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Indian Journal of Medical Microbiology, Vol. 26, No. 4, October-December, 2008, pp. 356-360 Brief Communication Increased prevalence of extended spectrum β lactamase producers in neonatal septicaemic cases at a tertiary referral hospital Bhattacharjee A, Sen MR, Prakash P, Gaur A, Anupurba S Department of Microbiology, Institute of Medical Sciences (IMS), Banaras Hindu University (BHU), Varanasi - 221 005, UP Date of Submission: 29-Oct-2007 Code Number: mb08109 Abstract Emergence of extended spectrum β lactamases (ESBLs) producing strains of gram negative bacteria, as one of the leading cause of septicaemia often complicates the clinical and therapeutic outcome. The present study was undertaken to investigate the prevalence of ESBLs in bacteria isolated from neonatal septicaemic cases along with their antimicrobial sensitivity pattern. Blood samples were collected from 243 suspected cases of neonatal septicaemia. Apart from susceptibility testing, all the gram negative isolates were subjected to phenotypic tests for ESBL production. Amongst the positive test samples (n = 115), 84 were gram negative rods. ESBL was detected in 26 (32%) isolates. Results indicate that routine ESBL detection should be made imperative and empirical use of third generation cephalosporins must be discouraged.Keywords: Extended spectrum β lactamase, Drug resistance, Neonatal septicaemia. Septicaemia is one of the leading causes of neonatal mortality along with perinatal hypoxia. [1] Although the common factors associated with these infections are low birth weight, length of time spent in hospital, invasive procedures, surgery and also colonisation by bacteria from hospital environment, a significant proportion of these septicaemic babies are those, who were born unattended outside the hospital in unhygienic environment. [2],[3],[4] The most common organisms responsible for these infections are multidrug resistant gram negative bacilli particularly members of the family Enterobacteriaceae and non fermenting gram negative rods. [2],[3] Several outbreaks of septicaemia by gram negative isolates have been reported and phenomenon of isolation of ESBLs producing isolates is not uncommon and is associated with increased mortality. [5] Further, as report of blood culture isolation and susceptibility are usually available after 72 hours or more, any delay in the initiation of correct empirical therapy or improper choice of antimicrobials cannot be justified. It is a common practice to use ampicillin and an aminoglycoside or a third generation cephalosporin in neonatal septicaemic cases. [1] Therefore, this study was designed to investigate the prevalence of ESBL producing gram negative rods in neonatal septicaemia and to observe antimicrobial susceptibility pattern of ESBL and non ESBL producing gram negative isolates, which would enable formulation of appropriate antimicrobial policy for such patients. Materials and Methods Blood samples were collected from 243 clinically suspected septicaemic neonates admitted to Neonatal Intensive Care Unit, S S Hospital, Banaras Hindu University, Varanasi over a period of 14 months. Samples were inoculated in to brain heart infusion broth (HiMedia, Mumbai, India). The broth was incubated aerobically at 37°C. A subculture was done after 18 hours; if no growth was obtained, the bottles were tested for seven consecutive days. Any sign of growth was followed-up by subculture. Media used for sub culturing included chocolate agar, blood agar and MacConkey agar (HiMedia). Isolates were identified using standard biochemical test. [6] Antimicrobial susceptibility tests were performed using the Kirby Bauer disc diffusion method as per CLSI guidelines. [7] Antimicrobials used were amikacin (30μg), cefuroxime (30μg), ciprofloxacin (5μg), gentamicin (10μg), imipenem (10μg), netilmicin (30μg), trimethoprim/sulfamethoxazole (1.25/23.75μg), cefoperazone/sulbactam (75/30μg) and piperacillin/tazobactam (100/10μg). All discs were obtained from Hi - Media, Mumbai India. Minimum inhibitory concentration (MIC) was determined by agar dilution method against cefotaxime, ceftazidime, ceftriaxone, cefpodoxime and aztreonam. E. coli ATCC 25922 was used as negative control. To screen for ESBL producers all the isolates were subjected to screening by MIC (agar dilution) method using cefotaxime and ceftazidime at 1 μg/mL concentration in Mueller Hinton Agar (Hi - Media Laboratories, Mumbai, India). Growth occurring at this concentration in any one of the above antibiotics was suspected as ESBL producer. Phenotypic confirmatory test for ESBL producers was done by both combined disc diffusion and MIC reduction method, for all isolates that were screened positive for the confirmation of ESBL production following CLSI guidelines. [7] K. pneumoniae ATCC 700603 was used as positive control and E. coli ATCC 25922 as negative control. Results Out of 243 suspected cases of neonatal septicaemia,117 were positive in culture for pathogenic organisms of which two were Candida spp. Rest 115 (48%) isolates comprised of gram positive cocci (n = 31) and gram negative rods (n = 84). The gram negative bacteria isolated included P. aeruginosa (n = 27), K. pneumoniae (n = 16), E. coli (n = 15), Acinetobacter baumannii (n = 14), Proteus mirabilis (n = 3), Proteus vulgaris (n = 2), Citrobacter koseri (n = 3) and Citrobacter freundii (n = 1). Of 84 gram negative rods, which were screened and tested for ESBL production, 26 (32%) isolates were confirmed to be ESBL producers by both methods [Table - 1]. ESBL production was observed in 62.7 and 46.5% of K. pneumoniae and E. coli respectively, whereas in P. aeruginosa only 18.5% were positive. None of the P.mirabilis , P. vulgaris , C. koseri and C. freundii isolates was ESBL positive. Greater resistance to β - lactam and non β - lactam antibiotics was evident in ESBL producers than in those which were ESBL negative [Table - 2] and [Table - 3]. Combination of β - lactam/ β - lactamase inhibitors showed greater activity in both groups particularly with piperacillin/ tazobactam against which organisms showed 100% susceptibility. All these strains were also found to be susceptible to imipenem. Among aminoglycosides, amikacin and netilmicin showed greater activity against all the isolates irrespective of their ESBL production status [Table - 2]. In MIC study, high minimum inhibitory concentration was observed for ESBL producers against third generation cephalosporins and monobactam compared to ESBL negative organisms [Table - 3]. Discussion In the present study, out of 115 bacterial isolates, majority were gram negative rods (73.04%), of which 32% were ESBL producers. Although significant difference was observed between ESBLs and non ESBL producers with regard to antibiotic susceptibility pattern our study showed that none of these gram negative isolates showed resistance to imipenem or piperacillin/tazobactam, and more than 80% of these were found susceptible to cefoperazone/sulbactam, amikacin and netilmicin irrespective of their ESBL status. It has been observed earlier that prevalence rate of ESBLs varies with the geographical location within the same country. [5],[8],[9],[10] ESBL production in septicaemic cases of our centre was higher than a South Indian study (13.54%) [11] but much lower compared to the study conducted in Lucknow (86.6%). [5] As, less than 39% of ESBL producing isolates were found susceptible to gentamicin, empirical use of amikacin must be preferred over gentamicin treatment in these cases. It was also observed that a considerable number of ESBL producers were sensitive to one or more third generation cephalosporins when tested in vitro . This study indicates that routine ESBL detection should be made imperative and empirical use of third generation cephalosporins must be discouraged. References
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