Diffusion of trimethoprim and sulfamethoxazole from susceptibility disks into agar medium

Pattern of infection and antibiotic activity among Streptococcus agalactiae isolates from adults in Mashhad, Iran

BACKGROUND

One of the main causes of sexually transmitted diseases is group B β- hemolytic streptococci (GBS) multiplying in the genital tracts. Penicillin is the most common drug for the treatment of infections caused by these bacteria, but in patients suffering from Penicillin allergy, Erythromycin and Clindamycin are used as alternative therapeutic drugs against GBS. Recently, resistance to these drugs has been reported more often. In this study, efforts have been made to determine the prevalence and antibiotic resistance of GBS.

METHODS

Modified Christie Atkins Munch-Petersen (CAMP) test was conducted on over 2400 samples of urine and discharge taken from vagina, urethra and prostate. The drug sensitivity was performed by double disk sensitivity tests to Bacitracin, Trimethoprim, and Sulfamethoxazole and then the resistant samples were investigated by E-test to determine the minimal inhibitory concentrations (MICs) value.

RESULTS

Twenty-three vaginal and 10 urethral discharge, 27urine and 6 prostatic secretion samples were GBS positive. The most symbiotic microorganisms with GBS were strains of Enterococci (90%), Staphylococcus saprophyticus (25%) and Candida albicans (6%). The disk diffusion method showed 18 cases with Penicillin resistance (MIC: 1.5 mg/ml).

CONCLUSION

Taken together, GBS carriers' rate in this study was found 20.65% (8.24% men and 12.4% women). Furthermore, findings showed high-level resistance to Erythromycin and Clindamycin.

The antimicrobial activities of trimethoprim and sulfonamides

The folate inhibitor trimethoprim (TMP) is active against and potentially cidal to a few higher microorganisms and a wide spectrum of pathogenic bacteria except for Bacteroides, Branhamella, Brucella, Chlamydia, Clostridium, Mycobacterium, Mycoplasma, Nocardia, Neisseria, Pseudomonas and Treponema. These organisms tend to be more sensitive to sulfonamides (SUL) than to TMP, whereas TMP is 10- to 100-fold more active than SUL against most other bacteria. Synergy between TMP and SUL occurs at drug concentrations equal to or less than their respective MICs and is often seen in vitro with isolates that are sensitive or moderately resistant to one or both of the components. Synergy occurs over a wide range of ratios between TMP and SUL, the optimal being that between their respective MICs when acting singly. In vitro synergy is more impaired by bacterial resistance than by suboptimal TMP:SUL ratios. The vast majority of clinical isolates of Haemophilus, staphylococci, streptococci and enteric bacteria are inhibited in vitro by the minimum concentrations of drug attained in plasma during therapy. Exceptions are found among Enterobacter, Citrobacter, Serratia, Proteus and in particular Klebsiella where SUL resistance is common and isolates with TMP MICs of 5 mg/l or more may occur and lead to failure of TMP-SUL therapy in systemic infections. In the urinary tract drug concentrations that are synergistic and therefore inhibitory in vitro against isolates moderately resistant to SUL (MIC less than or equal to 1 g/l) and/or TMP (MIC less than or equal to 0.1 g/l) are present during TMP-SUL therapy. However, whether the synergy and the bactericidal effect of TMP-SUL observed in vitro play a role in vivo is controversial.