Superiority of D-zone testing method over standard method to detect inducible resistance in gram positive bacteria: a prospective surveillance from a teaching hospital in Saudi Arabia

In this prospective study, we determined phenotypic resistance to erythromycin among gram positive bacteria. Bacterial isolates were identified by conventional methods and by the Micro Scan: D-test zone was performed according to the Clinical and Laboratory Standards institutes [CLSI] recommendations to determine inducible resistance to clindamycin on gram positive bacteria isolated from different clinical specimens. Bacterial isolates included: group A streptococci [GAS], group B streptococci [GBS], viridans streptococci, S pneumoniae, Staphylococcus aureus [S.aureus] [both methicillin susceptible [MSSA] and methicillin resistant [MRSA]. A total of 1072 gram positive bacterial isolates were tested. The majority was from swabs collected from outpatient clinics. Erythromycin resistance was 8/23 [35%] for S. pneumoniae, 12/91 [13%] for GAS and 17/300 [5.7%] for GBS. All GAS and viridans streptococci possessed the efflux phenotype only. 8[8.8%] and 1[20%], respectively. For GBS, cMLS[B] phenotype. Seventy five isolates [16.3%] of MSSA were resistant to erythromycin compared to 160[83%] of MRSA. The majority of MSSA, 31/460 [6.7%] had an efflux phenotype while 26/460 [5.6%] were of cMLS[B] and 19/460[4%] iMLS[B] phenotypes. Constitutive MLS[B] was the most predominant resistant phenotype, 152/193 [78.8%] among MRSA. D-test zone should be considered for routine testing to detect inducible clindamycin resistance among significant gram positive bacteria

Ciprofloxacin resistance among bacterial isolates in a teaching hospital in Riyadh Saudi Arabia 2001-2005

To present trends of resistance to ciprofloxacin among common organisms isolated at King Khalid University Hospital [KKUH] between 2001-2005. Ciprofloxacin susceptibility of all isolates of Gram negative and Gram positive organisms were retrospectively obtained during the period from 2001-2005 in KKUH. Data from intensive care unit [ICU] and non-ICU patients were separately analyzed. Escherichia coli [E.coli] resistance increased from 10% in 2001 to 22% in 2005. Enterobacter cloacae [Ent.cloacae] resistance decreased from 11-14% in 2003 -2004 to 7% as in 2001 and 2005. Klebsiella pneumoniae [K.pneumoniae] resistance fluctuated from 6% in 2002 and 2003, 13% in 2004 to 6% in 2005. Pseudomonas aeruginosa [P.aeruginosa] resistance ranged from 7% - 8% during this study period while that of Acinetobacter spp. ranged between 45% to 62% and Staphylococcus aureus [S.aureus] resistance doubled from 18% in 2001 to 39% in 2005. None of Streptococcus pneumoniae [S.pneumoniae] isolates showed resistance to ciprofloxacin. Isolates of E .coli, Acinetobacter spp. and S.aureus from non-ICU patients showed higher resistance to ciprofloxacin than isolates from ICU patients while K.pneumoniae and P.aeruginosa showed higher resistance from ICU patients than isolates from non-ICU patients. Ciprofloxacin resistance among many Gram negative species and S.aureus is an increasing threat among many Gram negative species and S.aureus in our hospital in both ICU and non-ICU patients

Comparison of susceptibility testing methods for the detection of methicillin/oxacillin resistance in Staphylococcus aureus

To compare the accuracy of disk diffusion method and E-test for the detection of methicillin resistance and low-level methicillin-resistance in Staphylococcus aureus [S. aureus] and the PBP2a latex agglutination test for confirmation. A total of 76 methicillin resistant S. aureus [MRSA] isolates from different clinical specimens were tested by disk diffusion method. Disk d i ffusion method was performed using methicillin [MET] 5microg disk, oxacillin [OX] 1 microg disk, moxalactam [MOX], and cefoxitin [FOX] 30 microg each on Mueller Hinton agar [MHA] plates supplemented with 2% NaCl and incubated at 35 °C for 24 hours. Minimum inhibitory concentration [MIC] was performed by E-test for MET and OX on MHA plates containing 2% NaCl. Results for all tests were read according to NCCLS recommendations for zone of inhibition and break points. Low-level MRSA strains were confirmed by PBP2a latex agglutination test. All strains were tested for ?-lactamase production. All MRSA strains were detected by disk diffusion methods using MET, OX and FOX [100%]. Four [5.2%] strains were low-level MRSA by MOX disk. E-test detected 72 [94.7%] using MET and 74 [97.3%] MRSA strains using OX. No heterogeneous growth within the zones of inhibitions was noticed. One MRSA was misclassified as methicillin sensitive by MET E-test [MIC 6 microg /ml], but was 32 microg/ml by OX E-test. Two strains were low-level MRSA by E-tests but showed resistance by MET, OX and FOX disk diffusion method. One strain had MIC of 12 microg/ml both by OX and MET E-tests. All four strains showed low-level resistance by MOX disk and were positive for PBP2a latex agglutination test. All the strains produced ?-lactamase. Conclusion: Disk diffusion method using MET, OX, and FOX can reliably be used to detect methicillin resistance in S. aureus. MOX and E-test can be used to detect lowlevel methicillin resistance and these can further be confirmed by PBP2a latex agglutination test in diagnostic laboratories