The Antibiotic Resistance Pattern in Citrobacter Species: An Emerging Nosocomial Pathogen in a Tertiary Care HospitalCorrespondence Address :
Dr. Ashish Khanna
538, Basant Avenue
Amritsar, India - 143001.
Phone: 9465128936 , 0183-2562919
Members of the genus, Citrobacter, a gram negative, nonsporing rod which belongs to the family, Enterobacteriaceae are emerging as important nosocomial pathogens. The study was carried out to determine the frequency and the anti-microbial sensitivity pattern of the Citrobacter species among the various gram negative isolates which were obtained from different clinical samples. Out of the total 1830 gram negative bacilli which were isolated over a period of one and half year, from February 2010 to August 2011, from various clinical samples which were submitted to the microbiology laboratory of the Sri Guru Ram Das Hospital, eighty six (4.70%) isolates belonged to the Citrobacter species, of which 58 were Citrobacter freundii and 28 were Citrobacter koseri. Sixty three (73.26%) out of 86 Citrobacter isolates were multi-drug resistant. There was a highly significant difference in the resistance of the Citrobacter isolates to all the antimicrobials including beta lactams, quinolones and aminoglycosides, among the hospital and outdoor isolates. ESBL production was seen in 61.64% of the hospital and in 30.70% of the outdoor isolates.
Citrobacter freundii, Citrobacter koseri, Antimicrobial resistance, ESBL, MBL
Antibiotic resistance is emerging in the isolates of Enterobacteriaceae and in other gram negative bacilli in many parts of the world and this is a major threat to the successful treatment of infections in hospitals (1). Nosocomial infections are major public health concerns because of the substantial morbidity and the mortality which are associated with them. Although Citrobacter spp. are infrequent nosocomial pathogens, a local or systemic breach in the host defenses can allow them to cause a range of infections. These include urinary tract infections, neonatal sepsis, pulmonary infections, brain abscess, meningitis and blood stream infections. The Citrobacter species are emerging as important nosocomial pathogens. The Citrobacter infections are associated with a high mortality rate. They are often resistant to the routinely used antibiotics, especially the extended spectrum cephalosporins, due to the overexpression of chromosomal beta lactamases (2). Keeping these facts in mind, this study was conducted to know the prevalence of the Citrobacter spp. amongst gram negative bacilli, its antibiotic resistance pattern and ESBL/MBL production in this part of the country.
A total of 1830 consecutive gram negative bacilli which were recovered from clinical specimens during the study period from 1-2-2010 to 30-8-2011 were included in this study. These were isolated from various clinical samples like urine, blood, pus (pus aspirate, chest tubes, I/V cannula and catheter tips). The isolates of the Citrobacter spp. were further identified by their colony characteristics; Gramâ€™s staining, and biochemical reactions by standard methods (3). The anti-microbial sensitivity testing of the isolates of Citrobacter spp. was performed on Mueller Hinton agar by the Kirby Bauer method by using the disc diffusion technique and the results were interpreted as per the Clinical Laboratory Standard Institute (CLSI) guidelines (4). The isolates which were resistant or intermediately susceptible to any of the third generation cephalosporins were further processed for ESBL detection by the double disc potentiation method (4) by using a disc of cefotaxime (30μg)/ ceftazidime (30μg), and combination discs of cefotaxime 30μg and clavulanic acid 10μg and of ceftazidime 30μg plus clavulanic acid 10μg. Klebsiella pneumoniae ATCC 700603 was used as the ESBL positive control. ESBL production was inferred if the inhibition zone increased by 5 mm towards the cefotaxime plus clavulanic acid disc or towards the ceftazidime plus clavulanic acid disc in comparison to the third generation cephalosporin disc alone. MBL detection was done by using imipenem and imipenem- EDTA discs (5) (Table/Fig 2).
