Colistin, one of the last-line treatment options for carbapenem-resistant microorganisms, presents challenges in determining its antimicrobial susceptibility. This study aims to compare colistin broth disk elution (CBDE), modified CBDE (mCBDE), the colistin agar test (CAT), and rapid polymyxin NP (RPNP) tests with the reference broth microdilution (BMD) in determining colistin susceptibility of 116 multidrug-resistant (MDR) Klebsiella pneumoniae isolates. Isolates were collected from blood and respiratory tract samples of different patients between 2022 and 2023 in Türkiye. For each isolate, a single 0.5 McFarland inoculum was prepared to inoculate CBDE, mCBDE, and CAT in parallel, then the suspension was adjusted to a density of 3-3.5 for RPNP. All tests were conducted simultaneously under the same incubation conditions. In the comparative analysis of the tests, bias, essential agreement (EA), and sensitivity were assessed according to ISO 20776-2:2021. Additionally, EA, categorical agreement (CA), major error (ME), and very major error (VME) were evaluated by the CLSI guidelines. The minimum inhibitory concentration (MIC) values for MIC50 and MIC90 were 2 µg/ml and 16 µg/ml, respectively. All methods achieved the CA above 90%, with no VMEs (0%). The ME rates for CBDE, mCBDE, CAT, and RPNP were 3.4%, 8.6%, 12%, and 10.3%, respectively. The EA rates of CBDE and CAT were 95.6% and 91.3%, respectively, while bias rates were 10.8% and 24.7%. The sensitivity of both mCBDE and RPNP was 100%. Consistent with other studies in this field, a comprehensive evaluation of all methods revealed that 58.3% (7/12) of the isolates responsible for MEs had an MIC value of 1 µg/ml, 25% (3/12) had an MIC of 2 µg/ml, and 16.6% (2/12) had an MIC of 0.25 µg/ml. Most errors occurred in isolates with MIC values near the breakpoint. The CBDE demonstrated the best performance in all criteria assessed. This study highlights the benefits of alternative phenotypic methods compared to reference BMD for assessing colistin susceptibility, including ease of use, cost-effectiveness, and rapid results. Our findings emphasize the need for more comprehensive multicenter studies to validate and improve these methods, especially those with more isolates with MIC values near the breakpoint.

Brucellosis is a zoonotic disease endemic in many developing countries, including Türkiye. Among the species that are pathogenic for humans; Brucella melitensis is isolated from livestock animals like sheep and goats, Brucella abortus from cattle and Brucella suis from pigs. Laboratory diagnosis of infection caused by Brucella species with gram-negative coccobacillus morphology; can be made through characteristic culture features, serological tests and molecular methods. Brucellosis, which has a wide distribution of clinical signs and symptoms; can cause various complications by affecting many organs and systems. Among all complications, the probability of thyroid abscess is less than 1%. In this case report; an example of thyroid abscess, one of the rare complications of brucellosis that is not frequently encountered in the literature, was presented. During the physical examination of a 45-year-old female patient who admitted with the complaint of pain in the neck area, fever, neck swelling, redness and pain that increased with palpation were detected. Leukocytosis, lymphopenia, high sedimentation and CRP, low TSH and high T4 values were detected in laboratory tests and subacute thyroiditis was considered as the preliminary diagnosis. Surgical abscess drainage was planned as the patient's clinical findings progressed during follow-up and spontaneous pus discharged from the midline of the neck. The abscess aspirate sample taken during surgical intervention and the blood culture samples taken before were evaluated microbiologically. Microorganisms that did not grow on EMB agar but grew on 5% sheep blood and chocolate agar at the 72-96th hour of incubation of culture plates; were detected to have gram-negative coccobacillus morphology and positive for catalase, oxidase and urease. Although the Wright test was negative with a titer of 1/20, the Rose Bengal test was positive, Coombs test was positive with a titer of 1/160 and the Brucellacapt test was positive with a titer of >1/5120. Microorganisms growing on culture plates were identified as B.melitensis at the species level with specific antisera. As a result of antibiotic susceptibility tests evaluated according to the European Committee on Antimicrobial Susceptibility Testing version 14.0 (EUCAST v14.0), the isolate was susceptible to rifampicin, doxycycline, gentamicin and trimethoprim-sulfamethoxazole at standart dosing regimen and susceptible to ciprofloxacin and levofloxacin at increased exposure. The patient, who was started on doxycycline and rifampicin combination treatment, was discharged without any complaints. In the diagnosis of infection due to Brucella species, which is one of the pathogens that early diagnosis and initiation of treatment greatly affects the prognosis; in addition to culture, which is the gold standard method, serological tests are also very important. If diagnosis is delayed, complications may develop due to involvement in almost every part of the body, depending on the affected organs and systems. In areas where brucellosis is endemic, patients with symptoms such as neck swelling, shortness of breath and difficulty in swallowing, thyroid tissue involvement due to brucellosis should definitely be considered etiologically.

Objective: Bloodstream infections (BSIs) following cardiovascular surgery and cardiovascular interventions are major postoperative complications associated with substantial morbidity and mortality. Although antimicrobial resistance (AMR) has become an increasingly important global public health concern, this study aimed to clarify its impact on clinical outcomes in patients who develop postoperative BSIs.Method: This retrospective study included 139 adult patients who developed BSIs after cardiovascular surgery or cardiovascular interventions at a tertiary referral center. The associations of multidrug resistance (MDR), carbapenem resistance (CR), methicillin resistance, and penicillin resistance with mortality, hospital length of stay (LOS), intensive care unit (ICU) stay, and mechanical ventilation duration were evaluated. Independent predictors of mortality were identified using multivariable logistic regression analysis.Results: The overall mortality rate was 30.9%. Gram-negative pathogens accounted for 56.8% of BSIs and Gram-positive pathogens for 43.2%. Staphylococcus species were the most frequently isolated pathogens (33.8%), comprising other Staphylococcus species (26.6%) and Staphylococcus aureus (7.2%), followed by Klebsiella pneumoniae (21.6%) and Acinetobacter baumannii (12.9%). Neither MDR nor CR was significantly associated with mortality (p>0.05). However, among patients with Gram-negative BSIs, carbapenem-resistant isolates were associated with significantly longer hospital, and ICU stays than carbapenem-susceptible isolates (both p=0.006). Univariable analyses showed significant associations between mortality and Gram-negative BSIs, diabetes mellitus, hypertension, and surgical procedure type. Multivariable analysis identified prolonged cardiopulmonary bypass (CPB) duration (OR=1.015, 95% CI: 1.005–1.025; p=0.003) and Gram-negative BSI (OR=3.938, 95% CI: 1.225–12.659; p=0.021) as independent predictors of mortality.Conclusion: AMR was associated with greater healthcare resource utilization, particularly prolonged hospital and ICU stays, but was not significantly associated with mortality in this cohort. In contrast, Gram-negative BSIs and prolonged CPB duration were independent predictors of mortality.