Antimicrobial sensitivity pattern of aerobic bacteria blood isolates: experience at a university hospital in Trinidad

Abstract

The morbidity and mortality associated with blood stream bacterial infections are increasing globally [1,2]. Bacterial resistance to the relatively inexpensive antimicrobials (e.g. ampicillin, tetracycline, co-trimoxazole) in developing countries have increased considerably both in hospitals [3] and the community [4] due to sales without a prescription at many pharmacies. This can lead to uncontrolled medication [4] and along with the indiscriminate use of antibiotics and absence of hospital antibiotic prescribing policies, may contribute to the emergence of resistant strains within the hospital environment. Relatively few studies on the levels of antibiotic resistance have been conducted in most Caribbean countries including Trinidad. This study was undertaken to evaluate and document the antimicrobial profile of the various pathogens isolated from blood cultures at a university teaching hospital in Trinidad. Between January and December 1998, 1002 consecutive blood specimens from 656 male and 346 female inpatients were received in the microbiology laboratory at the Eric Williams Medical Sciences Complex (EWMSC), Trinidad. Suspected positive cultures were identified using a non-radiometric assay Bactec (NR 600) and identified by using standard procedures [5]. Anaerobes were excluded. Antimicrobial susceptibility to several antibiotics used a diffusion technique and followed the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS) [6]. From a total of 1002 blood specimens received in the laboratory for culture 348 (34.8%) grew bacteria (Table 1). Coagulase-negative staphylococci (CNS) were the most frequently isolated organisms (100, 28.7%), followed by Staphylococcus aureus and Pseudomonas aeruginosa (each, 48, 13.8%). There were 40 isolates of Escherichia coli (11.5%), 24 of Klebsiella pneumoniae (6.9%) and 20 Enterococcus faecalis (5.7%). Three hundred and thirty-six (96.5%) cultures grew a single organism while 12 (3.5%) grew more than one species. More than 90% of CNS and S. aureus were resistant to ampicillin and more than 70% were resistant to augmentin and tetracycline but highly sensitive ( 95%) to erythromycin. No methicillin-resistant staphylococci were isolated from blood. The prevalence of resistance of the other Gram-positive organisms to all the drugs tested was less and ranged from an average of 32% to fully sensitive (Table 2). P. aeruginosa was fully sensitive to the cephalosporins, imipenem and aztreonam, but highly resistant (\80%) to gentamicin. E. coli and K. pneumoniae showed multi-resistance to