Bacterial Pathogens Isolated in Liver Transplant Recipients With Surgical Site Infection and Antibiotic Treatment.

OBJECTIVE: Surgical site infection (SSI) is the most common infection after liver transplantation in our hospital. In this study, the effect of microorganisms isolated in liver transplant recipients' (LTRs') culture with SSI on antibiotic treatment has been investigated. METHOD: Between January 2003 and December 2013, microbiological data and antibiotic management of LTRs were examined from laboratory and patients' records retrospectively. For diagnosis of SSI, the Centers for Disease Control and Prevention criteria were used. Infections have been classified into 3 groups according to agent existence (culture negative, monomicrobial, or polymicrobial). The data were analyzed with the SPSS 17 program. RESULTS: In the study period, 457 liver transplantations were performed. The study included 412 adult LTRs. In 122 (29.6%) of these patients, at least 1 infection was detected within 30 days after transplantation. Seventy-one (17.2%) were SSI. Of LTRs with SSI, there were 36 (50.7%) with blood stream infection, 16 (22.5%) with pneumonia, and 10 (14.0%) with urinary tract infection together. Eighteen (25.4%) cases were polymicrobial (especially Acinetobacter baumannii and Enterococcus species), 35 (49.2%) cases were monomicrobial (firstly methicilline resistant Staphylococcus aureus), and 18 (25.4%) cases were culture negative SSI. In 60 (84%) cases, combined antibiotic treatment was used. Mortality rate was 14.0%. CONCLUSION: In LTRs with SSI, the impact of the isolation of an infectious agent on antibiotic selection could not be determined. Whether or not there are bacteria, on the basis of the local epidemiological data and patient characteristics, at least 2 or more antibiotics were combined for treatment. According to the resistance of the isolated microorganisms prior antibiotics have been changed.

Clinical and microbiological efficacy of tigecycline for complicated skin-soft-tissue and intra-abdominal infections in a Turkish university hospital.

OBJECTIVE: Tigecycline, a new glycylcycline antimicrobial agent, is indicated for the treatment of complicated skin structure infection (cSSTI), intra-abdominal infection (cIAI) and community acquired pneumonia. We aimed to evaluate the clinical and microbiological data together about tigecycline therapy. METHODS: Patients with cIAIs and cSSTIs were included in a prospective, observational follow-up. Patient follow-up forms were developed and clinical and microbiological data were recorded. RESULTS: Of the 107 patients, 67 had cSSTIs, 40 had cIAIs. Tigecycline was used empirically in 37.5% of cIAIs and in 50.7% of cSSTIs. In 85.0% of the patients with cIAI and in 73.1% of the patients with cSSTI, clinical and/or microbiological response could be achieved. A drug change was made in 26.9% and 7.5% of the patients with cSSTI and cIAI respectively. Superinfection was detected in 14.9% of the cSSTI and 7.5% of the cIAI patients. CONCLUSION: As a result, tigecycline can be safely used in the treatment of different infections. Compared with cSSTIs, the treatment response is better and the duration of treatment is shorter in cIAIs. However, MIC value must be determined at any rate if tigecycline is to be used in the treatment of Acinetobacter (MDR Acinetobacter, in particular) infections. Clinical cure and microbiological eradication rate of tigecycline therapy changes according to different clinical diagnosis and microorganism.

Antimicrobial resistance in gram-negative hospital isolates: results of the Turkish HITIT-2 Surveillance Study of 2007.

Resistance rates to amikacin, ciprofloxacin, ceftazidime, cefepime, imipenem, cefoperazone/sulbactam and piperacillin/tazobactam in Escherichia coli (n= 438), Klebsiella pneumoniae (n= 444), Pseudomonas aeruginosa (n= 210) and Acinetobacter baumanni (n=200) were determined with e-test in a multicenter surveillance study (Hitit-2) in 2007. ESBL production in Escherichia coli and K. pneumoniae was investigated following the CLSI guidelines. Overall 42.0% of E.coli and 41.4% of K. pneumoniae were ESBL producers. In E. coli , resistance to imipenem was not observed, resistance to ciprofloxacin and amikacin was 58.0% and 5.5% respectively. In K. pneumoniae resistance to imipenem, ciprofloxacin and amikacin was 3.1%, 17.8% 12.4% respectively. In P. aeruginosa the lowest rate of resistance was observed with piperacillin/tazobactam (18.1%). A. baumanni isolates were highly resistant to all the antimicrobial agents, the lowest level of resistance was observed against cefoperazone/sulbactam (52.0%) followed by imipenem (55.5%). this study showed that resistance rates to antimicrobials are high in nosocomial isolates and show variations among the centers.

