antimicrobial therapy and ways to fight biofilm infections.

Changing Laboratory Practice for Early Detection of a Fetal Inflammatory Response: A Contemporary Approach

Neonates born with the fetal inflammatory response (FIR) are at risk of complications such as early-onset neonatal sepsis, meningitis, and pneumonia. Providing an early histopathological diagnosis of FIR is important to guide management but can be a challenge in busy laboratories. This is a retrospective cross-sectional study over a four-month duration recruiting all placental cases with histological chorioamnionitis in our institution. The diagnostic performance of the umbilical cord (UC) section in identifying FIR, relative to the corresponding subsequent placental sections, was assessed. Clinical predictors of umbilical cord FIR were also investigated. A total of 390 UC sections were analyzed, of which 206 (52.8%) were found positive for FIR: 111 cases (53.9%) stage 1, 87 (42.2%) stage 2, and 8 (3.9%) stage 3. Our data revealed a good diagnostic sensitivity, specificity, positive predictive value, and accuracy of 76.2% (95%CI: 68.6-82.7%), 82.4% (95%CI: 65.5-93.2%), 95.0% (95%CI: 90.2-97.6%), and 77.3% (95%CI: 70.6-83.1%) respectively, in cases when clinical chorioamnionitis, fever and/or prolonged rupture of membrane (PROM) were suspected, with the area under the curve of 0.793. A maternal inflammatory response (MIR) was correlated with FIR (p < 0.001). Multivariate logistic regression analysis indicated that the higher the gestational age, clinical suspicion of chorioamnionitis, fever, and/or PROM, and the higher the stage of MIR significantly increased the odds of FIR (p < 0.001). UC section diagnosis of FIR is reasonably accurate in cases with clinical chorioamnionitis, fever, and/or PROM. Changing current laboratory practice to rapid processing of UC ahead of the rest of the other placental sections can be recommended in busy pathology departments.

Antibiotic-induced depletion of Clostridium species increases the risk of secondary fungal infections in preterm infants

Preterm infants or those with low birth weight are highly susceptible to invasive fungal disease (IFD) and other microbial or viral infection due to immaturity of their immune system. Antibiotics are routinely administered in these vulnerable infants in treatment of sepsis and other infectious diseases, which might cause perturbation of gut microbiome and hence development of IFD. In this study, we compared clinical characteristics of fungal infection after antibiotic treatment in preterm infants. As determined by 16S rRNA sequencing, compared with non-IFD patients with or without antibiotics treatment, Clostridium species in the intestinal tracts of patients with IFD were almost completely eliminated, and Enterococcus were increased. We established a rat model of IFD by intraperitoneal inoculation of C. albicans in rats pretreated with meropenem and vancomycin. After pretreatment with antibiotics, the intestinal microbiomes of rats infected with C. albicans were disordered, as characterized by an increase of proinflammatory conditional pathogens and a sharp decrease of Clostridium species and Bacteroides. Immunofluorescence analysis showed that C. albicans-infected rats pretreated with antibiotics were deficient in IgA and IL10, while the number of Pro-inflammatory CD11c⁺ macrophages was increased. In conclusion, excessive use of antibiotics promoted the imbalance of intestinal microbiome, especially sharp decreases of short-chain fatty acids (SCFA)-producing Clostridium species, which exacerbated the symptoms of IFD, potentially through decreased mucosal immunomodulatory molecules. Our results suggest that inappropriate use of broad-spectrum antibiotics may promote the colonization of invasive fungi. The results of this study provide new insights into the prevention of IFD in preterm infants.

Prevention of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is considered to be one of the most devastating intestinal diseases seen in neonatal intensive care. Measures to treat NEC are often too late, and we need effective preventative measures to alleviate the burden of this disease. The purpose of this review is to summarize currently used measures, and those showing future promise for prevention.

