Sensitivities of Cefixime, Ceftriaxone and Sulfamethoxazole/Trimethoprim in SPICE-HaM-Associated Urinary Tract Infections in Children

Abstract

Background/Objectives: Third-generation cephalosporins are used to treat many infections, including urinary tract infections. Despite the risk of inducing resistance in SPICE-HaM microorganisms (Serratia, Providencia, indole-positive Proteus, Citrobacter freundii complex, Enterobacter cloacae complex, Klebsiella aerogenes, Hafnia alvei and Morganella morganii), a group of microorganisms with inducible beta-lactamase potentials, guidelines still recommend treating uncomplicated cystitis with third-generation cephalosporins. To improve outpatient pediatric antimicrobial practice, this study aimed to develop a five-year pediatric cumulative antimicrobial susceptibility testing report for SPICE-HaM microorganisms in urine and compare the in vitro sensitivity of cefixime/ceftriaxone with sulfamethoxazole/trimethoprim. Methods: Over 300 pediatric SPICE-HaM urine isolates, processed at regional microbiology laboratories of LifeLabs British Columbia between 2020 and 2024, were analyzed. Results: Compared to cefixime, sulfamethoxazole/trimethoprim demonstrated higher sensitivity against Citrobacter freundii complex (65% versus 95%, p < 0.05, n = 57), Enterobacter cloacae complex (49% versus 92%, p < 0.05, n = 89), and Morganella morganii (68% versus 92%, p < 0.05, n = 76). Compared to ceftriaxone, sulfamethoxazole/trimethoprim failed to show significantly different sensitivities for the SPICE-HaM microorganisms. Conclusions: Sulfamethoxazole/trimethoprim is possibly a more favourable oral agent for SPICE-HaM-associated urinary tract infections in the local pediatric community population compared to cefixime, a third-generation cephalosporin. However, compared to ceftriaxone, sulfamethoxazole/trimethoprim appears to have similar efficacy for SPICE-HaM-associated urinary tract infections.

1. Introduction

Citrobacter freundii complex, Enterobacter cloacae complex, Hafnia alvei, Klebsiella (previously Enterobacter) aerogenes, Morganella morganii, Proteus vulgaris, Providencia rettgeri, and Serratia marcescens are traditionally referred to as SPICE-HaM microorganisms [1,2,3]. They are Gram-negative bacilli that can inhibit the antimicrobial activity of certain antibiotics by producing AmpC β-lactamases [3]. Agents such as ceftriaxone can induce ampC expression, leading to cephalosporin resistance in approximately 20% of SPICE-HaM-related infections [3,4]. Due to inducible resistance, broad-spectrum third-generation cephalosporins are generally not recommended for SPICE-HaM infections, especially those caused by Citrobacter freundii complex, Enterobacter cloacae complex, and Klebsiella (previously Enterobacter) aerogenes, as treatment failure can still occur due to inducible resistance [5]. Therefore, at LifeLabs British Columbia (BC), Canada, sensitivity results for third-generation cephalosporins are not reported for SPICE-HaM microorganisms, even if the in vitro results indicate susceptibility. However, third-generation cephalosporins, such as cefixime and ceftriaxone, are recommended as one empiric treatment option for febrile urinary tract infections (UTIs) or uncomplicated cystitis, despite the risk of developing SPICE-HaM-related resistance [3,5,6]. For instance, according to the Canadian Paediatric Society (CPS), cefixime is recommended and commonly used for febrile UTIs [6]. The Infectious Diseases Society of America (IDSA) advises that ceftriaxone is a reasonable option for uncomplicated cystitis secondary to SPICE-HaM if in vitro susceptibility is shown [3]. This raised a controversy about whether laboratories should report the sensitivity results for third-generation cephalosporins among SPICE-HaM microorganisms in urine cultures.

UTI is common in children, with prevalence depending on factors such as gender, age, race, sexual activity, circumcision status, and comorbidities [3]. Complications of UTI can be serious, including dehydration, electrolyte abnormalities, sepsis, and renal scarring, potentially leading to end-stage renal disease [7,8]. Although around 80% of pediatric UTIs are caused by Escherichia coli, species such as Klebsiella, Proteus, Enterobacter, and Enterococcus are still common uropathogens [9]. As suggested by the Canadian Paediatric Society, local age-specific antibiograms are valuable for tracking local resistance patterns and supporting antimicrobial stewardship [10]. Antibiograms help practitioners choose appropriate empirical antibiotics to reserve broad-spectrum antibiotics and minimize step-down from broad-spectrum antibiotics to ineffective therapies [10].

