Two nosocomial outbreaks of sepsis caused by Serratia marcescens, which occurred in July 1999 and January 2002--Tokyo

Two nosocomial outbreaks of sepsis caused by Serratia marcescens, which occurred in Tokyo were the following cases. CASE A: In July 1999, 10 inpatients admitted to the third floor ward of the General Hospital A, developed sudden onset of high fever, coagulation disorders (disseminated intravascular coagulation), and acute renal failure, of which 5 died. Twenty-one strains of Serratia marcescens were isolated from the inpatient's blood and urine, nurse fingers and environmental samples from floor and cooling tower. Serratia infection was strongly suspected as the cause of sepsis. These cases were defined as "inpatients who developed fever 38 degrees C or more during July 26 to 29 and from whom S. marcescens was isolated by blood culture". Ten isolates were detected from the blood. In order to investigate the background of S. marcescens isolation in the hospital and to compare molecular and biochemical characteristics of S. marcescens, cultures were attempted from samples of other inpatients and staffs and hospital environment. Those were classified into 9 groups by various different typings: biotyping with Api Rapid 20; susceptibility typing of antimicrobial agents tested; pulsed-field gel electrophoresis (PFGE) typing of SpeI- or Xba I-restricted chromosome. All 10 isolates causing sepsis were found to be in the same group. CASE B: In January 2002, 24 inpatients, admitted to Neurosurgical Hospital B, developed sudden onset of high fever, of which 7 died. S. marcescens was isolated from a towel, environmental samples and inpatients. These cases were defined as "inpatients who developed fever of 38.5 degrees C and S. marcescens isolated by blood culture". Twelve strains were isolated from the blood samples in 12 cases. In order to investigate the background of S. marcescens isolation in the hospital, cultures were attempted from other inpatient's urine and environmental samples from medical tape, Tshake and a towel. These isolates were classified into 3 groups by the previous typings; biotyping with Api Rapid 20; susceptibility typing of antimicrobial agents tested; and PFGE typing. All 12 isolates in 12 cases were found to be in the same group. These cases of 2 nosocomial outbreaks of sepsis were defined as "in-patient who developed high fever and S. marcescens isolated by blood culture". However in both cases transmission routes of Serratia infection remain unknown by field investigation.     

Changes in drug sensitivity of human immunodeficiency virus type 1 during therapy with azidothymidine, dideoxycytidine, and dideoxyinosine: an in vitro comparative study.

Human immunodeficiency virus type 1 (HIV-1) strains were isolated from nine patients before and after prolonged therapy with either an alternating regimen of 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC) (AZT/ddC) or 2',3'-dideoxyinosine (ddI) alone. All strains obtained from four patients who received AZT/ddC for up to 41 mo were highly insensitive to AZT in vitro. Only one strain obtained after AZT/ddC therapy showed reduced susceptibility to ddC in addition to AZT and had previously unreported amino acid substitutions in the viral polymerase-encoding pol region, whereas three other strains had one or more of the five previously reported AZT-related mutations. In five HIV-1 strains from patients who received ddI for up to 29 mo, no appreciable decrease in sensitivity to ddI was detected. Two strains isolated after ddI therapy had no significant amino acid mutations, although three strains had a mutation reportedly associated with ddI administration. These data suggest that HIV-1 develops reduced susceptibility to AZT more readily than to ddC and ddI and/or that the reduced susceptibility to ddC and ddI is modest in degree. Moreover, the present data suggest that an alternating regimen of AZT and ddC does not block the emergence of AZT-insensitive variants. It should be noted, however, that the current results do not provide a basis for concluding that AZT/ddC or ddI is inferior, equivalent, or superior to AZT as therapy of AIDS.     

