Resistant Staphylococcus Dominates Bloodstream Infections in Northern Iran Hospitals

Coagulase-negative staphylococci, led by Staphylococcus epidermidis, were the most frequent pathogens in positive blood cultures at two tertiary hospitals in northern Iran, and a large share of the Gram-negative bacteria recovered from the same cultures carried multidrug-resistant phenotypes, according to a retrospective laboratory-based study published in Discover Bacteria. The analysis covered 792 non-repetitive positive blood cultures collected between March 2021 and March 2024 at Bou-Ali Sina Hospital in Sari and the Razi Infectious Disease Center in Qaemshahr, in Mazandaran Province. Only the first isolate per patient per infectious episode was included, and duplicate, incomplete, or contaminant cultures were excluded according to predetermined criteria.

The study was designed to fill a documented gap in surveillance data. The authors note that previous research on bloodstream infections and antimicrobial resistance in Iran has concentrated on central regions such as Isfahan and Tehran, or on southern areas, often focusing on intensive care units or pediatric populations, leaving northern Iran without comprehensive local data. The researchers argue that the region’s humid climate may influence microbial ecology and healthcare-associated infection patterns, making locally generated susceptibility data essential for guiding empirical therapy and antimicrobial stewardship programs.

Among the 792 isolates analyzed, 433 (54.6 percent) were Gram-positive bacteria, 357 (45.1 percent) were Gram-negative bacteria, and two (0.3 percent) were Candida species. Coagulase-negative staphylococci accounted for 340 isolates (42.9 percent), with S. epidermidis alone representing 297 isolates, or 37.5 percent of all positive cultures. S. saprophyticus was recovered in 43 cases (5.4 percent), while Staphylococcus aureus appeared in only 37 isolates (4.7 percent), a prevalence the authors describe as notably lower than that reported in many previous studies from Iran. The majority of coagulase-negative staphylococcal cultures came from patients with indwelling intravascular catheters or with repeated positive blood cultures, which the authors cite as support for the clinical relevance of these isolates.

Among Gram-negative bacteria, four major pathogens showed relatively similar frequencies. Pseudomonas aeruginosa was the most prevalent at 88 isolates (11.1 percent), followed by Enterobacter species (10.2 percent), Klebsiella species (9.2 percent), and Escherichia coli (9.0 percent), while Acinetobacter species accounted for a substantially smaller proportion (18 isolates, 2.2 percent). The patient population was predominantly female, with 470 cases (59.3 percent) compared with 322 male cases (40.7 percent), a mean age of 45.33 years with a standard deviation of 30.42, a range of 1 to 99 years, and a median age of 50 years.

Resistance patterns differed significantly between Gram-positive and Gram-negative isolates, with p values below 0.05 for several agents by Chi-square testing. Among Gram-positive isolates, S. epidermidis showed the highest resistance to ampicillin (53.1 percent) and the lowest to tetracycline (9.2 percent). Staphylococcus aureus exhibited a notably high prevalence of methicillin resistance, with 56.7 percent of isolates classified as MRSA based on oxacillin resistance. Enterococcus species (12 isolates) showed very high resistance to ampicillin (91.7 percent) and complete resistance to amoxicillin-clavulanate (100 percent), although the authors caution that species misidentification of some E. faecium isolates, which carry higher intrinsic ampicillin resistance, cannot be completely excluded. No vancomycin-resistant Staphylococcus or Enterococcus species were identified anywhere in the dataset.

Resistance among other Gram-positive organisms varied by species. Ampicillin resistance was observed in 36.8 percent of viridans group streptococci and in 50 percent of group A streptococci, while all Streptococcus pneumoniae isolates remained susceptible to ampicillin. On the Gram-negative side, resistance to ampicillin exceeded 81 percent in all major species, and resistance to third-generation cephalosporins reached 46.6 percent in Klebsiella species and 60.5 percent for cefotaxime in Enterobacter species. The authors state that these high rates are highly suggestive of ESBL or AmpC production, although no confirmatory phenotypic or genotypic testing was performed in the study.

