State of the art: typing Pseudomonas aeruginosa

[Various typing methods of Pseudomonas aeruginosa strains isolated from cystic fibrosis patients]

Typing methods are essential to understand the epidemiology of bacterial infections. Strain typing is important for the detection of sources or routes of infections, identification between endemic and epidemic strains and prevention of transmission between patients. Some Pseudomonas aeruginosa cystic-fibrosis strains could not be typed with conventional typing methods. Due to the diverse phenotypic nature of P. aeruginosa, phenotyping methods are not discriminatory enough to identify strains belonging to the same genotype. Thus, molecular typing methods are required. These methods should be applied when data from phenotypic typing analysis becomes ambiguous, such as in cystic fibrosis. Molecular typing methods, developed over the past decade, are highly discriminatory in capacity and reproducibility. However, they are more likely applied in specialized laboratories since they are expensive and increase the workload. A reliable and low-cost typing system is required for better defining the epidemiology of this pathogen and designing more rational policies of infection control. Comparison between typing methods will pinpoint the limits and effectiveness of each method and will improve in turn the choice of a nonspecialized laboratory in terms of simplicity, time and cost.

Bacteriocins: nature, function and structure

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.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

Serotype and serum sensitivity of Pseudomonas aeruginosa from children with cystic fibrosis: longitudinal studies and typing with monoclonal antibodies

Pseudomonas aeruginosa isolated from the respiratory tract of children with cystic fibrosis from Perth, Sydney or Brisbane, were serotyped with polyclonal antisera using the International Antigenic Serotyping System. Predominant strains were untypable among isolates from Brisbane (86% of 50 strains) and Sydney (60% of 50 strains) but 64% of the 408 isolates from Perth were polyagglutinating. The frequency distributions of typable strains showed differences from those reported in clinics in the northern hemisphere, but it appears that these local differences do not affect the emergence of strains with defective lipopolysaccharide antigens. Isolates from patients studied longitudinally showed correlation between duration of colonization, appearance of untypable or polyagglutinating strains and sensitivity to normal serum. Mucoid colonies were found more commonly from patients colonized for at least 12 months but, overall, there was no significant association between serotype and mucoid colonial morphology. Commercial monoclonal antibodies did not react with polyagglutinating or untypable strains and gave identical results to the polyvalent typing system with strains classified as typable.

Typing of Pseudomonas aeruginosa ear infections related to outcome of treatment

Of 142 patients with Pseudomonas aeruginosa (PSA) ear infections, 88 (62 per cent) had chronic otitis media and 54 (38 per cent) external otitis. Following serotyping and pyocin typing of their bacteria, and relating the type to outcome, patients could be divided into three groups: (1) 120 patients who had no recurrence with isolation of only one PSA strain, (2) 13 patients who had recurrent infections and in whom the same PSA strain was isolated in repeated cultures, and (3) nine patients who had recurrent disease, but who had a change in their PSA strains. Most of the PSA strains isolated from patients in groups (1) and (2) were stable to pyocin, and resistent to gentamicin. Patients in the first group were all cured initially by medical management. Of the nine patients in group (3) who had a different serotype on repeated cultures, medical treatment was successful in eight (89 per cent), but of the 13 patients in group (2) who had the same Pseudomonas aeruginosa serotype cultured, medical therapy failed in six (46 per cent) and mastoid surgery was required. Serotyping of Pseudomonas aeruginosa otitis may be helpful in predicting the type of management in patients who have recurrent infections.

Value of surveillance cultures in the management of neutropenic patients

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.

The use of a monoclonal antibody serotyping system in the study of the epidemiology of Pseudomonas aeruginosa

A monoclonal antibody method was used as a primary O serotyping method for 1084 isolates of Pseudomonas aeruginosa, using commercially available antibody reagents in slide agglutination tests with whole-cell antigen. Differences in distribution of serogroups were found between various hospitals in the district. Serotyping provided useful information in the investigation of suspected incidents of cross-infection. Colonization at multiple sites, or over periods of time, in a single patient usually involved only a single serogroup.

Subdivision of O serotypes of Pseudomonas aeruginosa with monoclonal antibodies

Sixteen murine monoclonal antibodies (MAbs) against serotypes O2, O5, and O16 (serogroup II) and subtypes O2b and O5d of Pseudomonas aeruginosa were evaluated by agglutination and enzyme-linked immunosorbent assay. Six MAbs that exhibited different specificities were compared with absorbed rabbit O-type antisera for the serotyping of 55 clinical isolates of serogroup II. There was good agreement between the antibodies for strains of serotypes O2 and O2b, but MAbs revealed reproducible differences between strains that were indistinguishable with rabbit antisera. The greater serotype specificity of MAbs was illustrated by the fact that only 5 of 20 strains which were agglutinated by rabbit antiserum O16 reacted with the MAb to that serotype. One antibody, M89, that reacted with 27 of 55 serogroup II strains, apparently bound to core lipopolysaccharide epitopes. Three MAbs to the frequent serotype O6 identified six subtypes, one of which accounted for over half of the clinical strains, while two subtypes were represented by single strains only. Overall, MAbs provided a greater discrimination between strains of P. aeruginosa of the same serotype than did absorbed polyclonal antisera.