1株粘质沙雷氏菌噬菌体的分离和鉴定

目的 以粘质沙雷氏菌为宿主菌,从河水中分离噬菌体,在体外和蚊虫肠道验证其裂解能力。方法 以粘质沙雷氏菌为宿主菌,在深圳周边河水中分离噬菌体,通过单、双层平板筛选单一的烈性噬菌体;利用噬斑形成实验验证噬菌体的裂解谱;通过饲喂实验验证噬菌体在埃及伊蚊肠道内的裂解作用。结果 从深圳河流污水中成功分离得到一株针对粘质沙雷氏菌的烈性噬菌体SHENZHEN01, 该噬菌体噬斑直径1 mm左右(培养10 h), 边界清楚;对粘质沙雷氏菌Sm01、Baz01具有明显的裂解能力,对其他粘质沙雷氏菌菌株、大肠杆菌、金黄色葡萄球菌、绿脓杆菌无裂解作用;对饲喂埃及伊蚊的粘质沙雷氏菌Sm01仍保持明显的裂解能力。结论 该噬菌体裂解作用具有特异性,而且在蚊虫肠道内仍能保持活性,具有可以用来治疗粘质沙雷氏菌引起的相关疾病的潜在价值。     

ICU呼吸机相关性肺炎病原菌分布和耐药性分析

目的了解我院ICU呼吸机相关性肺炎(ventilator-associated pneumonia,VAP)的病原菌分布和耐药性状况,为临床合理应用抗菌药物提供病原学依据。方法回顾性分析2014年1月—2016年12月我院ICU诊断为VAP的118例患者的基本资料,并分析气管深部分泌物的病原菌的构成比和药敏试验结果。结果从118例VAP确诊患者气管深部分泌物中共检出130株病原菌。其中革兰阴性菌103株(79.23%),革兰阳性菌20株(15.38%),真菌7株(5.38%)。革兰阴性菌主要包括:鲍曼溶血不动杆菌33株(32.04%),粘质沙雷菌20株(19.42%)、肺炎克雷伯杆菌18株(17.47%),铜绿假单胞菌11株(10.68%),大肠埃希菌10株(9.71%);革兰阳性菌主要为金黄色葡萄球菌10株(50.00%)。其中粘质沙雷菌、肺炎克雷伯菌、铜绿假单胞菌和大肠埃希菌对亚胺培南和阿米卡星的耐药率均低于10.00%,而鲍曼溶血不动杆菌对多种常见抗生素的耐药率均超过80.00%(美罗培南81.97%、阿米卡星83.61%、头孢曲松88.33%、左氧氟沙星80.33%)。金黄色葡萄球菌对万古霉素、利奈唑胺和替考拉宁均敏感。结论我院ICU中VAP患者感染主要以革兰阴性菌为主,且存在多重耐药现象。了解VAP的病原菌分布和耐药性,对于合理应用抗生素、提高治愈率等方面有极大帮助。     

In vitro combination effects of aztreonam and aminoglycoside against multidrug-resistant Pseudomonas aeruginosa in Japan

The aim of this study was to evaluate the in vitro combination effects of aztreonam (AZT) and aminoglycosides against multidrug-resistant (MDR) Pseudomonas aeruginosa strains in Japan. We investigated 47 MDR P. aeruginosa strains collected from 8 facilities. We selected the aminoglycosides amikacin (AMK), gentamicin (GM), and arbekacin (ABK) to examine their effects when combined with AZT using the checkerboard method. Of the 47 MDR P. aeruginosa strains, 41 tested positive for metallo-β-lactamase (MBL). In all combinations, aminoglycosides decreased the minimum inhibitory concentrations of AZT in a dose-dependent manner, and there was no apparent antagonism. The combination effects were scored on a scale of 0 to 4, and statistical analysis was performed using the Wilcoxon signed-rank test. In all 47 strains, AZT + ABK (mean score, 2.02) had the highest score, followed by AZT + AMK (1.68) and AZT + GM (1.38) (ABK versus GM, P < 0.0001). In 41 MBL-positive strains, AZT + ABK (mean score, 2.05) had the highest score, followed by AZT + AMK (1.56) and AZT + GM (1.37) (ABK versus AMK, P = 0.02, and ABK versus GM, P < 0.0001). AZT + ABK was the most promising combination regimen against MDR P. aeruginosa strains; the other promising combinations were AZT + AMK and AZT + GM.     

