Application of Pulsed Field Gel Electrophoresis (PFGE) for Typing of ...

Egyptian Journal of Medical Microbiology, July 2006 Vol. 15, No 3 

Application of Pulsed Field Gel Electrophoresis (PFGE) for Typing of 

Stenotrophomonus maltophilia Isolated from Nosocomial Ventilator 

Associated Pneumonia In ICU Patients 

Abeer Ezzat El-Sayed Mohamed 

Microbiology and Immunology Department Suez Canal University, 

Faculty of Medicine, Ismailia, Egypt. 

Stenotrophomonus maltophilia is a multidrug resistant nosocomial pathogen for which optimal 

typing methods are needed to estimate epidemiologic relatedness especially among Intensive Care 

Unit (ICU). Ventilator associated pneumonia (VAP) is a common complication in mechanically 

ventilated patients and it is accompanied by increased mortality. Pulsed field gel electrophoresis 

(PFGE) was applied to 12 nosocomial strains isolated from patients had VAP and six 

environmental specimens in ICU in Bahrain Hospital over 15 months period in 2004-2005. 

Antibiogram as a phenotypic marker failed to discriminate between these isolates. Five 

antibiogram patterns were identified among 18 isolates with predominance of pattern (I) that 

resisted five chemotherapeutic agents in 5 isolates (27.8%). All the strains were sensitive to 

trimethoprim–sulfamethoxazole but only 72.2%, 55.6%, 44.4%, 22.2% and 11.1% were sensitive 

to minocycline, levofloxacin, ticarcillin–clavulanic acid, ceftazidime and chloramphenicol 

respectively. All the strains were typable by the genotypic marker PFGE. It revealed 14 patterns 

among 18 clinical and innate environmental isolates with a small two clusters included 3 strains 

that were epidemiologically related. Ten genotypic patterns were detected among twelve clinical 

isolates meanwhile six patterns were detected among the six environmental isolates. There were 

similar isolated PFGE patterns between environmental and clinical isolates suggestive of the source 

of infection to those patients and evidence of patient to patient transmission.These different 

genotypic patterns indicated different sources and genetic diversity of this opportunistic pathogen. 

This study proved high typability, sensitivity and discriminatory power of PFGE method for typing 

of nosocomial Stenotrophomonus maltophilia. It is recommended to add another genotypic marker 

in further studies like random amplified polymorphic DNA analysis (RAPD) to increase and 

augment the sensitivity and discriminatory power for typing of this important pathogen and trace 

the different sources of nosocomial infection. 

INTRODUCTION 

Stenotrophomonus maltophilia is an 

aerobic non-fermentative gram negative 

bacillus that is generally considered an 

opportunistic pathogen 

(1) . Ventilator 

associatd pneumonia (VAP) is a common 

complication in mechanically ventilated 

patients and it is accompanied by increased 

mortality 

(2) . Patients compromised by 

debilitating illness, surgical procedures, 

indwelling catheters or on mechanical 

ventilator are most prone to 

(2, 

Stenotrophomonus maltophilia 

3) . It is 

considered one of nosocomial pathogen that 

plays an important role in respiratory tract 

infections and other nosocomial infections 

among critically ill patients (3, 4) . VAP is the 

most frequently observed nosocomial 

infection among mechanically ventilated 

intensive care unit (4, 5) . Stenotrophomonus 

maltophilia is a multidrug resistant organism 

for which optimal typing methods are needed 

as epidemiological investigations of 

nosocomial VAP outbreaks 

(5-9) . Long 

duration of endotracheal intubation leads to 

acquisition of potentially pathogenic 

organisms from the intensive care unit 

environment Antibiogram to this organism is 

less reliable since these isolates are frequently 

resistant to multiple antibiotics (6) . This study 

aimed to use DNA macrorestriction analysis 

by pulsed field gel electrophoresis (PFGE) as 

genotypic marker for typing of 12 nosocomial 

strains caused ventilator associated 

pneumonia and six innate environmental 

strains from ICU of Bahrain Hospital. PFGE 

can resolve much larger DNA fragments than 

conventional electrophoresis and has been 

found to be a highly discriminatory technique 

for strain differentiation compared to 

phenotypic methods like antibiogram, 

biotyping, serotyping and multilocus enzyme 

electrophoresis (5-10) . 

