ABSTRACT: Considering the limitations of screening with nalidixic acid to detect reduced susceptibility to fluoroquinolones of Salmonella enterica serovar Typhi (S.Typhi) strains, we evaluated the use of a 30 µg nalidixic acid disc screening method in Pakistan.
Non duplicate nalidixic acid susceptible S. Typhi isolates (246) from 2003-2008 were retrieved from the Salmonella strain bank. Minimum inhibitory concentrations of ciprofloxacin for all strains were determined by agar dilution and further rechecked by ciprofloxacin E-tests.E. coli ATCC 25922 was used as the control strain. The MIC data for ciprofloxacin were compared with nalidixic acid disk (30µg) zone diameters.
Repeat testing of all S. Typhi isolates with a nalidixic acid (30µg) disk showed 100% susceptibility with an average zone diameter of 26 mm. Agar dilution testing revealed reduced susceptibility to ciprofloxacin, with MICs of 0.125 µg /ml for three (1.2%) isolates only. Zone sizes of strains with higher MICs were significantly lower than the strains with lower MICs (20 versus 26 mm) (p value < 0.001). Conclusion: Estimation of fluoroquinolone MICs on every nalidixic acid susceptible S. Typhi strain is not cost effective in our setting; the proportion of strains with high fluoroquinolone MICs was found to be very low. We recommend periodic fluoroquinolone MIC determination to include all isolates with a nalidixic acid borderline zone (size 20-22 mm).
The Journal of Infection in Developing Countries 01/2012; 6(10):700-3. · 1.19 Impact Factor
ABSTRACT: To compare the chromogenic UTI medium (CUM) with cysteine lactose electrolyte deficient medium (CLED) in terms of isolation of uropathogens, turnaround time and cost.
A total of 251 urine samples were selected and inoculated on both CLED and CUM, growth was observed after 24 and 48 hours of incubation. Isolates were identified by colony's colour and biochemical tests. Turnaround time for identification and cost was calculated till final identification of microorganisms.
A discrepancy in isolation was observed in seven samples with growth on CUM in 24 hours while in 48 hours on CLED. There was 100% agreement in identification by both media. Almost 50% samples were identified within 24 hours by using CUM in contrast to CLED where most samples were identified in 48 hours. Total number of reagents used and total cost for processing of a specimen including technologist and consultant time by using CUM is significantly low in comparison to CLED.
CUM can replace CLED as a primary isolation media for urine culture in clinical laboratories in Pakistan as it is user friendly, facilitates early reporting and saves cost.
Journal of the Pakistan Medical Association 07/2011; 61(7):632-5.
ABSTRACT: To determine the minimum inhibitory concentrations (MICs) of ceftriaxone, azithromycin, pefloxacin, cefipime and imipenem for Salmonella Typhi (S. Typhi) and Paratyphi.
One hundred and fifty four isolates of Salmonella Typhi and S. Paratyphi A, B and C growing in blood culture were selected. MICs of ceftriaxone, azithromycin, pefloxacin, cefipime and imipenem were performed by agar dilution method as recommended by clinical laboratory standard institutes.
MIC90 of azithromycin and pefloxacin was 8 microg/ml, cefipime was 0.06 microg/ml and imipenem was 0.5 microg/ml. None of the strains were found to be resistant to ceftriaxone but 3 isolates showed higher MIC value of 2 microg/ml.
Azithromycin appears a suitable alternate for the treatment of typhoid in the community. Imipenem and cefipime are good options in complicated cases to be treated in hospital settings. Pefloxacin cannot be used as MICs are higher. Presence of isolates with higher MIC of ceftriaxone is serious and stresses upon continuous laboratory surveillance to guide clinicians appropriately.
Journal of the Pakistan Medical Association 05/2011; 61(5):462-5.
ABSTRACT: Shigellosis remains a major public health problem in developing countries. Antimicrobial resistance has complicated the empirical treatment. Knowledge of serotypes is crucial in vaccine development, as cross-protection between various serotypes is limited. Therefore we conducted a prospective study to determine the frequency of isolation of Shigella serotypes and antimicrobial resistance.
Stool samples from 8155 individuals, collected through a surveillance study conducted in four slums of Karachi from January 2002 to March 2004, were cultured.
Shigella was isolated in 394 (4.8%) of 8155 patients presenting with diarrhea. Two hundred and forty-two (62%) isolates were Shigella flexneri, 72 (18%) were Shigella sonnei, 43 (11%) were Shigella boydii, and 37 (9%) were Shigella dysenteriae. Thirteen S. flexneri serotypes were identified, of which the most frequent were 2a (38), 6 (37), and 1b (25), followed by 2b (23). Only 22 (5.6%) Shigella isolates were found to be pan-susceptible. Large proportions of isolates were resistant to co-trimoxazole (89% S. flexneri, 81% S. dysenteriae, 80% S. sonnei, and 56% S. boydii) and ampicillin (87% S. flexneri, 68% S. dysenteriae, 35% S. boydii, and 4% S. sonnei).
Concurrent circulation of multiple strains with high resistance is worrying and mandates surveillance at the national level to facilitate the control of shigellosis.
International journal of infectious diseases: IJID: official publication of the International Society for Infectious Diseases 02/2009; 13(6):668-72. · 2.17 Impact Factor
ABSTRACT: To determine the validity of nalidixic acid screening test in the detection of high MICs of fluoroquinolone against Salmonella(S.) typhi isolated from blood and correlate zone diameters of ofloxacin with that of MIC value for nalidixic acid sensitive and resistant strains.
Cross-sectional analytical study.
Clinical Microbiology Laboratory of the Aga Khan Hospital, Karachi from January 2002 to December 2003.
Two hundred S. typhi isolates from blood were included for nalidixic acid screening and ofloxacin susceptibility. Antibiotic susceptibilities for both the antibiotics were obtained by disc diffusion method whereas MICs were determined by standard agar dilution method as recommended by NCCLS guidelines. Sensitivity, specificity and correlation between both antimicrobial susceptibility methods were calculated and results expressed as scattergrams.
The results broadly classify S. typhi isolates into nalidixic acid resistant strains with no zone of inhibition around 30 mug nalidixic acid disc and nalidixic acid sensitive strains with mean zone of inhibition of 24.9 mm. All S. typhi isolates with ofloxacin MIC of capital ZHE, Cyrillic 0.125 microg/ml were found to be nalidixic acid resistant (MIC capital ZHE, Cyrillic32 microg/ml) whereas the isolates with ofloxacin MIC 0.06 microg/ml were nalidixic acid sensitive (MIC 8 microg/ml). Screening for nalidixic acid resistance was found to be 100% sensitive and 97% specific in identifying S. typhi strains with reduced susceptibility to fluoroquinolone (MIC capital ZHE, Cyrillic 0.125 microg/ml).
Nalidixic acid resistance as a screening method is proved to be significant in identifying S. typhi isolates with reduced susceptibility to fluoroquinolones. It is also suggested that inhibition zone of 25 mm around 5 microg ofloxacin disc is appropriate as a selection criterion to detect S. typhi isolates with reduced susceptibility to fluoroquinolones.
Journal of the College of Physicians and Surgeons--Pakistan: JCPSP 08/2005; 15(7):413-7. · 0.34 Impact Factor