This study aimed to develop a cumulative antimicrobial susceptibility testing (cAST) report for SPICE-HaM microorganisms in the community pediatric population of the province of BC, Canada, in 2020–2024. The study compared the sensitivity of commonly recommended antimicrobials, sulfamethoxazole/trimethoprim (SMX-TMP) and third-generation cephalosporins (cefixime and ceftriaxone), to analyze the potential role of third-generation cephalosporins in UTIs for pediatric patients.

2. Materials and Methods

2.1. Data Collection

This retrospective analysis was performed on finalized antimicrobial susceptibility results of urine cultures from LifeLabs BC from 2020 to 2024. The culture results were from patients under 18 years old, regardless of gender. The Microbiology Electronic Worksheet System (MEWS; Version 5.00.267; LifeLabs, Toronto, ON, Canada) was used to retrieve the data from specimens collected from 129 collection centres in rural and urban communities of BC, Canada. Only diagnostic isolates and initial isolation culture results were included. The ordering clinicians determined the test indications for urine cultures.

2.2. Identification of Microorganisms in Samples

Our methods were adapted from a previous publication [11]. Urine samples were processed as routine specimens if they were collected via midstream, catheter, pedi-bag, suprapubic catheter, ileal conduit, bladder stoma, nephrostomy bag, or if they were not specifically labelled. As per the Urine Culture Procedure from LifeLabs BC, a 0.001 mL loop of each routine urine specimen was cultured on BBL^TM CHROMagar^TM plates (Becton, Dickinson and Company, Sparks, MD, USA) and incubated at 35 °C under aerobic conditions for 18 h. The CHROMagar orientation medium facilitated the isolation of microorganisms for improved inspection and differentiation. Special samples that were collected via suprapubic bladder aspirations, cystoscopy, pre- and post-prostatic massage, renal stent, or nephrostomy tube were cultured on blood agar plates (Oxoid Company, Nepean, ON, Canada), containing 5% sheep blood, in addition to BBL^TM CHROMagar^TM plates. A 0.01 mL loop of each special urine sample was then incubated at 35 °C under aerobic conditions for 18 and 36 h to enhance yield.

To proceed to the microorganism identification stage, a minimum of 10,000 colony-forming units per millilitre (colony-forming unit (CFU)/mL) (equivalent to 10 colony counts) was needed to indicate significant growth after incubation [12]. Mixtures of three or more different microorganism types signified contamination, and these specimens were excluded from the identification stage [12]. The cultures were isolated in purity plates and processed using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (Bruker Daltonics GmbH & Company KG, Bremen, Germany), following the manufacturer’s guidelines.

2.3. Antimicrobial Susceptibility Testing (AST)

AST was reflexively performed for the identified potential uropathogens using the Vitek2 system (bioMérieux Incorporation, Durham, NC, USA) according to the manufacturer’s instructions. Ciprofloxacin, tetracycline, SMX-TMP, gentamicin, ertapenem, and meropenem were routine antibiotics tested for SPICE-HaM microorganisms. Tobramycin, amikacin, and amoxicillin/clavulanate were tested only as per clinicians’ requests; thus, fewer AST results were recorded for these antibiotics. Nitrofurantoin data were included in the study unless it was known to be intrinsically resistant to certain microorganisms [13]. Cefixime and ceftriaxone are third-generation cephalosporins routinely tested via Vitek2, but results for these antibiotics were routinely masked due to potential ineffectiveness among SPICE-HaM microorganisms; the current study unmasked the results from Vitek2 [5,6]. Traditional methods, such as Kirby–Bauer disks and Epsilometer (E-test) (bioMérieux Incorporation, Durham, NC, USA), were used when the Vitek2 system failed to produce AST results. All AST results were based on the breakpoints reported by the Clinical and Laboratory Standards Institute (CLSI) M100 Performance Standards for AST in the respective year, which correlate in vitro AST results with clinical outcomes [13]. Fosfomycin was excluded from the study as it only has breakpoints for Enterococcus faecalis and Escherichia coli based on the CLSI M100 Performance Standards for AST [13]. After the result and purity passed quality control, the final urine culture results were reported and recorded in the MEWS software (Version 5.00.267; LifeLabs, Toronto, ON, Canada).

