Ribotyping of selected isolates of Enterobacter cloacae and clinical data related to biotype, phage type, O-serotype, and ribotype

Population genetics of the nomenspecies Enterobacter cloacae

The genetic heterogeneity of the nomenspecies Enterobacter cloacae is well known. Enterobacter asburiae, Enterobacter cancerogenus, Enterobacter dissolvens, Enterobacter hormaechei, Enterobacter kobei, and Enterobacter nimipressuralis are closely related to it and are subsumed in the so-called E. cloacae complex. DNA-DNA hybridization studies performed previously identified at least five DNA-relatedness groups of this complex. In order to analyze the genetic structure and the phylogenetic relationships between the clusters of the nomenspecies E. cloacae, 206 strains collected from 22 hospitals, a veterinarian, and an agricultural center in 11 countries plus all 13 type strains of the genus and reference strain CDC 1347-71(R) were examined with a combination of sequence and PCR-restriction fragment length polymorphism (PCR-RFLP) analyses of the three housekeeping genes hsp60, rpoB, and hemB as well as ampC, the gene of a class C beta-lactamase. Based on the neighbor-joining tree of the hsp60 sequences, 12 genetic clusters (I to XII) and an unstable sequence crowd (xiii) were identified. The robustness of the genetic clusters was confirmed by analyses of rpoB and hemB sequences and ampC PCR-RFLPs. Sequence crowd xiii split into two groups after rpoB analysis. Only three strains formed a cluster with the type strain of E. cloacae, indicating that the minority of isolates identified as E. cloacae truly belong to the species; 13% of strains grouped with other type strains of the genus, suggesting that the phenotypes of these species seem to be more heterogeneous than so far believed. Three clusters represented 70% of strains, but none of them included a type or reference strain. The genetic clustering presented in this study might serve as a framework for future studies dealing with taxonomic, evolutionary, epidemiological, or pathogenetic characteristics of bacteria belonging to the E. cloacae complex.

Role of the clinical microbiology laboratory in infection control--a Danish perspective

Clinical microbiology laboratories in Denmark are located in hospitals and staffed by clinical microbiologists who are clinically trained medical doctors. Each county has its own clinical microbiology unit, serving a population of 0.3-0.6 million. The responsibilities of clinical microbiology unit cover many different aspects of infection control. They include detection of outbreaks of hospital-acquired infections, screening for multi-resistant organisms, advice to clinicians about disinfection, sterilization and isolation procedures, and the rational use of antibiotics. Clinical microbiologists work closely with infection control nurses. Together they form the infection control team, which is the executive part of the local infection control committee. The infection control team is also the main body responsible for the development of guidelines, which are approved by the regional infection control committee. The local microbiology laboratories work in close contact with the National Department of Hospital Hygiene and other reference laboratories at the State Serum Institute. The present structure of infection control was established 25 years ago. The main aim at that time was to decentralize infection control and establish facilities as close to clinicians and patients as practically possible. This has solved most basic problems related to infection control, and compliance by clinicians has been fairly good. However, the present organization will not meet future requirements for standardization and documentation of quality. Currently a national standard for infection control is being prepared. It consists of a main standard defining requirements for the management system and 12 subsidiary standards defining requirements for specific areas of infection control. Adoption of the standard will undoubtedly require additional resources for infection control at a local level, and some organizational changes may also be needed. Infection control should be maintained as an integrated part of clinical microbiology.

Molecular epidemiology of a nosocomial outbreak due to Enterobacter cloacae and Enterobacter agglomerans in Campinas, São Paulo, Brazil

A total of 73 isolates (57 Enterobacter cloacae and 16 Enterobacter agglomerans), recovered during an outbreak of bacteremia in the Campinas area, São Paulo, Brazil, were studied. Of these isolates, 61 were from parenteral nutrition solutions, 9 from blood cultures, 2 from a sealed bottle of parenteral nutrition solution, and one was of unknown origin. Of the 57 E. cloacae isolates, 54 were biotype 26, two were biotype 66 and one was non-typable. Of 39 E. cloacae isolates submitted to ribotyping, 87.2% showed the same banding pattern after cleavage with EcoRI and BamHI. No important differences were observed in the antimicrobial susceptibility patterns among E. cloacae isolates exhibiting the same biotype, serotype and ribotype. All E. agglomerans isolates, irrespective of their origin, showed same patterns when cleaved with EcoRI and BamHI. The results of this investigation suggest an intrinsic contamination of parenteral nutrition solutions and incriminate these products as a vehicle of infection in this outbreak.

The discriminatory power of ribo-PCR compared to conventional ribotyping for epidemiological purposes

Molecular typing techniques have become increasingly important for confirmation of epidemiological relationships and delimitation of nosocomial outbreaks. The discriminatory power of the two DNA-based typing methods, conventional ribotyping and ribo-PCR, was assessed to distinguish between selected strains of Acinetobacter calcoaceticus, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa. Overall, conventional ribotyping was more discriminatory than ribo-PCR.

