Bacterial pathogens responsible for blood stream infection [BSI] and pattern of drug resistance in a tertiary care hospital of Lahore

The present retrospective analysis was carried out to determine the pattern of bacterial agents responsible for blood stream infection [BSI] in a tertiary care hospital of Lahore and to get an updated knowledge about their antibiotic resistance pattern. It is a cross sectional descriptive study, carried out in the Microbiology Section, Department of Pathology, Services Institute of Medical Sciences [SIMS], Lahore during the period April, 2006 to December, 2006. Among the 1814 blood cultures 1382 [76%] were received from pediatrics/ neonatology wards and 432 [24%] from adult patients. In a total of 508 [27.9%] blood cultures, 465 yielded monomicrobial growth and 43 polymicrobial growth. A total of 454 [97.6%] of the monomicrobial growths were bacterial isolates and 11 [2.4%] were Candida Spp. Gram negative bacteria [Enterobacteriaceae + nonfermenter bacteria] comprised the majority of bacterial isolates. Amongst the gram-negative bacteria the most common organism was Klebsiella Spp. while amongst the gram-positive organisms Staph. aureus was the most common isolate. It was seen that 31.25% Staph. aureus isolates were resistant to Oxacillin, 93.7% of Klebsiella Spp. and E. coli isolates were resistant to 3rd generation Cephalosporins and 6.49% of Pseudomonas Spp. and Acinetobacter Spp. whereas resistant to Carbapenems in the present study. As BSI is an emergency, for appropriate management of these cases an updated knowledge about the causative agents and their susceptibility pattern to antibiotics is required to start appropriate empirical antibiotic therapy till the results of the microbiology report are available. The alarming finding is the high resistance seen amongst Enterobacteriaceae against 3rd generation cephalosporins [93.7%], oxacillin resistance among Staph aureus [31.25%] and increasing resistance against Carbepenems among Pseudomonas and Acinetobacter isolates [6.49%]. In conclusion there are grave implications of these findings for our already strained health care system as the presence of these multidrug resistant organisms leads to longer hospital stay, more expensive/ toxic drugs and higher mortality

Effect of variable incubation temperatures and salt concentration on susceptibility testing of methicillin resistant staphylococcus aureus [MRSA]

The effect of variable incubation temperatures and variable salt concentration in the sensitivity agar on susceptibility testing of MRSA was evaluated. For this purpose 58 MRSA strains were tested. For each MRSA strain nine Mueller Hinton agar plates, three plates each with 2%, 5% and 7.5% sodium chloride [NaCl] supplement were inoculated. One plate from each of the salt concentration was incubated at 30°C, 37°C and 40°C. It was found that with increase in temperature of incubation the size of inhibition zones increased. In the presence of 2% NaCl supplement in the sensitivity agar, 5 MRSA appeared falsely intermediate sensitive on incubation at 40°C. While on incubation at 37°C although all MRSA remained methicillin resistant, statistical analysis revealed the effect on inhibition zone size to be approaching significance level [0.1 > P > 0.05]. The effect of incubation temperature on inhibition zone size was statistically insignificant [P>0.05] if 5% or 7.5% NaCl was incorporated in the sensitivity agar. Therefore we recommend the use of 5% NaCl supplemented sensitivity agar and incubation temperature of 37°C for the accurate detection of methicillin resistance in Staphylococcus au aureus