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Within six months of opening of the new Dublin Dental Hospital in September 1998, areas of corrosion were observed on many of the baseplates of the hospital's 103 dental chair units (DCUs) at the site of attachment of the suction hoses. The corroded areas were heavily contaminated with Pseudomonas spp. and related genera posing a risk of cross-infection, particularly for immunocompromised patients. These species were used as marker organisms to investigate the source of the contamination. P. aeruginosa was the predominant species recovered from 41 selected DCU baseplates (61% prevalence), whereas P. putida (46% prevalence) and P. aeruginosa (43% prevalence) were predominant at the attachment ends of 37 selected high-volume suction hoses. Forty-one selected isolates of P. aeruginosa from 13 DCU baseplates, 16 high-volume suction hoses and 12 coarse filter housings (another suction system site) from 19 separate DCUs were serotyped to determine the similarity of isolates at each site. The majority of isolates (68.3%) belonged to serotype O:10, while the remainder belonged to serotypes O:6 (7.3%), O:11 (7.3%), O:14 (9.8%) and O:5/O:16 (7.3%). Of the isolates from DCU baseplates, additional isolates with the same serotype were recovered from other suction system sites in 10/13 (77%) cases. Isolates of only one serotype were recovered from each of the 19 DCUs investigated. Forty-one serotyped isolates were also subject to computer-assisted analysis of SpeI-generated DNA fingerprint profiles, and similarity coefficient (S(AB)s) values were calculated for each pairwise combination of isolate profiles. The data obtained showed that the isolates consisted of two distinct main populations, each containing separate clades corresponding to specific serotypes. Serotype O:6 (three isolates), O:11 (three isolates) and O:5/O:16 (three isolates) belonged to a single strain in each case. Serotypes O:14 (four isolates) and O:10 (28 isolates) belonged to two strains in each case. The two serotype O:10 strains, termed fingerprint groups I (four isolates from three DCUs) and II (24 isolates from 10 DCUs), were the most distantly related of all the strains identified. These findings demonstrated that the hospital DCUs had become colonized with a small number of P. aeruginosa strains, one of which (serotype O:10, fingerprint group II) predominated. These results also confirmed that DCU baseplate contamination was most likely to be due to leakage from suction system hoses at the baseplate attachment sites, probably due to loosening during use. Replacement hose connectors that firmly retained the suction hoses in the attachment sites so that they could not be loosened by movement of the suction hoses solved this problem, and eliminated further contamination of the DCU baseplates.

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Over the 8 year period 1988-1995, 1367 isolates of Serratia marcescens were isolated from 582 patients on 12 different wards of a large Dublin hospital and were particularly associated with the surgical intensive care unit. The annual incidence was over 200 isolates from 1990 to 1992 but fell to below 100 following the opening in April 1992 of a replacement surgical hospital incorporating a new intensive care unit on the same site. The most common source of S. marcescens was sputum from patients. Strain identities were determined by serotyping and phage typing at least one isolate from each of 311 of the 582 patients. The results showed that a single epidemic strain of serotype O14:K14 was present in 69% of these patients, and persisted throughout the hospital for the whole of the eight-year period. This strain was recovered from a variety of clinical specimens, including blood cultures. A minor outbreak involving a serotype O16:K28 strain also occurred and this strain also persisted from at least 1989 to 1994. Extensive surveillance failed to reveal an environmental source or faecal carriage. The likely mode of transmission appears to have been via staff hands from both symptomatic and asymptomatic patients acting as reservoirs of the organism, as has commonly been reported for this species.

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Over the last 30 years, Serratia marcescens has become an important cause of nosocomial infection. There have been many reports concerning the identification, antibiotic susceptibility, pathogenicity, epidemiological investigations and typing of this organism. Accurate identification is important in defining outbreaks. The API 20E system has been used widely, but is not individually satisfactory. The growth of S. marcescens in the environment has been investigated in relation to water, disinfectants and plastics such as blood bags. Certain extracellular products are unique to S. marcescens. Pigment (prodigiosin) biosynthesis by S. marcescens has been investigated fully since the emergence of the organism as a cause of infection. Many other aspects of the pathogenicity and virulence of S. marcescens have been studied, including adherence and hydrophobicity, lipopolysaccharide (LPS) and extracellular products. Two modes of adhesion to host epithelial surfaces have been suggested. These are mannose-resistant (MR) pili and mannose-sensitive (MS) pili. LPS, which is responsible for the biological activity of endotoxin, has been investigated fully and 24 somatic antigens have been described. The production of different enzymes by S. marcescens as virulence factors has also been reported, including chitinase, lipase, chloroperoxidase and an extracellular protein, HasA. Antibiotics used to treat serratia infection include beta-lactam agents, aminoglycosides and fluoroquinolones and a variety of different resistance mechanisms have been demonstrated. Typing methods used to study the epidemiology of S. marcescens include biotyping, bacteriocin typing, phage typing, plasmid analysis, polymerase chain reaction amplification of enterobacterial repetitive intergenic consensus sequences (ERIC-PCR) and ribotyping. Serological typing has also been used and this method seems to be a suitable first-line typing method for S. marcescens, although some strains remain untypable. RAPD-PCR has also been applied to a small number of isolates and seems to be a promising method, especially for rapid monitoring of an outbreak and tracing the source of initial infection.