Nosocomial outbreak of ceftazidime-resistant Serratia marcescens strains that produce a chromosomal AmpC variant with N235K substitution

Serratia marcescens is a Gram-negative bacterium that is often associated with nosocomial infections. Here we analyzed the resistance mechanism of the ceftazidime-resistant S. marcescens nosocomial strains. The five S. marcescens urinary tract infection-associated isolates were positive for chromosomal ampC and bla(TEM-1). Four of the five strains, ES11, ES31, ES42, and ES46, were single clone and ceftazidime resistant. The fifth strain, ES71, was susceptible to ceftazidime. Analysis of the deduced amino acid sequence revealed a Glu-235-Lys substitution in the third amino acid of the third motif of AmpC from both ES46 and ES71, and a site-directed mutagenesis experiment confirmed that this substitution is involved in the ceftazidime resistance phenotype. However, the resistance phenotypes of strains ES46 and ES71 to ceftazidime were quite different from one another, indicating that another mechanism, in addition to the AmpC mutation, is also involved in the determination of the resistance phenotype of these strains. Basal AmpC activity was more than two times higher in strain ES46 than in ES71, which could result in the differing resistance phenotypes of these two strains. The clinical significance and prevalence of extended-spectrum cephalosporin-resistant S. marcescens strains harboring the mutated chromosomal ampC gene are unclear in Japan and remain to be elucidated.     

Molecular analysis of R-factors from multiresistant nosocomial isolates

During an epidemic of infections at the Seattle Veterans Hospital, Washington, due to a multiresistant strain of Serratia marcencens, other enteric species were isolated that had antibiograms nearly identical to those of the epidemic S. marcescens. In 11 instances, these multiresistant species were isolated from specimens that also contained the epidemic serratia strain. All isolates of the epidemic serratia strain contained a conjugative 45-megadalton R-factor (pLST1000) coding for intermediate resistance to three amino-glycosides (minimal inhibitory concentrations, 4--8 micrograms/ml) and high-level resistance to ampicillin, carbenicillin, cephalothin, streptomycin, and sulfonamide. With the use of agarose gel electrophoresis and restriction endonuclease cleavage patterns after digestion with EcoRI, BamH1, and HindIII, it was determined that eight different enteric strains of six different species isolated from the patients contained an R-factor that was molecularly identical to the one isolated from the epidemic strain of S. marcescens. Thus, the epidemic of multiresistant infections at this hospital was caused both by the spread of an epidemic strain and an "epidemic plasmid." The molecular characteristics of pLST1000 appear to be different from previously described multiresistant plasmids.     

Genotyping of methicillin-resistant Staphylococcus aureus isolated from inpatients and medical workers in orthopaedics ward

Methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated from the inpatients in orthopaedics ward hospitalized from March 1998 to November 2000, hospital environments, medical workers and the inpatients transferred from TCC (Trauma and Critical Care Center). Genotype by pulsed field gel electrophoresis (PFGE) and biotype according to the production of coagulase, enterotoxin and toxic-shock syndrome toxin-1 (TSST-1) were determined for the MRSA strains to analyze the infection source and transmission route of the infection. Out of 673 S. aureus strains isolated from the inpatients, 390 strains (57.5%) were MRSA. In 89 medical workers in orthopaedics ward, MRSA were isolated in 23 (25.8%) and 7 (7.9%) workers from nasal cavity and hand, finger, respectively. In contrast, no MRSA was isolated from hospital environments. Eighty MRSA strains (80%) from the inpatients and 8 MRSA strains (75%) from the medical workers were shown to have same biotype; coagulase II-enterotoxin C-TSST-1 (+) (II-C- (+)). MRSA strains isolated from the inpatients were grouped into 24 types according to PFGE patterns, and types 17 (17 strains), 12 (13 strains), 1 (8 strains), 4 (8 strains) and 13 (6 strains) were dominant among the MRSA strains isolated. It was shown that MRSA strains with the same PFGE genotype were detected at the same time in the different wards. In addition, MRSA strains isolated from medical workers were all PFGE genotypes 1 and 4. MRSA strain isolated from a new inpatient had a different PFGE type from the 24 kinds of genotype. These results suggest that the involvement of the medical workers might be important as infection source and for transmission of MRSA in hospital.     