Use of tunnelled catheters in haematological malignancy patients with neutropenia.

This prospective study analysed 83 patients (age 45 +/- 17 years) with haematological neoplasms, implanted with 93 tunnelled catheters, who were neutropenic or developed neutropenia during treatment. Catheters were implanted in the right (n = 82) or left (n = 11) jugular vein by the same surgical team using the same technique. They remained in place for 124 +/- 88 days: 29% were removed due to infection; 18% due to treatment termination and 2% due to mechanical problems. Seventeen patients died with catheters in place. At 30, 60, 90, 120 and 200 days mean catheter duration rates were 82%, 75%, 65%, 60% and 35%, respectively, and freedom from catheter removal due to infection was 92%, 88%, 80%, 77% and 67%, respectively. Patient diagnosis and history of previous catheter infection did not increase catheter infection risk, but patients undergoing stem cell transplantation had an increased infection risk. Tunnelled catheters can be used in high-risk patients with neutropenia. Systemic infections can be managed in most patients without catheter removal.

Molecular epidemiology of PER-1 extended spectrum beta-lactamase among gram-negative bacteria isolated at a tertiary care hospital.

The bla(PER-1) presence was sought by PCR in 289 ceftazidime resistant Gram-negative bacteria isolated at Dokuz Eylul University Hospital (Turkey) between 1998 and 2003. PER-1 production rates were 32.3, 33.9, 14.9 and 37.9% in the 1998-2000 period, 2001, 2002 and 2003, respectively. bla(PER-1) was detected in 46.2 and 35.9% of ceftazidime-resistant Pseudomonas aeruginosa and Acinetobacter baumannii isolates, respectively. ERIC-PCR results revealed that dissemination of two endemic clones for both P. aeruginosa (X and Y) and A. baumannii (A and B) was responsible for the high prevalence. Results of the conjugation tests and plasmid curing experiments suggested that bla(PER-1) was located on the chromosome in the representative strains. It was also shown for the first time that bla(PER-1) in a clinical isolate was associated with class-1 integron which could facilitate dissemination of bla(PER-1) among bacteria.

Development of multiple sclerosis after vaccination against hepatitis B: a study based on human leucocyte antigen haplotypes.

The aetiology of multiple sclerosis (MS) is still not fully understood. Infectious agents are believed to play a role in the development of this multifactorial disease. Cases in which this disease occurs after administration of both plasma-derived and recombinant hepatitis B vaccines have been reported. In this study, we compared a group of 11 MS patients who developed first clinical symptoms after hepatitis B vaccination (group I) with 71 MS patients who were never vaccinated against hepatitis B and were negative for hepatitis B serology (group II), and 20 healthy controls (group III). Mean age was 27.75 years (19-39) in group I, 30.16 years (18-50) in group II, and 34.4 years (18-50) in group III. Mean attack rate after 2 years was 1.5 in group I and 1.63 in group II. Mean Expanded Disability Status Scale score after 2 years was 1.31 in group I and 1.89 in group II. Human leucocyte antigen (HLA) typing and serology for hepatitis B surface antigen were performed in all groups. In groups I and II, HLA-DR2 was more frequent than in normal healthy subjects. This reflects the general role of HLA in the pathogenesis of MS but suggests that antigen presentation by different HLA is not involved in the development of MS after hepatitis B vaccination. Since there was no difference in the clinical features between vaccinated and nonvaccinated MS patients, this study supports recent reports that hepatitis B vaccination is safe in MS patients and that hepatitis B vaccination is not involved in the development of MS.

Analysis of mutations in the pbp genes of penicillin-non-susceptible pneumococci from Turkey.

