Lactiplantibacillus sp. LH01 as an Adjuvant to Reduce Antibiotic Use in Recurrent Urinary Tract Infections in a Paediatric Patient with Hydronephrosis

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Lactiplantibacillus sp. LH01 may be used as an adjuvant to reduce antibiotic use in paediatric patients with recurrent urinary tract infections, thereby helping to prevent antimicrobial resistance.

Abstract

Background: Urinary tract infections (UTIs) represent a significant public health concern, particularly in children with structural abnormalities such as vesicoureteric reflux. Prolonged antibiotic exposure in these patients often contributes to the emergence of multidrug-resistant organisms and restricts therapeutic options. Probiotics have emerged as a potential adjuvant strategy to reduce infection recurrence. Case Presentation: A female infant born at term (38.6 weeks), with a prenatal diagnosis of bilateral hydronephrosis, experienced recurrent UTIs from the neonatal period despite both prophylactic and therapeutic antibiotic regimens. Serial urine cultures revealed infections caused by extended-spectrum beta-lactamase (ESBL)-producing E. coli and K. pneumoniae. Methods: The isolated strains were evaluated in vitro against Lactiplantibacillus sp. LH01, a probiotic strain derived from human milk. Following confirmation of its antimicrobial activity, an individualised intervention was initiated: daily oral administration of 1 mL of the probiotic (10⁹ CFU/mL) for one month, under medical supervision and without concurrent antibiotic therapy. Results: The probiotic demonstrated 89% inhibition efficiency against multidrug-resistant strains, accompanied by a notable reduction in UTIs frequency. Follow-up cultures showed reduced pathogen growth and a loss of the ESBL phenotype, facilitating clinical management and allowing previously contraindicated surgical interventions. Conclusions: Lactiplantibacillus sp. LH01 proved a safe and effective adjuvant in managing recurrent, resistant UTIs in a paediatric patient, highlighting the promise of probiotic therapies.

1. Introduction

Urinary tract infections (UTIs) represent one of the leading health concerns in the paediatric population, occurring more frequently in infants and female children. In Mexico, UTIs rank among the three most common infectious diseases, following respiratory and gastrointestinal infections [1]. Their prevalence varies according to age and sex: in neonates, bacteriuria is observed in approximately 1% of cases; in preschool-aged girls, the reported prevalence ranges from 2% to 3%, while in school-aged children, it is around 1.2%, often presenting asymptomatically [2].

Globally, between 8% and 10% of female children experience at least one episode of UTIs before the age of seven, with recurrence rates exceeding 30% following the initial episode [3].

In paediatric patients with congenital abnormalities of the urinary tract, such as hydronephrosis (HN), the predisposition to recurrent UTIs is significantly increased [4], leading to greater exposure to antibiotic therapies. Prolonged use of antibiotics poses additional risks, including the development of bacterial resistance, dysbiosis, and both short- and long-term adverse effects.

Given this issue, the pursuit of complementary strategies to reduce antibiotic dependency is of critical importance. From both medical and biotechnological perspectives, probiotics, particularly Lactiplantibacillus plantarum, have demonstrated potential as an alternative approach for the prevention and mitigation of symptoms associated with UTIs, including the reduction of febrile episodes [5]. Moreover, this probiotic species has been shown to attenuate inflammatory and oxidative stress in metabolic disorders [6]. Its use has emerged as a viable option for enhancing the urogenital microbiota and reducing the recurrence of UTIs.

The present case report describes the use of Lactiplantibacillus sp. LH01 (L. plantarum LH01), a microorganism isolated from human milk, as an adjuvant therapy in a paediatric patient with HN, assessing its impact on reducing antibiotic usage and the frequency of infectious episodes.

2. Materials and Methods

2.1. Patient Description

This case involves a female patient born via caesarean section at the Hospital General de Occidente Zoquiapan in Guadalajara, Mexico, on 20 January 2021, at 38.6 weeks of gestation. At birth, her weight was 2710 g and length was 50 cm, with an APGAR score of 8 and a Silverman score of 0. She was the product of a well-monitored pregnancy, during which right-sided HN was diagnosed prenatally through ultrasonographic studies.