Trend of antimicrobial drug-susceptibility of blood isolates at an oncological center (1998-2003)

OBJECTIVE: To describe the patterns of antimicrobial resistance organisms isolated in blood cultures from patients detected in a tertiary level of care, teaching oncological hospital. MATERIAL AND METHODS: All strains obtained from blood cultures from 1998 to 2003 were included and processed using the Bactec and Microscan system to determinate isolates and susceptibility to antimicrobials.The percent difference (increase or decrease) was obtained by comparing the frequency of resistance at baseline and at the end of the study. RESULTS: A total of 2071 positive blood cultures were obtained; 59.7% of isolates were Gram negative bacteria, 35.7% Gram-positive bacteria and 4.6% were yeasts. E. coli was the most frequent isolated (18.6%), followed by. Staphylococcus epidermidis (12.7%) and Klebsiella spp (9%). Throughout the study the susceptibility of Gram negative bacteria was stable and over 88% for most of the antimicrobials tested (except for Pseudomonas aeruginosa). Ciprofloxacin susceptibility for Escherichia coli stayed around 50%. Susceptibility to amikacin was higher than that to gentamicin.Staphylococcus aureus susceptibility for oxacillin was 96% and that for vancomycin 100%. S. epidermidis susceptibility for oxacillin was 14% and for vancomycin was 98.6%. No strains of vancomycin-resistant enterococci were found. All Streptococcus pneumoniae strains were penicillin susceptible. CONCLUSIONS: The drug-resistance found in this hospital is the result of the control in the use of antimicrobials, the hospital nosocomial infection program and the use of drug combination in all patients with bacteremia.     

Clinical characterization of blaIMP positive gram-negative rods isolated cases]

We detected the metallo-beta-lactamase gene blaIMP positive strains of the gram-negative rods (GNR) isolated in Oita Medical University Hospital between 1993 and 1999 and studied the clinical characteristics of patients infected or colonized with blaIMP positive GNR. 25 strains (20 Pseudomonas aeruginosa and 5 Serratia marcescens) were detected and most of them were isolated from urinary samples after 1997. In the studies of antimicrobial susceptibility, some strains had sensitivity to aztreonum or imipenem although most of the strains showed multidrug resistance. When blaIMP positive GNR were isolated from patients, these strains were thought to have caused infection in 88% of the patients. About half of the patients were over 65 years old and had malignant diseases. Most of the patients had inserted urinary tract catheters, intratracheal tube or intravernous catheters. It was suggested that the insertion of the catheters were related to infection of blaIMP positive GNRs. Two patients were not treated with any antibiotics before the isolation of blaIMP positive GNRs although more than half of the patients were administered carbapenems and cephems. Most of strains were isolated in the same department and showed the same genotype by pulsed field gel electrophoresis.     

脉冲场凝胶电泳在肠炎沙门菌食源性疾病溯源中的应用

目的对2006年广州地区食源性疾病中分离的肠炎沙门菌进行分子分型,探讨广州地区肠炎沙门菌的分子型别和多态性,为食源性疾病溯源及致病菌数据库的建立提供依据。方法采用限制性内切酶XbaI,对2006年分离到的菌株进行PFGE分子分型,使用BioNumericsVersion4.0软件(使用Dice系数和UPGMA法)对菌株进行聚类分析,并与深圳市的肠炎沙门菌PFGE型别进行比较。结果所有74株肠炎沙门菌均得到一致的PFGE克隆型,表明两次不同的食源性疾病均由同一PFGE型引起。广州与深圳的肠炎沙门菌PFGE图谱的比较表明,两地食源性疾病分离株具有很近的亲缘关系。结论PFGE分子分型与流行病学资料紧密结合可增强对肠炎沙门菌食源性疾病的溯源和预警。     