Marked increase of Pseudomonas aeruginosa serotype 012 in Belgium since 1982

Routine typing was performed on a total of 7089 Pseudomonas aeruginosa strains isolated in 16 Belgian hospitals in the period from 1977 to 1986. The annual number of strains received ranged from 318 to 1346. The incidence of serotype O:12 was less than 2% until 1981 when it rose to 4%, steadily increasing to become the predominant serotype in 1984 (22%), 1985 (18%) and 1986 (22%). Since 1980 the O:12 isolates have exhibited characteristic patterns on pyocin and phage typing, 89% of O:12 isolates belonging to pyocin types 1, 39, 43, 45 or 105, whereas only 51% of isolates of other serotypes belonged to those pyocin types. Ninety-three per cent of serotype O:12 isolates belonged to phage types 68/119x, 68 or 119x, or were non-typable, whereas only 24.37% of other serotypes isolates exhibited these phage patterns. These distinctive patterns of pyocin and phage types suggest a high degree of homogeneity within the O:12 strains isolated in recent years in Belgium. Multi-centre or country-wide survey of Pseudomonas aeruginosa strains isolated in hospitals using epidemiological markers may be of value in identifying a sudden increase in epidemic strains.

Prevalence of pyocin types of P. aeruginosa in a university hospital during 1981-1986

Strains of Pseudomonas aeruginosa isolated from patients in the University of Granada (Spain) from 1981 to 1986 were pyocin-typed in order to determine which types were the most common. The proportions of typable and non typable strains were similar to those obtained by other authors. A high percentage of typable strains were unclassifiable (UC) according to Govan's method. The most frequent types of typable strains were 580 (55 of Govan), 270 (UC), 280 (UC), 570 (UC), 670 (73 of Govan), 113 (10 of Govan), 470 (86 of Govan) and 180 (58 of Govan). These types were responsible for the appearance of several nosocomial outbreaks during the years of this study. Types 580, 113 and 280 remained constant for these six years; for this reason, they can be considered endemic of our hospital.

Hospital epidemiology of Pseudomonas aeruginosa from patients with cystic fibrosis

Pseudomonas aeruginosa colonizes the respiratory tract of most older patients with cystic fibrosis. The means by which these bacteria are acquired and the risk for patient-to-patient spread among subjects with cystic fibrosis are poorly understood. We studied the spread of Ps. aeruginosa within a hospital environment. Pseudomonas was rarely recovered from the inanimate environment surrounding patients with cystic fibrosis or from hand or rectal cultures of patients who were colonized in the oropharynx. There was transient cross-colonization with Ps. aeruginosa between patients with cystic fibrosis sharing a hospital room in three of seven pairs studied. In all cases the "new" isolate was recoverable only once and was not found during a 2-year follow-up. Three of four sibling pairs with cystic fibrosis shared the same Ps. aeruginosa serotype(s). The risk of sustained cross-colonization by Ps. aeruginosa between patients with cystic fibrosis appears to be minimal, except under conditions of prolonged close contact.

Improved, computer-generated system for pyocin typing of Pseudomonas aeruginosa

We applied numerical clustering algorithms to the selection of a new indicator strain set for the pyocin typing of Pseudomonas aeruginosa. The new indicator set is composed of selected indicator strains from the sets described in 1966 by Gillies and Govan (J. Pathol. Bacteriol. 91:339-345) and in 1974 by Jones, Zakanycz, Thomas, and Farmer (Appl. Microbiol. 27:400-406) and is designated the G-F set. This indicator set consists of 14 indicator strains which typed 99.5% of 114 test cultures, has a high degree of discrimination (10 patterns encompass 50% of the test strains), and provides 62.3% reproducibility of the same typing pattern in duplicate tests done on different days. The G-F set of indicator strains provides slightly higher percentages of typable cultures than either of the other two sets, has greater discriminatory capability, and is more reproducible than they are. We recommend that the G-F set of indicator strains be used instead of the two other sets for pyocin typing of P. aeruginosa. We also tested a recently described overlay procedure for pyocin testing of P. aeruginosa and found it to be superior to previous methods in that it is easier to perform, it provides answers in only 24 h instead of 48 h, and it can be used to type mucoid strains (which previous techniques could not readily do). Thus, the application of numerical clustering algorithms and use of a revised typing procedure have produced an improved system for pyocin typing of P. aeruginosa. Similar procedures may be applicable to other typing systems.

Possibility of using purified pyocins for typing Pseudomonas aeruginosa: purification of pyocins and sensitivity of P. aeruginosa in different tests

Two types of pyocins were simultaneously found in Pseudomonas aeruginosa strains HCP2. According to their structures, they belonged to the types classified as R and F, respectively, and were named HCP2-R and HCP2-F. The sensitivity of 87 strains of P. aeruginosa of clinical origin to pyocins of strain HCP2 was compared in different types of tests. Results indicated that the use of the purified pyocins for the typing of P. aeruginosa provides data which are easier to control and interpret.