The patient was discharged in a stable condition; however, on the sixth day of life, she was admitted to the paediatric emergency department, specifically to the External Intensive Care Unit at the Hospital Civil “Juan I. Menchaca” (HCJIM) in Guadalajara, Mexico, with a diagnosis of urosepsis and asymptomatic severe hypoosmolar euvolaemic hyponatraemia. She was treated with a 10-day course of meropenem for a perinatally acquired infection caused by extended-spectrum β-lactamase-producing Escherichia coli (ESBL E. coli). Considering these findings, a voiding cystourethrogram was performed, which revealed no structural abnormalities in the pelvic bones, urethra, or bladder (Figure 1).

Subsequently, a diagnosis of bilateral HN with vesicoureteral reflux (VUR) was confirmed, according to the classification established by the International Reflux Study Committee [7]. Left-sided VUR was graded as stage IV, characterised by ureteral dilatation and tortuosity, as well as dilated renal pelvis and calyces, with preservation of the papillary impressions. The right side presented with grade V VUR, showing marked dilatation of the ureter and calyces, loss of normal calyceal configuration, and absence of papillary impressions (Figure 1).

This condition has had a significant impact on the patient’s health, with multiple episodes of pyelonephritis throughout her life caused by multidrug-resistant microorganisms. At four months of age, right distal ureterostomy was performed to relieve the obstruction and reduce the risk of recurrent infections. Subsequently, at 18 months, a right ureteral reimplantation was carried out, and two months later, the double J stent was removed due to recurrent UTIs. At the age of four, to correct the bilateral VUR, bilateral ureteral reimplantation was performed using the Cohen technique. One month later, both double-J stents were removed with the standard protocol.

2.2. Previous Interventions

During the neonatal period, the patient received multiple antimicrobial regimens in response to clinical suspicions of sepsis and UTIs. These treatments were thoroughly reviewed in the electronic medical records of the Paediatrics Division, Nephrology Department, at the HCJIM. The first intervention occurred on the tenth day of life with meropenem, prescribed for a presumed prenatal urosepsis. This antibiotic was chosen due to its efficacy against ESBL-producing strains, its low neurotoxicity risk, and its limited gastrointestinal impact [8,9].

Subsequently, between February and March 2021, she underwent several empirical treatments combining ampicillin, amikacin, cefotaxime, and vancomycin, in response to persistent fever, thrombocytopenia, and elevated acute-phase reactants. In all cases, culture results were negative, and antibiotic therapy was discontinued following clinical improvement. Upon a new episode of suspected severe sepsis, treatment with meropenem and amikacin was reinitiated, which was again discontinued after clinical stabilisation and microbiological negativity.

These interventions reflect repeated exposure to broad-spectrum antibiotics during a critical window for immunological development and microbiota establishment.

Table 1. Antibiotic therapy and clinical progression during the neonatal period.

Date	Antibiotic(s)	Duration (Days)	Indication	Clinical Evolution and Observations
30 January 2021	Meropenem	10	Prenatal origin urosepsis caused by ESBL E. coli.	Clinical control of infection; good drug tolerance.
22 February 2021	Ampicillin + Amikacin	7	Neonatal fever, suspected sepsis.	Favourable evolution; negative blood cultures.
4 March 2021	Cefotaxime + Vancomycin	6	Persistent fever, thrombocytopenia, elevated inflammatory markers.	No bacterial growth in cultures; regimen discontinued.
10 March 2021	Meropenem + Amikacin	8	Suspected severe sepsis.	Clinical improvement and negative microbiological results.

provides a chronological summary of the patient’s clinical course and administered antibiotic treatments to facilitate comprehensive interpretation and support the rationale for considering L. plantarum LH01 as an adjunctive therapy.

2.3. Isolation and Identification of L. plantarum LH01

The L. plantarum LH01 strain (Figure 2b) used in this intervention was isolated from a human milk sample at the Human Milk Research Laboratory of the University Center of Exact Sciences and Engineering, Universidad de Guadalajara (CUCEI/UDG). Genomic DNA was extracted using a protocol optimised for human milk samples [10].