Epidemiology of cholera--a five year study

A total of 286 strains of Vibro Cholerae were isolated and tested over a period of five years. The strains were identified by standard methods and confirmed by slide agglutination tests with polyvalent, Ogawa and Inaba antisera. The non-agglutinating strains were tested with O-139 antisera. The maximum number of cases were found in the age group of 0-10 years. The number of females affected was more than the males. V. cholerae O-139 was isolated in the year 1998 and then again in 2000. V. cholerae serotype Inaba was found only in the year 1999. All of the other isolates belonged to the serotype Ogawa. The periodic shift between O1 and O-139 serogoups is reminiscent of the shifts from the Ogawa to the Inaba serotypes periodically witnessed among V. cholerae, possibly mediated by the immune pressure in the population.     

Relation of bacterial flora between upper and lower respiratory tracts in patients with long-term tracheostomy]

Throat secretions (TS) and bronchial secretions aspirated from tracheostomy (TSTA) were cultured at the same time in 9 subjects with long term tracheostomy every two weeks from January, 1990 to December, 1990. Total number of each examination in TS and TSTA were 200 times. Mean number of bacteria isolated by single culture were 2.9 strains in TS and 1.8 strains in TSTA. Isolated bacteria were mainly alpha-Streptococcus (84.8%) and Neisseria (69%) in TS, and Pseudomonas aeruginosa (53.5%) and Serratia marcescens (30%) in TSTA. Only 20% of P. aeruginosa or S. marcescens in TSTA were isolated from TS. In 8 cases of 9, P. aeruginosa in TSTA were isolated with every time or long term. There were 14 episodes of respiratory infections in 6 cases. P. aeruginosa were causative organisms in 7 episodes. It suggests that P. aeruginosa tended to colonize in lower respiratory tracts of the patients with long term tracheostomy and to become causative organisms in respiratory infections.     

An epidemiological analysis of Stenotrophomonas maltophilia strains in a university hospital

The aim of this investigation was to evaluate the epidemiology of Stenotrophomonas maltophilia in a university hospital of Turkey. From June 2000 to December 2001, S. maltophilia strains were collected, clinical presentations were noted, and MIC determinations were performed by means of E-test. Enterobacterial repetitive intergenic consensus sequences-PCR (ERIC-PCR) was used for molecular typing of the strains. Forty-four strains of S. maltophilia were isolated from 41 hospitalized patients in a teaching hospital. The majority of specimens were from the blood and respiratory tract. Antimicrobial sensitivities of these strains were as follows: 97.7 % trimethoprim-sulfamethoxazole, 15.9% ticarcillin, and 95.4% ticarcillin- clavulanate. The strains were evaluated using the ERIC-PCR method. It was of interest to note that epidemiological typing revealed three small outbreaks that were caused by a total of 12 strains. The remaining isolates generated singular DNA patterns. DNA amplification was possible in 38 isolates and yielded 26 different patterns in a period of 20 months, leading to the suggestion that commensal bacteria becomes selected in the presence of a suitable host.     

A case of penicillin-resistant pneumococcal meningitis and antibiotic susceptibility of Streptococcus pneumoniae isolated from children