Avirulence and altered physiological properties of cystic fibrosis strains of Pseudomonas aeruginosa

Twenty Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis in good and poor clinical condition were typed by the American Scientific (Difco Laboratories, Detroit, Mich.) Typing Scheme. Only five strains were agglutinated with a single typing serum. Ten strains were agglutinated with more than one serum, and five were not agglutinated with any serum, suggesting some type of lipopolysaccharide alteration in the majority of these strains. Of the strains from patients in good clinical condition, 72% demonstrated proteolytic activity, while 60% of the strains from patients in poor clinical condition demonstrated no proteolytic activity. Twenty-three cystic fibrosis strains of P. aeruginosa examined demonstrated reduced bacteremic virulence when compared with a virulent burn strain with a 50% lethal dose (LD50) of 1.5 X 10(1) CFU in an invasive burned mouse model. Ninety-two percent of the strains tested were avirulent at doses of 10(3) to 10(5) CFU. The LD50s were determined for 10 selected strains which exhibited specific important morphological and physiological deficiencies. Five of the strains tested gave LD50s greater than 10(6) CFU. Reduced virulence of these strains was associated with loss of two or more physiological characteristics associated with virulence. The cystic fibrosis strains of P. aeruginosa which morphologically and physiologically resembled the virulent burn strain were the most virulent (LD50s of 10(2) to 10(4). Results suggest that some degree of virulence is associated only with classic strains prevalent in early infections. The data suggest that a selection transition occurs in the lungs of patients with cystic fibrosis that favors P. aeruginosa avirulence. The avirulent state may be caused by alterations in the cell envelope, including associated factors such as motility and chemotaxis and protease production.

Revised pyocin typing method for Pseudomonas aeruginosa

In the Gillies and Govan method of pyocin typing for Pseudomonas aeruginosa a cross-streaking technique was used, and 105 main types and 25 subtypes were identified by the patterns of inhibition observed on 13 indicator strains. Disadvantages of the technique included the need to remove test strain growth before application of the indicator strains, the 48-h period needed to obtain a result, and the inability to reliably type mucoid P. aeruginosa. Recent studies have enabled us to overcome these disadvantages and significantly improve the speed and application of pyocin typing. Our revised technique utilizes the same 13 indicator strains which are already used internationally. Test strains were rapidly applied to the surface of agar plates with a multiple inoculator. After incubation for 6 h and exposure to chloroform, the indicator strains were applied in agar overlays without prior removal of the test strain growth. After 18 h of incubation, the pyocin type was recognized by inhibition of particular indicator strains. Additionally, the activity of particulate (R and F) and nonparticulate (S) pyocins could be distinguished on the basis of inhibition zone size, which thus allowed further discrimination. The revised technique allows typing within 24 h, increases the number of identifiable types, and can be used to type mucoid strains.

Types of Pseudomonas aeruginosa isolated from horses

Pseudomonas aeruginosa isolates from equine clinical material were categorised according to their serotype and phage type. Epidemiological evidence showed that serotypes 02a, 03, 04, 06, 09 and 010 were the cause of genital and non-genital infections; somatic type 03 accounted for 50 per cent of isolates. The laboratory tests used were of no value in predicting whether or not a particular isolate was likely to be a venereal pathogen, but all the serotypes encountered had the potential to be pathogenic, given a favourable environment in which to multiply.

Does pseudomonas cross-infection occur between cystic-fibrosis patients

Over a 12-months period respiratory Pseudomonas aeruginosa isolated from CF patients were typed by serology and pyocin production to determine whether cross-infection was occurring. Results of typing were interpreted in relation to the degree of contact patients had with each other. One strain appeared in 4 unrelated patients. However, since none of these patients had been in contact with each other the strains considered to have been acquired from the environment. Each of six pairs of siblings shared the same strain, but the pairs of strains were distinct from each other. These results suggest that the environment is the most important source of Pseudomonas strains for CF patients and that for cross-infection to occur prolonged intimate contact is required.

Serotypes of Pseudomonas aeruginosa in clinical specimens in relation to antibiotic susceptibility

Ninety-eight hospital strains of Pseudomonas aeruginosa isolated from six different hospitals in Athens were serotyped by a slide agglutination test with unabsorbed commercial antisera. Serotypes O6, O11, O12, and "pool E" strains (strains that agglutinated only in pool E, which contained antisera against O2, O5, O15, and O16 antigens, but did not agglutinate in the individual antisera) predominated, accounting for more than 62% of all isolates tested. In respect to serotypes, (i) there was no apparent correlation with hospital of origin, (ii) most strains of serotypes O6 and O11 were sensitive to gentamicin and carbenicillin (iii) most strains of pool E were from urine and were resistant to these drugs, (iv) all 9 strains of serotype O12 tested were resistant to carbenicillin and all 5 strains tested hydrolyzed this drug, and (v) 24 of 25 strains of pool E were resistant to carbenicillin but only 2 of 17 strains hydrolyzed it.