Out of the 1830 gram negative isolates, 86 belonged to the Citrobacter species (Citrobacter freundii-58, Citrobacter koseri-28). Among the 86 Citrobacter isolates, 73 (84.88%) were obtained from nosocomial samples, whereas 13 (15.12%) were obtained from outdoor specimens. A majority of these isolates were recovered from pus samples (44.19 %), followed by urine (36.05%) and blood (8.14%). [Table/Fig-3] Further statistical analysis showed a highly significant difference (p < 0.001) in the resistance of the Citrobacter species to all the antimicrobials including beta lactams, aminoglycosides and flouroquinolones among the hospital and the outdoor isolates [Table/Fig-4]. ESBL production was seen in 45 (61.64%) of the hospital and in 4(30.70%) of the outdoor isolates. The ESBL producing Citrobacter freundi and Citrobacter koseri among the hospital isolates and the outdoor isolates is shown in the graph. (Table/Fig 1).MBL production was seen in only 2(4.08) isolates.
The present study indicates that the Citrobacter spp. are mostly associated with nosocomially acquired infections. Of the total gram negative bacilli, 4.70% were of Citrobacter spp. and this rate of isolation was much higher than that which was reported by Ali et al (6) i.e. 1.35% of the Citrobacter freundii out of a total of 812 gram negative bacilli. This might be because of a lack of preventive measures during the handling of the patients in our institution, thus leading to the spread of this organism among the patients, especially the old, debilitated patients who were on IV catheters, CVP lines, urinary catheters, etc. A majority of the isolates were recovered from pus samples (44.19%), which was higher than that which was reported by Patil et al (7) (21.1%) and Shah et al (8) (22.85%). In our study, about 36.05% isolates were recovered from urinary samples, whereas other authors had reported the isolation of about 65.71% Citrobacter species from urinary samples (8). The antibiotic resistance pattern showed a significantly higher level of resistance among the hospital isolates as compared to that among the outdoor isolates. Similar results have been reported in other studies also (7),(9). The high level of antibiotic resistance among the hospital isolates in the present study may be due to the fact, that ours was a tertiary care hospital with a widespread use of broad spectrum antibiotics, which might have led to the selective survival advantage of these pathogens. In our study, Citobacter freundi was the commonest species which was isolated, followed by Citrobacter koseri, as was the case in other studies also (10). ESBL production was found in 45 (61.64%) of the hospital and in 4 (30.70%) of the outdoor isolates by the double disc potentiation method by using a disc of cefotaxime (30μg)/ ceftazidime(30μg) and combination discs of cefotaxime 30μg and clavulanic acid 10μg and of ceftazidime 30μg plus clavulanic acid 10μg (4). The rate of the ESBL production among the Citrobacter species in our study was higher than that which was reported by other authors (6),(11), which was 36.36% and 19.3% respectively. However, it was comparable with the finding of Rizvi et al (12) (62%) and lower than that which was reported by Uma A et al (13) who had reported it to be 86.50% amongst the hospital isolates. Excessive antibiotic exposure (especially the extended spectrum cepholosporins), extended hospital stay, recent surgery, admission to the ICU and instrumentation have been identified as the risk factors for the selection of the ESBL producing strains. The rate of the ESBL production was also much higher in the outdoor patients, which could have been due to the fact, that in our setup, extended spectrum cephalosprins were being prescribed injudiciously to the outpatients.
Citrobacter species are emerging as important nosocomial pathogens. Citrobacter. freundii was the commonest species which was isolated at our hospital. Multi-drug resistance and ESBL production are quite high amongst the Citrobacter species. The multidrug resistant Citrobacter species that were isolated in our study were mostly sensitive to a combination of piperacillin/tazobactum and sulbactum/ cefoperazone. So, greater caution is required in the selection of the antibiotics which have to be used, to avoid treatment failure. Carbapenems like imipenem and meropenem should be kept as reserve drugs, in case the organism becomes resistant to these combinations. This bacterium can become resistant to these drugs at any time and so, the indiscriminate, inadequate and the prophylactic use of these antibiotics should be avoided. Infection control measures like disinfection of the wards and equipments, barrier precautions against colonized patients and proper hand hygiene measures should be strictly adhered to, to prevent the spread of this pathogen. The antibiogram is a cost effective, easy and rapid typing tool in a low resource country like ours, where molecular typing tools are not easily accessible. Only in case of emergency, empirical therapy which is based on the antibiotic sensitivity pattern of that institute should be given to the patients.
Date of Submission: Jan 22, 2012
Date of peer review: Mar 03, 2012
Date of acceptance: Mar 29, 2012
Date of Publishing: May 31, 2012
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