Recently, isolation of penicillin-resistant S. pneumoniae has been increasing. The first Japanese case of penicillin-resistant pneumococcal meningitis was reported in 1988. We experienced a case of a one-year-old boy with penicillin-resistant pneumococcal meningitis who dead on arrival on his third day of illness. Minimal inhibitory concentration (MIC) of penicillin G or S. pneumoniae isolated from cerebrospinal fluid and blood was 0.6 micrograms/ml. We evaluated the antibiotic susceptibility of 163 strains of S. pneumoniae isolated from children from 1985 to 1988. Penicillin G (PCG), ampicillin (ABPC), cefotaxime (CTX), imipenem (IPM), and vancomycin (VCM) had good susceptibilities to S. pneumoniae. Twelve of the 163 isolates (7.3%) were penicillin-resistant strains whose MIC of PCG were more than 0.1 microgram/ml, and all of them were intermediately resistant. The annual penicillin-resistant rates were 12.5% in 1985, 1.3% in 1986, 0% in 1986, and 19.0% in 1988. We also evaluated the MIC distribution and MIC90 of antibiotics available for meningitis against penicillin-sensitive and -resistant S. pneumoniae. MIC90 of PCG and ABPC against penicillin-resistant strains was 1.56 micrograms/ml, and it might be dangerous to use PCG or ABPC for central nervous system pneumococcal infections. MIC90 of IPM against penicillin-resistant strains was 0.1 microgram/ml, and that of VCM was 0.4 micrograms/ml. There was little fall of susceptibilities of resistant strains in IPM and VCM. We evaluated the MIC distribution and MIC70 of antibiotics for oral usage against penicillin-sensitive and -resistant S. pneumoniae. Although there were falls of susceptibilities of resistant strains in PCG and ABPC, these two antibiotics had the best susceptibilities among the oral antibiotics.     

Emergence of nalidixic acid resistance in Shigella sonnei isolated from patients having acute diarrheal disease: report from eastern province of Saudi Arabia

During the 5 years of the study period (October 1999-October 2003), 110 strains of Shigella were isolated from fecal samples of patients having acute diarrheal diseases. Shigella sonnei phase 1 was the most prevalent (88/110, 80.0%) serotype. Resistance to nalidixic acid was not encountered from 1999-2002. Nalidixic acid resistance was observed in 6/13 (46.1%) of the S. sonnei phase 1 strains isolated from April-August 2003. Minimum inhibitory concentration to nalidixic acid among these strains was 48-96 microg/ml. All the six nalidixic acid resistant strains of S. sonnei phase 1 had reduced susceptibility (MIC 0.25 microg/ml) to ciprofloxacin.     

Infections Caused by Stenotrophomonas maltophilia– A Prospective Study

Background: Stenotrophomonas maltophilia is an opportunistic microorganism, often highly resistant to routinely tested antibiotics. This microorganism is isolated in specimens from patients with nosocomial infections with increasing frequency. Patients and Methods: During a 1-year period (1998/1999) S. maltophilia was isolated from 137 specimens (0.26% of all investigated specimens) from 80 patients who were treated in a 1,500 bed major tertiary care teaching hospital in Leipzig. The data of 76 patients (133 specimens) could be collected and analyzed completely. Results: The pathogen was most frequently detected in specimens from the respiratory tract (54%). In five patients (six cases) S. maltophilia was isolated from blood cultures (0.3% of all positive blood cultures; 1.4% of all gram-negative isolates from blood cultures). 70 of the infected patients were inpatients and 32 (42%) of them were treated on the internal medicine wards. Of these 32 patients only six (19%) were pretreated with imipenem. The length of stay at the hospital resulted in an independent increased risk of infection with S. maltophilia. In addition, this organism was detected in six infected outpatients. Conclusion: S. maltophilia is not only a nosocomial pathogen. Pretreatment with a carbapemnem is no longer an unequivocal risk factor for an infection with S. maltophilia. Received: April 13, 2000 · Revision accepted: February 27, 2001     

Significance of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) by medical staff in nosocomial infection

