neonatal group b streptococcus ( gbs ) infection ranging from 0.5 to 2 per 1000 live birth is the result of vertical transmission to the infant during delivery in colonized mothers .
attempts at identifying gbs colonized pregnant women near term by assessing the risk factors for gbs , failed to diagnose all cases .
universal screening of all pregnant women for gbs at 3537 weeks of gestation is currently recommended by the centers for disease control and prevention ( cdc ) in the usa .     
despite the variation in the adherence to cdc recommendations among different centers around the world , antimicrobial prophylaxis , offered to women colonized with gbs intrapartum ( after onset of labor or after rupture of membranes ) , lead to more than 70% reduction in early - onset gbs infection in neonates .
however , due to the variation in the rate of gbs colonization during pregnancy , the emergence of resistant colonizing strains   and the virulence potential of these strains , intrapartum screening of gbs genotypes   along with their antimicrobial resistance profiles , and virulence encoding genes become desirable .      
fortunately , gbs resistance to penicillin has not been reported so far ; however , rare gbs clinical strains with reduced sensitivity for penicillin have been recorded . on the other hand , early studies on gbs
isolates from pregnant women , showed antimicrobial resistance as high as 18% , 8% , and > 80% for erythromycin , clindamycin , and tetracycline respectively .       
the severity of neonatal disease in gbs infections could be determined mostly by a number of virulence factors encoded among others by the cps gene cluster coding for the capsule , the scpb gene coding for surface enzyme scpb ( a c5a peptidase ) which causes impairing of neutrophil recruitment and binds fibronectin to promote bacterial invasion of epithelial cells , the bca gene coding for alpha - c protein , a surface protein that helps the bacteria to enter the host cells , the lmb gene coding for lmb ( laminine - binding protein ) , a surface protein that plays a role in invasion of damaged epithelium , the cyle gene coding for -hemolysin , a toxin that plays a role in tissue injury and systemic spread of the bacteria and contributes to meningitis , and the rib gene encoding the surface rib protein mostly present in invasive strains .
other virulence factors involved in the process of gbs pathogenesis include beta - c protein which is encoded by bac gene .
beta - c protein function is comprised of interaction with iga - fc portion causing the inhibition of phagocytosis   and binding factor - h to maintain its role in inhibiting the complement activation via the alternative pathway .
other important virulence factors of gbs are the fibrinogen - binding proteins : fbsa and fbsb .
it protects the pathogen from opsonophagocytosis , and promotes its adherence to epithelial cells and to the human brain microvascular endothelial cells ( hbmec ) thus helping it to cross the blood brain barrier and developing meningitis [ 18 , 19 ] .
fbsb protein , encoded by fbsb gene , is also a surface protein that helps in gbs invasion of the epithelial cells .
finally , cell - surface - associated protein ( cspa ) is a surface protein encoded by cspa gene .
it is involved in maintaining the pathogen survival in the host by escaping the immune system .        in this study , genotypes were correlated to some of the virulence genes and the antimicrobial susceptibility profiles .
this information is useful to identify particular gbs strains with high virulence potential , with resistance to routinely administered antimicrobial agents , and possibly linked to particular geographical areas .
seventy six gbs isolates were cultured from specimen taken from the vaginas of pregnant women between 35 and 37 weeks of gestation , attending private clinics in two tertiary care centers in beirut , lebanon , between october 2007 and july 2008 . the first center ( a ) is located in the western part of the urban city of beirut , and the second one ( b ) in the eastern part of beirut .
these two hospitals serve two different populations , in the sense that patients attending the hospitals come from 2 different geographical areas , with very minimal intermingling between them . however , the local health care systems of the two areas are similar , and patients have similar antibiotics consumption habits .
the 76  gbs isolates consisted of 47 ( 61.8% ) isolates obtained from the first tertiary care center and 29 ( 38.2% ) isolates obtained from the second tertiary care center .
isolates were identified using conventional methods on the basis of colonial morphology , gram staining , haemolysis , and latex agglutination test with specific antisera using the slidex strepto plus ( biomerieux , marcy l'etoile ; france ) .
antimicrobial susceptibility testing was performed by the disk - diffusion ( kirby - bauer ) method on mueller - hinton agar ( difco laboratories , detroit , michigan ) supplemented with 5% sheep blood , using suspensions of 0.5 macfarland from fresh bacterial cultures .
the test was done using the following antimicrobial agents : penicillin , cefepime , ceftriaxone , chloramphenicol , clindamycin , erythromycin , levofloxacin , and tetracycline .
dna was extracted from all isolates using the illustra bacteria genomicprep mini spin kit ( ge healthcare uk ltd , buckinghamshire , england ) according to the manufacturer 's instructions .
total dna of the 76  gbs isolates was used to amplify five virulence factors encoding genes : cyle , rib , lmb , bca , and scpb   by pcr using specific primers .
standard pcr conditions were used to amplify cyle , lmb , and scpb , rib , and bca gene .       
amplicons were subjected to electrophoresis on 2% agarose ( sigma ) gels in 1  tris - borate - edta buffer ph 8.3 ( tris base 0.089  m , boric acid 0.089  m , and edta 0.002  m ) at 120  v for 45 minutes .        
agarose gels were stained with ethidium bromide ( sigma ) and photographed using a uv - transilluminator and an olympus digital camera with digi - doc it program .
genotyping using random amplified polymorphic dna ( rapd ) analysis was performed on all the isolates to determine strain diversity .
rapd was performed with the ready - to - go rapd analysis beads kit ( ge healthcare uk ltd , buckinghamshire , england ) and the gbs 2 primer , using sprint , thermo electric thermal cycler .