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PATIENTS, MATERIALS AND 

METHODS 

This study was carried out on 

mechanically ventilated patients admitted to 

the ICU of Bahrain Hospital that developed 

nosocomial VAP either early onset (Less than 

5 days of intubation) or late onset (≥ 5 days of 

intubation), during the period from January, 

2004 to March, 2005. Patients were subjected 

to thorough clinical examination, routine 

laboratory investigations, chest 

roentgenography and gasometry. VAP was 

diagnosed according to the clinical pulmonary 

infection score (CPIS) system of Garrard and 

Court (11) . It included body temperature, blood 

leukocytes, tracheal aspirates appearance and 

quantity per day, oxygenation, pulmonary 

radiography and culture of tracheal aspirates. 

Inclusion criteria:- 

Patients on mechanical ventilator who were 

diagnosed as nosocomial VAP ≥ 48 hrs after 

intubation according to Clinical Pulmonary 

Infection Score (CPIS). The range of the 

score is from 0 to 12 points with VAP defined 

by score of 7 or above (10, 11) . Clinical data 

from every patient were collected regarding 

age, sex, time of admission, duration of 

hospitalization, duration of intubation, 

presence of organ failure and any chronic 

illness. Environmental swabs were taken from 

surfaces, walls, water of humidifier, tubes 

from ventilator circuits and side tables. The 

swabs were plated on blood and 

MacConkey`s agar plates then incubated 

aerobically at 35 °C for 24 hrs for subsequent 

identification of the organism by colonial 

morphology and biochemical reactions. 

Quantitative culture of endotracheal 

aspirate (EA) (12) :- The endotracheal aspirate 

secretions (EA) were collected in sterile 

containers and immediately were sent to the 

microbiology laboratory then were liquefied 

and homogenized by adding an equal volume 

of sterile 1% N-acetyl-L-cysteine (Sigma) 

solution vortexing for 2 minutes and 

incubating at room temperature for 10 

minutes. 

The homogenized respiratory secretions 

were serially 10 fold diluted in sterile broth 

and 2 dilutions (1/100 and 1/1000) were 

inoculated in 10 µL volumes onto blood agar 

and MacConkey`s agar plates then incubated 

aerobically at 35 °C for 24 hrs. The bacterial 

isolates were identified by being gram 

negative bacilli using gram staining technique, 

non-lactose fermenter and oxidase negative. 

The suspected bacteria were further identified 

in addition to colonial morphology by using 

(13) 

API 20 NE (BioMerieux, France) 

according to the manufacture instructions. 

Significant bacterial count was considered ≥ 

10 6 CFU/ml. 

Bacterial strains were collected after 

identification and preserved in two tubes one 

in 1% trypticase soy agar incubated at 37 °C 

for 24 hrs. The other in trypticase soy broth 

with 13% glycerol as cryoprotectant then kept 

at -70 °C until processed for PFGE. 

Antibiotic susceptibility pattern was done 

to each isolate by disk diffusion according to 

Clinical and Laboratory Standards Institute 

guideline instructions (CLSI, 2005) (14) using 

the following disks :- trimethoprimsulphamesoxazole 

(1.25/3.75µg), minocycline 

(30µg), levofloxacin (5 µg), ticarcillin– 

clavulanic acid (75/ 10µg), ceftazidime (30 

µg) and Chloramphenicol (30 µg). 