To confirm the genus and species of the isolate, endpoint polymerase chain reaction (PCR) was performed [11] using specific primers (

Table 2. Primer pair information for Lactiplantibacillus plantarum, Limosilactobacillus fermentum, and Limosilactobacillus reuteri.

Species	Target Gene	Primer	Sequence (5′–3′)	Product Size (bp)
L. plantarum	Unique gene	plantarum-F	GCT GGC AAT GCC ATC GTG CT	147
		plantarum-R	TCT CAA CGG TTG CTG TAT CG
L. fermentum	Unique gene	fermentum-F	GAC CAG CGC ACC AAG TGA TA	129
		fermentum-R	AGC GTA GCG TTC GTG GTA AT
L. reuteri	16S–23S Unique region	reuteri-F	GAT TGA CGA TGG ATC ACC AGT	161
		reuteri-R	CAT CCC AGA GTG ATA GCC AA

) targeting DNA sequences characteristic of L. plantarum.

In this study, the amplification of genomic DNA (gDNA) from three Lactobacillus strains, L. plantarum, L. fermentum, and L. reuteri, was validated. Amplification was confirmed via agarose gel electrophoresis [11]. Figure 2a displays the results and the base pair comparison for each strain, highlighting the identification of L. plantarum in lane 3.

Once the microorganism was identified through genetic sequencing techniques, it was registered on 6 March 2025 in the microbial collection of the National Centre for Genetic Resources, under the registration number CM-CNRG1113 and the name L. plantarum LH01 (Figure 2b).

Figure 2a shows the agarose gel electrophoresis of PCR products obtained using two sets of primers. No bands were observed in lanes 1 and 2 for L. fermentum and L. reuteri, respectively. In contrast, L. plantarum LH01 (lane 3) exhibited a single band of the expected size, confirming its prior biochemical identification. The positive control amplified with universal V3–V4 primers (lane 4) produced the anticipated fragment, validating primer efficiency and reaction conditions. The raw human milk sample (lane 5) also yielded an amplicon of the predicted length. No amplification was detected in the no-template negative control (lane 6), ruling out reagent contamination.

2.4. Cultivation and Safety Assessment of L. plantarum LH01

L. plantarum LH01 was cultivated in MRS broth [12] under anaerobic conditions and incubated at 37 °C for 24 h to obtain cells in the exponential growth phase. The biomass was subsequently harvested by centrifugation and washed to remove residual culture medium. The final preparation consisted of 1 mL vials containing a concentration of 10⁹ CFU/mL, resuspended in 10% Nutraflora^® P-95 (Ingredion) as a prebiotic carrier [13], and stored at 4 °C for subsequent oral administration. Viability of the strain was monitored through weekly microbiological counts, showing no significant loss (<0.5 log CFU/mL) over a 30-day period.

The strain had previously been evaluated and classified as probiotic in accordance with international guidelines. It exhibited resistance to gastrointestinal conditions (gastric acidity and bile salts), adhesion to intestinal epithelial cells, antimicrobial activity against common pathogens, and immunomodulatory potential [14]. Safety was confirmed through the absence of haemolytic activity, toxin production, and antibiotic resistance genes. Clinical studies in preterm neonates have supported its efficacy in the prevention and management of gastrointestinal disorders and in promoting recovery during NICU hospitalisation [15].

2.5. Application of L. plantarum LH01 as an Adjuvant Strategy

Following the isolation of multidrug-resistant pathogenic bacteria via urine culture, in vitro assays were performed to assess the antimicrobial efficacy of L. plantarum LH01. Notably, antimicrobial activity was observed against the identified pathogens, with confirmed efficacy specifically against ESBL E. coli and Klebsiella pneumoniae (K. Pneumoniae).

Based on these findings, and after a comprehensive risk assessment conducted in collaboration with the Nephrology Department of HCJIM, an adjuvant ambulatory therapeutic intervention was implemented. The intervention involved the oral administration of 1 mL doses of L. plantarum LH01 at a concentration of 10⁹ CFU. This dosage, which proved effective in in vitro assays (

Table 3. Inhibition halo (mm) produced by L. plantarum LH01 against ESBL E. coli and K. pneumoniae.