antimicrobial susceptibility testing showed the following : all gbs isolates were susceptible to penicillin g , cefepime , ceftriaxone , and levofloxacin .
the following percentages of isolates , 4% , 11.8% , 15.8% , and 86.8% , were resistant to chloramphenicol ( chl ) , clindamycin ( cli ) , erythromycin ( ery ) , and tetracycline ( tet ) respectively .
six antimicrobial resistance ( ar ) profiles of isolates were detected : a ( resistant to cli , ery , chl , and tet ; 4.0% ) , b ( resistant to cli , ery , and tet ; 6.6% ) , c ( resistant to cli and tet ; 1.3% ) , d ( resistant to ery and tet ; 5.3% ) , e ( resistant to only tet ; 69.7% ) , and f ( susceptible to all ; 13.2% ) .
genotyping of all the isolates detected seven gbs clusters i , ii , iii , iv , v , vi , and vii with the following prevalence percentages : 18.4% , 13.2% , 19.4% , 7.9% , 11.8% , 11.8% , and 17.1% , respectively . a dendrogram of the seven clusters of genotypes
the most common cluster was iii ( 19.7% ) and the least prevalent was iv ( 7.9% ) .
the data show a prevalence of certain genotype clusters in both tertiary care centers while other genotype clusters were merely confined to a particular tertiary center ( table 2 ) . similarly , certain ar profiles were prevalent in both centers , whereas others were restricted to one center .
pcr detection of the virulence genes showed that cyle , lmb , scpb , bca , and rib genes were positive in 99% , 96.1% , 94.7% , 56.6% , and 33% of the gbs isolates respectively .
there was a wide prevalence of the cyle , lmb , and scpb genes among the total isolates , and hence all 3 genes were evenly distributed among the genotype clusters .
table 3 shows the prevalence of bca and rib genes among the gbs genotype clusters .
sixty eight isolates out of 76 ( 89.5% ) have either the bca or the rib gene and 8 isolates out of 76 ( 10.5% ) have neither bca nor rib detected .
neonatal gbs infection is a serious complication of the vertical transmission of the bacteria , from the mother to the newborn , at the time of vaginal delivery .
this is why universal screening for gbs vaginal colonization in pregnant women near term is recommended .      
fortunately , gbs resistant to penicillin has not been reported all around the world , and the drug of choice , in treating the infection , is still penicillin [ 7 , 9 ] .
however , the problem arises in cases , allergic to penicillin , where alternate antimicrobial agents such as cli and ery are commonly administered .
however , de azavedo et al .   found that 18% , 8% , and > 80% of gbs isolates in pregnant women were resistant to ery , cli , and tet . in our study ,
11.8% , 15.8% , and 86.8% of the gbs isolates , were resistant to ery , cli , and tet respectively , indicating percentages similar to previous studies .
the prevalence of this relatively high ar percentages , leads to the recommendation of requesting a sensitivity antibiogram for gbs cultured from women allergic to penicillin .       
genotyping of all the gbs isolates , utilizing rapd analysis determined a total of 7 genotype clusters .
the most common was genotype cluster iii ( 19.7% ) and the least common was iv found in 7.9% of all isolates .      
a correlation between ar and genotype clusters , showed an association between them ( table 1 ) .
resistance to chl was restricted to genotype clusters v , vi , and vii , whereas resistance to both cli and ery was found only in genotype clusters i , ii , and vii .
all the gbs isolates resistant to cli are also resistant to ery , indicating a correlating pattern of resistance amongst the genes responsible for this phenotype .
this can be expected since cli resistance in gbs is nearly always based on the presence of an ermb gene conferring resistance to macrolides , lincosamides , and streptogramin b .       
an important finding in this study was the correlation between the prevalence of particular genotype clusters with certain ar profiles in a given medical center .
this observation denotes that high prevalence of certain genotype clusters resistant to certain antimicrobial agents in a particular medical center entails the practice of caution by extrapolating the ar findings from one medical center to others .     
another observation is that bca and rib genes were not present concomitantly in the same genome .
rib protein encoded by the rib gene shares several properties with -c protein encoded by bca gene .
both proteins are resistant to trypsin digestion and belong to the same family of bacterial surface proteins with repetitive structures showing a 47% identity , their n - terminal sequences are related   and are 61% identical to each other .
further investigations are still needed to be performed in order to discover the functional relationship between bca and rib to determine if they have homologous functions .
 the antimicrobial 
                   susceptibility profiles of 76 
                   streptococcus agalactiae ( group 
                   b streptococci [ gbs ] ) isolates from vaginal 
                   specimens of pregnant women near term were 
                   correlated to their genotypes generated by 
                   random amplified polymorphic dna analysis and 
                   their virulence factors encoding genes 
                   cyle , lmb , scpb , rib , and bca 
                   by pcr . based on the distribution of the 
                   susceptibility patterns , 
 six profiles were 
                   generated . 
 rapd analysis detected 7 clusters of 
                   genotypes . 
 the cyle gene was 
                   present in 99% of the isolates , the 
                   lmb in 96% , 
                   scpb in 94.7% , 
                   rib in 33% , and 
                   bca in 56.5% of isolates . 
                   
 the isolates demonstrated a significant 
                   correlation between antimicrobial resistance and 
                   genotype clusters denoting the distribution of 
                   particular clones with different antimicrobial 
                   resistance profiles , entailing the practice of 
                   caution in therapeutic options . 
 all virulence 
                   factors encoding genes were detected in all 
                   seven genotypic clusters with 
                   rib and bca 
                   not coexisting in the same 
                   genome . 