PFGE analysis 

Genomic DNA was prepared according 

to Laing et al. (15) . The bacterial isolates were 

grown for 18 h in 5 ml of brain heart infusion 

broth (Difco) at 37 °C. The cells were 

harvested and suspended in 1.5 ml of buffer 

[1M NaCl, 10 mM Tris-Hcl (pH 7.6)]. One 

milliliter of this suspension was mixed with 1 

ml of 1.6 % low- melting temperature agarose 

at 50 °C (Imbed LMP agarose, New England 

Biolabs, Beverly, Mass), then pipetted into a 

plug mold (Bio-Rad Lab. Richmond, Calif.) 

and allowed to solidify for 30 min at 4 °C. 

Plugs were placed in 1.5 ml of fresh cold lyis 

solution (10 mMTris-Hcl (pH 7.6), 50mM 

NaCl, 100 mM EDTA (pH 8.0), 0.2% 

deoxycholic acid (Sigma Chemical Co. St. 

Louis, Mo), 1% N-Lauroyl sarcosine (Sigma) 

and 2 mg of lysozyme (Sigma) per ml) for 3 h 

at 35 °C. Samples were treated for 16 h at 42 

°C with the same volume of a proteinase K 

solution containing 50 µg of proteinase K 

(Boehringer Mannheim, Laval, Quebec, 

Canada) per ml, 100 mM EDTA (pH 8.0), 

0.2% deoxycholic acid and 1% N-Lauroyl 

sarcosine. After three 1-hour washes with TE 

buffer [10 mM Tris-Hcl, 0.1 mM EDTA (pH 

8.0)], the agarose plugs were stored in TE 

buffer at 4 °C for subsequent PFGE. 

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A 5 mm slice of an agarose plug was 

digested with 20 U restriction enzyme SpeI 

(Boehringer Mannheim) and incubated for 20 

h at 37 °C in a reaction volume of 0.25 ml 

according to the manufacturer ’ s 

recommendations. The resultant DNA 

fragments were separated on a 1% PFGE 

agarose (FastLane agarose; FMC, Rockland, 

Main), gel in a contour-clamped homogenous 

electrical field by using the CHEF DR-II 

system (Bio-Rad), with 0.5xTBE buffer [45 

mM Tris-borate, 1 mM EDTA (pH 8.0)] at 12 

°C. With the voltage set at 6.0 V/cm, Initial 

and final switch times were 25 to 45 seconds 

respectively with linear ramping factor and a 

run time of 20 hrs. Bacteriophage lambda 

concatemers (Mid-range; New England 

Biolabs) were run as molecular weight 

standards (range 50-1,000 Kb). Gels were 

visualized with UV light after staining with 

ethidium bromide (10µg /ml) and 

photographed using Polaroid camera. Isolates 

were differentiated by visual inspection of 

PFGE patterns on the agarose gels and were 

considered different if their PFGE patterns 

differed by more than one DNA band. 

Statistical analysis:- 

Statistical analysis was performed using the 

Statistical Package for Social Sciences (SPSS 

version 10) (16) . The mean and standard 

deviation (SD) were used for numerical data 

for description. 

RESULTS 

This study was carried out on 18 

stenotrophomonus maltophilia isolates from 

clinical and environmental specimens through 

15 months. Twelve clinical isolates were 

isolated from 36 (33.3%) tracheal aspirates of 

patients with nosocomial VAP after 48 hrs of 

intubation. Most of studied patients [30 out 

of 36 (83.3%)], had late onset pneumonia that 

was after or on fifth day of intubation. Ten 

patients (83.3%) out of twelve infected with 

stenotrophomonus maltophilia had late onset 

pneumonia. Eight patients out of 36 (22.2%) 