Dose (µL) L. plantarum LH01	UFC/mL	ESBL E. coli Inhibition Zone (mm)	ESBL K. pneumonae Inhibition Zone (mm)
Control (carbenicillin)	20 mg/mL	0	0
50	104	8	7.5
100	106	12	7.8
200	109	16	8.5
300	1012	18	9.2

), was administered daily for 30 consecutive days, followed by a 5-day discontinuation period prior to the initiation of antibiotic therapy, with the aim of promoting pathogen suppression.

Six probiotic administrations were conducted at critical stages of the infection, as outlined in

Table 4. Clinical characterisation of infectious episodes and applied antibiotic therapies.

Date	Event/Infection	Isolated Bacteria	Antibiotic Therapy	Duration of Treatment (Days)
January 2021	Pyelonephritis	ESBL E. coli	Meropenem	10
February 2021	UTIs	Multidrug-resistant K. pneumoniae	Prophylactic nitrofurantoin	7
March 2021	UTIs	Resistant K. aerogenes	Nitrofurantoin	7
April 2021	Complicated recurrent UTIs	Serratia marcescens	Cefotaxime + Amikacin	6
June 2021	UTIs	ESBL E. coli	L. plantarum LH01	30
July 2021	UTIs	ESBL E. coli	Amikacin, Ciprofloxacin, prophylaxis	6
March 2022	Complicated acute pyelonephritis	ESBL E. coli	L. plantarum LH01	30
April 2022	Complicated acute pyelonephritis	ESBL E. coli	Ceftriaxone + Amikacin, de-escalation to Ciprofloxacin	7
January 2023	UTIs	ESBL E. coli	L. plantarum LH01	30
February 2023	UTIs	Multidrug-resistant K. pneumoniae	Ertapenem	7
February 2023	UTIs	E. coli	L. plantarum LH01	30
March 2024	Febrile episode, probable pyelonephritis	E. coli	Fosfomycin	10
July 2024	UTIs	E. coli	L. plantarum LH01	30
March 2025	UTIs	E. coli	Amikacin	10
March 2025	Maintenance therapy	No growth of pathogenic bacteria	L. plantarum LH01	30

, during which L. plantarum LH01 contributed to the control of UTIs. A final administration was carried out in the absence of active infection, as part of the follow-up and progressive management of the infectious condition.

2.6. Statistical Analysis

The efficacy of L. plantarum LH01 against ESBL E. coli and K. pneumoniae was assessed using non-parametric statistical methods, as the data did not follow a normal distribution (Shapiro–Wilk test). The Kruskal–Wallis test was applied to detect overall differences, followed by Dunn’s test with Bonferroni correction for multiple comparisons [16]. All analyses were performed using R (4.5.1) and RStudio (V. 2025.05.1 +513), Statgraphics Centurion 19^® (Statistical Graphics Corp., The Plains, VA, USA), and Microsoft Excel [17,18]. A p-value < 0.05 was considered statistically significant.

3. Results and Discussion

UTIs represent a significant therapeutic challenge, as prolonged antibiotic treatments can lead to the development of resistance, increase morbidity rates, and raise healthcare costs [19].

The patient, with a prenatal diagnosis of bilateral HN and VUR grade IV on the left side and grade V on the right, has experienced multiple recurrent episodes of UTIs, including cases of acute pyelonephritis, which have been managed with various antimicrobial regimens over time. Table 4 outlines the most relevant infectious episodes during her clinical course, including the identified aetiological agents and the corresponding antibiotic treatments administered in each case.

Several studies have identified E. coli, K. pneumoniae, Enterococcus faecalis, Proteus mirabilis, and Staphylococcus saprophyticus as the main pathogens involved in UTIs, with E. coli being the most common uropathogen, implicated in approximately 85–90% of paediatric cases [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20].