Sequence analysis of the pbp genes from 20 Streptococcus pneumoniae isolates from Turkey (eight with high-level penicillin-resistance, nine with low-level penicillin-resistance, and three that were penicillin-susceptible) was performed and phylogenetic trees were constructed. Most isolates clustered together within a single branch that was distinct from sequences deposited previously in GenBank, which suggests that these isolates have probably evolved following new recombination events. The most prominent active-site mutations, which have also been associated previously with resistance, were T371A in PBP1a, E481G followed by T451A in PBP2b, and T338A in PBP2x. All isolates also possessed a (570)SVES/TK(574) block in the PBP2b sequence, instead of the QLQPT sequence of R6, which is fairly uncommon in GenBank sequences. This is the first study to analyse alterations in the pbp sequences of pneumococci isolated in Turkey.

Molecular epidemiology of Candida species isolated from urine at an intensive care unit.

Candida spp. has been the leading microorganism isolated from the urine specimens of patients hospitalized at the Anesthesiology and Reanimation intensive care unit (ICU) of Dokuz Eylul University Hospital, Izmir, since 1998. This study was undertaken to investigate the clonal relationship of Candida urine isolates in order to find the mode of spread among the patients. Epidemiological surveillance of 38 Candida albicans, 15 Candida tropicalis and 12 Candida glabrata recovered from the urine specimens of patients who were hospitalized in the ICU between June 11, 2000 and October 15, 2001 was carried out by antifungal susceptibility testing and randomly amplified polymorphic DNA (RAPD) analysis. Two short primers [Cnd3 (5'-CCAGATGCAC-3') and Cnd4 (5'-ACGGTACACT-3')] were used for RAPD. None of the isolates had high minimal inhibitory concentration (MIC) values (>1 microg ml(-1)) against amphotericin B with MIC50 values of 0.5 microg ml(-1), 0.5 microg ml(-1) and 0.125 microg ml(-1) for C. albicans, C. tropicalis and C. glabrata isolates, respectively. However, three C. glabrata isolates were resistant and one C. albicans and five C. glabrata isolates were dose-dependent susceptible (D-DS) to fluconazole. Among C. albicans isolates 19 and 20 patterns were detected with primers Cnd3 and Cnd4, respectively. When primers Cnd3 and Cnd4 were evaluated together, three and four genotypes were identified for C. tropicalis and C. glabrata isolates, respectively. Our results suggest that the source of C. albicans isolates was mostly endogenous. It is difficult to interpret the mode of spread of C. tropicalis and C. glabrata urine isolates as we obtained insufficient banding patterns for these species.

PER-1 production in a urinary isolate of Providencia rettgeri.

A Providencia rettgeri strain resistant to extended-spectrum cephalosporins and intermediate to aztreonam was isolated from the urine of a patient hospitalized in the urology clinic of SSK Educational Hospital in Ankara. Clavulanic acid restored the activity of extended-spectrum cephalosporins, suggesting that the strain was harboring an extended-spectrum beta-lactamase. Since the PER-1 enzyme is widespread in Turkey, and had been already detected in a related species such as Proteus mirabilis, the Providencia strain was suspected of harboring a PER-1 enzyme, which was indeed detected by PCR. This is the first description in a P. rettgeri isolate of a PER-1 enzyme which is widespread among Acinetobacter baumanni and Pseudomonas aeruginosa strains in Turkey.

[Mutations of gyrA in ciprofloxacin resistant Escherichia coli strains]. / Siprofloksasine dirençli Escherichia coli suslarinda gyrA mutasyonlarinin incelenmesi.

In this study, the relationship between gyrA mutations and ciprofloxacin minimum inhibitory concentration (MIC) values was investigated in Escherichia coli strains. For this purpose, ciprofloxacin MIC values of 46 E. coli strains, isolated from out-patients and hospitalized patients, were determined by the agar dilution method. The "Quinolone Resistance Determining Region" (QRDR) of gyrA gene was amplified and restricted by Hinf-I enzyme. Ser-83 mutation was observed in all strains that have ciprofloxacin MIC values of 0.062 mg/L and higher. Afterwards, eight strains, that were found susceptible (MIC < 1 mg/L, n: 1), intermediate (MIC: 1-4 mg/L, n: 1) and high level resistant (MIC > 4 mg/L, n: 6) to ciprofloxacin, were chosen and mutations in QRDRs of these strains investigated by DNA sequence analysis. Ser 83 Leu mutation was found in all the chosen strains and Asp 87 Tyr or Asp 87 Asn mutations were also observed except the ciprofloxacin susceptible (MIC: 0.062 mg/L) one. In addition, base substitutions that don't lead to aminoacid changes were detected. The strain in which only Ser 83 Leu mutation was observed, showed high level nalidixic acid resistance (MIC > 256 mg/L). This fact was in favour of that, one mutation is enough to develop high level resistance to nalidixic acid. It was concluded that high level ciprofloxacin resistance requires at least two mutations in the QRDR of gyrA gene.