had polymicrobial VAP. Three patients out of 

twelve (25%) had polymicrobial pathogens 

with Stenotrophomonus maltophilia. Two 

patients had pseudomonus aeroginosa and 

one patient had staphylococcus aureus 

pathogen. Six environmental strains were 

isolated from walls, water of humidifier, 

outside tube of one ventilator circuit and side 

table in ICU. Age of the patient ranged from 

44-86 years old with mean (59±12). Twenty 

two patients were males (61.1%) and 14 

(38.9%) were females. The mean duration of 

mechanical ventilation before suspicion of 

pneumonia was 10.3±5.2 days (range 2-45 

days). The mean and standard deviation of 

CPIS values were 10±2 among 36 patients 

who had VAP. The indications for 

mechanical ventilator in table (1), included 

metabolic causes in 6 patients (16.7%), as 

renal failure and diabetic ketoacidosis. 

Pulmonary diseases as severe bronchial 

asthma, neoplasm and chronic obstructive 

pulmonary disease were in 14 patients 

(38.9%). Cardiac failure was in 4 patients 

(11.1%). Cerebrovascular accidents were in 7 

patients (19.4 %) and head trauma in 5 

patients (13.9 %). 

Table (1): Indications of Mechanical 

Ventilation In The Studied 

Patients: 

Indications of mechanical No.= % 

ventilation 

36 

Metabolic causes 6 16.7 

Pulmonary diseases 14 38.9 

Cardiac failure 4 11.1 

Cerebrovascular accidents 7 19.4 

Head trauma 5 13.9 

Fifteen out of the 36 studied patients (41.7%), 

VAP was associated with a clinical 

presentation of severe sepsis or septic shock. 

Five (13.9%) of those patients were infected 

by Stenotrophomonus maltophilia. Those 

patients represented 41.7% from twelve cases 

infected with this pathogen. 

All the strains were sensitive to 

trimethoprim-sulphamesoxazole but only 

72.2%, 55.6%, 44.4%, 22.2% and 11.1% were 

sensitive to minocycline, levofloxacin, 

ticarcillin–clavulanic acid, ceftazidime and 

chloramphenicol respectively. Antibiogram 

failed to discriminate between the clinical and 

environmental isolates as these organisms 

were multidrug resistant. Five antibiogram 

patterns were detected among total 18 isolates 

with similarity between clinical and 

environmental isolates table (2). The most 

predominating pattern was pattern (I) that 

resists five chemotherapeutic agents in five 

isolates out of 18 strains (27.8%). 

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Table (2): Antimicrobial Susceptibility 

Patterns to Clinical and 

Environmental Isolates. 

Antimicrobial 

susceptibility pattern 

I 

II 

III 

IV 

V 

Antimicrobial agents 

that Isolates are R 

Min,LEV,C,CAZ,TIM 

LEV,C,CAZ,TIM 

CAZ,TIM 

CAZ,C 

C 

R=resistant, 

LEV=levofloxacin, 

CAZ=ceftazidime, 

TIM=ticarcillin/clavulanic acid. 

Clinical Isolates 

4 

2 

2 

2 

2 

Environmental 

Isolates 

1 

1 

0 

2 

2 

Min=minocycline, 

C=chloramphenicol, 

DNA restriction analysis with SpeI and 

subsequent PFGE showed fourteen different 

genotypic patterns as shown in table (3) and 

figure (1). Six different patterns were found 

among innate environmental isolates with 

similarity in patterns D, I with clinical isolates. 

Ten genotypic patterns were detected among 

twelve clinical isolates with two similar 

clones of clinical isolates in pattern D, I. 

Table (3): PFGE Patterns of Clinical and 

Environmental Isolates. 

PFGE Clinical Environmental 

Patterns No. % No. % 

A 1 8.3 0 0 

B 0 0 1 16.7 

C 1 8.3 0 0 

D 2 16.7 1 16.7 

E 1 8.3 0 0 

F 1 8.3 0 0 

G 0 0 1 16.7 

H 0 0 1 16.7 

I 2 16.7 1 16.7 

J 1 8.3 0 0 

K 1 8.3 0 0 

L 1 8.3 0 0 

M 1 8.3 0 0 

N 0 0 1 16.7 

Total 12 100 6 100 

Figure (1): PFGE Patterns of Clinical and 

Environmental Isolates by 

Agarose Gel Electrophoresis. 