This epidemiological profile aligns with the patient’s case, who presented episodes of urosepsis with isolation of an ESBL E. coli, a multidrug-resistant microorganism capable of inactivating broad-spectrum cephalosporins and carbapenems [21]. The limited clinical response observed with conventional treatment regimens highlighted the complexity of managing such infections in vulnerable paediatric patients.

Probiotic therapies have been used as an adjunct in the treatment of infections caused by multidrug-resistant pathogens by helping to restore the microbiome and modulate the immune response [22]. L. plantarum is a lactic acid bacterium with proven clinical efficacy in recurrent UTIs and bacterial vaginosis [23]. This strain acts by adhering to epithelial cells, competing with pathogens, and producing short-chain fatty acids and bacteriocins that inhibit their growth [24].

3.1. In Vitro Evaluation of Antimicrobial Activity

Given the multidrug-resistant profile of the ESBL E. coli and K. pneumoniae strains isolated from the patient both exhibiting resistances to more than 50% of the antibiotics tested in urine cultures, in vitro assays were conducted to evaluate the inhibitory effect of L. plantarum LH01. The probiotic demonstrated a mean inhibition of 89.0% ± 1.63, indicating a remarkable ability to suppress bacterial growth.

Table 3 summarises the different concentrations of L. plantarum LH01 evaluated to determine its antimicrobial efficacy. Five conditions were examined: a negative control with carbenicillin (20 mg/mL), which produced no inhibition zones, and four increasing volumes of the probiotic.

A progressive increase in the diameter of the inhibition zones was observed, being more pronounced against ESBL E. coli, suggesting a higher sensitivity of this strain compared with K. pneumoniae. Based on these results, a concentration of 10⁹ CFU/mL was selected, in line with the doses recommended by the World Gastroenterology Organisation for the clinical use of probiotics [25].

These findings support the potential use of L. plantarum LH01 as an adjuvant therapy in paediatric patients with infections caused by multidrug-resistant bacteria, offering an alternative in the context of rising antimicrobial resistance.

3.2. In Vivo Evaluation

Based on the established therapeutic intervention, systematic clinical follow-up was conducted to evaluate the patient’s in vivo response to treatment. Infectious episodes were monitored (Table 4), along with the progression of clinical parameters and the need to initiate or adjust additional antimicrobial regimens. The primary objective was to determine the effectiveness of the administered probiotic in terms of reducing the frequency, duration, and severity of infectious episodes during the follow-up period.

Prior to the initiation of the first therapeutic regimen (June 2021), the patient presented with an acute infectious episode characterised by leucocytosis (12.64%), hyperkalaemia (5.20 mmol/L), and impaired renal function, with blood urea levels of 15.6 mg/dL and decreased creatinine at 0.15 mg/dL. Urinalysis revealed findings consistent with a urinary tract infection, including pH 7.0, haematuria, proteinuria, abundant bacteriuria, and altered macroscopic characteristics (amber-coloured, turbid urine with a foul odour).

To assess the antimicrobial potential of L. plantarum LH01 against multidrug-resistant uropathogens, susceptibility profiles from antibiograms collected between January 2021 and January 2025 were reviewed. Clinical isolates of ESBL E. coli were included, as well as K. pneumoniae, the latter identified during two acute episodes recorded in February 2021 and June 2023.

In both instances, pathogen eradication was achieved following a combined regimen consisting of oral administration of L. plantarum LH01 for 30 days, followed by treatment with prophylactic nitrofurantoin in the first episode and ertapenem in the second. No recurrences attributable to K. pneumoniae were documented following this intervention.

In contrast to the findings with K. pneumoniae, reinfections caused by ESBL E. coli persisted throughout the follow-up period, prompting a more rigorous comparative evaluation between treatments.

3.3. Statistical Analysis of the Inhibitory Response of the Probiotic and Antibiotics Used in the Patient

A post hoc analysis, presented in Figure 3, was conducted using Dunn’s test with correction for multiple comparisons. This analysis identified five homogeneous groups (a, ab, abc, bc, and c). Treatments sharing common letters do not show significant differences between them, as their medians overlap.