Neonatal multidrug-resistant gram-negative infection: epidemiology, mechanisms of resistance, and management

Infants admitted to the neonatal intensive care unit, particularly those born preterm, are at high risk for infection due to the combination of an immature immune system, prolonged hospitalization, and frequent use of invasive devices. Emerging evidence suggests that multidrug-resistant gram-negative (MDR-GN) infections are increasing in neonatal settings, which directly threatens recent and ongoing advances in contemporary neonatal care. A rising prevalence of antibiotic resistance among common neonatal pathogens compounds the challenge of optimal management of suspected and confirmed neonatal infection. We review the epidemiology of MDR-GN infections in neonates in the United States and internationally, with a focus on extended-spectrum β-lactamase (ESBL)-producing Enterobacterales and carbapenem-resistant Enterobacterales (CRE). We include published single-center studies, neonatal collaborative reports, and national surveillance data. Risk factors for and mechanisms of resistance are discussed. In addition, we discuss current recommendations for empiric antibiotic therapy for suspected infections, as well as definitive treatment options for key MDR organisms. Finally, we review best practices for prevention and identify current knowledge gaps and areas for future research. IMPACT: Surveillance and prevention of MDR-GN infections is a pediatric research priority. A rising prevalence of MDR-GN neonatal infections, specifically ESBL-producing Enterobacterales and CRE, compounds the challenge of optimal management of suspected and confirmed neonatal infection. Future studies are needed to understand the impacts of MDR-GN infection on neonatal morbidity and mortality, and studies of current and novel antibiotic therapies should include a focus on the pharmacokinetics of such agents among neonates.

Evaluating the Incidence of Sepsis Post-Central Catheter Removal When Using Prophylactic Vancomycin in the Neonatal Intensive Care Unit

OBJECTIVE

With no consensus, the practice of using prophylactic antibiotics prior to central venous catheter (CVC) removal in NICU patients remains controversial. The objective of this study was to compare the incidence of sepsis post-CVC removal in those who received a dose of vancomycin prophylactically with those who did not.

METHODS

This single-center, retrospective chart review included NICU patients who had CVCs removed. Patients were excluded if they had a confirmed or suspected infection at the time of CVC removal or if the indwelling CVC was removed prior to 30 days from insertion. Primary outcome was the occurrence of a sepsis evaluation within 72 hours from CVC removal. Secondary outcomes included the development of acute kidney injury, source and identification of positive cultures, time to onset of suspected or confirmed sepsis, and the appropriate administration of intravenous vancomycin.

RESULTS

Eighty-two CVC removals received prophylactic vancomycin (P-VAN), and 22 CVCs did not receive prophylactic vancomycin (NP-VAN) prior to CVC removal. There were no significant differences in patient demographics between groups and median duration of indwelling CVC. Two clinical sepsis evaluations occurred in the P-VAN group compared with none in the NP-VAN group. Of all the P-VAN CVC removals, 45 (55%) received vancomycin appropriately. There were no statistical differences in all evaluated secondary outcomes.

CONCLUSIONS

Vancomycin administered prophylactically prior to CVC removal did not reduce the number of subsequent clinical sepsis evaluations or infections in NICU patients.

Impact of Probiotic B. infantis EVC001 Feeding in Premature Infants on the Gut Microbiome, Nosocomially Acquired Antibiotic Resistance, and Enteric Inflammation

Background: Preterm birth is a major determinant of neonatal survival and morbidity, but the gut microbiome and associated enteric inflammation are also key factors in neonatal development and the risk of associated morbidities. We prospectively and longitudinally followed two cohorts of preterm infants, one of which was fed activated Bifidobacterium longum subsp. infantis (B. infantis) EVC001 8 × 109 CFU daily, and the other was not fed a probiotic. Hospital feeding protocol assigned all infants born at <1500 g and/or < 32 weeks corrected gestational age to the probiotic feeding protocol, whereas infants born at >1500 g and/or >32 weeks corrected gestational age were not fed a probiotic. Fecal samples were opportunistically collected from 77 infants throughout the hospital stay, and subjected to shotgun metagenomic sequencing and quantification of enteric inflammation. De-identified metadata was collected from patient medical records. Results: The gut microbiome of preterm infants was typified by a high abundance of Enterobacteriaceae and/or Staphylococcaceae, and multivariate modeling identified the probiotic intervention, rather than degree of prematurity, day of life, or other clinical interventions, as the primary source of change in the gut microbiome. Among infants fed B. infantis EVC001, a high abundance of total Bifidobacteriaceae developed rapidly, the majority of which was B. infantis confirmed via subspecies-specific qPCR. Associated with this higher abundance of Bifidobacteriaceae, we found increased functional capacity for utilization of human milk oligosaccharides (HMOs), as well as reduced abundance of antibiotic resistance genes (ARGs) and the taxa that harbored them. Importantly, we found that infants fed B. infantis EVC001 exhibited diminished enteric inflammation, even when other clinical variables were accounted for using multivariate modeling. Conclusion: These results provide an important observational background for probiotic use in a NICU setting, and describe the clinical, physiological, and microbiome-associated improvements in preterm infants associated with B. infantis EVC001 feeding.