Lane 1,20 : DNA standard ladder of Lambda 

phage DNA marker from 50-1,000KB. Lane 2 

pattern A, lane3 pattern B, lane 4 pattern C, 

Lane 5,13, 17 pattern D, lane 6 pattern E, lane 

7 pattern F, lane 8 pattern G, lane 9 pattern H, 

lane 10,11,12 pattern I, lane 14 pattern J, lane 

15 pattern K, lane 16 pattern L, lane 18 

pattern M,lane 19 pattern N. Number of 

bands ranged from 10-14 bands. 

DISCUSSION 

Episodes of infections caused by 

Stenotrophomonus maltophilia have become 

increasingly important in the hospital setting 

especialy among ICU patients. VAP is 

thought to increase the lengh of stay in the 

ICU, mortality, morbidity and the costs 

attributed to it are therefore high (2, 3, 5, 9) . 

Tracheal colonization caused by potentially 

pathogenic microorganisms occurs prior to 

lung infection in many patients admitted to 

intensive care units. Stenotrophomonus 

maltophilia is one of important nosocomial 

pathogens causing multidrug-resistant 

infections in hospitalized patients (1, 2) , Most 

of the cases 30/36 had late onset VAP (83.3%) 

that developed after or on the fifth day of 

intubation. Ten (83.3%) out of twelve cases 

infected by Stenotrophomonus maltophilia 

had late onset VAP this may be due to 

colonization of this potentially pathogenic 

organism in respiratory secretions or 

endotracheal tube biofilm formation that 

plays a contributing role in sustaining tracheal 

colonization. These previous results agreed 

with Safdar et al. (9) that explained the 

pathogenesis of the development of VAP 

507


caused by this potentially pathogenic 

organism that may be acquired from the 

intensive care unit environment and under 

certain debilitating factors it leads to infection. 

In the present study 36 patients in ICU 

diagnosed of nosocomial VAP were included 

using quantitative EA culture and CPIS 

values. Most of the included patients were old 

age with chronic illness, exposure to invasive 

techniques, long hospital stay, bedridden and 

with long duration of intubation, suggestive 

of the predisposing factors for development of 

VAP (9, 17-18) . Five patients out of twelve 

(41.7%) infected with Stenotrophomonus 

maltophilia had severe sepsis and septic 

shock donating the severity and importance of 

this pathogen among such illness and this 

supports what has been observed in previous 

studies (9, 17-20) . It is possible to use the time of 

occurrence of VAP as an important indicator 

of mortality and may be used to identify 

patients at risk and initiate appropriate 

therapy at an earlier stage especially that 

studied patients had long intubation time with 

mean and SD of 10.3±5.2 days. Twelve 

strains of Stenotrophomonus maltophilia were 

isolated from 36 patients (33.3%) within 15 

months among patients in ICU of Bahrain 

Hospital. This showed the importance of this 

pathogen among critically ill patients. Three 

patients out of twelve infected with 

Stenotrophomonus maltophilia (25%) had 

other pathogens that were polymicrobial. Two 

patients had pseudomonus aeroginosa and 

one had staphylococcus aureus. This result 

(3, 19, 

has been emphasized by several authors 20) . This reflects the pattern of microbial 

infection among critically ill patient as they 

are exposed to multiple pathogens and these 

results coincide with Bedewy et al. (20) . 