However, significant differences were observed between the extremes of the classification. Group c, composed exclusively of the probiotic L. plantarum LH01, exhibited a significantly higher efficacy compared with all other treatments, establishing it as the most effective in this study. In contrast, group a, represented by amoxicillin/clavulanic acid, showed the lowest inhibitory efficacy, with statistically significant differences when compared with the probiotic and other superior treatments.

These findings indicate that L. plantarum LH01 demonstrates superior efficacy compared with the conventional antimicrobials used in this case, suggesting its potential application as an adjuvant therapy in the management of recurrent UTIs caused by ESBL E. coli.

These results were also significantly associated with a reduction in antimicrobial resistance, evidenced by the restoration of sensitivity to six out of nine antibiotics administered to the patient during the follow-up period (

Table 5. Reduction of antimicrobial resistance in multidrug-resistant strains of E. coli and K. pneumoniae following administration of L. plantarum LH01.

Antibiogram
Antibiotic	E. coli					K. pneumoniae
	2021	2022	2023	2024	2025	2021	2022	2023
Amikacin	S	S	S	I	I	S	S	S
Amoxicillin/Clavulanic Acid	R	R	R	I	S	R	R	S
Ampicillin/Sulbactam	S	I	S	I	S	S	R	S
Ampicillin	R	R	S	R	S	R	R	R
Cefepime	R	R	S	S	S	S	R	S
Cefotaxime	R	R	S	I	I	S	R	S
Ceftazidime	R	R	S	S	S	S	R	S
Ceftriaxone	R	R	S	S	S	S	R	S
Oral Cefuroxime	R	R	S	S	S	S	S	S
Cefuroxime	R	R	S	S	S	S	R	S
Ciprofloxacin	S	S	R	I	S	S	S	S
Ertapenem	S	S	S	S	S	S	S	S
Gentamicin	S	R	S	S	R	S	R	S
Imipenem	S	S	S	S	S	S	S	S
Levofloxacin	R	R	R	I	I	S	S	S
Meropenem	S	S	S	S	S	S	S	S
Piperacillin/Tazobactam	S	S	S	S	S	I	I	S
Tetracycline	R	R	R	S	S	R	R	S
Tigecycline	S	I	I	S	S	S	S	S
Tobramycin	S	I	I	S	R	S	S	S
Trimethoprim/Sulfamethoxazole	R	R	S	R	R	S	R	S
Fosfomycin	R	R	S	S	S	R	R	R
Aztreonam	R	R	R	S	S	--	--	--
Cefoxitin	R	R	R	S	S	R	R	R
Cefazolin	R	R	R	I	S	--	--	--
Nitrofurantoin	S	S	I	I	S	R	R	R

S: susceptible, I: intermediate, R: resistant.

). This finding aligns with those of previous studies demonstrating the probiotic’s ability to modulate the immune system and exert anti-inflammatory and antimicrobial effects [23].

3.4. Nephrotoxicity Risk Assessment

In the paediatric setting, not all antibiotics are suitable due to physiological differences, pharmacokinetic variations, potential adverse effects, and the risk of bacterial resistance, all influencing antibiotic selection and dosing [26]. Amikacin, the most frequently used antibiotic in this case, showed only intermediate resistance (67.3% ± 6.1), despite prolonged exposure, suggesting that the probiotic mitigated resistance progression.

The use of potentially nephrotoxic agents such as amikacin in paediatric patients with renal conditions may be justified under strict renal function monitoring, with dose and interval adjustments based on creatinine levels [27,28]. The risk–benefit ratio is carefully evaluated, especially when high efficacy against multidrug-resistant bacteria is required. Therapeutic efficacy can be maintained, and toxicity minimised through individualised dosing, therapeutic drug monitoring [29,30], and concurrent adjuvant therapies such as probiotics, which may reduce bacterial load and the need for more aggressive treatments.

Nevertheless, risks include acute tubular injury, progressive renal function loss, and in severe cases, renal replacement therapy. Therefore, the use of these agents must be supported by close monitoring and sound clinical criteria [31].

