Value of phenotyping methods as an initial screening of Pseudomonas aeruginosa in epidemiologic studies

Rapid identification of Pseudomonas aeruginosa by pulsed-field gel electrophoresis

Twenty clinical Pseudomonas aeruginosa isolates recovered from patients admitted to The General Hospital in Ismailia Governorate (Egypt) were examined in this study. We analysed P. aeruginosa ATCC 9027 (as a control strain) and 19 of the isolates after digestion with SpeI restriction endonuclease. After this we conducted a pulsed-field gel electrophoresis (PFGE) and typed the obtained 10 unique patterns, designated as A, A1, B, B1, C, C1, D, D1, E and F. We evaluated the genetic relatedness between all strains, based on ≥87% band identity. As a result, the isolates were grouped in the 10 clusters as follows: patterns A, A1, B, B1, C contained two strains each and patterns C1, D, D1, E contained a single strain each; the five remaining strains were closely related (genomic pattern F). One isolate belonged to antibiotype ‘b’. The genotype patterns of the P. aeruginosa ATCC 9027 control strain and isolate no. 11 were closely related and had two different antibiotypes ‘d’ and ‘c’, respectively.

[Pseudomonas aeruginosa isolated in immunocompromised patients: antimicrobial resistance, serotyping, and molecular typing]

OBJECTIVE

Our study dealt with antibiotic resistance and serotypes of Pseudomonas aeruginosa strains isolated from immunocompromised patients in the National Bone Marrow Transplant Center of Tunis as well as molecular typing of ceftazidime resistant strains (CAZ-R).

DESIGN

We studied a total of 87 non-replicate P. aeruginosa isolates from 36 patients (84 strains) or the hospital environment (3 strains).

RESULTS

Rates of antimicrobial resistance were 36% for ceftazidime, 16% for imipenem, 38% for amikacin, and 57% for ciprofloxacin. The 31 CAZ-R strains were associated with O:11 serotype in 84% of the cases. Genetically characterization of CAZ-R strains by Pulsed Field Gel Electrophoresis (PFGE) after digestion of genomic DNA with SpeI revealed 2 genotypic groups. The first was composed of strains isolated from one outpatient between November 1998 and April 1999. Resistance phenotypes of these strains varied after use of antimicrobial drugs. The second was predominant (18/31 CAZ-R strains) in both hematology and graft units and persisted from June 1998 to June 2000 among 5/8 patients. These strains had O:11 serotype in 78% of the cases. The strains of this group were not isolated on patient admission and were isolated from 2 washbasins in the graft unit in May 1999.

CONCLUSION

These results suggest the spread of multidrug-resistant O:11 P. aeruginosa clone from a tap water among hospitalized patients in our center, emphasizing the need of standard control of washbasins to eradicate this reservoir.

Clinical surveillance of surgical imipenem-resistant Pseudomonas aeruginosa infection in a Japanese hospital

In order to elucidate any changes in imipenem-resistant Pseudomonas aeruginosa (IRPA) infections in Japan, we examined 511 P. aeruginosa stains isolated from our surgical ward between 1987 and 2001. These isolates were subjected to susceptibility testing against various antipseudomonal agents including imipenem, meropenem, ceftazidime, gentamicin and ciprofloxacin. They were serotyped with the slide agglutination test and genotyped using pulsed-field gel electrophoresis (PFGE). The annual incidences of IRPA infections were particularly high in the early 1990s. Epidemiological investigations revealed that these outbreaks were due to dissemination of hospital-acquired IRPA isolates. Intensive use of imipenem promoted the selection of highly resistant strains. Further study of resistance mechanisms revealed that none of the 110 IRPA strains were metallo-beta-lactamase (MBL) producers. Polymerase chain reaction (PCR) analysis using bla(IMP) specific primers confirmed that no IMP-1 type MBL gene-positive strains were detected from our ward. Susceptibilities of those IRPA strains against other antipseudomonal agents showed relatively low levels, suggesting that imipenem resistance was mainly due to impermeability of the OprD porin. In conclusion, hospital-acquired outbreaks of IRPA were recently reduced by guidelines for, and surveillance of, appropriate use of antimicrobial agents. When the rate of IRPA isolation increases, serotyping should be performed initially and PFGE is required to confirm outbreaks. A computer-assisted genotyping technique is available to perform epidemiological studies of IRPA isolates.

[Recovery method of serotypable character in non serotypable pseudomonas aeruginosa strains]

Serotyping is one of the most used techniques for typing Pseudomonas aeruginosa strains. During chronic infections, and especially in cystic fibrosis, the decrease of lipopolysaccharide production is responsible for difficulties in determining O antigens. The possibility of serotyping can be simply restored by using a primary culture broth containing amikacin (1/6 of the strain MIC for this antibiotic); this is due to the ability of this antibiotic to inhibit alginate production. This technique allowed us to determine the serotype of 108 non-serotypable strains of P. aeruginosa isolated in 14 different hospitals. Among these isolates, serotype O:1 and O:13, had a high prevalence; the origin is a deficiency in D-glucose and L-rhamnose, required for the synthesis of lipopolysaccharide. In contrast, these sugars are not present in lipopolysaccharide of O:12, and these strains are always serotypable. The main protein is Alg C; this bifunctional enzyme is required in the exopolysaccharide and lipopolysaccharide production, according stress conditions in the bacterial-cells' environment. Determination of the serotype, as Antibiogram, is essential for genotypic inquiries.