Different innate environmental swabs were 

taken in ICU and six strains were detected 

suggestive of the different sources of 

infection that were from water of the 

humidifier, walls, side tables and tubes of the 

ventilator circuits. Isolation of this pathogen 

from the environment assures that infection 

control measures regarding regular 

disinfection of the environment have great 

role in prevention of VAP (21) . This study also 

proved the role of the special care with 

patients on mechanical ventilator for 

prophylaxis against VAP (22) . Pulmonary 

diseases (severe bronchial ashma, neoplasm 

and chronic obstructive lung diseases) 

represented the highest percentage (38.9%) 

(table, 1) among 36 patients indicated for 

mechanical ventilation. This estimated the 

risk factors for development of VAP and 

subsequently infection with this opportunistic 

pathogen. All the 18 isolates were susceptible 

to trimethoprim-sulphamesoxazole but only 

72.2%, 55.6%, 44.4%, 22.2% and 11.1% were 

sensitive to minocycline, levofloxacin, 

ticarcillin–clavulanic acid, ceftazidime and 

chloramphenicol 

respectively. 

Stenotrophomonus maltophilia is notoriously 

resistant to most currently available 

antimicrobial agents leaving trimethoprimsulfamethoxazole 

as the primary drug of 

choice for infections caused by this species (5, 

6, 10). 

Antibiogram failed to discriminate 

between the clinical and environmental 

isolates as this organism is considered one of 

multidrug resistant pathogens and this agree 

with previous studies (5, 6, 17-19) . This study 

suggests that hospitals represent a wellestablished 

reservoir for resistant organisms 

due to misuse of antibiotics among critically 

ill patients (5, 19, 22, 23) . Pattern (I) was the most 

predominating antimicrobial suceptibility 

pattern in five isolates (27.8%) that resist five 

agents (table, 3). For that reason using 

antibiogram alone is not sufficient for 

discrimination between closely related 

isolates and needs to be powered by other 

genotypic markers. 

All 18 Stenotrophomonus maltophilia 

isolates were typeable by PFGE using SpeI 

restrictive enzyme. Fourteen genotypic 

patterns were detected among total clinical 

and environmental isolates with 2 small 

clones included three strains in patterns D, I. 

Pattern D included 2 clinical isolates that 

were isolated from 2 patients cohorting the 

same room with near beds, suggestive of the 

patient to patient transmission of infection. 

One innate environmental strain isolated from 

the water of humidifier had similar PFGE 

pattern D (table, 3) wth 2 clinical isolates. 

From the previous result the source of 

infection is traced to some patients and 

infection control preventive measures were 

important to prevent development of 

nosocomial outbreaks. Pattern I also included 

three strains with 2 clinical and one 

environmental isolated from the wall of the 

ventilator tube circuits. Isolation of the same 

genotype from the tube of the ventilator 

indicates that it may be the source of infection 

508


or contamination from the patient secretions 

but there is possibility of patient to patient 

transmission of this organism. This study 

proved the high discriminatory and sensitivity 

power of PFGE marker for typing of 

Stenotrophomonus maltophilia beside its 

ability for identification of nosocomial 

sources suggesting multiple independent 

acquisitions from a variety of environmental 

sources.This agree with Yao et al, 

(24) , 

Gordillo et al., (25) and Mazloum et al., (26) as 

they found that PFGE was superior to other 

techniques for typing of nosocomial isolates. 

There was no outbreak detected with 

Stenotrophomonus maltophilia during 15 

months inside ICU but PFGE genotypic 

technique proved the genetic diversity of this 

microbe and thus the different sources of 

infection. These results coincide with 

previous studies (5, 15, 27-31) . From the previous, 

it is recommended to use PFGE method as a 

discriminatory genotypic technique for typing 

nosocomial pathogens, estimation of the 

genetic relatedness and tracing the sources of 

infection by this pathogen. Another genotypic 

marker like random amplified polymorphic 

DNA analysis (RAPD), using a single 

arbitrary oligonucleotide primer selected for 

its ability to discriminate among 

epidemiologically distinct isolates (30, 32, 33) . It 

could be added for typing of this organism as 

an attempt to augment the sensitivity and 

discriminatory power of PFGE method and to 

trace the different sources of infection. 