2.4. Statistical Analysis

Five years of data were accumulated to increase the sample sizes. The CLSI M39 guidance suggests a minimum sample size of 30 isolates for antibiograms [2]. However, focusing on the local pediatric population, not all sample sizes met this minimum. Thus, a cAST report rather than a true antibiogram was produced. For completeness and consistency, sample sizes of less than 30 were kept in the study.

Third-generation cephalosporins cefixime and ceftriaxone were compared to a non-beta-lactam antibiotic, SMX-TMP, a common empirical treatment for UTIs [5]. Statistical tests were performed using GraphPad QuickCalcs Calculator (https://www.graphpad.com/quickcalcs/; accessed on 30 June 2025). Two-tailed Fisher’s exact tests were performed, in which p-value (p) < 0.05 was considered statistically significant.

3. Results

This cAST report (

Table 1. Cumulative Antimicrobial Susceptibility Testing (cAST) Report for Serratia, Providencia, indole-positive Proteus, Citrobacter freundii complex, Enterobacter cloacae complex, Klebsiella aerogenes, Hafnia alvei and Morganella morganii (SPICE-HaM) Microorganisms.

Microorganisms	Amikacin †	Amoxicillin/Clavulanate †	Ampicillin †	Cefixime †‡	Ceftriaxone †‡	Ciprofloxacin	Ertapenem	Gentamicin	Meropenem	Nitrofurantoin †	Sulfamethoxazole/Trimethoprim	Tetracycline	Tobramycin †
Citrobacter freundii complex % susceptible	100	R	R	65	95	91	100	96	100	95	95	88	94
n =	39			57	57	57	57	57	57	57	57	57	50
Enterobacter cloacae complex % susceptible	100	R	R	49	83	97	96	98	100	42	92	96	99
n =	75			89	89	89	89	89	89	89	89	89	88
Hafnia alvei % susceptible		R	R	0	100	100		100		100	100	100
n =				1 *	1 *	1 *		1 *		1 *	1 *	1 *
Klebsiella (previously Enterobacter) aerogenes % susceptible	100	R	R	89	89	97	100	100	100	13	100	97	100
n =	33			38	38	38	2 *	38	38	38	38	38	35
Morganella morganii % susceptible	100	R	R	68	99	87	100	99	100	R	92	44	97
n =	59			76	76	75	76	76	76		76	75	70
Proteus vulgaris % susceptible	100	100	R	100	96	100	100	100	100	R	89	R	100
n =	21 *	1 *		28 *	28 *	28 *	28 *	28 *	28 *		28 *		27 *
Providencia rettgeri % susceptible		R	R	100	100	100	100	100	100	R	100	R
n =				10 *	10 *	10 *	10 *	10 *	10 *		10 *
Serratia marcescens % susceptible	100	R	R	100	100	100	100	100	100	R	100	20	100
n =	17 *			20 *	20 *	20 *	20 *	20 *	20 *		20 *	20 *	18 *
	90–100% of the identified microorganisms are susceptible to the corresponding antibiotic in vitro
	50–89% of the identified microorganisms are susceptible to the corresponding antibiotic in vitro
	0–49% of the identified microorganisms are susceptible to the corresponding antibiotic in vitro
R	The microorganism is intrinsically resistant to the corresponding antibiotic
	Susceptibility testing data is not available

* The susceptibility of these microorganisms should be interpreted with caution, as the sample size was less than 30. ^† These antibiotics were not routinely reported for SPICE-HaM microorganisms in urine samples. ^‡ Original in vitro antimicrobial susceptibility testing (AST) results were presented for cefixime and ceftriaxone, and inducible resistance of third-generation cephalosporins should be considered before making clinical decisions.

) summarizes the urine AST results of all pediatric patients (<18 years old) recorded in LifeLabs BC regarding SPICE-HaM microorganisms, including Citrobacter freundii complex, Enterobacter cloacae complex, Hafnia alvei, Klebsiella (previously Enterobacter) aerogenes, Morganella morganii, Proteus vulgaris, Providencia rettgeri, and Serratia marcescens from 2020 to 2024. The Vitek2 system was used according to the manufacturer’s instructions for AST, using the recommended breakpoints reported by CLSI M100 Performance Standards for AST in each corresponding year.

Table 2. (A) Comparison of the Susceptibility of Serratia, Providencia, indole-positive Proteus, Citrobacter freundii complex, Enterobacter cloacae complex, Klebsiella aerogenes, Hafnia alvei and Morganella morganii (SPICE-HaM) Microorganisms to Cefixime and Sulfamethoxazole/trimethoprim. (B) Comparison of the Susceptibility of SPICE-HaM Microorganisms to Ceftriaxone and Sulfamethoxazole/trimethoprim. (C) Comparison of the Susceptibility of SPICE-HaM Microorganisms to Cefixime and Ceftriaxone.