The comparison of the efficacy of fluticasone propionate with cetirizine in perennial allergic rhinitis.

BACKGROUND: Allergic rhinitis is an IgE mediated hypersensitivity reaction of the nasal mucosa characterised by nasal discharge, obstruction, and pruritus. PATIENTS AND METHODS: In this study, 43 patients with perenneal allergic rhinitis were enrolled in order to compare the efficacy of Fluticasone Propionate (FP), a corticosteroid nasal spray, with Cetirizine, a systemic oral antihistaminic preparation, which is supposed to have nonsteroidal antiinflammatory activity. Cetirizine (10 mg daily as a single dose) was administered to 22 patient for 45 days. On the other hand, FP (400 micrograms/day) was administered into each nostril twice a day in the remaining 21 patients for 45 days. Skin test was obtained from each patient before therapy. Total eosinophil count, eosinophil count in nasal smear, electrorhinomanometric investigation, PGE2 and ratio of LTC4 to LTD4 both in the serum and in the nasal secretions were determined before and after therapy. In addition, percentage of eosinophils, and mast cells count in the biopsy specimens taken from anterior edge of middle choncha were evaluated before and after therapy, and than the results were graded for each patients. RESULTS: When we compared the eosinophil count in nasal smear, eosinophil percentage and total eosinophil parameters between two groups, it was shown that FP was more effective than Cetirizine. On the other hand, when we compared the ratio of LTC4 to LTD4 in serum and nasal smear, level of PGE2 and mast cell and nasal airway resistance measured by ERM, there were non statistical difference between two groups. CONCLUSION: These results suggest that FP and Cetirizine may be used alternatively in case of an adverse reaction to any of them.

Vancomycin-resistant enterococci in neonates.

Fecal-oral transmission of vancomycin-resistant strains of Enterococci (VRE), which colonize the human gastrointestinal tract, has led to nosocomial epidemics in recent years. The aim of this study was to establish the incidence and associated factors of fecal colonization with VRE in neonates. In our hospital 110 rectal swab specimens collected in the neonatal intensive care unit (NICU) were examined for VRE. For comparison, rectal swabs collected from 42 healthy neonates on the obstetrics ward were also analyzed. Of the NICU patients, 8 had VRE MICs of 8-64 microg/ml for vancomycin and 2-32 microg/ml for teicoplanin, whereas none of the healthy newborns, had VRE (p < 0.05). All patients positive for VRE had factors known to be associated with VRE carriage, such as low birth weight or long-term antibiotic therapy.

Clonal spread of imipenem-resistant Pseudomonas aeruginosa in the intensive care unit of a Turkish hospital.

Pseudomonas aeruginosa may cause life-threatening infections, especially in nosocomial settings. Although carbapenems are considered as one of the most effective alternatives in antipseudomonal therapy, resistance to the carbapenem group of antibacterials is a growing problem. In the first 6 months of 1997, P. aeruginosa isolates that were resistant to almost all antipseudomonal agents including imipenem were recovered from various specimens from intensive, care unit (ICU) patients. Isolates with the same antibiogram profile caused a small outbreak in May 1997. A retrospective case-control study revealed that the major risk factors for infection/colonization with multiresistant P. aeruginosa were prolonged stay in the ICU (p<0.001), previous and lengthy imipenem usage (p<0.001 and p<0.0001, respectively), and mechanical ventilation (p<0.001). Analytical isoelectric focusing of the sonicates prepared from the isolates showed that each isolate produced 1-5 beta-lactamases, enzymes with isoelectric points (pIs) of 5.1, 6.4, 8.5-8.7 being the most prevalent. DNA macrorestriction patterns of imipenem-resistant isolates were distinct from those of the imipenem-sensitive isolates recovered from ICU patients during the same interval and from the environmental isolates (controls). Thus, our results indicate that colonized patients appear to be the major source for cross-contamination of other patients and if imipenem is selected for empirical therapy, emergence of resistant strains should be anticipated and appropriate precautions taken.