3.5. Evaluation of Inhibitory Effects of Probiotics and Conventional Antibiotics Against ESBL E. coli

In addition to the analysis focused on antibiotics frequently used in the patient, other antimicrobials included in the susceptibility profile were also considered, as shown in Figure 4. To facilitate the analysis of the probiotic therapy effect over time, antibiotics were grouped according to their mechanism of action: cell wall inhibitors (β-lactams), penicillins, carbapenems, protein synthesis inhibitors, and agents with other mechanisms of action.

The data were statistically analysed using the Kruskal–Wallis and Dunn tests for non-parametric data, assessing differences in antimicrobial efficacy ranks. The probiotic demonstrated a mean inhibitory efficacy of 89.0% ± 1.63, significantly higher than that observed for all β-lactam antibiotics (p < 0.0001; 95% CI). Within this group, oral cefazolin (27.05% ± 9.7) and parenteral cefuroxime (18.64% ± 4.12) showed the lowest activity against multidrug-resistant strains.

Within the penicillin group, the probiotic also demonstrated statistically significant differences (p < 0.0001; 95% CI) compared with amoxicillin/clavulanic acid, ampicillin, and ampicillin/sulbactam. However, the combination of piperacillin with tazobactam achieved efficacy comparable to that of the probiotic (91.45% ± 1.69).

Although piperacillin/tazobactam demonstrates high efficacy against ESBL E. coli, its use in paediatric patients with bilateral HN is limited due to the risk of nephrotoxicity. Therefore, it is essential to calculate creatinine clearance prior to initiating therapy and to closely monitor serum urea, creatinine, and electrolytes [32].

Additionally, the administration regimen requires a high loading dose followed by a reduction in dosing frequency, with the route of administration initiated intravenously. Given that treatment may extend up to 14 days, its use is reserved for patients with severe infections, representing a second-line therapeutic alternative in such cases [33].

In the carbapenem group, no statistically significant differences were observed, as both the probiotic and meropenem, imipenem, and ertapenem achieved ≥89% efficacy. Despite this similarity in effectiveness, the use of carbapenems must be carefully considered in patients at risk of renal impairment, such as those with bilateral HN and pyelonephritis, due to their potential nephrotoxicity [34].

Conversely, although the probiotic exhibited a comparable effect, its action was slower. This suggests that a combined therapeutic strategy, initiating treatment with antibiotics for rapid infection control followed by probiotics to consolidate the effect, could be a safe and effective option in these cases.

Within the protein synthesis inhibitor group, the probiotic L. plantarum LH01 demonstrated significantly superior efficacy compared with the antibiotics analysed, with statistically significant differences (p < 0.0001; 95% CI). Notably, amikacin—one of the most frequently used antibiotics in the patient—showed an efficacy of only 67% ± 6.1. However, when combined with the probiotic, a progressive reduction in infection was observed, accompanied by a decrease in the frequency of febrile episodes, ultimately resulting in the patient remaining asymptomatic. These findings suggest that combining antibiotics with probiotics could represent a less aggressive therapeutic strategy for treating UTIs in patients with HN.

In the group classified as “others,” the probiotic L. plantarum LH01 demonstrated significantly higher efficacy against ESBL E. coli compared to trimethoprim-sulfamethoxazole, levofloxacin, and fosfomycin (p < 0.0001; 95% CI). In contrast, no statistically significant differences were observed compared with nitrofurantoin (70.45% ± 6.8) or ciprofloxacin (65% ± 7.35), both of which exhibited moderate inhibition against the tested strain.

However, the use of nitrofurantoin and ciprofloxacin in paediatric patients with HN and pyelonephritis presents significant clinical limitations. Nitrofurantoin, while effective for uncomplicated lower UTIs, achieves therapeutic concentrations only in the bladder, making it unsuitable for treating upper UTIs. Furthermore, in cases of impaired renal function, its excretion may be compromised, increasing the risk of toxicity [35].

Ciprofloxacin use in paediatrics is restricted due to the risk of fluoroquinolone-induced arthropathy, which can affect the growth cartilage [36]. Additionally, renal elimination may be altered in patients with HN, potentially raising plasma concentrations and increasing the risk of neurological, gastrointestinal, and renal toxicity. For these reasons, its use should be reserved for specific situations where no safer therapeutic alternatives exist [37].