Multidrug resistance, defined as non-susceptibility to at least one agent in three or more antimicrobial categories according to the European Centre for Disease Prevention and Control expert proposal, was widespread. Within the Enterobacterales, including E. coli, Klebsiella species, and Enterobacter species, 71.3 percent of isolates exhibited a multidrug-resistant phenotype. Non-fermenting Gram-negative bacilli also showed what the authors describe as alarming resistance levels: P. aeruginosa demonstrated 59.1 percent multidrug resistance, while Acinetobacter species displayed the highest rate, with 88.9 percent of isolates classified as multidrug-resistant.

Amikacin emerged as the most active agent against Gram-negative pathogens. Resistance rates ranged from 16.04 percent in Enterobacter species to 26.1 percent in Klebsiella species, with relatively low resistance among the P. aeruginosa isolates, which showed 90.91 percent susceptibility to the drug. The authors suggest that the relatively preserved activity of amikacin may be attributed to its more restricted clinical use compared with third-generation cephalosporins and fluoroquinolones, whereas the high resistance to those latter agents likely reflects their frequent empirical administration in hospitalized patients. Vancomycin, tested by minimum inhibitory concentration using broth microdilution according to Clinical and Laboratory Standards Institute 2023 guidelines, demonstrated favorable activity against the predominant Gram-positive pathogens.

The methods behind these figures were conventional but standardized. Antimicrobial susceptibility testing used the Kirby-Bauer disk diffusion method on Mueller-Hinton agar with a panel of antibiotic disks including ceftazidime, cefotaxime, gentamicin, amikacin, trimethoprim-sulfamethoxazole, ciprofloxacin, ampicillin, amoxicillin-clavulanate, erythromycin, and clindamycin, with E. coli ATCC 25922 and S. aureus ATCC 25923 as quality control strains. Ampicillin results were not interpreted for the intrinsically resistant non-fermenters, P. aeruginosa and Acinetobacter species. Coagulase-negative staphylococci were considered clinically significant only when isolated from at least two separate blood culture sets, or from a single set in patients with intravascular devices and compatible clinical signs of infection as judged by treating physicians; isolates failing these criteria were deemed contaminants and excluded.

The authors acknowledge substantial limitations arising from the retrospective, laboratory-based design. Susceptibility testing for carbapenems, piperacillin-tazobactam, and colistin was not performed routinely, and phenotypic screening for ESBL, AmpC, and carbapenemases, as well as molecular confirmation of mecA-mediated resistance, was not conducted. Detailed device utilization ratios, catheter-related bloodstream infection rates, and the total number of blood cultures performed were unavailable, limiting the ability to fully exclude contamination as a contributor to the high coagulase-negative staphylococcal prevalence. Ward distribution, community versus healthcare-associated acquisition, comorbidities, and clinical outcomes such as 30-day mortality were also not recorded. The authors conclude that third-generation cephalosporins may no longer be reliable as empirical monotherapy for suspected hospital-acquired or device-related bacteremia in their setting, and they call for prospective multicenter studies with molecular resistance mechanisms, clinical correlation, and outcome data, alongside urgent implementation of antimicrobial stewardship programs, strict catheter care bundles, and ongoing local surveillance.

Subject of Research: Epidemiology and antimicrobial resistance patterns of bloodstream infection pathogens in two tertiary hospitals in northern Iran

Article Title: Epidemiology and antimicrobial resistance patterns of bloodstream infection pathogens in northern Iran

Article References: Karimbakhsh, M., Gholami, M., Khodsooz, Z., & Ahanjan, M. (2026). Epidemiology and antimicrobial resistance patterns of bloodstream infection pathogens in northern Iran. Discover Bacteria, 3(1), Article 22. https://doi.org/10.1007/s44351-026-00060-y

Image Credits: AI Generated

DOI: 10.1007/s44351-026-00060-y

Keywords: bloodstream infections, antimicrobial resistance, coagulase-negative staphylococci, Staphylococcus epidermidis, MRSA, multidrug resistance, Pseudomonas aeruginosa, amikacin, vancomycin, Iran, tertiary hospitals, antimicrobial stewardship