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important microorganisms in nosocomial infection. Healthy medical staff working in MRSA endemic wards are known to have MRSA in their nasal cavity, swabs, but the significance of their positive nasal swab cultures in infections among the patients has not been confirmed. The purpose of this study was to compare the antibiotic susceptibility and coagulase typing of strains isolated from the infected patients and from nasal swab cultures of medical staff working in ICU. Twenty-six nurses and 20 doctors working in ICU where MRSA was endemic were examined. Six nurses and 10 doctors gave positive nasal swab cultures for S. aureus, and 2 of the nurses' strain and 5 of the doctors' strains were methicillin-resistant. These strains were sensitive to IPM, GM, MINO and OFLX, while the strains clinically isolated from infected patients were resistant to these antibiotics. MRSA isolated from nasal swab cultures from medical staff developed marked resistance to IPM, GM, MINO, and OFLX by incubating with these drugs, whereas they remained sensitive to VCM when they were incubated in VCM-containing medium. Methicillin-sensitive S. aureus (MSSA) isolated from nasal swab cultures of medical staff became resistant to DMPPC, CMZ, in addition to IPM, GM, MINO, and OFLX, but these strains did not develop resistance to VCM. Resistance to these drugs developed by incubating with these drugs did not diminish by incubating in drug-free medium for 3 weeks. The patients infected by MRSA had been previously given several kinds of antibiotics, whereas the medical staff had not been exposed to any kind of antibiotics during the same period. (ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of phenotypic tests for the detection of metallo-beta-lactamases in clinical isolates of Pseudomonas aeruginosa

Metallo-β-lactamase (MBL)-producing gram-negative bacteria are an increasing public health concern worldwide. Screening tests for the rapid and specific identification of these pathogens are essential, and should be included among routine diagnostics in laboratories. This study aimed to determine the MBL frequency among carbapenem-resistant Pseudomonas aeruginosa isolates, and to evaluate the accuracy of different tests in screening for MBL production. From January 2001 to December 2008, a total of 142 imipenem-non-susceptible P. aeruginosa strains were isolated from distinct clinical samples from hospitalized patients. These isolates were examined by PCR, MBL E-test, double-disk synergy test (DDST), and combined disk (CD) test. The minimal inhibitory concentration (MIC; μg/mL) was determined by agar dilution, and pulsed field gel electrophoresis (PFGE) was performed on all samples. Sequencing was performed to confirm and define the MBL variant and subtype. Using PCR and DNA sequence analysis, 93 strains were confirmed positive for MBLs, 91 strains for the blaSPM-1 gene, 1 strain for the blaIMP-1 gene, and 1 strain for the blaIMP-16 gene. PFGE displayed a clonal pattern. The sensitivities, specificities, positive and negative predictive values were evaluated for all tests. The DDST assay (CAZ-MPA) was the optimal method for screening MBL production in P. aeruginosa strains. However, the results of the CD assay (IMP/EDTA) showed close agreement with those of the DDST. In addition, the CD assay allowed a more objective interpretation and did not require the use of a toxic substance.     

Gentamicin/amikacin-resistant gram-negative bacilli at Detroit General Hospital, 1975–1976

During a consecutive 10 month period from November 1975 through August 1976, all gram-negative bacilli isolated at Detroit General Hospital were tested for gentamicin and amikacin resistance on Mueller-Hinton agar using 10 μg discs utilizing Bauer-Kirby methods. Amikacin-resistant strains (and many gentamicin-resistant bacilli) were similarly tested using tube dilutions in Mueller-Hinton broth. The two methods correlated well for gentamicin but did so imperfectly with amikacin. In analyses for amikacin susceptibilities, values for minimal inhibitory concentration(s) and minimal bactericidal concentrations obtained in broth were subsequently employed. In this survey, 4,640 gram-negative bacilli were isolated; 1,199 strains (26 per cent) and 37 strains (0.8 per cent) were resistant to gentamicin and amikacin, respectively. Thirty-six of the strains had combined gentamicin/amikacin resistance, and they represented 3.1 per cent of all of the gentamicin-resistant isolates. Gentamicin/amikacin-resistant gram-negative bacilli were widely spread throughout medical and surgical services of the hospital. These organisms clustered in the adjacent intensive and respiratory care units. Amikacin-resistant bacilli were recovered from sputum (15 times), wounds (12 times), urine (five times) and blood (five times). Pseudomonas aeruginosa was isolated six times, Ps. cepacia 13 times and Serratia marcescens six times. These strains were usually susceptible to chloramphenicol, tetracycline and trimethoprimsulfamethoxazole but were regularly resistant to amikacin, gentamicin, tobramycin, kanamycin, streptomycin, carbenicillin and cefoxitin.