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Serratia marcescens has emerged in the last few years as an important nosocomial pathogen. Many methods for typing this organism have been described. In this study the random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) was shown to be a convenient typing method for S. marcescens. Different combinations of primers previously used for typing other gram-negative bacilli were assessed. The combination of primer HLWL-74 and 1254 gave distinguishable patterns for different serotypes and proved to be the most satisfactory. By applying this combination to 175 isolates of S. marcescens, which could be classified into 38 groups on the basis of serotyping and phage typing, 73 different RAPD patterns with good reproducibility were obtained. This is, to our knowledge, the first application of the method to a large collection of S. marcescens representing a wide range of serotypes.

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Bacteriocins are extracellular substances produced by different types of bacteria, including both Gram positive and Gram negative species. They can be produced spontaneously or induced by certain chemicals such as mitomycin C. They are biologically one of the important substances, and have been found to be useful in membrane studies and also in typing pathogenic microorganisms causing serious nosocomial infections. Bacteriocins are a heterogeneous group of particles with different morphological and biochemical entities. They range from a simple protein to a high molecular weight complex: the active moiety of each molecule in all cases seems to be protein in nature. The genetic determinants of most of the bacteriocins are located on the plasmids, apart from few which are chromosomally encoded. These bactericidal particles are species specific. They exert their lethal activity through adsorption to specific receptors located on the external surface of sensitive bacteria, followed by metabolic, biological and morphological changes resulting in the killing of such bacteria. This review summarises the classification, biochemical nature, morphology and mode of action of bacteriocins as well as their genetic determinants and the microbiological relevance of these bactericidal agents.

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A study was undertaken to determine the distribution, antibiotic susceptibility and phage type pattern of nasally-carried Staphylococcus aureus in the community. Coagulase-positive staphylococci were isolated from 180 of 440 individuals. The rate was higher in the inner city and among young adults and middle-aged males. The isolates were examined for phage-type patterns and antibiotic susceptibility. Most (60.6%) of the isolates were typable either at Routine Test Dilution (RTD) or at 100 RTD. Most belonged to phage group I (53.2%) and phage group III (21.1%). Susceptibility to penicillin and ampicillin was low at 12.3 and 15.5% respectively. All were susceptible to vancomycin. Methicillin-resistance was unexpectedly low at 0.6% whereas tetracycline and erythromycin resistance were in line with recent trends at 4.5 and 2.7%. The rate of multiple resistance was low at 2.3%.

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Three methods, O-serotyping, phage typing and susceptibility to bacteriocins, were used to type 357 clinical isolates of Enterobacter cloacae cultured from 219 patients. One hundred and sixty isolates were typed by serology and phage typing. When these two methods were used, primary classification of isolates was based on serology (65.7% typable) and phage typing for further subdivision (94.1% typable). When all the isolates were typed by cloacin susceptibility, 81.5% of them were typable. Maximum discrimination between cultures was achieved when the three methods were used together; no single method was sufficiently discriminatory. There was a close parallel between serotyping and bacteriocin lysis pattern. The latter was easy to perform and the results were achieved within 48 h. By applying this typing system two episodes of cross-infection were identified in a haematology/oncology unit and intensive care unit.

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Direct Antibiotic Sensitivity Testing (DST) is a rapid means of diagnosing urinary tract infection (UTI) and obtaining antibiotic sensitivity patterns of the infecting organisms. In this study 227 urine samples from general practice were analysed using this technique with those obtained using the standard laboratory method. DST was shown to be 94.6% sensitive, and 80.7% specific. Escherichia coli was the commonest infecting organism. Augmentin was the most effective antibiotic tested, all organisms tested in vitro, being susceptible. Direct Sensitivity Testing is rapid, inexpensive, easy to perform, highly sensitive and specific. It should be considered by general practitioners as an alternative to the problems and delays involved in sending urine samples to the laboratory and in awaiting the results.

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The observation that Enterobacter cloacae has emerged as a cause of infection in a haematology/oncology ward prompted a prospective study over an eight-month period. Sensitivity to antibiotics, plasmid screening and typing methods were used to describe the epidemiology of the organism which was isolated from 22 patients. There was evidence of a limited amount of cross infection. No common sources were found. A large number of distinct strains were identified. E. cloacae infection was associated with prolonged profound leucopenia and broad-spectrum antibiotic therapy.