The association of HLA-DR4 antigen with juvenile chronic arthritis and slipped capital femoral epiphysis.

Seventeen children who met the criteria for juvenile chronic arthritis (JCA) were reviewed. Throughout the study, the clinical examination, HLA phenotyping, and radiological assessment of the hips were performed by separate authors who were blinded to other data. At the end of the study, the results were also compared with 25 healthy, age- and sex-matched children. Six of the children with JCA also had radiological signs of slipped capital femoral epiphysis (SCFE; five with minimal slip pattern, one with moderate slip), and five of them had DR4 in their genotypes, in contrast to the remaining 11 patients who did not (p < 0.001). On the other hand, only 2 of 25 children in the control group had DR4 (p < 0.01). The difference was not significant when the patients without SCFE were compared with the control group (p = 1.0). The relative risk of cases with DR4 antigen for SCFE was 57.5, while it was below I for the other antigens. These results suggest that although DR4 is not specific for JCA, it is the common HLA antigen for those who have SCFE, and patients with JCA and HLA-DR4 antigen should be examined for evidence of SCFE, which was not reported before to exist with JCA.

In-vitro synergistic effect of fluconazole with nonsteroidal anti-inflammatory agents against Candida albicans strains.

The in-vitro interaction and synergistic activity of the combination of fluconazole with some nonsteroidal anti-inflammatory drugs (sodium salicylate, piroxicam, tenoxicam and diclofenac sodium) were investigated in Candida albicans strains (n=7) by the microdilution checkerboard assay. The results were evaluated visually and by a spectrophotometric microplate reader at 492 nm wavelength. Fractional inhibitory index was calculated for every strain and combination according to the minimal inhibitory concentration (MICs). The combination of fluconazole with sodium salicylate, tenoxicam and diclofenac sodium showed synergy against 5, 5 and 3 of the C. albicans strains, respectively. The effect of fluconazole with piroxicam was synergistic against one strain but indifferent/additive against the others. These data suggest that combinations of sodium salicylate, tenoxicam and diclofenac sodium with fluconazole may prove to be useful as chemotherapeutic agents for the treatment of C. albicans infections caused by especially fluconazole-resistant strains. However, additional preclinical work and in vivo studies are necessary to determine their definite clinical use.

Beta-lactamase patterns and betalactam/clavulanic acid resistance in Escherichia coli isolated from fecal samples from healthy volunteers.

Fecal specimens from 50 healthy volunteers living in Izmir, Turkey, were examined for the presence of beta-lactamase producing Escherichia coli by selection on agar plates containing ampicillin (10 mg/L). Thirty-nine (78%) of the strains were ampicillin-resistant and ampicillin MIC50 values for these isolates were > or =1024 microg/ml (range 32- > or =1024 microg/ml). Ampicillin MIC values remained above 64 microg/ml in 16 (41%) strains despite addition of clavulanic acid (2 mg/L). Beta-lactamase production of the clavulanate-resistant strains was further investigated by analytical isoelectric focusing (pI). Enzymes with pIs of 5.4, 5.6, 7.4, 7.6 and >8.5 were detected. Sixty-nine percent of the isolates produced a pI 5.4 enzyme that cofocused with TEM-1. Beta-lactamase assays revealed that hyperproduction of these enzymes was the predominant mechanism for clavulanate resistance. Twelve (75%) of the isolates were able to transfer their ampicillin resistance. The ampicillin and ampicillin plus clavulanic acid MIC values of all transconjugants were above 256 microg/ml. Transferable ampicillin resistance was associated with resistance to other antibacterials at the following frequencies: tetracycline 92%, trimethoprim 83%, streptomycin 50%, gentamicin 25%, and chloramphenicol 8%. In conclusion, it has been suggested that commensal bacteria in normal populations make up the largest reservoir of antibiotic-resistant genes. Although the exact molecular mechanisms could not be determined, the current study shows that the incidence of ampicillin and clavulanic acid resistance is also high in commensal fecal flora.

High prevalence of extended spectrum beta-lactamase production among Klebsiella pneumoniae strains isolated at a University Hospital in Turkey.