Phenotyping and genotyping methods applied to investigate the relatedness of Brazilian isolates of Enterobacter cloacae

In order to evaluate the resolving power of several typing methods to identify relatedness among Brazilian strains of Enterobacter cloacae, we selected twenty isolates from different patients on three wards of a University Hospital (Orthopedics, Nephrology, and Hematology). Traditional phenotyping methods applied to isolates included biotyping, antibiotic sensitivity, phage-typing, and O-serotyping. Plasmid profile analysis, ribotyping, and macrorestriction analysis by pulsed-field gel electrophoresis (PFGE) were used as genotyping methods. Sero- and phage-typing were not useful since the majority of isolates could not be subtyped by these methods. Biotyping, antibiogram and plasmid profile permitted us to classify the samples into different groups depending on the method used, and consequently were not reliable. Ribotyping and PFGE were significantly correlated with the clinical epidemiological analysis. PFGE did not type strains containing nonspecific DNase. Ribotyping was the most discriminative method for typing Brazilian isolates of E. cloacae.

Epidemiology of Klebsiella bacteraemia: a case control study using Escherichia coli bacteraemia as control

Epidemiological data from 117 episodes of Klebsiella bacteraemia were compared with those from matched controls with Escherichia coli bacteraemia. Cases and controls were obtained from 20,631 blood cultures taken from patients in Hvidovre Hospital between 1990 and 1992. The data studied included: sex and age, risk factors, portal of entry, outcome, nosocomial acquisition and distribution within the hospital. The incidence of Klebsiella bacteraemia was 9.3/10,000 admissions (76% Klebsiella pneumoniae; 24% Klebsiella oxytoca). Patients with Klebsiella and E. coli bacteraemia had many common features, including a high incidence of neoplastic disease, biliary tract disease, and renal failure. Many had undergone surgery or received therapy with steroids, antacids or antibiotics. Klebsiella bacteraemia was more often found in males, in patients with hospital contact within the previous month, and polymicrobial infection. Logistic regression analysis showed that use of invasive plastic devices and diabetes were significantly associated with Klebsiella bacteraemia. The urinary tract was the commonest source, followed by the biliary tract; 27% of patients had no obvious focus of infection, and in many of these an invasive device may have been involved. Forty-five K-serotypes were found--the largest number being nine strains of type K3; only a few strains had acquired resistance characters to antimicrobial agents. There were no differences between community- and hospital-acquired strains; indicating that our hospital does not have a resident strain of Klebsiella.

Enterobacter spp.: pathogens poised to flourish at the turn of the century

Knowledge of the genus Enterobacter and its role in human disease has expanded exponentially in recent years. The incidence of infection in the hospital and the community has increased. New clinical syndromes have been recognized. Enterobacter spp. have also been implicated as causes of other syndromes that traditionally have been associated almost exclusively with more easily treatable pathogens, such as group A streptococci and staphylococci. Rapid emergence of multiple-drug resistance has been documented in individual patients during therapy and in populations and environments with strong selective pressure from antimicrobial agents, especially the cephalosporins. Therapeutic options for patients infected with multiply resistant strains have become severely limited. Carbapenems or, alternatively, fluoroquinolones are the most predictively active options, although resistance to both classes has been observed on rare occasions. Enterobacter spp. appear well adapted for survival and even proliferation as the turn of the century approaches.

A comparative study of nosocomial and community-acquired strains of Escherichia coli causing bacteraemia in a Danish University Hospital

In a previous study we found a considerably higher mortality rate in patients with nosocomial (NO) compared with community-acquired (CA) Escherichia coli bacteraemia. To establish whether this was due to host differences or to differences in the infecting bacteria, we compared 205 NO with 172 CA bacteraemic isolates of E. coli with respect to serotype, virulence factors and antimicrobial susceptibility. Overall the six most frequent O antigens were O18ac, O6, O1, O2, O15 and O75, respectively. The six most frequent capsular antigens were K1, K5, K52, K2, K7 and K34, respectively. No major differences were found regarding O-antigens, capsular antigens, production of haemolysin, P-fimbriation, serum sensitivity or antimicrobial susceptibility. Surprisingly we found 17 strains of serotype O15:K52:[H1] of both NO (eight) and CA (nine) origin with similar phenotypic characteristics to a strain causing a CA outbreak in London 1986-1987. Possibly the Danish and the English strains belong to the same clone. Our findings argue against the existence of a distinct NO flora. NO E. coli bacteraemia strains seem to originate primarily from the patients' own flora.

Resistance characteristics of blood culture isolates of Enterobacter cloacae with special reference to beta-lactamases and relation to preceding antimicrobial therapy

Resistance characteristics of 53 blood culture isolates of E. cloacae were examined and correlated with antimicrobial treatment preceding bacteraemia. Resistance patterns of 22 antimicrobial agents, presence of resistant mutants, and inducibility of beta-lactamase were investigated; furthermore, population analysis and investigation of beta-lactamase production of selected isolates were performed. Thirty-two isolates (60%) were resistant to cephalothin and/or cefoxitin and/or ampicillin, and 14 isolates (26%) had further resistance characteristics, 7 of the 14 being resistant to non-beta-lactam antibiotics. All ampicillin-susceptible and 76% of cefotaxime-susceptible isolates had resistant mutants in the zone of inhibition when high inoculum was used. All isolates investigated had inducible chromosomal beta-lactamases, and, in addition, two isolates had an enzyme corresponding with TEM-1. Correlation of resistance patterns and antimicrobial treatment preceding bacteraemia showed that treatment with a third-generation cephalosporin was associated with beta-lactam multiresistance. In conclusion, susceptibility testing of beta-lactam antibiotics of Enterobacter must be interpreted with caution and monotherapy with an extended-spectrum cephalosporin should be avoided unless presence of resistant mutants and inducibility of beta-lactamase can be excluded.