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An alternative method for detecting the production of slime by coagulase negative staphylococci was compared with the routinely used Christensen method on 124 isolates of coagulase negative staphylococci from carriage sites, blood cultures, and infected peritoneal dialysis fluids. The alternative method requires the use of a specially prepared solid medium--brain heart infusion broth, supplemented with 5% sucrose, and Congo red stain. Of the 124 tests, there was complete agreement between methods in 107 and only one strain was clearly negative by Christensen's method while positive on Congo red agar. The Congo red method is rapid, sensitive, and reproducible and has the advantage that colonies remain viable on the medium. It is also not subject ot interbatch variation of media which sometimes affects the reproducibility of the Christensen method.

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Septicaemia is the commonest cause of morbidity and mortality following transurethral prostatectomy. Routine blind antibiotic prophylaxis is not always effective and there is a tendency to over-use potent new and expensive antimicrobials. Attempts to "sterilise" the urine preoperatively are also expensive and disruptive. However, appropriate treatment/prophylaxis can be administered economically using rapidly obtained laboratory results. We describe here a technique of routine direct antibiotic sensitivity testing (DST) of the patient's urine pre-operatively and before catheter removal. Such testing can be performed by junior medical staff in a ward side-room. An appropriate antibiotic may then be administered parenterally 1 h before surgery or catheter removal. A total of 102 consecutive patients underwent TURP and only 1 of those with infected urine became septicaemic. In this instance, an appropriate antibiotic had been incorrectly given orally before removal of the catheter. If the antibiotic sensitivities of a patient's urine are known, and an appropriate antibiotic is given parenterally 1 h pre-operatively or before catheter removal, the incidence of septicaemia following transurethral surgery may be significantly reduced.

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To assess whether bacteriological surveillance cultures can be used to predict infection in neutropenic patients, cultures were performed during the period of neutropenia of nose, throat and urine specimens collected once weekly and faeces specimens collected twice weekly. Seventy-six consecutively observed patients undergoing chemotherapy for haematological or non-haematological diseases were investigated. Severe infection including septicaemia, lower respiratory tract infection, anorectal lesion and urinary tract infection occurred in 32 patients. Enterobacter cloacae, Escherichia coli and Pseudomonas aeruginosa were the organisms most commonly involved. In the majority of cases of septicaemia the organisms were isolated from the faeces, often in pure culture, prior to the onset of septicaemia. Most of the isolates of Enterobacter cloacae were resistant to the empiric antibiotic therapy used in the unit and were able to colonise multiple sites, presumably increasing the risk of subsequent infection. Faecal culture is the most useful approach in bacteriological surveillance in neutropenic patients.

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Forty-one isolates of multiply resistant gram-negative bacteria causing infection in a urological unit of a Dublin hospital were collected during a 6-month period. Twenty-one isolates transferred multiple resistance to an Escherichia coli K-12 recipient in liquid matings. Serratia marcescens, Proteus morganii, Proteus vulgaris, and E. coli isolates harbored similar 120-megadalton IncC plasmids, whereas Enterobacter cloacae strains transferred a 160-megadalton plasmid of a different Inc group. Southern hybridization experiments were performed with purified fragments cloned from one IncC plasmid as probes. They were hybridized to plasmid sequences in total cellular DNA extracts, showing that the IncC plasmids were very closely related. This suggests that the same plasmid has transferred to different bacterial species in the hospital environment.

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A total of 185 strains of methicillin resistant Staphylococcus aureus was investigated for sensitivity to five other antimicrobial agents. The vast majority of these strains were also resistant to gentamicin and fusidic acid. Rifampicin was the most active drug tested (MIC90, 0.007 mg/l), while two newer compounds teichomycin and ciprofloxacin showed equal and appreciable activity (MIC90, 0.5 mg/l).

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In a 6 week period, three of 50 patients developed Pseudomonas aeruginosa septicaemia following Endoscopic Retrograde Cholangiopancreatography (ERCP). Pseudomonas aeruginosa serotype 10 was isolated from each of the patients and from the endoscope. The outbreak was related to inadequate disinfection of the air and water channel of the endoscope. Following the introduction of a modified decontamination technique, which involved rinsing the air and water channel with glutaraldehyde, no further cases of pseudomonas infection occurred, and the organism could not be isolated from the instrument. Obstruction of the biliary tract was a predisposing factor in the development of infection; and administration of antibiotics immediately following the procedure failed to prevent it. This may have been due to inadequate dosage. We suggest that patients presenting for ERCP, in whom obstruction of the biliary tract is suspected, should come prepared for immediate drainage of the obstructed system at the time of the procedure.

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Seventy isolates of Serratia marcescens were obtained from 30 patients in different units of one hospital between April 1982 and February 1983. No common source was found. Not all isolates were multi-resistant and nearly all that were, fell into two main groups, A and B. These groups were defined by phage typing and cephalosporin sensitivity, all apart from one Group B isolate were multi-resistant, whereas Group A isolates contained multi-resistant and sensitive strains. Plasmid screening, resistance transfer studies and plasmid elimination experiments demonstrated that the multi-resistant phenotype was due to a 120 Mdal transmissible plasmid. Resistance to cephalosporins was chromosomally encoded.

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