Correlation of phenotypic tests with the presence of the blaZ gene for detection of beta-lactamase

Abstract

Staphylococcus aureus and Staphylococcus saprophyticus are the most common and most important staphylococcal species associated with urinary tract infections. The objective of the present study was to compare and to evaluate the accuracy of four phenotypic methods for the detection of beta-lactamase production in Staphylococcus spp. Seventy-three strains produced a halo with a diameter ≤28 mm (penicillin resistant) and all of them were positive for the blaZ gene. Among the 28 susceptible strain (halo ≥29 mm), 23 carried the blaZ gene and five did not. The zone edge test was the most sensitive (90.3%), followed by MIC determination (85.5%), but the specificity of the former was low (40.0%). The nitrocefin test was the least sensitive (28.9%). However, the nitrocefin test together with the disk diffusion method showed the highest specificity (100%). The present results demonstrated that the zone edge test was the most sensitive phenotypic test for detection of beta-lactamase, although it is still not an ideal test to detect this type of resistance since its specificity was low. However, the inhibition halo diameter of the penicillin disk can be used together with the zone edge test since the same disk is employed in the two tests. Combined analysis of the two tests shows a sensitivity of 90.3% and specificity of 100%, proving better sensitivity, especially for S. saprophyticus. This is a low-cost test of easy application and interpretation that can be used in small and medium-sized laboratories where susceptibility testing is usually performed by the disk diffusion method.

Resistance Profile From Staphylococcus Aureus And Pseudomonas Aeruginosa Obtained From Tracheostomized Children

“…In the present study, of the 27 S. aureus isolated, were found resistance that are similar to the study developed by Cavalcanti et al 29 30,31 .…”

Genotypic and Phenotypic Evaluation of Biofilm Production and Antimicrobial Resistance in Staphylococcus aureus Isolated from Milk, North West Province, South Africa

“…In this study, the diameter of the zone of inhibition of penicillin (PD) was higher in S. aureus isolates without the blaZ gene than those with the blaZ gene. In a similar study, Ferreira et al reported that S. aureus isolates with a penicillin diameter less than 28 mm carried the blaZ gene [42]. However, a large inhibition halo did not rule out the presence of the blaZ gene, as reported by other colleagues [43,44].…”

“…A total of 77 S. aureus were isolated from the milk samples, out of which 7 (9.1%) and 70 (90.9%) isolates were from pasteurized and unpasteurized milk, respectively (P < 0.05). The distribution of isolates with respect to the study location presented in Table 1 revealed that more of the isolates (33,42.9%) were from Mafikeng, while only two isolates (2.5%) were from Zeerust.…”

Characterization of Antibiotic and Biocide Resistance Genes and Virulence Factors of Staphylococcus Species Associated with Bovine Mastitis in Rwanda

“…isolates (100%) in the current study. This gene encodes a narrow-spectrum β-lactamase which confers penicillin resistance [10,25].…”

“…Staphylococcal DNA was extracted as described previously [57]. PCR was used to detect the presence of the following antibiotic resistance genes: blaZ (confers resistance to penicillins except isoxazolyl-penicillins) [25]; mecA, mecC (confer resistance to all penicillins and cephalosporins approved for veterinary use) [58]; erm(A), erm(B), erm(C), erm(F), erm(T), erm (33), erm (43), and erm(44) (confer resistance to macrolides, lincosamides, and streptogramin B), vga(A), vga(A) v , vga(C), vga(E), vga(E)v and sal(A) (confer resistance to streptogramin A, lincosamides and pleuromutilins); Isa(B) and Inu(A) (confer elevated MICs or resistance to lincosamides) [23,[59][60][61][62][63][64][65][66][67][68]; msr(A) (confers resistance to macrolides and streptogramin B) [57]; cfr (confers resistance to all phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A) [69]; fexA (confers resistance to all phenicols) [69]; cat pC194 , cat pC221 , and cat pC223 (confer resistance to non-fluorinated phenicols, e.g., chloramphenicol) [70]; ant(6 )-Ia and str (confer resistance to the aminoglycoside streptomycin) [14]; dfrA, dfrD, dfrG, and dfrK (confer resistance to trimethoprim) [57,71]; tet(K) and tet(L) (confer resistance to tetracyclines except minocycline and glycylcyclines) [57]; tet(O) and tet(M) (confer resistance to tetracyclines, including minocycline, but excluding glycylcyclines) [72].…”