Metrics of neonatal antibiotic use

Responsible use of antibiotics is critical to preserve their effectiveness and to minimize adverse outcomes associated with overuse and misuse. Newborn infants are a unique population with high rates of antibiotic exposure. In order to improve neonatal antibiotic use, accurate and meaningful metrics are required. In this review, we highlight and compare existing antibiotic use metrics in detail, including definitions, current applications, advantages, and limitations of each metric, with a focus on applicability to neonatal populations. We explore future directions for identification of accurate and meaningful metrics that will allow hospitals and stakeholders to pinpoint antibiotic utilization practices that should be emulated or avoided, and ultimately improve the safety and quality of neonatal care.

The ongoing challenge of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis in Europe: an epidemiological analysis of bloodstream infections

Vancomycin-resistant enterococci infections are of great public health significance due to limited therapeutic options. We investigated epidemiological trends and risk factors of vancomycin resistance in enterococci isolates from patients with bloodstream infections in the EU/EEA from 2012 to 2018. Routine vancomycin susceptibility data of clinical E. faecium (n = 67,022) and E. faecalis (n = 103,112) blood isolates from the European Antimicrobial Resistance Surveillance Network were analysed using descriptive statistics and multivariable regression analyses. In Europe, proportions of vancomycin-resistant E. faecium (VREFm) increased from 8.1% (95%CI 6.7-9.7%) in 2012 to 19.0% (95%CI 16.8-21.5%) in 2018. Rising VREFm proportions were observed across all European regions, both genders and all age groups except children and adolescents (1-19 years). Adults (20-59 years) and elderly (≥60 years) had an increased likelihood of VREFm compared to children and adolescents (1-19 years) (OR: 1.99 [95%CI 1.42-2.79, p < 0.001] and OR: 1.56 [95%CI 1.09-2.23, p = 0.014], respectively). Inpatients hospital units, including internal medicine and ICUs, were associated with an increased likelihood of VREFm (OR: 2.29 (95%CI 1.58-3.32, p < 0.001) compared to the emergency department which reflects patients with community origin of E. faecium infections. The mean proportion of vancomycin-resistant E. faecalis in Europe was found to be low (1.1% [95%CI 0.9-1.4%]). Local and regional authorities should intensify efforts directed at diagnostic and antimicrobial stewardship for vancomycin and all last resort drugs for the management of VREFm, particularly for hospitalized elderly patients.

Review of Drug Utilization Studies in Neonatal Units: A Global Perspective

Rational prescribing is challenging in neonatology. Drug utilization studies help identify and define the problem. We performed a review of the literature on drug use in neonatal units and describe global variations. We searched databases (EMBASE, CINAHL and Medline) from inception to July 2020, screened studies and extracted relevant data (two reviewers). The search revealed 573 studies of which 84 were included. India (n = 14) and the USA (n = 13) reported the most. Data collection was prospective (n = 56) and retrospective (n = 26), mostly (n = 52) from one center only. Sixty studies described general drug use in 34 to 450,386 infants (median (IQR) 190 (91-767)) over a median (IQR) of 6 (3-18) months. Of the participants, 20-87% were preterm. The mean number of drugs per infant (range 11.1 to 1.7, pooled mean (SD) 4 (2.4)) was high with some reporting very high burden (≥30 drugs per infant in 8 studies). This was not associated with the proportion of preterm infants included. Antibiotics were the most frequently used drug. Drug use patterns were generally uniform with some variation in antibiotic use and more use of phenobarbitone in Asia. This study provides a global perspective on drug utilization in neonates and highlights the need for better quality information to assess rational prescribing.