(A)
Microorganism	Fisher’s exact test (p-value)
Citrobacter freundii complex	<0.0001
Enterobacter cloacae complex	<0.0001
Hafnia alvei	1.0000
Klebsiella (previously Enterobacter) aerogenes	0.1151
Morganella morganii	0.0004
Proteus vulgaris	0.2364
Providencia rettgeri	1.0000
Serratia marcescens	1.0000
(B)
Microorganism	Fisher’s exact test (p-value)
Citrobacter freundii complex	1.0000
Enterobacter cloacae complex	0.1093
Hafnia alvei	1.0000
Klebsiella (previously Enterobacter) aerogenes	0.1151
Morganella morganii	0.1163
Proteus vulgaris	0.6110
Providencia rettgeri	1.0000
Serratia marcescens	1.0000
(C)
Microorganism	Fisher’s exact test (p-value)
Citrobacter freundii complex	0.0001
Enterobacter cloacae complex	<0.0001
Hafnia alvei	1.0000
Klebsiella (previously Enterobacter) aerogenes	1.0000
Morganella morganii	<0.0001
Proteus vulgaris	1.0000
Providencia rettgeri	1.0000
Serratia marcescens	1.0000

Statistically significant results are shaded in green, and non-statistically significant results are shaded in red.

A,B illustrate the statistical results comparing the susceptibility of SPICE-HaM microorganisms to cefixime (Table 2A) or ceftriaxone (Table 2B) compared to sulfamethoxazole/trimethoprim (SMX-TMP). Table 2C illustrates the susceptibility of SPICE-HaM Microorganisms to cefixime compared to ceftriaxone.

4. Discussion

4.1. Summary of Key Findings

In comparison to cefixime, SMX-TMP showed higher sensitivity for Citrobacter freundii complex (65% versus 95%, p < 0.0001, n = 57), Enterobacter cloacae complex (49% versus 92%, p < 0.0001, n = 89), and Morganella morganii (68% versus 92%, p < 0.05, n = 76) (Table 2A). In comparison to ceftriaxone, SMX-TMP showed no statistical difference (p > 0.05) in its sensitivities for all SPICE-HaM microorganisms (Table 2B). Both cefixime and ceftriaxone demonstrated 100% sensitivities against Klebsiella aerogenes, Proteus vulgaris, Providencia rettgeri, and Serratia marcescens (Table 1), suggesting that third-generation cephalosporins remain useful as empirical therapy for UTIs in children in the local community. However, compared to cefixime, ceftriaxone demonstrated superior sensitivity for Citorbacter freundii complex (65% versus 95%, p < 0.01, n = 57), Enterobacter cloacae complex (49% versus 83%, p < 0.01, n = 89) and Morganella morganii (68% versus 99%, p < 0.01, n = 76) (Table 2C), suggesting the intravenous ceftriaxone may be preferred over cefixime when these microorganisms were identified.

4.2. Clinical Significance

Cumulative antimicrobial susceptibility patterns are worth discussing to minimize clinical failures and enhance antimicrobial stewardship. Among the SPICE-HaM microorganisms, Citrobacter freundii complex, Enterobacter cloacae complex, and Klebsiella (previously Enterobacter) aerogenes have a higher risk of inducible resistance [3,13]. For the rest of the SPICE-HaM microorganisms, less than 5% produce clinically significant AmpC β-lactamase levels; therefore, the IDSA recommends selecting treatments based on AST results to rule out intrinsic resistance [3,4]. The recommendation of cefixime for empirical treatment of febrile UTIs by the CPS could be based on the consideration that UTIs are mostly caused by Escherichia coli [6]. Treatment adjustment after receiving susceptibility results is not clearly specified, but the CPS recommends further clinical assessment and testing for persistent infections only [6]. According to our data, SMX-TMP seems to be more effective than cefixime in terms of in vitro susceptibility; thus, SMX-TMP would be a better option to prevent inducible resistance-related treatment failures for SPICE-HaM-induced febrile UTIs.