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إستخدام طريقة الفصل الكهربى ذى المجال النابض لتصنيف سلالات ستينوتروفوموناس 

مالتوفيليا المعزولة من الالتهاب الرئوى المرتبط بجهاز التهوية الالية فى مرضى العناية المرآزة 

عبير عزت السيد محمد 

قسم الميكروبيولوجى والمناعة آلية الطب ‏–جامعة قناة لسويس 

يعد ميكروب ستينوتروفوموناس مالتوفيليا من الميكروبات سالبة الجرام الانتهازية التى تسبب العديد من 

العدوى المكتسبة من المستشفيات خاصة بمرضى العناية المرآزة.‏ ويعد الالتهاب الرئوى المرتبط بجهاز التهوية 

الآلية مضاعفة شائعة لدى مرضى العناية المرآزة ويؤدى إلى نسبة عالية من الوفيات.‏ وقد اجريت هذه الدراسة 

على ٣٦ مريض تم تشخيصهم باصابتهم بالالتهاب الرئوى المرتبط بجهاز التهوية الآلية والمكتسب من المستشفى 

بمرضى العناية المرآزة بمستشفى البحرين وتم عزل ١٨ سلالة من الميكروب منهم فى خلال ١٥ شهر وتم التعرف 

على الميكروب بواسطة اختبار 

الهوائية للمرضى و‎٦‎ 

للميكروب وآانت 

API 20NE 

١٢ وآان منهم 

سلالة معزولين 

سلالات معزولة من مسحات بيئية مختلفة بالعناية المرآزة.‏ 

(%٣٣٫٣) 

%١٠٠ 

من افرازات القصبة 

وتم عمل اختبارات حساسية 

من السلالات حساسة للتراى ميثوبريم سلفاميسوآسازول بينما آانت 

،%٧٢٫٢ 

%١١٫١ 

،%٢٢٫٢ 

،%٤٤٫٤ 

،%٥٥٫٦ 

سفتازيديم،‏ 

آلورامفينيكول 

حساسة للمينوسيكلين،‏ 

ليفوفلوآساسين،‏ 

تيكارسيلين آلافولينيك أسيد،‏ 

على التوالى.‏ تم الحصول على خمسة انماط مختلفة من الحساسية للمضادات الحيوية 

المختلفة ولم تستطع هذة الطريقة التمييز بين السلالات المختلفة للميكروب.‏ وبإستخدام طريقة الفصل الكهربى ذى 

المجال النابض تم الحصول على 

١٤ 

نمط جينى للسلالات.‏ 

آانت هناك سلالات مشترآة بين المسحات البيئية 

والعينات الاآلينيكية المعزولة من المرضى وتشابهت بعض السلالات الاآلينيكية بين المرضى ما يدل على تنوع 

مصادر العدوى بهذا الميكروب وبالاستقصاء الوبائى تبين ان التشابه بين سلالات المرضى يرجع الى اشتراآهم فى 

نفس الغرفة وتجاورهم مما يدل على امكانية نقل العدوى من مريض الى آخر.‏ ولقد تم تصنيف ١٠ انماط بين الاثنى 

عشر سلالة الاآلينيكية و‎٦‎ انماط مختلفة بين الستة سلالات البيئية بطريقة الفصل الكهربى ذى المجال النابض مما 

يدل على اختلاف وتنوع اجناس الميكروب وان هناك مصادر متعددة للعدوى به.‏ 

ومن هنا ندرك أن طريقة الفصل الكهربى طريقة حساسة ودقيقة وذات تمييز عالى لتصنيف هذا 

الميكروب المكتسب من عدوى المستشفيات ويوصى بإضافة نوع آخر من الدلالات التصنيفية الجينية فى دراسات 

أخرى مثل التكبير العشوائى للحامض النووى لزيادة دقة البصمة الجينية لهذا الميكروب فى دراسات مستقبلية 

أخرى.‏ 

512

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