Early Bacterial Colonization and Antibiotic Resistance Gene Acquisition in Newborns

Several studies have recently identified the main factors contributing to the bacterial colonization of newborns and the dynamics of the infant microbiome development. However, most of these studies address large time periods of weeks or months after birth, thereby missing on important aspects of the early microbiome maturation, such as the acquisition of antibiotic resistance determinants during postpartum hospitalization. The pioneer bacterial colonization and the extent of its associated antibiotic resistance gene (ARG) dissemination during this early phase of life are largely unknown. Studies addressing resistant bacteria or ARGs in neonates often focus only on the presence of particular bacteria or genes from a specific group of antibiotics. In the present study, we investigated the gut-, the oral-, and the skin-microbiota of neonates within the first 72 h after birth using 16S rDNA sequencing approaches. In addition, we screened the neonates and their mothers for the presence of 20 different ARGs by directed TaqMan qPCR assays. The taxonomic analysis of the newborn samples revealed an important shift of the microbiota during the first 72 h after birth, showing a clear site-specific colonization pattern in this very early time frame. Moreover, we report a substantial acquisition of ARGs during postpartum hospitalization, with a very high incidence of macrolide resistance determinants and mecA detection across different body sites of the newborns. This study highlights the importance of antibiotic resistance determinant dissemination in neonates during hospitalization, and the need to investigate the implication of the mothers and the hospital environment as potential sources of ARGs.

Antibiotics and their alternatives in Artificial Breeding in livestock

Antibiotics are mandatory components of semen extenders for the control of bacterial contamination and growth. The increasing rate of worldwide resistance to conventional antibiotics in semen preservation media requires the development of new antimicrobial alternatives. This review provides an update on this topic and also highlights the improvement of hygiene in Artificial Insemination centers in order to prevent the development of bacterial resistance. Ideas are shared on future diagnostic tools for bacterial contamination in Artificial Breeding. Finally, new methods to remove or reduce bacteria in semen will be discussed.

Impact of hygiene on bacterial contamination in extended boar semen: An eight-year retrospective study of 28 European AI centers

Antibiotic agents such as gentamicin represent essential components of semen extenders in order to reduce bacterial contamination. But antibiotic resistance increases and AI centers start utilizing antibiotic agents which are more potent. Therefore, a shift to preventing bacterial contamination has to take place. In this study, we could demonstrate that hygiene is a tool capable of reducing bacterial load. In order to analyze 1434 extended semen samples and nine specially established hygienic critical control points (HCCPs, n = 828), 92 quality control audits have been carried out in a time period from 2012 until 2019 in 28 European AI centers. The results show the process of introducing a basic hygienic standard in audit 1 (2012/2013) and 2 (2014/2015) and the resulting achievements by means of improved hygienic conditions in audit 3 (2016/2017) and 4 (2018/2019). Within the scope of audit 1, 19% of the semen samples were contaminated with bacteria (cutoff ≥100 colony-forming units/mL). Audit 2 showed a bacterial load of 13.6% whereas during audit 3 and 4 very low bacterial contamination rates were recorded (4.5 and 5.5%, respectively). In the same manner, analysis of hygiene at different CCPs during semen production showed a decrease in all average HCCP-scores (score 1-6) comparing audit 4 to 1. By regression analysis we could show a significant audit-dependent association of the bacterial contamination in semen samples and hygiene of HCCPs. Furthermore, analysis of the odds ratio (OR) reveals that the bacterial contamination of certain HCCPs poses an increased risk of receiving bacterially contaminated semen samples (filling machine: OR = 3.02, P = 0.06; extender: OR = 8.97, P < 0.001; inner face of dilution tank lids: OR = 3.14, P = 0.09). Around 60% of the variance of the bacterial contamination in semen samples could be explained by hygienic conditions at different control points and their interaction with audit period and AI center. Antimicrobial agents are essential to protect human and animal health but excessive or inappropriate use can lead to the emergence of resistant bacteria. As shown in our study, hygiene management can significantly reduce bacterial contamination and is therefore capable of preventing antibiotic resistance.