Beta-lactam susceptibility and beta-lactamase patterns of a random sample of 44 Klebsiella pneumoniae strains that had been isolated from nosocomial infections at Dokuz Eylül University Hospital in Izmir, were investigated. All strains were amoxycillin resistant but in the presence of clavulanic acid 26 became sensitive. Similarly 39 of the strains were resistant to ceftazidime and cefotaxime; clavulanic acid restored sensitivity to ceftazidime in 28 and to cefotaxime in 25 of these resistant strains. Extended spectrum beta-lactamase (ESBL) production was positive in 84% of the isolates as determined by the double disk synergy test. Isoelectric focusing revealed that each strain produced one to four beta-lactamases, pI 7.6 enzymes being the most prevalent. Other enzymes with pIs of 8.4, 8.2, 5.4, 7.8 were also detected. Resistance to ceftazidime was transferred from 18 of the 44 isolates to the recipient Escherichia coli K-12 at 37 degrees C. The transconjugants were examined for their plasmid content and the plasmids were characterized by their size and resistance profile. Fourteen different restriction pattern groups were identified with Eco R1. The results indicate a high prevalence of ESBL production in nosocomial K. pneumoniae isolates in Izmir and have major implications concerning the clinical use of later generation cephalosporins.

Stenotrophomonas maltophilia pneumonia in a premature infant.

Stenotrophomonas (Xanthomonas) maltophilia is an aerobic, non-fermentative, gram-negative bacillus that is generally considered an opportunistic pathogen. Infections due to S. maltophilia have become increasingly important in the hospital environment. Patients compromised by debilitating illnesses, surgical procedures or indwelling vascular catheters are most prone to S. maltophilia infections. To our knowledge, we report the first case of S. maltophilia pneumonia in a premature infant of 31 weeks gestational age. Although the therapy of choice for severe infections caused by S. maltophilia remains to be decided, this patient was successfully treated by amikacin.

Transferable trimethoprim resistance in Shigella strains.

The susceptibility patterns of 35 Shigella isolates (16 S. flexneri, 14 S. dysenteriae and 5 S. sonnei) to trimethoprim (Tp) and various antibiotics including amoxycillin, amoxycillin-clavulanic acid, nalidixic acid, ciprofloxacin, ceftazidime and ceftriaxone, were investigated. Twenty-two (62.8%) strains were resistant to Tp with a minimal inhibitory concentration (MIC50) value of 512 mg/L. Only six isolates were amoxycillin resistant, to which clavulanic acid restored sensitivity in all of them. None of the isolates were resistant either to extended spectrum cephalosporins or to quinolones. Resistance to Tp was transferred from 7 of the 22 isolates (31.8%) to the recipient Escherichia coli K12. Tp MIC values of the transconjugants were 512 mg/L. In no strain could amoxycillin resistance be transferred. Our results indicate that as the prevalence of transferable Tp resistance in Shigella isolates in Izmir is substantially high, alternative antimicrobial agents should be considered for empirical antibiotic therapy.

Anti-candidial activity of natural killer (NK) and lymphokine activated killer (LAK) lymphocytes in vitro.

The natural cytotoxic effects of peripheral blood lymphocytes (PBL) on Candida stellatoidea and several other Candida species were examined by a colony forming inhibition (CFI) assay. Peripheral blood mononuclear cells (PBMC), were incubated with C. stellatoidea yeast cells. After the incubation period the colony-forming ability of the yeast was significantly reduced. In similar experiments, six different Candida species (C. albicans, C. krusei, C. stellatoidea, C. tropicalis, C. pseudotropicalis, C. guillermondii) were used as target cells. There was no statistically significant difference in the anticandidial activities of PBL against the Candida species used. It was demonstrated that a fraction of lymphocytes, natural killer cells (NK), had the major natural anti-candidial activity by using anti-Leu M1 (CD 15) and anti-Leu 11b (CD 16) monoclonal antibodies (mAbs) plus complement (C'). It was observed that inhibition of colony-forming ability of C. stellatoidea was significantly (78-96%) reduced when anti-Leu 11b plus C' were used. In addition, the colony formation inhibition capacity of NK cells was increased by recombinant human interleukin-2 (rhIL-2) while anti-interferon-gamma (IFN-gamma) had no effect. Besides the fact that NK cells are among those responsible for natural immunity against Candida species, this colony-forming inhibition assay performed with C. stellatoidea yeast cells as target and monocyte-depleted PBMC as effector cells, is a simple method to assess NK cell activity.