Typing of Pseudomonas aeruginosa from hospitalized patients: a comparison of susceptibility and biochemical profiles with genotype

Typing techniques are essential for understanding hospital epidemiology, permitting the elucidation of the source of infection and routes of bacterial transmission. Although DNA-based techniques are the "gold standard" for the epidemiological study of Pseudomonas aeruginosa, antibiotic profiles and biochemical results are used because they are easy to perform and to interpret and relatively inexpensive. Antibiotypes (susceptibility profiles) and biotypes (biochemical profiles) were compared to genotypes established by DNA restriction enzyme analysis in 81 clinical isolates of P. aeruginosa from three hospitals in Porto Alegre, Brazil. The epidemiological relationship among patients was also evaluated. Susceptibility and restriction profiles were discrepant in more than 50% of the cases, and many antibiotypes were observed among isolates from the same genotype. Furthermore, susceptibility profiles did not allow the distinction of isolates from unrelated genotypes. Since a large number of isolates (63%) yielded the same biochemical results, only 10 biotypes were detected, showing that this typing method has a low discriminatory power. On the other hand, DNA restriction enzyme typing allowed us to establish 71 distinct types. Epidemiological data about the relation among P. aeruginosa isolates were not conclusive. The results of the present study indicate that the only method that can establish a clonal relation is DNA restriction enzyme typing, whereas the other methods may cause misleading interpretations and are inadequate to guide proper infection control measures.

Pseudomonas aeruginosa: study of antibiotic resistance and molecular typing in hospital infection cases in a neonatal intensive care unit from Rio de Janeiro City, Brazil

This study had the objective of to analyze the demographic and bacteriologic data of 32 hospitalized newborns in an neonatal intensive care unit of a public maternity hospital in Rio de Janeiro city, Brazil, seized by Pseudomonas aeruginosa sepsis during a period ranged from July 1997 to July 1999, and to determine the antimicrobial resistance percentage, serotypes and pulsed field gel electrophoresis (PFGE) patterns of 32 strains isolated during this period. The study group presented mean age of 12.5 days, with higher prevalence of hospital infection in males (59.4%) and vaginal delivery (81.2%), than females (40.6%) and cesarean delivery (18.8%), respectively. In this group, 20 (62.5%) patients received antimicrobials before positive blood cultures presentation. A total of 87.5% of the patients were premature, 62.5% presented very low birth weight and 40.6% had asphyxia. We detected high antimicrobial resistance percentage to b-lactams, chloramphenicol, trimethoprim/sulfamethoxazole and tetracycline among the isolated strains. All isolated strains were classified as multi-drug resistant. Most strains presented serotype O11 while PFGE analysis revealed seven distinct clones with isolation predominance of a single clone (75%) isolated from July 1997 to June 1998.

Characteristics of polyclonal endemicity of Pseudomonas aeruginosa colonization in intensive care units. Implications for infection control

We investigated the endemicity of Pseudomonas aeruginosa in intensive care units (ICUs) through analyses of surveillance cultures (from the rectum, stomach, oropharynx, and trachea; n = 1,089), and clinical cultures (n = 2,393) from 297 consecutive patients. Multiple isolates of P. aeruginosa (n = 353) were genotyped. Variables associated with acquisition of respiratory tract colonization (RTC) were tested in a risk factor analysis. The mean daily prevalence of colonization was 34%. On admission, 22 patients had intestinal colonization and 13 had RTC. Twenty patients acquired colonization in the intestinal and 24 in the respiratory tract. Forty-four different genotypes were found; 38 (86%) were isolated from individual patients only. In all, 37 patients had RTC with a total of 38 genotypes: 13 (34%) were colonized on admission, 9 (24%) acquired RTC with a novel genotype during a stay in the ICU, five (13%) acquired colonization from their intestinal tract and three (8%) were colonized via cross-acquisition. In eight patients (21%), no route could be demonstrated for colonization. Antibiotics providing P. aeruginosa with a selective growth advantage were associated with acquired RTC. Endemicity of colonization with P. aeruginosa is characterized by polyclonality, and seems to be maintained by continuous admittance of colonized patients and selection pressure from antibiotics rather than by cross-acquisition.

Cross-colonisation with Pseudomonas aeruginosa of patients in an intensive care unit

BACKGROUND

Ventilator-associated pneumonia (VAP) caused by Pseudomonas aeruginosa is usually preceded by colonisation of the respiratory tract. During outbreaks, colonisation with P aeruginosa is mainly derived from exogenous sources. The relative importance of different pathways of colonisation of P aeruginosa has rarely been determined in non-epidemic settings.

METHODS

In order to determine the importance of exogenous colonisation, all isolates of P aeruginosa obtained by surveillance and clinical cultures from two identical intensive care units (ICUs) were genotyped with pulsed field gel electrophoresis.

RESULTS

A total of 100 patients were studied, 44 in ICU 1 and 56 in ICU 2. Twenty three patients were colonised with P aeruginosa, seven at the start of the study or on admission and 16 of the remaining 93 patients became colonised during the study. Eight patients developed VAP due to P aeruginosa. The incidence of respiratory tract colonisation and VAP with P aeruginosa in our ICU was similar to that before and after the study period, and therefore represents an endemic situation. Genotyping of 118 isolates yielded 11 strain types: eight in one patient each, two in three patients each, and one type in eight patients. Based on chronological evaluation and genotypical identity of isolates, eight cases of cross-colonisation were identified. Eight (50%) of 16 episodes of acquired colonisation and two (25%) of eight cases of VAP due to P aeruginosa seemed to be the result of cross-colonisation.

CONCLUSIONS

Even in non-epidemic settings cross-colonisation seems to play an important part in the epidemiology of colonisation and infection with P aeruginosa.