Regarding ceftriaxone, IDSA states that it is a reasonable antibiotic for SPICE-HaM-induced uncomplicated cystitis, as it adequately concentrates in the urinary tract despite the potential for resistance development [3]. In addition, IDSA suggests that treatment adjustment or extension is generally not necessary for uncomplicated cystitis with observed clinical improvement, despite knowing the ineffectiveness of empirical treatment in AST [3]. However, although no statistical significance was found between SMX-TMP and ceftriaxone in our results, the difference in dosage forms might be a reason to favour one over the other. Oral medications, such as cefixime and SMX-TMP, are more convenient and accessible than intravenous therapy in community settings. The CPS does not specify treatment recommendations for uncomplicated cystitis caused by SPICE-HaM microorganisms, but recommends cefixime for febrile UTI; it recommends two to four days of oral antibiotics for general uncomplicated cystitis in pediatric patients older than three months [6,14]. Our data suggest that SMX-TMP may be another reasonable empirical oral option for uncomplicated cystitis secondary to SPICE-HaM. However, it would be more informative to gather data from direct comparison of the efficacy of SMX-TMP versus cefixime in clinical trials.

4.3. Comparison with Other Studies

To our knowledge, there are no studies on SPICE-HaM-associated UTIs in the pediatric population that directly compare third-generation cephalosporins with SMX-TMP in the province in recent years. One single-centred study on AmpC-associated UTIs in the adult population suggested that the development of ceftriaxone resistance was seen starting on the seventh day of treatment, and recent usage of beta-lactam agents increased the risk of inducible resistance [15]. It also concluded that AmpC-susceptible antibiotics, such as third-generation cephalosporins, produced similar 30-day clinical outcomes compared to AmpC stable agents, such as SMX-TMP [15]. More studies are needed in the pediatric population; if the same pattern is observed, a trial of third-generation cephalosporins for less than seven days might be worth considering, if clinically appropriate, to avoid inducible resistance.

4.4. Strengths and Limitations

This study is a multicentre retrospective study with a centralized laboratory collection approach. Some advantages of centralized laboratory studies are that all isolates were processed with control and high standards, using common breakpoints [2]. However, one major limitation of this study was the limited sample size due to its retrospective nature and regional pediatric focus. The current study data was limited to urine specimens in the community collection centres in LifeLabs and could not be easily extrapolated to province-wide and nation-wide use. Therefore, this cAST report should be interpreted with caution when making clinical decisions. Like other antibiogram studies, our study did not analyze urinalysis results or any patients’ clinical information or treatment progress and influence from various urine sample types and collection methods. Thus, asymptomatic bacteriuria cases might be included in the analysis. Because the current study was on outpatient urine specimens, it was assumed that most patients had query uncomplicated cystitis who were reasonably investigated by their clinicians in community, rather than more serious conditions like pyelonephritis and urosepsis which would generally require intravenous antimicrobials as initial management in hospitals.

Other medications such as nitrofurantoin and ciprofloxacin are also commonly used for UTI [5]. They were not directly compared with third-generation cephalosporins in this study, as some SPICE-HaM microorganisms are intrinsically resistant to nitrofurantoin. Fluoroquinolone antibiotics are reserved for selected cases due to the risk of serious adverse reactions, such as tendinitis and corrected QT interval (QTc) prolongation, especially in children [3,5]. Antibiotics such as carbapenems have great in vitro activity against bacteria with moderate to high AmpC production, but are recommended to be reserved for antimicrobial stewardship practice, and thus not included for further analysis in the current study [4]. Cefepime can be used to treat infections secondary SPICE-HaM microorganisms, but it is a broad-spectrum intravenous antimicrobial not available for testing in LifeLabs BC since it is rarely used in community settings [3].

4.5. Future Studies

Clinical outcomes of using third-generation cephalosporins for UTIs with SPICE-HaM microorganisms should be investigated in the pediatric population to enhance local age-specific antimicrobial practice. Prospective clinical trials can also be valuable in mitigating the limitations of small sample sizes, further guiding appropriate microbiology laboratory culture and sensitivity reporting, as well as outpatient antimicrobial prescribing for SPICE-HaM-associated infections.

5. Conclusions

Although third-generation cephalosporins are feasible options for uncomplicated cystitis, this retrospective study demonstrated that sulfamethoxazole/trimethoprim possibly has higher sensitivity against SPICE-HaM-caused UTIs among the pediatric community population in the province, compared to cefixime. However, compared to ceftriaxone, sulfamethoxazole/trimethoprim appears to have similar efficacy for SPICE-HaM-associated UTIs. Additional studies are needed to support this finding.