The results highlight the efficacy of the probiotic against antimicrobials, particularly those less effective against resistant strains. Its action, comparable to that of carbapenems, indicates significant potential as an adjuvant in managing multidrug-resistant pathogens, which is crucial in paediatrics to preserve the microbiota and reduce adverse effects.

Combining antibiotics for initial infection control with probiotics such as L. plantarum LH01 could represent an innovative strategy that enhances antimicrobial action, reduces recurrence, and minimises side effects associated with prolonged treatment.

Together, these findings open new possibilities for the development of safer and more effective integrated therapies. However, further studies involving controlled clinical models and diverse paediatric populations are needed to validate these effects and establish standardised therapeutic protocols.

3.6. Phenotypic Modulation of Resistance in Gram-Negative Bacilli

Since 2024, the loss of the ESBL phenotype in E. coli strains has been observed (Table 5), as reflected in antibiograms by the restored susceptibility to third-generation cephalosporins (cefotaxime, ceftazidime, and ceftriaxone) and aztreonam, in the absence of cross-resistance. This phenotypic change suggests a possible interference of the probiotic L. plantarum LH01 with resistance mechanisms, either through competitive exclusion, inhibition of ESBL-encoding plasmids, or epigenetic modulation of bacterial gene expression [38].

In parallel, K. pneumoniae showed a significant reduction in its multidrug-resistant profile, decreasing from 14 to only 3 antibiotics to which it exhibited resistance [39,40]. These findings support the hypothesis of L. plantarum LH01 as an effective adjuvant therapy in the management of UTIs caused by multidrug-resistant Gram-negative bacilli. The persistence of certain resistance mechanisms highlights the need for ongoing microbiological surveillance, particularly given the clinical risks associated with ESBL and carbapenemase producing strains.

3.7. Clinical Findings in the Patient

The patient showed favourable clinical progression, with gradual improvement attributed to effective control of the UTIs. By 2023, the reduction in antimicrobial resistance of the isolated pathogens demonstrated a significant impact, correlating with the absence of febrile episodes and a decrease in symptomatic UTIs. Urinalysis reflected more favourable parameters: reduced turbidity, normalization of colour and odour, as well as a decrease in bacterial load from abundant to moderate.

At two and a half years of age, the patient remained clinically stable, with biochemical parameters within normal ranges: leucocytosis at 9%, procalcitonin at 0.0790 ng/mL, and urea at 36.38 mg/dL. Despite the persistence of abundant bacteria, positive nitrites, mild haematuria, and the presence of ESBL E. coli and K. pneumoniae, creatinine levels remained low (0.19 mg/dL). This improvement enabled the performance of right ureteral reimplantation surgery, highlighting the pivotal role of adjuvant therapy with L. plantarum LH01 as a therapeutic alternative for clinical improvement.

4. Conclusions

This clinical case highlights the therapeutic potential of L. plantarum LH01 as an adjuvant in managing antimicrobial resistance. Its administration demonstrated an efficacy of 89% ± 1.63 against extended-spectrum β-lactamase ESBL Escherichia coli and 64% ± 2.42 against Klebsiella pneumoniae. Furthermore, the results suggest modulation of the pathogenicity of these pathogens, leading to tangible clinical benefits and facilitating control of recurrent UTIs in a paediatric patient with bilateral HN.

A significant reduction in the antibiotic resistance profiles of both bacteria was documented: in K. pneumoniae, resistance decreased from 14 to 3 antibiotics (out of 24 evaluated), and in ESBL E. coli, from 15 to 3 (out of 26 evaluated), alongside the loss of the ESBL phenotype.

Notably, the probiotic’s effect was comparable to that of carbapenem antibiotics, achieving similar bacterial inhibition without the adverse effects associated with these broad-spectrum drugs.

L. plantarum LH01, isolated from human milk, emerges as a safe and viable therapeutic alternative in the paediatric clinical setting. These findings open new avenues for investigating its mechanisms of action and applicability in other clinical contexts.